I agree that the improvements in air source heat pumps over the last couple decades, with operation down to as low as -25 F (albeit at low COP) has been a game changer. For one thing, I think they have made ground source heat pumps non-competitive due to their much higher cost. But I am not so sure they are always the best solution.
I've looked at this for my house, and this specific case illustrates some of the variables. I can build a solar thermal system, collectors, pumps, insulated storage tank and plumbing, with 200 ft^2, collector area for less than $3k. This system will provide about 33kWh, 112,600 BTU, of heat to the storage tank per day (50% efficiency, measured), and about 30kWh into the house assuming a small amount of loss in the plumbing to the liquid-air heat exchangers. Using a cost of around $2.00 per Watt owner-installed, including racks, inverter, wiring, etc), this $3k would purchase about a 1.5kW PV system (example prices: http://www.wholesalesolar.com/gridtie.html#SolarSkySolarWorld). In my area that would supply about 7kWh electric per day yearly average, based on 6 years of data on my 5.6kW system. Heat pumps have to be purchased to turn this into heat into the house. An 8kW (27,000 BTU) heat pump is around $3k (for example: https://www.acwholesalers.com/Fujitsu-Air-Conditioners/AOU24RLXFZ-ASU9RLF-ASU9RLF-ASU9RLF-27000-BTU-18-SEER-Ductless-HeatPump/14513.ac?gclid=CLb7ifC5lsMCFdgHgQod_7UAIg). With COP of 3 this would deliver about 21kWh of heat using the 7kWh of electric per day, about 30% less than the solar thermal. But as someone said, I may use that power year around, but not the heat from the solar thermal. In our area we need to heat about 7 months of the year. The 200 ft^2 collector would only supply part of the energy required to heat the house over most of the winter, so I would use the full output over at least 5 of the 7 months. So for 5 months of the year I get 30kWh from solar thermal, and about 20kWh from PV. For the other 7 months I get nothing from solar thermal (not quite, some used for about 2 months) and 7kWh per day, or about $0.84 per day ($.12/kWh) from solar PV, or about $175.00 per year. I had to pay an additional $3k for the solar PV and heat pump system, which would be paid back in about 17 years at current utility rates. After that the PV/heat pump system would save me $175 per year in electric costs at current rates if I use its full output year round, or the utility pays me retail rate for surplus electric I supply. But I am not going to use that full output over the rest of the year unless I run AC enough during the 7 months to use the same energy I used from the system for heating during the 5 months of winter. I don’t. I just open the windows at night. In addition, we have net metering in my state, balanced over a year. So any surplus I have supplied at the end of the year is tossed out, I get no payment for it, so I wouldn’t gain $175 per year to pay back the $3k high cost of the PV/heat pump system and bank after that. In this case I pay twice as much for the solar PV/heat pump system and get less roi from it over a year since I won’t get paid for most of the surplus electric. In my specific case the solar thermal looks like a better roi. It also can be set up to run the pumps off of batteries which are charged by solar, so independent of the grid. A consideration where I live since the power goes out around a half dozen times per year. With grid tied PV and heat pump I would not have heat at these times unless I purchase a backup generator, or a different inverter and battery backup, further increasing cost. I think this is a complex calculation with many dependencies, such as available solar insolation, type of dwelling, type of metering by the utility, use of AC, installation costs (diy or not), etc, which can vary greatly with user and location. It is impossible to give a simple answer that is accurate for most users in most areas. Each case needs to be examined in detail. -- View this message in context: http://electric-vehicle-discussion-list.413529.n4.nabble.com/Re-EV-Demand-Response-solar-thermal-NOT-tp4673447p4673482.html Sent from the Electric Vehicle Discussion List mailing list archive at Nabble.com. _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
