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

michaels

Reed_Richards said:

But the Utility Warehouse best rate for export is 8p per kWh, as far as I can see.  The economics of a battery must include charging it cheaply overnight then discharging it for more money paid for export.

I think Scottish Power still do a 12p SEG open to anyone so that is a nice 6p on the turn (lass any round trip losses) - lets say a 30kwh battery could give an average of 15kwh per day import/export for 6 months (180) days, lets assume 5p per unit markup between buy and sell after losses, 15 x 0.05 x 200 = £135 a year on top of the own use savings.

My contention is that rather than talking about PV+battery we should be talking about heat pump plus battery as the default option.

TroubledTarts

Still not £1000 a year payback you suggested in your first post as the numbers were squewed.

Realistically, as stated,10-20 year payback period and in that time you might have to replace the inverter out of warranty and reduced battery performance needs to be taken into consideration.

It could be a good idea however for the Government to initiate a scheme where they can control emptying when the grid needs more power. I could see that as a benefit to both parties.in the mean time no vat is an incentive to get the ball rolling.

michaels

For info, our numbers at the moment are average 100kwh per day, average price per unit 8.5p with 75kwh of battery via 2 leafs on V2H.  WE do as much as we can overnight but when it is cold in our 19 hour peak slot we use up to 2.5 x 19 = 47.5kwh on the heat pump and 10kwh on hot water which is via immersion plus any usage for lights, TV, cooking etc.

Cosy might be a bit less than 25p per unit but we would still need to use a lot of peak rate and we would not benefit form running the dishwasher, washing machine and hot water (another 12kwh) on night rate.

1st March we are going to Tomato so hopefully our rate will fall to 6p per unit average.

TroubledTarts

Cosy obviously has a 1-4pm.amd 10pmto midnight slot as well as 4-7am slot to run heavier loads of dishwasher washing machine tumble dryer, heating hot water etc.

Interestingly we now heat our hot water in the 1-4pm slot when typically that's the hottest ambient temp for the heat pump so most efficient time to perform that. Then temp int he cylinder drops just 3 degrees from the afternoon to the morning showers.

That said no one can beat tomato it's just if they survive or not is the question and if they do not does that mean being stuck with them on the price cap for some weeks before a SOLR is found? That wouldn't help you figures much paying 25p for everything.

NedS

michaels said:

Cosy might be a bit less than 25p per unit but we would still need to use a lot of peak rate and we would not benefit form running the dishwasher, washing machine and hot water (another 12kwh) on night rate.

We are averaging around 20p import on Cosy this winter. We do have solar but that is negligible in winter and does not really affect our average cost of import, just how much we import on sunny days.

We turn the heat pump off between midnight and 4am. Heating comes back on at 4am and works hard during the cheap slot to reheat the house, and we also reheat DHW during this cheap slot ready for the day.

We then run the heating slow and slow all day, bumping it up in the cheap 1-4pm slot as we then turn off again during the 4-7pm peak period. The house does get a bit cold by 7pm but it's manageable (although the wife may think otherwise!)

Up until 7pm, it's all pretty efficient with most of the heavy lifting done during cheap slots. Turning the heating back on at 7pm does then create a bit of a spike in usage, but only for the first hour whilst the system gets back up to temp. We then run through to midnight low and slow again before turning off for the night.

Obviously a battery would help enormously, as much with usability and comfort as reducing overall costs. Assuming we could shift everything using the battery (certainly possible with something like the 13.5kWh Tesla PW3), we could achieve an import of 12.86p per kWh at current Cosy rates. A smaller 5kWh battery could probably get us 70-80% of the way there with a bit of management (maybe turning down flow temps to minimum rather than turning off when on battery), but a 13.5kWh battery would be enough for us not to have to worry.

For us, I calculate it's closer to a 20 year payback for something like a Telsa PW3. What I can't put a price on is the increased usability and comfort of not having to clock watch and resist the temptation to cook at peak rates, and for that reason we are now considering a battery.

michaels

NedS said:

michaels said:

Cosy might be a bit less than 25p per unit but we would still need to use a lot of peak rate and we would not benefit form running the dishwasher, washing machine and hot water (another 12kwh) on night rate.

We are averaging around 20p import on Cosy this winter. We do have solar but that is negligible in winter and does not really affect our average cost of import, just how much we import on sunny days.

We turn the heat pump off between midnight and 4am. Heating comes back on at 4am and works hard during the cheap slot to reheat the house, and we also reheat DHW during this cheap slot ready for the day.

We then run the heating slow and slow all day, bumping it up in the cheap 1-4pm slot as we then turn off again during the 4-7pm peak period. The house does get a bit cold by 7pm but it's manageable (although the wife may think otherwise!)

Up until 7pm, it's all pretty efficient with most of the heavy lifting done during cheap slots. Turning the heating back on at 7pm does then create a bit of a spike in usage, but only for the first hour whilst the system gets back up to temp. We then run through to midnight low and slow again before turning off for the night.

Obviously a battery would help enormously, as much with usability and comfort as reducing overall costs. Assuming we could shift everything using the battery (certainly possible with something like the 13.5kWh Tesla PW3), we could achieve an import of 12.86p per kWh at current Cosy rates. A smaller 5kWh battery could probably get us 70-80% of the way there with a bit of management (maybe turning down flow temps to minimum rather than turning off when on battery), but a 13.5kWh battery would be enough for us not to have to worry.

For us, I calculate it's closer to a 20 year payback for something like a Telsa PW3. What I can't put a price on is the increased usability and comfort of not having to clock watch and resist the temptation to cook at peak rates, and for that reason we are now considering a battery.

What would the payback period be if you used the utility warehouse midnight - 7am 7p, 33p otherwise rate?

NedS

michaels said:

NedS said:

michaels said:

Cosy might be a bit less than 25p per unit but we would still need to use a lot of peak rate and we would not benefit form running the dishwasher, washing machine and hot water (another 12kwh) on night rate.

We are averaging around 20p import on Cosy this winter. We do have solar but that is negligible in winter and does not really affect our average cost of import, just how much we import on sunny days.

We turn the heat pump off between midnight and 4am. Heating comes back on at 4am and works hard during the cheap slot to reheat the house, and we also reheat DHW during this cheap slot ready for the day.

We then run the heating slow and slow all day, bumping it up in the cheap 1-4pm slot as we then turn off again during the 4-7pm peak period. The house does get a bit cold by 7pm but it's manageable (although the wife may think otherwise!)

Up until 7pm, it's all pretty efficient with most of the heavy lifting done during cheap slots. Turning the heating back on at 7pm does then create a bit of a spike in usage, but only for the first hour whilst the system gets back up to temp. We then run through to midnight low and slow again before turning off for the night.

Obviously a battery would help enormously, as much with usability and comfort as reducing overall costs. Assuming we could shift everything using the battery (certainly possible with something like the 13.5kWh Tesla PW3), we could achieve an import of 12.86p per kWh at current Cosy rates. A smaller 5kWh battery could probably get us 70-80% of the way there with a bit of management (maybe turning down flow temps to minimum rather than turning off when on battery), but a 13.5kWh battery would be enough for us not to have to worry.

For us, I calculate it's closer to a 20 year payback for something like a Telsa PW3. What I can't put a price on is the increased usability and comfort of not having to clock watch and resist the temptation to cook at peak rates, and for that reason we are now considering a battery.

What would the payback period be if you used the utility warehouse midnight - 7am 7p, 33p otherwise rate?

@michaels Good question, but for that we'd either need more battery capacity to cover full day usage (ideally ~35kWh, and be able to fully charge it in the available cheap rate window), or we'd have to factor in using the excess at 33p during winter.

Assuming 6000kWh usage, and being able to import that at 7p vs our current 20p average, we'd save £780/year. Assuming a 10 year lifespan, we'd need a 35kWh system for ~£8k. Or 2.5 Powerwalls, so 25 year payback for a sufficiently sized system, and that's just the break even point.

Two PW3's (27kWh) would probably do it for us (or at least get close 90% of the time) as maybe ~5kWh of our usage (DHW and some heating) would occur during the cheap overnight period leaving 27kWh for use between 7am-midnight (doubling our solar capacity would help with any shortfall during winter, even if we're only generating 3-4kWh per day). A 30kWh system (of usable capacity) would be better as the misses is not going to like conversations at 6pm about choosing between heat that evening or coking dinner if the battery is starting to run low.

Going back to the original question - is it a no brainer to get batteries if you have a heat pump - I've yet to see a clear argument which suggests it is. What is clear is that a tariff other than SVR is required to reduce costs and make savings vs gas, and that a battery certainly helps but isn't necessarily going to pay for itself, let alone give you a return on your capital outlay over the savings a tariff like Cosy can give you.

michaels

NedS said:

michaels said:

NedS said:

michaels said:

Cosy might be a bit less than 25p per unit but we would still need to use a lot of peak rate and we would not benefit form running the dishwasher, washing machine and hot water (another 12kwh) on night rate.

We are averaging around 20p import on Cosy this winter. We do have solar but that is negligible in winter and does not really affect our average cost of import, just how much we import on sunny days.

We turn the heat pump off between midnight and 4am. Heating comes back on at 4am and works hard during the cheap slot to reheat the house, and we also reheat DHW during this cheap slot ready for the day.

We then run the heating slow and slow all day, bumping it up in the cheap 1-4pm slot as we then turn off again during the 4-7pm peak period. The house does get a bit cold by 7pm but it's manageable (although the wife may think otherwise!)

Up until 7pm, it's all pretty efficient with most of the heavy lifting done during cheap slots. Turning the heating back on at 7pm does then create a bit of a spike in usage, but only for the first hour whilst the system gets back up to temp. We then run through to midnight low and slow again before turning off for the night.

Obviously a battery would help enormously, as much with usability and comfort as reducing overall costs. Assuming we could shift everything using the battery (certainly possible with something like the 13.5kWh Tesla PW3), we could achieve an import of 12.86p per kWh at current Cosy rates. A smaller 5kWh battery could probably get us 70-80% of the way there with a bit of management (maybe turning down flow temps to minimum rather than turning off when on battery), but a 13.5kWh battery would be enough for us not to have to worry.

For us, I calculate it's closer to a 20 year payback for something like a Telsa PW3. What I can't put a price on is the increased usability and comfort of not having to clock watch and resist the temptation to cook at peak rates, and for that reason we are now considering a battery.

What would the payback period be if you used the utility warehouse midnight - 7am 7p, 33p otherwise rate?

@michaels Good question, but for that we'd either need more battery capacity to cover full day usage (ideally ~35kWh, and be able to fully charge it in the available cheap rate window), or we'd have to factor in using the excess at 33p during winter.

Assuming 6000kWh usage, and being able to import that at 7p vs our current 20p average, we'd save £780/year. Assuming a 10 year lifespan, we'd need a 35kWh system for ~£8k. Or 2.5 Powerwalls, so 25 year payback for a sufficiently sized system, and that's just the break even point.

Two PW3's (27kWh) would probably do it for us (or at least get close 90% of the time) as maybe ~5kWh of our usage (DHW and some heating) would occur during the cheap overnight period leaving 27kWh for use between 7am-midnight (doubling our solar capacity would help with any shortfall during winter, even if we're only generating 3-4kWh per day). A 30kWh system (of usable capacity) would be better as the misses is not going to like conversations at 6pm about choosing between heat that evening or coking dinner if the battery is starting to run low.

Going back to the original question - is it a no brainer to get batteries if you have a heat pump - I've yet to see a clear argument which suggests it is. What is clear is that a tariff other than SVR is required to reduce costs and make savings vs gas, and that a battery certainly helps but isn't necessarily going to pay for itself, let alone give you a return on your capital outlay over the savings a tariff like Cosy can give you.

Tesla powerwall is the Rolls-Royce solution for batteries though - I have seen elsewhere on these boards suggestions that you could source 30kwh of storage and an inverter for £5k and pay £1k to have it fitted.

NedS

michaels said:

Tesla powerwall is the Rolls-Royce solution for batteries though - I have seen elsewhere on these boards suggestions that you could source 30kwh of storage and an inverter for £5k and pay £1k to have it fitted.

Yes, but that said the Tesla does not overly priced when compared to other comparable systems. PW3 is priced at £5500 and £650 for the gateway to installers (not available direct), but that compares well with the wholesale prices of systems like the GivEnergy AIO (£6860 for AIO and gateway), Enphase 5kWh battery only (£3122) or SolarEdge 10kWh battery only for £5138 (pricing from Midsummer wholesale). Even something considered lower end (certainly not high end) like a Fox ESS system of 3x5kWh batteries (90%DoD) and a 6kW inverter is going to cost £5500 and isn't close to the Tesla.

Only GivEnergy and Enphase are currently certified for Intelligent Octopus Flux, with Tesla and SolarEdge thought to be coming soon.

Then there's the Fogstar batteries at the other end of the spectrum, where a 15kWh unit costs around £2500, plus you'd need something like the Growatt 6kW inverter at £600 and assorted sundries probably bringing the system in at £3.5k or just over half the price of the Tesla battery/inverter unit.

benson1980

We have a 12kW ASHP, 4kw solar array, and post ASHP install we went for the PW3 (cost £7400).

I ran some calcs for January and using the battery to take advantage of the Cosy dips (as others have said very little benefit from solar this time of year) we saved around £130 compared with if we were paying standard tariff of 22p. We are quite high electricity users anyway so with the ASHP we used about 1900kW- hence the larger saving I guess. I think of average it worked out that we paid 15p per kW. Daily usage has been in the range of 40 to 90kW.

Before powerwall install I had a rough guesstimate that it would save between £700-800 pa. We seem to be on track for that if over the coldest months we save around £100, and then when milder/sunnier we might be saving £50 per month minimum again from dips, but also exploiting solar storage. The guesstimate above would therefore seem to be about right giving us a payback period of 9-10 years. It did seem to be a bit of a no brainer for us, on this basis.