Going on from that, I was aware of the wonderful tariffs that Octopus offer as well as the Tesla Energy Plan with its 11p/kWh both ways tie-up. It would be a huge step forward to be able to take advantage of that for hall and home alike (I have 6 hungry EVs!).
Unfortunately the hall and shop have separate meters but early indications are that some sort of very local microgrid might be feasible, possibly even outside of the existing local grid.
Actually, that's got me wondering. Is there any possibility of a small amount of PV on the shop as well? If so then you could put 1x Powerwall on the shop (providing backup to the refrigeration units), and sign both up for the Tesla Energy Plan. Assuming the same organisation pays the bills for both, you're essentially tying the two together without needing to do any complex wiring or fiddling about with electricity meters. It's a bit of a risk since it isn't guaranteed to be around in the long term, but generally I think splitting the PV and batteries might be a better option anyway - particularly if there is refrigeration and a dodgy grid.
Annual energy use for the hall alone is ~12MWh but that's historical so I'm not sure how accurate it is.
Is this the place you're talking about?PVGIS says you should get 17 MWh per year from a 20kW system - not a lot in winter though, maybe 10kWh/day. Enough to keep the lights on in winter, but not a lot more.
Tesla PW2s are 13.5kWh a piece with a 5kW continuous output (each). One of the burning Q's is how to connect them for best effect given that the hall has a 3 phase system with loads shared across phases in the usual way but with the limitation of PWs that only a phase with a PW can continue to generate from the PV array in a grid failure scenario... and I think only one phase can have a PW. So, they'd both have to be on the one phase...? Or not?
You're not likely to be allowed to stick 20kW of PV on a single phase (it unbalances the grid), so that either means a 3-phase inverter or three single-phase inverters. Three single phase inverters makes more sense if you're only looking to have enough batteries to back up part of it - then it's essentially three single-phase systems behind a common meter.
Ideally we'd like to use stored power across the whole microgrid. So, hall needs first (with a hierarchy of demand eg, lights, sockets, hot water storage, cooking facilities (all electric), heating), then the service point and then the shop. There are a couple of business units nearby, too, but I doubt there would be much left over from the others even in max sunlight... but one of them *is* a brewery...
Remember that electricity isn't worth a whole lot per kWh, and wiring infrastructure like you're talking about costs money and adds a lot of complexity (fully segregated circuits to avoid creating loops between the two grids, etc.). Unless you're talking about taking over the whole local grid yourselves and putting a whole community behind a single meter (which opens up a new can of worms with regard to billing, etc. but has been done before -
http://www.communitypower.scot/case-studies/projects/eigg-electric/ ) then it's a lot of investment and headaches for very little added value.
It's also worth pointing out that if using the battery as a grid backup you need to decide what the hierarchy is well in advance - anything on that circuit will be provided with power, everything else won't be. Assuming you want year-round backup then a 20kW array will give you something like 10kWh/day - split 3 ways (3 phases) then each Powerwall would get maybe 3kWh on an
average December day. Unless you've got multi-day power-cuts as a threat then the Powerwall is going to be almost purely in grid backup mode at that time of year, although things will obviously improve as the days get longer - in May you'll average 8x as much. At a guess you can probably back up lighting and sockets, and cooking if it's gas rather than electric. Hot water and heating would drain the batteries in no time.
Discussions with DNO are being handled by one of the other team members so I don't know what progress has been made there. I was hoping that the inclusion of storage would make the application more likely to succeed than without...?
Basically the power companies care about the amount of power being taken from or injected into their grid, the power quality (how close to a perfect sine wave it is, and what the power factor is), and how well balanced it is across the three phases. Depending on how you drive a battery it can make things better (supporting the grid when it's under strain) or worse (stopping charging just as the solar hits it's peak causing rapid change in demand). At a guess if you had one Powerwall per phase on all 3 phases it would support the application, two might not actually help very much.
No ground-mount PV facility and the roof is next to perfect so seems a shame not to use it!
Generally ground-mount is cheaper and performs a bit better - no need for scaffolding on installation, no risk of a leaking roof and better ventilation plus better alignment to the sun means slightly more power produced. Most people don't have anywhere to put it though.
