We're talking about electricity generation here, not heat generation. People have tried generating electricity using solar heat, but we've stopped doing that because it's too expensive.
> We're talking about electricity generation here, not heat generation
As a peer post noted (without back it up but seems reasonable):
> Only 20% of our energy needs are supplied by electricity.
It is a fair viewpoint to talk about energy instead of only electricity. For exemple the current EV are build using charcoal (steel and cement for the infrastructure) and parts/final product are moved around continent with oil (ships). Same for solar panels and their underlying steel structure. Same for the road were using those EV, etc… there’s technical solutions for those, but they didn’t prove to be economically competitive yet. So I’ll happily take that 80% efficiency when we need relatively low heat : domestic and commercial AC and water heating. Those are by far the most energy intensive usage in the residential sector when there isn’t an electric vehicle and are most needs in pick time (mornings, evening at winter). We better take that +60%.
Any low heat solution is going to have a very difficult time competing economically with heat pumps, which often have an efficiency > 300%.
The most economical solution for reducing our carbon emissions by 95% is doing these two steps in parallel:
1. Use electricity instead of fossil fuel
2. Generate electricity in carbon free manner
Yes, there are some use cases this doesn't work well at yet: steel & ocean transport are two you listed. But it does cover the 4 biggest sources of carbon emissions: ground transport, heating, electricity generation and agriculture. The big 4 are 95% of our carbon emissions.
The Rheem heat pump for domestic hot water that I have in my home claims a maximum energy savings of 75%. That implies that at 20% efficiency out of my solar panels, the efficiency of photovoltaic panels + the heat pump is equal to the 80% efficiency of solar hot water. However, this ignores losses from DC to AC and the lines.
The photovoltaic panels have the added bonus that the energy can be used for other purposes (e.g. transport, HVAC, computers, cooking, laundry, A/V equipment) should my hot water needs be low compared to what the system is designed to produce. However, from a pure efficiency standpoint, it is unclear to me which approach is better. They seem to be a rough tie, with losses for both approaches making the real world worse than ideal conditions. I am not sure if one is better than the other in the actual real world and if anyone who knows the answer is kind enough to share it, I would find the answer enlightening.
I mean, from a distribution standpoint, electricity is way easier to distribute than heat (pressurized steam? Hot water?) and has less loss over longer distances.
Doesn't matter that much if you have excess solar available, beyond that many who do solar also tend to go to a heat pump water heater which is 400% efficient bringing photovoltaics in line with solar hot water without running plumbing up to the roof and now that roof space can be used to power many things rather than just hot water.
The two being equal in efficiency is true in a best case scenario, but that ignores real world effects such as inverter losses. I wonder which would be superior in a real world test.
That said, in my home, I use net metered photovoltaic panels with a Rheem heat pump for domestic hot water. This was not done because I considered it to be a better solution, but because it was the only solution available to me from local installers.
Solar hot water has to account for pumping losses as well, its going to be in the same ballpark but the electric heat pump hot water system is much more flexible in how the power is used and decouples production from use along with electrical vs plumbing on the roof which is simpler and dare say less prone to issues.
Solar thermal heating used to make more sense but cost of photovoltaics has come down so much along with relatively cheap heat pump systems nobody is doing the former anymore it seems.
I just got a large solar system installed and next up is a heat pump water heater as thats the second largest user of power next to the HVAC, plus it will cool and dehumidify my garage some where the solar inverter and batteries are located, converting some of the waste heat from the inverter into hot water at the same time.
This is getting away from the topic, but the capital cost of most solar hot water heaters and their inflexibility with regard to clouds, solar angle, and outside temperatures has made using photovoltaics to resistively heat water a better deal even at the residential level for the past ten years.
https://www.energy.gov/energysaver/solar-water-heaters
I recall hearing that they are 80% efficient while photovoltaics tend to be around 20% efficient.