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[[File:RooftopSolar1.jpg|thumb]]
Rooftops are a good place to put [[solar]] panels, because:
Rooftops are a good place to put [[solar]] panels, because:
* They are close to where the [[energy]] is typically used.
* They are close to where the [[energy]] is typically used.
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** Exception: [[heating]] in cold parts of the world
** Exception: [[heating]] in cold parts of the world
** Exception: high-density cities
** Exception: high-density cities
** Note: People would have to charge their electric vehicles during the day.
* '''Hard problems:'''
* '''Hard problems:'''
** Manufacturing enough solar panels without needing too many rare [[minerals]]
** Manufacturing enough solar panels [[solar/challenge 1|without]] needing too many rare [[minerals]]
** [[solar panel recycling|Recycling solar panels]] at their end-of-life
** [[solar panel recycling|Recycling solar panels]] at their end-of-life
** [[Energy storage]]
** [[Energy storage]]
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==Charging electric vehicles==
==Charging electric vehicles==
If we assume one electric car per house, we'd need to add another 543 watts per household. Note: This is ''power averaged over time''. Peak power would be significantly higher, but that's not a big deal as vehicles could be charged during peak sunlight.
If we assume one electric car per house, we'd need to add another 543 watts {{x|Note: This is ''power averaged over time''. Peak power would be significantly higher, but that's not a big deal as vehicles could be charged during peak sunlight.}} per household:


{{dp
{{dp
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==Energy storage==
==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.
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'' {{x|obviously this also depends on a lot of factors, such as time-of-year and consumption patterns. Let's do a generous estimate that assumes that heating doesn't need to be done at night, as heat can be stored in other ways much cheaper than batteries.}} for that:
{{dp
|<nowiki>usa.residential_essential_baseload</nowiki>
|<nowiki>641 billion kWh/year</nowiki>
|<nowiki>Bare minimum residential electricity that must be available 24/7, in the USA</nowiki>
|<nowiki>Does not include heating/cooling, because there are ways to store warmth/cold more cheaply than storing electricity.</nowiki><br /><nowiki>
</nowiki><br /><nowiki>
Source: https://www.eia.gov/tools/faqs/faq.php?id=96&t=3</nowiki><br /><nowiki>
</nowiki><br /><nowiki>
Using rows in table: "Total consumption", minus "Space cooling", minus "Space heating", minus "Water heating", minus exactly 1/2 of "Other uses".
</nowiki><br /><nowiki>
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.</nowiki>
}}
{{dp
|<nowiki>usa.homes</nowiki>
|<nowiki>142153010</nowiki>
|<nowiki>Number of households in the USA</nowiki>
|<nowiki>Includes houses, apartments, condos and more.</nowiki><br /><nowiki>
</nowiki><br /><nowiki>
Housing units - U.S. Census Bureau QuickFacts: United States</nowiki><br /><nowiki>
[https://www.census.gov/quickfacts/fact/table/US/VET605221]</nowiki>
}}
{{calc
|12 hours usa.residential_essential_baseload / usa.homes
|kWh
}}
Electric vehicles already contain energy storage. Best-case scenario, people charge them during the day. {{x|People would be motivated by the massive price difference between daytime electricity (incredibly cheap) and nighttime electricity. Daytime charging comes with a few other logistical challenges,<!--TODO: make a new section or page on this--> but it still has the potential to become a social norm.}}


==Safety==
==Safety==
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See also: [[Solar powered factories]]
See also: [[Solar powered factories]]
==External links==
* [https://www.energy.gov/eere/solar/solar-rooftop-potential Solar Rooftop Potential] - U.S. Department of Energy