Jul 08 2010
Coping with our dodgy grid
In the UK’s fledgling PV industry there are some unexpected issues emerging.
One of those is related to the grid or ‘mains’ voltage. This should be, as in the rest of Europe, fixed at 230V. However it can vary, and in reality the legal limit is 230V plus or minus 10 percent, generally being higher voltage close to the nearest transformer, and getting lower voltage as you move away.
This is important for PV systems because the inverter must convert direct current into mains compatible AC with an acceptable voltage level. Inverters are also designed to shut down if there is a problem with the grid for safety reasons.
In Germany, the voltage level is very precise (perhaps as you might expect) and since Germany is the world’s largest solar market by far, most inverters in Europe have their settings with Germany in mind. This means that when the
grid strays slightly away from 230V, the inverter temporarily shuts down. In the UK, the grid is much more likely to deviate from 230V, meaning that with German settings, an inverter could well spend more time off than on.
Luckily the problem is generally easily fixed by changing the inverter to new settings which make it tolerant to a wider voltage range. The key point to remember is that with the inverter shortage, products are being sold
which are completely unchanged from their German settings. This means you need to be extra vigilent when buying an inverter to ensure compatibility.
A related topic, that I will soon cover, is to do with how lots of solar energy connected to the grid can actually affect the grid voltage and frequency – but that’s another issue.
If an inverter is used in the UK without any change in settings then chances are, with our fluctuating grid, you will have peaks or dips in the voltage that shut off the inverter from time to time. The solution is simply to
change the settings via the firmware to allow the inverter to carry on working in a wider range of voltages.
