Solar Power
Michael H. Fox
Why We Need Nuclear Power
The Environmental Case
Read Chapter 4 for more detailed information.

I am a proponent of renewable energy.  I built a mountain cabin that is off the
grid.  All of the electricity comes from photovoltaic (PV) panels with battery
storage, using an inverter to provide AC power.  I also have a solar system
on my house that ties into the grid.  But there are big limitations to solar
power.  The efficiency of converting solar power into electricity is very low.  I
get about 11% conversion efficiency, which is pretty typical.  Why is it so
bad?  Solar panels are about 15% efficient and there are losses from dirt on
the panels, the inverter, wiring and other electronic components.  Overall, the
National Renewable Energy Laboratory estimates a derating factor for
converting rated DC to AC of 0.77, or a loss of 23%.  They have an excellent
program called
PVWatts that gives the average daily solar energy falling on a
square meter of land at many locations in the United States and around the
world. It then calculates the amount of AC energy you can expect to generate
for a given size of solar system; it will also calculate how much money that
will save you.

Capacity Factor:  When companies rate the size of a solar farm, they always
give the maximum power output, such as 100 MW (megawatts).  But
remember that the efficiency is only about 12% so you have to multiply the
maximum rating by 12% to get the actual output expected.  The
US Energy
Information Administration rates the capacity factor of different energy
sources and it gives PV solar a 25% capacity factor.  Why is it double the
actual efficiency?  Because they use the high end of the utilization range,
which would be in the best solar areas and they take into account the load
characteristics of the area.  Thus, solar would provide more energy during
the daytime when it is needed and thus gets a higher capacity factor than the
true efficiency.

Location:  A big problem for solar is the best solar is not where the most
people live.  This is obvious when you compare the NREL map of solar
resources with the NASA map of lights at night.  This requires building large
transmission lines to bring the solar energy to population centers.
Solar Energy
Industries
Association
NREL-PVWatts
Intermittency:  By its very nature, solar varies in intensity through the day,
through the seasons, and when it is cloudy or snowy.  This means it cannot
be relied on to provide power and must be backed up with other resources.  
It is best in the southwest where it can help meet the air conditioning load
during the afternoon.

The electrical load on a utility varies during the day and depends on the
season.  Residential demand varies differently than commercial demand.  
Residential demand peaks in the morning and evening, when solar is very
low.  Commercial demand rises during the day, matching solar output
better.  
A typical summer electrical demand curve is shown below.
Photo from
NASA
Figure 4.1
Figure 4.3
Figure 4.2
Footprint:  The large footprint of solar is due to the fact that solar energy is
very diffuse and its conversion to electricity is very inefficient, no matter how
you do it. If you scale up the solar utility-scale facilities to be equivalent to a 1
GW nuclear power plant, it takes about 50 square miles of panels or mirrors
to generate the same amount of electricity as an average nuclear power
plant. A nuclear power plant sits on about a third of a square mile. This huge
solar footprint is not entirely benign. Environmentalists are already up in
arms about scraping away vast areas of the desert to build solar facilities
and in the process destroying fragile ecosystems and endangering desert
tortoises and other plants and animals.  The Ivanpah solar tower uses 3,500
acres (5.5 square miles) of mirrors to generate its power (see below).  

Cost:   Solar power is expensive.  The EIA estimates that the 2018 levelized
cost of PV solar power will be 33% more than nuclear power on average.  
Another type of solar power is a thermal power tower.  Mirrors shine the sun
onto a tower containing a transfer fluid that produces steam and generates
electricity.  As one relevant comparison, the
Ivanpah solar power tower in the
Mojave Desert is rated at 377 megawatts, about one-third of a nuclear power
plant.  But it is only 30% efficient so it produces about one-third of its rated
power.  It costs about 2.2 billion dollars and is subsidized to the tune of 1.6
billion dollars by guaranteed federal loans.  To scale it up to a one gigawatt
nuclear power plant would cost 16 billion dollars!  It will provide electricity to
140,000 homes, but the San Onofre nuclear reactors that are being closed
powered 1.4 million homes.  The EIA gives the levelized cost of thermal
solar as 241% higher than nuclear power.