PV and/or solar water on part-time occupied house

L1011

I'm about to buy / take ownership of a family holiday home that is currently unused, but which I intend to use fairly often. It has a decent amount of south facing roof, which I'm hoping to put skylights through to provide some warmth and light to the house (its slightly dug in to a hill! back windows bring little light), but this would still leave a lot of space for solar of either kind. Bungalow with an extension so probably has 3x the roof area of a modern semi D.

I don't think PV makes financial sense for the time I'd use it with no or low FIT - but clearly worth investigating if there is a decent FIT

Is it safe to have solar water heating mostly unused water? 60 days a year would be an optimistic estimate of how often it'll be used, really; and some of those will be around Christmas with minimal benefit. Mid week in peak Summer it will frequently be unusued.

House is Really Quite Old but has late 1990s wiring and a new mid 00s roof (timbers included), there are not many quick wins energy wise left as it has a condensing boiler, double glazing and attic insulation

I'd estimate daytime energy use when unoccupied to be well under 1kW - fridge/freezer not being opened, router and some IoT kit.

Jonathan

https://www.boards.ie/discussion/2058218816/pv-and-or-solar-water-on-part-time-occupied-house

I have both Solar PV and Thermal on my house.

Installing Solar Thermal is an option, but I think the low occupancy rate will be a problem. You need to avoid the gylcol (fluid which is pumped around) stagnating (overheating and decaying). You can avoid this by either installing a dedicated heat dump radiator, or wire the thermal controller into the heating system to dump surplus heat from the cylinder using the existing radiators (a bit more tricky if the system is zoned).

To be honest, I'd just install PV. It will cover the water and daytime load when you aren't around. FIT (whenever it arrives) will pay a few cents towards the night time electricity bills too.

MAULBROOK

https://www.boards.ie/discussion/2058218816/pv-and-or-solar-water-on-part-time-occupied-house

Go with the Solar pv only.

the_amazing_raisin

+1 for the solar PV, less chance of something going wrong while you're away. Use the FIT to pay for the electricity you use while there

Might be best to not bother with a battery of its going to be sitting around for a long time unused

MAULBROOK

https://www.boards.ie/discussion/comment/118200857#Comment_118200857

A small battery would be no harm

the_amazing_raisin

https://www.boards.ie/discussion/comment/118203412#Comment_118203412

True, but it could be sitting for a long time without being used so you'd want to be careful about maintaining its charge level

If I remember correctly, lifepo cells should be charged to 50% if they're going to be unused for a long time

Seems like a lot of hassle for not much return initially. Maybe best to do panels first and then battery?

Alternatively, if you had something modular like a pylontech you could just bring them home with you after the holiday

the_amazing_raisin

I was thinking there and one idea that might work would be using an electric heater as a PV diverter

You'd generally want to ensure the house doesn't get too cold in winter when it's unoccupied to avoid problems with damp or mould

You could have some PV panels and a couple of electric heaters hooked up to a diverter and on a medium setting to give the house a bit of warmth during the winter months when there's a bit of sun during the day

I know that an Eddi can vary the amount of power going to an immersion heater so it isn't using more than the PV is providing. I wonder would it work as well for a heater

slave1

Heater will need resistive element