Going back to Mary Whittington's original question, there is nothing to stop you plugging a storage heater into your mains system and consuming some of the solar electricity which would otherwise go unmetered into the local network. No electricity companies are installing export meters; they are guessing that 50% of the solar electricity will be used by you and 50% exported, and paying you for 50% (in addition to the Feed in Tariff). I suspect that most of us will be exporting 90% of what we generate because of the mismatch between generting it when it is summer daylight and consuming it when it is winter darkness.
In winter you can set up a storage or fan heater to run when there is spare generation. It is very crude and fiddly, even with 1 kW and 2 kW output settings. Everytime a cloud goes past you would need to switch the heater off. To automate this you would need an export meter, a control box, and a thyristor block to limit the heater input to match the free power available. There is nothing on the market at the moment and the sukaelectroheating.co.uk equipment is not suitable. I expect someone out there will be inventing such a system in their garage before too long, but it is a minority market and unlikely to be on general offer. In any case, you might be able to shave £20 off your gas bill each winter doing this (£20 off economy 7 bill too). Hence it's not really worth investing in, especially if electricity companies might fit export meters in the future, which would make it all poinless.
One key point many are missing is that in the UK most electricity meters do not run backwards (see the little ratchet symbol on the meter). For this reason "storing" electricity in the grid is impossible. selbs is right, I am already hearing that there will soon be ways of storing at least some electricity, but as others have pointed out, the real problem is sensing what is being exported and can therefore be used for free. On a cold cloudless day with a new PV system it is fun to turn on the fan-heater for free, but that is not really a solution.
From Energy Saving Trust Website [quote]Export tariff - you will get a further 3.1p/kWh from your energy supplier for each unit you export back to the electricity grid, so you can sell any electricity you generate but don't use yourself. This rate is the same for all technologies. At some stage smart meters will be installed to measure what you export, but until then it is estimated as being 50% of the electricity you generate (so that if your solar PV system is less than 30kWp you do not need to have an export meter fitted)[/quote] So it seems you need a smart meter for it to work correctly. Thanks to EagleDisplayed for pointing this out. I know with one energy supplier we had a current transformer and a monitor plus internet link unit which sent information to the supplier. As to if this was used for billing I don't know. I now see why there is such a push for the role out of smart meters. As to using the power I don't know of any simple meter or switch that can measure which way the current in running in an AC system so one would need to measure the power from the inverter and how much the house was using and switch on items to use power when the inverter output exceeded the power used by the house. I am sure this can be done but not sure how much it would cost and for how long you could use it before the smart meter role out stopped it being of any benefit.
The easies way to measure your PV system scale is to collect data from Utility Bill, which provides consumption and prices for a year. Also, it would help installer know the precise geographical location. Following information are necessory if a site visit could not proceed: 1. The are available; 2. Orientation possibilities; 3. Shading issues; 4. Grid connection 5. Electrical interface.
For your information, 3 are roof area could build a 10Wp solar farm, which could generate electricity 18,000 Kwh per year. If the FIT is $0.25 / KWh tariff, the average annual price gain is $ 4,500 for 10KW solar photovoltaic power station; 25-year price gain was $ 112,500 USD.
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