Solar, battery, worth it for partly occupied house?

AndrewKnight_2

Questions for the group. I'm lucky enough to have a second house (before you get jealous, it's in that well-known Northern resort of Bolton). It's occupied around 30% of the time. I need to fit an EV charger at the house. So the questions are:

• Given the occupancy, is it worth fitting a battery?
• Given the occupancy, is it worth considering solar panels? For context, the roof is the classic Lego house roof, with slopes on all four sides and no gables. The front of the house faces just West of South across a road, and the more Westerly side is not overlooked. I would guess that we could fit ~6 panels on the front and ~4 on the more West-facing roof.
• Again, because of the occupancy, we have not considered an ASHP. The gas boiler is only a couple of years old, so it is not due to be replaced, but we would welcome any thoughts.

NedS

Regardless of the occupancy, I'm guessing you will probably want to approach it from an annual usage / cost basis. I'm not sure the occupancy is really that relevant - we are here all day every day, and still only manage to consume ~30% of the solar we generate in summer, so the vast majority of solar you generate will be exported anyway once your continuous background usage has been covered (and I expect this figure to be worse for those out at work all day).

Regarding the different roof aspects - each will benefit from being on a different MPPT string, so you'd ideally want an inverter with a minimum of 2 MPPTs for two roof aspects, or 3 if you plan to use the third aspect. An alternative is to consider micro-inverters such as those from Enphase, but they are expensive and have limited output so you will not benefit from the full output of modern ~450W panels.

If the numbers stack up financially, then the occupancy is irrelevant.

Let's see what others think

Screwdriva

Given the low usage, I would recommend skipping the battery. Battery warranties are shorter, prorated and they are really pay for themselves only with heavy consumption (in excess of 4000 kWh per year). If you suffer from frequent blackouts, then a battery offering whole house backup becomes invaluable.

I recommend installing panels on any West/ East and South aspects only. You can do this easily with a SolarEdge system (with optimizers).  A ball park cost for SolarEdge system with 14 panels is around £6k installed with a 20 year warranty on the inverter. 

QrizB

I generally agree with everyone else 🙂

If solar PV can make financial sense in a field or on the roof of a barn, it should be viable for a second home.

A battery is less likely to be worth it, unless you're looking for resilience from power cuts or planning to hide out during the zombie apocalypse.

Reed_Richards

I think EV chargers are a waste of money for many people.  A granny charger with, if necessary, it's own dedicated circuit is a fraction of the cost and could meet your needs almost all of the time.  The exception might be if the journey to Bolton uses up mot of your EV battery and you don't stay long enough to recharge it again at the 2.35 kW a granny charger will give you.  Possibly you don't, in which case there might be a stronger case for a dedicated EV charger in your second home than there is to have one in your first home.

In my case, last week I did have to charge my car for about 8 hours at peak rate to build up enough charge for a second trip shortly after the first one.  So that might have cost me about £4 more than if I could have charged it overnight.  But something like this happens maybe 3 times a year so I could save myself £12 a year by shelling out £800 or more to have an EV charger fitted.  Instead I paid £110 for a granny charger and I already had a dedicated circuit to the charging socket.   

AndrewKnight_2

Thanks all, I need to think more about solar and battery and get some actual costings.
On the charger front, we make the trip about three times every two months and stay for about a week at a time. So that's eighteen trips a year. We would pretty much discharge the battery between the journey up (~200 miles) and running around. On a rough calculation, we would save about £250 pa by having a charger, so it would pay for itself in three to four years.
On a related note, can anyone recommend installers in the Bolton area?

Screwdriva

Once you crunch the numbers against a good export tariff you will see that PV only systems have a ~15% return on cost annually. The more panels you can fit, the better this gets (& vice versa).

I use an extremely well reviewed (& liked) installer based out of Leyland. Feel free to reach out if you’d like an intro! 

Martyn1981

AndrewKnight_2 said:

Thanks all, I need to think more about solar and battery and get some actual costings.
On the charger front, we make the trip about three times every two months and stay for about a week at a time. So that's eighteen trips a year. We would pretty much discharge the battery between the journey up (~200 miles) and running around. On a rough calculation, we would save about £250 pa by having a charger, so it would pay for itself in three to four years.
On a related note, can anyone recommend installers in the Bolton area?

That makes sense, but what Reed_Richards was suggesting is that you might not need a 7kW charger, as you could just slowly charge it back up at ~2kW whilst you are there. We got BEV's during Covid (and just before) and the installation of a fast charger had to be delayed, so we lasted about a year with a granny charger, and it was fine.

But, I would suggest limiting power just a bit, to avoid the plug, socket and cable getting hot. So if you will be charging for more than a few hours, then consider dialling back the amps, if the BEV does this. Teslas let you choose 5-10A (and upto 32A on a fast charger), so I choose 8A. We had an older IONIQ and that could select 50%, 75% and 100% for both a granny and rapid charger, so again on the granny cable, I would select 75%. Also worth doing, or IMO essential, if using an extension cable, which on a few occassions we've done. And then, also ensure it's a shorter extension cable, 13A, and fully unwound.

QrizB

Worth noting there's now a specific, er, spec for EV charging 13A sockets. If you're planning to use a Mode 2 charger (a "granny charger") regularly it might be worth having one installed.

Details here (this isn't intended as a recommended supplier):

https://toughleads.co.uk/products/ev-socket

More technical info from the IET here:

https://electrical.theiet.org/bs-7671/faqs/electric-vehicle-charging-installations-faqs/

Or you might prefer to have a 32A industrial socket installed, which would let you use a 7kW Mode 2 charger - uncommon, but available.

Qyburn

You can also get  chargers that plug into 16A or 32A "Commando" sockets. 

QrizB

Qyburn said:

You can also get  chargers that plug into 16A or 32A "Commando" sockets. 

I might've mentioned those too

For the OP, we mean this sort of thing:
https://evonestop.co.uk/products/ev-charging-cable-type-2-to-32a-commando-7-2-kw-5-metre-mode-2

(Just an example, not a recommendation.)