Is solar battery storage worth it?

VladtheCount

Good first introduction to panels and storage. However riddled with technical errors eg 4kW solar panels can produce 8kW per day, in full sun they will produce 8kWh ie 8 units in 2 hours. I have 3kW panels which produce at best 26kWh per day therefore the factor is 8 not 2 in peak summer on a totally sunny day. Essential to get articles technically vetted not just collate 'facts' and publish.

Haughley

My  battery (10kw, Solar Edge) was installed outside (weight and space).  Room for another if wanted. 5.2kW max solar panels. Have an EV and charge o’nite at 7p and have been using dishwasher, washing machine and dryer at same time. Also now top up house battery at night and hot water (plus 2hr boost midday). Average use 30kw per day, baseload about 1/2 kw. We are home most of the time. At the moment, our peak use is minimal and export tariff also offsetting remaining bill. Gone down from £205 to £165 by getting off-peak tariff. Now, with panels and battery, down to £35 bill this month. If I can save £1000 per year, payback will be just over 14 years on the whole system. Can’t be certain until Had a whole year. The installer said it would be 8-9 years on panels alone and 10 years on battery alone, based on OI tariffs back in May. These figures take no account of savings from car fuel and oil boiler use for hot water in the summer.  The panels have 25 yr life.  Inverter and battery will probably need replacing once in that time. So it would be cost saving eventually, and a good hedge against rising energy prices, especially if we have to change our oil central heating boiler eventually. 

Qyburn

VladtheCount said:

Good first introduction to panels and storage. However riddled with technical errors eg 4kW solar panels can produce 8kW per day, .

In other words not really a good article at all. Just the fact of using a unit of power to describe the quantity of energy produced suggests the author didn't really have much idea. Sizing the battery to store one full day's generation makes no sense either, even if their figures and units had been correct.

retireby50

OK, so this is primarily a money saving site so, understandably, the focus is on the financial aspect for individuals/families. Having read most of the posts in this thread the financial side of battery with solar seems as clear as mud! Someone made an interesting comment about thinking of the (electricity) grid as a giant battery, which makes me wonder about the overall environmental impact of household battery storage. Can't help thinking it's negative - use of scarce resources with no actual change to total energy use/production (assuming that surplus solar PV produced and sent back to the grid is all utilised).

ed110220

retireby50 said:

OK, so this is primarily a money saving site so, understandably, the focus is on the financial aspect for individuals/families. Having read most of the posts in this thread the financial side of battery with solar seems as clear as mud! Someone made an interesting comment about thinking of the (electricity) grid as a giant battery, which makes me wonder about the overall environmental impact of household battery storage. Can't help thinking it's negative - use of scarce resources with no actual change to total energy use/production (assuming that surplus solar PV produced and sent back to the grid is all utilised).

I don't think the assumption at the end is true, especially as we get more and more renewables on the grid. Maybe when renewables made a much smaller contribution it was true. More storage allows more renewables on the grid by soaking up energy at times when it is abundant and might otherwise be curtailed either because there is insufficient demand or lack of grid capacity to transport it to where needed, then releasing it later and displacing FF. Also, if storage means gas generators don't have to ramp up and down so rapidly they can operate more efficiently.

BitOfaNerd

NedS said:

BitOfaNerd said:

I wouldn't get solar panels installed without a battery to maximise their usefulness. 

I'm not convinced. I may have previously agreed with you when SEG payments were really low (4p), but now SEG payments of 15p are available against an import cap of 22p the financial benefit is much reduced.

Assuming you have solar, excess solar can be exported for a SEG of 15p to the grid at no cost (think of this as a large free battery). Current Ofgem cap is around 22p, which constitutes a 7p margin (or cost) per kWh to store your excess solar for free and use it again later. Storing energy in a battery and taking it back out again is inefficient (not 100% efficient), so that 7p margin will be reduced, to maybe 6p.

How many kWh at a 6p margin will you have to store and later use to cover the cost of a £3500 5kWh battery installation with a usable life expectancy of 10 years? £350/year = 5,800kWh per year cycled through your battery, which means you'd need to cycle 16kWh/day to break even through your 5kWh battery. Not going to happen.

Now maybe you can improve the margins by charging the battery at cheap import rates and then exporting or using at peak times, but again I'm still not convinced the numbers stack up. At best, you may be able to cover the costs of the battery in the 10 year life of the battery.

IMHO a better (and simpler) financial solution is to fill your roof with as many solar panels (with a 25 year lifespan) as possible and export as much as possible at 15p SEG to offset annual usage. A battery simply adds to the costs and diminishes returns. I'd spend the cost of the battery on more solar panels and a larger inverter, and stick the rest in the bank at 5% as it will give a better financial return than adding a battery based on today's prices and rates.

My experience is different.  Our estimated pay back time for the panels and 10kWh battery is 6 years (at current energy prices).  As I said we have high energy usage because of an electric car and air-source heat pump so our annual savings would probably be greater than for those with lower usage.
It is also the case with Octopus that you can't have the cheap overnight tariff and also the high export tariff ( we get 8p/kWh).  Even at an export tariff of 15p, to generate the savings we get with Octopus Go we would need to export over 5000kWh annually which would require a lot more panels on our roof (space is always an issue) and permission from the DNO (I'm not sure how easy that is to get around here), so for us the battery makes more financial sense.  It's always interesting to hear other people's experiences. 

Martyn1981

retireby50 said:

OK, so this is primarily a money saving site so, understandably, the focus is on the financial aspect for individuals/families. Having read most of the posts in this thread the financial side of battery with solar seems as clear as mud! Someone made an interesting comment about thinking of the (electricity) grid as a giant battery, which makes me wonder about the overall environmental impact of household battery storage. Can't help thinking it's negative - use of scarce resources with no actual change to total energy use/production (assuming that surplus solar PV produced and sent back to the grid is all utilised).

Agreed (past tense) with you 100%, in fact I think I've said something along those lines 5 or so years ago, when pondering batts. Taken to the extreme, battery storage actually introduces some losses, so even less green leccy reaches the grid.

[Edit - Just to say, no criticism of early adopters, as they are critical to developing products, and reducing prices.]

However, now I'm firmly in the ed110220 camp, and have very recently gotten batts. So things are changing.

Plus, there is an added factor, regarding export limits and the DNO's. Typically you can export 3.68kW, and if you ask the DNO they let you go a bit higher - I've got a 5.9kW limit. But, by having a DC side battery on my 3.68kW inverter, I've now added more panels taking the PV up from 3.58kWp to 6.725kWp, and should be able to avoid clipping (where the inverter caps output to 3.68kW on the AC side) by directing the excess DC generation to the battery.

I appreciate this isn't a common situation, but the battery actually allows my property to produce more green leccy pa than it otherwise would be able to.

Going forward, new installs with a DC side battery (and a hybrid inverter), may be a partial solution for properties that can't get a higher export limit, thus allowing bigger PV systems.

There's also the possibility that the DNO allows a limit based on the properties actual export, rather than the inverter(s) potential. In such cases, an AC side battery would work just as well, with a larger PV system, coupled with a larger inverter (say 5kW), but the inverter is set to cap at 3.68kW* export (not generation), so it monitors how much escapes the house, which will be net of household demand, and the battery sucking up some of it too.

*Or whatever the DNO permission is.

EricMears

BitOfaNerd said:

It is also the case with Octopus that you can't have the cheap overnight tariff and also the high export tariff ( we get 8p/kWh).  Even at an export tariff of 15p, to generate the savings we get with Octopus Go we would need to export over 5000kWh annually which would require a lot more panels on our roof (space is always an issue) and permission from the DNO (I'm not sure how easy that is to get around here), so for us the battery makes more financial sense.  It's always interesting to hear other people's experiences. 

If you were on Octopus Intelligent Go,  you could have 6 hours (more if actively charging) of ultra-low priced imports (currently 7ppu) and be able to export at (currently) 15ppu.

OIG isn't alas compatible with all EVs or all charging units but worth bearing in mind that if you need to change car or charging unit you could make sure you choose something that is compatible.

Vaux

Given recent stories on battery fires our battery has been installed outside. The figure for 4kw solar producing up to 8kw per day is very misleading. Ours will produce up to 25kw per day in Summer and sometimes less than 1kw on a dark day in Winter. Our panels are over 10 years old and still generate over 4000 kW over 12 months. The software will manage max & min charges to protect the battery. Why no mention of a Gateway - without that you will neither generate solar nor be able to use your battery storage in a power cut. Given the current lack of energy security and the prospect of "back to the 1970s" this was a significant factor for us. Our software allows us to set a battery reserve figure for use only in a power cut situation. 

Solarchaser

ed110220 said:

retireby50 said:

OK, so this is primarily a money saving site so, understandably, the focus is on the financial aspect for individuals/families. Having read most of the posts in this thread the financial side of battery with solar seems as clear as mud! Someone made an interesting comment about thinking of the (electricity) grid as a giant battery, which makes me wonder about the overall environmental impact of household battery storage. Can't help thinking it's negative - use of scarce resources with no actual change to total energy use/production (assuming that surplus solar PV produced and sent back to the grid is all utilised).

I don't think the assumption at the end is true, especially as we get more and more renewables on the grid. Maybe when renewables made a much smaller contribution it was true. More storage allows more renewables on the grid by soaking up energy at times when it is abundant and might otherwise be curtailed either because there is insufficient demand or lack of grid capacity to transport it to where needed, then releasing it later and displacing FF. Also, if storage means gas generators don't have to ramp up and down so rapidly they can operate more efficiently.

Absolutely. 
I have recently moved to a model of charging fully off peak, overnight, and discharging when the grid is under most strain, (and when my house is likely using the most) at 7:30 -9:00 and then again at 15:30 - 19:30.

So my storage is definitely helping take excess from renewables and helping to keep the grid cleaner when it's dirtiest.

Octopus is again making moves to prove this type of concept with asking people to use (at lower cost) at certain times (to stop curtailment) and not use (for mild financial gain) at other times to keep the grid cleaner.
There's has been several free use periods in the last few weeks and on Monday they are offering half price charging if you then don't charge on Tuesday.

Once again octopus proving themselves as the good guys of energy production/distribution. 

For me personally, charging over 30kwh at 7p to then get paid 15p to discharge it at a better time for the grid is a financial incentive to do the right thing, or do my tiny part or however you want to put it.

If I can take what would be a £3-4k energy bill and reduce it to a couple of hundred in a year, id say that makes the batteries very financially viable

Edit to say not all that saving is from batteries alone, some is charging my EV off peak and heating water tanks off peak. The batteries mean the rest of my consumption also means that 98.3% of my energy use for last year (going by energy bills) was off peak