Solar, Battery, TOU tariff a goer?

thisreallyisme

I think this might work for me. Annual consumption - very high, 8500 kwh

Solar pv 5.7 kwp, restricted by inverter to 3.68 kwp
Tesla battery 13.5kw
Immersion controller

Because consumption is so high I think this system could increase self consumption of solar to near 100%
So 3680 produced, cost nil, saving £588 at 16p (used first by house with any surplus going to battery)
Then I import 4820 into battery at saving of 8p/kwh on night rate - £385 saving

First year saving £973 on a system costing £13000 = 7%

Ok these ballpark figures are optimistic, I agree. I assume I can self consume all solar and buy in all the rest at night rate, but it looks a goer to me because I will be buying in future electricity at today's prices.

Also no FITs included because I'm not banking on these as I think smart meters (for TOU tariffs) will eventually replace the deemed 50% with actual export. Also I don't think I will get a D rating for efficiency for decent generation FIT.

Am I mad?

Martyn1981

I don't think you're mad (well, we're all a little mad).

I think your self consumption will be very, very high. But assuming 8,500kWh, and less than 1/12th in the summer (that may be wrong) so about 600kWh, then in a really good generation month you may export some, but I'm nit picking here.

Also, your night rate to battery calcs are correct, but when you add the cost of the battery (£'s / lifetime kWh's), approx 10p/kWh, it will probably breakeven, so might be better to avoid unless a really cheap night rate becomes available, and instead work the battery lighter so its capacity stays higher, and lasts longer.

Regarding 5.7kWp and 3.68kW, that will obviously cap a fair bit during the middle of summer days. Is all the PV on the same orientation, any chance you can get the DNO to allow for a bigger inverter, could you get a DC side battery, so storage is before the 3.68kW limit ..... etc etc?

Zarch

thisreallyisme wrote: »

Also no FITs included because I'm not banking on these as I think smart meters (for TOU tariffs) will eventually replace the deemed 50% with actual export.

Why would this happen? If you sign up to the FIT contract, its there and locked in for 20 years isn't it?

thisreallyisme

Thank you Martyn!

Yes, consumption will be slightly lower during summer months.
I have actually done some brain hurting calcs with monthly sun hours which show I may need to buy in around 1000 kwh at full price but hoping that will be 'offset' by immersion controller reducing oil bill.

I have come across Octopus Go which charges only 5p for 4 hours during the night but not sure whether this is long enough time to fully charge the Tesla - I am seeing conflicting info on this. If 4 hours is long enough this will add to my plus side.

DNO are not shifting under any circumstances on their 3.68 inverter - not even with an export limiter set at zero export! They say this is because there is up to a 5 second delay for a limiter to kick in which could compromise the grid. (We are end of line with little capacity left for export)

Yes a lot of capping in summer with 3.68, but oversizing should allow more solar during shoulder season?

I guess that even though battery might just be break even it maximizes use of solar and makes us less dependent on the overstretched grid.

thisreallyisme

Zarch, I think the FIT is locked in for 20 years but not at the deemed 50% export. For those who go on to smart meters (which will eventually work as they should!) and which measure actual export, actual export will be used instead of deemed 50%.

This will benefit the average household who are exporting more than 50% to the grid. I think I have seen around 35% is average self consumption, so 65% export

But in my situation, I hope to use most of my solar so my export will be not worth the paper it's written upon!

EricMears

thisreallyisme wrote: »

I have come across Octopus Go which charges only 5p for 4 hours during the night but not sure whether this is long enough time to fully charge the Tesla - I am seeing conflicting info on this. If 4 hours is long enough this will add to my plus side

You might care to look at my assessment of Octopus elsewhere in this part of forum (https://forums.moneysavingexpert.com/discussion/comment/75120412#Comment_75120412)

In particular, note that Octopus are only offering the 'Go' tariff to first 1000 customers and I imagine that figure has already been reached

thisreallyisme

Thanks Eric, it is still available as they sent me list of all available tariffs a few days ago, including those for smarts but I don't know how many spaces are left.
And so yes, say 4-6 weeks to switch and then 2-3 months for a meter fitting and who knows - a blind switch!

EricMears

thisreallyisme wrote: »

Thanks Eric, it is still available as they sent me list of all available tariffs a few days ago, including those for smarts but I don't know how many spaces are left.
And so yes, say 4-6 weeks to switch and then 2-3 months for a meter fitting and who knows - a blind switch!

From their webpage, I couldn't find any details of the 'Go' scheme apart from the 5ppu for 4hrs/day and the 1000 customer limit. The only option was to apply for an interim tariff - all of which were far dearer than my present supplier.

I wonder if you could tell me what rate they proposed charging
for the other 20 hrs/day ?

thisreallyisme

I asked by email for list of available tariffs and this came back from them, (applicable to South Wales area)
Octopus Go
Electricity:
Unit rate: 14.02 p/kWh
Super cheap electricity for 5p/kWh between 00:30 - 04:30 every night
Standing charge: 25.00 p/day

In a previous email a couple of days earlier they quoted 13.45p standard rate for my postcode

I also asked if it was continuing after the 1000 customers in a separate email but they didn't answer the question.

Smoke and mirrors.

EricMears

thisreallyisme wrote: »

I asked by email for list of available tariffs and this came back from them, (applicable to South Wales area)
Octopus Go
Electricity:
Unit rate: 14.02 p/kWh
Super cheap electricity for 5p/kWh between 00:30 - 04:30 every night
Standing charge: 25.00 p/day

In a previous email a couple of days earlier they quoted 13.45p standard rate for my postcode

I also asked if it was continuing after the 1000 customers in a separate email but they didn't answer the question.

Smoke and mirrors.

Not quite as bad as I thought but still getting towards the 15p I guessed at.

I was with octopus for a month after Iresa collapsed and was paying 15.9p day, 8.7p night + 19.1ppd

Now with OneSelect at 13.1 , 8.1 & 20.7 respectively (all rates inc of vat and all more than Iresa)

Call me suspicious if you like but I can't help thinking they're trying to sucker people in to their 'intermediate' tariff then telling them they've just missed being in the first 1000.

Martyn1981

thisreallyisme wrote: »

DNO are not shifting under any circumstances on their 3.68 inverter - not even with an export limiter set at zero export! They say this is because there is up to a 5 second delay for a limiter to kick in which could compromise the grid. (We are end of line with little capacity left for export)

Yes a lot of capping in summer with 3.68, but oversizing should allow more solar during shoulder season?

I'm with you, nobody wants to be capped, but it won't be too bad at the end of the day.

I can see where the DNO are coming from, I think Tesla have said that they believe their battery could be accurate enough to operate during a powercut by reducing export to zero, but they aren't there yet, and that kind of management is very tricky.

Shame they've dropped the DC side option from the Powerwall, are there any other suitable DC side batts worth considering, or perhaps just too much faff given your reasonableness over the capping impact?