Solar Panels UK - is it worth it?

[Mrklaw]

Well, technically a heatpump.will.use ~4 x less of that E7 power

Need to be careful introducing cold air where it's not expected? Could cause condensation where it's not wanted? No expert tho, just a thought.

right but if you're talking maybe 5-6kwh electric for a hot water tank per day, and you have solar (as in the example post from the person talking about an ASHP HW tank), then its also a question of
- 5kwh electric a day would only be maybe 1.5kwh electric for a HP to generate the same HW.
- but that 5kwh is 100% solar generated in summer months (either direct or from a battery), 80% generated in shoulder months, so its back to only winter.
- if I also have a ToU tariff the cost per kwh is much lower and therefore effective savings even lower.
- additional complexities and possible need to yearly service a HP to maintain warranty may erode savings to the point a simple cylinder is no more expensive in practice

 

[Avendit]

right but if you're talking maybe 5-6kwh electric for a hot water tank per day, and you have solar (as in the example post from the person talking about an ASHP HW tank), then its also a question of
- 5kwh electric a day would only be maybe 1.5kwh electric for a HP to generate the same HW.
- but that 5kwh is 100% solar generated in summer months (either direct or from a battery), 80% generated in shoulder months, so its back to only winter.
- if I also have a ToU tariff the cost per kwh is much lower and therefore effective savings even lower.
- additional complexities and possible need to yearly service a HP to maintain warranty may erode savings to the point a simple cylinder is no more expensive in practice

Agree, do need to do the sums. I just have a kneejerk aversion to direct heating now.

Also solar collectors are way more efficient than PV if you want heat.

 

[thewishy]

I had a long conversation at fully charged live. The conclusion was that using the existing duct work was inadvisable due to condensation, which the existing ducting won't be designed to deal with. And that the flow temp of the existing aquaair unit meant that I'd need a more expensive Hi-Temp ASHP with poorer coop than A2A.

Likely it'll be a shootout between a sunamp and a ASHP.
+ASHP - Lower usage, but we're on TOU, so that might not translate to huge savings. It depends on how TOU progresses over time, right now, we're in the minority charging overnight, but as more people buy EVs, rates will possibly increase
+ASHP - 700w load, which will easily be managed as part of the "house load", whereas 3kw for immersion would need to be more or less the only thing running, and likely supported by battery, or be attached to an Eddi (and I just lost half of the savings).
+ASHP - won't hit the 100a fuse load calculations nearly as badly
-ASHP - Given the charge times, might need to use the immersion anyway to keep within the 4hr window. We're not high hot water usage though
-ASHP - Sealed tank, so would technically need annual inspections
-ASHP - About a grand more expensive than sunamp
-ASHP - Space, although we did have a tank where the boiler is now, and we should be able to make it fit

Don't have any space for solar collectors, the whole roof is PV covered now, and that's still only 3.95kWp and covers about 2/3rds of our usage. We do dump a moderate amount in the car, and it would be nice to have somewhere to dump juice when the car is away. (Or buy a second EV!)

My gut feel is "Go efficient", I don't have much excess solar that I'm getting paid a pitiful 4.1p for, and in the long run energy is expensive. Maths need to be done, but that wouldn't be a swap for another year or two. Other gut feel is not mixergy, because anything that isn't locally controllable isn't welcome in my house unless there are zero alternatives.

 

[ringi]

Well, technically a heatpump.will.use ~4 x less of that E7 power

But it takes a very long time to recover the additional cost of a heatpump and a heatpump is not likely to last 30+ years with only very cheap/simple element replacement. I expecting within a few year there to be times most days with very cheap cheep (low CO2) electricity that can be stored as heat in a E7 hot water tank.

Need to be careful introducing cold air where it's not expected? Could cause condensation where it's not wanted? No expert tho, just a thought.

I was assuming a AC unit would be put in the rooms that will be cooled with the existing hot air duct only being used to heat other rooms hallway, wc, etc.

But if the duct is large enough, then few likely issues putting cooled air into it, provided the air is not cooled below about 18c. The UK dew point on days we need AC is normally well below a reasonable target for comfort cooling, but that depends on being able to move enough air, so the air in the ducts is never much below target temperature.

 

[ringi]

I had a long conversation at fully charged live. The conclusion was that using the existing duct work was inadvisable due to condensation, which the existing ducting won't be designed to deal with. And that the flow temp of the existing aquaair unit meant that I'd need a more expensive Hi-Temp ASHP with poorer coop than A2A

I assuming A2A wall units in the rooms that need most cooling and that a A2A duct unit will be used to feed the duct to heat other rooms. (I would not consider a A2W unit to heat air that is in a duct as there are A2A units designed to do it.)

Another option is to fit a MVHR unit, with the preheated air going into the existing ducts. (I assume the main duct could be connected to from the loft) Or just use the large existing ducts to run new MVRM small ducts to each room. This would tend to move heat between the large rooms with A2A units and the other spaces.

 

[yessuz]

so interesting...

I have 8.3 kwp system (20 x 415 east/west)
originally came as growatt SPH3000 + SPH4000 inverters. when I look at all stuff delivered - it is SPH6000. It is maxed at 8kW, and I am aware that I will not be ale to get whole 8 kw out of my system anyway.

but since instead of 2 inverters I will get 1 - it means the overall cost should be reduced.

what I see online is:
SPH3000 - ~1200 gbp
SPH4000 - ~1300 gbp
SPH6000 - ~1400 GBP.

so I would presume that I should be ~1000 better off :/

I think SPH6000 will cover whole system anyway

 

[thewishy]

But it takes a very long time to recover the additional cost of a heatpump and a heatpump is not likely to last 30+ years with only very cheap/simple element replacement. I expecting within a few year there to be times most days with very cheap cheep (low CO2) electricity that can be stored as heat in a E7 hot water tank.

Looks like we used 50kWh of gas last month, which will all be DHW.
I need to add 1.6kWh/day for thermal losses with the new system, total 100kWh/month, 1200kWh/year. Total £120 / year thermal vs £40 ASHP
That just about scrapes a payback in 12 years if no parts need replacement. Also suspect that in 15 years if parts are needed, it might be "New tank time" rather than "new element time". I'll have to switch to twice daily showers to make the economics work

I was assuming a AC unit would be put in the rooms that will be cooled with the existing hot air duct only being used to heat other rooms hallway, wc, etc.

But if the duct is large enough, then few likely issues putting cooled air into it, provided the air is not cooled below about 18c. The UK dew point on days we need AC is normally well below a reasonable target for comfort cooling, but that depends on being able to move enough air, so the air in the ducts is never much below target temperature.

I assuming A2A wall units in the rooms that need most cooling and that a A2A duct unit will be used to feed the duct to heat other rooms. (I would not consider a A2W unit to heat air that is in a duct as there are A2A units designed to do it.)

Another option is to fit a MVHR unit, with the preheated air going into the existing ducts. (I assume the main duct could be connected to from the loft) Or just use the large existing ducts to run new MVRM small ducts to each room. This would tend to move heat between the large rooms with A2A units and the other spaces.

Rather the complicate the design, I could keep the "blower" element of the existing J&Sm Aquaair unit, and use that to balance out the heating across the house. Cooling is really a luxury thing for rooms we spend a significant time in.
We can also look at radiant heat for the low use rooms too, but my immediate feel is "inefficient"

 

[WannabeOwner]

One option is to use a duct AC unit to feed into your existing hot air duct system rather then putting separate AC units to cover every space.

Need insulated ducting if introducing cold air (into the ducts) otherwise the first few metres will be sufficiently cold that it will cause condensation.

Another option is to fit a MVHR unit, with the preheated air going into the existing ducts.

Heated air would be OK, but MVHR will need an air-tight building to start with (otherwise the exhaust air is a lot less than 100% of the incoming, and the heat-recovery will be very disappointing as a consequence, and thus the make-up heat requirement would be the same as in a drafty building )

What we needed to do was the build the buildings better (more air-tight / better insulation) in the first place, but we still don't have building regs that are close to what is needed.

Also solar collectors are way more efficient than PV if you want heat

I've had solar thermal (for DHW) for 15-ish years. Problem with it is that it produces heat that has to go somewhere, so the snag is what to do with it when the hot water tank is up to temperature. Can just let it expand and replace itself with steam! but personally I think that approach, and the stresses it causes, is undesirable. (I have an accumulator, and can dump excess heat into pool) If you've got a swimming pool, and can dump the heat there then you are good to go although you may find your pool gets far too hot in summer ... you can dump it to your radiator circuit of course Actually the water temperature around the Rads won't amount to much, but any room-heating in Summer is probably undesirable.

In that vein I wouldn't install solar thermal for Pool heating (I have that, but don't use it any more). Whilst the per-unit-area collection of solar thermal is good I would prefer to have Electricity and a Heat Pump. Heat the pool in the early part of the season using the Grid, use PV thereafter, and in mid Summer when no pool heating required use the electricity for something else. Grid again at the end of the season. Much more flexible the Solar Thermal which can only produce heat, and excess heat is a problem to solve.

 

[RedMod3]

What Brand do you have installed? Thanks.

Toshiba one 7.5kW unit drives 3 units and a 5kW unit drives the other 2. I'm running with 2/5 running now as it is hot, but cool inside.

 

[ringi]

but MVHR will need an air-tight building to start with

Not true, I installed MVHR in our home and it greatly improved our qualify of life as it removed all issues with mold etc.

 

[ringi]

Looks like we used 50kWh of gas last month, which will all be DHW

If using a system boiler, other then when running CH, the heat loses from the pipework between the boiler/tank can be very high.

 

[WannabeOwner]

Not true, I installed MVHR in our home and it greatly improved our qualify of life as it removed all issues with mold etc.

Surely that is ventilation, rather than heat recovery?

You can't get heat recovery if the building leaks ... well not "efficiently"

 

[WannabeOwner]

Toshiba one 7.5kW unit drives 3 units and a 5kW unit drives the other 2. I'm running with 2/5 running now as it is hot, but cool inside.

Thanks is that the Haori like @PITA? I think that looks nice on the wall (if any of them do ...) and seems very quiet

 

[ringi]

Surely that is ventilation, rather than heat recovery?

You can't get heat recovery if the building leaks ... well not "efficiently"

Recovering (for examplep 50% of the heat to preheat the incoming air is better then no heat recovery. Preheating the incoming air can advoid lots of damp problems.

 

[Avendit]

Surely that is ventilation, rather than heat recovery?

You can't get heat recovery if the building leaks ... well not "efficiently"

I need to find the sources again, but I did read that MVHR is more effective at low airtightness levels than sap gives it credit for. My suspicion is that it depends on your exposure and local average wind speeds.

OTOH, more air tight is still better, what ever your heating source and ventilation approach is.

 

[thewishy]

If using a system boiler, other then when running CH, the heat loses from the pipework between the boiler/tank can be very high.

Combi

 

[WannabeOwner]

I did read that MVHR is more effective at low airtightness levels than sap gives it credit for

Would be interesting to see what the Inlet / Outlet temperature differences are on a really cold (or hot ) day on MVHR in a somewhat leaky house.

I can't get my head around comparing a draughty house (allowing in external air) or MVHR in a leaky house (forcing air in under pressure, such that, presumably?, more of it will leak out than if the house did not have MVHR)

Retro-fit MVHR completely fixed our mould problems (and the condensation running on the windows) in the old part of our house. We made insulation improvements on cold bridges at the same time, but we are fortunate that the house is 60's poured concrete and was consequently very air tight to start with.

In the new Passive Haus part some vanity design elements <sigh>, and also that the new part is open to the old part, meant that the MVHR there is not perfectly balanced and the heat loss is noticeable. But still, our winter heating fuel bill is small.

 

[ringi]

forcing air in under pressure, such that, presumably?, more of it will leak out than if the house did not have MVHR

If the MVHR is reasonably balanced and there are large enough gaps under doors, then a MVHR system will not increase the pressure in a building.

 

[DaveNN]

Combi

Or do what I have.
Combi for the kitchen, cloak and utility room..but have an UV cylinder for the bathrooms and outside mixed feed for the pressure washer...with the cylinder directly next to the boiler.

 

[yessuz]

guys, is there any limitation on cable lengths or installers are just morons and want to escape the easiest and cheapest way possible?

they proposing cable routing in the middle of the house, like some stupid scar, instead of routing cable under ground for additional 6 meters... wtf?!