Solar Panels

Discussions about serious topics, for serious people
User avatar
bjn
After Pie
Posts: 2416
Joined: Wed Sep 25, 2019 4:58 pm
Location: London

Re: Solar Panels

Post by bjn » Fri Jan 20, 2023 4:45 pm

My big blocker on the heat pump is that I'd likely need extensive and expensive pipework throughout the house, involving ripping up flooring and all sorts. However if that were needed, I'd use the opportunity to install underfloor heating, which does not need to run as hot as a radiator. Given we had the floors redone in the house about 8 years ago, this would be a painful thing to see happen.

User avatar
lpm
Junior Mod
Posts: 5365
Joined: Mon Nov 11, 2019 1:05 pm

Re: Solar Panels

Post by lpm » Fri Jan 20, 2023 5:04 pm

Have you thought about air to air? Get rid of the water system entirely.

Advantages

- often cheaper
- summer aircon
- High COP
- get rid of radiators

Disadvantages

- a/c unit in each room which some find ugly
- can be complicated conduits, particularly for rooms in centre of house
- can need two heat pump units, e.g one at front of house, one at back, each feeding through to 3 or 4 inside units
- likely to have rooms missed out, needing a 100% resistive heater as infill
⭐ Awarded gold star 4 November 2021

User avatar
lpm
Junior Mod
Posts: 5365
Joined: Mon Nov 11, 2019 1:05 pm

Re: Solar Panels

Post by lpm » Fri Jan 20, 2023 5:21 pm

Oh, forgot the big disadvantage that A2A can't do hot water. So you need space for a hot water tank and cheap electric heating of that water - via solar, overnight cheap electricity or a heat pump hot water tank (currently expensive).
⭐ Awarded gold star 4 November 2021

User avatar
Grumble
Stummy Beige
Posts: 3909
Joined: Mon Nov 11, 2019 1:03 pm

Re: Solar Panels

Post by Grumble » Fri Jan 20, 2023 5:33 pm

Heat Geek disagree that you need an amazingly insulated house before getting a heat pump. Does need to be a good quality install though with good control system.
A bit churlish

User avatar
lpm
Junior Mod
Posts: 5365
Joined: Mon Nov 11, 2019 1:05 pm

Re: Solar Panels

Post by lpm » Fri Jan 20, 2023 5:45 pm

Absolutely, it's a myth about amazing insulation. That's totally invented by the fossil fuel industry and pushed to The Times/Telegraph/Spectator at every opportunity.

But you do need to get all basic EPC measures done in order to get the £5,000 government subsidy. For most people that's loft and cavity wall. And you'd want to anyway.
⭐ Awarded gold star 4 November 2021

User avatar
Opti
Dorkwood
Posts: 1341
Joined: Mon Nov 11, 2019 11:21 pm
Location: On the beach

Re: Solar Panels

Post by Opti » Fri Jan 20, 2023 6:05 pm

Unfortunately, even though I live in one of the sunniest places in Europe, I don't have enough roof space/land for a worthwhile solar installation. I do, however, have enough roof space for a solar water heating system. I'm pricing this up right now.
Now that the late evenings are getting pretty chilly (8º) last night, the one inverter aircon unit is providing enough heat without crazy cost. Mind you electricity prices, complicated as they are here, seem to be massively less than in the UK.
Time for a big fat one.

Imrael
Fuzzable
Posts: 323
Joined: Tue Nov 12, 2019 5:59 am

Re: Solar Panels

Post by Imrael » Fri Jan 20, 2023 6:35 pm

Heat Geek disagree that you need an amazingly insulated house before getting a heat pump. Does need to be a good quality install though with good control system
Our heat pump went in last autumn (replacing a terminally broken ancient back boiler in a Rayburn, so we've had some cold spells to evaluate it.

The house is a late 70's build and I dont have amazing insulation. It does have vintage double glazing (K-glass but not a modern standard frame), cavity wall foam and we did improve loft lagging and reskin some dormer bedroom walls.

Most of the rooms with radiators are fine. A couple probably need a radiator change and one rad seems to be blocked. The heating system is now filled with a rather thick gycol mix rather than water and took ages for all the rads to start flowing normally) The heating zone with radiators is not running all the time even in the cold snap a few weeks ago.

The disappointment is the area with Underfloor heating - its more "chill off" than cozy and runs pretty much 24/7 when the temperature falls below about 2-3C. This surprised me a bit - I thought the issues would be the other way round.

And the solar-plus-battery went in about 6 months earlier and has worked beautifully. The only snag is that a change in family plans means I'll probably move out before anything resembling payback. But the system isnt to blame for that.

User avatar
bjn
After Pie
Posts: 2416
Joined: Wed Sep 25, 2019 4:58 pm
Location: London

Re: Solar Panels

Post by bjn » Fri Jan 20, 2023 6:43 pm

lpm wrote:
Fri Jan 20, 2023 5:04 pm
Have you thought about air to air? Get rid of the water system entirely.

Advantages

- often cheaper
- summer aircon
- High COP
- get rid of radiators

Disadvantages

- a/c unit in each room which some find ugly
- can be complicated conduits, particularly for rooms in centre of house
- can need two heat pump units, e.g one at front of house, one at back, each feeding through to 3 or 4 inside units
- likely to have rooms missed out, needing a 100% resistive heater as infill
A2A would be a right pain in my 1880s house, unless I ran the ducting down the chimneys. Hmmm. Another advantage would be you could run it in a reverse cycle in summer and cool the house down. Selling that to MrsBJN might be difficult, she is very small C conservative, I couldn’t even convince her that we should swap out our dead gas range for one with an induction hob.

User avatar
lpm
Junior Mod
Posts: 5365
Joined: Mon Nov 11, 2019 1:05 pm

Re: Solar Panels

Post by lpm » Fri Jan 20, 2023 6:48 pm

Imrael wrote:
Fri Jan 20, 2023 6:35 pm
The disappointment is the area with Underfloor heating - its more "chill off" than cozy and runs pretty much 24/7 when the temperature falls below about 2-3C. This surprised me a bit - I thought the issues would be the other way round.
That's odd. What's the thermal mass of the floor like? Other people say it comes up to temperature then acts as the base load for the entire house.
⭐ Awarded gold star 4 November 2021

User avatar
lpm
Junior Mod
Posts: 5365
Joined: Mon Nov 11, 2019 1:05 pm

Re: Solar Panels

Post by lpm » Fri Jan 20, 2023 6:52 pm

bjn wrote:
Fri Jan 20, 2023 6:43 pm

A2A would be a right pain in my 1880s house, unless I ran the ducting down the chimneys. Hmmm. Another advantage would be you could run it in a reverse cycle in summer and cool the house down. Selling that to MrsBJN might be difficult, she is very small C conservative, I couldn’t even convince her that we should swap out our dead gas range for one with an induction hob.
As I understand it, the ducting just runs a couple of narrow flexible pipes from outside unit to the various inside units, carrying hot gloop. So it can be run through ceiling voids or across roof spaces. But also needs mini pumps to expel condensates when running as cooling in summer, if it can't do simply gravity to the outside.
⭐ Awarded gold star 4 November 2021

IvanV
After Pie
Posts: 1759
Joined: Mon May 17, 2021 11:12 am

Re: Solar Panels

Post by IvanV » Fri Jan 20, 2023 10:43 pm

lpm wrote:
Fri Jan 20, 2023 3:46 pm
Electricity is currently 3.4x the cost of gas. So a COP of 340% is the basic target. Actually a bit easier, 290% say, because of the inefficiency of gas boilers running at about 85%.
I have just checked what I am paying on my regulated tariff from 1 Jan, and the ratio is even lower at 3.27. I read the numbers upthread which were like 4, but probably that was the last quarter. What an amazingly fast change from around 5 a short while ago.

Best performing condensing boilers are about 94%, so I tend to take 90% as a practical reality.

COP varies with the outdoor temperature, lower when it is colder. A simple average doesn't really do it, because when the weather is cold and COP falls below the average, you need to run it harder to get more heat out of it. I think the 3.3 number was been calculated taking into account both the performance of gas boilers, and the practical averaging of COP, taking into account that you need it more energy just when the COP is worst.

Another factor is that, because a gas system can heat your house up quickly, you can cycle the heating and let your house cool off when you aren't in it, or are asleep. With a heat pump, you will have to keep it warmer when you aren't there, or are asleep, because it will take longer to bring it up to temperature. I don't know if that is also incorporated in that factor.

But, anyway, 3.3 has been the traditional number. And, amazing to report, we have now passed that traditional ratio where it is reckoned that air source heat pumps are the cheaper option to heat your house. Assuming that your house is sufficiently well insulated, and/or otherwise arranged, that you can adequately heat it with an air source heat pump. I'm pretty astonished, but heartened, that has happened so fast. If we hadn't had the crisis, I doubt that would have happened.

User avatar
bjn
After Pie
Posts: 2416
Joined: Wed Sep 25, 2019 4:58 pm
Location: London

Re: Solar Panels

Post by bjn » Sat Jan 21, 2023 3:57 am

There has been speculation that gas isn’t taxed enough, while electricity is taxed too much and green levies should be shifted. If that were to happen, heat pumps would be much more competitive.

User avatar
dyqik
Light of Blast
Posts: 6456
Joined: Wed Sep 25, 2019 4:19 pm
Location: Masshole
Contact:

Re: Solar Panels

Post by dyqik » Sat Jan 21, 2023 5:40 am

bjn wrote:
Fri Jan 20, 2023 6:43 pm
lpm wrote:
Fri Jan 20, 2023 5:04 pm
Have you thought about air to air? Get rid of the water system entirely.

Advantages

- often cheaper
- summer aircon
- High COP
- get rid of radiators

Disadvantages

- a/c unit in each room which some find ugly
- can be complicated conduits, particularly for rooms in centre of house
- can need two heat pump units, e.g one at front of house, one at back, each feeding through to 3 or 4 inside units
- likely to have rooms missed out, needing a 100% resistive heater as infill
A2A would be a right pain in my 1880s house, unless I ran the ducting down the chimneys. Hmmm. Another advantage would be you could run it in a reverse cycle in summer and cool the house down. Selling that to MrsBJN might be difficult, she is very small C conservative, I couldn’t even convince her that we should swap out our dead gas range for one with an induction hob.
To retrofit a two storey house, the obvious set up would be a split system, with an air handler unit in the attic, with ducting to bedroom ceilings, and an air handler unit in the basement/crawl space (under floor space), with ducting to downstairs floors. Obviously the outside unit is outside, and supplies refrigerant to each of the two air handler units in small diameter pipes.

That replaces radiators with some air grilles in floors and ceilings, and gives separate control of upstairs and downstairs heating/cooling.

Wall mounted mini-spilts might make more sense downstairs in a house with a reasonably open floor plan, and would be necessary with a slab foundation.

User avatar
TopBadger
Snowbonk
Posts: 604
Joined: Mon Nov 11, 2019 6:33 pm
Location: Halfway up

Re: Solar Panels

Post by TopBadger » Sat Jan 21, 2023 8:21 am

lpm wrote:
Fri Jan 20, 2023 3:51 pm
TopBadger wrote:
Fri Jan 20, 2023 3:45 pm
My Solar + Battery is being installed next week - I'm looking forward to see how it goes in terms of generation...
It would be interesting to hear how the experience goes, with all the hassle of install and new wiring etc, as well as approximate prices and sizes?
I can answer the last part first... £13k for 5kWp system (12 panels), 4kW inverter and 6.5kWh battery. I had a number of quotes that were within several hundred pounds of each other, so whilst they were all more than I was expecting that seems to be the going rate here in the SE. The quote I chose was the most expensive of the bunch but specified equipment from companies I've heard of (which i figured could be important in trying to take up the 25 year panel warranty down the line if necessary).

Based on our annual consumption and energy costs the break even point is expected to be around 10 years.

Install apparently takes one day... we'll see. Should only be one cable run to contend with but may be awkward as the consumer unit is under a central staircase rather than on an outside wall.
You can't polish a turd...
unless its Lion or Osterich poo... http://dsc.discovery.com/videos/mythbus ... -turd.html

User avatar
lpm
Junior Mod
Posts: 5365
Joined: Mon Nov 11, 2019 1:05 pm

Re: Solar Panels

Post by lpm » Tue Jan 24, 2023 11:22 am

Has anyone done a heat loss calculation for their house?

Must be fairly straightforward - measure rooms, window sizes, estimate leakiness? Then shove it into equations?
⭐ Awarded gold star 4 November 2021

IvanV
After Pie
Posts: 1759
Joined: Mon May 17, 2021 11:12 am

Re: Solar Panels

Post by IvanV » Tue Jan 24, 2023 5:49 pm

bjn wrote:
Sat Jan 21, 2023 3:57 am
There has been speculation that gas isn’t taxed enough, while electricity is taxed too much and green levies should be shifted. If that were to happen, heat pumps would be much more competitive.
It has been said for a very long time by many sensible people. It keeps on getting mentioned, and then Nothing Is Done. I guess it is inconvenient for some people with the government's ear. It's like the GP's pension issue, which makes GPs avoid overtime and retire early, which the government has acknowledged for quite a long time now, and has still done nothing about it despite saying it would.

Be aware that the price of electricity is largely set by gas prices. So if gas is taxed, that increases the price of electricity. So it comes back and bites you on the bum in the electricity price too. But clearly to a lesser extent than currently.

User avatar
bjn
After Pie
Posts: 2416
Joined: Wed Sep 25, 2019 4:58 pm
Location: London

Re: Solar Panels

Post by bjn » Tue Jan 24, 2023 6:37 pm

Decoupling electricity prices from the marginal price of gas generation would be a very good idea. I'm not sure how that would look exactly, but what we have now is silly.

User avatar
nekomatic
Dorkwood
Posts: 1125
Joined: Mon Nov 11, 2019 3:04 pm

Re: Solar Panels

Post by nekomatic » Tue Jan 24, 2023 7:08 pm

lpm wrote:
Tue Jan 24, 2023 11:22 am
Has anyone done a heat loss calculation for their house?

Must be fairly straightforward - measure rooms, window sizes, estimate leakiness? Then shove it into equations?
It’s fairly straightforward to estimate leakiness (and insulation quality, and insulation value of windows) but rather harder to estimate them accurately enough to be very useful, I suspect.

There’s a simpler way of finding out the heat loss of your house though, which is to heat it up a bit, turn the heating off again, and record how fast it cools down. Shove that and the outside temperature into some equations and there you are. Now that connected things that can measure temperature are widespread, this isn’t too hard to do - for example.
Move-a… side, and let the mango through… let the mango through

IvanV
After Pie
Posts: 1759
Joined: Mon May 17, 2021 11:12 am

Re: Solar Panels

Post by IvanV » Tue Jan 24, 2023 7:20 pm

bjn wrote:
Tue Jan 24, 2023 6:37 pm
Decoupling electricity prices from the marginal price of gas generation would be a very good idea. I'm not sure how that would look exactly, but what we have now is silly.
It depends what you think is silly about it.

It is true that decisions about the mechanism for funding renewable energy were based upon what had long been the typical market parameters, and that the large change in the price of gas has made that look silly. There have also been windfall gains to people with gas production rights, which consumers are paying for, and which again got set without the expectation of recent events. Those gains can be taxed away when they are local, but are hard to address when they are foreign.

Markets tend to price things at the price of the marginal producer in the market. The market is very efficient in many ways and has done much to improve the efficiency of the sector. It just so happens that is usually gas is the marginal producer in the UK, and indeed EU, electricity market. Interfering in markets like that usually presents has unpleasant side-effects.

So recent events have made past decisions very unattractive. But be careful which past decisions you adjust. The electricity market wouldn't be my first point of complaint, at least on the basis of what I currently know.

But I'm prepared to hear alternative views and be persuaded otherwise.

User avatar
basementer
Dorkwood
Posts: 1470
Joined: Mon Nov 11, 2019 1:03 pm
Location: 5713, Aotearoa
Contact:

Re: Solar Panels

Post by basementer » Wed Jan 25, 2023 12:29 am

nekomatic wrote:
Tue Jan 24, 2023 7:08 pm
lpm wrote:
Tue Jan 24, 2023 11:22 am
Has anyone done a heat loss calculation for their house?

Must be fairly straightforward - measure rooms, window sizes, estimate leakiness? Then shove it into equations?
It’s fairly straightforward to estimate leakiness (and insulation quality, and insulation value of windows) but rather harder to estimate them accurately enough to be very useful, I suspect.

There’s a simpler way of finding out the heat loss of your house though, which is to heat it up a bit, turn the heating off again, and record how fast it cools down. Shove that and the outside temperature into some equations and there you are. Now that connected things that can measure temperature are widespread, this isn’t too hard to do - for example.
Heh.
There are also regional differences in government programs to financially support retrofitting improved home insulation...

“The UK is a leader in smart technology adoption but is lagging behind Europe"
Money is just a substitute for luck anyway. - Tom Siddell

User avatar
dyqik
Light of Blast
Posts: 6456
Joined: Wed Sep 25, 2019 4:19 pm
Location: Masshole
Contact:

Re: Solar Panels

Post by dyqik » Wed Jan 25, 2023 1:37 am

lpm wrote:
Tue Jan 24, 2023 11:22 am
Has anyone done a heat loss calculation for their house?

Must be fairly straightforward - measure rooms, window sizes, estimate leakiness? Then shove it into equations?
It's called a Manual J-Load calculation in the US, and you can find free online tools for doing it.

User avatar
lpm
Junior Mod
Posts: 5365
Joined: Mon Nov 11, 2019 1:05 pm

Re: Solar Panels

Post by lpm » Wed Jan 25, 2023 10:40 am

nekomatic wrote:
Tue Jan 24, 2023 7:08 pm
lpm wrote:
Tue Jan 24, 2023 11:22 am
Has anyone done a heat loss calculation for their house?

Must be fairly straightforward - measure rooms, window sizes, estimate leakiness? Then shove it into equations?
It’s fairly straightforward to estimate leakiness (and insulation quality, and insulation value of windows) but rather harder to estimate them accurately enough to be very useful, I suspect.

There’s a simpler way of finding out the heat loss of your house though, which is to heat it up a bit, turn the heating off again, and record how fast it cools down. Shove that and the outside temperature into some equations and there you are. Now that connected things that can measure temperature are widespread, this isn’t too hard to do - for example.
I've just done a quick estimate. 10 kW. Seems reasonable, google says the average UK house is 8kW.

I don't need anything accurate, it's not like I'm going to size and self-install a system. Just very advanced planning. When I get time I'll do a proper estimate for every room in the house.

I was considering leaving some rooms out. Like the spare bedroom which can be heated only when visitors are here. But on reflection a heat pump needs to be future proof for any subsequent house owner, who might return that room to regular use.
⭐ Awarded gold star 4 November 2021

User avatar
dyqik
Light of Blast
Posts: 6456
Joined: Wed Sep 25, 2019 4:19 pm
Location: Masshole
Contact:

Re: Solar Panels

Post by dyqik » Wed Jan 25, 2023 6:44 pm

nekomatic wrote:
Tue Jan 24, 2023 7:08 pm
lpm wrote:
Tue Jan 24, 2023 11:22 am
Has anyone done a heat loss calculation for their house?

Must be fairly straightforward - measure rooms, window sizes, estimate leakiness? Then shove it into equations?
It’s fairly straightforward to estimate leakiness (and insulation quality, and insulation value of windows) but rather harder to estimate them accurately enough to be very useful, I suspect.

There’s a simpler way of finding out the heat loss of your house though, which is to heat it up a bit, turn the heating off again, and record how fast it cools down. Shove that and the outside temperature into some equations and there you are. Now that connected things that can measure temperature are widespread, this isn’t too hard to do - for example.
You probably want to do this experiment at night, btw, and in "normal" wind and cloud cover conditions/with curtains closed.

Solar gain is a big part of a Manual J load calculation, and draughts and IR losses from windows are important at night.

Post Reply