photo voltaic solar panels

IT WAS 10:43 GMT in Harrow when we started this article and the sun was shining. That means that our 15 Sanyo 210NHES photo voltaic panels were feeding DC into the inverter and delivering AC 1837W at 7.59A and at 242V.

A bit like a sunflower, the inverter wakes up when the PV system is generating enough juice and goes to sleep when dusk comes - it's no nighthawk, and doesn't party on into the wee small hours.

The inverter is connected to our mains power box and in a week or two we'll be able to sign an agreement with the National Grid which means we'll be paid for excess juice the panels generate.

We don't have the panels connected to batteries - this means that if you want to run your washing machine or other serious watt eaters, you should do so during the day to take advantage of the fact you're generating and the fact you're getting paid for your micro-generation.

The Euro figure in the Fronius total system screen shot below is notional - rates vary and the software that uses the USB based datalogger allows you to change the currency and payment rate to match your own agreement.

The Fronius inverter has slots for a datalogger and a sensor card - the datalogger we have connects to the inverter via an Ethernet cable, and from there via a USB cable to our PC. The datalogger unit also has a serial port at the back which you can connect to a modem so you can access your system while you're out and about. Don't ask me why you can't do this more directly - ask Fronius. The software supplied lets you download the data held on the inverter and export it using CSV (comma separated value) format. You're probably wondering why we don't have a wi-fi system to log the data? Apparently such wi-fi systems are not too reliable, yet.

Naturally, the amount of juice the PV panels generate depend on how bright a day it is, the declination of the sun, the tilt of the roof and the direction the panels are facing. The roof on this house faces SSW, and is unobstructed, meaning the panels get a good photon bashing for most of the hours of daylight. Right now, at 11:00AM GMT, the panels are delivering 2002W. Each of the Sanyo 210NHES panels weighs 15Kg, measures 1597mm by 815mm and includes 72 photovoltaic cells.

Are the panels economical? The fact is, without a 50 per cent grant from the Department of Trade and Industry through the Energy Saving Trust (EST) they probably would take a heck of a while to repay the initial investment. The panels themselves are designed to last 25 years but estimates are that they're likely to last longer - the system installed here largely replaces a large area of roof tiles which would have needed changing on this 1926 house anyway, soon enough.

Installation of the panels, inverters and cabling took about four days - the guys we used, Solstice Energy, were very pleasant, efficient, friendly and unobtrusive. If you're based in London, we've no hesitation in recommending them.

Do you need planning permission? We've already ranted about this in the pages of the INQ. After some humming and hawing, Harrow Council finally decided we should apply for a cert of lawful development - listed buildings, conservation areas may well need planning permission.

As Richard Warren from Solstice pointed out, the panels jut out from the roof less than those skylights people install, which don't seem to need planning permission in Harrow. After a bit of solar agitprop with the help of local councillor Bill Stephenson and local MP Gareth Evans, Harrow Council eventually arrived screeching into the 21st century and issued its own guidance. These panels were supposed to have been in place since November last. µ

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