Solar Thermal – Solar Tribune https://solartribune.com Solar Energy News, Analysis, Education Sun, 13 Apr 2025 17:35:23 +0000 en-US hourly 1 https://wordpress.org/?v=5.1.21 CSP: PV Not the Only Game in Town https://solartribune.com/csp-pv-not-the-only-game-in-town/ Sun, 14 Jun 2015 19:24:44 +0000 http://solartribune.wpengine.com/?p=9069 With the price of photovoltaic (PV) panels plummeting and the advent of the era of PV “solar farms,” large scale solar thermal projects have not been getting much love lately, at least not in the USA. Concentrating Solar Power (CSP) is a workhorse technology for large-scale solar power generation. So why aren’t we hearing more […]

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]]> With the price of photovoltaic (PV) panels plummeting and the advent of the era of PV “solar farms,” large scale solar thermal projects have not been getting much love lately, at least not in the USA. Concentrating Solar Power (CSP) is a workhorse technology for large-scale solar power generation. So why aren’t we hearing more about it?

What is CSP? According the the Solar Energy Industry Association’s Website: “Concentrating solar power (CSP) plants use mirrors to concentrate the energy from the sun to drive traditional steam turbines or engines that create electricity. The thermal energy concentrated in a CSP plant can be stored and used to produce electricity when it is needed, day or night. Today, over 1,400 MW of CSP plants operate in the United States, and another 390 MW will be placed in service in the next year.” Built-in storage. That’s the holy grail of solar, right? Why are we not all over this?

Casandra Sweet of MarketWatch.com is not-so-optimistic about CSP. In an article published last week, she points out that “The $2.2 billion Ivanpah solar power project in California’s Mojave Desert is supposed to be generating more than a million megawatt-hours of electricity each year. But 15 months after starting up, the plant is producing just 40% of that, according to data from the U.S. Energy Department.” Technical difficulties are cited as the reason for the slow takeoff.

Ivanpah is not the only California CSP project to take a hit lately. Another project by Ivanpah’s developer, BrightSource, has officially been canceled, with local officials citing concerns over danger to wildlife as well as the area’s drought-stricken groundwater supply as the primary reasons for cancellation.

solar-irradiation-in-Saudi-Arabia-from-Wikipedia-commons-While CSP is taking a beating stateside, plans for giant expansions in CSP generation are underway across the globe, mostly in equatorial regions where conditions are perfect for massive solar generating projects. The kingdom of Saudi Arabia alone plans to add as much as 54 GW of concentrating solar generation in the next few decades. Morocco’s ambitious Noor-Quarzazate Concentrating Solar Plant project has received $47.8 million in financial backing from the European Union (EU), and plans are in the works to connect the Noor stations to the EU grid. The Noor project consists of three phases: Phase 1 includes a160 MW parabolic trough-power project. Phase 2 includes two projects, Noor II and Noor III, with generating capacities of 200 MW for Noor II and 150 MW at Noor III. Phase 3 of Noor-Quarzazate project will not be a CSP plant, but rather a 50 MW solar photovoltaic generating facility. Tunisia is also looking to sell into the EU power market with a 2 GW CSP plant called TuNur. British renewables investor Low Carbon, developer Nur Energie and Tunisian investors, with funding from the African Development Bank, would transport the energy via a 600km cable from Tunisia to Italy, where it has already secured approval for a grid connection. This would be the beginning of delivering major amounts of Middle Eastern solar to all parts of the EU.

Photo by Amble via Wikimedia Commons


Photo by Amble via Wikimedia Commons

In the Americas Spanish CSP developer Abengoa has put in a plant in Mexico, and recently one in Chile. They also have several plants in the USA, but development here seems to have stalled. Why? It seems that the USA’s unique system of government-sanctioned utility monopolies, along with inconsistent state and federal environmental regulations concerning power generation technologies make it a tough market for CSP. Also, in states like California, where the market for CSP is favorable, the population density makes it impractical. Until desert states like Arizona and New Mexico recognize the full potential of their solar resources, the energy producers of the Middle East may continue to dominate, even in the post-fossil fuel economy.

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]]> Solar Water Heating: In the Shadow of PV https://solartribune.com/solar-water-heating-in-the-shadow-of-pv/ Tue, 21 Oct 2014 12:36:28 +0000 http://solartribune.wpengine.com/?p=8101 It would be hard not to notice the rush of activity in the worldwide photovoltaic marketplace in recent years, but you may not have noticed that at the same time, solar thermal technology has been rapidly overshadowed by the unprecedented growth and popularity of PV. Once heralded as the most cost effective way to capture […]

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]]> It would be hard not to notice the rush of activity in the worldwide photovoltaic marketplace in recent years, but you may not have noticed that at the same time, solar thermal technology has been rapidly overshadowed by the unprecedented growth and popularity of PV. Once heralded as the most cost effective way to capture and store the sun’s energy, sales of solar water heating systems have not kept pace with the new generation of “plug and play” PV products. The reality of solar thermal’s technical complexities, in combination with misinformation about solar thermal’s versatility and practicality have lead to stagnation in the marketplace. In fact, the rise of cheap PV lead to Martin Holladay’s pronouncement that “Solar Thermal is Dead” in a 2012 article at greenbuildingadvisor.com.

“Solar water heating is only practical in southern climates…”

We often hear that solar water heating doesn’t make sense in northern states, like Minnesota and Wisconsin. In fact, Holladay makes the case that with plummeting PV prices, it may actually be cheaper to heat water with PV now than it is to us a solar thermal system. With PV panel prices dropping below $1/watt, this may be even more true than when Holladay’s article was initially published. Still, thanks to incentive programs, affordable solar domestic hot water (sdhw) systems are still going up in northern states. According to the Daily Northwestern, The city of Evanston Illinois has had 85 new DSHW systems installed this year. In addition, niche markets for solar water heating are popping up, in the hotel industry, greenhouses and residential and public pool heating.

The solar heated greenhouse at Dickinson college photo: dickinson.edu

The solar heated greenhouse at Dickinson college photo: dickinson.edu

Meanwhile, SDHW continues to see modest growth and continued popularity in southern states like Arizona and Florida. Can solar water heating make a comeback in the US? As with PV, the key will be seeing the installed price come down, and sadly, right now, that isn’t happening.

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]]> Liquid Solar Space Heating https://solartribune.com/thermal-fluid-heaters/ Thu, 20 Oct 2011 00:35:04 +0000 http://solartribune.wpengine.com/?p=927 Liquid solar thermal heating systems are best for central heating in the home. The solar collectors use either water or a non-toxic glycol antifreeze to absorb the thermal energy. With the help of a controller, a circulating pump moves the fluid through the collector. The liquid flows quickly through the collector, resulting in an increase […]

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]]> Liquid solar thermal heating systems are best for central heating in the home. The solar collectors use either water or a non-toxic glycol antifreeze to absorb the thermal energy. With the help of a controller, a circulating pump moves the fluid through the collector. The liquid flows quickly through the collector, resulting in an increase in temperature of 10°–20°F (5.6°–11°C).

The warm liquid flows to a storage tank or a heat exchanger. The heat is then spread through the home via one of the methods described below.

Radiant Floors

An example of radiant flooring. Photo Credit: Savings by Design

Heated liquid from the solar collector travels through pipes in a concrete slab flooring, usually covered with tiles. The heat radiates to the room.

This kind of solar home heating system can work without a heat storage tank, although a tank is needed to control the temperature.

These systems take longer to warm up but, once operating, provide a consistent temperature. Carpets and rugs will reduce the effectiveness of radiant floors.

Hot Water Baseboards or Radiators

These need water heated between 160° and 180°F (71° and 82°C). However, flat-plate solar collectors – the most common type of collector – heat liquid to a lower temperature. In this case, the liquid from the collectors needs to be heated more by the backup system, or that a higher temperature collector be used (such as an evacuated tube collector).

Central Forced-Air System

This kind of system works through a heat exchanger in the air duct. As air from inside the home passes over the heat exchanger, the liquid inside heats the air. The coil must be big enough to transfer enough heat to the air at the collector’s lowest operating temperature.

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]]> Solar Home & Space Heating Systems https://solartribune.com/solar-thermal-heating/ Mon, 17 Oct 2011 02:48:39 +0000 http://solartribune.wpengine.com/?p=908 Active solar home heating employs solar thermal energy to heat space in the home. First, solar collectors transfer the sun’s heat to air or liquid. Once the solar radiation is absorbed, the air or fluid is transferred either directly to a space in the home or to a storage tank. Often a back-up system provides […]

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]]> Active solar home heating employs solar thermal energy to heat space in the home. First, solar collectors transfer the sun’s heat to air or liquid. Once the solar radiation is absorbed, the air or fluid is transferred either directly to a space in the home or to a storage tank. Often a back-up system provides any additional heat that the solar home heater cannot produce.

One type of home solar space heating system. Credit: Solar Panels Plus

Learn more about different types of solar heating:

  • air space heating is best for directly heating rooms
  • liquid space heating is best for central heating

Cost and Performance

Solar space heating systems are most economical when they are used for the majority of the year – that is, in cold climates with good solar resources where the home requires heating – and when used in place of more expensive heating methods.

EnergySavers.gov recommends installing a solar heating system to provide 40%-80% of your heating needs. A heating system to satisfy your full heating needs may be impractical or expensive. Also, many building codes and loan lenders require a back-up heating source.

Most solar heating systems have at least a 10 year warranty, and some states offer tax credits for home solar thermal heating. If using a liquid space heating system, it is more economical to use the solar collector for hot water heating, too.

Because air-based systems produce heat earlier and later in the day, solar air heaters may produce more usable energy over a longer time period.

Solar Air Home Heating

Air in the solar collectors cannot freeze in the winter, and small cracks in the collectors or piping are not problematic. But air is a less efficient than liquid for transferring heat.

air-space-heating

Photo Credit: GenPro

Air space heating systems are usually room air heaters, which directly heat individual rooms. A fan pulls air from the room into the collector. The air is heated as it travels through the collector, and is then blown back into the room. There are two ways to mount a solar air heater:

  • roof-mounted room heaters need ducts to transport air from the collector to the room
  • wall-mounted room heaters are placed on a south-facing wall, with holes cut through the wall to allow the air to pass through to the room

Liquid solar thermal heating systems are best for central heating in the home.

Solar Water Home Heating

The solar collectors use either water or a non-toxic glycol antifreeze to absorb the thermal energy. With the help of a controller, a circulating pump moves the fluid through the collector. The liquid flows quickly through the collector, resulting in an increase in temperature of 10°–20°F (5.6°–11°C).

The warm liquid flows to a storage tank or a heat exchanger. The heat is then spread through the home via one of the methods described below.

Radiant Floors

An example of radiant flooring. Photo Credit: Savings by Design

Heated liquid from the solar collector travels through pipes in a concrete slab flooring, usually covered with tiles. The heat radiates to the room.

This kind of solar home heating system can work without a heat storage tank, although a tank is needed to control the temperature.

These systems take longer to warm up but, once operating, provide a consistent temperature. Carpets and rugs will reduce the effectiveness of radiant floors.

Hot Water Baseboards or Radiators

These need water heated between 160° and 180°F (71° and 82°C). However, flat-plate solar collectors – the most common type of collector – heat liquid to a lower temperature. In this case, the liquid from the collectors needs to be heated more by the backup system, or that a higher temperature collector be used (such as an evacuated tube collector).

Central Forced-Air System

This kind of system works through a heat exchanger in the air duct. As air from inside the home passes over the heat exchanger, the liquid inside heats the air. The coil must be big enough to transfer enough heat to the air at the collector’s lowest operating temperature.

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]]> Concentrating Solar Power https://solartribune.com/solar-power-plants/ Mon, 10 Oct 2011 12:28:43 +0000 http://solartribune.wpengine.com/?p=3418 Concentrating solar power (CSP, or also known as concentrated solar power) uses mirrors or lenses to reflect sunlight onto a surface that absorbs the solar radiation. The heat from the sun – thermal energy – is used to power a conventional generator (often a steam turbine), producing electricity on a utility-scale. Today, many power plants […]

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]]> Concentrating solar power (CSP, or also known as concentrated solar power) uses mirrors or lenses to reflect sunlight onto a surface that absorbs the solar radiation. The heat from the sun – thermal energy – is used to power a conventional generator (often a steam turbine), producing electricity on a utility-scale.

Today, many power plants use nuclear or coal power to boil water to spin the steam turbines. Concentrating solar power systems provide a clean alternative power source. “Hybrid” systems, which use both natural gas and CSP, are also popular.

The technology is known as ‘concentrating’ because sunlight is focused on to a relatively small space.

There are three main types of concentrator systems, which produce varying amounts of energy. Larger CSP systems (up to 100 MW) are used by utilities, whereas smaller systems (say, 10 KW) can be used to provide power for remote villages.

Types of Concentrating Solar Power Systems

Linear Concentrator Systems
Long, rectangular U-shaped mirrors are tilted toward the sun. The incoming light focuses on linear receiver tubes that run the length of the collectors. Fluid inside the tubes is heated by the sun’s rays, and this heat energy is used to power a conventional generator.

A parabolic trough linear concentrator system. Credit: U.S. Department of Energy

This system is known a parabolic trough system (based on the shape of a parabola, i.e. a curve), and a collector field has many troughs in parallel rows. A sun-tracking system enables the mirrors to follow the sun from east to west, maximizing sunlight absorbed.

The largest trough systems generate 80 MW of electricity, although there are systems under development capable of generating 250 MW. Linear Fresnel reflector systems operate on the same principles, but the receiver tube is situated above the mirrors.

Dish/Engine

A dish/engine system. Credit: U.S. Department of Energy

A dish/engine system consists of a solar concentrator and a power conversion unit. A dish-shaped collector, similar in shape to a satellite dish, concentrates sunlight onto a receiver in the center of the dish. A fluid in the receiver is heated, and the thermal energy is transferred to an engine generator.

The most common type is a Stirling engine, hence the name dish/Stirling. A Stirling engine uses the heat to move pistons, creating mechanical power to run the generator. This type of system produces the least amount of electricity out of all concentrating solar power plants, usually around 3 to 25 KW.

Solar Power Towers
Large, flat mirrors (heliostats) on top of a tower track the sun, and focus the sunlight on a receiver atop the tower. A fluid inside the receiver generates steam which powers a conventional generator to produce electricity. Solar power tower technology is less advanced than trough systems, but these systems are very efficient. Though there are few power tower facilities in the U.S., more projects are underway.

The Solar Two solar power tower near Barstow, California. Credit: U.S. Department of Energy

The drawbacks of CSP and the road ahead

Proponents highlight the benefits of using a clean, renewable energy – rather than the traditional fossil fuels or nuclear power – to power utility-scale steam turbines.

As with photovoltaics, one concern with CSP is the ability to produce energy under low sunlight conditions. But while some use water as the heat transfer medium, most new systems us oil or molten salt. These fluids allow the heat energy to be stored for use during cloudy periods or at night.

Another concern is cost. Currently, CSP is one of the most expensive ways to produce energy. According to the Energy Information Administration, the cost of electricity from CSP plants will be much more expensive than natural gas in the next few years.

But some analysts predict that the cost of electricity at CSP plants currently under development will be around the same as natural gas powered plants. While current cost estimates vary, the future cost will depend on continued investment in CSP technology, as well as a global movement away from fossil fuels.

There are currently 514 MW of CSP projects operating in the U.S., though another 1,349 MW are under construction and 4,100 MW are in the development phase. Experts predict an expansion of CSP, with one study claiming that by 2050 CSP could provide up to 25 percent of the world’s energy demand. As of now, Spain has the most CSP plants in the world, but analysts foresee strong future growth in Africa, Mexico and the U.S.

The CSP industry formed a coalition, the Concentrating Solar Power Alliance (CSPA), in March 2012. The group aims to educate U.S. regulators, utilities and grid operators about the benefits of CSP.

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]]> Solar PPAs https://solartribune.com/ppa-solar/ Tue, 16 Aug 2011 18:15:12 +0000 http://solartribune.wpengine.com/?p=772 A solar power purchase agreement – PPA – is a way to use solar energy in your home without the initial high costs of the purchase and installation of a PV system. It is a third party ownership model, wherein the system owner installs and maintains the PV system on the customer’s property. The customer […]

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]]> A solar power purchase agreement – PPA – is a way to use solar energy in your home without the initial high costs of the purchase and installation of a PV system. It is a third party ownership model, wherein the system owner installs and maintains the PV system on the customer’s property.

PPAsolar

Photo Credit: NREL.gov

The customer enters into a contract to buy the electricity generated by the system, but not the PV system itself. The price for the electricity is equal to or less than the grid price.

The PV system is connected to the grid, and if the local utility has a net metering arrangement, the owner of the PV system collects any credits for electricity funneled into the grid.

PPAs can last from 6-20 years, making them suitable for the longer-term. This arrangement is suitable for small businesses, homes and landlords of rental properties who want to provide solar power for tenants.

With some specific changes to the terms and conditions of your home lease agreement, power purchase agreement can be a viable option for renters.

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]]> Leasing Solar Panels https://solartribune.com/leasing-solar-panel/ Tue, 16 Aug 2011 18:14:35 +0000 http://solartribune.wpengine.com/?p=729 A solar panel lease works similarly to other leases: the homeowner rents a PV system from the system owner for a monthly fee. If the local utility has a net metering system, the homeowner receives any credit for electricity fed into the grid. This arrangement is in contrast to a solar PPA, where the homeowner […]

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]]> A solar panel lease works similarly to other leases: the homeowner rents a PV system from the system owner for a monthly fee. If the local utility has a net metering system, the homeowner receives any credit for electricity fed into the grid.

This arrangement is in contrast to a solar PPA, where the homeowner only pays for the electricity used and the system owner receives credits from energy fed into the grid.

leasing-a-PV-system

A solar lease usually lasts for at least five years. Some solar leasing arrangements have a purchase option at the end of the lease period.

Solar leasing avoids the high initial costs of buying and installing a system. Furthermore, many solar lease packages include operation and maintenance services. This option also lessens the cost and the inconvenience for homeowners interested in going solar.

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]]> Energy Efficient Mortgages https://solartribune.com/eem/ Tue, 16 Aug 2011 18:14:07 +0000 http://solartribune.wpengine.com/?p=787 An Energy Efficient Mortgage (EEM) is a loan financing option that takes a home’s energy efficiency into account. EEMs are available both for purchasing new energy efficient homes, or for purchasing homes with planned efficiency improvements. EEMs are available through both government-insured and conventional loan programs. EEMs allow borrowers to include solar PV and thermal […]

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]]> An Energy Efficient Mortgage (EEM) is a loan financing option that takes a home’s energy efficiency into account. EEMs are available both for purchasing new energy efficient homes, or for purchasing homes with planned efficiency improvements. EEMs are available through both government-insured and conventional loan programs.

green-mortgage

Photo Credit: ASE.org

EEMs allow borrowers to include solar PV and thermal systems in the mortgage itself, and thus stretch debt-to-income ratios needed to qualify for a loan. Borrowers can obtain a larger loan amount for a more energy-efficient home.

A certified home energy rater must conduct an energy rating inspection before a bank approves financing. The rating will provide the lender with an Energy Savings Value – an estimate of the monthly energy savings.

Another option is an Energy Improvement Mortgage (EIM), which is used to purchase homes that will have energy efficient improvements made to them in the future. Borrowers can include the cost of the improvements (e.g. PV panel installation) in the mortgage without any increase in the down payment.

Learn more about EEMs at the U.S. Department of Housing and Urban Development or check out this EnergyStar factsheet.

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]]> Thermosiphon Water Heater https://solartribune.com/thermosiphon-solar/ Mon, 15 Aug 2011 19:37:52 +0000 http://solartribune.wpengine.com/?p=1310 A thermosiphon system – also called a thermosyphon solar water heater – has a tank connected to a flat plate-collector. Thermosyphon systems are passive: no pumps are needed to aid water flow. The water tank is installed above the collector, directly on the roof. As hot water rises in the tank, cold water flows to […]

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]]> A thermosiphon system – also called a thermosyphon solar water heater – has a tank connected to a flat plate-collector. Thermosyphon systems are passive: no pumps are needed to aid water flow.

The water tank is installed above the collector, directly on the roof. As hot water rises in the tank, cold water flows to the bottom and into the collector. The cold water directs the heated water through the collector outlet and into the top of the tank. This heated water flows from the rooftop tank to the ground-level storage tank.

thermosyphon-system

Photo Credit: ClimateChange.gov.au

Thermosiphon systems are very efficient as they are simple and rely only on the laws of thermodynamics, allowing them to function even when mains power is down. However, these systems’ efficiency declines in colder climates.  Plus, other factors make such systems unsuitable for some households: the roof may not be able to support the weight of the storage tank, and the appearance of a fully roof-mounted system does not appeal to all property owners.

Nowadays, with the development of new technologies, the use of thermosiphon systems has decreased. Contact your installer to find out whether such a system is appropriate for your home.

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]]> Solar Water Heater Efficiency https://solartribune.com/solar-hot-water-panels-efficiency/ Sun, 14 Aug 2011 17:13:23 +0000 http://solartribune.wpengine.com/?p=1257 Efficiency ratings for solar thermal collectors refer to either the thermal energy output or the “amount of energy offset” by a system (the extent to which the solar water heating system reduces conventional gas or electric energy use). Below are the three main indicators of solar hot water efficiency. Solar Energy Factor (SEF) The SEF is […]

The post Solar Water Heater Efficiency appeared first on Solar Tribune.

]]> Efficiency ratings for solar thermal collectors refer to either the thermal energy output or the “amount of energy offset” by a system (the extent to which the solar water heating system reduces conventional gas or electric energy use). Below are the three main indicators of solar hot water efficiency.

Solar Energy Factor (SEF)

The SEF is the energy delivered by the system divided by the conventional energy input (energy used by the backup heater plus any energy used to power pumps or controllers in the solar water heating system). The values range from 1 to 11, with most residential systems having a water heater efficiency of 2 or 3. The higher the value, the more energy efficient the system. That means the solar thermal system contributes more to water heating so less conventional energy is required.

hot-water-heater-panel

Photo Credit: SOLARNOR

Solar Fraction (SF)

The SF is the portion of the total hot water heating load provided by solar energy. The higher the SF, the greater the solar contribution to water heating. The value of the SF ranges from 0 to 1, with residential water heating systems typically having a solar factor of 0.5–0.75. The SF is a standard developed by the Solar Rating and Certification Corporation (SRCC), and is outlined in the OG-300 standard.

Btu/(ft²day)

This rating comes from the Florida Solar Energy Center, which provides a rating for most models of solar collectors. Btu stands for British thermal units – the measurement of the thermal energy needed to heat water. Btu/(ft²day) indicates how much thermal energy per square foot of collector is generated in a day. A higher Btu/(ft²day) rating means that fewer square feet of collector space can heat the same amount of water.
You can use this rating to compare the energy supplied per dollar invested of a collector. To do so, divide the Btu/(ft²day) by the total system cost. Multiply the result by the number of collectors used.
Note that these ratings consider solar water heating efficiency in terms of thermal energy output. Such ratings do not judge the reliability or longevity of a collector.

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]]> Is Solar Water Heating Worth It? https://solartribune.com/hot-water-tank-installation/ Sat, 13 Aug 2011 19:40:08 +0000 http://solartribune.wpengine.com/?p=1183 For a homeowner, solar water heating often produces better returns than photovoltaics. Depending on a circumstances specific to you, solar hot water heating can be a great investment. Before you install solar hot water, consider the following factors:  solar resource: the amount of sunlight reaching your solar collectors impacts the efficiency of your solar thermal system. […]

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]]> For a homeowner, solar water heating often produces better returns than photovoltaics. Depending on a circumstances specific to you, solar hot water heating can be a great investment. Before you install solar hot water, consider the following factors: 

  • solar resource: the amount of sunlight reaching your solar collectors impacts the efficiency of your solar thermal system. Learn about solar radiation in your region.
  • climate: a cooler climate may require an active heating system, whereas a passive system could suffice in warmer climates.
  • local building codes and regulations

What direction should the solar heating system face?

Ideally, solar thermal collectors should face south to maximize the amount of solar radiation reaching the collectors. If your roof faces another direction, an extra frame can be installed to angle the collector toward the south.

solar-hot-water-collectors

Photo Credit: Arizona Solar Hot Water

Can water heaters be placed in the shade?

Avoid mounting solar collectors in areas that are shaded by trees, electrical cables, buildings, chimneys, vents or any other source. Shading in an area can change with the sun’s path, from summer to winter. An installation professional can estimate the shading your system will receive.

If installing a solar water heater seems like a viable option, why not also estimate the annual cost of solar hot water heating for your home.

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]]> How Much Does a Solar Hot Water System Cost? https://solartribune.com/cost-solar-water-heater/ Sat, 13 Aug 2011 01:00:22 +0000 http://solartribune.wpengine.com/?p=1173 The cost of solar water heaters, like solar PV systems, is reasonably high up-front, but is likely to be less than conventional water heating in the long run. According to the Department of Energy, your water heating bills should drop by 50%-80%. Plus, there are plenty of non-financial benefits of using solar power. The cost […]

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]]> The cost of solar water heaters, like solar PV systems, is reasonably high up-front, but is likely to be less than conventional water heating in the long run. According to the Department of Energy, your water heating bills should drop by 50%-80%. Plus, there are plenty of non-financial benefits of using solar power.

A rooftop solar thermal collector.

The cost of solar thermal energy depends on:

  • price of fuel from local utility, used to heat water
  • federal, state and local government incentives
  • the amount of hot water you use
  • your system’s performance
  • the type of back-up heating you use
  • the solar radiation resource in your area

Reinforcing your roof to hold the weight of a solar collector can add to the solar water heating cost. Another factor to keep in mind is that some systems require more frequent and costly maintenance than others.

You can estimate the annual operating cost of a solar water heating system once you know your system’s solar energy factor (the measurement of efficiency for solar thermal systems) and the cost of your backup heating. Check out this great U.S. Department of Energy guide to calculating the cost of the system you have in mind.

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]]> What Size Should My Solar Water Heater Be? https://solartribune.com/what-size-water-heater/ Mon, 08 Aug 2011 23:58:19 +0000 http://solartribune.wpengine.com/?p=1094 You should decide on the size of your hot water heating system with the advice of a solar professional. Here are the two primary considerations when sizing your system. Solar Collector Size The conventional estimates for surface area of solar collectors are as follows: 20 square feet of collector area for two family members 8 […]

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]]> You should decide on the size of your hot water heating system with the advice of a solar professional. Here are the two primary considerations when sizing your system.

Solar Collector Size

The conventional estimates for surface area of solar collectors are as follows:

  • 20 square feet of collector area for two family members
  • 8 square feet for each additional household member in the U.S. Sun Belt region or
  • 12-14 square feet for each additional household member in the northern U.S.

Storage Tank Size

In general, an active water heating system requires 1.5 gallons of storage per square foot of collector. Some specialists suggest installing an even larger storage tank – about 2 gallons per 1 square foot of collector – in very warm, sunny climates. The more tank space, the less likely the system is to overheat when demand for hot water is low.

water-system-sizeThis water heater size chart is an approximate guide to choosing the right collector area and tank capacity. Households using a lot of hot water – for example, for spas or dishwashers – should consider the next largest system size.

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]]> Components of a Solar Hot Water Heating System https://solartribune.com/solar-hot-water-parts/ Mon, 08 Aug 2011 22:25:59 +0000 http://solartribune.wpengine.com/?p=961 The following components commonly found in a solar water heating system. Your system may not require some of these components, depending on the type of solar collector you use: Solar collectors convert sunlight to heat energy. Learn more about the different types of solar collectors. Heat transfer fluids carry the heat from solar collectors to […]

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]]> The following components commonly found in a solar water heating system. Your system may not require some of these components, depending on the type of solar collector you use:

solar-hot-water-panels

Photo Credit: U.S. Department of Energy

  • Solar collectors convert sunlight to heat energy. Learn more about the different types of solar collectors.
  • Heat transfer fluids carry the heat from solar collectors to water storage tanks. In warm climates, the heat transfer fluid may be potable water; in cold climates, a non-toxic anti-freeze. Learn about the importance of heat transfer fluids.
  • Heat exchangers transfer solar heat from the transfer fluid to the home water supply. Learn more about the types of heat exchangers.
  • Storage tanks store hot water when it is not in use. Find out what type of storage tank is best for your home.
  • Pumps control the flow of the transfer fluid through the collector and storage tank.
  • Pump station/system controller. These are optional.

In addition to the various parts needed for a solar hot water heating system, you will need to select the correct system size for your household.

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]]> Solar Hot Water Storage Tanks https://solartribune.com/solar-storage/ Mon, 08 Aug 2011 12:53:46 +0000 http://solartribune.wpengine.com/?p=1139 Solar water heating systems need a storage tank to keep water heated by the collector. Storage tanks are also used for liquid-based solar space heating systems. Cold water from the bottom of the tank is pumped to the solar collector. After passing through the collector, the hot water returns to the tank. Because hot water […]

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]]> Solar water heating systems need a storage tank to keep water heated by the collector. Storage tanks are also used for liquid-based solar space heating systems.

tank-solar-hot-water

Photo Credit: Department of Climate Change and Energy Efficiency of Australia

Cold water from the bottom of the tank is pumped to the solar collector. After passing through the collector, the hot water returns to the tank. Because hot water rises, the water coming from the collector stays at the top of the tank. Hot water for the home is drawn from the top of the tank as needed.

Materials

Solar storage tanks should be well-insulated against heat loss, and may need a protective coating to prevent leaks or corrosion. Tank material will be dependent on your water quality and whether you are connected to the mains water supply. The following are the most common types of tanks:

  • vitreous enamel or mild steel: most susceptible to corrosion, thus needing a sacrificial anode (a metal rod down the center of the tank) to avoid corrosion. This anode must be replaced periodically.
  • stainless steel: less susceptible to corrosion and requires less maintenance, but are not recommended for areas with poor water quality

Placement

Solar water storage tanks are typically placed in one of two locations. Depending on available space, it may be more convenient to use several small storage tanks rather than one large one.

  • roof mounted tanks are placed horizontally above collectors. This is called a thermosiphon system, which does not require pumps or controllers and leaves your ground level space free. The drawback is that such a system is a heavy load on the roof (650-1500lbs).
  • a split system, with the tank on ground level, needs a pump to circulate the solar transfer fluid. A pump needs electricity to power it and requires maintenance. The tank should be placed close who where hot water is used the most, such as near a bathroom or kitchen, to minimize heat loss on the way.

Solar storage tanks should also meet all local regulations. The simplest option is to use a standard domestic water heater, because these are already made to comply with all building codes.

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]]> Solar Heat Exchangers https://solartribune.com/what-is-a-heat-exchanger/ Sun, 07 Aug 2011 20:28:44 +0000 http://solartribune.wpengine.com/?p=977 These facilitate solar heat exchange between the transfer fluid to the home water supply. Solar heat exchangers are often made from copper, a good thermal conductor and less likely to corrode, but can also be made from other metals like steel. The main type of heat exchanger is liquid-to-liquid, which uses transfer fluid, with one […]

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]]> These facilitate solar heat exchange between the transfer fluid to the home water supply. Solar heat exchangers are often made from copper, a good thermal conductor and less likely to corrode, but can also be made from other metals like steel. The main type of heat exchanger is liquid-to-liquid, which uses transfer fluid, with one or two barriers between the transfer fluid and the water supply. These are described below:

solar-hot-water-diagram

Photo Credit: Tallahassee Energy & Construction

  • single-wall: fluid in the pipe and outside of the pipe are different.
  • double-wall: used as a safety measure when the transfer fluid is toxic. These are less efficient because the heat must go through two surfaces instead of one.

The most common designs of heat exchangers are:

  • coil-in-tank where the exchanger is a tube in the storage tank
  • shell-and-tube, where two tubes with water and heat-transfer fluid circulating in opposite directions are encased in a metal shell outside the storage tank.
  • tube-in-tube, with the two tubes of water and heat-transfer fluid  in direct thermal contact with each other, is the most efficient type.

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]]> Heat Transfer Fluids https://solartribune.com/thermal-transfer-fluid/ Sun, 07 Aug 2011 20:28:28 +0000 http://solartribune.wpengine.com/?p=981 Heat transfer fluids transmit the heat from solar collectors to the water for the home. The heat transfer fluid flows through the collector to the water storage tank, passing on the thermal energy by way of a heat exchanger. There are many potential heat transfer fluids. The right fluid depends on the type of solar […]

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]]> Heat transfer fluids transmit the heat from solar collectors to the water for the home. The heat transfer fluid flows through the collector to the water storage tank, passing on the thermal energy by way of a heat exchanger.

There are many potential heat transfer fluids. The right fluid depends on the type of solar hot water heating system and the climate. Factors to consider are: freezing point, boiling point, and viscosity (which determines how much energy is needed to pump the fluid). at transfer fluids used in solar hot water systems are non-toxic. The most common transfer fluids are:

thermal-solar-liquid

Different heat transfer fluids are suitable for different climates.

Water

  • non-toxic, easy to pump, inexpensive and efficient
  • not suitable for extreme heat or cold due to it’s high freezing point and low boiling point
  • water with a high mineral content can lead to corrosion in the pipes

Propylene Glycol 

  • known as anti-freeze in solar thermal systems
  • works in freezing temperatures
  • must be replaced every 3-5 years
  • requires additional components
  • non-toxic

Glycerine

  • higher boiling point
  • works in freezing temperatures
  • requires addition components

Hydrocarbon Oils

  • need more energy to pump than water
  • low freezing point
  • some types are toxic, requiring a double-walled, closed-loop heat exchanger

Silicones

  • low freezing point and high boiling point
  • non-toxic and non-corrosive
  • leak very easily
  • require more energy to pump

 

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]]> Solar Air Collectors https://solartribune.com/solar-hot-air-panels/ Sun, 07 Aug 2011 20:27:18 +0000 http://solartribune.wpengine.com/?p=1078 Solar hot air collectors are mounted on south-facing vertical walls or roofs. Solar radiation reaching the collector heats the absorber plate. Air passing through the collector picks up heat from the absorber plate. Freezing, overheating and leaks are less troublesome for solar air collectors than for liquid collectors. But since liquid is a better heat […]

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]]> Solar hot air collectors are mounted on south-facing vertical walls or roofs. Solar radiation reaching the collector heats the absorber plate. Air passing through the collector picks up heat from the absorber plate.

Freezing, overheating and leaks are less troublesome for solar air collectors than for liquid collectors. But since liquid is a better heat conductor, solar collectors using water or a heat transfer fluid are more suited to hot water heating for the home. A solar hot air collector is most often used for space heating. There are two types of air collectors: glazed and unglazed.

air-collector

Photo Credit: U.S. Department of Energy

Glazed Air Collectors

Glazed air collectors heat air through circulation. A fan moves cold air from the home to the collector. After passing through the collector, the heated air is ducted back to the home. There are multiple system designs:

  • through-pass air passes through from one side of the absorber to the other. This system has the most surface area, making it an efficient way to transfer heat. Lower pressure, though, can require more fan power. Deterioration of select types of absorber materials after years of exposure to solar radiation can worsen air quality and performance.
  • back, front and combination passage in these cases, air is directed to either the back, front or both sides of the absorber. This system is more prone to dust accumulation, which eventually lowers the absorber efficiency. In cold weather, the air passing by the glazing is also prone to heat loss.

Unglazed Air Collectors

An unglazed solar air collector is relatively inexpensive. These collectors are best for areas with high ventilation needs and fewer space heating needs. Therefore these collectors are most commonly used in commercial applications, and are less suitable for residential use.

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]]> Evacuated Tube Collectors https://solartribune.com/old-evac-tube/ Sun, 07 Aug 2011 20:27:16 +0000 http://solartribune.wpengine.com/?p=1019 An evacuated tube solar collector is composed of hollow glass tubes. All the air is removed from the tubes to create a vacuum that acts as an excellent insulator. An absorber coating inside the tube absorbs the solar radiation. This energy is transferred to the fluid moving through the collector and then to the hot […]

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]]> An evacuated tube solar collector is composed of hollow glass tubes. All the air is removed from the tubes to create a vacuum that acts as an excellent insulator. An absorber coating inside the tube absorbs the solar radiation. This energy is transferred to the fluid moving through the collector and then to the hot water storage tank. In cooler climates a heat exchanger is used to separate the potable water from the non-toxic anti-freeze in the collector.

Performance

The vacuum prevents heat loss, making these the most efficient collectors. An evacuated tube collector can work well in cloudy conditions and in temperatures as low as -40°F. This characteristic is most advantageous in colder climates, or during the winter, where other solar collectors may not produce as much energy.

Cost and Durability

tube-evacuated-solar

Photo Credit: Solar Colorado

Depending on the brand, evacuated tube collectors can cost more than flat plate collectors – though the additional up-front cost may be made up for in utility bill savings. Flat plate collectors are usually more cost-effective for residential solar water heating systems. Thus evacuated tube collectors are more commonly used for commercial applications. The added winter and cold climate efficiency makes them a good choice for solar space heating.

Evacuated tube technology has been around since the 1980’s and most evacuated tube collectors have a similar warranty to flat plate collectors. A major benefit is that individual tubes can be replaced as needed, rather than replacing the whole collector.

If you’re considering a solar water heating system, we highly recommend you purchase this comprehensive guide to solar water heating systems by Bob Ramlow.

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]]> Flat Plate Solar Collector https://solartribune.com/solar-flat-plate-collector/ Sun, 07 Aug 2011 20:26:37 +0000 http://solartribune.wpengine.com/?p=1050 A flat plate solar collector is an insulated box covered by glass or plastic with a metal absorber plate on the bottom. The weatherproofed collectors are usually glazed with a coating to better absorb and retain heat. Heat transfer fluid flows through metal tubes lying below the absorber plate. The fluid then flows through a […]

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]]> A flat plate solar collector is an insulated box covered by glass or plastic with a metal absorber plate on the bottom. The weatherproofed collectors are usually glazed with a coating to better absorb and retain heat. Heat transfer fluid flows through metal tubes lying below the absorber plate. The fluid then flows through a heat exchanger before entering the storage tank. Unglazed flat-plate collectors (without insulation or absorber coatings) do not operate in cool or windy climates but are excellent for heating water in a pool.

solar-collector-flat-plate

Photo Credit: Physics World

Performance

Flat plate solar collectors suffer more heat loss than other types of solar collectors, and are thus not the most efficient type. However, flat plate collector are suited to a wider range of climates. Because these collectors can use a heat transfer fluid such as antifreeze, rather than directly heating the domestic water supply, this type of solar thermal panel can be used in colder climates.

Cost and Durability

While they are not the most efficient solar collectors, flat plates last for over 25 years and are one of the most cost-effective options for a residential solar water heating system. Typically, one flat plate collector can supply adequate energy to heat about 40 gallons of water for domestic hot water use. According to EnergyStar.gov, a family of four can obtain about half its hot water from two collectors.

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]]> Batch Solar Water Heaters https://solartribune.com/batch-solar-water-heater/ Sun, 07 Aug 2011 20:26:23 +0000 http://solartribune.wpengine.com/?p=1037 Batch solar water heaters, also called integral collector-storage (ICS) systems, are made up of a water tank or tubes inside an insulated, glazed box. Cold water flows through the solar collector. The water is heated and then continues on to the backup water heating storage tank. Some water can be stored in the collector until […]

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]]> Batch solar water heaters, also called integral collector-storage (ICS) systems, are made up of a water tank or tubes inside an insulated, glazed box. Cold water flows through the solar collector. The water is heated and then continues on to the backup water heating storage tank. Some water can be stored in the collector until it is needed. ICS systems are a type of direct solar water heating system which circulates water to be heated, rather than using a heat transfer fluid to capture the solar radiation.

Performance

solar-ics-system

Photo Credit: Florida Solar Energy Center

Batch systems are only suitable for warmer climates. The collector itself and any outdoor pipes are susceptible to freezing in cold weather, and the batch collector can become very hot if the water is not drawn during the day. Batch systems lose heat during the night time. Nevertheless, batch systems are very good for heating water during the day. They are best for households with most hot water demand during the day and evening.

Cost and Durability

ICS systems can be quite heavy when filled with water and may require extra roof support. But aside from that, batch solar water heaters are simpler than other types of solar collectors, and are correspondingly less expensive. These can be one of the most cost-effective solar water heating systems for warm, sunny climates. Colder climates require additional components to the system, in which case another type of solar collector is likely more economical.

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]]> Types of Solar Thermal Collectors https://solartribune.com/solar-thermal-collectors/ Sun, 07 Aug 2011 20:25:17 +0000 http://solartribune.wpengine.com/?p=940 Thermal solar collectors turn the sun’s radiation into heat and then transfer that heat to air or water. This process is facilitated by a hot water solar collector. There are multiple types of solar thermal collectors: Evacuated tube collectors are the most efficient but most costly type of hot water solar collectors. These collectors have […]

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]]> Thermal solar collectors turn the sun’s radiation into heat and then transfer that heat to air or water. This process is facilitated by a hot water solar collector. There are multiple types of solar thermal collectors:

solar-thermal-power

Photo Credit: Erneuerbare Energien

  • Evacuated tube collectors are the most efficient but most costly type of hot water solar collectors. These collectors have glass or metal tubes with a vacuum, allowing them to operate well in colder climates. Learn more about evacuated tube collectors.
  • Batch solar water heaters, also called integral collector-storage systems, have storage tanks or tubes inside an insulated box, the south side of which is glazed to capture the sun’s energy. Learn more about batch systems.
  • A flat plate collector is a box covered by glass or plastic with a metal absorber plate on the bottom. The glazing, or coating, on the absorber plate helps to better absorb and retain heat. Learn more about flat plate collectors.
  • Unglazed flat plate collectors, typically made from rubber, are primarily used for heating pools.
  • Air collectors are used primarily for space heating in the home. Learn more about solar air collectors.

Learn how such systems can provide solar water heating and solar space heating for your home, or how you can use solar thermal energy to heat your pool.

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]]> Solar Thermal Energy https://solartribune.com/solar-thermal-energy/ Sun, 07 Aug 2011 20:00:18 +0000 http://solartribune.wpengine.com/?p=1103 In contrast to photovoltaic (PV) energy, solar thermal systems turn the sun’s radiation into heat and then transfer that heat to air or water. This process is facilitated by a solar collector. There are multiple types of solar thermal collectors: evacuated tube, batch systems, air collectors and flat-plate collectors. These can be mounted to a […]

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]]> In contrast to photovoltaic (PV) energy, solar thermal systems turn the sun’s radiation into heat and then transfer that heat to air or water. This process is facilitated by a solar collector.

solar-thermal-power

Photo Credit: Erneuerbare Energien

There are multiple types of solar thermal collectors: evacuated tube, batch systems, air collectors and flat-plate collectors. These can be mounted to a roof or wall to provide solar water heating and space heating for your home.

Unglazed flat-plate collectors are usually used to heat swimming pools. Learn more about using solar thermal energy to heat your pool.

Note that since solar thermal collectors are more efficient than PV panels, the payback period for solar thermal systems is much shorter.

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]]> Evacuated Tube Collectors https://solartribune.com/evacuated-tube-solar-hot-water/ Sun, 07 Aug 2011 18:33:55 +0000 http://solartribune.wpengine.com/?p=3045 An evacuated tube solar collector is composed of hollow glass tubes. The air between the tubes is pumped out, while the outside of the tubes are heated, creating a vacuum. This mechanism creates excellent insulation, trapping the heat inside the tube, making solar hot water evacuated tubes highly efficient. An absorber coating inside the tube […]

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]]> An evacuated tube solar collector is composed of hollow glass tubes. The air between the tubes is pumped out, while the outside of the tubes are heated, creating a vacuum. This mechanism creates excellent insulation, trapping the heat inside the tube, making solar hot water evacuated tubes highly efficient.

An absorber coating inside the tube absorbs the solar radiation. Evacuated tube solar collectors heat the transfer fluid (often simply water) moving through the collector and then to the hot water storage tank. In cooler climates a heat exchanger is used to separate the potable water from the non-toxic anti-freeze in the collector.

tube-evacuated-solar

Photo Credit: Solar Colorado

Generally, evacuated tube collectors are used to heat greater volumes of water, or to heat water to higher temperatures, as is often the case in commercial applications. These types of collectors can also be used for steam production and solar space heating.

Efficiency of Evacuated Tube Collectors

The vacuum is a very effective insulator that keeps the water inside the collector hot while the actual tubes are only a few degrees warmer than ambient air temperature. This low heat loss makes these the most efficient of all solar thermal collectors.

An evacuated tube collector can work well in cloudy conditions and in temperatures as low as -40°F. This characteristic is most advantageous in colder climates, or during the winter, where other solar collectors may not produce as much energy. The cylindrical shape also allows the collector to catch ground reflected radiation, known as the “passive tracking effect,” when facing true south.

Nevertheless, a less efficient collector (such as a flat plate collector) is often sufficient for a residential hot water heating system in warmer climates, as the added solar radiation makes up for any efficiency loss. But the higher efficiency makes an evacuated tube system preferable when collector space is limited.

Cost and Durability of Evacuated Tube Collectors

The cost of evacuated tube collectors can be significantly more than flat plate collectors – though the additional up-front cost may be made up for in utility bill savings. Because flat plate collectors are usually more cost-effective for residential solar water heating systems, solar hot water evacuated tube collectors are more commonly used for commercial applications.

solar-hot-water-panels

Photo Credit: metaefficient.com

Evacuated tube solar collectors have been around since the 1980’s and most have a similar warranty to flat plate collectors at around 20 years. But these types of collectors tend to need more repairs for the following reasons:

  • the thin glass (less than 2 millimeters thick) is more susceptible to breaking, and
  • the reliance on a vacuum seal means that over time, the seal can be lost

Despite these issues, the tubes can be replaced individually without having to replace the entire collector.

Maintenance of evacuated tube collectors is slightly more complicated than for other types of collectors. It is true that an evacuated tube solar water heater can be easily cleaned by falling rain water. But snow tends to melt more slowly off these collectors, and due to the fragility of the glass, it cannot be removed with a snow rake. Thus the practicality of cleaning the solar collector can vary depending on climate.

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]]> Flat Plate Solar Collectors https://solartribune.com/flat-plate-solar-system/ Mon, 25 Jul 2011 14:42:11 +0000 http://solartribune.wpengine.com/?p=3170 Flat Plate Solar Collector Design A glazed flat plate solar collector is an insulated box covered by glass or plastic with a metal absorber plate on the bottom to absorb the sun’s radiation. The weatherproofed collectors are usually glazed with a coating to better retain heat. Heat transfer fluid flows through metal tubes lying below […]

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]]> Flat Plate Solar Collector Design
solar-collector-flat-plate

Photo Credit: Physics World

A glazed flat plate solar collector is an insulated box covered by glass or plastic with a metal absorber plate on the bottom to absorb the sun’s radiation. The weatherproofed collectors are usually glazed with a coating to better retain heat. Heat transfer fluid flows through metal tubes lying below the absorber plate. The fluid then flows through a heat exchanger before entering the storage tank.

Unglazed flat-plate collectors (without insulation or absorber coatings) do not operate in cool or windy climates but are excellent for heating water in a pool.

Efficiency of Flat Plate Solar Collectors

A number of factors influence how well the collector is able to heat water, including the ambient temperature and available sunlight.

Flat plate solar thermal collectors suffer more heat loss than other types of solar collectors, and are thus not the most efficient type. However, flat plate solar water heaters are suited to a wider range of climates. Because these collectors can use a heat transfer fluidsuch as antifreeze, rather than directly heating the domestic water supply, this type of solar thermal panel can be used in colder climates.

A flat plate collector installation. Photo Credit: Viessman

Evacuated tube collectors are often more efficient than flat plate collectors as they are able to reach higher temperatures. However, higher temperature capability should not be the sole characteristic to focus on when choosing a solar water heating system.

Evacuated tube systems are more suited for commercial purposes, when greater amounts of water at higher temperatures are needed, such as at a laundromat.  In most instances, a flat plate system is suitable for heating water for your home.

Cost of Flat Plate Solar Collectors

While they are not the most efficient solar collectors, flat plates last for over 25 years and are one of the most cost-effective options for a residential solar water heating system. Flat plate collectors are the most durable type of collector, and can be cheaper than evacuated tube systems.

Typically, one flat plate collector can supply adequate energy to heat about 40 gallons of water for domestic hot water use. According to EnergyStar.gov, a family of four can obtain about half its hot water from two collectors.

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