Rooftop solar
Rooftops are a good place to put solar panels, because:
- They are close to where the energy is typically used.
- They need no extra land (unlike solar farms). That's an environmental footprint avoided.
Summary:
- In most cases, rooftop solar could provide enough energy for homes, other buildings, and charging electric vehicles.
- Exception: heating in cold parts of the world
- Exception: high-density cities
- Note: People would have to charge their electric vehicles during the day.
- Hard problems:
- Manufacturing enough solar panels without needing too many rare minerals
- Recycling solar panels at their end-of-life
- Energy storage
Potential
First let's estimate how much rooftop area is available globally. For lack of better data, let's just assume that rooftops
Does not include most farm land.
https://ourworldindata.org/land-use
(calculation loading)
Assume we find a way to manufacture this many solar panels without overrunning our mineral reserves. How much energy could we generate?
https://www.newport.com/t/introduction-to-solar-radiation
http://www.ftexploring.com/solar-energy/insolation.htm
Does not include the fuel used in generating electricity. See [energy.tes] for that.
Citation: "Key World Energy Statistics 2020" IEA
- Page 47 - Simplified energy balance table - World energy balance, 2018
(calculation loading)
In simple terms, this means we could just about meet the world's energy demand, with solar alone. [''']Less energy would be available if the solar panels were less efficient due to using fewer minerals.
Energy demand could also decrease, given certain factors:
- walkability and public transit
- voluntary frugalism in the western world especially
- electric vehicles as long as they don't take too much energy to manufacture
Energy demand could also increase, given other factors:
- more nations becoming 'developed' in a way that copies the current western world
For all intents and purposes, let's assume that all these factors would balance each other out, roughly.
However, some of the energy might be generated in the wrong places. Low-density cities/towns may generate too much; high-density cities may not generate enough.
Locality
High-rise buildings don't have enough rooftop surface to power the whole building. But in some cases, a dense inner-city could be powered by excess energy from suburban house rooftops nearby. In what cases is this viable? Population density could be a useful measuring stick:
(calculation loading)
^ If your whole municipality's population density is greater than this number, you would probably need solar farms.
Charging electric vehicles
If we assume one electric car per house, we'd need to add another 543 watts
https://www.api.org/news-policy-and-issues/blog/2022/05/26/top-numbers-driving-americas-gasoline-demand
ecocostsavings.com › average-electric-car-kwh-per-mile
from wikipedia; haven't found original source yet
Would the average suburban rooftop be able to provide this? (calculation loading)
Yes, seems doable. Obviously it depends on the size of the rooftop (in this example, we assume 1000 square feet). (calculation loading)
Energy storage
So far we've looked at watts averaged over time, but actual raw watts are much higher during the day, and almost zero at night. We need energy storage to smooth things out.
As a bare minimum, a house should at least have nighttime electricity for lights, appliances, cooking, computers, entertainment, etc. Assume we need to store about 12 hours of average-case power consumption
Source: https://www.eia.gov/tools/faqs/faq.php?id=96&t=3
Using rows in table: "Total consumption", minus "Space cooling", minus "Space heating", minus "Water heating", minus exactly 1/2 of "Other uses".
Note: This can be understood as ''average power''. The required ''peak power'' may be higher, as this consumption may be concentrated into afternoon/evening hours.
Housing units - U.S. Census Bureau QuickFacts: United States
[https://www.census.gov/quickfacts/fact/table/US/VET605221]
(calculation loading)
Electric vehicles already contain energy storage. Best-case scenario, people charge them during the day.
Safety
- The roof needs to be able to support the weight of the solar panels.
- Installing the panels, without the proper skills and knowledge, could result in electrocution or fire hazards.
- Maybe this risk could be mitigated with enough engineering: Could rooftop solar kits be designed to be user-friendly and safe enough for non-professionals to install them?[RESEARCH needed]
Challanges
- Some roofs might be more suited for solar panels than others.[RESEARCH needed]
- Installation might need very specialized labor.[RESEARCH needed]
- Keeping snow & ice off the panels
- Making solar panels cheaper, more lightweight, less demanding of rare minerals. This is generally at odds with having more efficient solar panels.[RESEARCH needed]
- Environmental tradeoffs for houses that are surrounded by tall trees
Combined photovoltaic and thermal panels
Solar thermal panels use the sun to directly heat water & air, without electricity as an intermediate. There are some designs that integrate with photovoltaics, to really make the most of the sun for both heating and electricity. But in which weather conditions is this viable - would it still work in colder winters?[RESEARCH needed] How does it compare to pure photovoltaics combined with heat pumps?
Factories
Factories make up a significant share of global energy demand - more than homes and other buildings. Factories could also mostly run only during the day to make use of peak solar energy without much need for energy storage. But could a factory's rooftop provide most of energy needed to power the factory?[RESEARCH needed]
If not, there may be other solutions:
- If the factory is near a city with many houses producing excess energy from their rooftops during the day, the factory could use that as an energy source.
- If the factory is far from cities, it might happen to be in an area where wind power is viable.
- Perhaps the factory could scale down and decentralize production. Beware of caveat:
(...)( This could easily be overall worse for the environment if existing factory equipment has to be abandoned in favor of smaller equipment to be built from scratch. But there are probably some cases where this wouldn't have to happen. )
See also: Solar powered factories
External links
- Solar Rooftop Potential - U.S. Department of Energy