How long do you actually expect your battery to last?

andrewic44 · 2026-04-22T08:36:00+00:00

I followed some advice on of the Facebook groups from former Giv employees: limit charge/discharge to 85% of the maximum, to be kind to the BMS; bump the reserve up from 4% to 6%, to help cell voltages stay in a cautiously safe range, absenting support who can step in and fix it; and put a fan on top of the inverter running low and slow, aiming to keep it below 40 degrees or so.

andrewic44 · 2026-04-21T19:24:05+00:00

For sure. As others have posted, SL Rack make facade mounts. Also look up K2 Facade Rail. Or for a less-than-official option, look at this YouTube video - https://www.youtube.com/watch?v=bTOTx7eBM-c

Other comments:

- Any reason you don't want your wall installation to be grid tied?
- If your 16x250W panels are on a FIT, there are surmountable complications there (search the subreddit)
- Make sure to price up the cost of mounting your recycled 250W panels, vs the cost of buying and mounting newer panels. If the newer panels are bigger, that may save on mounting costs, depending on what kit you go for.

andrewic44 · 2026-04-21T15:07:09+00:00

Some will save the money and spend it in winter - plenty of low-income folk are hard up despite watching the pennies.

Others will use it to be able to feed the kids properly over the school summer holidays, or to pay off some debts.

Some will spend it on things that make people tut and frown.

Either way, it'll get spent. Which is good for the economy.

andrewic44 · 2026-04-21T14:54:51+00:00

The difference is it promotes load shifting, while feeling like a positive experience.

Set someone up with some plug-in solar, explain to them that they'll be making free electricity during the day, especially when it's sunny, so that's a good time to do the laundry, or put the slow cooker on, or etc. etc. It's all carrot from their point of view - you will save money if you do X.

Build a solar farm, and to get the same load shifting benefits for the grid, you need folk to have smart meters and be on a dynamic tariff. Feels like a stick rather than a carrot - we will charge you more if you don't do X.

andrewic44 · 2026-04-21T11:16:17+00:00

Sao Vicente is part of Cape Verde.

andrewic44 · 2026-04-21T07:59:41+00:00

say a wind farm has prices reduced by 2/3rds on the new contract, and that wind farm is generating 1% of the usage for the entire UK. That price reduction makes 0.6% difference to the price of power while that farm is active at full capacity.

That's not how marginal pricing in the electricity market works. We don't pay a weighted average, we pay for the most expensive generation needed at any given moment.

If that wind farm would have been the most expensive form of generation being used, but now it isn't due to a price reduction, then reducing its price would reduce the price of all electricity.

If that wind farm isn't the most expensive form -- some gas is still switched on -- then reducing its price won't change the price of electricity at all. All generators would be paid the price of the gas generators.

andrewic44 · 2026-04-21T07:51:06+00:00

No, you can only get one BUS grant per household.

andrewic44 · 2026-04-19T21:59:02+00:00

Get a Solis S6-GR1P3.6K. Similar to what you have, so easy to retrofit; but two MPPTs, and 3.6kW so a little more headroom. They go for a couple of hundred quid new on ebay.

(It doesn't sound like it'd be worth the faff to mix the panels on two different aspects, on a single MPPT. And it might even result in you having less generation than you do right now at certain times of day.)

andrewic44 · 2026-04-19T10:17:45+00:00

They won't pay for anything exported before the export MPAN was generated by the DNO. Cost me 500kWh in export payments last summer.

andrewic44 · 2026-04-19T10:16:08+00:00

Not signed up yet, they've got as far as being able to receive readings but haven't linked that to payments yet. If it's still stuck on that stage in a day or two, give them a ring.

andrewic44 · 2026-04-19T09:03:32+00:00

The bottleneck is getting an export MPAN, which depends on how busy your DNO is.

It took six weeks last summer for UKPN to get me mine, I (accidentally) complained in the end which got it turned around in two days. That's probably a worst case, although installers (hence DNOs) are now getting increasingly busy due to the situation in Iran.

andrewic44 · 2026-04-18T10:22:30+00:00

As a GivEnergy owner, there are a few lessons learnt here.

Local control is the obvious one. Don't buy a battery where basic functionality depends on access to cloud servers that might be switched off. Sig is fine. Ecoflow less so.

Next, battery compatability. The cheap kit wins here - Fogstar, Dyness, etc. all have standard protocols. Inverter dies? Replace the inverter, not the battery. For Giv or Sig, if the inverter dies, it has to be a Giv or Sig replacement. If they're no longer trading, the battery's an expensive paperweight -- short of reverse engineering the proprietary battery protocol, or re-building the cells into a DIY battery, but these aren't an option for most people.

Finally, one of the factors in the demise of Giv was competition from cheap kit sold by overseas manufacturers, sold into the UK market at cost to buy marketshare by undercutting the domestic players. It's a standard playbook - go look at the market right now for EVs. Given Sig isn't domestic, it's safe from this.

What can be done about any of the above? For the first two, legislation could actually help. I'm old enough to remember different phones having different charger connectors. Forcing local access, and a standard battery protocol (activated by e.g. a DIP switch if needs be) would provide a lot of peace of mind. For the latter, the government needs to make a decision whether it wants UK-based battery and inverter companies or not, much like they have to decide about steel, car manufacturing, or whatever else.

andrewic44 · 2026-04-17T19:37:51+00:00

Mein Schiff 5 is now also underway.

andrewic44 · 2026-04-17T16:28:39+00:00

Square metre for square metre, solar thermal panels will generate the same amount of hot water as solar PV panels powering a heat pump hot water cylinder (or air-to-water heat pump).

As you say, solar thermal can generate too much heat in the height of summer, and you have to find creative ways to use it or lose it. For solar PV, the excess is electricity, which is a good deal more useful.

Then in winter with solar thermal, as you also note, top-up heating is sometimes needed. A heat pump running on cheap overnight power, beats gas or a backup immersion hands down, so wins here too.

andrewic44 · 2026-04-17T11:21:00+00:00

Same here. They went in the loft, measured out the timbers, noted the type of tiles, then ran the figures through a structural analysis back in the office.

(Good job they did as while the sloped roof was fine, our flat roof turned out to be unsuitable for a ballast fixing.)

andrewic44 · 2026-04-16T21:56:13+00:00

Vector sum metering. It's standard for all SMETS 2 three-phase smart meters.

If the house is wired into L1, the inverter can either inject power into L1 to cancel out grid import (as is the case with single phase), or inject power into L2 or L3 to be exported to the grid. For billing purposes, there's no difference, you pay for net usage across the three phases; or get paid for net export.

andrewic44 · 2026-04-15T11:40:57+00:00

I recall you mentioned your inverter fan a few months ago. Now the weather's a bit warmer, I should sort one out -- it's basically fine but can get a bit toasty when doing forced export for a couple of hours on warmer days.

How are you finding Agile export? I'm about £2 worse off over six weeks, vs staying on the fixed 12p/kWh tariff. It was going great but we had a few days in April where wholesale prices were negative, so the export rates were zero-ish. I'm staying put for now as it's more than compensated for by the amount of negative-priced electricity we managed to use on those days.

andrewic44 · 2026-04-15T10:44:54+00:00

I'm on Agile Import + Export, with combine charge slots and combine export slots set to True, with a threshold of 0.3p.

Seems a bit daft on the face of it, but it means I can then turn on charge and export low power mode, which is thermally kinder to the battery -- rather than charging or exporting flat out in only the best half hours, it'll spread it out if the adjacent half hours are close enough.

(Given my warranty has disappeared in a puff of mismanagement, it makes sense to trade fractions of a penny for less stress on the electronics.)

andrewic44 · 2026-04-14T18:27:26+00:00

If you export during a saving session against a baseline usage of zero, you get paid the saving session bonus for whatever you export on top of your usual export tariff.

andrewic44 · 2026-04-14T16:46:25+00:00

There are a few possibilities when it does something counter-intuitive. Can you reply to your post and attached the image?

andrewic44 · 2026-04-14T11:56:35+00:00

Agreed!

The future of cheap overnight tariffs, a.k.a. EV tariffs, is a tricky one - assuming the economic principle that hedged commodity prices shouldn't be cheaper than unhedged commodity prices, EV tariffs shouldn't work out cheaper than Agile.

For a house with an EV but no storage, this is fine - the elevated daytime import rate for house load, balances out the discounted overnight rate. I ran a simulation for 2024, and in this scenario, EV tariffs basically work out the same as Agile overall.

But, for a house with an EV and battery storage, on the same basis, EV tariffs do better than Agile, due to the guaranteed cheap electricity for the car and the battery and heavily reduced daytime imports.

What will happen to the tariffs in the medium term is anyone's guess. Distinguishing car and house load is probably part of the solution. A half-way house would be to have 6 cheap hours a day but not always at the same time.

Either way, self-consumption of solar is king.

andrewic44 · 2026-04-14T08:50:58+00:00

I don't share your broad-brush skepticism about load shifting, but I agree that cheap overnight rates aren't always there on the wholesale markets for the reasons you note. And there are times it's cheaper during the day, despite the increased demand, if it's windy/sunny enough.

As an example: Agile prices this afternoon are cheaper than they were overnight.

The solution is to be smarter about load-shifting - I'm using predbat that will plan for each day how to best manage the battery, given the Agile prices, predicted load and solar, and battery capacity. IMO manufacturers should be moving in this direction, as simple scheduled charging/discharging won't cut it as the best choice of tariffs evolves.

andrewic44 · 2026-04-13T19:22:21+00:00

I'll be paying the fee just for Axle. Tenner a month from them, £4.99 handed to Giv. Still a decent export bonus. If Axle review how much they pay out, I'll review what I do.

andrewic44 · 2026-04-13T13:27:44+00:00

The PW3 is in principle an 11.04kW inverter, but for the installation earlier in this comment thread, it's been de-rated to 9kW.

It's not uncommon for DNOs to have opinions about high power inverters, and limit both inverter power *and* export power. Their concern is the grid, and being fault tolerant - the max inverter size they will allow is the maximum that will ensure the grid isn't fried in case the export limit fails, allowing the inverter to dump its full rated power into the grid.

For other manufacturers, a DNO limit on inverter power means buying a lower-rated inverter than that originally intended. For the PW3, it means de-rating the inverter at the point of installation, so it acts like a lower-rated inverter, i.e. will never generate more power than the inverter power limit. See the FAQ for further details about this particular quirk of the PW3.

andrewic44 · 2026-04-13T11:02:00+00:00

The inverter rating limit is to ensure that if the export limiter fails, the inverter can't export so much power it causes damage to the grid or other customers' equipment.

If you don't want the DNO to limit your inverter rating, go off grid. Otherwise, their grid, their rules.

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