Photovoltaics
Photovoltaics (PV) are any solar panels that produce electricity.
Not to be confused with solar thermal panels (non-electric) which just heat air or water in the sun.
Status quo
As of 2023, solar provides about 1% of the world's energy (5% of electricity). If we want to phase out fossil fuels, then solar might need to scale up by over 50x. This comes with challenges.
Intermittency
Short-term fluctuation: Solar panels only produce electricity during the day, not at night. Cloudy & overcast days still produce a generous amount of power, although slightly less. Days with heavy rain produce less.[QUANTIFICATION needed]
Long-term fluctuation: Solar panels produce less energy in the winter than in the summer.[QUANTIFICATION needed / case studies]
So if solar were to be scaled up enough to phase out fossil fuels,
- We'd need at least enough battery energy storage to cover a full 24-hour cycle - or maybe a bit more.
- Some excess summer daytime energy may be worth storing by producing hydrogen gas (which could be burned in the winter for heating).
- Energy storage is an ongoing challenge. Best candidates for solar batteries might be iron-redox flow batteries or sodium-sulfur batteries.
- To reduce the need for energy storage, it would help if people were to charge their electric vehicles mostly during the day, and if factories were to run only during the day (and maybe even temporarily shut down in the winter).
Rare metals
Thin-film photovoltaics are the most common types of solar panels used today. They are relatively efficient, but depend heavily on rare minerals. There's simply no way they could be scaled up enough to replace fossil fuels.
Read more: Solar panel minerals
Solution: Find some other photovoltaic tech based on more abundant minerals. Sacrificing some efficiency is okay, for the sake of making cheaper, more scalable solar panels.
Read more: solar/challenge 1
Need for land
Solar rooftops have enough surface area to power most of the world. Very dense cities are an exception, if they aren't surrounded by enough suburbs. Houses, if the rooftop is fully covered in solar panels, can generally produce surplus power which could power inner cities.
Read more: Rooftop solar
Solar farms would be needed in cases where solar rooftops aren't enough. Some amount of land would be needed[QUANTIFICATION needed], but far less than what is used for agriculture. Solar panels should best be placed in areas with no fertile soil. They don't play well with agriculture, because (unlike wind power) solar panels block the sun that plants need to grow. Sure there are some crops that like the shade, but they could have just as well been grown in the shade of full-sun crops. See: polyculture.
Energy in production
Energy return on investment: about 7.5.
Solar panels are estimated to have an "energy payback" of about 4 years.[citation needed] In other words, for all the energy it takes to manufacture a solar panel, the solar panel will generate the same amount of energy after about 4 years of being installed. Since a solar panel is expected to last about 30 years, this comes out to an EROI ratio of 7.5.
4 years is a long time, which means that switching to solar might need a lot of fossil fuels to "get the ball rolling". A shorter energy payback time is a worthwhile goal, mentioned in: solar/challenge 1.
See also