Batteries

powerful_Rogue

QrizB said:

powerful_Rogue said:

QrizB said:

powerful_Rogue said:

Jumping into this thread, i've got a system being installed  next month including a 6.5kWh battery.

Looking at previously months, we use on average 10kWh a day. I've been told I can have a second 6.5kWh battery installed at the same time for £2300.

My plan during the the autumn/winter is to charge up overnight as on Eco7 at 16p kWh. Day time useage would be 43pkWh.

Just trying to work out whether it's worth getting the extra battery, espeically as i'll be saving on VAT.

You have (or are getting) solar too? In which case, the number of days in the year where you'll need more than the 6kWh or so of storage that your battery offers will be fairly small. Let's say a quarter of them, 90 days a year.

And let's say that on those 90 days you'll need an average of 3kWh extra. That's 270kWh per year that you'll be able to buy for (at current prices) 27p/kWh less, a saving (ignoring losses) of £73 per year and a 32-year payback period.

Financially, I don't think an extra battery makes much sense at that price.

Many thanks for your reply. I'm getting solar installed at the end of October.

A good way of looking at things. On ECO7 my day rate will be 43pKwH, so using that rough guide would work out at a saving of £161 a year, or a 14 year payback period. That makes it seem a bit more interesting!

I'm not following your maths, sorry. We might be doing different calculations. Here's how mine went:

• You use 10kWh a day, every day.
• You've already budgeted for a 6kWh battery.
• The maximum same-day benefit from another battery is 4kWh, but you'll only need that in the winter quarter - and you won't need all 4kWh every day, so I've guesstimated an average of 3kWh.
• You'll buy those 3kWh for 16p/kWh instead of 43p/kWh, a saving of 27p/kWh - so, for 3kWh, a 81p saving.
• Multiplied by 90 days makes £73 of benefit a year from the extra battery.
• The extra battery is £2300, and dividing that by £73/yr makes 32 years.
  

Missing from my calculations is any allowance for conversion losses, or for the inevitable fall in retail electricity prices in the medium term.

How did you manage to calculate double the saving and half the payback period?

I've also used the calculator at https://great-home.co.uk/solar-export-guarantee-seg-calculator/

That gives a rough payback of 7.6 years with 6.5kWh battery and 9 years with 13kWh battery. Seems there are so many varibles in working these calculations out, but one common theme I see is a lot of people always regretting not getting a bigger battery at time of install.

Ectophile

I don't regret buying a smaller battery.  The bigger the battery, the longer the payback period.  Eventually, the payback period exceeds the life expectancy of the battery.

uk1

Ectophile said:

I don't regret buying a smaller battery.  The bigger the battery, the longer the payback period.  Eventually, the payback period exceeds the life expectancy of the battery.

Isn’t the issue (unknown detail) that in your calculation today the calculation is completed and considered using today’s parameters but what is advancing towards us is an accelerating price per kwh.  Against my own argument is of course the option to simply delay.  But todays payback figure can very quickly change and how many people will then regularly review the options of adding batteries once they have completed their initial system instal? 

ispookie666

Ectophile said:

I don't regret buying a smaller battery.  The bigger the battery, the longer the payback period.  Eventually, the payback period exceeds the life expectancy of the battery.

Life expectancy of the battery would depend on the chemistry, capacity, charging C and discharging C. Which unfortunately will be unfavorable for smaller batteries. 

Magnitio

I chose a 10kWh battery and am a relatively light user at roughly 5kWh/day on average. If looking at return on investment, I would have been better off just going for the solar panels. On their own, the panels would have provided roughly 6 year return, with the battery it is currently working out about 8-9 years. However, a lot of our energy usage is in the evening and the orientation of our house means the panels don't generate much at that time of day. I also wanted the security of having power available in the event of a grid outage which seems to be happening more frequently where we live.

sundarm

Hi Magnitio
I wonder if your Battery will save you from grid outage as our  would be installer thinks not.

Magnitio

sundarm said:

Hi Magnitio
I wonder if your Battery will save you from grid outage as our  would be installer thinks not.

I have a backup unit installed that feeds 4 sockets. We have our freezer permanently plugged into one of these and will use the others to connect essentials to in the event of an outage. This includes the central heating boiler (still on gas) so we have a source of heat. It has been tested and works well.

Mikeyboy01443

Ectophile said:

I don't regret buying a smaller battery.  The bigger the battery, the longer the payback period.  Eventually, the payback period exceeds the life expectancy of the battery.

'life expectency' a battery isnt going to just stop working after 10 years or whatever they guarantee.. my nissan leaf still has full capacity after 8 years, give or take, well out of the warranty period...