The document summarizes solar power as an energy source. It notes that the amount of solar energy that reaches the United States each day is over 5,400 times the total annual energy consumption, but capturing this would require covering the entire country with solar panels. While solar power has advantages of being renewable and pollution-free, it also has challenges of only being available during daylight hours and taking up significant space to generate enough power. The document concludes that solar can be part of a sustainable energy plan, especially in sunny areas, but challenges remain in relying on it alone to power needs around the clock.

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Solar power
2008-03-12, Reading time: 5 minutes
How much power could the sun give us?
The sun is a nuclear fusion reactor contained by gravity. It
emits unfathomable amounts of energy. This map of the
power that comes to the USA each day (averaged over the
year) has been compiled by the National Renewable
Energy Laboratory. It shows that the average power
incident on the US is around 6 kWh/m /day. To put this in
perspective, notice that this means that the surface of the
USA on average receives 7x10 Joules of energy / year .
In 2007, the entire power consumption of the USA was about 1.4x10 J. This means that there is
about 5400x the energy we use coming down from the sun. Clearly there is more than enough
solar power available. This would, of course, require that the entire USA was covered head to toe with
solar panels. Since we don’t need 5400x the energy we use, we could shrink the area down by this
factor. Running the numbers shows that if we covered something just 1% the size of Texas with 30%
efficient solar panels, we’d have all of our power from solar power.
Pros and Cons of Solar Power
Pros
Solar power is a very ideal power source. We can capture it passively with solar panels or other
collectors. Once the collectors are manufactured, there is no pollution or waste products. There are
no moving parts to hurt wildlife. There is no dependence on foreign entities. The energy is produced
and delivered for free by the sun.
Cons
The sun doesn’t shine at night. This means that in order to power our factories and hospitals through
the dark periods, we can’t rely on the sun alone without somehow storing massive amounts of
energy. Solar panels take up a lot of space. In overcrowded cities where power consumption is
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highest and space is scarcest, building massive banks of solar panels could be very challenging
indeed. The solar panels and collectors traditionally need banks of expensive chemical batteries and
controls that make the cost of using solar power higher than the same amount of power would cost
coming from fossil fuels or nuclear power.
As an example of cost of solar power, consider covering 1% of Texas (or 90% of Delaware) with solar
panels. Today, a 10% efficient panel costs about $600/m . Let’s assume that technological advances
will allow us to manufacture 30% efficient panels for the same cost soon. At that price, it would cost
$3.6 trillion for the solar panels alone, not including the real-estate, battery packs, and infrastructure.
Today’s solar panels are sold with a design lifetime of around 26 years, meaning we would have to re-
manufacture the panels every several decades. With that money, we could build over 900 nuclear
power plants at $4 billion and 1000MW each. That many plants would produce twice as much energy
as we use in a year, and they have lifetimes of at least 60 years.
The role of solar
Solar power is a major player in a sustainable energy plan. In sunny areas, many people have installed
panels on their roofs to help power air-conditioning, lighting, and other household necessities and
found that the panels pay for themselves. Research in solar collection and storage should be a major
effort around the world. Even in less sunny areas, there are a few expensive houses that run 100% on
solar power, using large battery banks to power them through the nights.
When it comes to powering New York City through the night or manufacturing factories and
computer datacenters 24/7, solar has major challenges. Well-funded office buildings and residential
areas can find much benefit from solar power, but we will struggle to rely on it alone. As is often said
on the news these days, there is no silver bullet, all clean energy must ally and work together.
Non-photovoltaic solar
The energy from the sun can be used in other ways that by converting light to electricity in solar
panels. In fact, wind and hydroelectric power are both forms of solar power . Water can be heated
by the sun and used in showers. Heat can be reflected onto an engine that turns a turbine,
generating electricity. Well-designed buildings can use the greenhouse effect for passive heating on
colder days.
References
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http://www.sailgb.com/c/solar_panels/
http://www.nrel.gov/gis/images/us_pv_annual_may2004.jpg
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