this is interesting. i have been told about using 319 steel insulated tank to store hot water, i was also told that this is a "pretty big deal in terms of cost" but i am willing to make that investment.
here is my idea.
300Litre solar water heater+200Litre air source heat pump + storage + FCU.
I don’t have intuition for how large a 300L solar water heater would be — you mean the solar array on the roof, right?
If you have infloor radiant heat with concrete floors, then you might not need much water storage — the concrete provides heat mass. I would look more at deploying PV arrays for offsetting the electricity usage of the heat pump than adding more water storage and solarthermal. Solarthermal is technically more efficient in providing heat alone than equivalent electrical energy, but a heat pump uses that electricity to gather heat from outside, operating at 200-400% efficiency. Electricity is also more useful across the whole house, and of course is a great help in the summer for providing air conditioning.
yeah, the problem with infloor is that the floor is already laid down so i would have to redo the flooring for all rooms.
my use case is winter nov-feb which occasionally has snow, some year there is 0 snow, some year there is 12 inches, usually inbetween.
electricity from the grid is often down during this time period but when it does come, we could use the heat pump to heat up the "storage". 300L water heater in this case means 300L/day of water heater (yeah, rooftop solar water)
the storage can be anything, 500L, 1000L, 2000L, that is cost dependent only. if we feel more storage is needed, we just add another tank
Ok, you're in Kashmir and don't have a reliable grid. I'm not sure it would make sense to spend the money on a heat pump if you didn't have reliable electricity to operate it (if you had sufficient PV panels, then it might be worth it).
Build It Solar has a ton of DIY projects for improving efficiency and using solar energy in various ways. You might find inspiration there: https://www.builditsolar.com/. In particular, they have plans for a solar collector that's a wood frame box with clear plastic sheeting and window screen material — extremely cheap and simple to build. It provides hot air, and it's best if you can fit a few cheap fans (like 120mm 5v PC fans) into it, powered by a small PV panel. I want to build one of these to heat my garage.
Some of the nice things about air-based solar collectors is that they're cheap, low maintenance, can't leak, and can't freeze. The downside is that storage is harder. If you have enough heat mass inside the house it might not matter, though.
here is my idea.
300Litre solar water heater+200Litre air source heat pump + storage + FCU.