How Efficient are Solar Panels?

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The efficiency of solar panels refers to the proportion of the energy input from the sunlight that is converted to power output from a solar module.

There are various measures of solar cell efficiency to consider when looking at specific solar panels for your home. The most common ratings are:

  • The standard test conditions (STC) or peak watt (Wp) rating is the maximum power of a PV module under laboratory conditions of high light, favorable air mass, and low cell temperature. These are the ideal conditions, but also not typical in reality.
  • The normal operating cell temperature (NOCT) rating is determined under more realistic conditions and results in a lower efficiency value than the STC rating.
  • The AMPM standard takes account of a whole day of sun rather than “peak” sunshine hours. The test parameters for light, temperature and air mass are based on a standard solar global-average day.

The graph below indicates that of the varieties of residential solar panels, monocrystalline panels are the most efficient, followed by polycrystalline and finally thin-film.

efficiency-of-solar-module

Photo Credit: NREL.gov

However, efficiency of solar cells alone is not the only factor to consider when choosing solar panels for your home. An important point to consider is the solar resource in your area, as some panels work better in shaded conditions.

Budgetary and spatial constraints allow for different ways to generate the amount of power you need. For example, a larger surface area of cheaper, less efficient panels could be sufficient if space is plentiful. Conversely, a more expensive but more efficient solar module may be more suitable if space is limited. Learn more about sizing your solar module.

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