Pairing heating system with Solar panel system

[EnergyDude]

My house is in an ideal location for a solar panel system - on a hill, no obstruction (except for clouds) and plenty or south facing roof surface. I am not a big user of electricity with $370 over the past 12 months; most of my utility cost were for gas with $1200 over the past 12 months. I have a bid for a 4.5 kW system which can handle all my electric needs plus more. The payback for my system is about 4.5 years. My roof can accommodate 3x as many solar panels.

I am looking for suggestions on how to use solar energy towards my heating energy cost. My gas furnace, which is not high-efficiency, is old but works; age-wise, it is close to end of life. Because of its location, I am unable to replace it with a high efficiency gas furnace. We already have an AC, which we do not use. Does it make sense to replace the old gas furnace with an electric furnace so that I can use the electricity generated by the solar panels. I looked at a heat pump system but I am not inclined to spend so much considering that I may not stay in this house beyond 5 years.

The house in the Seattle area, so the weather is pretty moderate.

If you have any ideas on what I should consider, please share them. Thanks!

[inetdog]

My house is in an ideal location for a solar panel system - on a hill, no obstruction (except for clouds) and plenty or south facing roof surface. I am not a big user of electricity with $370 over the past 12 months; most of my utility cost were for gas with $1200 over the past 12 months. I have a bid for a 4.5 kW system which can handle all my electric needs plus more. The payback for my system is about 4.5 years. My roof can accommodate 3x as many solar panels.

I am looking for suggestions on how to use solar energy towards my heating energy cost. My gas furnace, which is not high-efficiency, is old but works; age-wise, it is close to end of life. Because of its location, I am unable to replace it with a high efficiency gas furnace. We already have an AC, which we do not use. Does it make sense to replace the old gas furnace with an electric furnace so that I can use the electricity generated by the solar panels. I looked at a heat pump system but I am not inclined to spend so much considering that I may not stay in this house beyond 5 years.

The house in the Seattle area, so the weather is pretty moderate.

If you have any ideas on what I should consider, please share them. Thanks!

The cost per BTU for resistance heating is typically at least three times the cost of piped natural gas. Locally stored propane comes in close to electric resistance.
Heat pump is the best way to go if you have to use electric.
Remember that the energy from your PV system is not "free" and if you are on net metering and do not produce more than your total consumption, you will be paying for added consumption anyway.

A low efficiency gas furnace is still far better than electric resistance heating.

One more thing to look into is whether your utility will approve interconnection of a system that vastly overproduces compared to your current/historical consumption, given that you plan to add electric heating. Not all POCOs will allow this.

PS: A payback of less than 5 years is exceptional, even for grid tie. Are you sure you are calculating correctly, including foregone interest (opportunity cost) on the initial investment?

[J.P.M.]

1.) How many heating degree days in a typical year at your location ?

2.) How well is your dwelling insulated ?

I'd suggest you scrap the idea of electric resistance heat. VERY cost ineffective.

If you are in a moderate climate, say < ~ 4,000 F. degree days or so, consider a heat pump.

Still, if the price of CH4 stays relatively low for a while, a high eff. gas furnace can have advantages like faster warmup and maybe a bit less maint. due to a bit less complexity.

Whichever you choose, don't oversize a heat pump or gas furnace - that's a waste, and make sure the ducting is insulated/updated as necessary.

If your climate is moderate, your home well insulated and you know your heat load, adding to the solar PV size to offset a heat pump load for space heating MAY be cost effective.

You gotta run some #'s however.

[emartin00]

Mini split heat pumps are great. I installed one a couple years ago, and heat my entire first floor with it until the temperature drops below 20F. If I had more open concept, I could go colder, but the farther rooms start to get a little cold at that point.
They're very easy to install, and the price isn't bad.

[EnergyDude]

The cost per BTU for resistance heating is typically at least three times the cost of piped natural gas. Locally stored propane comes in close to electric resistance.
Heat pump is the best way to go if you have to use electric.
Remember that the energy from your PV system is not "free" and if you are on net metering and do not produce more than your total consumption, you will be paying for added consumption anyway.

A low efficiency gas furnace is still far better than electric resistance heating.

One more thing to look into is whether your utility will approve interconnection of a system that vastly overproduces compared to your current/historical consumption, given that you plan to add electric heating. Not all POCOs will allow this.

PS: A payback of less than 5 years is exceptional, even for grid tie. Are you sure you are calculating correctly, including foregone interest (opportunity cost) on the initial investment?

Thank you for the response. I'll look into whether my utility company will approve of the interconnection of a system that overproduces compared to past usages. The payback number of 4.5 years were computed by a reputable solar company. I did not take into the consideration of lost opportunity cost of the initial investment considering how low the interest rates are these days.

[peakbagger]

I have net metering in NH and in a far colder climate, I build up a power surplus in the summer and run a minisplit for "shoulder season" which is any time the overnight temps are over zero. The unit will runs down to minus 10 F but its heat output is reduced quite a bit. One thing to get used to is the unit doesn't put out really hot air it just puts out a lot of warm air. You pretty much need to set it and let it run rather than letting the place cool down. A mini split is also a lot more efficient than a window air conditioner. I find I use the mini split much more in the summer than I ever did with window unit. Its also a lot quieter.