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Air Source Heat Pump (ASHP)

Does what it says on the tin
Wasp427
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Air Source Heat Pump (ASHP)

#219177

Postby Wasp427 » May 3rd, 2019, 9:56 am

Hi I am thinking of trying to go green. Our house is a 3 bed detached built in the early 2000s with an EPC of C/D. It is not suitable for a ground heat pump. Does anyone have any experience of installing an Air Heat Pump? Did the economics stack up?

Thanks in Advance

427
Moderator Message:
Thread title altered. - Chris

doug2500
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Re: Air Source Heat Pump (ASHP)

#219192

Postby doug2500 » May 3rd, 2019, 10:24 am

I can't help you directly but we're in the process of renovating a house and have chosen an air source heat pump on our architect's advice.

We were a bit wary of this as we don't know anyone with one but have heard negatives about heat pumps, although mainly ground source.

Our architect insists air is better than ground and will work great as long as the house is designed for it.

It will run at about half the temperature of e.g. an oil boiler, so unless the heating system is designed for it, it would have to run flat out and would cost a lot to run and may not heat the house enough. It is not just a straight swap for whatever heating you use now. For example our underfloor heating pipes have to be much closer together than for an oil system to compensate for the reduced temp. If you have radiators they would have to be replaced with ones twice the size.

I'm not an expert on this, just repeating what I've been told.

dspp
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Re: Air Source Heat Pump (ASHP)

#219213

Postby dspp » May 3rd, 2019, 11:14 am

ASHP and GSHP are not my specialist area, but what doug has said is correct.

The fluid (which is inhibited water) that circulates through the radiators from an ASHP is at a lower temperature than the same fluid that comes from a gas/oil boiler circuit. This means that to get the same amount of heat into a room the radiator size must increase.

In my case I expect to go ASHP when my fairly new boiler conks out (ETA: 10 years as it is 5 years old now; the last one did 40 years mind you). My wet loop radiator system was 'designed' and installed when the house was an uninsulated brick building in the 1960s/1970s era. My crude guess is that, with all the insulation I am putting in the house, that by the time I come to install my ASHP the original radiators will be able to deliver the required heat without me needing to change the radiator size.

The underlying point is that you would be wise to consider the insulation aspects of your house as part of the overall project of installing an ASHP as a boiler replacement. Otherwise you are perhaps going to have to increase your radiator sizes as part of the project. There is a thread here (viewtopic.php?f=40&t=17293) that is largely about insulation and includes some useful numbers for comparison.

It is also worth considering what is your energy source. If you have your own solar PV panels then running an ASHP can be considerably cheaper than if you are having to buy the same amount of electricity from the grid.

If you post some house size & energy consumption numbers up people may be able to give tips.

regards, dspp

PhaseThree

Re: Air Source Heat Pump (ASHP)

#219246

Postby PhaseThree » May 3rd, 2019, 12:33 pm

A few things to be aware of with air to water ASHPs.
- The efficiancy of an ASHP is expressed as the COP value (coefficiant of performance) and is effectively the ratio of energy in to energy out.
- The efficiancy of the ASHP is a function of the outside air temperature and the internal water flow temperature.
- The efficiancy drops as the outside air temperature drops.
- The efficiancy drops as the required water flow temperature is increased.
- In cold, humid weather (typical UK autumn/winter) extracting heat from the moist external air can cause the ASHP to freeze. To counteract this effect the ASHP will defrost itself by running in reverse for a period or by using an emmersion heater to warm itself. This defrost energy is not included in the manufactureres efficiancy data and seems to be a big cause of "performance disappointment".

So to get the best out an ASHP you need to keep the flow temperature down which means the emmiters inside the house (Radiators, UFH etc) need to be sized accordingly and the use of an ASHP to generate high temperature domestic hot water needs to be carfully considered.

Mine is used to feed 35C water to the UFH system only.

Edit:-
ASHPs are simple things - effectively a fridge running backwards - however the "greenwash" industry that has spung up around them likes to make them sound difficult, complex and hence expensive. The govenment MCS acreditation scheme just adds to the problem. I bought mine online and installed it myself.

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Re: Air Source Heat Pump (ASHP)

#219250

Postby richlist » May 3rd, 2019, 12:47 pm

If you have solar pv panels it makes sense to heat your hot water tank via an immersion heater from your solar energy for free.

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Re: Air Source Heat Pump (ASHP)

#219260

Postby dspp » May 3rd, 2019, 1:07 pm

richlist wrote:If you have solar pv panels it makes sense to heat your hot water tank via an immersion heater from your solar energy for free.


Yes, that is true. However by putting the same amount of elec through an ASHP you can essentially multiply it by about x4 to get even more warmth into your house. If, of course you have both an ASHP and PV fitted.

regards, dspp

PhaseThree

Re: Air Source Heat Pump (ASHP)

#219275

Postby PhaseThree » May 3rd, 2019, 1:43 pm

Unfortunately you are unlikey to get anywhere near a COP of 4 even in summer.

Take a look at http://www.narecde.co.uk/wp-content/uploads/2014/11/COP-of-water-heating-technologies.pdf for a real world analysis of an ASHP used for hot water. Their conclusion :-"The ASHP system daily COP for the month of September is reasonably consistent within the range 1.44 to 1.88, with average for the month of 1.59".

It's easy to imagine the COP falling below 1 in the cold and wet of winter at which point you would do better with the immersion.

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Re: Air Source Heat Pump (ASHP)

#219281

Postby tea42 » May 3rd, 2019, 2:08 pm

I am wondering about the noise generation from the fan? How noisy are they?

I would go for a Ground source heat pump. Better performance, quiet....

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Re: Air Source Heat Pump (ASHP)

#219283

Postby dspp » May 3rd, 2019, 2:09 pm

PhaseThree wrote:Unfortunately you are unlikey to get anywhere near a COP of 4 even in summer.

Take a look at http://www.narecde.co.uk/wp-content/uploads/2014/11/COP-of-water-heating-technologies.pdf for a real world analysis of an ASHP used for hot water. Their conclusion :-"The ASHP system daily COP for the month of September is reasonably consistent within the range 1.44 to 1.88, with average for the month of 1.59".

It's easy to imagine the COP falling below 1 in the cold and wet of winter at which point you would do better with the immersion.


Yes I know, that is absolutely correct. I have seen real COPs of <1 for almost all of the 15-years I have had direct involvement in this sector, with both ASHP and GSHP. That's why I personally went with a new gas boiler when the old one failed, and put all my efforts into insulation. I am reading the CCC report with interest:

https://www.theccc.org.uk/wp-content/up ... rt-CCC.pdf

"Deployment of heat pumps has remained stagnant, accounting for under 1% of annual heating system sales" (p66)

Nonetheless I think that ASHP are likely to be a large part of the solution for large scale deployment, as so many properties cannot go the GSHP route, which is why Wasp427's original post is so relevant. The best advice I can offer him/her is to take a holistic approach to it, which includes insulation + radiator sizing + consider PV. It will be really useful if he/she can come back to us in a year or so and tell us how it has gone in practice.

regards, dspp

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Re: Air Source Heat Pump (ASHP)

#219336

Postby richlist » May 3rd, 2019, 4:43 pm

dspp wrote:
richlist wrote:If you have solar pv panels it makes sense to heat your hot water tank via an immersion heater from your solar energy for free.


Yes, that is true. However by putting the same amount of elec through an ASHP you can essentially multiply it by about x4 to get even more warmth into your house. If, of course you have both an ASHP and PV fitted.

regards, dspp


My solar PV panels produced 420Kwh of energy during the whole of April. Hot water used 54Kwh of that so plenty left for running other stuff like ASHP.........

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Re: Air Source Heat Pump (ASHP)

#219452

Postby Wasp427 » May 4th, 2019, 9:10 am

Dear All

VMT for your comprehensive and interesting replies. Lots for me to think about and investigate.

Yours

427

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Re: Air Source Heat Pump (ASHP)

#219464

Postby fisher » May 4th, 2019, 9:57 am

I have an ASHP which is our only source of heating and hot water production in the house other than a wood burner that we use as additional heating in the depths of winter. It is a NIBE ASHP and was fitted five years ago. The house is a large 5 bed room house with 3 reception rooms, dining room, kitchen, utility, 2 bathrooms and downstairs cloakroom. The house was built in the 60s and has been greatly extended since. We live in the countryside and prior to the ASHP we had an oil boiler. I have spent a long time insulating the house, particularly the loft and in the roof slopes (it is a large dormer bungalow type house).

I am a huge fan of the ASHP. It has performed very well and better than my expectations. As we have no gas we use electricity for all our heating, lighting, hot water and cooking as well as TVs, computers etc. I track my annual electricity usage in some detail and over the last year we have spent £1,100 on electricity - so just under £100 a month. We have Solar PV as well and this, no doubt, contributes to keeping the electricity costs down. We have the house heated to 21 degrees downstairs and 18 degrees upstairs most of the time, and we are at home during the day. We are on an Economy 7 electricity tariff and I have the ASHP set to make maximum use of the cheap electricity during the night. The house does not drop below 19 degrees in temperature in the living areas and we sleep with summer duvets all year round. You can't have large fluctuations in the target heat in the house when using an ASHP as they are good at keeping the temperature ticking over but bad at doing large increases in the temperature. That is, warming the house from 19 degrees to 21 degrees will take a couple of hours, warming it from 15 degrees to 21 degrees will take a couple of days in winter!

Swapping a conventional boiler for an ASHP is a complicated process and a lot of changes need to be considered. As has been mentioned, an ASHP will perform more efficiently the lower you can get the temperature of the water in the radiators to be. If you previously had radiators being fed by water from your boiler at 60 degrees and you then feed them from your ASHP with water at 45 to 50 degrees then your existing size of radiator will most probably not cope with heating the room. You may have to double the size of your radiators. This is why ASHP works best with underfloor heating. I was not in a position to retrofit underfloor heating so mine works with radiators throughout. We were lucky that some of the radiators were already oversized. I went through quite a detailed calculation for each room of what size radiator would be required based on how many outside walls it had, how many windows it had, what the target temperature of the adjoining rooms was and what the insulation of walls, ceilings and floors was. This was in order to have a target to heat most living areas to 21 degrees, bathrooms to 22 degrees and bedrooms to 18 degrees. The target was calculated based on a minimum temperature of -3 outside. I was lucky that about 50% of our radiators were of the right size already. The other 50% we had changed. We swapped some single radiators for double radiators and then some of the radiators that we removed because they were too small for a room were then used in other (smaller) rooms. So we could reuse a lot and in the end only threw 3 radiators away.

It cost me about £11,000 to have the system installed including all new pipework, new radiators, the ASHP and Controller, electrics, and a 300L pressurised how water cylinder which is also NIBE and which has sensors in that are monitored by the ASHP controller. Of this we get back about £7,000 from the RHI (Renewable Heat Incentive) grant over 7 years.

There is a complicated controller which is really a bespoke computer system which fits to the wall in the utility room and which monitors a number of sensors (hot water temperatures in hot water and heating tanks, outside temperature, ASHP compressor stats) and it makes decisions on what to do and what temperature to heat things to depending on the information in these sensors. I have a computer programming background and I have made adjustments to many of the settings to get the system to work in an optimum way for us. It doesn't really work "out of the box" without a lot of tinkering and the installers (although competent) are not really in a position to do this. I overtook them quite quickly in my knowledge of the programmability of the system.

I think the efficiency of my system is much higher than some of the COPE figures given above but I have no statistics to prove this. However, I can easily see how an ASHP installation could be much less efficient if it is not correctly set up and programmed. Setting the heat curve correctly is very important to ensure the ASHP is not trying to heat the water in the radiators higher than it needs to. I am sure this is why some installations will be relatively inefficient - trying to heat the water in the radiators to a higher than necessary temperature. Some installations have a backup electric water heater to kick in when the ASHP can't cope and I think this can often be set up so it kicks in too frequently and costs more money to operate. Better IMHO to not have a backup water heater and to be forced to configure the ASHP settings correctly so it copes in all scenarios. The only point at which mine won't cope well is if outside temperature drops down below -5 for prolonged periods, but this is extreme (even out here in the countryside) and when it happens I have a wood burner and some backup fan heaters etc. I could use if I needed to. Better to design the system so it copes 99% of the time and use special measures in the 1% than spend money over-designing it in order to cope with every extreme.

This is a bit of a ramble I'm afraid and there is a lot more detail I could give. Ask if you want more information on anything specific.

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Re: Air Source Heat Pump (ASHP)

#219483

Postby dspp » May 4th, 2019, 11:22 am

fisher wrote:I have an ASHP which is our only source of heating ... Ask if you want more information on anything specific.


fisher,
That is very good to hear, and full of useful explanation for people considering installing an ASHP. Are you able to give some data that I can pop in my before/after/etc comparison spreadsheet (viewtopic.php?f=40&t=17293&start=20#p216111) .

I would ideally need for both the BEFORE and AFTER condition:
m2 of habitable rooms
elec use (kWh/yr)
oil or gas use (kWh/yr) or litres/year
elec generated (kWh/yr) and - if you know it - the % export fraction

many thanks, dspp

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Re: Air Source Heat Pump (ASHP)

#219501

Postby fisher » May 4th, 2019, 12:51 pm

dspp wrote:Are you able to give some data that I can pop in my before/after/etc comparison spreadsheet


I will have a look later on but I'm afraid i have little info from before the ASHP was installed. The house was very poorly insulated with drafts coming in under upstairs floors from the eaves and we were getting through a lot of heating oil while the house seemed cold and draughty. I only started keeping more thorough records once the house was extended, insulated and the ASHP fitted.

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Re: Air Source Heat Pump (ASHP)

#219531

Postby GoSeigen » May 4th, 2019, 3:50 pm

richlist wrote:
dspp wrote:
richlist wrote:If you have solar pv panels it makes sense to heat your hot water tank via an immersion heater from your solar energy for free.


Yes, that is true. However by putting the same amount of elec through an ASHP you can essentially multiply it by about x4 to get even more warmth into your house. If, of course you have both an ASHP and PV fitted.

regards, dspp


My solar PV panels produced 420Kwh of energy during the whole of April. Hot water used 54Kwh of that so plenty left for running other stuff like ASHP.........


What size is your PV installation? Bigger than 4kW? Is the domestic hot water heated by immersion heater? If so, what power does it draw? And how many people are in your household?

GS

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Re: Air Source Heat Pump (ASHP)

#219532

Postby richlist » May 4th, 2019, 4:00 pm

Solar PV is just under 4kW ....14 panels. 2 person household.

Domestic hot water is heated by a 3kW immersion heater powered by solar. The system has an auto controller that feeds my spare solar power to the immersion heater until water temp achieves thermostat setting. The figure quoted of 54kwh for April was the solar energy used to provide domestic hot water during April. Obviously that figure will vary depending on hot water usage/ number of occupants etc.

Therefore average solar production is 14 kwh per day. Approx 2kwh of that used per day to provide domestic hot water.I

Average solar production in July/August is about 20 kwh per day BUT in December it averages only about 2.5 kwh........so not enough to charge either a Tesla Powerwall or an electric car.
Last edited by richlist on May 4th, 2019, 4:13 pm, edited 1 time in total.

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Re: Air Source Heat Pump (ASHP)

#219533

Postby GoSeigen » May 4th, 2019, 4:02 pm

fisher wrote: That is, warming the house from 19 degrees to 21 degrees will take a couple of hours, warming it from 15 degrees to 21 degrees will take a couple of days in winter!


Interesting anecdotal view, but the above makes no sense to me. You are saying:

1. warming the house from 19 to 21 degrees will take a couple of hours , so
2. warming the house from 17 to 19 degrees will also take a couple of hours (if not, why not?), so
3. warming the house from 16 to 17 degrees will take less than a couple of hours, so
4. six hours max to warm from 16 to 17, then 17 to 19, then 19 to 21.

YET...

to warm the house from 16 to 21 degrees will take a couple of days? Could you explain why this is so?


GS

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Re: Air Source Heat Pump (ASHP)

#219566

Postby fisher » May 4th, 2019, 6:23 pm

GoSeigen wrote:
fisher wrote: That is, warming the house from 19 degrees to 21 degrees will take a couple of hours, warming it from 15 degrees to 21 degrees will take a couple of days in winter!


Interesting anecdotal view, but the above makes no sense to me. You are saying:

1. warming the house from 19 to 21 degrees will take a couple of hours , so
2. warming the house from 17 to 19 degrees will also take a couple of hours (if not, why not?), so
3. warming the house from 16 to 17 degrees will take less than a couple of hours, so
4. six hours max to warm from 16 to 17, then 17 to 19, then 19 to 21.

YET...

to warm the house from 16 to 21 degrees will take a couple of days? Could you explain why this is so?


GS


You're right. What I wrote is completely wrong. If it takes 2 hours to heat the house from 19 to 21 (a 2 degree jump), all other things being equal it would take 3 times that (i.e. 6 hours) to heat the house from 15 to 21 degrees (a 6 degree jump). In fact, it would probably take less than that given the loss of heat through the walls at a constant outside temperature would be less at 15 degrees than at 19 degrees.

What I was trying to explain was the difference between using a standard boiler and an ASHP and how you wouldn't usually let the house cool down too much. In my haste I used the term "a couple" when I meant "a few" and I probably exaggerated how long heating the house would take from 15 degrees. I was trying to explain too much succinctly and in a hurry and I got it wrong.

Let me try again.

When I had a boiler I would have the thermostat at 21 degrees during the day, and from about 10 p.m. I would have it set to 15 degrees. At about 6 a.m. the thermostat would go back up to 21 degrees and the boiler would have 2 hours to heat the house from 15 degrees to 21 degrees to get it to target warmth by 8 a.m. at the latest. The boiler would heat the water in the radiators to 60 degrees and could maintain this consistently so that a 6 degree jump in 2 hours was easily possible. It would depend to some degree on the outside temperature and the insulation in the house, but the boiler would almost always cope.

With an ASHP this isn't really possible. To achive a 6 degree jump in 2 hours when it's cold outside (let's say close to freezing) would be impossible with my system. Not only is the ASHP heating the water in the Radiators to a much lower temperature (50 degrees maximum) the coldness outside would cause it to have to be off-line more often performing defrosting cycles and the time it would then take the compressor to restore the flow temperature to 50 degrees at a cold outdoor temperature (the ASHP is using the air outside to extract its heat) means that the temperature of the water in the radiators would drop way below 50 degrees for a good percentage of the time. Exact figures are going to vary depending on the ASHP construction and the outside temperature but I wouldn't be surprised to see the temperature being below 50 degrees for at least 25% of the time. The ASHP will also cycle on and off in order to stop the compressor frequently starting and stopping.

The way I have my ASHP thermostat configured at the moment is 21 degrees during the day. From 10 p.m. it reduces to 19 degrees (this dissuades the ASHP coming on just before the cheap rate electricity kicks in). From 12 a.m. (when the cheap rate electric starts) it targets 20 degrees. From 3 a.m. it goes up to 22 degrees. At this point is it effectively just "on". The house will rarely reach 22 degrees and so the ASHP will just stay on trying to get there using the cheap rate electricity. From 7 a.m. (when cheap rate electric ends) the thermostat goes back down to 21 degrees. In addition to this I also have some scheduled changes to the heat curve that the ASHP is following. In a nutshell I am trying to encourage the ASHP to use hotter water to get to achieve its goals when the cheap rate electric is in force and then back to a more standard curve when electricity is more expensive. The overnight heat curve means that it will achieve its goals more quickly but it will be less efficient in doing so.

With this set up the house rarely gets down to 19 degrees and it if does, it is usually 21 to 21.5 degrees by 7 a.m. How long it takes to achieve this depends very much on the outside temperature. When it is close to freezing I think it takes most of the time from midnight to 7 a.m. to get there - i.e. a 7 hour period to get the house from 19 to 21 degrees. More than the "couple" I stated above. In late spring with overnight outside temperatures at 6 to 10 degrees it will probably take more like 3 or 4 hours.

If I let the house temperature go down to 15 degrees and it is freezing outside I think it would take the best part of 24 hours for the ASHP to get it back up to 21 degrees again on its own and probably longer. If I put the wood burner on as well it would reduce this and take some strain off the ASHP. There are times in the winter when we go away for a day or two and I turn the thermostat down to 17 degrees. When we get in, I set it back to 21 degrees and put the wood burner on and it won't be right throughout the whole house until the next morning although the lounge with the wood burner will get to 21 degrees fairly quickly - a couple of hours maybe.

To summarise, with my setup, I think it would take over 24 hours to get the house from 15 degrees to 21 degrees when outside is at 0 degrees. I think it would take about 7 hours to get from 19 degrees to 21 degrees overnight when outside is at 0 degrees. All of these timescales reduce drastically as the outside temperature increases.

It is hard to measure any of these things and come up with concrete figures as there are so many variables, the primary of which is the fluctuation in outside temperature.

I hope that clarifies somewhat.
Last edited by fisher on May 4th, 2019, 6:30 pm, edited 1 time in total.

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Re: Air Source Heat Pump (ASHP)

#219567

Postby fisher » May 4th, 2019, 6:28 pm

richlist wrote:
dspp wrote:
richlist wrote:If you have solar pv panels it makes sense to heat your hot water tank via an immersion heater from your solar energy for free.


Yes, that is true. However by putting the same amount of elec through an ASHP you can essentially multiply it by about x4 to get even more warmth into your house. If, of course you have both an ASHP and PV fitted.

regards, dspp


My solar PV panels produced 420Kwh of energy during the whole of April. Hot water used 54Kwh of that so plenty left for running other stuff like ASHP.........


How do you ensure that your immersion only kicks in when the solar PV panels are producing energy? Do you have some sort of relay switch being triggered by the electricity generation?

I also have 4KW of Solar Panels but I rarely use the electricity generated for the Immersion. Most of the time it used by washing machines or tumble driers but this does require us to switch them on manually when the sun shines. Otherwise, our ASHP heating, Fridges or Computers will soak up what they can when they're running automatically.

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Re: Air Source Heat Pump (ASHP)

#219583

Postby richlist » May 4th, 2019, 8:48 pm

fisher wrote:
richlist wrote:
dspp wrote:
Yes, that is true. However by putting the same amount of elec through an ASHP you can essentially multiply it by about x4 to get even more warmth into your house. If, of course you have both an ASHP and PV fitted.

regards, dspp


My solar PV panels produced 420Kwh of energy during the whole of April. Hot water used 54Kwh of that so plenty left for running other stuff like ASHP.........


How do you ensure that your immersion only kicks in when the solar PV panels are producing energy? Do you have some sort of relay switch being triggered by the electricity generation?

I also have 4KW of Solar Panels but I rarely use the electricity generated for the Immersion. Most of the time it used by washing machines or tumble driers but this does require us to switch them on manually when the sun shines. Otherwise, our ASHP heating, Fridges or Computers will soak up what they can when they're running automatically.


The installed system has a box of electronics wired to the immersion circuit that talks via Wi-Fi to the PV inverter......the system is totally automatic. It can be overridden at any time if, for example, you want a bath or shower and the water isn't hot enough......which can happen on those dark, overcast days in winter. The package was a very reasonable £200 extra when I had the solar panels installed. Pity the Tesla Powerwall isn't a similar bargain.

The process that the electronics use is......any solar energy goes first to running anything in the house, if there is surplus energy it then goes to the immersion heater and if there is any further surplus/ or the water temperature has been reached it's fed into grid.

Fridges, freezers and computers are really quite light on electricity consumption. My fridge is just 80w, freezer is 160w. My
TV's are 35w - 60w modern led bulbs are even less. We switch on wash machines, dishwashers and tumble driers only when the sun shines.....and they don't need switching on every day. However, they along with food and drink prep are usually the biggest energy consumers.


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