geoffdg

What boiler to go with Solar thermal and wood burner

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1 minute ago, scottishjohn said:

retro fits are always going to be problems .

from new you just wouldn,t do that 

 

 

For a new build there's no real reason to ever consider fitting a solar thermal system, though, as they just don't make economic sense.  The only reason to consider fitting one would be if the roof layout was such that there was only a small area available to fit any system, perhaps because of shading.

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so tell me how many kw,s do you need per day to heat your house 

with a floor temp of 24 c

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2 hours ago, scottishjohn said:

I do not see how it is viable to start  off now with PV

You do a survey, like I do, and prove that its worth it ;)

Current client;

£13.5k cost for a 9kW system. 

Breakeven at year 10.5.

System guaranteed output of min 85% at the 25 year anniversary, with an expected lifespan of 30+ years.

Over £25 years the array will produce ( offset the purchase of ) around £34.5k of electricity.

Worst case of 2.5 inverter changes in the 25 year lifespan ( Solaredge with 12 year warranty, not cheap Chinese crap ) so allow ~£2.5k for known maintenance.

RoI = £18.5k over 25 years, plus whatever additional free electricity it then goes on to produce until it dies. 

 

See it now? 👌

 

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Or my case hypercheap DIY install 4KW for £1500, I hope it to have paid for itself in 5 years.

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4 minutes ago, Nickfromwales said:

You do a survey, like I do, and prove that its worth it ;)

Current client;

£13.5k cost for a 9kW system. 

Breakeven at year 10.5.

System guaranteed output of min 85% at the 25 year anniversary, with an expected lifespan of 30+ years.

Over £25 years the array will produce ( offset the purchase of ) around £34.5k of electricity.

Worst case of 2.5 inverter changes in the 25 year lifespan ( Solaredge with 12 year warranty, not cheap Chinese crap ) so allow ~£2.5k for known maintenance.

RoI = £18.5k over 25 years, plus whatever additional free electricity it then goes on to produce until it dies. 

 

See it now? 👌

 

Is that fitted by MCS 

and where in uk  

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2 hours ago, scottishjohn said:

the 7year payback is now twice or more .

That is an assumption which is unfounded. Comments like that do nothing to contribute to a thread where the OP will only benefit from / rely on factual information produced by individuals who are doing these installs many, many times a year.

I comment with high frequency on plumbing etc as I've done it for over 23 years, and would consider that information I give out is subsequently robust. I dont offer opinion unless after giving my opinion I put ( IMO ) to make folk aware.

No PV system would have a payback of 14+ years, unless it was surveyed, sized and specified by a tool. ;) 

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1 minute ago, scottishjohn said:

Is that fitted by MCS 

and where in uk  

Yes MCS, and Gloucestershire. The fit and export figures were a pittance, and should NOT be any point of focus in a well designed and conciencious installation.

The figures to focus on are the breakeven point, less the nonsense, and the amount of electricity costs it will offset over it's expected useful lifespan, less maintenance.

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well that what the last quotes i got was working out at when fitted by MCS ,

why would you think i,m just trying to argumentative if i could see a gain in my pocket  .

I have no system at this time --no axe to grind -nothing fixed in stone

so that is why i ask where in uk (rad level) and is that fitted price by MCS --cos the er will be no government money unless it is 

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6 minutes ago, ProDave said:

Or my case hypercheap DIY install 4KW for £1500, I hope it to have paid for itself in 5 years.

Yes, but you hand-crafted each panel from milk-bottle tops :D 

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6 minutes ago, Nickfromwales said:

Yes MCS, and Gloucestershire. The fit and export figures were a pittance, and should NOT be any point of focus in a well designed and conciencious installation.

The figures to focus on are the breakeven point, less the nonsense, and the amount of electricity costs it will offset over it's expected useful lifespan, less maintenance.

srtaight away even before i go check the rad level will be more than where i am --so that will alter things

and at what cost per kw you calculated the savings.

 

 

Edited by scottishjohn

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Just now, scottishjohn said:

why would you think i,m just trying to argumentative if i could see a gain in my pocket  .

If I thought you were being argumentative I would say;

" @scottishjohn stop being argumentative". I have said nor implied that so be mindful of how you read things please :) 

I'm stating facts, and offer that information for the benefit of the forum / thread etc, and I only stated one example to dispel what you have said eg ( and to quote ) "the 7 year payback is now twice or more" which is not the rule, clearly its the exception, but is a statement you conveyed as definitive aka a bum steer to the OP. 

If you have been quoted to that effect by someone then I suggest you look elsewhere ;) All the members here receiving PV installations that I'm around are all walking around with smiles, and respectable figures for the RoI. Longest breakeven I've seen is 13 years, on a heavily fragmented and difficult array, but still worthwhile as the equipment had such long warranties and expected productive output / lifespan.  

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8 minutes ago, scottishjohn said:

srtaight away even before i go check the rad level will be more than where i am --so that will alter things

and at what cost per kw you calculated the savings.

 

 

I dont have the figures to hand as that was a quote I passed on, but I could get them with little difficulty if you want?

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7 minutes ago, Construction Channel said:

Yeah @Nickfromwales. I do wish you would stop making assumptions like this

I'm a bad person ✌️😎

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Hi Geoffdg,

 

For some reason architects love drawing pretty pictures of houses with solar thermal panels on the roof with no thought on how it goes together.

 

Are you planning to use your wood burner for heating/hot water?

 

Solar thermal is not a bad thing but it is a one trick pony,  you MAY be eligible for RHI which will probably refund your installation cost (inc a large premium for being RHI) over 7 years.

 

Simplest way to mix solar thermal and oil boiler is with a twin coil cylinder, this is the industry standard crude but does work. If you want to mix a log boiler it gets slightly more complicated but can be done. One way is use a thermal store and throw all heat inputs into one tank inc option of solar PV via immersion and take out DHW via a coil or plate heat exchanger. You can run UFH and radiators from the thermal store as well. You can also mix vented and non vented system with extra coils this can be handy for mixing a open vented log boiler with a sealed pressurised oil boiler.

 

The biggest problem with thermal that the solar panel has to be hotter than the bottom half of the cylinder, you could easily end up with a tank at 30 degree from last nights log burn and solar panel at 29 degree so you get no energy from the solar panel but the sun is out. Solar PV will dump energy into tank whatever temp the cylinder is at (within safety temp limits).

 

We have a mix of 5kw of PV and 8m2 of solar thermal,20kw log gasification boilers and ASHP and have the solar thermal connected to a 500L pre heat thermal store getting max out of the solar thermal,  but i have done all this DIY and most material of ebay. If I was paying a professional no way would it be worthwhile!

 

 

 

 

Edited by Alexphd1

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2 minutes ago, scottishjohn said:

well that what the last quotes i got was working out at when fitted by MCS ,

 

Costs for MCS installs up here are crazy numbers IMO. I only managed to get 1 ASHP quote and that was 14.5k. Given the cost of the parts it was several thousand to install and commission, way more than could surely be justified based on effort / time to install. Up here we seem to suffer from not having enough installers, a tendency for installers to concentrate on more lucrative commercial work, and the government providing interest free loans to pay for the installs. The final point is no bad thing of course but it means more people are applying to install renewables and demand outstrips supply. I wrote some Facebook messages on local groups when I was struggling to get ASHP quotes and was inundated with replies from others saying the same thing. The local ‘green’ consultants in the high street said the same thing and the woman from the Energy Saving Trust told me to widen my search area and try some in England and further north in Scotland. Great approach if something goes wrong and needs servicing. How likely would it be for someone to come to my house quickly to rectify? 

 

In addition the RHI scheme rewards those with leaky houses. A ‘D’ graded property stands to gain far more in RHI payments than an ‘A’ graded one so in theory their payback time would be less. 

 

 

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1 hour ago, scottishjohn said:

so tell me how many kw,s do you need per day to heat your house 

with a floor temp of 24 c

 

Not sure if that reply was to me or not, but here goes anyway.

 

Not sure whether you mean power or energy, but I'll answer for both.  In very cold weather (-10°C outside), with no incidental heat gain, the house needs a heat input power of about 1.6 kW to maintain 21°C room temperature.  That equates to about 38.4 kWh of heat energy over 24 hours.  However, our heating does not use PV generation, as in winter it's both low and unreliable (same goes for solar thermal), so we use off-peak E7 to run an ASHP at a COP of around 3.5, so the energy usage for heating in very cold weather is about 11 kWh per day.  We've never had temperatures that low here though, the lowest we've seen is about -5°C, and then only for around half a day at most, so in reality that 11 kWh/day figure is more than double our normal cold weather usage.

 

We don't ever need to heat the floor as high as 24°C, as that would give us a heat output of about 2.4 kW, far more than we ever need in the coldest weather.  The highest temperature we ever need to heat the floor to is about 23°C.

 

 

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53 minutes ago, Nickfromwales said:

Yes, but you hand-crafted each panel from milk-bottle tops :D 

 

I'm saving all my take away containers to build a system. 

 

Thread to be titled "Cheap Chinese Panels".

 

.....I actually have hammered one flat. Surprising amount of good thick tin foil in them.....

 

:ph34r:

 

 

 

 

 

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7 minutes ago, dpmiller said:

enough for a hat?

 

I'll need it for all the flak! :)

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46 minutes ago, Alexphd1 said:

The biggest problem with thermal that the solar panel has to be hotter than the bottom half of the cylinder, you could easily end up with a tank at 30 degree from last nights log burn and solar panel at 29 degree so you get no energy from the solar panel but the sun is out. Solar PV will pump energy into tank whatever the tank cylinder is at (within safety temp limits).

Thats the killer with multiple heat inputs. Need a lot of thought and timed control to maximise on each discipline.

 

47 minutes ago, Alexphd1 said:

We have a mix of 5kw of PV and 8m2 of solar thermal,20kw log gasification boilers and ASHP and have the solar thermal connected to a 500L pre heat thermal store getting max out of the solar thermal,  but i have done all this DIY and most material of ebay. If I was paying a professional no way would it be worthwhile!

Just done one with a log gasification boiler, and not everyone realises they're eligible for RHI, vs a wood-burning stove with back boiler which is not eligible. Guys getting £12k back over 7 years. Bingo.

The above collection of 'technologies' would indeed be very expensive to have properly designed and installed, so you do need to look closely at how much capital investment you would need / can afford, and the RoI.

For me, I'd only recommend ST for somebody with a swimming pool. Right amount of energy at the right grade, at the right times of the year.

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2 minutes ago, Onoff said:

 

I'll need it for all the flak! :)

You'll only get flak if your still grouting in 2020 ;).

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49 minutes ago, JSHarris said:

 

Not sure if that reply was to me or not, but here goes anyway.

 

Not sure whether you mean power or energy, but I'll answer for both.  In very cold weather (-10°C outside), with no incidental heat gain, the house needs a heat input power of about 1.6 kW to maintain 21°C room temperature.  That equates to about 38.4 kWh of heat energy over 24 hours.  However, our heating does not use PV generation, as in winter it's both low and unreliable (same goes for solar thermal), so we use off-peak E7 to run an ASHP at a COP of around 3.5, so the energy usage for heating in very cold weather is about 11 kWh per day.  We've never had temperatures that low here though, the lowest we've seen is about -5°C, and then only for around half a day at most, so in reality that 11 kWh/day figure is more than double our normal cold weather usage.

 

We don't ever need to heat the floor as high as 24°C, as that would give us a heat output of about 2.4 kW, far more than we ever need in the coldest weather.  The highest temperature we ever need to heat the floor to is about 23°C.

 

 

yes it was  you JS 

so actual heat input for 24hrs is around  38-40 kw 

that's fine thank you 

 

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2 minutes ago, Nickfromwales said:

You'll only get flak if your still grouting in 2020 ;).

 

Keep up, it's DONE!

 

20190210_170955

 

Edited by Onoff
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