It's taken me a while to get round to writing this up, but here it is:
I've been thinking about PV for a while but it was (sensibly) decreed by my tolerant wife that I was supposed to sort out our internal insulation and sun-room/porch extensionny thing before starting any more major projects.
I did a bit of reading anyway in order to understand what's requireed and got a quote for some idea of costs. I was somewhat disappointed to find that even with LCBP grants a DIY install still looked significantly cheaper:
http://www.navitron.org.uk/forum/index.php/topic,5789.msg60880.html#msg60880So it looked like I was going to be following St Barnabas down the DIY route (which is clearly most fun and likely to lead to the best system), but that would have to wait till the other jobs were done. But then there was a post in one of St Barnabas' massive DIY install threads where we we grumbling about the cost of professional installs when some fellow called Aidan piped up to say not all commercial installers were charging £5/Wp - he could do £3.50/Wp (post grant).
I decided to test this fellow's claims, and soon had a quote from EvoEnergy of £10,200 for a 2.88kWp system which worked out to being only a couple of hundred quid more than I could do the thing myself for. That sounded like quite an incentive for saving several weekends of faffing about on the roof and arguing with recalcitrant DNOs to get it all approved and connected up.
The system is 16 180W sharp E1 panels connected in two equal strings to a Fronius IG30 inverter. The two strings are because we have a couple of large trees which shade the bottom edge of the roof in the morning at some times of the year. It seemed wise to split the strings so that at least the upper string would always be shade-free. Fitting the PV has also meant that plans to raise the angle of the solar thermal panels have to be abandoned as they would shade the PV if propped up. I'd have preferred an SMA inverter for open data access reasons or a platinum inverter because it's more efficient but the SMA isn't suitable for a 2-string layout here due to a higher MPPT minimum voltage and I couldn't have a platinum inverter because EvoEnergy only do Fronius and SMA - that's one of the disadvantages of a professional install - you can't mix and match the best kit from anywhere. The difference is only a percent or two so probably doesn't matter much on the scale of things.
But over 10 grand was still quite a lot of money. Were we really going to spend it all on PV? The decision was clinched by the FIT consultation from the govt, which made it clear that the second half of 2009 was a particularly good time to install PV because both the old LCBP grant system and the new FIT scheme applied. The fact that both the equipment and the install had to be 'approved' to qualify for the FIT clinched the 'don't do it DIY' aspect. There was a small risk that the whole FIT thing would be abandoned as the country went bust and/or governments changed, but even if it all went wrong the thing should return nearly 6%, which seemed quite a good investment under current conditions.
Aidan of EvoEnergy seemed a very sensible chap happy to answer questions and accommodate my requests on the details of how the electrics should be done, and also keen to discuss logging systems, because he'd like something cheaper and better than the stock options available from Fronius and SMA. So he was happy to lend me some data collection gear in exchange for doing some geekery investigations. All good.
He also explained how the export charging worked, which showed that my spreadsheet was all wrong. A 2.9kWp system in Cambridge should generate around 2320kWh/yr (figures from PVGIS site) and I'd assumed that with a consumption of 1600kWh/yr we should have 720kWh to export. That's completely wrong because the metering is done on an instantaneous basis so in fact it's not a zero-sum thing. You could export much more than 720kWh because unless you use a lot of power during summer daylight hours you will have huge excess then. Equally you will still import a load of power even if you produce much more than you use during the year, because much of that use will be between sunset and sunrise. Unintuitively, you actually make more money per kWh by using power locally than exporting (because you get paid 5p/kWh for export, but save ~12p/kWh for not-importing).
After looking at the house the quote rose a little to £10500 (£13,000-£2500) because they needed to fit scaffolding to go over our living room bay (their tower wouldn't work), making £3.54/Wp.
Once we signed up things moved pretty quickly. There is a complicated dance with the LCBP such that you need to have a receipt from the Installer before you can apply, and in some cases you might need building control approval. Once you've got grant approval (which takes about 5 minutes one you fill in the form!) the installer can set a date and you can start trying to get an MPAN number from the electricity company which is necessary to fit an export meter.
3 weeks after committing the EvoEnergy boys (3 of them) arrived, having left their Northampton base at 5:30am to drive to Cambridge. The scaffolders arrived at the same time and did their thing round the back. It was very odd having other people fettling my house for 2 days, as I've never done anything non-DIY before. Once we worked out where things were going to go in the loft and Tess's office and the leccy cupboard they just got on with it, doing inside stuff first whilst scaffolding went up. We decided to fit the inverter in Tess's office rather than the loft to take advantage of waste heat from it and allow reading the display without going up into the loft. We'll find out in the summer if it turns out to be annoyingly loud. So far it just hums gently like a PC, but it hasn't got over 1.4kW input yet due to being fitted in mid-October. They spent the rest of the day fitting all the brackets under tiles, and struts to those.
On the second day the team was augmented by Justin the electrician who had to add an earth connection to our water main (because the house didn't come with one) and helpfully fitted the new CU I had bought so that they could use one way of it for the PV. This will be convenient later when I switch over the existing 1960s fusebox over to a modern CU, giving me more than 6 circuits. The only catch was that they needed a 16A MCB and it didn't come with one of those so Eddie got to scour the electrical factors of Cambridge for a compatible MCB, which definitely counts as going out of you way to satisfy customer. They spent quite a while fitting panels so they looked square (as for most customers that's the only bit they can really see :-). I had to catch a train to Grenoble halfway through the day, so missed the great switch-on but it was all just about done in time to catch the tail-end of the day for checking it worked.
EvoEnergy's insurance doesn't allow anyone else to use the provided scaffolding so we definitely didn't use it to examine their handiwork and re-point all the pantiles the following weekend using the luxurious access afforded :-) It was still there 3 weeks later and we had to hassle the scoffold company quite hard to come and take it away before we went on holiday. Funny how they don't really want the stuff back, and are happy to store it round people's houses.
I have a load of pics here:
http://wookware.org/pics/solar/PV/
Those show a couple of minor defects in the screwing of brackets that I could easily get at to check and a bit of cabling that wouldn't be quite how I'd do it, but overall the standard of workmanship was fine, and I can heartily recommend EvoEnergy as being good value installers. It is quite something to see a system go in in 2 days flat, rather than the several weekends it would take me to DIY.
Here is my spreadsheet for calculating how much money you will make for a given system size, cost and grant for Ebico and Good Energy tariffs and microgeneration schemes, plus proposed FIT scheme. You need to fill in output from the PVGIS website and you have to guess what your export ratio is going to be, although it also shows max and min possible outcomes.
http://wookware.org/solar/PV/We're very pleased with our PV. It's generated 202kWh since the 14th October, which is about 4kWh more than we've used in the same period (we cheated a bit there by going on holiday for 3.5 weeks). Sadly we haven't yet got an Export meter because Ebico/SSE, despite being very helpful took nearly a month to get an MPAN number and send meter fitter round, and then when he arrived he said there wasn't space on the board:
and he refused to move anything to make some. Then we went on hols. I've now rearranged things (which took all of half an hour) and am waiting on Siemens to deign to come round again. We might get an export meter before the FIT comes in...
I've done some work on getting data out of the IG30 inverter, which I'll report in another thread.
