The plummeting cost of solar.

[DrFfybes]

Thanks for your post Paul. I'll try to answer all your questions.

All the quotes include scaffolding.
The smaller number of panels would fit on an east facing roof and the 20 panels would be on two parts of the roof, east and SW.
The battey(s) would go in the integral garage.
We do not have an electric car and are unlikely to get one.
Our current electric consumption is a bit irrelevent at this point since we are in the process of going all-electric and eliminating gas completely.

In that case quote 3 sounds the best, and add another 2.5kWh of battery for about £1200. The extra couple of panels on the East face will give a bit more power in the late afternoon/evenings. Quote 1 sounds a little bit expensive compared to the others, but it might include the 'all in one' inverter/battery system which keeps the power on in the event of a supply failure but is more expensive than the 'normal' battery/inverter bundle.

https://midsummerwholesale.co.uk/buy/giv-energy for an idea of equipment and prices for extra batteries and kit.

Make sure you have the 5kw inverter.

[yieldhog]

Thanks for your post Paul. I'll try to answer all your questions.

All the quotes include scaffolding.
The smaller number of panels would fit on an east facing roof and the 20 panels would be on two parts of the roof, east and SW.
The battey(s) would go in the integral garage.
We do not have an electric car and are unlikely to get one.
Our current electric consumption is a bit irrelevent at this point since we are in the process of going all-electric and eliminating gas completely.

In that case quote 3 sounds the best, and add another 2.5kWh of battery for about £1200. The extra couple of panels on the East face will give a bit more power in the late afternoon/evenings. Quote 1 sounds a little bit expensive compared to the others, but it might include the 'all in one' inverter/battery system which keeps the power on in the event of a supply failure but is more expensive than the 'normal' battery/inverter bundle.

https://midsummerwholesale.co.uk/buy/giv-energy for an idea of equipment and prices for extra batteries and kit.

Make sure you have the 5kw inverter.

Thanks again.

Quote 3 also has the advantage of being more local than the other two.

Y

[9873210]

the small battery would need topping from solar or the grid if you boil a kettle.

Or get a smaller, less powerful kettle -- part of demand management.

[DrFfybes]

the small battery would need topping from solar or the grid if you boil a kettle.

Or get a smaller, less powerful kettle -- part of demand management.

It was more an illustration that the battery won't power the house,rather than a suggestion to change their appliances to suit a small battery. It costs about 4p to boil enough water for 2 cuppas on import, about 2p on solar/battery. If the kettle takes you over the battery and it is not sunny then you probably use 10-20% of the kettle power from the grid, so on a dull day or in the evening you'd save 0.4p. At that rate the £20 or so on the new kettle would be covered in 5000 cuppas.

Low power kettles are also smaller, they are fine for one or 2 people, but having to boil it twice if you have visitors or want enough to cover some potatoes is an inconvience compared to a couple of pence of imported electric every day.

We have a 5kWh battery, I do stagger things a bit in summer when I'll be a net exporter and the panels are producing at a decent rate, eg toaster, kettle, microwave, but if you have a fridge freezer or telly (or in our case fish tank) on as background then a washing machine, grill, or dishwasher would all take you over the battery output, and forget about using an oven. In winter I don't bother as the battery doesn't last the day.

Besides, the question was from someone going to electric heating. In their case a bigger battery makes a lot more sense, especially if they can charge at overnight prices.

Paul

[yieldhog]

Besides, the question was from someone going to electric heating. In their case a bigger battery makes a lot more sense, especially if they can charge at overnight prices.

Part of my plan is to get an electric boiler to replace the gas one we have now.
I haven't yet done my research on the current electric boilers available, so would appreciate any advice from anyone who is currently using one or in the process of getting one.

Y

[9873210]

Or get a smaller, less powerful kettle -- part of demand management.

It was more an illustration that the battery won't power the house,rather than a suggestion to change their appliances to suit a small battery. It costs about 4p to boil enough water for 2 cuppas on import, about 2p on solar/battery. If the kettle takes you over the battery and it is not sunny then you probably use 10-20% of the kettle power from the grid, so on a dull day or in the evening you'd save 0.4p. At that rate the £20 or so on the new kettle would be covered in 5000 cuppas.

Low power kettles are also smaller, they are fine for one or 2 people, but having to boil it twice if you have visitors or want enough to cover some potatoes is an inconvience compared to a couple of pence of imported electric every day.

We have a 5kWh battery, I do stagger things a bit in summer when I'll be a net exporter and the panels are producing at a decent rate, eg toaster, kettle, microwave, but if you have a fridge freezer or telly (or in our case fish tank) on as background then a washing machine, grill, or dishwasher would all take you over the battery output, and forget about using an oven. In winter I don't bother as the battery doesn't last the day.

Besides, the question was from someone going to electric heating. In their case a bigger battery makes a lot more sense, especially if they can charge at overnight prices.

Paul

It was more an illustration that demand management is possible and often desirable. You can get a modulating boiler that will run at say 25% of maximum power at 100% duty cycle rather than 100% power at 25% duty cycle when it is not the coldest hour of the year. The same can be done for ovens.

Having said that kettles are a singularly peaky load, the other things you mention should be significantly less peaky, even combined. If your freezer, toaster, telly, washing machine or fish tank is drawing 3kW it needs to be looked at.

All of this really depends on the tariffs which should reflect actual effects on the grid. As long as kettles aren't synchronized* they don't affect grid operations the way the coldest day of the year does, so a tariff that encourages people to manage kettles is counterproductive.

* Maybe the grid operator should arrange for random 10 minute delays in peoples cup final feeds.

[DrFfybes]

Part of my plan is to get an electric boiler to replace the gas one we have now.
I haven't yet done my research on the current electric boilers available, so would appreciate any advice from anyone who is currently using one or in the process of getting one.

Y

Have a look at the newer high temp Air Source Heat Pumps. Technology is changing all the time, but they can supply water at up to 80C, and we find 65C flow from our gas boiler is adequate to heat the house and water, so on the face of it one of these could be a direct replacement for a gas boiler with no changes to piping or rads.

What I haven't found info on is their flow rate at these higher temps or how it compares to a gas boiler, so whilst it might be able to heat water to 65C output the speed at which it circulates could be lower so longer lag time in getting the rads hot.

I bet Mike4 knows this sort of stuff though

Paul

[BullDog]

Part of my plan is to get an electric boiler to replace the gas one we have now.
I haven't yet done my research on the current electric boilers available, so would appreciate any advice from anyone who is currently using one or in the process of getting one.

Y

Have a look at the newer high temp Air Source Heat Pumps. Technology is changing all the time, but they can supply water at up to 80C, and we find 65C flow from our gas boiler is adequate to heat the house and water, so on the face of it one of these could be a direct replacement for a gas boiler with no changes to piping or rads.

What I haven't found info on is their flow rate at these higher temps or how it compares to a gas boiler, so whilst it might be able to heat water to 65C output the speed at which it circulates could be lower so longer lag time in getting the rads hot.

I bet Mike4 knows this sort of stuff though

Paul

Just do your research before buying a high temperature heat pump. Last week, I looked at one of these high temperature heat pumps data sheets (as it happens, it was a Mitsubishi, though there's plenty of others out there). There was a glowing write up in the press about them. I looked at the one that was cited in the article. Yes, it is indeed "capable" of 70 degrees c water. But the CoP is highest at about 35 degrees c and that's what's highlighted. The heat pump data sheet doesn't actually give performance figures for water temperatures over 55 degrees c. Naturally, the higher the water temperature attained, the lower the CoP.

I would be very sceptical indeed of buying one of these high temperature heat pumps based on the numbers I saw. Just because a heat pump is "capable" of heating water to 70 degrees c, it doesn't automatically follow that it's sensible to do so. The refrigerant gas used to get to these higher temperatures is propane. The design life of the compressor and associated kit is ten years (guessing a replacement cost of low single digit thousands every ten years?) . Add in the cost of servicing every year, I'm not convinced these devices are really meeting the hype that seems to be growing around them.

One last thing, the happy customer cited in the article was off the mains gas grid. I imagine that was a key fact in the decision to buy a high temperature heat pump. It replaced an old oil fired boiler.

[servodude]

Have a look at the newer high temp Air Source Heat Pumps. Technology is changing all the time, but they can supply water at up to 80C, and we find 65C flow from our gas boiler is adequate to heat the house and water, so on the face of it one of these could be a direct replacement for a gas boiler with no changes to piping or rads.

What I haven't found info on is their flow rate at these higher temps or how it compares to a gas boiler, so whilst it might be able to heat water to 65C output the speed at which it circulates could be lower so longer lag time in getting the rads hot.

I bet Mike4 knows this sort of stuff though

Paul

Just do your research before buying a high temperature heat pump. Last week, I looked at one of these high temperature heat pumps data sheets (as it happens, it was a Mitsubishi, though there's plenty of others out there). There was a glowing write up in the press about them. I looked at the one that was cited in the article. Yes, it is indeed "capable" of 70 degrees c water. But the CoP is highest at about 35 degrees c and that's what's highlighted. The heat pump data sheet doesn't actually give performance figures for water temperatures over 55 degrees c. Naturally, the higher the water temperature attained, the lower the CoP.

I would be very sceptical indeed of buying one of these high temperature heat pumps based on the numbers I saw. Just because a heat pump is "capable" of heating water to 70 degrees c, it doesn't automatically follow that it's sensible to do so. The refrigerant gas used to get to these higher temperatures is propane. The design life of the compressor and associated kit is ten years (guessing a replacement cost of low single digit thousands every ten years?) . Add in the cost of servicing every year, I'm not convinced these devices are really meeting the hype that seems to be growing around them.

One last thing, the happy customer cited in the article was off the mains gas grid. I imagine that was a key fact in the decision to buy a high temperature heat pump. It replaced an old oil fired boiler.

Indeed, there's a good few variables to be looked at.

It's not uncommon in these parts (Aus) to find houses where the older central heating (ducted air, or hydro) has been abandoned (or radiators removed) for a couple of well placed split systems (air to air pumps basically).

Harder to do if you don't have the space - or want every room to be as warm (or cool) as each other

[funduffer]

I would be very sceptical indeed of buying one of these high temperature heat pumps based on the numbers I saw. Just because a heat pump is "capable" of heating water to 70 degrees c, it doesn't automatically follow that it's sensible to do so. The refrigerant gas used to get to these higher temperatures is propane. The design life of the compressor and associated kit is ten years (guessing a replacement cost of low single digit thousands every ten years?) . Add in the cost of servicing every year, I'm not convinced these devices are really meeting the hype that seems to be growing around them.

Yes, efficiency drops off with flow temperature. For example, for a Vaillant aeroTHERM plus 7 the COP data are:

Flow Temp / COP
40 / 4.13
45 / 3.91
50 / 3.65
55 / 3.39

So I imagine if you have a 'high temperature' ASHP operating at 70C flow temp, it will have a pretty low COP, much less than 3.

I am sceptical of high temperature ASHP's as well.

All this is true for condensing gas boilers as well (low flow temp = great efficiency).

Better to insulate your home and enable at low flow temperature to be used.

(Note. The current gas combi boiler flow temperatures I use at home: radiators 55C, hot water 50C. Perfectly adequate, now I have insulated the house. I am using 40% less gas than I used 3 years ago).

FD

[9873210]

Yes, it is indeed "capable" of 70 degrees c water. But the CoP is highest at about 35 degrees c and that's what's highlighted. The heat pump data sheet doesn't actually give performance figures for water temperatures over 55 degrees c. Naturally, the higher the water temperature attained, the lower the CoP.

I would be very sceptical indeed of buying one of these high temperature heat pumps based on the numbers I saw. Just because a heat pump is "capable" of heating water to 70 degrees c, it doesn't automatically follow that it's sensible to do so.

Any heat pump should be set to modulate, so that it runs 100% duty cycle with variable output rather than 100% output with variable duty cycle. Even if it outputs 70C water on the coldest day of the year it should output water just above room temperature on the warmest day that needs heat. Ideally somebody should give you a seasonally adjusted figure that convolutes the COP with your local climate.

[BullDog]

I would be very sceptical indeed of buying one of these high temperature heat pumps based on the numbers I saw. Just because a heat pump is "capable" of heating water to 70 degrees c, it doesn't automatically follow that it's sensible to do so. The refrigerant gas used to get to these higher temperatures is propane. The design life of the compressor and associated kit is ten years (guessing a replacement cost of low single digit thousands every ten years?) . Add in the cost of servicing every year, I'm not convinced these devices are really meeting the hype that seems to be growing around them.

Yes, efficiency drops off with flow temperature. For example, for a Vaillant aeroTHERM plus 7 the COP data are:

Flow Temp / COP
40 / 4.13
45 / 3.91
50 / 3.65
55 / 3.39

So I imagine if you have a 'high temperature' ASHP operating at 70C flow temp, it will have a pretty low COP, much less than 3.

I am sceptical of high temperature ASHP's as well.

All this is true for condensing gas boilers as well (low flow temp = great efficiency).

Better to insulate your home and enable at low flow temperature to be used.

(Note. The current gas combi boiler flow temperatures I use at home: radiators 55C, hot water 50C. Perfectly adequate, now I have insulated the house. I am using 40% less gas than I used 3 years ago).

FD

One thing I notice there. The hot water needs to get occasionally hotter than 50c or you have (an admittedly low) legionella risk.

[DrFfybes]

(Note. The current gas combi boiler flow temperatures I use at home: radiators 55C, hot water 50C. Perfectly adequate, now I have insulated the house. I am using 40% less gas than I used 3 years ago).

FD

One thing I notice there. The hot water needs to get occasionally hotter than 50c or you have (an admittedly low) legionella risk.

Bulldog said "combi boiler" so no stored hot water.

50C will the the 'on demand' flow temp.

For the High Temp Air Source Heat Pumps you cannot have 'on demand' hot water from them, so need a cyl, which can come with an immersion heater, so in reality you'd probably be running the HTASHP nearer 50-55C except on the coldest days where the COP would be [edit] better.

The only reason I run our gas boiler at 65C is because we also heat the cylinder with it, and as our wiring doesn't differentiate between heating water or rads then I just use that for a mix of economy, safety, and convenience when it gets cold.

Last summer I tested using the immersion or using the gas to heat the cyl. It seemed pretty cost neutral even with half price solar electric, so I stuck with using gas as I figured the boiler might be better being run for 30 min a day than left idle for 6 months. In winter the hot water comes on for 30 min before the heating so no real waste heating the (insulated) pipework to the diverter valve up twice.

Paul

[funduffer]

Yes, efficiency drops off with flow temperature. For example, for a Vaillant aeroTHERM plus 7 the COP data are:

Flow Temp / COP
40 / 4.13
45 / 3.91
50 / 3.65
55 / 3.39

So I imagine if you have a 'high temperature' ASHP operating at 70C flow temp, it will have a pretty low COP, much less than 3.

I am sceptical of high temperature ASHP's as well.

All this is true for condensing gas boilers as well (low flow temp = great efficiency).

Better to insulate your home and enable at low flow temperature to be used.

(Note. The current gas combi boiler flow temperatures I use at home: radiators 55C, hot water 50C. Perfectly adequate, now I have insulated the house. I am using 40% less gas than I used 3 years ago).

FD

One thing I notice there. The hot water needs to get occasionally hotter than 50c or you have (an admittedly low) legionella risk.

Yes, with a tank you need to have hot water >65C to avoid legionella. Combo boiler you don’t need this, so can be lower temperature.

[9873210]

Space heating typically uses 3-4 times the energy as water heating. You should not optimize the system for tap water at the expense of space heating efficiency.

Ideally you use a controller and plumbing designed to do both efficiently and somewhat separately, probably with multiple valves and distinct operating modes. Selecting a single output temperature for the heat pump on the worst case for both is horribly inefficient. It will almost certainly be much better to run an immersion heater cycle every few weeks than continually run a heat pump at high temperature.

You also need a plumber or HVAC technician who understands this and will not do a "drop-in" replacement and set all the optimizations to "off". Might as well store your gas in a coal scuttle.

[jaizan]

Part of my plan is to get an electric boiler to replace the gas one we have now.
I haven't yet done my research on the current electric boilers available, so would appreciate any advice from anyone who is currently using one or in the process of getting one.

From what little I've seen, electric boilers are resistive heating devices. This will be expensive when electric is 3~4 times the price of gas.

Surely if you install electric heating, is better to install a heat pump, rather than an electric boiler ?
Then benefit from the far higher efficiency.