• How is the Effectiveness of a Solar Panel Measured?

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How is the Effectiveness of a Solar Panel Measured?

Jun 25 2015

The advance in solar power technology and the accompanying drop in the price tag of solar panels have meant that many households around the UK are now equipping their roofs with renewable energy. Such a measure allows them to cut down on energy bills in the long run, as well as doing their bit for the environment by reducing fossil fuel consumption and the pollution that inevitably results from its production.

But how do you know how efficient your panels will be? A typical efficiency rating on a household panel system is anywhere between 11% and 15% efficient. This means that between 11% and 15% of the sun’s rays which hit the panels can be converted into electricity. Although this figure might sound low, it should be more than enough to power a typical home’s needs and perhaps even have surplus to sell back to the grid for an additional profit.

Here’s how to go about determining the efficiency of the photovoltaic cells which will make up your own personal solar panels.

Getting to Grips with Standard Test Conditions

Standardised testing of photovoltaic cells means that different products and models from different laboratories can be compared and contrasted fairly. The agreed upon Standard Test Conditions are as follows:

  • An air mass spectrum of 1.5 (AM1.5) for terrestrial cells and an air mass spectrum of 0 (AM0) for space cells.
  • Cell temperature of no more than 25°C.
  • Sunlight intensity of 1000W/m2.
  • Four-point probe to offset the resistance imbalances caused by the contact between the probe and the cell.

For more information on how such values are measured, check out the illuminating article Measurements for Solar Power, Greenhouse Lighting and Architectural Lighting Applications.

How to Conduct a Test for Peak Efficiency

When browsing for solar panels for your own home, they will most likely come with a series of ratings and guidelines. You can conduct your own efficiency test using the following simple steps:

1)Calculate the surface area of the panel itself. This is easily achieved by multiplying the length of the panel by its width, to come up with the total surface area. In this calculation, you should include the frame of the panel as well.

2)Read the name plate rating from its accompanying explanatory information sheet. For example, a 235 W solar panel will have a rating of 235 watts at Standard Testing Conditions.

3)Divide the rating by the surface area of the panel. For example, a standard panel size is 1,666 cm2. Therefore, for a 235 W panel, the calculation of 235/1,666 reveals an efficiency rating of 14.2%.

4)Each panel will also come with a power tolerance rating. This indicates the variation of power that a panel will produce; for example, it could +/- 3%. Therefore, the panel could generate between 11.2% and 17.2% efficiency, depending upon the variables on any given day.

Changing Variables

You should also be aware of the variables which will affect the performance of a solar panel. These include, but are not limited to:

  • Strength of sunlight
  • Duration of sunlight hours
  • Panel direction
  • Panel pitch
  • Temperature
  • Propensity to shade

Fine-tuning all of these variables (or at least, those within your power) will increase the efficiency of your panel and lead you to getting the best return on your investment.


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