Sunday, 13 November 2011

How solar power works

It might sound simple enough to turn sunlight into electricity but there is a lot more to a Solar PV system than you might first think. Here is my quick not too technical guide to Solar PV.

Solar panels generate DC electricity something like a battery cell hence them being called solar cells or solar batteries. The panels will typically generate 40-50V each and are wired in series as "strings". An array of 12 to 16 panels will usually be split into two even sized strings which are then connected to an inverter. The inverter takes the DC electricity and converts to AC at the correct line voltage to feed into your house mains supply. The reason for splitting the array into strings is two fold,  first it keeps the DC voltage at a suitable level for the inverter to work efficiently with, typically between 200 and 400V. Second there is also the chance that should one panel have a fault you will only lose half of your system, only the string with the faulty cell would cease to work.

In practice the inverter does quite a lot more than just do the DC to AC conversion. Most home Solar PV systems are "on-grid" which means that they are permanently connected to the grid, this is necessary for you to export electricity and earn money for it. For the system to work the inverter has to sense that the grid is up and then synchronise to the voltage and phase of the grid when it generates electricity. If the grid goes away it shuts down and stops generating. Most prospective owners dream that they can be self sufficient in electricity to some degree at least when it is sunny, sadly this is not the case.

I hope this simple description helps to shed some light on how the systems work, there are quite a few good technical articles available which go into the full details of how systems work which you can find with a bit of Googling.

Just a quick update on how our system is doing this month. We are currently well behind the predicted yield due to two weeks of almost unbroken grey cloud. Today was only the second really sunny day of the month, and we managed to generate 9.5kWh. The total for the whole month so far is only 41.6kWh, we are going to need  a decent run of sunny days for the rest of the month to get anywhere near the predicted yield.

In the next post I will discuss the changes to the FIT after the 12 December.

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