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Understanding Solar Energy

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261 points chmaynard | 5 comments | 20 Mar 25 12:09 UTC | HN request time: 0.658s | source
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losvedir ◴[20 Mar 25 14:39 UTC] No.43424138[source]▶
This is a great summary of the situation. I've been thinking about installing solar panels on my house, and been thinking about these same sorts of issues. Unfortunately, for my situation here near Chicago, things are much worse than the author's Atlanta: winter requires tons of energy here because it's very cold, and we have even less sun then.

It's one of the things that makes me think about wanting to move to Texas or Phoenix or something. Ample year round sun, and the big energy expense: climate control, corresponds much better to when you have it (you need to "cool" in the summer and the day). It rubs me the wrong way that here, our big energy cost is heating in the winter. It doesn't fit well with the utopian solar future I'm envisioning.

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danans ◴[20 Mar 25 15:02 UTC] No.43424385[source]▶
Assuming you would stay in Chicago for other reasons, the solution for a high heating bill is 1) air seal and upgrade insulation in your house, and then 2) replace your furnace with a low temperature heat pump.

Chicago has electricity prices 25% lower than the national average. If you want to see an example in your area, watch Technology Connections heat pump videos on YouTube.

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1. bityard ◴[20 Mar 25 18:33 UTC] No.43427141[source]▶
Air seal and upgrading insulation: correct me if I'm wrong, but that implies either tearing open all of the exterior walls or ripping off all of the siding, no? If so, it feels like it would take a LONG time to recoup the cost of materials and labor for that job, unless there was literally no insulation in there to begin with.

Alex is a smart guy, and he makes a lot of convincing agruments in favor of heat pumps, but the thing he consistently sweeps under the rug is that for about half the US (and all of Canada), the annual cost to run a heat pump sits well between a natural gas furnace and resistive heating. And the further north you go, the more it shifts to the right. I run the numbers every few years and for my specific house, I'd pay 30% more to run a heat pump instead of a furnace. (Before factoring in the cost of the unit itself and installation labor.)

Where I live, the only way heat pumps make economical sense is if natural gas gets dramatically more expensive, or if solar gets cheap enough that every household can afford a roof full of solar panels and a basement full of batteries. (Which to be honest is kinda my dream situation anyway.)

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2. pfdietz ◴[20 Mar 25 23:52 UTC] No.43430386[source]▶
We had an insulation upgrade recently when we ripped out our gas furnace and put in a heat pump. The biggest improvement was from spraying foam into the space below the first floor, where it rests on the outer basement walls. There had been too much air leakage there. There was also attic insulation upgrading. No walls had to be penetrated.

The house (built just a decade ago) feels much better insulated now.

3. danans ◴[21 Mar 25 05:04 UTC] No.43431996[source]▶
> Air seal and upgrading insulation: correct me if I'm wrong, but that implies either tearing open all of the exterior walls or ripping off all of the siding, no?

If you do the exterior walls yes, but most heat loss is through the attic and roof. Air sealing and super- insulating the attic floor is pretty cost effective. Likewise sealing cracks around windows and doors.

4. hnaccount_rng ◴[21 Mar 25 12:58 UTC] No.43435110[source]▶
> the annual cost to run a heat pump sits well between a natural gas furnace and resistive heating.

Why is that? Maybe I'm missing something fundamentally, but this should be a strict function of COP, $/kWh (elect.) and $/kWh (gas) right? The insolation thing is kind of red herring, because that saves kWh-needed and that goes into both, right?

And yes COP will probably be bad/worst on some days of the year. But on most days even Chicago should get a pretty decent COP from a low-temperature heat pump. Is natural gas just so cheap in Chicago?

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5. Calwestjobs ◴[21 Mar 25 23:59 UTC] No.43441986[source]▶
for price of heat pump you can buy 3-6 times bigger PV array.

heatpumps are not expensive but they are not cheap COMPARED to other alternative. cop is not constant, it changes. closer the outside temperature and indoor temperate is, less work is needed / higher COP heat pump provides.

buying 4 times more panels gives you always 4 times more energy. in -40F you get 4 times more energy from 4 times bigger pv array. heat pump will probably just start running integrated resistive heater IN THESE temperatures.

heat pump can be configured in a way that it not only heats but also cools, so yes in that situation heat pump can be cheaper. then not having one and be less comfortable / productive because of it.

you can buy PV system and after it paid itself, it still works, still generates electricity. gas can not be 0 $. so depends what / how you calculate things.