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How grid-connected home-generated electricity works

Posted by Cathy Debenham on 2 February 2011 at 8:45 am

Understanding how a home microgeneration system switches from solar PV (or wind) generated power to mains electricity and back again is much simpler than you might think. It's all completely automatic and requires no human intervention.

The system comes with an inverter, which converts the home generated electricity from direct current (DC) to alternating current (AC). It converts it at a slightly higher frequency than the electricity that comes from the national grid.

This means that whenever your microgeneration system is producing electricity, appliances in your house will draw on that electricity first. If there isn't enough it will top it up by calling for more from the grid. It all happens smoothly and continuously, so you're unaware of what's happening.

The more of your own generated electricity you use, the more you benefit. The cost of importing electricity is significantly greater than the amount you are paid for exporting your surplus. The trick is to try and do the things that use most electricity when the sun is shining.

Given that many people are out of the house for much of the day, this isn't always easy. But gettting a timer switch so you can run the washing machine or dishwasher or turn on the immersion while the sun is out will make a difference.

Photo by Stewart Chambers


If you have a question about anything in the above blog, please ask it in the comments section below.

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14 comments - read them below or add one

Cathy Debenham

Cathy DebenhamComment left on: 16 April 2012 at 1:59 pm

Hi Gramm7168

If you've got an old meter it will go backwards whenever your solar panels are producing more electricity than you are using in the house - ie when you are exporting electricity. If you tell your electricity company they should replace it free of charge. If you don't, you will have lower bills, but they will eventually find out and you may have a bit of a struggle working out who owes who what.

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gramm7168Comment left on: 5 April 2012 at 7:25 pm

Back in November I had Solar Pv panels fitted 3.5Kw.

The question I would like to ask is I have noticed my energy meter actually goes backwards when I am not using the energy produced, by this I mean the numbers go back. Is this normal and how do the energy providers view this? What happens if the meter reading goes back further than a previous meter reading?

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Gilly Jones

Gilly JonesComment left on: 28 November 2011 at 2:55 pm

Hi NorthGlosEPC

Under FITs your receive a fixed payment from your electricity supplier for every kilowatt hour (kWh) your system generates, whether your using it or selling back the surplus electricity (you get an additional export tariff for this which is currently 3.1p on top of the FITs).

Make sense now?

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NorthGlosEPCComment left on: 27 November 2011 at 12:20 am

"The more of your own generated electricity you use, the more you benefit. The cost of importing electricity is significantly greater than the amount you are paid for exporting your surplus. The trick is to try and do the things that use most electricity when the sun is shining".

Can you explain this statement?

Perhaps in error I thought the opposite. Imported electricity costs the normal price everyone pays, say around 10p per Kwh, whereas I thought electricity exported from say a PV array earns 43p FiT. So is it not better to sell the 43p stuff during the day and use the 10p stuff at night? Or am I missing something?

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Teifi Energy GroupComment left on: 20 May 2011 at 10:04 am

G83 allows connections up to 16A per phase = 3.6kW for a single phase - without the need to get prior approval from the DNO. But if your turbine is 6kW then this can't apply and you will need approval from the DNO. (Technically G83 doesn't apply to wind turbines in any case - but most DNOs are happy to accept suitable sized turbines under it.)

More info on G83 here -

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smither79Comment left on: 19 May 2011 at 9:44 pm

Hi folks,

Our chosen installer has gone and let our grid connection agreement with SSE expire before our wind turbine has been installed......  I have been told of a "g83" connection that we could undertake which would allow 3.6kw out (the turbine is 6kw) and allow us to commission.  Can anybody explain what this entails?

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Cathy Debenham

Cathy DebenhamComment left on: 16 May 2011 at 9:46 am

Hi Stuart

Do you have two separate electricity meters - one for the house and one for your garage? If not, there must be some connection coming from house to garage at the moment, and so it will be possible to run a connection back again. You're right in thinking there must be a connection to the house for you to be able to use the electricity - but it's probably best to ask the installer who suggested the idea how, exactly, he would do that, and what the cost implications would be.

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Stuart B

Stuart BComment left on: 15 May 2011 at 12:33 pm

We are sriously considering installing solar panels. One company has suggested we put them on our garage roof.This seems a reasonable idea but the garage is not connected to the house although it obviously has an electric supply. I'm trying to get my head around how this would affect the use of electricity generated as this would feed into the garage and not the house. Would the household appliances, washing machine etc., still be making use of the solar electric or would it only be anything plugged in in the garage. Would there have to be a feed back to the house for any household appliances to benefit.

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Cathy Debenham

Cathy DebenhamComment left on: 26 April 2011 at 9:50 am

Hi Chas

Sorry not to have answered this sooner. Click here to read our expert's opinion.

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Chas Reavill

Chas ReavillComment left on: 2 March 2011 at 5:26 pm

We're seriously exploring getting solar panels. "Enecsys microconverters" produce microconverters to be fitted to each panel so that low DC voltage is converterted to AC rather than a PV string producing a very high voltage DC. This sounds like a highly desirable safety feature. Is this correct and if so, can I ask our chosen supplier to use these microconverters in their assembly?

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Cathy Debenham

Cathy DebenhamComment left on: 2 March 2011 at 3:22 pm

Hi Keith

It's complicated, but I don't think I was contradicting myself. 

There are three aspects of income:

The generation tariff is the most significant. For a small solar pv system you get 41.3p for every unit you generate.

Then you get 3p per unit that you export. For most small systems will be deemed at 50% of what you generated, and it's not worth the cost of getting an export meter.

Then, there's what you save on your bill because you're using some of the electricity you've generated. This is what you can influence by doing your washing while the sun shines for example. This is more valuable than what you export because it costs significantly more to buy electricity from the grid, than the 3p they give you if you export it.

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KeithHeywoodComment left on: 2 March 2011 at 1:30 pm

You say "The more of your own generated electricity you use, the more you benefit. The cost of importing electricity is significantly greater than the amount you are paid for exporting your surplus. The trick is to try and do the things that use most electricity when the sun is shining."

but this directly contradicts what you said on 25 Oct 2010 (Deeming export of electricity for feed in tariff) where you said "I asked Ofgem what the situation is - and the answer is that installations of over 30kW must have an export meter. If they are less than 30kW it's optional, but if you do have an export meter you must use it. If you don't, the amount exported will be 'deemed' at 50% for solar PV

If you do not have an export meter I would interpret Ofgem's statement to mean that you get a credit for 50% of your electricity generated against your electricity bill irrespective of whether you consume it immediately or not (plus 3p per unit for the other 50%).

 Can you please clarify?

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Cathy Debenham

Cathy DebenhamComment left on: 24 February 2011 at 9:06 am

I'm not a techie either, but my understanding is that it's slightly different so that the home system knows to use the home generated electricity first. 

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Fred1Comment left on: 23 February 2011 at 10:16 pm

Higher frequency ? would that be good for the grid connection having two different frequencies, would  they not  fight ?????

Perhaps the home generated power would flow into the grid if it came out of the invertor at a slightly higher voltage, but at exactly the same frequencyas the mains... who knows...I am not a techie ???

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