Posted By: andrew_rigamontiWe were going to put on solar over the top of our slates but the man-made slates were end of life, or at least wouldn't handle walking on to add the solar.

The 'walking on the slates' bit is what always gave me concerns about not doing this myself! When re-roofing this roof with Welsh slate, I put on all the slates with me suspended above the roof on extending ladders that ran from scaffolding at the eaves to above the line I was slating. A bit akin to an artist using a stick to suspend their painting hand above the canvas. When you look at how slates are lapped, then any walking on will produce a bending force on the slate. On real slate, that can crack them, often unseen up underneath the slate above. Less of an issue of course with concrete tiles or something man made and more flexible.

Have seen "solar installers" even here in Orkney walking over natural slated roofs and its just cringeworthy, thinking about the potential damage being done.

As for the "nicheness" of solar as mentioned in a previous post - Its a bit of a shame that the Feed-in-tariff gold rush skewed the whole market as badly as it did. We all use hot water, and that was what prompted me to go solar rather than PV. All self installed and no RHI or FiT. Just a desire to capture the energy that was making the loft space warm in the summer. With a good working solar thermal panel, I believe efficiency in these climes is about 65% when the water is up at 60 degrees C and the ambient is 20. Compare to a PV panels efficiency of around 22% compounded with an inverter efficiency of about 94%. So more efficient in both technical efficiency and financial efficiency. Unless of course, you never take a shower! :-) Even my old duff panel, lets assume its efficiency has dropped off to 25%, is more efficient than PV.

For the longevity, I think I have to assume its coastal air corrosion here that has been the issue. Definately a case then for evacuated tube to mitigate that.

I wrote a long comment but it vanished before I posted it... Solcast and other websites show you recent likely solar PV generation via irridance on a map https://www.solcast.com/solar-radiation-map/united-kingdom" >https://www.solcast.com/solar-radiation-map/united-kingdom

MCS certified solar installers give you standardize calcs in advance including likely payback time, usually that's 7-15 years. For us, in one of the worst UK zones for solar (north, heavy rain, lots of cloud) we had our system installed in mid Oct and immediately went to 100% solar PV except for a weird 0.1kwh grid import per day regardless of how much battery there is (we got extra batteries). Now with lots of rain clouds in early Nov it is probably 40-45% solar PV and thecrest from the grid, but it has been really dark clouds this week - fluffy white clouds seem to affect it less.

Re: re-roofing - slate is coming from Brazil. Not ideal eco wise and quarried of course, but the sample of reclaimed we had was visibly far thinner and we actually broke it! Clay tiles or insulating thermoplastics and new materials would be better - concrete is an environmental disaster with no insulating value.

With reroofing we had the roofline extended because of the EWI, and had to have a gutter and all battens replaced due to terrible condition (period house). The roofers assures us that the membrane was waterproof well it isn't during storms, especially not when it has nails through it for battens! We had room in roof (sloped ceilings) in some rooms and got caught out during a storm when a huge chunk of ceiling came down - needed redoing but it was a big mess of buckets with roofers needing to come back twice to cover the membrane. See pic.

On roof vs integrated - integrated was about 5-10% lower capacity but is far better in strong winds and saves on roofing costs (we got slate), there is no bird mesh needed and no risk of animals getting caught. With 45 degrees from South and only doing that one side of roof the MCS estimate is 8,000kwh for a 150 sq m house (2 floors, footprint 75 sq m, taking into account our exact location including height above sea level). Some people do have solar thermal but I wouldn't like to think how it is when it's -5C, often our very coldest days are pretty xlear skies especially Feb.

We went with Cambridge based company Viridian for ClearLine Fusion PV, and GivEnergy for batteries (All in One) with Solis string inverter, plus Givenergy gateway which is fitted outside where our electricity comes in and is needed if you want to generate power during power cuts (but won't have a good payback time). Even with daytime occupancy there are really clear am and evening spikes from boiling the kettle, cooking, using the microwave - washing machine we now put on in the day when batteries are well charged or good solar generation is predicted.

Givenergy have a cloud portal, a good community portal, and an optional solcast API solar forecast (link at the top of this post).

See photo for what happened with ceiling...

Posted By: stonecoldexcept for a weird 0.1kwh grid import per day regardless of how much battery there is (we got extra batteries).

We have that quirk also. I think, well almost sure it is to do with any load that comes on that is greater than what the max of the inverter is. Our max from the battery is 5kw so if you use a big load like a shower or an induction hob it can peak over and above the battery supply. When using the induction hob we dont put it full on but ramp it up. We can see the spike on the inverter app as long as it coincides with the sampling timing point.

Octopus Agile have been charging (on average) 15.5p/kWh for buying power from them this summer, outside of the 4-7pm when it's 32p average.

So generally you can sell power to them at 15p and they sell it back later at 15.5p (if you have a SM, sorry to hear your troubles there Stonecold).

It's hard to see how they can do that long term, but also hard to see the benefit of having our own batteries, beyond what we unavoidably have to use 4-7pm..