Battery with heat pump but no solar - your thoughts

michaels

Patrol said:

michaels said:

It does for me meaning I pay 8p per unit on average which is a lot cheaper than cosy - then again I have v2g and pup to 80kwh of storage to call upon.

Fair point, if you have large battery capacity. Is there a restriction on transfer rate from the car, e.g if household demand is 3-4kWh can v2g support all of that

Up to 6kw.  I have two leafs so the medium term plan is to sell one and replace it with battery and invertor so we have the same total capacity but a higher charge/discharge rate.

Patrol

HorseWhisperer said:

We consume 1600 litres of oil at a cost of approx £1200 annually, but only run the heating for 5 hours a day and heat water for 2 x 1 hour in 24. To double the heating would costs us around £2000 annually. Our electricity bill is already approx £1,500. We don't really want to double the amount of emissions we're producing or give any more money to the oil barons. The idea is to try and bring our energy costs per KwH down rather than increase them and eventually become more self-sufficient.

OK. It will take approximately the same energy (ignoring inefficiencies and so on) to heat a property regardless of source. Heat pump CoP should be a more sustainable source than oil, far more so if self-generated and/or imported to a battery at low generation times of day. That would certainly seem to meet your objectives above

If your house isn't warm all the time and you want it to be, that suggests increasing insulation or additional heating input. Sure, if you had solar and a large battery and a heatpump and a flexible electric tariff you could do 'more for less' but you had stated you could not do all of the first three together. So would you prioritise reduced environmental impact or reduced cost. Or go for increased comfort at the expense of the other two

Maybe I'm not understanding, I'll bow out now. Hope you find a decent way forward

ed110220

Depending on how much you can get the battery/batteries for, this could make a lot of sense. I have solar and a battery (but no heat pump yet). I'm on Octopus Go so from 00:30-05:30 electricity costs 8.55p/kWh and we hardly import anything at the higher day rate.

UncleK

We moved into a sixties house a few years ago with an oil fired boiler and some storage heaters in the bit they had extended. Insulation wasn't as good as it should be. Our plan is to stay here until we're carried out in our coffins (so hopefully 30 years or so). We spent A LOT on insulation - mainly the floors - but cheaper stuff like the loft. We installed a GSHP, UFH and solar panels with batteries.

I calculate the payback of the complete solar panel and battery system as 9 years. However, if I calculate the payback of just the batteries, in terms of them storing cheap night time electricity to use during the day - and in the winter that's mainly for the GSHP - the payback for the batteries is 4.6 years. It's all GroWatt kit, which may get some boos from the gallery but has served us well so far.

QrizB

UncleK said:

I calculate the payback of the complete solar panel and battery system as 9 years.

If fitted today, for most people solar panels should pay back in 6-7 years.

UncleK said:

However, if I calculate the payback of just the batteries, in terms of them storing cheap night time electricity to use during the day - and in the winter that's mainly for the GSHP - the payback for the batteries is 4.6 years.

That's interesting, most people find it's longer than that. Could you share your calculations, if they're not too sensitive?

UncleK

Our batteries cost £6,776 to buy and install. I am missing the cost of the inverter which was included in the solar installation, so maybe that drives the cost artificially down - I don't have the breakdown of the solar install.

The batteries are 3 x 6.5 kWh and discharge down to 10%.

I thus assume that I get 3 x 6.5 x 90% kW of power at night rates instead of day rate.

I take the delta between day rate and night rate (that varies every quarter), add those up and divide that by the number of days elapsed to give me savings due-to-battery per day (so averaging the delta).

I have updated my calculation and now come up with £3.48 per day so payback of 1944 days so 5.3 years.

Maybe this dodgy if you are not using enough electricity during the day in summer to drain the batteries, but I'd suspect you would be, what with lights, cooking and the like, but whatever. The batteries make sense for me because of the solar panels - other opinions are available!

QrizB

As man-maths goes, I've seen worse

You're right about probably not using ~18kWh a day in the summer months. I can't speak for your household but here (and ignoring EV charging) we're using about 3kWh of electricity and 5-10kWh of gas daily - which would be another 2-3kWh of electricity of we had a heat pump with a COP of 3.

Nevertheless, I'm glad it works for you!

matelodave

We aren't particularly frugal with our electricity usage and our summer average consumption is around 8-10kwh a day (including heatpump heating water, cooking etc plus computers and a 3D printer).

That does increase a bit when washing is done as SWMBO seldom puts stuff on the line, so it goes into the tumble dryer - that probably pushes it up to around 15kwh on washing days.

However in the winter when the heatpump is doing its bit  (11kw Daikin) we can easily get through 40-50kwh a day, sometimes more if its everso cold. So 18kwh of batteries would work for us in the summer with plenty to spare but fall well short between November and March

Our annual consumption is approx 7200kwh - an average of just under 20kwh a day. 

I try to get fixed rate deals as there's no point in my trying to get her indoors to change her habits to suit a ToU tariff (after 56 years you get to know what's possible) and she whinges if she even thinks I've turned it down a bit.

 I'll accept that it may cost me a bit more but as they say, a happy wife makes for a happy life

michaels

QrizB said:

As man-maths goes, I've seen worse

You're right about probably not using ~18kWh a day in the summer months. I can't speak for your household but here (and ignoring EV charging) we're using about 3kWh of electricity and 5-10kWh of gas daily - which would be another 2-3kWh of electricity of we had a heat pump with a COP of 3.

Nevertheless, I'm glad it works for you!

Depending on tariff, even though the summer might not be as lucrative in terms of time shifting, with a decent SEG there is still profit to be made on the round trip.

NedS

matelodave said:

We aren't particularly frugal with our electricity usage and our summer average consumption is around 8-10kwh a day (including heatpump heating water, cooking etc plus computers and a 3D printer).

That does increase a bit when washing is done as SWMBO seldom puts stuff on the line, so it goes into the tumble dryer - that probably pushes it up to around 15kwh on washing days.

However in the winter when the heatpump is doing its bit  (11kw Daikin) we can easily get through 40-50kwh a day, sometimes more if its everso cold. So 18kwh of batteries would work for us in the summer with plenty to spare but fall well short between November and March

Our annual consumption is approx 7200kwh - an average of just under 20kwh a day. 

I try to get fixed rate deals as there's no point in my trying to get her indoors to change her habits to suit a ToU tariff (after 56 years you get to know what's possible) and she whinges if she even thinks I've turned it down a bit.

 I'll accept that it may cost me a bit more but as they say, a happy wife makes for a happy life

Your usage is not a million miles away from ours. We are going with a 13.5kW battery combined with the Octopus Cosy tariff in winter. With three cheap slots spread throughout the day, we estimate the battery capacity should just about be sufficient to carry us through to the next cheap rate slot in winter, and should cover a full day's usage in summer, where we can switch to a more lucrative tariff.

As you say, installing 50kWh of battery capacity is not financially practical for most ASHP households.