Have we underestimated the solar power potential?
After an interesting discussion at lunch yesterday, I did a quick calculation:
Power consumption in the US is about P=3.3 TW in 2005 (source DoE)
Given an efficiency E of solar collectors, and assuming a mean of F=300 W/m2 insolation at the top of the atmosphere (pretty good for mean annual insolation 45 N latitude), an atmospheric transmittance of T, then the total solar irradiance converted to electrical power is
I_converted = E*F*T
Thus the area of solar panels required to generate P, assuming E=10% (a low estimate) and T=0.8
A = P/I_converted = 3.3x1012/(E*F*T) = 1.4x1011 m2
This is a square 220 miles on a side.
It would appear to me that solar power is clearly viable.
Next, we can Another way to look at it is to ask how much of an area would be required per person (assuming E=0.1). For 300 million people, this comes out to be:
1.4x1011 m2 / 300x106 = 470 m2, 21x21 m.
We can compare this requirement with how much land is dedicated to farming. Each person consumes about 100 kg of grain per year. A hectare of land (10,000 m2) produces about 7000 kg of grain with today's fertilizer yields. Thus, each person needs an area of 140 m2 for wheat production, but wheat-for-human food is a small part of the total farming requirement per person, because only 30% is used for food, and the rest is used for animal feed and fuels. Corn farming comes to a whopping 1200 m2 per person in the US (source USDA). So the total farming requirement per person is likely to exceed 1800 m2 or an area of approximately 4-5 times that we would need for solar power (even with today's low-efficiency solar collectors).
I admit that storage issues are still a problem, but I think the real problem is one of willpower.
Regards
Rob
posted by Rob Wood @ 8:38 AM
1 Comments
1 Comments:
Excellent idea to do this calculation, Rob. Scientific American has a thoughtful piece on this topic and draws similar conclusions to yours, although they think that some increase in efficiency (which will be met within the next decade) is still required for commercial viability.
Solar Grand Plan
They note that we are quickly approaching the efficiency at which solar power becomes feasible. They outline the process of a conversion to a solar powered nation that focuses on (stage 1: present-2020) incentives and loans to make solar power competitive at the mass-production level, building 84 GW of photovoltaics, and the backbone of the High Voltage DC power transmission grid necessary for efficient energy transfer; (stage 2: 2020-2050) incentives for enough photovoltaic grid to be laid down for 69% of U.S. electricity usage and 35% of total energy to be supplied by solar power; this sets the stage for self-sustaining growth after 2050; (stage 3: 2050 & beyond) 165,000 square miles of suitable land available in the Desert SW would be required for the solar grid. Combined renewables would account for 90% of total energy usage in 2100. Their estimate assume that total energy demand in 2100 will be 7x today’s electric generating capacity.
The article concludes:
“The greatest obstacle to implementing a renewable U.S. energy system is not technology or money, however. It is the lack of public awareness that solar power is a practical alternative—and one that can fuel transportation as well. Forward-looking thinkers should try to inspire U.S. citizens, and their political and scientific leaders, about solar power’s incredible potential. Once Americans realize that potential, we believe the desire for energy self-sufficiency and the need to reduce carbon dioxide emissions will prompt them to adopt a national solar plan.“
In my mind, the question remains whether it is worth generating solar power in the Northwest. The purchase of solar grids in the Puget sound region may raise the demand and price of an already scarce commodity (solar grids, at least in the short term), potentially making it less cost effective where it will be most efficient (i.e. in desert regions). Some of this depends upon the efficiency of transport and storage with the HVDC grids and pressurized caverns. I’d be interested to hear somebody else’s take on this matter. My suspicion is that energy conservation, development of wind resources, and investment in solar energy technology might be most worth the attention of environmentally conscious citizens in the Puget sound region.
Rob’s efficiency estimate appears quite reasonable:
“To provide electricity at six cents per kWh by 2020, cadmium telluride modules would have to convert electricity with 14 percent efficiency, and systems would have to be installed at $1.20 per watt of capacity. Current modules have 10 percent efficiency and an installed system cost of about $4 per watt. Progress is clearly needed, but the technology is advancing quickly; commercial efficiencies have risen from 9 to 10 percent in the past 12 months. It is worth noting, too, that as modules improve, rooftop photovoltaics will become more cost-competitive for homeowners, reducing daytime electricity demand.”
“The main progress required, then, is to raise module efficiency to 14 percent. Although the efficiencies of commercial modules will never reach those of solar cells in the laboratory, cadmium telluride cells at the National Renewable Energy Laboratory are now up to 16.5 percent and rising. At least one manufacturer, First Solar in Perrysburg, Ohio, increased module efficiency from 6 to 10 percent from 2005 to 2007 and is reaching for 11.5 percent by 2010.”
Robert
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