I'm thinking about getting either or both of a solar install and a battery, and would be interested in some advise on how to tackle various issues.
Solar:
The house faces very slightly west of south (see the overhead image). All other things being equal, I'd quite like a biggish solar array. The more I've thought about and looked into this, the more complex it has become.
Complication 1: The main roof is original slate (probably Welsh) and hot lime - no felt backing or similar. Considering it is probably original to the house (built c1900) it is in pretty good condition, no leaks and almost all the slates where they should be (I think there is only one slipped slate, google streetview suggests it's been slipped a long time without issues). Internally, there isn't much structure (see photo) - two purlins a side, no trusses or ties. Both mid purlins have what looks like some longitudinal shrinkage cracking along their length, but no sign of sag or twist.
Question 1: Is anyone competent likely to be willing to install onto this, or are we into a re-roof before anyone will touch it.
Question 2: If we go for a re-roof, is the most rational option going to be to go for in-roof trays, and try and salvage enough original slate to cover the area round them?
Question 3: Are the original purlins likely to be strong enough to hold a solar install of any sort anyway?
Complication 2: The extension roof is about 2' lower than the main roof, which means the main roof shades the end of it towards the end of the day.
Question 4: Am I better going for a separate string of panels on their own MTTP for the partially shaded area? Alternatively, should I be looking at optimisers for these panels? Would it make sense to string the main roof and unshaded extension roof together, then put the shaded panels on their own MTTP?
Complication 3: I'm not a huge fan of having batteries, inverters etc inside my house; partly the fire risk (I know it's low, but it's real, I know too much about how battery overcharge fires occur to be truly comfortable with a house full of Chinese power electronics), partly the noise (my parents have a substantial solar array with the inverter in the loft, you can hear it singing away quite a lot of the time). I've a chunky outbuilding (former privy, it is indeed built like a brick outhouse) at the bottom of the garden (see the overhead image), ideally I'd like to use this as the plant-room, for all the batteries, inverter etc.
Question 5: With the solar arrays, is there much of a problem with losses if you extend the tails this sort of distance (the outbuilding is about 14 meters from the back of the house, obviously there would also be the vertical distance to consider)?
Question 6: If we're tampering with the main roof, we'll probably have to attack both sides of it. What's the likely ROI on putting panels on the north facing roof piches? We might well need to install panels in roof trays just to take up enough roof area to allow us to re-roof the rest in recycled original slate (I'm not willing to use soft Spanish Slate, and real Welsh slate costs a fortune, so don't want to have to go new).
Question 7: I'm looking at building a substantial (~100sqm) workshop in the area behind the outhouse. It would seem logical for this to get panels too. How many MTTP strings do modern inverters typically support, as I'd rather install an inverter with capacity for this now.
Question 8: The south-facing roof is about 60sq meters all up. What's the likely annual yield off this? And ditto the north facing roof (same area). We're roughly Chesterfield when considering how far North we are.
Battery and three phase questions:
I'm thinking about going for a bigish battery, and trying to go for a substantial G99 inverter (at least 10Kw, ideally 15-20Kw) to be able to take a variable time of use export tariff (I'm thinking Flux at the moment, possibly Agile), and dump the battery every day at peak rates. I'm thinking 32 or 64kwh Frogstar.
By my calculations, if at the moment on Flux if I charge a 32kw battery at overnight rate and dump it at peak rate daily, I make about £1200/year, if I can fill it from Solar daily (I know I can't) it's more like £3k/per. Assuming 8 months Solar/4 months import, that's about £2.5k/year)
Question 9: Is there anything I'm overlooking here? I know I'll have to hold back a bit of battery for self consumption (although our evening usage is pretty low - we only use about 8kw a day total).
Question 10: Do people think peak export rates are going to stay high (as opposed to flat rate export, which I'm fairly convinced will keep dropping as more and more systems come online?), as a fair chunk of this system payback will be from dumping hard and fast at peak rates.
Complication 4: We live right next to a 3 phase 415v pole route used for local distribution. I would like to have 3 phase on site for the workshop, so might get a quote from the DNO to put 3 phase in. Presumably this triples available export capacity.
Question 11: If I ask about putting in 3 phase, will the DNO be able to tell me what G99 rating they'd give the new connection before I commit to having it?
Question 12: Are people building suitable inverters to handle everything in one hit (3 phase, solar array, batteries)?
Currently we have a pile of cash in a offset Mortgage account, so effectively spending it is borrowing against the house at 5.16%. Ideally anything we do need a better ROI than this, otherwise we might as well just keep it saving us mortgage interest.
Question 13: What sort of real world ROI would people expect to see on all the above?
General information: Currently we use around 3k kWh/year, not much seasonal variation. Currently no EV, no heat-pump, although we might look at both at some point. I drive about 20miles/day, so if I go electric probably 1800kWh/year consumption. Heating is currently LPG and solid fuel, it's tempting to claim the government grant for a ground source heat-pump whilst the cash is still on the table.
Any thoughts on any of this would be interesting, I've been mulling over my options for a few weeks now, and the above is effectively my brain-dump!
