PV only, or Solar Thermal too?

valiant24

Hi

We're building a new house in Somerset. It'll be very well-insulated and energy-efficient ; almost a "passive house" but not quite ...

It'll have an air pump.   There are two options for heating: StoreEdge 5.3kW Solar PVs only; or 3.9 PV and Solar Thermal.  There will be a 10kWh StoreEdge battery.  The PV-only option is about £9k, and the PV-plus-Thermal £15k.   Can't really see the point of Solar Thermal myself on these numbers.

I wondered if anyone else has any experience, good or bad, and/or advice?

Thanks
V

PS One specification from the architect is MVHR (Mechanical Ventilation with Heat Recovery). Which is the best forum to ask about this on please? 

ABrass

PV only, thermal doesn't really make sense these days as you get more out of putting additional PV panels up instead.

I'm guessing both numbers there include the battery?

I assume you're out of roof space with the 5.3kW?

valiant24

ABrass said:

PV only, thermal doesn't really make sense these days as you get more out of putting additional PV panels up instead.

I'm guessing both numbers there include the battery?

I assume you're out of roof space with the 5.3kW?

No the battery is another £7k.
Yes there's only enough roof space for the 5.3kWh PV; or the 3.9 and the Solar Therm.

ABrass

That's expensive. £9k for a 5kW system is very high. This isn't an in-roof system?

At the moment retrofit installation of panels is up to £1.5 per W for solar edge, so a 4kW system can be found for £6k. Adding more panels generally should bring the price per W down.

If you're building it into the house then it should be cheaper than that. The Storedge batteries are expensive for what you get, I'd go for a different model. I believe the solar edge kit works with Pylontech which are cheaper and widely used.

70sbudgie

I looked at solar thermal before I looked at PV, but didn't go for it because I couldn't make the finances work (our DHW usage was too low for the payback to be even vaguely sensible). When I did go for PV, I looked at solar thermal again, but even with sharing some of the general costs (scaffolding etc), I still couldn't make the finances work. Then I did the calculations for a solar diverter (using excess PV generation to heat DHW) and by comparison with the solar thermal, is was a no brainer (payback 1-2 years).

Alnat1

Have a good think about how much hot water you use on a daily basis. How many showers/baths each day? Most appliances are now cold fill (washer/dishwasher) and if you wash up at the sink you can always boil a kettle when needed. 

We fitted solar last March and decided for now to continue heating our tank by gas, the excess solar in summer earned more going back to the grid (Octopus prices for SEG are decent). If prices change over time we can fit a solar diverter when it makes economic sense.

valiant24

70sbudgie said:

I looked at solar thermal before I looked at PV, but didn't go for it because I couldn't make the finances work (our DHW usage was too low for the payback to be even vaguely sensible). When I did go for PV, I looked at solar thermal again, but even with sharing some of the general costs (scaffolding etc), I still couldn't make the finances work. Then I did the calculations for a solar diverter (using excess PV generation to heat DHW) and by comparison with the solar thermal, is was a no brainer (payback 1-2 years).

Thanks.  What is "DHW" please?

valiant24

Alnat1 said:

Have a good think about how much hot water you use on a daily basis. How many showers/baths each day? Most appliances are now cold fill (washer/dishwasher) and if you wash up at the sink you can always boil a kettle when needed. 

We fitted solar last March and decided for now to continue heating our tank by gas, the excess solar in summer earned more going back to the grid (Octopus prices for SEG are decent). If prices change over time we can fit a solar diverter when it makes economic sense.

We're the last people in England who like baths, so are already wondering if the specified 230 litre tank is big enough.

We're out in the sticks so there's no gas (or sewerage!).  It's electricity or nothing sadly ... unless we want an oil boiler, which we do not.

Reed_Richards

valiant24 said:
What is "DHW" please?

Domestic Hot Water i.e. what comes out your hot taps.  I guess it's a plumbers' acronym.

70sbudgie

valiant24 said:

70sbudgie said:

I looked at solar thermal before I looked at PV, but didn't go for it because I couldn't make the finances work (our DHW usage was too low for the payback to be even vaguely sensible). When I did go for PV, I looked at solar thermal again, but even with sharing some of the general costs (scaffolding etc), I still couldn't make the finances work. Then I did the calculations for a solar diverter (using excess PV generation to heat DHW) and by comparison with the solar thermal, is was a no brainer (payback 1-2 years).

Thanks.  What is "DHW" please?

Sorry, Domestic Hot Water.

I should add, that having done the calcs for solar thermal vs solar pv with diverter, I still haven't fitted my diverter. This is because with E-W panels I wasn't sure if I'd generate enough excess solar to make it worthwhile. Once I had a year of data, it was clear I would, but the outgoing Agile prices made exporting PV and burning gas the more cost effective solution.

However, if you don't have an alternative fuel source to electric, the calculation use vs export wouldn't be relevant to you.

But it will probably make batteries more viable, as this will also allow you to maximise a ToD (time of day) tariff and buy electricity more cheaply.

I would also suggest checking out the various discussions on this board about heat pumps, including the one on hot water cylinder with its own heat pump. This will enable you to make much more efficient use of your electricity. As long as the initial cost isn't prohibitive.

valiant24

Thanks everyone!   Which is the right forum for a question about MVHR?