We had our panels installed by Joju (a link to us as a case study here) in early June - just about when the sunny weather stopped and we started the least sunny summer for 18 years. Our estimated generation is 2,300 kWh each year so a fraction over 900 kWh for what should be the sunniest months of the year is slightly disappointing - hopefully better weather would lead to another 10% or so but then when do we ever have a sunny summer....
Because of the shape and configuration of our roof we ended up with installing some high end Sanyo panels which gives us a total installed capacity of 2.88 kWh - basically these panels are a bit smaller so we could fit more on the back roof and if we wanted to put some cheaper ones on the other then we would need two inverters which would be more expensive anyway.
(The highest number I've spotted being generated is 2,798W)
Our roof faces roughly SW which means that the panels don't start working properly until after 10 in the morning but then keep going after that.
The installation cost about £13,000 and we've just had a cheque for about £400 based on 900kWh. Of course that doesn't take into account what is saved in consumption
(For ease of comparison we pay roughly 20p per kWh for first 225kWh per quarter followed by 10p - interestingly we get paid 3.1p for each kWh for the export tariff)
The estimate is half used so on that basis it's a further £45 - I suspect it's more than that however as we are making an effort to do as much as possible when it's sunny.
All this is tax free.
If we assume an interest rate of 3% over 20 years then our £13,000 would turn into £23,479.45 (that makes no allowance for tax)
| Reading Date | Reading | Incremental Value kWh | End Date | End Reading |
|---|---|---|---|---|
| 05-09-11 | 874.6 | 38 | 12-09-11 | 913 |
| 29-08-11 | 818.8 | 56 | 05-09-11 | 875 |
| 22-08-11 | 760.3 | 58 | 29-08-11 | 819 |
| 15-08-11 | 702.1 | 58 | 22-08-11 | 760 |
| 08-08-11 | 639.1 | 63 | 15-08-11 | 702 |
| 01-08-11 | 565.9 | 73 | 08-08-11 | 639 |
| 25-07-11 | 491.1 | 75 | 01-08-11 | 566 |
| 18-07-11 | 426.6 | 64 | 25-07-11 | 491 |
| 11-07-11 | 350.6 | 76 | 18-07-11 | 427 |
| 04-07-11 | 277.9 | 73 | 11-07-11 | 351 |
| 27-06-11 | 214.5 | 63 | 04-07-11 | 278 |
| 20-06-11 | 132.7 | 82 | 27-06-11 | 214 |
| 13-06-11 | 53.1 | 80 | 20-06-11 | 133 |
| 10-06-11 | 31.2 | 22 | 13-06-11 | 53 |
Changes to our consumption
It's quite hard to tell because we had a faulty meter last year but saving a third seems like a good guess.As we don't have a smart meter (even though it's less than a year old) the energy company assumes that we consume 50% of our generated power and export the other 50% - this means that we were paid for 450 kWh. What this assumption means is that when we're generating anything we use is effectively free!
| Bill period | Number of days | Total | Daily Average |
|---|---|---|---|
| 22/07/11 - 10/09/11 | 51 | 343 | 7 |
| 06/06/11 - 21/07/11 | 46 | 275 | 6 |
| 22/04/11 - 05/06/11* | 45 | 407 | 9 |
| 31/01/11 - 21/04/11 | 81 | 916 | 11 |
* We were on holiday for a week during this period
