December and January are both coldest and cloudiest months of the year. The highest energy demand corresponds with the lowest solar energy supply
A large hot water tank (200+ gallon) is difficult to store in a tiny living space
Putting the storage tank outside greatly increases the heat loss in during the coldest months when the heat storage is needed most. It also likely increases the distance from tank to shower meaning long shower warm-up times and more heat lost
Putting the tank under the house, inside the Climate Battery, is as good or better than having in the living space from a thermal perspective since the heat lost from the tank is captured. However maintenance and repairs would be difficult and it would be a long distance to the shower
Strategies
First use heat saving technologies to reduce energy demand and storage requirements
Capture enough energy for seven days in three peak sunlight hours
Store enough energy for showers and dishwasher though seven days of no sun
Insulate the tank well to minimize heat loss
Use the highest temperatures the tank materials can withstand to minimize tank size.
Low-thermal-mass and more-air-tight shower stall slows heat and humidity loss. This means the showerer is more comfortable with less, lower temperature water. It also reduces humidity and mold problems which is important for a well-air-sealed house.
I estimate 50% water savings and 57% energy savings for showers using this technology alone. spreadsheet
A cube constructed of marine plywood and 2x lumber
Polyisocyanurate insulation inside the plywood cube
EPDM Liner on the inside the insulation
Inside water tank 300ft coil of 1" diameter PEX tube that is on mains pressure. This is the heat exchange and holds about 9 gal of water that will be at full tank temp
Spreadsheet shows 80gal tank with R30 insulation will hold enough energy for 7 days. Real world testing indicates the insulation is loosing 50% more heat than calculated, so might have to compensate with more more water and insulation.
Photovoltaic + Resistance Heat
Since PV is cheaper by the pallet (7-8kW) and the relatively high lifetime costs of heat pumps, it seems resistance heating is more cost effective since we meet 80% of energy needed though conservation. It's even worse when including costs of inverters and batteries. Spreadsheet being finalized.
I also doubt an air-source heat pump can use 10f air to heat water to 170f, a major design constraint
I think Flat-plate and Evacuated tube solar thermal collectors will also have trouble with a delta-T of 160f
No inverter or lithium batteries needed. Resistance heat elements will work fine on 0-90V DC daylight drive. A thermostat with a solid state relay or otherwise rated for DC needs to be used as normal AC thermostats will arc weld their contacts together
Thermostat can be set lower ~130f during the warmer months to reduce heat loss and wear on tank liner.
13-17 kWh need to "charge" the hot water means 4.3-5.6 kW of PV sufficient to charge in three peak sun hours. In summer months extra electricity can be used for other things such as charging EV or air conditioning.
Paraffin
Using PCM Stainless Steel balls filled with +58C ( 136F) PCM material, designers managed to increase the standard domestic solar hot water calarifier capacity three fold and in return this higher capacity satisfied the excessive hot water demand during the games as the occupancy levels evry almost three times than an average family as these houses are designed to be offered to public after the games. ref1ref2
If we need better performance we could do a low-cost version with low melt temp 127F candle paraffin from ebay inside used 20oz plastic soda bottles.
A gallon of paraffin almost doubles the heat storage of the replaced water from 100F-170F, and nearly triples performance from 100F-130F.
