Battery and extra panels?

Screwdriva

Wolfkeeper said:

The EV night rates that are available are as low 8-12p/kWh. That compares very, very favorably with ~33p/kWh rates you can otherwise achieve.

None taken. OP didn't specify an EV. You can hard code your cheapest available tariff (E7?) into the calculator to get a close representation of the battery vs. no battery ROI. For us, it's 8 years without and 10+ with, which coincidentally is the end of warranty period for the best batteries. 

Wolfkeeper

The EV rates I checked are all actually available to people with or without EVs, they just give you a four hour window to charge a battery, or do anything else you want-run dishwashers, washing machines, fan, or immersion heaters, clothes dryers, charge house or car batteries or whatever you have. They're cheaper because they pick the cheapest four hours. If you go economy 7, the tariff is about 50% higher. The day rate on an EV tariff is more expensive than economy 7, but you size the battery and solar panels to make it that you hardly use the day rate over the year (except in winter when there's no solar, but that averages down.) Exactly how quickly it pays back depends on what angle your solar panels are, and your usage patterns.

Screwdriva

Wolfkeeper said:

The EV rates I checked are all actually available to people with or without EVs, 

As I understand it, this is no longer true (if it ever was?). Your cheapest option with an EV is now Bulb (assuming they still accept new customers) or E7. As I've shared, regardless of Octopus Go/ Go Faster/ Intelligent/ E7, our ROI for a battery system is less favourable, as our consumption is ~2.2 mWh vs. our production of 3.9 mWh per annum.  

Not to mention, the upfront capital saved is working hard elsewhere. 

Wolfkeeper

I don't know how you calculated that ROI. The calculator you mentioned is unreliable.

I think it's worth pointing out that our solar panels will only provide half of our needs around the year (about 2.7 MWh), and most of the rest will be cheap rate electricity stored in batteries. The batteries we've chosen cost about as much as the solar panels, so it looks like our system cost significantly less than yours relative to our yearly demand (5.2 MWh), while hopefully still slashing our electricity bill by about 2/3 to 3/4.

That seemed to be the best mix. Anyway, that's the theory, we should start to see how well it's working in the Spring provided the system actually arrives.

I did run the figures for E7 and our scheme worked fairly well too, if not quite as well. These systems last quite a while, so it has to be robust to changes in tariffs. Provided there's cheap night rates available, that's likely to continue.

orbit500

I managed to get onto EDF EV at 4.5p 12am-5am fixed until may24. Also saw this all coming in January and got 28kWh of us3000c at £900 each!
With 12kWp pv on FITs my payback is very fast.

Wolfkeeper

That's a pretty sweet deal on the tariff and those batteries were well priced.

I fear you may have trouble getting another deal that sweet in 2024, but I don't think that will remotely stop it paying back.

Shortsy

Reading this thread with interest as I'm planning to get 10 380W panels but can't decide what to do about the storage (we have no hot water tank). I would have done the battery after a year or two, but then VAT is liable. I've been quoted for a 8.5 battery, but a smaller one might be enough? It only seems worthwhile if both capturing spare PV and overnight tariff - but my understanding is that you can't store grid electricity on the DC battery, only the AC ones (which then compromise on the efficiency of going between DC and AC). I'd be interested to hear if anyone has solved this problem.

ABrass

Shortsy said:

Reading this thread with interest as I'm planning to get 10 380W panels but can't decide what to do about the storage (we have no hot water tank). I would have done the battery after a year or two, but then VAT is liable. I've been quoted for a 8.5 battery, but a smaller one might be enough? It only seems worthwhile if both capturing spare PV and overnight tariff - but my understanding is that you can't store grid electricity on the DC battery, only the AC ones (which then compromise on the efficiency of going between DC and AC). I'd be interested to hear if anyone has solved this problem.

No, you can charge either from the grid.

Shortsy

Thanks for letting me know. So I could buy a DC battery connected to the panels via a hybrid inverter, and could join an overnight rate and charge up the battery from the grid overnight as well as from the panels during the day. That would make the battery a more appealing investment.

1961Nick

Shortsy said:

Thanks for letting me know. So I could buy a DC battery connected to the panels via a hybrid inverter, and could join an overnight rate and charge up the battery from the grid overnight as well as from the panels during the day. That would make the battery a more appealing investment.

That's correct.

All batteries are DC. Charging them from solar is more efficient with a hybrid inverter because you're not going from AC>DC.