Solar Testing: The Why and How.

When a cell is at its highest level of efficiency we receive accurate, repeatable and reliable results from it. The reason we test solar cells is to make sure the cell itself is positioned correctly so that it is capable of achieving its maximum efficiency. The cell itself needs to reach this level of performance if it is to stand the test of time as this can seriously affect the output of a PV system and decrease the amount of power it generates.

How to Efficiently Test

An installer must carry out solar testing on each panel that is being installed to ensure they are working correctly before they begin. Conditions for testing are best on clear days and when the sun is closest to the AM1. Obviously you can test your cells at any time, but the downside of not testing them in these conditions means that the results may not reflect their full potential output.

To measure the efficiency of a solar panel you will need to measure the voltage and current of the cell to make sure it is performing correctly. Be sure to compare your findings with the output ratings given on the manufacturer’s datasheet as this will give you an idea of the cells expected capability. It is best to obtain these measurements on the ground prior to installation because you don’t want to lift the panels onto the roof only to find you have a faulty panel.

How you measure the voltage and current of a PV cell is up to you; most would argue the best way to measure these capacities would be through an AC/DC Clamp Meter. This tool is widely used throughout the industry as it helps limit contact with the cell which is the safest way to obtain the measurements you need. The price of an AC/DC Clamp Meter can range from £38.00 to £199.99 plus VAT, but would be a worthwhile investment.

An AC/DC Clamp Meter, as you know is an all-round instrument that measures both AC and DC current and voltage. It’s cost effective and can be used to test in two ways – by clamping the tool over the wires you would like to test or through plugging in your MC3 or MC4 test leads into the clamp meter and connecting them to the module itself to obtain a reading. The fact that you can use the meter like this makes it very useful to test the panel on the ground before installation and then again once it’s installed on the roof. Some installers use a multimeter to test the voltage and current of the panel but whichever way you choose to do it, it is always good, safe practice to test to your equipment first to make sure the tools you are using are performing correctly.

Testing the Panel

Please note: PV cells are live the minute they are put in daylight so it is important to carry out solar testing with caution.

Firstly, switch your meter to read in Volts and make sure your panel is facing south. On the back of the module you will have a connection box with various terminals; connect the positive probe into the positive terminal and the negative probe into the negative terminal. This will give you a voltage reading and if the panel is performing correctly it should be within the output rates set in manufacturers guide. You should then measure the short-circuit current of the panel; the short-circuit current is the current through the solar cell when the voltage across the solar cell is zero. To test the current of the PV cell we should turn the panel away from the sun, (north) this also helps to limit the danger of measuring a live cell. The short-circuit current is due to the generation and collection of light-generated carriers. For an ideal solar cell at most moderate resistive loss mechanisms, the short-circuit current and the light-generated current are identical. Therefore, the short-circuit current is the largest current which may be drawn from the solar cell.

It is important to remember that factors such as daylight, pollution, pollen and moisture levels vary from day to day. It is best to obtain all measurements for all cells on the same day to ensure an accurate reading is obtained across the board.

Once voltage and current has been measured and you are happy that the panels are working efficiently on the ground, the next step is ensure they are working to their full potential when their up on the roof. This will include taking both these measurements again and using other tools to make sure that the panels are positioned correctly to work to their full potential.

Efficiency on the Roof

Whilst it’s a popular misconception that photovoltaic (PV) solar panels need sunlight in order to operate, it’s still important to ensure that they are mounted in such a way as to obtain the maximum exposure to available daylight. PV modules are consistently evolving and are able to generate electricity even on the cloudiest of days. It is possible to install PV systems which automatically adjust their positioning angle in accordance with the daily movement of the sun, however because this equipment is slightly out of the average consumers price range, it is very important to ensure that you position the panels in the optimum spot to receive constant daylight. To calculate the optimum installation spot you will need to use various tools such as an angle finder and an irradiance meter. There is more kit available to help with the positioning element however these are the two pieces worth mentioning and also the tools your MCS assessor will expect you to use during your onsite assessments.

All the solar testing equipment mentioned in this article can be bought from distributor Solar PV Tools.co.uk.

Solar PV Tools.co.uk is the cheapest distributor in the UK and are currently price matching their products should you see the same product at a lower price anywhere else. Call 01293 529777 for more information.