Is it a financial no brainer to get a battery system if you are getting a heat pump?

michaels

Suppose you use 5,000kwh of hot water and 12,000kwh of heat per year and assume the scop for hot water is 2.5 and for heat is 3.5.

Assume a tariff with 7p night rate and 25p day rate available if you have a battery or 25p all units if not.

Assume you can only heat hot water at night and use 30% of your heat at night rate period and 70% in the day.

Without a battery hot water costs 5000/2.5 x 25p = £500pa and heat costs 12000/3.5 x 25p = £857pa total £1357

With a battery the usage is the same but at an average per unit cost of 7.5p (including battery losses) the total cost is £407 or £950 less a year.

If a 30kwh battery system costs £6k to install (doable) then the payback is only a little over 6 years and actually the savings will be much greater because the battery will also support the same low night price for most if not all usage.

It will also be really helpful to the grid if heat pump users can time shift demand.

Surely it would make sense if the govt set their incentives to support combined heat pump and battery wherever possible?

Alnat1

Then there's the option of say a 10k battery and Cosy tariff where you can fill it up/heat water 3 times a day.

Or even Cosy with no battery, extra 1C on heating, plus water heating and heavy use appliances in the cheap slots.

FlorayG

I'm about to have a heat pump fitted, I already have solar panels and a battery, I honestly haven't a clue which tariff I'm going to choose once its done!

QrizB

michaels said:

Assume a tariff with 7p night rate and 25p day rate available if you have a battery or 25p all units if not.

That sounds like an EV tariff, so you'll need to own an EV too.

A conventional E7-style tariff is currently priced at eg. 13p night, 32p day. The maths are less convincing with that.

michaels said:

Assume you can only heat hot water at night and use 30% of your heat at night rate period and 70% in the day.
Without a battery hot water costs 5000/2.5 x 25p = £500pa and heat costs 12000/3.5 x 25p = £857pa total £1357
With a battery the usage is the same but at an average per unit cost of 7.5p (including battery losses) the total cost is £407 or £950 less a year.

With the E7 tariff I've quoted, the average cost is more like 14.5p/kWh, so total £787. Saving is £570.

michaels said:

If a 30kwh battery system costs £6k to install (doable) then the payback is only a little over 6 years

More like 10 years, on the E7 tariff.

michaels said:

Surely it would make sense if the govt set their incentives to support combined heat pump and battery wherever possible?

Government incenties are typically for things that don't make financial sense otherwise.

You've just demonstrated that home storage batteries *do* make sense, even without incentives. Even my ~10 year version of the calculation is reasonable.

So no, there's no reason for the Government to subsidise home storage batteries.

Reed_Richards

michaels said:

Suppose you use 5kwh of hot water and 12kwh of heat per year 

My daily consumption, averaged over a year, is around 16 kWh on heating and hot water.  Is that what you mean or are you confusing kWh with MWh?  From your subsequent calculation it looks like it's the latter but could you confirm this please.

TroubledTarts

On Agile with no solar and not batteries or EV we averaged 13.4pkwh last year

We are looking at batteries but not blindly believing the savings should be based on the SVT only.

Our £6k investment for 32kwh of storage would need us to switch to Tomato energy and believe they will still be viable for the payback period. Charging at 5p kwh (don't forget to add 10% charge/discharge losses so that's 5.5p kwh

7250kwh at 13.4pkwh = £971.50
7250kwh at 5.5pkwh = £398.75

So our outlay would be £6k and savings amounting to £572.75

10.5 years payoff if tomato stay in business if not it would be cosy and likely to be a couple hundred a year saving and 30 years payback

If Agile never returns to the rates of last year the only option for comparison I Octopus Cosy and we will average 17p kwh going by our Jan and Feb usage to now. Presuming Tomato go rotten the most we could save us down to the cheap Cosy rate of 13.23p kwh so a yearly savings with batteries of £273.33 so a payback period of 22 years

michaels

Reed_Richards said:

michaels said:

Suppose you use 5kwh of hot water and 12kwh of heat per year 

My daily consumption, averaged over a year, is around 16 kWh on heating and hot water.  Is that what you mean or are you confusing kWh with MWh?  From your subsequent calculation it looks like it's the latter but could you confirm this please.

Thank you and doh - I will correct the OP.

michaels

TroubledTarts said:

On Agile with no solar and not batteries or EV we averaged 13.4pkwh last year

We are looking at batteries but not blindly believing the savings should be based on the SVT only.

Our £6k investment for 32kwh of storage would need us to switch to Tomato energy and believe they will still be viable for the payback period. Charging at 5p kwh (don't forget to add 10% charge/discharge losses so that's 5.5p kwh

7250kwh at 13.4pkwh = £971.50
7250kwh at 5.5pkwh = £398.75

So our outlay would be £6k and savings amounting to £572.75

10.5 years payoff if tomato stay in business if not it would be cosy and likely to be a couple hundred a year saving and 30 years payback

If Agile never returns to the rates of last year the only option for comparison I Octopus Cosy and we will average 17p kwh going by our Jan and Feb usage to now. Presuming Tomato go rotten the most we could save us down to the cheap Cosy rate of 13.23p kwh so a yearly savings with batteries of £273.33 so a payback period of 22 years

I think first utility do an E7 of about 7p per kwh no EV required?

I did add on for round trip losses in my calcs.

john-306

I had a 6.5kwh battery installed with my solar that worked well with my usage.
Since heat pump added the battery runs out in this cold weather about an hour before the next Cosy 12.52p cheap rate top up.
Adding another 1k battery cost to keep everything inside cheap Cosy rate would only save less than £50 a year, so not worth it.

michaels

john-306 said:

I had a 6.5kwh battery installed with my solar that worked well with my usage.
Since heat pump added the battery runs out in this cold weather about an hour before the next Cosy 12.52p cheap rate top up.
Adding another 1k battery cost to keep everything inside cheap Cosy rate would only save less than £50 a year, so not worth it.

What if it let you  run 24/7 on Tomato 5p or first utility 7p per unit though?

NedS

I think it's going to be different for everyone.

I have a heat pump, solar and am on Octopus Cosy.

At this time of year, I'm using 30-40kWh per day with minimal solar contribution. My average import price is 20p per kWh. I'd love to decrease this, but the numbers don't really stack up (although I may just go ahead and do it anyway)

If I buy a 10-13kWh battery, I can probably shift all my usage to the Cosy cheap slots at 12.86p, saving around 7p per kWh at most. I estimate that may save me £4-500 per year. A Tesla PW3 costs around £8k installed, so may take 16-20 years to break even, before allowing for conversion losses etc, so not really economical for me (cheaper batteries are available). I don't see installing 30kWh of capacity and charging once overnight any more appealing (would need a minimum of 6 hours of cheap rate and a 5kWh inverter to charge 30kWh of batteries) plus I have no use for 30kWh of battery storage capacity for 8-9 months of the year when I import very little and have a negative bill due to solar export.

The numbers can change though. What if SEG rates plummet or electricity prices rise significantly.