Battery or no battery?

[Walshie]

Hi all,

I'd appreciate some advice on whether there is any value in having a battery as a part of my solar set-up?

We have a relatively small roof footprint and so we can only generate approx 3.6KW from solar.

I had originally intended to have a battery but have been advised that it is unlikely to be very effective given the 3.6KW constraint.

 

I don't want to go to the expense and hassle of installing a battery if I could use that investment better elsewhere.

Can anyone help me with this please?

Thanks in advance,

 

W

[SteamyTea]

There is a lot more to it than just the ability to time shift.

 

Start with looking at your current usage patterns, download your half hour usage if you have a smart meter.

Then see if you can get a better tariff that will fit your usage better, or if some simple changes will make a difference.

 

The biggest thing you can probably change, for nothing, is reducing parasitic loads.

Half the time my house pulls no power at all.

 

Many battery systems have a minimum load requirement, so running a laptop and a light may not be enough to start the battery system.

[JohnMo]

13 minutes ago, Walshie said:

only generate approx 3.6KW from solar

Is that a rate of generating of kW or amount per day kWh?

 

We have a battery AC coupled and PV, we charge battery overnight on cheap rate, and then charge battery, run immersion and heat pump during the day at the moment mostly on PV.

 

Last month's average per kWh price came out at about 9p. We utilised 92% of all PV generated. 72% of all electric came from PV or battery. Almost every thing else was cheap rate.

 

You just have to do the maths to see if it works for you

[nod]

If you are putting PV to save the planet Get at least one battery and as many panels as possible 

If you are looking to save money Forget the PV As it will take Decades to pay for itself 

Or buy cheap and self install 

[JohnMo]

27 minutes ago, nod said:

buy cheap and self install 

Yep the only way, anything else is a plain expensive.

[Alexphd1]

You could install a hybrid inverter and have the option of adding batteries later without the need to upgrade the inverter.

[Nickfromwales]

2 hours ago, nod said:

Forget the PV As it will take Decades to pay for itself 

I've been doing solar surveys for my clients for each self build, and not one of them has had a payback (breakeven / ROI) that has been more than 11 years, most are in single digits now as it's becoming a buyers market.

 

Recently priced a big system for a hotel and they'd breakeven in year 3.9, so insane value for money.

[Nickfromwales]

10 minutes ago, Alexphd1 said:

You could install a hybrid inverter and have the option of adding batteries later without the need to upgrade the inverter.

Best advice ever.

[joth]

37 minutes ago, Alexphd1 said:

You could install a hybrid inverter and have the option of adding batteries later without the need to upgrade the inverter.

Only snag with this is you probably want to oversize the inverter as most batteries can deliver 5kW plus, which is some upfront wasted capital on a 3.6kW array and also some unnecessary paperwork to jump through.

 

The underlying point is sound, if money is tight don't spend capital on something easy to retrofit like a battery (and probably getting cheaper with time) at the detriment of anything hard to improve later like insulation or draft proofing. Even PV is fairly easy retrofit in the big scheme of improvements 

[Nickfromwales]

New Solarwatt inverter for 1ph can be loaded up at 80-100% of it's design capacity, so bags of headroom there to add later. A few different configs, so needs the nose in the book obvs!

[nod]

Regardless of all the sales talk The figures don’t add up 

 

We where quoted 11 k with an  a saving of around £200-250 per year 

The buyers of our first build have have covered my beautiful slate roof with PV not a great look Considering our build came under Heritage and we had to match everything to the 500 year old farm Even the chimney pots 

17k including two batteries 

No heat pump yet 

The salesman has promised a saving of £500 per year Even if the PV wipes out the £960 per year that we were paying Your still 20 years to recoupe  the cost That’s if you haven’t replaced one or both the batteries That Mr google says have a lifespan of 12-15 years 
At least the salesman didn’t promise a break even in 3.9 years 😁

[Nick Laslett]

@Walshie, 3.6kW is loads of energy. Don’t feel bad. Outside the oven, kettle and tumble dryer that is everything else covered for 8 months of the year, assuming you have gas central heating. 
 

Just get a solar diverter for your hot water tank. Then 6 months of the year the solar is heating your domestic hot water. The tank is your battery. 
 

Obviously an EV car is also a good place to put excess solar energy and is also a massive battery. In 5 years time vehicle to grid will be a more viable system setup. My long term plan has been to use my EV battery when that approach becomes available. 

[MikeSharp01]

13 hours ago, SteamyTea said:

Half the time my house pulls no power at all.

How do you keep the data loggers running - batteries?

[JohnMo]

57 minutes ago, Nick Laslett said:

tumble dryer

I was shocked every time the normal tumble dryer went on (used so much electric), then installed a heat pump dryer, uses almost no electricity in comparison.

[SteamyTea]

1 hour ago, MikeSharp01 said:

How do you keep the data loggers running

They draw so little power that they do not register at the Wh level very often.

Unlike when I first started data logging and was using an old desktop that was pulling about 200W.

They obviously do take some power.

 

Looking at the data from 2019 to now, the mean 'no power' is 53.7% of the time.

This does give a quirk to mean averages, so I calculate the total mean and the 'power draw only' mean, 0.44 kW and 0.62 kW respectively.

Maximum power is obviously the same for both, 13.16 kW, but minimum power above 0W is different, 0.001 kW, or a watt.  That is probably the logging power usage, radio alarm clock and washing machine on standby.

 

As I am on E7, time of use gives different numbers depending on time.

During the E7 window, they are 1.14 kW and 1.47 kW, higher number excluded 0 power draw times.  During the 'day' the numbers are 0.1 kW and 0.19 kW.

84.6% of my usage is at night.

Would be hard to justify a battery system to offset 15.6% of my usage as the marginal price difference is 18.9p/kWh, and I only use 1.6 kWh during the day (over the last 6 years), and last year, I got that down to 1.26 kWh.  So would only save about 29p/day.  I am not sure how much it would cost to cobble together a battery system, got to be £1000, so would take 11.4 years to recoup my costs at today's electricity prices.

 

Fun to do though.

Edited Thursday at 07:31 by SteamyTea

[SteamyTea]

27 minutes ago, JohnMo said:

I was shocked every time the normal tumble dryer went on

I bought a washing line and pegs from Poundland, cost 2 quid, it is the biggest saving I have ever made.  When I changed my washing machine, I realised that I had not used the dryer on it for over 2 years, so got a new machine without a built in dryer.

[MikeSharp01]

One thing I have noticed, although I guess I could have worked out it was there, is the amount of power the inverter (ours is hybrid so ready for a battery) draws. I have not done the long term math yet but if feels like about 5-7% so for example at 6kW of generation the Inverter is using around 350W. I am somewhat with @nod - the numbers on the battery just don't add up but if I take the 'save the planet' line I can square the circle so if there is any money left at the end of the build we will get a couple of batteries. 

[SteamyTea]

1 minute ago, MikeSharp01 said:

but if I take the 'save the planet' line I can square the circle

There are probably better ways to do that.

Swapping a car to a more fuel efficient and lower CO₂ emissions would make the bigger difference to my personal carbon budget.

But last month, my 16 year old Mondeo Eco diesel averaged 66.3 MPG.  That is about 1,700 kWh for the month.  Almost half what my house uses in a year.

[JohnMo]

So some real numbers (PV and battery)

 

We generated 5500kWh in 2024, 500kWh went back to grid the rest used in the home. So 5000 x £0.25 (cost per kWh) is £1250.

 

Battery took 5000kWh from grid at £0.13, so cost £650. Without battery that energy would have cost £1250, so a saving of £650.

 

Total saving of £1900. Our self installed solar was about £3k and battery installed £8200 = £11200. £11200 / £1900, so just under 6 years payback. Battery and PV costs have dropped since I bought.

[Nickfromwales]

2 hours ago, nod said:

Regardless of all the sales talk The figures don’t add up 

 

We where quoted 11 k with an  a saving of around £200-250 per year 

The buyers of our first build have have covered my beautiful slate roof with PV not a great look Considering our build came under Heritage and we had to match everything to the 500 year old farm Even the chimney pots 

17k including two batteries 

No heat pump yet 

The salesman has promised a saving of £500 per year Even if the PV wipes out the £960 per year that we were paying Your still 20 years to recoupe  the cost That’s if you haven’t replaced one or both the batteries That Mr google says have a lifespan of 12-15 years 
At least the salesman didn’t promise a break even in 3.9 years 😁

It’s not sales talk though, or a guesstimate, it’s all done on MCS software and ROI is calculated using and export value 50% lower than you would actually get; this means (has meant) that all clients to date have reported that the systems are performing better than they anticipated thus further narrowing the time to get to break even.

 

At 20 years break even I doubt we’d have sold a single system tbh!

[Nickfromwales]

55 minutes ago, JohnMo said:

I was shocked every time the normal tumble dryer went on (used so much electric), then installed a heat pump dryer, uses almost no electricity in comparison.

I looked at these a lot, but, according to each manufacturers literature, the drying times were massively elongated vs a regular one, so I didn’t buy a HP one. We’re a busy family of 6 so I can’t have a large load taking 4-6 hours to dry, we’d all be walking around in the buff at that point 😝

[JohnMo]

2 minutes ago, Nickfromwales said:

large load taking 4-6 hours to dry

We really haven't noticed a difference in dry time, we changed the washer at the same time, and perhaps the spin performance is better, so stuff goes in to dryer, dryer at the start.

[Nickfromwales]

23 minutes ago, JohnMo said:

So some real numbers (PV and battery)

 

We generated 5500kWh in 2024, 500kWh went back to grid the rest used in the home. So 5000 x £0.25 (cost per kWh) is £1250.

 

Battery took 5000kWh from grid at £0.13, so cost £650. Without battery that energy would have cost £1250, so a saving of £650.

 

Total saving of £1900. Our self installed solar was about £3k and battery installed £8200 = £11200. £11200 / £1900, so just under 6 years payback. Battery and PV costs have dropped since I bought.

So, if you allowed another £3k for an installer (overheads and profit), assuming the client supplies scaffold, then you’re still in single digits. 
£6-7k for a ~4kwp system (commercially installed) seems about the average.

 

People forget that with batteries, if you can’t empty them every 24 hrs then they’re oversized. You don’t bank electricity over days you should generate / shift / consume every 24 hrs. 

[Nickfromwales]

2 minutes ago, JohnMo said:

We really haven't noticed a difference in dry time, we changed the washer at the same time, and perhaps the spin performance is better, so stuff goes in to dryer, dryer at the start.

Interesting! I was really put off by the MI’s, and frustrating to hear as my electric meter glows in the dark during winter……

 

Maybe I’ll review again, thanks for the feedback. 

[torre]

2 hours ago, JohnMo said:

Without battery that energy would have cost £1250, so a saving of £650

 

2 hours ago, JohnMo said:

battery installed £8200

6 years payback for the whole system sounds great but payback for just the battery sounds like 8200 / 650 = 12.6 years . That's pushing the lifespan of the battery to payback at all.

Factor in that battery prices approx halved in 5 years (and keep dropping) and I end up thinking that (unlike planting a tree) 'some time in the future' always ends up being the best time to install a battery.

Using the above figures as an example, you could instead start without a battery and spend 5 x 650 = 3250 on 5 years electricity and as long as by then the battery price has dropped to no more than 5k you'll still be better off buying later. (and have a new battery)

+1 for the heat pump dryer but drying times are much longer. Great if say you work from home and can make those longer cycles work, esp off peak.