how to count exported pv home electricity

andy_ross

website team CRAGger Glasgow Leamington

Would be interesting to know what the Danish figure is now that it has gone over big time to wind!

I went to a Royal Society of Edinburgh energy forum yesterday (in Glasgow!) where Scotland was described in Alex Salmond’s phrase as “the Saudi Arabia of Renewables”.

Roll on wave power!

http://www.royalsoced.org.uk/enquiries/energy/full_report.pdf

PS. Check out lovely colourful figures and pie charts!

It is a 1.3kwp system which is forecast to generate 1106 kwhs in a year, with my own consumption last CRAG year (Dec 2007 – Nov 2008) being 1030 kwhs. So I could be just about a net exporter, but of course largely in the summer and in the daytime so will be requiring very much other electricity to be imported. Does anybody have any links to datasets from houses that have good records on before and after installation and how much net exports are made?

Anybody here know of any tips and tricks or gadgets to maximise the on site usage of electricity?

I have thought about things such as small UPS style systems which will ‘collect’ at the point of usage, say a washing machine so will store enough for a wash instead of exporting it to the grid. Other elements I have thought about would be to put fridge/freezers on a timer so they only take electricity during the day (outside of peak hours).

Are there any ways for electronic items to ‘understand’ that the onsite generation is producing at a time so again things like a fridge or freezer would ‘know’ when to switch on and off to utalise this. Possibly some RF gadgets to inform the appliances?

An email recieved from Segen yesterday sets out the prices and conditions for PV and wind:

“The Government has announced yesterday the details of the proposed feed-in tariff for microgeneration from systems like small wind turbines and solar photovoltaics. The new tariff will pay for all energy generated by your system, irrespective of if you use it yourself or sell it back to the grid. The amounts paid are in addition to any saving you will make by purchasing less electricity from your supplier and any income you earn from selling your surplus power to your electricty supplier.

The key points of the announcement are:

- 36.5p/kWh for small solar photovoltaic systems up to 4kW and 28p/kWh for systems up to 10kW.

- 23.0p/kWh for small wind turbines between 1.5kW and 15kW.

- Replaces the current ROC system which pays 10p/kWh.

- Effective as of the 1st April 2010, but all systems commissioned from now on will qualify.

- Systems installed from now until April 2010 will be eligible for both LCBP grants AND the new tariff.

A typical home solar photovoltaic system of 3kW, generating approximately 2,300kWh per annum will therefore earn around £1,000 per annum, which is an additional £600, dramatically reducing payback times.

An Evance Iskra R9000 small wind turbine will typically earn £2,000 – £3,000 per annum which is an additional £1,000.

A Gaia 133 small wind turbine installed at a modestly windy site will earn £6,000 – £9,000 per annum which is an additional £3,000, making it a very economic proposition with likely payback times of less than 5 years on a typical site.

All of Segen’s solar photovoltaic and small wind turbines installed from today onwards will qualify for the feed-in tariff and Segen is a fully accredited Microgeration Certification Scheme installer for small wind and solar photovoltaics as required by the new tariff.

To find out how you may progress getting a solar photovoltaic or small wind system from Segen, please respond to this email as soon as possible, as the one thing which is certain is that demand will be high.”

I agree that strictly speaking if you calculate imported electricity minus exported this over estimates the benefit of the exports a little, but as a person with solar pv I say what is wrong with that? I want to encourage as many people as possible.

The vast majority of home generators do not have export meters as they are too expensive – we simply have a “total generation” meter which measures what your system generates irrespective of whether you consume it in the home or export it to the grid. The FIT will be paid based upon this “total generation” and an estimate will be made as to the proportion which is exported, so 41p/KWh will be paid for the total generation, plus an additional 3p/KWh for the proportion deemed to have been exported. This proportion has yet to be decided by DECC/DEFRA.

This has 2 impacts – First it means that no-one (incuding DECC) knows how much electricity is being exported by home generators, so any effect upon the grid average will be an estimate. Second it means that as a home generator I do not know how much I am exporting and strangely it means that I no-longer know how much I am using because my “normal” electricity meter only measures what I import in the evenings etc. I have no way of knowing how much electricity I have used during the day. I have an Owl electricity monitor but that cannot seem to differentiate import from export, it simply measures what is passing through the cable. I know that in March I have generated 180 KWh so far, which is more than the 150 KWh that I used to use per month at this time of year prior to installing solar pv.

As you may expect, I find the argument that my electricity use is not carbon-neutral, even though I am producing more than I am using, rather academic. I want to encourage as many people as possible to invest in home generation, so I believe more carrot is needed and less stick. After all, people who measure their carbon footprint over a period of time soon realise that home heating and transport tends to produce a lot more carbon than electricity use, so we are talking a fairly small percentage of an individuals footprint here.

Thanks for listening if you got this far,
Peter

Thanks John, I would say that solar PV generated and consumed on site should be zero rated for carbon accounting purposes. Its zero-carbon at the point of generation. I think this would be consistent with the DEFRA / DECC approach to conversion factors which gives figures for fossil fuels based on the CO2 emitted at combustion and ignores CO2 emissions from extracting, processing and transporting those fuels. These upstream carbon costs are significant but are simply not accounted for in the conversion factors.

There will be a carbon cost to producing solar panels but I would assume it can be neglected it over the lifetime of the panels ( See Post Script below ).

POST SCRIPT George Monbiot quotes 2 to 4 years for carbon pay back on solar PV in Europe in his book Heat (p125 of the 2007 paperback edition). This compares with an expected operational lifetime of 25 years.