Can I compare my solar panel output with that of other local installations?
Posted by Tasha Kosviner on 17 March 2014 at 8:48 am
Q. I had a 4kWp solar panel system installed on my roof last October and on the face of it, it seems to be working really well. I have the owl intuition system installed and can monitor my system’s output online. What I would like to do now is to compare this output with what I should be getting for the postcode area I live in (TW20). Is there a site where I can carry out this kind of comparison online?
A. Your best bet is probably to take a look at the Microgeneration Database at the Sheffield Solar Farm.
This is a project run by Sheffield University which monitors the output of solar panel installations across the UK.
With 6,500 installations plotted on a map of the UK, you’re sure to find an installation near you with which you can compare output. The data is updated regularly, on average once a week, so you can get contemporaneous information with which to compare your system’s performance.
You can even create your own account so that you can add your own performance data to the mix. The benefit of doing this is that you will be able to see your own system’s performance plotted on a graph and overlay the graphs from other local installations for a clear visual comparison.
The size, orientation and inclination of each installation is also logged on the site so you can check whether any variations between installations are due to these very common reasons.
You can compare performance with other local installations of different sizes by selecting ‘performance ratio’ under the ‘report type’ drop down menu. This will divide each system’s output by its peak panel output to give a percentage efficiency figure.
If, once you have compared data, you think your system may be underperforming, it is worth remembering that there are a lot of different variables, not just size, orientation and inclination that may mean you output differs from that of other arrays in your area.
As you will be aware, the amount of shading affecting your system will have a significant effect on its performance, but there are other equipment-specific variations to take into consideration too. These include the characteristics and manufacturing tolerances of your particular brand of panel, the efficiency of your inverter, how well your inverter is matched to your array, the losses incurred in your cabling, the cleanliness or otherwise of your panels and any potential periodic losses due to failures in your equipment.
You will need to take all these factors into account before you conclude that there is something wrong with your system’s performance.
If you do not find any installations near to you on the Micregeneration Database, there is another tool you could use to ascertain whether your installation is performing as expected.
The Microgeneration Certification Scheme (MCS) produces region-specific data to help installers predict the potential kWh/kWp output per annum of a planned installation (note the use of the word ‘potential’ rather than actual here). This data was put together for the purposes of calculating what an installation might earn through feed-in tariffs (FITs). If your installation was made under the MCS scheme, your performance estimate would have been made using this data and the best thing you can do is compare these predictions to your actual output to see whether your array is performing as expected for your particular installation in your particular region. If not, there’s nothing to stop you using the data retrospectively to do the calculations yourself.
To do this, you need to first work out what zone you are in by locating your postcode on the table on page 61. A TW20 postcode puts you in zone one.
You must then calculate the orientation of your array. An array that faces due south is said to have an orientation of 0 degrees, an array facing either SW or SE has a value of 45 degrees while one facing either east or west has a value of 90 degrees. You’ll probably need a compass for this bit as the value has to be correct to the nearest 5 degrees.
Next, you must calculate your installation’s inclination. A completely horizontal array has an inclination of 0 degrees whilst 90 degrees represents a vertical array. This needs to be calculated to the nearest degree.
Once you have determined these figures, you can scroll down to the tables starting on page 96 to cross reference your inclination with orientation, to figure out what your kWh/kWp output per annum should be. The average figure for those in zone 1 is 985kWh/kWp.
From the blog
Comparing the performance of solar PV panels (Sept 2011)
If you have a question about anything in the above blog, please ask it in the comments section below.
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