Understanding Solar Energy

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-...

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

Converting a gas water heater to electric and/or solar is one of the best bang for the buck on decarbonization too. Something that should be done before buying an electric car or swapping out your gas furnace for a heat pump. Though I'm terrible at following my own advice, I still have a gas water heater, just because I needed to replace my car and furnace before I needed to replace my water heater. That said, the sunk cost fallacy applies to carbon emissions just as hard as it does to dollars so I have little excuse for not replacing it except laziness (and space on the breaker panel...)

If you want to DIY a solar PV water heater I made a whole website about it with instructions and a simulator to estimate what your payback period could be.

https://www.pvh2o.com/

Resistance heating is so 20th century. Granted, you likely cannot do a DIY air source heat pump build, but the COP is so high for such systems, that it's probably worth it to just buy it.

My mom had a Heat Pump water heater at her house and I was always having to go and fix it or clean the filter. It would start beeping loudly in the middle of the night when it wanted attention. The hot water was frequently not very hot.

Hopefully the new heat pump water heaters are better. The advantage of resistance heating is simplicity and cost, with no moving parts. Solar panels are so cheap now they make it hard to justify the expense of the heat pump, assuming you have room to mount the panels.

a COP of 4 can certainly justify having to install 3-4x less panels.

it disappoints me (but thrills me) that improvements in PV efficiency and cost have made solar thermal hot water more or less pointless.

Heat pumps have COP of 4 when reaching temperatures needed for room heating. Hot water is way hotter than that. The more the difference between outside air and heated water, the less the COP becomes. I don't expect COP of 4 at 200 fahrenheit

True, but you never need 200F for DHW. This is even dangerous (scalding) and harmful to the piping. Typical temperatures for heat pump derived DHW are around 120F (45-50C), with some (bi)weekly cycles to avoid legionella build up at 150F(65C). Your statement is generally true, because a heating installation that is optimized for heat pump works at 85-100F, however in practice not many installations in old buildings are like that.

If your concern is storage you want as hot as possible, less boiling. Thermostatic mixing valves can bring the temp down to a safe temperature for use.

Losses are higher but you store more energy per L, which is often the limiting factor.