I can have my lights, computers, entertainment system, A/C and fridge all running without a single kW of electricity from the power company. I will be nice and cozy in the coldest winter nights and can shower as long as I want to without worrying about running out of hot water. All without using a single CCF of natural gas from the gas company. In the rare event of a week long period where it is cold and cloudy, I can fire up my wood stove.
Every house, apartment building, school, factory, office building, in fact every structure with either a flat roof or a roof with any exposure to the sun should have solar electric and/or solar thermal.
1/4 of all fossil fuels are used for domestic or process heat. 1/3 of all fossil fuels are used for electricity. All of the carbon used for heating and electricity can be replaced by solar. That is more than 1/2 of the total fossil fuel consumption.
The cost of installation and interconnection components is more than half of the total cost of a solar system. At least half of the cost of installation is due to mismatched or exclusive components that don’t work together and require you to adapt them to fit or use more expensive components than you would otherwise need to. This unnecessary cost must be eliminated.
Solar installers currently take days to design and assemble the control systems for a solar home when they should be able to do the entire job in less than 1/2 hour. The only part of a solar installation that should legitimately take significant time is installing the panels and routing the wire and pipes down to the basement. Everything else should be assembled from snap together components that “Just Work”.
The Government has a big part in this. The Justice Department should allow all solar component makers to cooperate on interconnection standards without fear of anti-trust suits. There should be a patent sharing pool with tax incentives to participate. We need to drive down the unnecessary costs of solar installations that are due to component mis-match or exclusivity. Part of our trade agreements should be a global “detente” pact to encourage rapid development and standardization of solar components to reduce prices fast enough to eliminate almost all fossil fuels used for heating or electricity.
If you live in a normal 1 family house you can go 90% off grid with solar energy alone. A 24’x36’ roof can provide 5kW Electric plus unlimited domestic hot water and enough extra to heat your home down to freezing temperature. Add a wood stove and you are good to 10 below zero. Put the unused space in your basement to work for energy storage. Drop your Utility bills to the minimum payment or cut the cord entirely.
If your area has net metering you should take advantage of it and size your solar electric system to match your monthly usage. If you don’t have net metering then you should consider a battery system with the power company as backup to your solar system. Your battery system should be sized slightly greater than one nights usage.
For a single family house in northern states of the U.S. 500K BTU/day is enough to heat your house in all but the coldest days of the year. An 10’x10’ unused area in the basement is enough to hold a storage tank for more than 1.5 Million BTUs which is enough heat for more than 3 days without sunshine.
A 4 person family with normal appliance usage uses about 2kW average power over a 24 hour period. This usage can be matched by a 5kW solar electric array with net metering or 5 hours of storage. Most appliance, computer and lighting usage ends by 5 hours after sundown.
During the peak sun hours [8 hours centered on solar noon] the battery storage system is recharged. During the morning and evening hours the solar system can keep up with demand but cannot charge the batteries. During the late evening hours, the batteries supply the requirements for lighting, computers and entertainment systems but generally don’t need to provide for high power appliances.
5Kw Solar Electric system with 7 to 25 kWh of battery storage.
500K BTU/day Solar Thermal system with 1.7 Million BTU heat storage tank in the basement.
Solar Heat Storage Calculation
20000[BTU/hr]*(24*3.5)[hr] = 1,680,000 BTUs
1 BTU = 1F° ∆T for 1lb. Water
Max Water Temp = 165°F
Min Water Temp = 95°F
∆T 165-95 = 70°F
Water Density = 62.4 lb/Cu.Ft.
Specific Heat@70° ∆T = 62.4*70 = 4,368 BTU/Cu.Ft
1680000 BTU/4368 BTU/Cu.Ft. = 384 Cu.Ft.
Water Tank capacity calculation
Large outer tank with nested inner tank.
384Cu.Ft. - 2872 Gal. membrane lined box outer tank.
120 Gal. Stainless Steel inner tank.
12” insulation around outer tank. [R50+]
3” insulation around inner tank. [R15]
Tank size: 8’*8’*6’ = 384 Cu.Ft.
7.48 Gal. = 1 Cu.Ft.
384*7.48 = 2872 Gal.
Solar Thermal Panel Calculation
Evacuated Tube Solar HW Collectors 18 * 20 tube Collectors in 3 rows of 6 collectors 28,000 BTU/day per collector 504,000 BTU/day for entire system 3 days 8 hours to max Storage Tank Temp at no load 24000BTU/day reserve at max load [57.5 Gal./day DHW]
Battery System Selection
Tesla Powerwall Tesla Powerwall
(cash SolarCity) (lease SolarCity)
Lifetime 13+ years 9 years
Cycles 5,000 3,285
Run Time 2.9h 2.9h
Volts 48V 48V
Amps 40A 40A
Power 2kW 2kW
kWh 7.00kWh 7.00kWh
Derating 83% 83%
kWh/cycle 5.80kWh 5.80kWh
Total kWh 28,980 19,040
Total Cost $7,140 $5,000
$/kWh $0.25 $0.26
Tesla Powerwall Tesla Powerwall
(wholesale Tesla) (retail distributor)
Lifetime 13+ years 13+ years
Cycles 5,000 5,000
Run Time 2.9h 2.9h
Volts 48V 48V
Amps 40A 40A
Power 2kW 2kW
kWh 7.00kWh 7.00kWh
Derating 83% 83%
kWh/cycle 5.80kWh 5.80kWh
Total kWh 28,980 28,980
Total Cost $3,000 $3,600
$/kWh $0.10 $0.12
Aquion Energy Aquion Energy
Model S20P 6*S20P M100-L082P
Lifetime 13+ years 13+ years 13+ years
Cycles 5,000 5,000 5,000
Run Time 4.4h 4.4h 5.7h
Volts 48-54V 48-54V 48-54V
Amps 10A 60A 80A
Power 480W 2.8kW 3.8kW
kWh 2.13kWh 13kWh 25.56kWh
Derating 85% 85% 85%
kWh/cycle 1.81kWh 11kWh 21.73kWh
Total kWh 9,050 55,000 108,650
Total Cost $1,155 $6,930 $15,795
$/kWh $0.13 $0.13 $0.15
Iron Edison Panasonic
NiFe Battery NiMH Battery
Model Industrial Series BK-10V1S BK-10V10T
Lifetime 25+ years 13+ years 13+ years
Cycles 10,000 10,000 5000 5000
Run Time 5h 5h 5h 5h
Cell Size 100A-hour 300A-hour 90A-hour 360A-hour
Volts 48V 48V 48V 48V
Amps [max] 20-50A 60-150A 18-45A 72-180A
Power 960W-2.4kW 2.9-7.2kW 864W-2.2kW 3.5-8.6kW
kWh 4.8kWh 14.4kWh 4.3kWh 17.3kWh
Derating 80% 80% 80% 80%
kWh/cycle 3.84kWh 11.5kWh 3.5kWh 13.8kWh
Total kWh 38,400 144,000 17,280 86,400
Total Cost $3,880 $11,400 $???? $????
$/kWh $0.12 $0.13 $0.?? $0.??
RedFlow Harvard University
ZnBr Flow Battery Quinone Flow Battery
Lifetime 14+ years [replace cell membrane]
Cycles 5,000+ 5,000+ 20,000+
Run Time 2.7h 2.2h [tank size/flow rate]
Volts 48-52V 48-52V 48V
Amps [max] 60A 96A [cell area]
Power 3.0kW 5.0kW [flow rate @18.8Whr/L]
kWh 8.00kWh 10.0kWh [tank size 140Gal=10kWh]
Derating 100% 100% 100%
kWh/cycle 8.00kWh 10.0kWh Unlimited
Total kWh 40,000 50,000 Unlimited
Total Cost $7,100 $9,600 Unknown
$/kWh $0.18 $0.19 Cost/[tank size]
NOTE: Panasonic has not published prices for it’s NiMH Batteries.
NOTE: Harvard has not commercialized it's Alkaline Quinone Flow Battery so no prices are available but their research papers have indicated that the amperage, run time and number of cycles will be unlimited.