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Understanding Solar Energy

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261 points chmaynard | 2 comments | 20 Mar 25 12:09 UTC | HN request time: 0.414s | source
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bryanlarsen ◴[20 Mar 25 14:23 UTC] No.43423941[source]▶
Great article. Unfortunately his California duck curve graph only shows 2023. A graph including 2024 shows how batteries are dramatically flattening the duck curve:

https://cdn-ilcjnih.nitrocdn.com/BVTDJPZTUnfCKRkDQJDEvQcUwtA...

https://reneweconomy.com.au/battery-storage-is-dramatically-...

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Calwestjobs ◴[20 Mar 25 17:00 UTC] No.43425755[source]▶
Hot water tank heated by electricity and powering on at noon is flattening curve. You can say hot water tanks are cheapest, simplest and fastest deployed energy storage device.

Solar + hot water tank can provide any house in US with 100% solar hot water (from PV!) for 80% of time, remaining 20 % of time you can have 10-99% solar heated water.

So we should focus on saying to people that if they buy solar and add electric heating element to hot water tank, then PV system will pay itself much sooner and their batteries will last longer. Becasue it is known and predictable load, you need hot water every day. And hot water is order of magnitude more energy then TV, lighting...

By lowering household usage like this we can make energy transition faster, cheaper.

Also proper construction - house heated only 10 days in a year - https://www.youtube.com/watch?v=5KHScgjTJtE

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kavalg ◴[21 Mar 25 08:59 UTC] No.43433336[source]▶
Why are people even considering an electric heating element, when you can get at least 2-3 times the efficiency of a DHW heat pump that would probably cost you ~ $4000. In my experience, I have found that for PV panels it is often the roof area / orientation that limits the energy capacity that you can install. Installing a heat pump instead of resistive heater can effectively reduce this 2-3 times.

Yes, heating DHW with a heat pump is not that trivial. There could be problems when the tap water is hard (limescale problems in heat exchangers), you often need 2-3 times larger tank in order to cover the daily cycle, but still looks more efficient than a big battery and an electric heater.

PS: I've accumulated lots of knowledge on the topic. DM me if you are interested in exchanging on this.

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1. megaman821 ◴[21 Mar 25 15:21 UTC] No.43436758[source]▶
How about lifetime costs? A resistive water heater is going to last longer and you can get non-metallic water heaters for extremely long life.

If you don't have net metering (or just a terrible power purchase rate), why not just sink that extra solar energy into a water heater?

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2. kavalg ◴[21 Mar 25 16:06 UTC] No.43437314[source]▶
That is a good question. The usable life of a combined heat pump (space heating/cooling + DHW) is somewhere between 10-15 years. For the ones, dedicated to DHW, I cannot really tell, but I would expect it to be longer, because they are usually less heavily loaded. Then the answer of your question will depend on the price of installation (e.g. heat pump vs 3 x extra PVs), local climate (affects efficiency) and price of electricity. Heat pumps don't work well in very cold climates, but for most US/EU cities they will work fine. For very hot climates it may be better to use solar water heaters, although for commercial installations there is the option to use the exhaust heat from cooling to heat DHW (it is essentially free energy).