Putting the pieces all together...

[KAScot]

Hi guys, 

 

Really fascinating forum, I've enjoyed trawling through old posts, so much knowledge here. 

 

I'm considering replacing my 11 year old Worcester Bosch gas combo boiler but retaining the pipework and radiators, if possible, but aware radiators may need to be oversized. I'm motivated to do my bit for the planet but also to secure future energy needs. 

 

I live in a late 1950s detached house, solidly built and extended to 150m2 across 1 1/2 storey's over the years. House is pitched clay tile roof due South facing in Dundee, Scotland, which is supposedly very sunny! I've had loft and cavity insulation done but floor insulation is on my to do list. Have a large garden but not big enough for a GSHP. 

 

I work permanently at home, so house is pretty much occupied 24/7 by any of our family of 4 people, inc 2 young kids who like nightly baths and warm bedrooms sadly. Due to this our energy bills are quite high, about 22000 kWh gas for heating (nightly cooking inc) plus about 3000kWh for DHW. Additionally, electricity needs are about 3000kWh, although I've recently bought an EV (8k miles a year) and have a 7kW sauna so this could easily double to 6000kWh. My EPC says 18000kWh heating and 2500kWh hot water demand, however the heating in particular is very underestimated. 

 

So, on to renewable technologies, currently in Scotland there is a grant of 75% on heat pumps (up to £7.5k) and solar thermal (up to £3.75k) but sadly nothing on solar PV, I've missed the boat there. RHI can also be applied on ASHP but the impact is relatively minor over 7 years, returning an additional £1k net. 

 

After researching I'm tempted to get supplier quotations for an ASHP and solar thermal system. I'm aware that solar thermal is a one trick pony but the fact I could purchase it for circa £1k net cost after grant means it could make financial sense. I'd also have concern about splashing out £5k on a solar PV system as I don't think I'd ever make the additional £4k back. In my head the solar thermal allows me to limit use of ASHP from Apr - Oct when heating demands are negligible and provide a small amount of top up heat to ASHP in winter. 

 

I'd really love your feedback on all of this to understand if I'm missing something. Alternatively if there is something clever I could do with hardware or controls to integrate ASHP and solar thermal systems to maximise their relationship and efficiencies that would be appreciated. I also heard about Nibe combined solar PV and thermal panels but these seemed aimed at GSHP. 

 

Thanks, 

 

Kevin

 

Edited October 15, 2021 by KAScot

[SteamyTea]

1 hour ago, KAScot said:

about 22000 kWh gas for heating

 

1 hour ago, KAScot said:

My EPC says 18000kWh

Find out why such a difference.  It may be that you like a hotter house, or you have an underperforming house.  The EPC assessor probably used default values for when the house was built i.e. no insulation, single glazed windows, high air infiltration.

 

Solar Thermal, is not only a 1 trick pony, it also needs servicing.  PV does not.

The electricity from the PV can be used for many different things, including warming up the sauna (though a simple, small greenhouse would almost get as warm).

So rather than try and integrate two wet systems to work with each other, and in reality, there is little difference between an ASPH and a GSHP, let PV power the ASHP during the day.  Or charge the car, that will give you the best return (compared to an ICE powered one).

 

All this RE business is really playing with averages and probabilities i.e. Most likely time of maximum generation is between 10AM and 2PM, the weekly mean generation will drop in the winter, and rise in the spring, peaking in the summer.  Take advantage of that, don't think that a box of electronics will make it produce more than it can.

 

But work on the house first and reduce those losses, then look at what you can buy the kit for.  Subsidies and grants have skewed the market.

[KAScot]

I suspect it's being based at home all the time and a hotter house at night for example as wife likes kids to have big baths and hot rooms etc. No doubt there are some other improvements to be made and I'll look into that. 

 

I would rather have PV to be frank, but it's £5k v £1k and I'm not convinced I'd ever make that £4k difference back. The car seems to cost peanuts to charge at night with Octopus Go coupled with free charging for residents in my city whilst out and about, plus we don't actually use it that much. The sauna is used mostly in the winter after 8pm, so sadly it wouldn't help there either. I just can't see solar PV working well for me (and worth the additional £4k) without battery storage, but that's another £5 - 7k with no grants. 

 

I'd probably just go for ASHP if there were no other grants around but it seems for only £1k extra the solar thermal would likely pay itself back in 10 - 12 years so it doesn't seem much extra for the additional option it brings?

Edited October 15, 2021 by KAScot