Best investments to leverage the output of a small 2.3kWh PV array to reduce household running costs?

[Lull]

We are in the middle of a deep eco/traditional retrofit of a small mid-victorian terrace in Bristol. We have been going for a 'fabric first' breathable approach with Hempcrete internal wall insulation to improve the thermal fabric of the building (partially completed)

A 2.3kWh south-facing Solar system has recently been installed under a council grant scheme, with a Solis inverter & over the first 32 days since it's install, it has generated 290.12kWh total (9.07kWh per day). I am keen to maximise this modest system with sensible investment to minimise the impact of the running costs going forward. It is likely I will rent some rooms out in the short term whilst I travel.

The property has been rewired with a modern consumer unit & the lead water main has been replaced with a 32mm MDPE pipe.
The bathroom is being moved to the front of the house and the 2009 combi boiler in a rear bedroom is on its last legs - it needs to be moved anyway & an unvented mains pressure cylinder would be preferable.

I'm therefore considering investing in an Eddi to divert solar to an unvented cylinder (ideally needs to be short to fit underneath future loft stairs) This will partly be to monitor generation usage/export better etc, although also considering the open-source approach via EmonPi since I have been burned by proprietary tech being unsupported after a few years too many times!

I am also considering an ASHP in future, although that would need to wait until the limcrete floor & underfloor heating is installed next year some time. I worry about the very high install & (debatable) running costs of this, so another alternative would be a cheaper gas system boiler (maybe hydrogen ready?) or a pellet boiler stove in a living space.

Another consideration is whether a battery storage system, ideally with UPS functionality would be a worthwhile investment - especially given current crazy price rises and possible power cuts (plus I have always liked remaining as flexible/independent as possible in one way or another!) What battery options are the best? I considered Puredrive due to the number of cycles, LifePo4 tech, UPS functionality, but I've heard good things about GiveEnergy. What about Pylontech? Which AC inverter? Tesla Powerwall seems to open up access to good export tariff rate, but I can't work out whether that investment would be returned with such a small PV system. I am currently with Bulb, but considering moving to Octopus if possible since I like their approach.

Also does anyone know if you can get a check meter installed , or keep the old meter when getting a smart meter? Currently I don't have one since I have heard so many horror stories with them miscalculating usage - I'd rather pay my electrician friend a little extra to fit an export/import meter of my own whilst doing other works to verify the smart meter readings if there's any concerns arising.

Currently the house only has one careful occupier (my 'housemate' and fellow renovator) and Elec usage is ~2600kWh p/y and Gas is ~7000kWh p/y (more like 20000kWh when I was there too since I struggle to stay warm in winter & have the heating on constantly). In future this would likely increase substantially if I had 3-4 occupants living there who may not be particularly careful with usage.

The budget is not huge but I want to get best 'value' for a modest approach.

 

[binky]

hot water is probably better than a battery with a small Pv system, as this directly saves from gas bill.

Personal opinion, insulate under the floors rather than UFH, and if you can get a grant, external wall cladding is brill! If you can get the inuslation right, it'll save a fortune on heating. I fitted 1 inch of polystrene internally to my bathroom walls which is in a drafty tennement - what a difference!

 

[Lull]

hot water is probably better than a battery with a small Pv system, as this directly saves from gas bill.

Personal opinion, insulate under the floors rather than UFH, and if you can get a grant, external wall cladding is brill! If you can get the inuslation right, it'll save a fortune on heating. I fitted 1 inch of polystrene internally to my bathroom walls which is in a drafty tennement - what a difference!

Cheers! The floors will be insulated with Glapor/foamed glass. The original wooden floor has been taken up due to extensive settlement/rot and damp issues. We trained up in Hempcrete installation which remains vapour permeable - to avoid the need for PIR board insulation which can cause damp after a few years in solid-walled properties. Our u-values for the walls and floor should be pretty good and we have paid good attention to air-tightness as well.

I hear you about the hot water diversion! I think I was leaning that way anyway.

 

[Chrisbee]

Note on hot water diverters:

Diverting 1kWh of solar to heat my water saves me 5.5p of gas. If it is exported to grid I get 5.5p for it.

But if it is used to charge my battery and I consume it as electricity later, that saves me 21.5p.

 

[Murdoch]

Using a divertor to the immersion makes good sense as its far cheaper to implement than batteries

 

[Lull]

Diverting 1kWh of solar to heat my water saves me 5.5p of gas. If it is exported to grid I get 5.5p for it.

But if it is used to charge my battery and I consume it as electricity later, that saves me 21.5p.

Really good to know & well worth bearing in mind. I guess the question then is what the payback time might be on a battery system & I wouldn't know where to start with that calculation.

What battery setup do you use? What diverter do you use for your water/battery and does it work smoothly/remain tweak able depending upon usage needs?

 

[Murdoch]

If the top of my head

If a battery pack costs say 4k to install, then devide 4k by 0.3 = about 13500

So you would need to save 13500 kWh before you broke even. Personally I think you would struggle to do that

 

[sparky308]

Battery pack doesn't cost £4k. 3.5Kwh Pylontech currently available at £1700. My panels are on a southeast facing roof and in the current glorious sunshine the batteries are fully charged by early afternoon. Generation drops off considerably in late afternoon due to the panel orientation, but the batteries power the house right through the evening.

 

[Lull]

Battery pack doesn't cost £4k. 3.5Kwh Pylontech currently available at £1700. My panels are on a southeast facing roof and in the current glorious sunshine the batteries are fully charged by early afternoon. Generation drops off considerably in late afternoon due to the panel orientation, but the batteries power the house right through the evening.

Sounds great! Whats the rest of your setup like? What inverter did you go with? I'm guessing by your name you might have installed it yourself... but any ideas on probable approx cost to supply/fit a similar system, just as a ballpark?

 

[Murdoch]

Battery pack doesn't cost £4k. 3.5Kwh Pylontech currently available at £1700. My panels are on a southeast facing roof and in the current glorious sunshine the batteries are fully charged by early afternoon. Generation drops off considerably in late afternoon due to the panel orientation, but the batteries power the house right through the evening.

My post above said cost to install, not to buy. And that was cavaeted by “say”

 

[sparky308]

Solis hybrid inverter, 10 x 400w panels. I used an MCS certified company to install. I'm interested to know if a hot water diverter e.g. Eddi will co-exist happily with the batteries, opinions seem to differ. I haven't got a smart meter because I can't see the system generating enough extra energy to export much. So long as it can charge the batteries and run the house day by day it's doing its job.

 

[binky]

Solis hybrid inverter, 10 x 400w panels. I used an MCS certified company to install. I'm interested to know if a hot water diverter e.g. Eddi will co-exist happily with the batteries, opinions seem to differ. I haven't got a smart meter because I can't see the system generating enough extra energy to export much. So long as it can charge the batteries and run the house day by day it's doing its job.

It should be fine, personally I like Solic as they are cheaper. Question is which works first, I suspect the batteries will charge first with a hybrid inverter, so I would wire the immersion controller in parallel with existing immersion controls so you can still use the immersion if necessary.