excess PV capacity used for heating

tuulikki · 09-30-12, 04:17 PM

Hi everyone, first post here though I've read many threads in the past.

We're looking at having a roof-mount solar system installed. Our home is located in the Boston MA area and is heated by one-pipe steam, powered by a new natural gas boiler. I'm trying to do the mental arithmetic around what the natural gas savings would be if we have more electricity generation capacity than we need and use some of it to power space heaters, for example as extra heat in a bathroom or in the basement.

Don't laugh--I realize it's probably not the best idea, I'm just trying to get the numbers to show me how bad an idea it is and so far haven't been able to set up the problem correctly.

I've read here about some of the ideas of using excess electricity as a preheater for HW but we're not up to any hacking right now.

Numbers that may be useful:
--Total natural gas usage last year (all for heat/HW): 926 therms, at about 80 cents a therm.
--tentatively looking at 4.000 kW DC system, expect it to generate ~4700 kWh AC annually. (House is good but not great re tilt, azimuth, shade.)
--our annual electricity usage is ~4300 kWh.

I'm trying to figure out what else we can do to minimize our CO2 footprint; initially (pre-new gas boiler) had hoped for geothermal but $$ didn't work at all, so we stuck with steam.

Thanks for any thoughts. I have to go now but will try to write out my calculations later and maybe someone can figure out what I'm messing up.

09-30-12, 04:17 PM	#1
tuulikki Lurking Renovator Join Date: Sep 2012 Location: Boston Area, MA Posts: 6 Thanks: 2 Thanked 1 Time in 1 Post	excess PV capacity used for heating Hi everyone, first post here though I've read many threads in the past. We're looking at having a roof-mount solar system installed. Our home is located in the Boston MA area and is heated by one-pipe steam, powered by a new natural gas boiler. I'm trying to do the mental arithmetic around what the natural gas savings would be if we have more electricity generation capacity than we need and use some of it to power space heaters, for example as extra heat in a bathroom or in the basement. Don't laugh--I realize it's probably not the best idea, I'm just trying to get the numbers to show me how bad an idea it is and so far haven't been able to set up the problem correctly. I've read here about some of the ideas of using excess electricity as a preheater for HW but we're not up to any hacking right now. Numbers that may be useful: --Total natural gas usage last year (all for heat/HW): 926 therms, at about 80 cents a therm. --tentatively looking at 4.000 kW DC system, expect it to generate ~4700 kWh AC annually. (House is good but not great re tilt, azimuth, shade.) --our annual electricity usage is ~4300 kWh. I'm trying to figure out what else we can do to minimize our CO2 footprint; initially (pre-new gas boiler) had hoped for geothermal but $$ didn't work at all, so we stuck with steam. Thanks for any thoughts. I have to go now but will try to write out my calculations later and maybe someone can figure out what I'm messing up.