In the two previous August-August years, our import had been 8500 kWhr in each year, close enough, causing a likely annual electricity bill of about £1156 including VAT.
In the year Aug'09 to Aug'10 , there has been as astonishing reduction, despite the cold winter. We have used precisely 6220 kWh in the same period! - for all heating, hotwater, cooking, power, lighting. That is 2280 kWh off the previous amount, and will be an annual bill of £860 in the same period - a £300 saving in one year.
I guess there are four things at work here:
1. Metering: When you start metering daily, the competitive instinct cuts in and you economise more, to see if you can maintain low figures - that means fewer lights on, use power when the roof is working, etc. I keep a simplified weather record too, so I can recognise when cold/ cloudy/ hot/ sunny days affect the readings.
2. Photovoltaic: The PV contribution is very good, although we didn't start it until Oct '09, at the start of the Winter, during which it is sometimes less than 1 kWh in an entire day. The Summer has been good, but doesn't account for as much as 2300 kWh!
3. Sunboxes: they were not working until mid March'10, and was followed by a mild spell and warm April and May. So it is difficult to know how much contribution they have made until next year. But they must have made some, as the heat pump power consumption seems to be lower - but as it is only doing hot water at the moment, we will not know fully until the winter.
4. Heatpump: I have 'tuned' the ground source heatpump (GSHP) - installed switches to confuse the thermostat or stop the compressor, immaculate work in insulating the internal water tank, and mastering the internal time clock to be able to leave the GSHP running but have it not actually generating heat.
I know there were bad days last winter when the heat pump over heated, or when we needed heat on a day when there had been heavy dark cloud. Hopefully, the effect of the sunbox will reduce consumption on those days.
We expect further savings in the coming year.... We are going into the next Aug-Aug year with all systems operational!
The only thing remaining to do on the present setup is to add a time clock so that the fake external thermostat is automatically on during the night, and off by day. The other item, the Savita Sunbox, I might do, or might fit it to another house instead of this one.The next main metering anniversary point will be 1st October - unless we have a very cold September, I can predict now that the annual total 1 Oct- 1 Oct is likely to be more like 6,050 kWh, a saving of 2,450 in one year - 30%.