Solar batteries, how do they add up?

Octopus do a tariff where by you can charge the battery overnight at a cheaper rate and then use it during the day.  It will be more useful in winter when there is less solar generation but still useful all year round as a top up on dull days.

There are other batteries than Tesla, which are cheaper and more easily available. My 10Kw battery/hybrid inverter was less than half of what the Tesla is. In fact my whole 4KW solar array and battery/inverter and install was less than the Tesla battery.

<p style="text-align: left;">The Tesla battery costs more than my entire solar and battery set up was installed. It's a huge capacity battery, you need to look at your average daily consumption to work out what would be appropriate but I'd be surprised if it was 13kwh.</p>
Having the battery either means you can up your self consumption of power as you typically aren't using it when solar is generating, or even better (on the right tariff) you can manage your consumption to optimise import & export to optimise the benefits.

Tesla isn't really the value option. As with the cars.

We were not big users and still worked out that 10kwh was optimum battery for us for usage and storing solar.

I had solar for 18 months without a battery and it just didnt make sense we were never able to use it all export was derisory without the battery and it just meant we were importing at horrible high carbon times just like everyone else. - ergo hi cost on tracker tarrifs.

Load shifting is proving to be much more beneficial than solar to tracking the grids excess and thus keeping costs down. Also means we use all we generate from solar either at time or by proxy for sell high buy low.

What are the go to cheaper than Tesla batteries ?

literally having my 3.9 kw + 10.4 kw/h givenergy setup for jsut over 11k commisoned right now

plan is to work on octops flux/intelligent flux to reap some import/export money back

the batteries are rated to 6000 cycles/10 years.. but i think the larger or newer batteries cover an unlimited cycle warranty

I went for givenergy as it's the only setup currnetly configured for intelligent fluux, allowing octopus to control the import and export, in return for better unit rates

The cost of a 13 kWh Tesla battery is around £10k.

Our 10 KW battery cost half that....

But even then, the payback is a very long time.

2 years ago we bought a house with 10 year old solar panels.

I asked a couple of solar companies for quotes for batteries. Before energy prices went mad, they said there was no cost reason for getting a battery.

They said that the battery would take years to pay for itself, at which point it might well be degrading.

As the price of electricity has gone up, so did the price of big batteries.

Have I missed something ?

Not everything is about return on investment, or doing things as cheaply as possible.

If I had the capital available, I’d have a full solar and battery setup, simply so that I was consuming less from the grid, and thus fossil fuels. Not because it’d cost less in the long run.

In my opinion solar and battery does not make financial sense for the average user - payback times tend to be in the region of 10 years, so it simply isn’t a good financial investment yet. That may change in the future with lower prices for panels and batteries, and higher electricity prices.

The only real reason to go for solar now is because you want to do your bit to reduce use of fossil fuels, and to support the nascent solar industry.

We went with a battery to maximise self consumption and the allow load shifting.

What @bensales said.

I’ve used the Bill Nye ‘the planet is burning’ reference before. Deciding on ROI is a reasonable, but limiting, way of thinking about this choice.

we got a bunch of panels and a Tesla Powerwall in February. we moved to Octopus Flux a few weeks back. Our overall ‘impact’ from the Tesla app is now at ‘56% self-powered’.

Once the sun goes down the house mostly subsists on the battery. ‘Mostly’ as our grid draw changed when we moved to Flux and I changed the battery options to ‘time based control’ (was ‘self-powered’) and ‘allow charging from grid’. The battery tops up to 100% during the super off-peak period. We also constrain car charging to the super off-peak period too.

Batteries plus lots of panels plus Octopus Flux working well for us so far.

3800kWh generated on panels in first 5.5 months (since early march) and with flux we have received over £300 credit to our Octopus account since tariff went live late April.

Our installer (recommended on here!) used us for a case study:

https://p4solar.co.uk/case-study/conrad-hart-brooke-leeds-ls26/

ROI for solar and batteries should, IMO be thought of more as like a home improvement than energy use.

It may well still be cheaper over 10 years, but it also adds value to the property.

It also adds significant energy security no matter what people in power do to energy and carbon taxation in the future.

We have almost 20kWh of batteries but only 18kWh is usable and another 3.5kWh is protected in the lowest 20%, so in reality there's only 15kWh of usable battery.  Tesla PW and other batteries are the same. they have a "usable" capacity, but in reality, once you're into the last 20%, you can only draw a very reduced rate and below 10% it will force charge from the grid.

Even with this, batteries make sense to me.  Despite being fully electric for everything except water, we haven't used the grid since February.

True that . No one looks at the ROI of the new kitchen.....

^^ this

the initial outlay adds some value to the property, likely to decline slightly over time but still

you also have the infrastructure in place for upgrades and repair as time goes on.. panels are expected to last for 30 years now..although technology may make it worth replacing before then, who knows

my inverter will have a 10 year guarantee

likewise batteries

the calculations from all of the companies i got quotes from put approx 7 years ROI, granted i wasn't wholly happy with the figures used.. they work it out using inflation etc, they didn't calculate in any fancy load shifting tarrifs.

And, I'm 46... when i retire, having the potential to have much lower energy bills, or even 0, is worth a lot to me.

where do you install the batteries? are the inside or outside?

Mine are in the attic despite people sayin I should put them in the garage.

Temperature data loggers in both areas have shown that my attic is far more thermally stable than the (insulated) garage

I looked at it like hedging my energy costs. Although I did jump on it before the mass energy hikes. Folks at work thought I was mad as the math didn't math. Although are on the other side of their face now. The energy costs going sky high means my solar panels have all but paid them selves off.Just need the batteries to do the same now. Have not had to make a payment to octopus this year so far since Feb. Including standing charge and any grid charging I do they have paid about 100quid into my account infact so far.

For most batteries you can do either.  Ours are outside in a small enclosure that I built for them.  They're IP65 rated, but it just keeps the worst of the sun, rain and frost off them.

where do you install the batteries? are the inside or outside?

If you lift your house up there's a battery compartment underneath. Just undo the little screw and pop them in.

HTH!

Ours are bolted to the wall on the back of the house.

[url= https://live.staticflickr.com/65535/52544514390_6bfe0470f4_o.jp g" target="_blank">https://live.staticflickr.com/65535/52544514390_6bfe0470f4_o.jp g"/> [/img][/url][url= https://flic.kr/p/2o4bnvh ]10 kWh battery and inverter[/url] by [url= https://www.flickr.com/photos/brf/ ]Ben Freeman[/url], on Flickr

We are in a rural area. The thought of bolting the batteries to the wall outside gives me the fear.

If you lift your house up there’s a battery compartment underneath. Just undo the little screw and pop them in.

shit, that’s where i’ve been putting the bodies!

and thanks for the sensible replies.

interesting stuff

We are in a rural area. The thought of bolting the batteries to the wall outside gives me the fear.

is that fear of theft?

I have solar already, had it for about 12 years.  I did the sums as best I could (more solar, more solar + battery, just big battery, just little battery etc) and couldn't get a payback financially that I was happy with.  Least not because payback needs to factor in your £1 today not being worth £1 in 15 years time.

I can't afford financially to factor in any environmental assumptions.

Solar PV + Immersion Heater or Solar Thermal for hot water?

I like the simplicity of the Solar PV approach, but interested to hear view on it.

might be thinking about it wrong..

your £1 certainly wont buy the same amount of electricity in the future as it does now

BUT, if you can generate most of your electricity for an upfront investment, you effectively have done that

is that fear of theft?

Yes. Nice convienant boxes to remove and sell on even if they do they they are locked down to the original owner.... They are still worth recycling value of the cells. See also heating oil theft.

Solar PV + Immersion Heater or Solar Thermal for hot water?

Be better off exporting the solar and heating the water at the offpeak rate.

But it is an alternative to a battery if you need to use the power because you can't load shift your peak rate power.

I've just bought solar thermal* panels to reduce my dependence on heating oil. Will supliment with off-peak immersion through winter

*Based on the warranties of the various bits it makes absolutely no economic sense. Other than that I know a few folk with 15+ year old solar thermal systems locally that paid them selves off years ago. - I guess by the same token my parents 8kwh inverter is stamped up as made in 2000.....

@alan1977.  I meant inflation generally meaning if you want to truely work out financial RoI you need to get back more than the value of your investment.  Saying that, it's a fair point - I had no idea to work that in either (what 1Kw of electric will cost in 1/5/10 years) so opted to leave both of them out and assume one cancels the other out 🙂

Least not because payback needs to factor in your £1 today not being worth £1 in 15 years time.

That works in the sums favour here.

The way to look at it is is that the battery enhances the overal efficiency and capacity of a solar PV system.  Even with a moderate solar instal you are unlikely to be able to use all the power you are generating, the energy is worth more to you than sellling to the grid and, crucially, solar PV can only generate power during daylight. Our basic system is a 3,6 kWh solar panel system with a 3kWh battery (Pylontech). The battery cost about £1100-£1200 extra as part of the system install but means that during most of the summer our energy from gid requirement is minimal: a full battery means we can run the house on it from sunset to sunrise, and during the winter we can hang on to any (usually some of) energy that is generated during the day and use it in the evening.

Basicaly our PV system alone gives about 50% of the power we need across the year , the Battery pushes this figure up to 65-70% of the electricity we need per year,  in the summer its closing on 100%. I'm buying another battery soon as this will reduce our electricity from grid requirement further still and should improve things through the winter.

As for the ROI, if you want to do that, fine (I dont as it view this as a sunk cost) , but for us we saw an immediate and frankly, dramatic drop in our electricity bill.  The price rise last autumn meant that the break even point reduced from about 8-10yrs to about 6.... My SEG (selling excess solar generated power to grid) tarrif has been tripled recently so I'm now earning/saving about £250ish per year from that but even so, its still more worthwhile to store and use the power that I'm generating that sell to grid. Companies like Octopus will pay you more and do smart tarrifs too.

So OP in answer to your question, if you can afford it then yes, yes it really really does add up.

Yes. Nice convienant boxes to remove and sell on even if they do they they are locked down to the original owner…. They are still worth recycling value of the cells. See also heating oil theft.

This is another reason why mine are in a locked box outside.  It's not secure, but at least it's not visible.  They had blue lights on them which could've guided and aircraft to a carrier in a force 12 hurricane without difficulty.  Why so bright?

where do you install the batteries? are the inside or outside?

Tesla Powerwall can be either inside or outside I believe. Outside is more typical. My installer balked at the idea of putting it in the cellar. He explained that getting a 125kg+ fairly tall metal box down the cellar steps might not be that easy or safe.

It’s mounted on some frame anchored to the wall.

I'd want any Tesla power wall battery more than about 18months old outside as well to be fair and it's nothing to do with getting it up or down stairs.

Given the difficulty moving our battery when it was installed I don't worry too much about it walking off. Ours is outside, did not want it inside, especially not under the stairs like one provider suggested!

I initially wanted it outside...

it's now in the loft (2x63kg batteries were amusing to get up there)

I'm now of the understanding that the latest LifePo batteries are incredibly safe.

I do intend to fit a linked smoke detector however

Mine are in the attic despite people sayin I should put them in the garage.

only went in loft as you had the fear of trying to clear a space in "garage"   😂

I’m now of the understanding that the latest LifePo batteries are incredibly safe

That's where I am too but anything pre latest gen Powerwall2 were still NMC

only went in loft as you had the fear of trying to clear a space in “garage”

And risk having to get rid of bikes....... No danger Trevor

As an owner of an electric car I know first-hand how batteries lose both capacity and charging efficiency in cold weather.

As a researcher in fire detection and suppresion I know how worrying li-ion battery fires are.

So I’d buy a battery system from a reputable manufacturer which is CE/UKCA marked and install it inside my house. With a smoke alarm nearby.

Fires are only happening with crap unapproved batteries with crap unapproved chargers.

Why can’t I use the 90+ kWh battery sat on my drive most of the time to help balance out peaks and troughs with nightly rates and solar pv?

obvs scheduling to allow it to be used when I need to go somewhere could be sorted.

any significant engineering challenges?

Because annoyingly those systems are still in the experimental stage.

Ive got solar and 4.8kw of batteries.

Because i dont work from home we dont get to use the majority of solar we produce. Im still working it out as ive only had it since December.

without batteries solar didnt work out at all for us (25 yr +payback)  with it drops it between 7-9yr. Its all usage case dependent though. In the end i was worried about he potential for huge bills so jumped on it in a way to try and offset that.

When I did the sums in March last year - batteries (and a lot of them) made a significant difference to the ROI.  at 40p/kWh (which was where we were heading without government intervention), it was 6.6y, at 32p/kWh, that was 7.5y.  At 15-20p.kWh (which I think is where it might stabalise), it's now more like 10y.  Given the also dramatic rise in available export rates, I'm not sure big batteries make sense any longer.  I think 5kWh to get you through the peak period between 16:00 and 19:30 and to act as a store for intermittent solar in the autumn/winter reduces your investment cost by £4-5k and only marginally increases you annual electricity bill by maybe £200-£250 - perhaps not even that if managed correctly or if you use gas for cooking.

I have and 8.7kW battery and a 5.8kW array. I keep a track of the numbers using Home assistant on a Pi connected to my inverter.

The payback period changes based on tariff changes and the per kW costs, not to mention the amount of solar but I estimate ours will be paid back in around 6.5 years. Lucky to have a well placed roof!

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Why can’t I use the 90+ kWh battery sat on my drive most of the time to help balance out peaks and troughs with nightly rates and solar pv?

You will be able to soon if it's a Tesla, apparently Tesla have or are applying to become an electricity supplier in the UK...

When we started planning a new build, battery was a "nice to have" -- now - with power outages last year, flexible off peak tariffs, and a bit of "go for it" attitude, I think we'll install a decent battery with intention of using the in summer as power bank from solar PV, and when seasons go to autumn, winter and spring, use it as an off-peak storage to be released during day.

Thanks for the replies.  The octopus tariff looks interesting, however it could be pulled at any point, so basing what is an investment decision on one tariff is risky.

Definitely food for thought though.

Have you done research ? It's not one tariff there's a handful of good options across a few companies - with a few even better options currently coming to market - if your in the south east today there's a glut of renewable predicted they want rid of to grid balance so there is actually a free power hour this afternoon

Yes they could be pulled but equally electric prices could go through the roof.

My maths was working pre electric prices going mental but then installs were cheaper (lots)than the last 18 months or so.

Unless you want to make a hobby out of scanning weather forecasts and working out when to put the washing on and cook the roast etc you'll probably lose 30-50% of your solar generation unless you have a home battery, expecially if you are out during the day. Batteries also let you make use of time based tarriffs in winter.