The amount of solar energy by any measure is also enormous. Every hour more energy strikes
the surface of the Earth than is consumed globally in a year. According to the DOE's Solar
Energy Technologies Program, there is on average between 2.8 and 6.2 kilowatt–hours (kWh)
of sunlight available per square meter (m2) each day. The exact amount of sunlight
depends on the region and the season. In the United States, the annual average is 4.8 kWh/m2
One way of using this solar energy is to transform it directly into electricity at the
location where it is to be consumed. Two types of photovoltaic technology that have been
developed for this purpose are photovoltaic panels (PV) and photovoltaic concentrators (CPV).
For PV panels, the efficiency – or ability of the photovoltaic cells to capture solar
energy and convert it into electricity – ranges from 12 to 25%. The panels themselves have
efficiencies slightly lower than the actual cells because of structure and wiring. Traditionally,
the highest efficiencies have come from expensive, thick silicon panels. Recent work by several
scientists, however, has led to the development of cheap, flexible thin film panels capable of
at least 15% efficiency. These panels have begun to be produced on a significant scale.
As a result, with existing technology, PV could make a significant contribution to U.S.
energy production. According to a recent Energy Foundation study, assuming 15% panel efficiency
and a conservative estimate of at least 7,854 million m2 available residential and
commercial rooftop space, the U.S. could accommodate about 1 million MW of PV by 2025, which
would generate approximately 1.9 trillion kWh per year – almost half of current U.S.
electricity use. This does not include other distributed forms of PV electric generation, such
as ground mounted PV, PV shingles, covered parking lots, windows, awnings, and sides of
buildings. It also does not take into account additional improvements in panel efficiency.
According to a recent NREL analysis, the total long–term technical potential of PV in the
U.S. is around 219 TW – which could provide over three times current world energy use.
Investing the many billions of dollars presently proposed to be spent in Nuclear electricity
generation would, in the opinion of this author, be better spent on solar generation to yield a
far sooner, significant reduction of harmful GHG emissions and preserve vast environmentally
sensitive areas otherwise to be compromised by increased transmission lines which would be
unnecessary with the generation at the place of use.
Photovoltaic concentrators (CPV) – systems that reflect or focus light from a wide area
onto a small photovoltaic panel – could also make a significant contribution to meeting U.S.
energy needs. Solar concentrators move to track the sun, produce a more constant level of "peak
energy" throughout the day, and operate at higher efficiencies than PV panels.
Concentrators can also reduce costs by using less PV material per unit of energy generated (although
they do require an inexpensive optical element and a support structure and tracker).
Concentrators could be well–suited for stabilizing the generation of wind farms and for
installation along highways and transmission corridors.
America could meet all of its current electricity needs with large central concentrating
solar power plants according to a report released May 8, 2008, "On the Rise: Solar Thermal
Power and the Fight Against Global Warming" by Environment America. There is only limited
application at present for portable electricity generation, for example in recreational boating
as a back up supply. However, electricity distribution costs are kept to a minimum when used in
the location where it is generated.
Solar thermal power plants covering an area of 100 x 100–mile area in the Southwest (slightly
more than what has already been excavated for strip mining for coal across the country), could
power the entire nation while slashing global warming emissions.
Because solar thermal energy battery storage allows electric generating capacity even when
the sun is not shining, it can provide "baseload capacity," replacing traditional hydrocarbon
energy sources like coal, natural gas and nuclear power.
Unlike coal and uranium, sunshine as a fuel is free. Considering the cost of
energy (kilowatt–hours, kWh) alongside the cost of power (watts), the Solar Energy
Industries Association conservatively calculated that $6.32 per watt for PV translated into $0.18
per kWh. This seems high compared to mercury–laden coal energy, but it is competitive with
gas–fired peak energy, which PV most seamlessly replaces, and with the generating costs
many utilities already incur with other technologies.
Looking forward, PV carries no fuel price risk, nor will its use raise the price of any fuel.
Unlike fission and combustion plants, PV can be located in any unshaded site, without waste,
safety issues, emissions, noise, water usage or wildlife impacts. Because PV is modular,
construction work in progress (CWIP) ratepayer charges are unnecessary.
Grid–tied PV benefits both the utility corporations and their customers. Inverters, which make PV output
grid–compatible, are transistorized power conditioners. Their presence in a distributed
generation (DG) network maintains power quality and line voltage, protecting computers from
hiccups and other devices from burnout. DG relieves pressure on the transmission system,
mitigating the sorts of problems that darkened much of the East in August 2003. In these days of
terrorism paranoia, a million widely–dispersed 5 kW PV arrays offer a harder target than
one 1,000 MW nuke or coal plant. Moreover, PV capital expenses are usually borne voluntarily by the
homeowner who installs the system, not by the utility's other customers.
With net metering, the homeowners' electric meters run backward whenever his grid–tied
system generates a surplus. In effect, the utility buys peak–time electricity at retail.
Since peak power frequently costs more at wholesale than it sells for at retail, this seemingly
even trade actually profits utility companies.