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Generating my own electricity

Posted by Cathy Debenham on 10 March 2010 at 9:05 pm

Our new photovoltaic solar panels started generating electricity a month ago today. It was dusk on a cold February day when the system was all ready to go, so I was suprised to see the light flashing on the generation meter and the inverter showing that, even in such poor light, it was making a little bit of power.

The next day was even more exciting. Cold and crisp, with a bright sun, it was a perfect day for generating electricity. I even found myself sharing the generation figures on Twitter!

We've got a 2.1kWp array. That's 12 Sharp panels on a steep (45 degree angle) roof over the garage. The front of the house faces south west, and we has solar thermal panels for hot water installed a few years ago. With those panels, and two dormer windows, there isn't enough room to add PV panels.

I'd more or less given up on the idea, because there are a couple of big trees that shade the south east facing garage roof, so I didn't think it was suitable. Until, that is, I talked about it with Stuart Houghton, director of much recommended installer Abacus Renewable Energy, and he offered to come and measure the potential of the site using a Solar Pathfinder gizmo. This predicts how much energy can be generated taking any shading into account.

It calculated that without shading, and with a better roof angle of 38 degrees, our system would generate 1,948 kWh a year. With the shading, that falls to a predicted 1,589 kWh. However, as the measurement was taken at the lowest part of the roof, and the panels have been installed rather higher up, Stuart is confident we will generate more that that.

The predictions are broken down by month. February's is 83.31kWhs and March's 133.84. To date we've generated a total of 96kWh, so it looks as if we're on track. Things go up quickly as we go into spring and summer, as the shade only falls on the roof in the winter months.

I regularly add our meter readings to the imeasure site, both as a record of our usage, and to compare with others. It's really satisfying to see the line on the graph that measures our electricity use - which is normally very stable - start to go down. So far that's just because we're using the power we've generated, rather than importing it.

The next challenge is to learn how to work with the system and get the most we possibly can out of it. The easy one is running the washing machine. We already prefer to do a wash on a sunny day, so it dries on the line. Now it makes sense to put the load in slightly later in the day, when the panels are generating at full tilt. I never need an excuse to put off Hoovering, although a sunny day isn't going to be my preferred time! Working out how to get the best out of our solar thermal panels took a bit of trial and error. I think that getting the best out of the PV will be easier.

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Comments

5 comments - read them below or add one

Cathy Debenham

Cathy DebenhamComment left on: 26 August 2010 at 8:27 am

Hi Blue UK

It will depend. On bright days (summer and winter) it will probably generate more than you can use, and some of that will be exported. On days like yesterday (dark grey, and tipping down with rain all day) it might not generate all you need, and you'll buy some in from the grid. Of course, it will also depend on how much electricity you use during the day.

 As far as I know you can store some in batteries and still claim the FiTs - you'll just export less (but I need to check up on that). Most people with a grid connected system don't use batteries though. Maybe someone else can shed some light on that...

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Blue UK

Blue UKComment left on: 25 August 2010 at 3:09 pm

Will solar panels supply 100% of electricity that is needed through the day time ? summer and winter ? and with the new fit scheme can you store power for evening use ?

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Alternative

AlternativeComment left on: 15 June 2010 at 2:12 pm

My 4kWp solar PV system faces east and was predicted to be around 12% down on south facing. In practice, however, it seems only to be around 6% down. The last two years have seen around 3,600kWh per year generated. We are very pleased!

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Cathy Debenham

Cathy DebenhamComment left on: 4 May 2010 at 5:00 pm

Hi Clive

As a rule of thumb, a 1kWp PV system will generate an average of 850kWh of electricity in the UK. Most domestic systems are between 1.5 and 3 kWp. So you'll need to calculate how much electricity your new house will use and go from there. 

How many panels you choose to install will depend on how you want the economics to stack up. Check out the feed-in tariff pages for the details of how it all works, but essentially the incentive is skewed towards generating electricity that you use, rather than electricity you export. If you generate lots that you don't need during the day, you'll only get 3p a unit for exporting it; and will have to pay considerably more than that for the electricity you need to use in the evening when the sun's not shining.

We can't advise on specifics, so for more detail I'd get a few recommended local installers to quote on your plans and see what they suggest.

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clivee

cliveeComment left on: 4 May 2010 at 1:13 pm

How do I calculate how many PV panels I should have to generate a surplus to sell back to EDF please, I am looking at a new build so I have masses of almost directly due-south facing roof with no shade. My new build will be a two bed house built with hemcrete, large south facing windows and good thermal mass in the floor. I intend using solar for heating domestic water and underfloor heating with an electric top up on cold cloudy days. Thanks.

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