Renewable Energy: Help me pick a grid tied home battery, please

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- CommentAuthorRobinB
- CommentTimeDec 11th 2021
I'm currently looking at options for our all-electric home (we have PV getting feed in tariff and ASHP) .
4.8kw LUX AC Battery storage system
â€¢ LUX AC Unit
â€¢ 2x 2.4kw Uhome Batteries

second option being Powervault whose prices have annoyingly just vanished from their website.

and what else should we consider?
- CommentAuthortony
- CommentTimeDec 11th 2021
A note from me, I like Energy use reduction, batteries increase energy demand as they are slightly inefficient.

To knowingly waste energy has no part in energy use reduction

In practice for the foreseeable future as I see it this increases emissions too.
- CommentAuthorRobinB
- CommentTimeDec 11th 2021
Interesting POV Tony and I partly agree. If we're going to use a set amount of energy anyway is it better to grab more solar and some cheap rate off peak to use when we need it or not. I shift my use around to suit sunshine and off-peak but not everyone in the household thinks the same.

Any thoughts on choice of battery anyone?
- CommentAuthorJonti
- CommentTimeDec 12th 2021 edited
Posted By: tonyA note from me, I like Energy use reduction, batteries increase energy demand as they are slightly inefficient.

To knowingly waste energy has no part in energy use reduction

In practice for the foreseeable future as I see it this increases emissions too.

Whilst I wholeheartedly agree with the idea of reducing the use of energy I am not sure what your point about inefficient batteries is meant to point out. Energy is also lost/wasted through transmission so does that mean you think energy should be produced purely on site and on demand?
- CommentAuthorrevor
- CommentTimeDec 12th 2021 edited
I have a BMZ battery (German made) 10 kW.This is married to a hybrid Delios inverter and 6kW of panels. There are complications I think around continuing to get FIT you need to check this out as you will be using the export power you are been paid foe if you are on the assumed 50% rather than metered but I think there are ways around this, my system is new from scratch. During the summer was getting excellent self sufficiency close to 98% and the export (measly 5.5p) went to cover the rest of usage. One thing I have discovered that this time of year with very little sun the system is not efficient. The battery management system manages the battery by monitoring all of the cells and ensuring they are all equally charged. With little sun the system takes grid power to use to trickle charge the battery then calls on this later when we use power. Each conversion is about 97% efficient so it is costing more to maintain the battery than using directly from the grid. This is a small cost more than recovered during sunny days however.
I have been looking at a small wind turbine but at moment finding it difficult to get quality answers to possible ways of doing it.
- CommentAuthorRobinB
- CommentTimeDec 12th 2021
Thanks Revor, are you tempted to (part)fill those batteries with cheap rate electicity during these dark winter days?
- CommentAuthorrevor
- CommentTimeDec 12th 2021
Posted By: RobinBThanks Revor, are you tempted to (part)fill those batteries with cheap rate electricity during these dark winter days?

Don't think I can as don't believe can have an export payment and cheap night time tariff. I note from my inverter graphs that the system looks to be preprogramed at night to trickle charge the battery so to maintain a level above 10% SOC so from the system point of view it looks possible but at moment do not know how I would up the level. It could be self defeating as I could be filling the battery overnight get a very sunny following day and sending it back to the grid at a loss maybe. Yesterday it was charging up to fill during day time think the BMS was initiating it. It is not as simple as some would make it out I am finding.
- CommentAuthortony
- CommentTimeDec 12th 2021
You should consider the capital cost, replacement cost and depreciation
- CommentAuthorJonti
- CommentTimeDec 12th 2021
Posted By: tonyYou should consider the capital cost, replacement cost and depreciation
- CommentAuthorrevor
- CommentTimeDec 13th 2021 edited
Posted By: Jonti
Posted By: tonyYou should consider the capital cost, replacement cost and depreciation

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From figures I have seen a typical cost is around the 12 to 14 p per kWh over life of battery. In other words your investment is paying in advance for your electricity. My current rate is 20.4 p and rising so saving about 7 p per unit.
- CommentAuthorWillInAberdeen
- CommentTimeDec 13th 2021 edited
Think a lot depends on what you are getting paid for your PV exports. Today, octopus are paying 25p/unit for PV exports during the daytime, so you'd make more money by exporting, but they are not taking new customers. They are paying 38p/unit at 5pm, so effectively they would pay (38-25) = 13p/unit extra for you to store the electricity for a few hours.
The price situation at the moment might be very unusual, or maybe this is the new normal, who knows!

From a green perspective, it would be better to store electricity when the carbon intensity is low, usually overnight, then release it during the daytime. Unfortunately, storing PV for self consumption is completely the reverse of this and it's a shame that the prices/subsidies work that way.

The grid do night-to-daytime storage using pumped hydro dams with efficiency about 70% round trip, so if you can do better than that with a battery then that's helpful, even though the battery is not 100% efficient.

I was looking at buying in grid electricity overnight, storing it, then releasing it during the following day. That would reduce the carbon by about 50% on many days. The economics don't seem to add up if you have to buy a dedicated battery to do this, but when/if V2G is available it should be good.

(Edit: it seems to me that round numbers Â£10k for a 10kWh battery system installed, lasting 10years, cycled 100% every day, works out at a cost of 30p per kWh stored. Obvs those numbers are not accurate, but gives a scale).

I'm surprised that more utility-scale storage is not yet being built to smooth out the peak prices. Previously I tended with Tony that it would be more efficient for the country to do this collectively with grid-scale storage, but as that hasn't happened yet, it's good that individuals are dipping into it.
- CommentAuthordjh
- CommentTimeDec 13th 2021 edited
Posted By: WillInAberdeenI'm surprised that more utility-scale storage is not yet being built to smooth out the peak prices.

I'm just guessing but is this simply the result of market forces? i.e. it's cheaper to continue running existing gas turbines than build new battery systems. Especially when the price of batteries is reducing so quickly and the technology is changing so fast. It would be easy for a firm to be left with an expensive stranded asset, or at least to see that as a possibility.

Yet again, lack of a clear direction from government is perhaps to blame. If they increased incentives to build battery systems and increased the costs of operating gas turbines (carbon tax, anyone?) and if people believed they weren't likely to change their minds next week and again in the new year ...

edit: There's an interesting article at https://www.power-eng.com/energy-storage/energy-storage-not-at-tipping-point-thoughts-on-why-and-when-2/ which seems like a good summary even though it's a few years old and about another country.
- CommentAuthorWillInAberdeen
- CommentTimeDec 13th 2021 edited
SSE have been developing the Coire Glas pumped hydro scheme (3x Dinorwig) for years and years, and it hasn't happened because the economics didn't work. Is being reworked as a multi-day store, rather than a night-to-day or interseasonal store, to improve the cashflow. It would double GB's electricity storage capacity, if they could make it viable. No amount of tinkering with batteries comes close to that, so if it can't work there then it's difficult to see significant grid-scale PS storage happening anywhere.

Gas turbines pay ETS carbon charge, recently that has gone way up, which is one of the reasons electricity prices have gone up. That should encourage people to do renewables/storage at home, as well as on the grid. But discourage electric cars and heating, they compete with petrol and domestic gas whose taxes have not increased.
- CommentAuthordjh
- CommentTimeDec 13th 2021
Posted By: WillInAberdeenSSE have been developing the Coire Glas pumped hydro scheme
There's a very relevant point on https://www.coireglas.com/project "In the drive to a net zero carbon electricity system, the UK government has created mechanisms to de-risk other electricity infrastructure investments to drive forward the low carbon agenda such as Contracts for Difference for nuclear power, offshore wind, onshore wind, and cap and floor support for interconnectors. There is currently no mechanism to de-risk electricity storage investment." Although it doesn't seem to me there's much risk. More a case of cash-flow to be funded. It seems like large companies have so thoroughly captured the state that they want absolute guarantees before they lift a finger.

The Coire Glas website doesn't seem to be very well maintained. It's all very pretty, but there are several broken links.

Gas turbines pay ETS carbon charge, recently that has gone way up, which is one of the reasons electricity prices have gone up. That should encourage people to do renewables/storage at home, as well as on the grid. But discourage electric cars and heating, they compete with petrol and gas whose taxes have not increased.
But this is all yet more evidence of the government fiddling while Rome burns. The ETS price is getting to be somewhere reasonable - it's above the German target price for once - but it doesn't have a floor so anybody basing an investment decision on it is chancing their arm. And subsidising gas heating and petrol because they're scared of the voters is plain stupid.
- CommentAuthorWillInAberdeen
- CommentTimeDec 13th 2021 edited
Let's wildly assume that they borrow Â£1bn to build the dam and repay the investors 5%pa capital+interest, they buy wind electricity at Â£40/MWh and store it at 80% efficiency, they sell 1.5GW for 2 hours a day on average. That would cost ~ Â£100/MWh , 10p/unit, which is comparable with the Hinckley nuclear plant, but would be much cheaper than people installing home batteries at the moment. Again those numbers are not accurate but give us a flavour.

You can build a lot of spare renewable capacity for that, or generate with gas and pay carbon tax, so there's a risk they would be undercut. I think they have a fair argument for the public to underwrite some of their risk.

Robin, sorry for diversion, did you see this list of systems? https://www.solarguide.co.uk/solar-batteries#/
- CommentAuthorRobinB
- CommentTimeDec 13th 2021
Thank you for the interesting comments and links. I love a good diversion!
- CommentAuthordjh
- CommentTimeDec 13th 2021
There's an assessment of Coire Glas at http://euanmearns.com/coire-glas-the-raging-best-of-pumped-hydro-storage/ with some interesting comments and links as well. The conclusion seems to be that the whole thing is uneconomic, so it's not a risk management issue at all. That's a fudge for trying to hook some subsidies.

On the domestic front, one thing to consider is why you want a battery. If it's just to store solar power so you can use it later, then that's relatively straight forward to assess. If you want backup against power failures then things get a lot more complicated. First thing to watch out for is that many 'backup' systems involve the power going out for several seconds before coming back on again. You need 'UPS' style behaviour if you don't want that. Second thing to think about is the the power rating. Many battery systems are quite low powered, so in a backup situation they'll handle lights and TV etc, but not kettles or cooking or heating. That's not just inconvenient, it means you have to rewire your house to split the loads into those that remain powered and those that don't.

My county council recently did an offer of a battery. They offered me a SOLIS 3.0KW 5G RAI ENERGY STORAGE
AC COUPLED BATTERY CHARGER and some PYLON US2000 PLUS LI-ION BATTERY. I don't know enough to know whether that was sensible or not (I didn't take up their offer).
- CommentAuthorphiledge
- CommentTimeDec 13th 2021 edited
Posted By: djh it means you have to rewire your house to split the loads into those that remain powered and those that don't.

Thats likely to be pretty onerous but surely you can avoid that by not switching on any high loads when youre on backup? We get more than our fair share of power cuts and manage fine on a 1.5kVA generator when the power is off.
- CommentAuthorWillInAberdeen
- CommentTimeDec 13th 2021 edited
I read that blog sometime back, but I don't think that's how the PS is intended to operate. The blogger is suggesting that the dam would be held full for weeks waiting for a no-wind period, so would have no income. But if you look at the other PS sites in operation, they are filling and discharging a few hours every day to meet the evening peak load, which is predictably many GW greater than the overnight load. So the operator gets a few hours of income every day, proportional to their GW turbine power, not the GWh dam capacity, most of which never gets used. They also get paid for grid backup services.

ISTR that Drax Cruachan (the biggest existing PS in Scotland) are thinking of installing more turbines to get more income, while leaving the dam capacity unchanged. Same as was done to get the Coire Glas design moving.

The implication is that PS is not good for interseasonal storage, as the operator would prefer the cashflow of operating it every day rather than once each year. I wonder if that applies to other storage technologies that might store summer PV for winter use, otherwise PV energy starts to look less useful long term as it would need 100% winter backup.

Interested that the conditions this week seem ideal for PS - windy overnight, coal power running during the day, high power prices. But it looks like only 1-1.5 GW of PS are operating each day, out of ~3GW capacity in GB. I wonder why not - it would be great if more PS could eliminate the need to fire up the coal stations each evening.
- CommentAuthorrevor
- CommentTimeDec 13th 2021
Posted By: djhMy county council recently did an offer of a battery. They offered me a SOLIS 3.0KW 5G RAI ENERGY STORAGE
AC COUPLED BATTERY CHARGER and some PYLON US2000 PLUS LI-ION BATTERY. I don't know enough to know whether that was sensible or not (I didn't take up their offer).

was that coupled to an existing PV system?
You did well not to choose it would not power you for long.
My battery will provide 32 amps when grid connected and with minimum top up from grid or solar if available and drive a shower. Coming off the battery at say 55V DC it is some amperage feeding the hybrid inverter. On a power cut (which I have yet to commission this bit) will provide 20A but as I am finding it will only work if you have a decent capacity in the battery. When you need it, it is this time of the year but one has not had enough solar power It would probably come into its own if one could charge from the grid selectively which I need to explore at some point

Posted By: philedge
Posted By: djhit means you have to rewire your house to split the loads into those that remain powered and those that don't.

Thats likely to be pretty onerous but surely you can avoid that by not switching on any high loads when youre on backup? We get more than our fair share of power cuts and manage fine on a 1.5kVA generator when the power is off.

Posted By: philedge
Posted By: djhit means you have to rewire your house to split the loads into those that remain powered and those that don't.

Thats likely to be pretty onerous but surely you can avoid that by not switching on any high loads when youre on backup? We get more than our fair share of power cuts and manage fine on a 1.5kVA generator when the power is off.

How it is configured depends on the inverter one needs to decide what are going to be the "privilege loads" and these to have their own CU. So you would choose light loads. This CU is connected to the inverter and grid and when grid goes down the inverter does some checks and sends power from the battery to the inverter to provide the AC to the designated CU. As far as I can make out there are no UPS type systems I think the Tesla Powerwall and gateway come the closest to being almost instant (a few seconds) at a price off course and possibly a Victron setup might be close as well. You could off course have a manual set up so you switch over the supply from grid to battery with changeover switch that disconnect you grid supply which is presumably what is done with a generator back up system. My inverter has the facility to connect a generator to it which will auto start if grid goes down but requires the addition of an ancillary circuit board.
- CommentAuthordjh
- CommentTimeDec 13th 2021
Posted By: revorwas that coupled to an existing PV system?
You did well not to choose it would not power you for long.

Yes and how long it powered me for would depend on how many batteries I installed.

Posted By: philedge
Posted By: djhit means you have to rewire your house to split the loads into those that remain powered and those that don't.
Thats likely to be pretty onerous but surely you can avoid that by not switching on any high loads when youre on backup? We get more than our fair share of power cuts and manage fine on a 1.5kVA generator when the power is off.
The problem is that if you happen to have say an oven switched on when the power cut happens then the inverter sees an overload and shuts down. It's the same problem as the emergency supply in an office (usually red sockets, IME).

Posted By: revorAs far as I can make out there are no UPS type systems I think the Tesla Powerwall and gateway come the closest to being almost instant (a few seconds) at a price off course and possibly a Victron setup might be close as well.
Victron claim to offer UPS-type backup. I have no idea whether they really do. Tesla does not and you can see the changeover in a Fully Charged video.

Generator systems are normally automatically switched. One place I worked had a great big flywheel to cover the interval whilst the generator came online. Since the flywheel was permanently in circuit, the mains there was the cleanest I've ever seen. Last place I worked the generator was supposed to keep on working even if it was on fire and it had lost its main fuel tank. (It powers bio level 4 containment)
- CommentAuthordjh
- CommentTimeDec 13th 2021
Posted By: WillInAberdeenI read that blog sometime back, but I don't think that's how the PS is intended to operate. The blogger is suggesting that the dam would be held full for weeks waiting for a no-wind period, so would have no income.
I think the blogger was examining it from the point of view of backing up renewables (particularly as might be the case when we are 'carbon neutral'). As you say, most pumped hydro systems rely on daily operation to work economically and even then derive most of their income from balancing and stability operations and black start provision etc rather than from generation.

The implication is that PS is not good for interseasonal storage, as the operator would prefer the cashflow of operating it every day rather than once each year. I wonder if that applies to other storage technologies that might store summer PV for winter use, otherwise PV energy starts to look less useful long term as it would need 100% winter backup.
I think pumped hydro is the lowest cost storage technique so yes it applies to all present technologies. PV also takes away a lot of the need for daily operation in summer, since it can cover the evening peak. The intermittancy of renewables seems to be a problem for storage as much as it is for use.

Never mind - 'Tokamak Energy' announced they were half way to their target temperature and they'll be going live before you know it. So that's alright then. I love optimists. I hope they're right.
- CommentAuthorphiledge
- CommentTimeDec 13th 2021
Posted By: djhThe problem is that if you happen to have say an oven switched on when the power cut happens then the inverter sees an overload and shuts down

That depends on the appliances you have as all of our high load items switch off when theres a power cut. If you have an oven, or any other appliance, that stays switched on then its likely considerably cheaper to replace the appliance with one that switches off on power loss than it is to rewire and fit a separate consumer unit for maintained loads.

Posted By: djh

Generator systems are normally automatically switched.

For critical businesses yes, but likely prohibitively expensive for domestic setups as auto changeover/auto start systems are Â£1000s
- CommentAuthorDoubting_Thomas
- CommentTimeJul 21st 2022
Resurrecting this thread in light of recent uptick in energy prices.

We recently suffered a complete power outage on a sunny day & it was frustrating that our PV panels on the roof couldn't help to run our house because they are reliant on grid power.

This led to the inevitable discussion over whether we should invest in a small home battery. Ours is all-electric & a certified passivhaus, so we've already reduced most of our usage to fairly low levels.

With caveats on working from home (so energy use was a bit higher), in 2021 we imported 4200 kWh and generated 3600kWh, but clearly this wasn't all used on site and we exported a proportion to the grid throughout the summer.

I'd appreciate any guidance from the forum on how to go about sizing & calibrating a home battery for optimum 'point-of-generation' storage. Ideally, in the summer months, it feels like we'd be able to be almost entirely self-sufficient by shifting some of the daytime generated energy to help during the peaks of cooking dinner and making breakfast in hours when the sun isn't shining.
- CommentAuthordjh
- CommentTimeJul 21st 2022
Posted By: Doubting_ThomasThis led to the inevitable discussion over whether we should invest in a small home battery.
Very important - you need not only a battery, but also one that is equipped with a (certified) grid disconnect unit to allow it to operate in 'islanded' mode. Some of those result in a disconnect followed by internal power-up, so are no use for keeping stuff running from the banal oven clocks to computers. I'm not clear which, if any, allow uninterrupted power supply (so-called UPS operation).

Ours is all-electric & a certified passivhaus, so we've already reduced most of our usage to fairly low levels.
Sounds like us. Your numbers are also quite similar to ours, although I expect our consumption to increase a bit (1000 kWh) since we got an electric car.
- CommentAuthorDoubting_Thomas
- CommentTimeJul 22nd 2022
Thanks @djh

I had a feeling it wouldn't be as simple as picking whatever's popular on the market. Searching for 'grid disconnect' led me to this article: https://www.jojusolar.co.uk/batteries-smart-grids/using-home-battery-power-cut/
which suggests it may not be possible to use the solar panels anyway (depending on inverter size).

More research required..!
- CommentAuthordjh
- CommentTimeJul 22nd 2022
Posted By: Doubting_ThomasSearching for 'grid disconnect' led me to this article: https://www.jojusolar.co.uk/batteries-smart-grids/using-home-battery-power-cut/ which suggests it may not be possible to use the solar panels anyway (depending on inverter size).
Hmm, generally a useful article and an interesting company to explore, thanks. But I don't think it says you can't combine solar and batteries, just that it's possible if you choose a bad combination of bits. And BTW, AFAIK, Tesla is one that does not offer 'UPS-type' continuity of supply (there's a Fully-Charged video showing the disconnect). Victron, I think, is better. But I'm not an expert!
- CommentAuthorJamster
- CommentTimeJul 25th 2022
Others will know more / better than me I am sure, but while you can have a setup that allows your home to be 'locally energised' a) it does need to be an automatic disconnect from the wider distribution network, b) not all technology choices can do this and c) as above, while automatic, its likely not instantaneous (not a UPS).

To see if its worthwhile or not, you need as resolution in your generation and usage data as possible; I built a relatively simply spreadsheet to track a notational positive / negative generation balance over time. Any excess power I simply summed; you can I am sure set a variable cap to what you sum that to (your battery capacity) and then see how long that might last for later on.

I need to download R and see if it can do any further analysis on the different scenarios perhaps.
- CommentAuthorqeipl
- CommentTimeAug 16th 2022
@Doubting_Thomas
I installed 10kWh of Pylontec batteries this year and a Victron Multiplus II GX inverter/charger.

I have just created a power cut by turning off the grid at the consumer unit and am now running on battery power and a solar array that's connected to the battery via a Victron MPPT charge controller. There was no loss of power when I flicked the switch.

I chose Victron kit because it was available from my panel supplier and I am familiar with Victron in marine applications. If you go with Victron and are DIY-ing beware that the software configuration isn't straightforward. I found it to be a frustrating learning experience, but now that it's up and running I am pleased with the system. With a bit of load management I can keep my monthly consumption on both day and night meters close to zero at this time of year.
- CommentAuthordjh
- CommentTimeAug 16th 2022
Thanks, Malcolm. That's very useful to know. Do you mind me asking what the approx cost was?

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Renewable Energy: Help me pick a grid tied home battery, please