I have only got a heat pump and new glow worm boiler  and new radiators. But the elect gone through. The roof. And hardly any gas used. 

Hi @JanB57 and welcome to the OVO online community,

A really important point to raise here about making sure your heating system is running as efficiently as possible. Just to clarify is the heat pump you mention an Air Source Heat Pump? If so we’d recommend checking out this related thread:
 

As you also mention a new boiler, I’m not certain if this is a hybrid system? Let us know a few more details as I’m sure our community members would be happy to offer advice to help.

Im just in the middle of weighing up the economics of battery storage.  I have oil-fired ch, (boiler 3 years old) ,thermal panels, 2.45KW solar panels installed 2011 , and current usage of 3200 KWH annually.   Immersion heater for H/water never used though installed, very large cylinder installed.

Incoming quotes for battery storage vary between 3.3 and 5.5 KW storage and prices from £4800 to £6000 plus Vat for installation.

How can I check a) battery the right size

                                b) the calculations for payback time are correct? - and how are these done?

We are in the house all day.   getting full FIT and now SEG at 6p/kW on actual export ( but this is too recent to offer accurate info)

Should I wait for accurate export Kw ( say 12 months) before acting on battery storage installation?

Help please!

I assume you know how much you've exported in previous years so you could use those figures to help calculate a payback time.

As for what size battery to get, there are people who will say go as big as you can afford but you then risk never recouping the cost. Other people say get enough to get you through the night, which is more sensible but the hours of darkness change.

I would go as big as you can while maintaining a sensible payback period. 5.5kWh isn't a very big battery so you could go bigger if the figures add up.

If you want a second pair of eyes to look at your calculations, post them and I'll be happy to have a look. I'm no expert but I'd did a fair amount of cost benefit calculations when we were considering solar PV.

Thanks M.sterW .  Generation over a 10 year period is Average 5.77KW per day. The best price looks to be  £5200 inc VAT  for 1 x Pylontech 6.4kw battery and Lux Charger unit all including installation.   This from a local recommended installer.

Im still unsure about how to do the calculations…. At present the cost of electricity bought in is £4.62 per day including standing charges.

You need to know how much you're exporting over a year, as that's the electricity you could potentially put in a battery and use.

Assuming you use 70% of the amount you previously export the calculation would be.…

(Export amount * 0.7) * (35p - 6p) = the amount you'd gain by using the electricity instead of exporting it.

You'll have to take an educated guess on how much of your export you can use with a battery. In winter it will be 100% but in summer in will be less.

How about adding some more capacity to your solar PV at the same time as the batteries. You can get the batteries ex VAT that way unless i am mistaken?

I don't know how much of your water is already via the thermal panels you mentioned. Would a diverter like this be useful for hot water heating?

https://www.immersun.co.uk/

The immersun works with some types of space heaters as well so given the cost you might find that worth considering. You don't have to use for water heating.

The Octopus Outgoing tariff is 15p per kWh fixed or an agile variable rate. This is considerably more than the SEG rate you quoted. It can be used in the same way as your SEG rate with the FiT. Might be worth considering 

https://octopus.energy/outgoing/

We added battery storage just over a year ago @jaybell and that has been very useful. Not as quick to payback as solar PV but still worthwhile to maximise generation. 
We initially went with 4.8kw batteries but quickly doubled these to 9.6kw and these are also Pylontech. If you size your control system in the right way you should be able to add if needed as Pylontech are a modular system. 
It’s also likely that the other options suggested will be useful

Useful, thanks. 

How does your solar pv compare to the 2.45 kW of @jaybell ?

3.75kw installed early 2012 (to stay within max gen at the time)

Thanks ..Jeffus:     I have no room for extra panels…  and the thermal panels along with the oil fired ch boiler heat all the necessary hot water, baths, showers and hot water-feed dishwasher. On very rare occasions we switch on immersion for a 30 min boost. 

I’m stuck with my present SEG buyer for another 9 months.  I would add that if extra panels were to be added they could not go on to my existing FIT which is at top rate and inflation-proofed.

My max payback period for battery is 5 years.  Im assuming 4% as available tax free income on savings over that period on the capital cost if the money was invested rather than spent.

As soon as some more new fixed price deals for electricity are available I’ll be looking at switching without penalty. Keeping an eye on this!

Out of curiosity 

Do you use your oil boiler all year to heat your water? Or does the solar thermal do it all in the summer?

I don't suppose you know how much oil you use for hot water? Does the system give you that sort of information? 

That sounds like a good payback @jaybell 

Did you work out a similar payback for your system @BPLightlog

Is your payback different as you have a higher solar PV capacity and more battery capacity?

With the higher battery storage, the payback is a little longer (possibly 7-8 yrs) but with the first part of the system we were getting to full capacity too quickly we found and therefore not utilising the generation fully

Do people just assume the batteries last forever and don't degrade when doing these payback calculations to keep things simple. Or do you assume a level of depreciation on the batteries down to zero at some time in the future? 

There’s a 10 year manufacturer warranty (installer supported) but I’ve actually factored in a 15 year life with a decay in storage capacity of 2% per year after 8 years

I took up an offer from my local council to get a company to quote for battery storage. This resulted in a home vist and examination of my solar system. My system is 8 years old and would require a new inverter as well as batteries.  The quote was over £6000 with a pay back period of 5 years.  I challenged this because I would have to pay nothing for electricity to achieve this. I never heard from this company again. As previously posted the ideal set up would to have an Electric car which would act as a battery to my solar system. Surely possible in the near future.

Hey @SRF,

£6000 is quite an investment, I wonder if @Heatherd or @BPLightlog have any advice here? 

This topic has some interesting insight:

Unfortunately we’re no longer taking participants for our home battery trial, but our Home Battery webpage might still be of interest to you. 

‘As previously posted the ideal set up would to have an Electric car which would act as a battery to my solar system.’ do you think getting an EV would be an option for you in the future? 

Battery storage is often a longer payback but it is often worthwhile as you never match usage to solar production and so solar on its own is not ideal. 
I always recommend an inverter which will allow battery storage at some point and most solutions allow a modular approach. We started with 2 batteries 10 years after having solar PV installed and have now added further batteries. 
I am always cautious of an indirect approach as installers are a mixed bunch and may not have the knowledge needed on pre-installed equipment. 
 

Thanks for the responses I decided against paying for batteries and a upgraded inverter on personal grounds.  I am 74 years of age so any payback period would take me well into old age.my annual electricity bills would have to be close to zero to get to the 5 years payback time. Even though prices have increased I can buy a lot of electricity for £6000