First the bad news for heat pumps. The Energy Saving Trust heat pump survey in 2009 found that many users were not impressed at all. The follow up in 2013 improved the results but the final average system COPs of 2.45 (air source) and 2.82 (ground source) were still way below the headline figures quoted for these machines a lot of which are claiming over 4 these days. So maybe heat pumps are intrinsically good but tricky to install?
Despite all that, what is really good about heat pumps is that they can deliver more energy than they consume in electricity.
The power multiplier
So a small one would be just like this diagram; working on the power of an electric kettle but delivering the power of 3 to your hot tank – a COP (Coefficient Of Performance) of 3 then. By contrast your immersion heater delivers and also consumes the power of an electric kettle so it has a COP of 1.
Heat pumps are all sold with an industry standardised COP. This is misleading to say the least and the reason why optimism is defeated by experience. Far from being a fixed figure the COP actually swings widely depending on outside air temperature and temperature delivered in the home. The COP plots here show how a kick is engineered to give a good headline figure; that kink in the graph is exactly at the publication point.
A sneaky kink
You might buy a machine with a quoted COP of say 3.75 but while making domestic hot water on a cold night it will be working at less than 2. There are benign swings however and given a sunny winter day with some warm air to chew on an ASHP can see COPs almost up to 5. You can see this on the blue line on the graph. Delivering 35c water to the underfloor heating the COP goes over 5 as the outside air goes over 10c. Note that the pale blue line (delivery temperature 50c for radiators) still only goes to around 3 so for most of the time the average COP will only be near 2.5. So, heat pump with radiators – think carefully.
Gas per kW.hr costs about a third of electrical power so after adjusting for efficiency a gas boiler is similar to a heat pump with a COP of 3. Many people in the survey would be comparing their new heat pump to a gas boiler; a formidable opponent when running on cheap gas. A gas boiler is much more powerful than most heat pumps and delivers at usefully high temperatures so a heat pump must have an overall COP of over 3 to justify a hefty purchase price. Perhaps the performance could be lifted further?
The next bit is a bit dull – you might want to skip on to conclusions below.
To winkle out some ideas we’ll take daily temperature data for January in Guildford (http://www.wunderground.com/) and relate that to a COP matrix made from the published data from a modern ASHP (inverter drive scroll, r410a, delivering to under floor heating at 35 degrees). We will be looking to lift the COP by running the ASHP at the warmest ambient temperatures possible. A look at a January temperature trace shows: There is usually a 5 degree swing between the mean night time temperatures and the daytime mean. Night time temperatures are flatter and longer than the sharper daytime peak at 1-2pm. The morning transition from lows to highs is halfway there by 10am. Temperature rises coincide with sunrise, not surprisingly.
Relating the above to the COP matrix: Running a 7hr shift from 10am gives an average COP of 3.86 – much better than gas. The equivalent night time shift only gives a COP of 2.92 – but almost as good as gas. If the pump has to make hotter water for radiators these day/night figures drop to 2.7 and 2.11 and for 55 degree hot water making 2.3 and 1.85– gas beats this hands down. Storing daytime running means that delivery temperatures probably need to be around 50 degrees leading to an average COP of under 3 although bigger storage tanks improve this. ASHPs can be smaller if they run continuously day and night on an average COP of 3.4 – still 13% better than gas. Direct electrical heating is often used to boost hot water making (COP = 1) and this can lower the average COP. If we can avoid this practice and run predominantly in the daytime it should theoretically be possible to get a COP of 3.35 (7hrs day, 2hrs night, 2hrs hot water).
Transmission: Put 100W/square metre through your floors and your feet will be uncomfortably hot so somewhere near half that will be a good yardstick for calculating the power you need.
Conclusions A small ASHP can run a bit more efficiently than a gas boiler in a modest well insulated house. Fan-coil units in bedrooms and underfloor heating elsewhere are essential. The heat pump should run in daylight except maybe for a boost before dawn to guarantee morning showers and take the chill off the floors.
Of course, with PV panel prices falling relative to electricity prices, the time is coming when your heat pump will run for free while the sun shines. At the moment it looks like we are firmly in no brainer territory and it is certainly worth checking now to see how the sums stack up.
A tip to make your heat pump installation cheaper. Use the PV panels and an energy diverter (e.g. Eddi) to heat your existing immersion heater. then you won’t need the special tank to accompany the heat pump which will just do central heating. Your installation might get a lot nearer to the £5,000 grant.
And while we are at it, don’t forget to consider a mini-split heat pump air conditioner. It’s an air to air unit and relatively so cheap it’s hard not to go and get one right away. I did.
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It’s no good just working out how much per kilowatt hour a heat pump costs to run compared to, say, a gas boiler. What’s more to the point is what is the total hit to your pocket will be after a reasonable length of time. Your system might have to generate around 15,000 kW.hrs or more each year. After about 6 years that will come to a neat 100,000 kW.hrs which is handy for making the maths easier. Say you spend £5,000 on a boiler then the cost per kW.hr is 5p – we just need to shift the decimal point along. Add to that the actual running cost of the plant in question and we can get a good idea of the total long term cost. In the same way, the total cost of the energy component is also a decimal point or two away. So, say, 12p for gas is £12,000 for the 100k.
What about in the longer term when the cost of the kit is spread out? The grey bars go to 200k kW.hrs with the kit cost remaining the same, so that’s a good 10 years where the differences become even more marked.
These sums illustrate the danger of adding more kit to your mix. Follow the government lead on hybrid heat pumps and you’d add about 10p/kW.hr to your existing set up but the 100k target doesn’t move.
And here’s a graph with the results. Double click on it to get a bigger view.
Bearing in mind that the bottom scale shows your future heating bills and those figures are £thousands the differences are significant.
Electricity £1,500 – As you can buy cheap electric radiators this might have fared better, but the sheer weight of expensive electricity has made this the worst choice by a long way. £70,000 for 10 years!
Stove and tank £5,200 – A stove connected to a heat bank is expensive but fares well compared to electricity. Even better if you can access cheap wood.
Heat pumps £10,000 – The heavy up front cost and use of the most expensive fuel makes heat pumps, sadly, the third worse choice.
Battery on Go £6,500 – An expensive battery grabbing cheap night time electricity from Octopus works out well but it’s always a limited supply.
Pellet boiler £4,000 – Who cares?
Gas boiler £2,500 – Getting better and reassuring seeing that this is what most people already have.
Oil boiler and tank £4,500- Expensive to buy and install. Expensive to service. We can do better.
Mini-split and battery £8,500 – Expensive battery meets cheap heat pump and the result is magic. Not the winner here because the battery will wear out eventually. Not shown on the graph but solar + split is the way to go – this was only evident after the graph was there to see.
LPG gas boiler and tank £3,500 – Not too bad up front and cheap to run. The winner by miles and leaves you much better off than with a heat pump.
Solar £7,000 for 20 panels – Not a fair comparison with this list as it would take 10 years to make the 100,000 kW.hrs but they would cost no more than the price of the panels. So whatever you chose above, the panels will always be sort of better but you’d need them as well. Add a mini-split and that’s proper magic.
Conclusion – LPG gives plenty of power for not too much up front. Add lots of solar panels and a mini-split or two (without the battery) and you’ll be cushtie – relatively. Remember you will have electricity costs as well as all this heating. Solar panels reduce the electricity bills considerably and often run the mini split free of charge. Free aircon in the summer is a bonus.
While I hope my figures are correct please check before making any decisions.
All this talk of nuclear fusion makes me laugh. Our area has been connected to a local nuclear fusion plant for ages and myself along with a few neighbours are already connected.
The benefits certainly compare well with other forms of energy. Unlike conventional sources there are no wires or pipes because the transmission is wireless. It’s hard to imagine how that works, but the energy is sort of beamed across the airwaves. It is necessary to have line of site from the reactor to the receiver so this may not be available for everyone. There was no cost to actually connect to the source reactor although the receiver was fairly expensive at around £5,000. Possibly the major benefit though is that there is no charge for the energy supplied as it is beamed, free of charge, directly to the receiver. In these times of hugely expensive energy, it seems impossible that this fusion power can be free but it’s true, there is no charge for the power and no sneaky daily charges either. Furthermore, the price is fixed at zero and it is guaranteed that there will be no price increases ever.
On the downside the transmission has been fairly erratic and a bit limited over the winter. This deficiency can be largely remedied by having a battery to tide us over the downtimes.
So far, reliability of the fusion reactor itself has been good and I’m told it is unlikely to fail for well past our own lifetimes. It is comforting to know that it has never been known to fail; unlike some other supplies.
So, you may well ask, if it’s free energy with free and quick connection why isn’t everybody doing it? Well, it beats me but I have noticed that a few savvy people round here have got the message and have fitted receivers to their rooftops.
You might not have heard about all this because the big energy suppliers want it to be kept secret. So, keep it to yourself. Mum’s the word.
It looks bad but as gas prices are falling and summer approaches these rates will probably revert to somewhere near to the same as this winter when next winter sets in. Anyway, I’ve remade the chart and this is what it looks like.
Double click the image for a better view.
Since last year oil prices fell but are recovering leaving heating oil largely unchanged at near £1 a litre. LPG on the other hand has fallen dramatically, off the highs, leaving a chance to lock in to some attractive prices under 50p a litre. The 10,000 kW.hrs mark half way across the chart could be only half of your likely energy demand and £1,000 worth of LPG is the only energy source that directly gets you that far.
The price of electricity at 51p brings some serious consequences for some. You’d have to multiply the electricity bar by 5 just to get to the 10,000 mark so that’s £5,000! Direct heating with electricity is not a good idea. Consider a cheap mini-split heat pump to escape that bind. More on that later.
Heat pumps, as usual, nearly tie with natural gas on running cost but both are even more expensive and the Government push for heat pumps for all looks even more dubious.
Solar panels suddenly get a massive kick in the incentive calculation when generated electricity becomes worth 50p. They have been a no brainer for a while but even more so now. Just three panels make about 1,000 kW.hrs a year, or at these rates £500, so you can see how quickly you can get your money back.
E.g. 10 panels, 4kW for £5,000 make over 4,000 kW.hrs or £2,000 worth. As I say, it’s a no brainer.
LPG is unregulated and didn’t go up on April 1st so if you are choosing a gas boiler make it LPG and lock in to some relatively cheap energy while you can. Just because you have access to town gas doesn’t mean you have to use it. What’s happened here is that tankers of gas from the U.S. saw increased demand due to the war but warm weather suddenly reduced it so the supply chain – tankers on the sea – got flooded. This is temporary of course but you can lock into long term LPG contracts for half the price of town gas while the going is good. Have a look on YouTube at ‘Updata Charts Today’ for a daily look at the gas prices where the fall off the highs is insane. Also, if you have an old oil boiler, now would be a good time to think about a change to LPG.
Batteries
A new era arrives and a new twist to eco heating. After April a typical 10kW.hr battery can store 10 x 50p worth of electricity i.e. it can hold £5 worth of electricity gathered free from your solar panels and then keep the power on after the sun goes down. So, some £5 a day saved during the 8 sunny months which comes to about £1,200 a year. For the other 4 months, when solar panels are not making enough to store, there is another game. Octopus Go will sell you electricity for 12p for 4 hours a night. Typically the battery will only accept charging at 2.5kW so the 10kW.hrs it can take on board matches that. The day time rate for Octopus Go is 44p so your mix is as follows:-
Free from PV + 12p nights + 44p day
…. and hopefully not too much of the 44p. Note that the night rate is close to the price of natural gas so charging up a night storage heater at that rate is OK but not too clever if you are on LPG. However, if we use a heat pump to triple the output from the cheap electricity then an entirely different picture emerges. A full size heat pump would produce heating for about 4p/kW.hr which is astonishing but it would hammer the battery very quickly. But 4p – wow!
And that bombshell brings us neatly onto mini-splits.
Mini-splits
Mini-splits are just small air to air heat pumps which are easy to install and you could get one fully installed for about £1,200. That quote for a £15,000 heat pump installation pales by comparison doesn’t it?
My mini-split has been running for a year so I can tell you how it’s been.
In the shoulder months the PV panels (4kW) run it free a lot of the time
It often draws well under a kilowatt so we run it when needed without worrying about the cost too much
It provides enough background heat to enable the main heating to be left off sometimes
It blows hot air so makes a great laundry drying machine.
Summer air conditioning is really good, cooling the whole ground floor
It actually cost under £1,000 installed and that took just 4 hours
It was bought from Saturn Sales who gave good advice and delivered on time
The best bit though is that batteries will enable a mini-split to be a major asset without particularly draining your bank balance (or the batteries) and most of their running time is either free or making heat at 4p/kW.hr
Conclusion
While the Government is trying to force us into unworkable heat pump arrangements at a cost of about £10,000 after incentives we can do much better for a bit less money and with less hassle too. The new ultimate mix is:
Solar panels with 10kW battery
Octopus Go
Mini-split
LPG gas boiler if that’s a choice.
I anticipate a panic surge in demand for solar and batteries after April 1st – Now is the time to get going.
While I hope my figures are accurate please do your own research before making any commitments.
Is it worth getting a heat pump? Is a £1,000 mini-split a heat pump? Does Liz Truss know?Who is Liz Truss?
Heat pumps in theory will save the world. For each unit of electricity they use they move about 3 units into your house. However, most of us live in houses that are already built (best kind to live in if you ask me) and not designed for heat pumps. You can see a discussion about heat pumps and radiators here – Radiators and heat pumps – but basically your house is almost certainly not going to work well with a heat pump unless you already have underfloor heating, fan coils or a passivhaus build. Otherwise, you’ll need to almost rip it apart and start again.
Heat pump power
What are the snags?
Apart from the radiator issue there are other integration snags. If you have a combi boiler there is no hot water cylinder but the heat pump will be too weedy to heat water on the fly so a tank will be needed. If you have a hot water cylinder already don’t be too smug. The coil in the tank is designed for very hot water from a boiler. Heat pump cylinders have much bigger coils so you’ll need the upgrade. In practice these tanks usually need a daily boost from an immersion heater which runs on the most expensive energy source you can buy.
So, it’s not just the cost of the heat pump; the new tank etc is very likely to push the cost to circa £15,000. (£5,000 from the Government so make that £10,000).
Assuming you are still up for it you might want to study this chart of current (winter 2022 Truss revision + Sunak) energy costs compared.
Here you can see that the cost of running the heat pump compares well with natural gas, oil, lpg and wood so the cost of running it won’t be too bad – or will it? Wholesale electricity prices are literally around double the artificially fixed price on the chart so for how long do you think those prices can be subsidised?
It seems to me that you can buy an awful lot of gas for £10,000 so why not stick to a nice powerful and cheap gas boiler while you can still get one.
Ah but I’ve got solar panels
Good for you. And if your array is big enough then a heat pump is the way to go. If we all had a big solar array and a heat pump the energy crisis would be over. It has to be a big array though because on a short winter day the panels lose their sparkle to a large extent and then quit altogether by tea time. Batteries step in here but they are unlikely to make financial sense unless you get them free in a leased electric car and don’t pay for their degradation – all that is another story for another day.
Moving away from the big money discussion let’s talk about mini-splits. Just like air source heat pumps in this note they are proper heat pumps but they are air to air so they blow hot air into the house. With no connections to water they are quick and easy to install and only about £600 odd to buy. As part of a hybrid solution one of these makes so much sense that the Government should incentivise them along with a bonus if they are paired with solar panels. At least this is something most people actually can do, rather than something that they should do, but can’t.
Here’s one I installed in my house paired with a 4kW PV array.
What’s it like?
The panels run it for free on most days of Spring and Autumn but not in the depths of winter although it is so cheap to run that it regularly dries the laundry by blowing hot air over the drying racks. In Summer the air conditioning is a big bonus as the cold air spills across the whole house and on a hot day electricity is always free.
The whole cost was under £1,000 fully fitted in just 4 hours. You might consider one with more than one indoor unit or another completely separate one. A pair of these would work well with solar panels – you could run both when the sun is out or just one on a cloudy day. Free heating should be enough to keep the old gas system switched off and when the sun is stronger the immersion heater will make your hot water. On dark winter evenings the choice is yours. Mini-splits and gas both cost about the same to run per kW.hr but the splits let you do more localised heating at less cost. So, to sum up. £2,000 not £10,000. Non disruptive installation. Works with your legacy system. Air conditioning. Some free running with solar panels. Dries the laundry really quickly.
During the last big freeze I avoided any burst pipe stress by running the split all night – dried a load of laundry at the same time
N.B The £8,000 you saved by not having a regular heat pump would buy a 20 panel – 8kW car port!
The difference between this and a £15,000 air to water system is so massive you’d think the Government should take note. Feel free to forward this to your MP if you agree.
My note on Radiators and heat pumps gives some essential clarity on heat pump issues. If you didn’t click through earlier I’d urge you to do so now.
When hydrocarbons like oil or gas are burnt they produce a fair bit of water in the form of steam and that steam contains energy that can be reclaimed if it can be cooled enough to condense. If your heating system returns water to the boiler at 55c or below then condensing happens in the boiler and that plume of steam outside disappears. The benefit to you, the boiler owner, is immense. The boiler that was sold to you as 97% efficient actually gets there instead of the mid eighties which is probably where it is now. On a gas bill of £3,000 a reduction of £300 – £450 makes this a topic worthy of some perusal. Plough on, it’s boring but not difficult.
There are different accepted design targets for the temperature drop across heat emitters (like radiators). A Dt of 20c or 11c. Both so widely apart to be pretty unhelpful. Maybe all of that is irrelevant as your system already exists and you can only move on by measuring what Dt you get.
So, say a radiator circuit might be set at 90c in and 70c out (Dt of 20) the desired return flow at 55c is far out of reach. Owners of oil boilers are a bit stuck here as the boilers don’t modulate which means they work on full power and are either on or off. Gas boilers, however, can have their output temperature turned down and this is the place to start but, unless you can tolerate a lot less heat in the house, it isn’t the full solution. The trouble is that the radiators don’t move as much heat at lower temperatures so they won’t achieve a Dt of 20 – maybe only 15 or less – so say you drop the input temperature down to 75c the return only drops to 60c. Getting close, but the heat to the house will be down to 12kW from 16kW for example, and we are still not condensing. Turning on more radiators will drop the return temperature and this where the juggling needs to begin. If you time the hot water heating to coincide with the heating that will help too. Looking at that standardised Dt of 11c and working back from a return of 55c the feed would have to be 66c which is quite low for radiators. The chances are your current set up is a bit above that.
Taping thermometer sensors to the feed and return pipes next to the boiler is essential for seeing what is going on.
DIY fan-coil unit
There is one tweak that could help reach down to those last few degrees and this will be particularly useful where oil boilers are concerned. Check out the DIY fan-coil unit featured here.
This works well at lower temperatures, such as the reduced return flow you are reaching for, so it will work just on the return flow pipe alone (via a diverter loop) anywhere towards the boiler end. It’s all about removing power to widen the Dt and it doesn’t make too much difference where this happens but removing heat from the return will leave the main circuit running hotter and with a higher Dt. So, when you have turned down the supply temperature as much as can be tolerated the return flow pipe can be tapped for energy and maybe you’ll reach the magic 55c.
Hardly anyone has a heat-bank based system but these have a return feed to the boiler drawn from the cooler bottom of the tank and that results in the boiler running in condensing mode most of the time and with much longer runs which is particularly good for oil boilers and their short cycling problems. If you are starting from scratch there are many other reasons why a heat-bank is the way to go. There’s a case study on one here. https://originaltwist.com/2016/01/21/eco-heating-news/
How much does electricity cost? How much does gas cost?
Following the Government paring back of the price rises the graph below has been updated – thank goodness. So 34p for electricity and 10.3p for gas.
The chart here shows how many kW.hrs £1,000 gets you for each type of energy source. Electricity is disproportionately the most expensive source of power. Your average house needs about 20,000 kW.hrs to heat over the winter – 1” to the right off this chart then and about £7,000! – so electric heating will be out of the question but the chart raises other issues which we’ll discuss below.
Electric
You see advertisements for electric heaters that are 100% efficient. They may deliver every kilowatt they consume but the claim is a meaningless dupe for the technically illiterate, they still use the most expensive power available.
Heat Pumps vs. condensing gas boilers
On a typical COP of 3 your electrical input is trebled but the latest hike still makes this about the same as natural gas. Conclusion? Forget all this stuff about heat pumps and make sure you have a modern condensing gas boiler while you can still get one. Heat pumps only make sense if you have solar panels to make them run mostly free but it’s dark after tea time in winter just when you need the heat.
Don’t ignore mini-split aircon units though. For about £1,200 they are proper heat pumps and with solar panels the free summer cooling is welcome. For most people, and the planet, this is the answer but strangely the government offers no help here. To reinforce this point my 10 panels easily run my mini-split during daylight hours in October and the house stays chill free. The aircon in summer was fantastic with cool air washing across the whole ground floor.
Pellets
Noisy high maintenance things and so close to gas so why bother. Another glass of wine by the pellet stove anyone?
Oil
Oil looks like a reasonable choice here but there are some negatives that need to be aired. Oil boilers don’t modulate so they short cycle a lot and don’t run very efficiently. Trying to get your oil boiler to run efficiently in condensing mode could be a challenge. Oil is easier to steal and the tanks need condensate sludge cleaning out from time to time. LPG looks very attractive in comparison and locking in to the longest deal could be the best choice. Another consideration is that a modulating gas boiler makes a much better partner to a heat pump if you ever want to go to a hybrid solution.
Wood
Near the top of the energy sources here so worth having that wood burning stove. An open fire is far less efficient especially when it’s really cold outside and negative efficiency is even possible. Anyway, a stove makes a lifesaving backup in the event of power cuts – always a possibility. However, unless you are huddling round the wood burner with the rest of the heating off it would be cheaper to heat a whole house with an LPG boiler.
Bulk LPG
The star of the show at the moment and you can lock in these rates for two years. So, gas cookers good – electric cookers bad.
Considering a heat pump? No way. Dig a hole in the garden and go for LPG. Note that although the bar for LPG looks good on the graph it could still be made even longer with simple system tweaks to make the boiler run more efficiently.
Natural gas
As I’ve said, same as a heat pump and 3 times better than electricity. Not brilliant though but there’s a tweak to think about. Your gas boiler will probably be a condensing type but that only works when return temperatures are below 55c so you need to turn down the output temperature to about 75c and see how that works. If you still get a cloudy plume on the exhaust flue then turn it down a bit more. Do this and you might get near the 97% efficiency the boiler boasts it can do. The difference this makes to your bills will be huge. If you are turning off radiators to save energy the return temperature will rise so it’s better to turn down the boiler as your first move. Elsewhere on this site you’ll find a simple hack that will enable high radiator temperatures and low return temperatures; probably the quickest and cheapest way for most people to get over 10% heating bill reduction.
Of course, like incandescent light bulbs, all non-condensing boilers should have been in the skip long ago but even more so now.
Octopus go
Octopus offer late night electricity for car charging at 12.5p/kW.hr. That is very good indeed and works for everything, not just cars. A heat pump kicking on in the early hours is super cheap and not only off this chart but off the page too. A kW.hr for about 4p when running a heat pump; makes you want to rush out and buy a mini-split immediately. Storing this energy for later is the main issue but running the immersion heater and charging up night storage heaters directly is an idea.
Hard to chart here because the power is free but the sharp rise in electricity prices means that PV payback times have tumbled. Take a cluster of three panels for around £1,000. They will produce over 1,000 kw.hrs over a year which is worth £340 if you used it all. A three year payback then. More panels decrease the likelihood of consuming all the production but a diverter, like the Eddi, to power your immersion heater or a car charger will help you consume all you make.
The charts
A lot of work went into the comparisons and I hope they are accurate. However please check for yourself before committing to any changes. The figures are skewed for the efficiencies of the kit that is using them so, for example, gas boilers are calculated at 86% efficiency rather than the 97% that might be theoretically possible.
After next winter you could have spent over £3,000 on energy. That’s a sickening amount of money gone forever. I have written a lot about some elegant solutions, and indeed, if you have sufficient money you can literally reduce the cost of energy to under 3p/kW.hr instead of the 34p (for electricity) and 10.3p (for gas) we are soon going to bear. However rising prices from all directions are already stretching budgets so a fresh look at some less expensive options is needed.
So what’s the plan?
Stage 1: We need energy and solar panels are the answer. A modest but useful array of 4kW is going to cost about £5,000. The returns on capital are about 30% so borrowing to do this makes sense. Bimble Solar offers interest free credit so there are definitely ways to get going without producing much cash up front. With electricity heading towards 50p/kW.hr (34p for winter 2022) there is absolutely no question that solar panels make sense and paying off the loan is better value than buying electricity. Solar panels don’t just mitigate your electricity bills, they can form an important part of your heating strategy too. Have a think about adding an ‘Eddi’ or similar to the mix. This channels all surplus energy to your immersion heater. Self consumption is key here – don’t export anything, it’s too valuable to give away cheaply.
Stage 2: Once you have free daytime electricity you need the magic multiplier to leverage your investment; a heat pump. Although the Government will chip in £5,000 this is a step too far for most people when the total bill could be over twice that when all the connections to the existing system are factored in. But all is not lost. A mini-split (air to air) heat pump doesn’t get the grant but the cost, fully installed, is around £1,200. It doesn’t connect to your wet heating system to heat the whole house but it will provide a core of heat that runs free off your panels during the daylight hours. With one of these suitably sited the existing heating system can be left off for a lot of the time. An added bonus is that you’ll have air-conditioning in the summer too. Typically, these consume about 1kW and produce 3kW and there is a lot of choice to go bigger or smaller. I bought one from Saturn Sales and it works really well. It often consumes less than the rated figure so I wish I had opted for a slightly bigger one. It easily runs for free in the summer sun so the bigger version would provide even better air conditioning. Because the cold air sinks it pools across the whole ground floor; an unexpected bonus.
Stage 3: You can sign up for an Octopus Go car charging account that will sell you cheap power. 4 hours every night for 7.5p/kW.hr. This is a fixed contract for a year so you can lock in with confidence. They don’t mind what you use it on so the heat pump can bring the house up to temperature in the early hours, night storage heaters can be topped up, the immersion heater can kick in, appliances can run. You need to have an electric car on order at least – with a two year waiting list on some that’s not a problem. Just order one you can’t have now then cancel it later. You never know, you might even be able to flip your new car for a profit when it becomes available. Daytime rates for ‘Go’ are higher which means having solar panels is a good part of this mix.
Stage 4: Cooking with gas and electricity is a big expense and needs addressing with two essential bits of kit. A microwave and a slow cooker. The microwave can cook so cheaply that at current electricity prices it could be just as cheap to buy ready made meals than to cook them yourself. Even cheaper of course is to build up some expertise on microwave cookery. A slow cooker consumes very little power and a hot stew is quick to prepare and always a good winter warmer. If you had solar panels they would trickle charge your meal free of charge. The kettle – to boil a litre twice a day for a year costs around £20 so unfortunately, filling the kettle less won’t save much.
Stage 5: We all know about carrying our heat around with us in the form of a good pullover and the localised heat theme can be extended. An electric blanket on the bed of course but another one under the sofa cushions? If you have read my bit about turning down the thermostat here you might be glad of a localised hotspot.
Stage 6: Elsewhere on this site I have written about forcing your boiler to run in condensing mode. The savings will be in the order of £300- £400. Read about it here.
The choice, before next winter arrives, is to do nothing and watch your money start to erode, or to start taking action at the early stages of this crisis and end up even better off than when it began. To consolidate your ideas check out a deeper discussion on Heating News – Spring 2022
Energy crisis edition Nearly free electricity and a free car!
Price caps for everyone.
Oil and gas now costs the energy suppliers so much that they all have to charge right up to the government price cap and there’s worse to come in October.
All offers therefor will settle at about the same level, 34.64p for electricity and 8.38p for gas with some sneaky increases on daily charges. Meanwhile energy prices continue upwards so future caps are very likely to be even higher. The new norm for total domestic energy costs looks more like £3,000 – £4,000 and that’s money that has been taxed. I make this point because any savings you can make are tax free. As usual the discussion for remedies largely revolves around PV solar panels and heat pumps, preferably both at once. We’ll have a look at turning down the thermostat too – what actually happens.
Solar panel returns – worth it?
The 1,000 cluster: By a strange coincidence 3 solar panels cost about £1.000 fitted. They will have a bit over 1,000W power rating and make over 1,000 kW.hrs in a year. At 35p per kW.hr saved on your bills the 3 panels will make you £350 a year paying you back the £1,000 in 3 years.
So the deal goes a bit like this. You give me £1,000 and I’ll pay you back £350 a year for 3 years. Only then are you back where you started, which doesn’t sound so clever. However, by then prices could be up by 50%, at least, so you get £525 a year for the next 3 years (£1,575 ahead at this point) and then on the same basis another £2,360 over the next 3 years and so on. Crazy maths? Well electricity price rises have been steady at 8% a year and that was before the energy crisis so this all looks pretty real. Remember we are just looking at 3 panels for £1,000 here. Your real installation could be 6 times as big.
Not spending money on fuel bills puts money in your pocket but unlike other investments this is tax free and very like a pension scheme. On that basis PV panels make more sense for higher tax payers but still a good deal for … er … the rest of us.
New 240v solar panels
In the last issue I featured an Enphase Micro inverter with the comment that soon PV panels will have them built in as a matter of course. Since them Hanwha Q-Cells have launched a lovely all black, 385W panel (Q.Peak Duo BLK-G6+/AC 340-345 ACM) with the Enphase Inverter built in. So instead of high voltage wires going to one inverter box the panels all link up easily and deliver 240V directly to your mains circuit. The days of balancing strings, matching inverters etc are over. Now you can put panels in any shaped clusters that suit you. Enphase are having a major focus on Europe so we’ll hear much more from them in future especially when they use their superior electronics skills to launch a new electric car charger.
Turn down the thermostat – the real savings
‘The rate of loss of heat is proportional to the excess temperature of the surroundings’ So the warmer your house is relative to the outside the more energy you lose, and it’s a linear relationship. That makes the maths easy. If, say, your house is at 20c and its 5c outside the difference is 15c so a reduction of 1c on the thermostat reduces the heat loss by 6.66%. So, it’s the percentage reduction on the difference in temperatures. If it is 10c outside the difference will be 10c so a 1c reduction on the thermostat reduces the loss by 10%. Your bills corelate directly to this so whatever percentage is saved on the day is what comes off your energy bill, so the chances are you will be saving £200 or more over the year. One extra click down on the stat doubles the saving!
Solar PV annex building – the Powerhouse
Recently I have been pondering on the idea of an annex building with an integrated all solar roof. This involved juggling various layouts of panels, roof angles etc, so to prevent a whirling descent into madness I have constructed an Excel model that does all the calculations, right down to the finished size of the whole building. Happy to share if you are wrestling with the same ideas.
PV panels don’t like being roof integrated because they get too hot. The annex roof has an air gap under the panels so that air flowing upwards under them raises their efficiency. This slightly warmed air is directed into a void in the peak of the roof and then ducted down to your air source heat pump which runs very nicely on the warmer air giving a double whammy; better PV efficiency and better ASHP efficiency. In addition, the ASHP avoids the colder ground air and largely avoids costly defrosting cycles. A similar concept is even easier to implement on a car port or garage.
The combination of an ASHP and the PV is a marriage made in heaven. Free power is turned into over 3 times more heat as all our small gains in efficiency are multiplied up by the COP of the ASHP. The Powerhouse makes electricity and heating and pretty much covers most domestic energy needs.
One attraction of the powerhouse is that it can be sited to point south unlike some houses which also suffer from shaded roofs, chimneys etc. Also, the local planning committee will tend to look more favourably on applications that involve innovation and ecologicalness.
What about batteries?
After the sun goes down batteries deliver free solar energy back to you; …… or do they? Actually, the batteries cost money to buy and they degrade with every cycle so there is effectively a charge to your pocket for each kilowatt.hour they store and you’d be shocked by how much. Ordinary lead acid batteries will charge you nearly 50p to recycle a kilowatt.hour, so more expensive than the mains. It gets better with lithium batteries with 20p a regular figure and 5.5p seems to be the limit. So, if you choose carefully the batteries will beat the mains on delivery cost. The Bimble Solar web site lists masses of batteries with their energy delivery costs so check it out before you buy.
Cheeky thought of the day. The Tesla power wall costs about £8,600 and stores 13.5kW.hrs and like all batteries it wears out in time and has to be replaced. However, the battery in your electric car is much better than that and if you are leasing the car you don’t care about degradation. So check out two way charging where you can get power out as well (V2H). The cost comparison is interesting. 4 Powerwalls would cost £34,400 but the batteries in a Nissan Leaf store more for the same money and they come with a free car thrown in as well! I admit it’s early days for this type of thinking; V2H chargers are expensive and not many cars support V2G or V2H but you might as well get ahead of the curve for your future energy strategy. At the moment you are probably looking at a Nissan Leaf and within a year a VW.
Late night power for car charging costs 7.5p/kW.hr with Octopus Go. What this all means is that two way charging with a battery makes your electricity cost 7.5p/kW.hr as opposed to 35p++ and that makes a leased electric car a viable consideration. I’d still think twice about buying one with ready money though as depreciation is likely to be bad while electric car pricing changes from a premium to a discount.
To underline the significance of all this. Your car battery will easily run a 3kW heat pump over a winter afternoon and evening consuming say 21kW.hrs and delivering 63kW.hrs or more to your heating. A 7kW wall charger will recharge your battery with 28kW.hrs later that night for £2.10. There will be some efficiency losses but the astonishing fact is that solar panels + car + heat pump will slash your energy costs to below 5p when everyone else will be paying 50p odd.
While doing your sums, don’t forget night storage heaters. They store energy more efficiently and cheaply than batteries. Everybody hates this old technology, especially with electricity prices soaring, so you might find some cheap ones on Ebay.
The technology for all of this exists now, heat pumps and electric cars will soon be the norm so many of us will be ready for this anyway. Storing energy makes renewables work better so it makes one wonder if we need to build more nuclear power stations.
Heat pumps update
The renewable heat incentive on heat pumps ended in March 2022. Instead, you can get £5,000 for an ASHP and £6,000 for a GSHP. Your installer makes the claim so you might not actually find all this money in your own pocket. All this leaves a big question over heat pump viability especially with daft quotes from the suppliers.
If you have town gas, why bother? Heat pumps run on electricity that costs 4 times as much as gas.
Gas boilers are cheaper and usually much more powerful and they almost certainly suit your existing system.
In favour though:
If you make your own electricity then a heat pump is a perfect partner.
A small mini split system (air to air) is about £1,000 and will run free on your panels – it does not qualify for the grant though.
Using surplus electricity to run the immersion heater means you don’t need a new water tank so a heat pump installation will cost less. Knocking say £2,000 off your heat pump quote will buy you some PV panels.
There’s a theme emerging here: Get some panels running before you even think about a heat pump.
Solar car port
A simple car port with some 240v panels must be an early consideration in the energy battle. Cheap to put up, no scaffolding, no roof attachments just useful power and a new useful building. A 4×5 panel layout is likely, so about 7kW and £7,000. By the way – have you seen postcrete in action? Stick a post in the hole, pour the dust around it, make sure it’s straight then pour in some water; job done. That car port will be up in no time.
The latest 240v panels, with their own microinverters built in, allow us to make some improvements as they don’t need string matching and we can vary the tilt angles. The highest row can be tilted up slightly without making the car port too high and the lowest row can be tilted down to pick up more winter sun. Assuming you are going to put panels somewhere on your property the car port makes a sensible option. With no rooftop scaffolding costs this is an easy construction with space for as much power as you need and you add value to your property too.
The air cooled roof idea works really well with a PV car port and even more so with my air assisted hybrid ground source heat pump. The hot air under the car port panels is blown down through a string of radiators and that warmed water makes the ground source system work better. See https://wordpress.com/post/originaltwist.com/4622
I was plugging this idea when the incentives were in the order of £20,000 ….. too late now and not worth doing on the reduced payment but an air source heat pump working with the car port makes sense.
Driveable solar annex. The latest energy costs have made it time to review my mad idea for a solar powered driveable house. Apart from being a massive power supply with its sun tracking solar array (makes £2,500+ worth of electricity a year) it can earn over £1,000 a week on AirBnb. The transmission has been made much simpler and easier with regular car parts and the panels now mount on one side – the other side is all sliding glass doors for your viewing pleasure. Catch up here.
Since this drawing further thoughts have made the design even easier. A bespoke container room dropped on a 4×4 chassis makes it all easier and a slab of solar panels across the top help to make an awning over the sun deck. Job done.
Driveable housesliding
Trivia
Casio LCW-M170TD-1AER Lineage Waveceptor
You might remember me going on about my Casio solar powered and radio timed watch. Some 15 years on with no new batteries or straps it is still ticking on faithfully. However, Casio have made a new watch which has been reviewed as maybe the best watch in the world. I’ve bought one and it’s hard not to agree. Super light, slim and with solar and radio timekeeping. One amusing feature is the second hand. It figures there is no need to tick if you can’t see it, so in the dark it just parks until light returns then it shoots round to find the exact second. The titanium case and strap are a dull grey colour which gives a more grown up, less bling, look to a very understated watch. I love it.
Tents makes sense – a small package opens up to become a big thing. On that logic a caravan looks daft. Towing a big thing full of empty space – dooh. It is more sensible to have something that can be towed easily, still full of all your kit, and then be opened up on site at the press of a button. A full off-grid energy system built in would be the cherry on top and a satellite dish that gets the footie running straight away wouldn’t hurt either. And that brings us to the
Original Twist Camping trailer.
You know those tool boxes where the top parts push away to reveal the box underneath? Well this trailer is just a big one with wheels on. The door frames at each end support the roof and lift it just like a four poster car lift. You arrive on site, the roof lifts up, the sides pop out and the roof closes down on them to lock and stabilise. The links that control the movement of the sides are steadied with torsion bars and chain and sprocket ties so powering it all is quite simple. Just one electric motor to make it all open up. The drawing shows one half closed and the other open; in practice both sides deploy together. The roof lift easily copes with the weight of the solar panels, dish, awning etc.
The side pods can contain beds with lights and TV built in and/or a kitchen unit. The choice is yours.
A shower room can be fitted over the draw bar as a separate cubicle that is entered privately from the main living quarters.
This design could be scaled up or down. Here it starts as the size of an SUV, for easy storage and towing, but still sleeps up to 5 when you get there. A bigger version would be sensational when deployed; imagine rolling into the campsite and opening up straight away, the dish locks on, footie on, beers out, all in about 2 minutes. A caravan that’s 4 metres wide before any canvas extensions go out! Stand by for a crowd of onlookers.
Heating is by a truck cab mini heat pump or gas.
The generous PV array raises an interesting question. If your electric tow car also had panels on the roof there could be significant range extension when all the panels are combined. In the new electric era tow cars will need all the help they can get. Note that the PV still works when you get home so it makes a useful uninterruptible power supply for your house – unless you park in your garage of course.
So there’s the idea. Does it exist? No, not yet, but let me know if you would like to build it and I’ll let you know how all the links work.
Features
Fits in a normal garage
Easy to tow – only as wide and as high as a car
Aerodynamic for economical towing
Automatic opening out and closing in a minute or two
Moulded in satellite dish recess on one roof, covered when stowed
The drawing is done to fit existing solar panels but they are already bigger and better with 400W panels a good fit. Imagine a matching moulded roof on your tow car with another 3 panels fitted. A fantastic look and 2.4KW in total which is over 3 horsepower. Quite possibly this combination might be more economical to tow than a car on its own!
Plug all that in when you get home and watch those heating bills crumble. At next winter’s projected prices that’s well over £1,000 worth every year. While turning over energy ideas consider that your electric tow car has the equivalent of four Tesla powerwall battery things built in so your trailer is not only a monstrous power house when on the move but also a major part of your domestic energy strategy too.
Vehicle to grid chargers are the next big thing. At the moment it’s all possible if your tow car is a Nissan Leaf.
Microinverters have passed an important tipping point and will soon be all the rage, but first, what are they? Grid tied PV panels usually feed high voltage DC current to a single inverter which converts that power to 240v AC. High voltages present safety issues and shading can reduce efficiency of the whole set, although, as thousands of examples testify, this system works well enough. But there is another way gaining traction – microinverters. These neat little boxes bolt up under each solar panel and make 240v right there, on the spot, with simpler wiring too. At a stroke the shading problem disappears, voltages are reduced and individual panel monitoring is possible. The monitoring is the best bit with the whole array mirrored on your PC screen. Each panel shows how it is performing and all the relevant history is retained for your viewing pleasure. The system is completely expandable and more panels can be clipped on at any time. The only drawback is higher cost with prices around £100 for each microinverter compared to a single inverter like the £1,000 Sunny Boy 5kW, but as you will see below that balance will soon swing the other way.
Panels – More power for same money
The case for going solar gets more compelling by the day. How about an all black JA 370W for just £130! Three of these with micro-inverters would cost £690 plus fitting etc so the ball park is around £1,000 for 1,000W of power (or better) and just over 1,000 kW.hrs a year of production. 1000 for 1000 for 1000!
So how many panels do you want? And what do you get back? Well, that 1kW pack of 3 will make £180 worth of electricity (at 17p/kW.hr) if you consume all they make, but only £58 if you sold the remainder to Octopus for 5.5p. That makes annual paybacks of a rather good 5.5 years or a bad 17 years so there must be a sweet spot in the panel count. Your background domestic consumption with lights computers and fridges will often be around 1kW so the first 3 panels/1kW are definitely worthwhile. However because panels rarely produce their rated output, and never in winter, the first 9 panels/3kW should be deemed good. All the rest will boil kettles and run appliances from time to time but after around 4kW and 12 panels any extra will be bad ones unless you can increase your self consumption. One great way of doing this is to route any excess production to your immersion heater and a SOLiC 200 for £195 will do that for you. With that fitted your 12 panels will always be enough to spin up a domestic appliance with all the excess being used to heat water and give a 5.5 year pay back. A couple more panels might be justified to give better utility without diluting the payback too much so it looks like 14 panels might be the sweet spot for most households. All this kit is expected to last for 20 years: pretty compelling when electricity prices have been increasing by 8% a year. If that 8% persists then payback falls under 5 years and you’d recoup the same amount again after just three more years and then 10 times your money over the expected life of the panels. As I say, it’s pretty compelling
Of course, if you are running a heat pump then more self consumption will justify more panels but If you have town gas you’ll be making hot water much cheaper than with electricity and that will drop your panel count.
And what about car charging you say. Well, yes, that too makes for more self consumption but, just to rain on that parade, Octopus are offering power for car chargers at 5p/kW.hr for 4 hours a night so don’t up your panel count too much and maybe not at all.
Astonishing high power panels – 540W!
High powered panels are here. For example Canadian (it’s a company) are offering a 540W panel for £200. Expensive alright but with micro-inverters it’s a game changer. Take our 3 panel set above for 1,020W and, with 3 micro-inverters, £690. Then compare 2 x 540W Canadian panels for 1,080W and only 2 inverters for a total of £600. Overnight, higher powered panels have made microinverters the best choice. The best you can get is the cheapest option. No doubt that is going to be the way forward from now on and it would make sense if panels started to come with inverters built in too.
C.E. approved ground source pump for £1,600
You might recall my design for a hybrid ground source heat pump that optimally combined air and ground heat sources. Full RHI payments and less digging etc. If you are contemplating this you’ll be interested to know that a 10kW C.E. approved ground source heat pump unit can be found on Ebay for £1,600. That makes a great start when you think that around £20,000 is the usual cost of a regular installation.
Mini-split heat pump – up and running
We had an unheated laundry room and a small Mitsubishi mini-split (an air to air heat pump) has made a perfect addition. It heats the room while blowing warm air over the clothes racks. In summer the cooling setting will make ironing bearable and some cold air will spill out to make a cool refuge in the adjacent room. Brilliant.
The kit was installed in about 4 hours and the total cost, fitted, was under £1,000. As soon as the solar panels are installed it will run for free but when I checked recently it was only drawing about 350W so no stress there. Solar panels output can be excessive in the summer so running the air conditioning will increase self consumption and be guilt free too.
Original Twist 
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