Air source heat pump and solar.

matt_drummer

lohr500 said:

Not trying to be clever but out of interest how does your 4000kWh solar/battery setup generate £70k profit over its lifetime?

I have 13.5 kW of solar in total and 38 kWh of usable battery storage.

My energy costs would have been £2,500 to £3,000 a year but I pay nothing plus my income from it is around £2,500 a year (including FIT payments of £900 from the original 4 kW array).

The whole lot is worth around £5,000 a year to me and most of it will last twenty years.

So the value to me is £100,000 in total and it cost £30,000.

Profit is £70,000.

Very round figures and I will probably have to replace some parts over time but I would also expect energy prices to rise.

I will be happy if I break even but in the context of this thread I am just demonstrating what is possible and how much headroom there is in it.


I only mentioned the 4 kW array in the post you quote to show that it generates enough electricity annually to run the heat pump.

I calculate the costs and benefits on an annual basis as that is what counts.

Assessing the costs and benefits over days or weeks to does give the full picture.

A relatively small array can generate enough to fund the costs of running a heat pump.

wrf12345

There seems to be a lot of vested interest in installing the large air to water heat pumps rather than having individual air to air heat pumps in each room (air conditioner types), the latter are way less than a grand a room inc installation so unless you have more than seven rooms would be covered by the govn grant of £7500, just leaving some on-demand water heating to sort out that would almost always be covered by solar pv generation revenue, although a case could be made for banning hot water, the saving from the health benefits of cold showers would help the NHS.

lohr500

Thanks @matt_drummer

Really helpful and puts some of my own thinking on solar for our property into perspective. I have concluded that research is key and not signing up for something unsuitable offered by some suited and booted sales person!

matt_drummer

lohr500 said:

Thanks @matt_drummer

Really helpful and puts some of my own thinking on solar for our property into perspective. I have concluded that research is key and not signing up for something unsuitable offered by some suited and booted sales person!

The key for me was working out what I use and when.

I wanted a heat pump and I want to run it from the cheapest electricity possible which is E7 night rate.

E7 gives me the lowest cost for the longest time to charge sufficiently sized battery storage to run the heat pump on the worst day.

That energy use determined the size of the batteries.

The additional panels were added partly to save VAT on the battery installation (done at the same time) but also with a view to generate as much income as possible when the sun is shining.

The amount of solar panels I have also give a useful boost even in December, it's not loads but something like 10 kWh a day in December on average is enough for our normal house loads with the heat pump being fed by battery storage. Of course, it all gets mixed up a bit but on the whole the electricity use comes from solar and E7 night rate.

Our house isn't huge, actually quite modest at around 120 m2 but I have a large garage.

The house face south west so I have panels south west and north east. It's not ideal but the north east is pretty good, about 85% of the south west panels.

I have some shading issues from the house to the garage but I have a mix of micro inverters and Tigo optimisers. This ensures that I get the most from every panel and I can also monitor each of my 38 panels performance individually.

I have also found that the north east panels do unexpected things. On a bright but cloudy day, broken white fluffy clouds, the light reflects off the clouds and really boosts the generation, it's quite surprising.

The north east panels have performed better than I expected and they really add to the spread of electricity we generate.

I get a steady generation from early in the morning to late in the evening, it's really at a pretty constant level for most of the day. In June I sit at around 6 kW per hour for the whole day.

On the best days we generate about 75 kWh and export 65 to 70 kWh.

A day like that in June pays for heating on two of the coldest days of the year.

I hope this is useful and you have some idea how it works. It doesn't have to be a perfect south facing set up and it doesn't matter when you generate as long as you get paid about the same for the exports in the sunny times as you pay for importing in the winter.

matt_drummer

wrf12345 said:

There seems to be a lot of vested interest in installing the large air to water heat pumps rather than having individual air to air heat pumps in each room (air conditioner types), the latter are way less than a grand a room inc installation so unless you have more than seven rooms would be covered by the govn grant of £7500, just leaving some on-demand water heating to sort out that would almost always be covered by solar pv generation revenue, although a case could be made for banning hot water, the saving from the health benefits of cold showers would help the NHS.

Air to air heat pumps require planning permission unless it can be shown they are not used for cooling.

You also need planning permission to install more than one heat pump at a property, only one heat pump is allowed under permitted development.

You probably wouldn't have one heat pump for each room. You would use a multi split system where one outdoor unit feeds multiple indoor units. You can go up to four or five indoor units on a single outdoor unit.

That sort of installation would cost more than £1,000 per room using a reputable brand.

Most suppliers will not sell you an air to air heat pump unless you are FGAS registered.

Air to air heat pumps are VAT free from installers at the moment but they are not eligible for any grants and certainly not the BUS grant.

The BUS grant requires an MCS registered installer, it' does not fund DIY jobs.

As you say, a hot water source would be required by most people so that is an additional cost.

Finally, not everybody likes blown air heating, I don't find it particularly pleasant.