Despite the claim by developers that a solar farm’s generating capacity is X megawatts (MW) of electricity, a solar facility plant won’t generate X MW of energy 24 hours a day, seven days a week.
Much of the time it won’t produce anything.
Engineers who’ve worked with electric utilities say solar facilities generate no power most of the day, and seldom reach peak generation, yet they are marked by how many megawatts of electricity they can produce during the rare times they are at maximum output.
The ratings are ambiguous at best, and deceptive at worst, raising significant public policy concerns, engineers say.
It is important for county officials who approve permits for solar facilities to understand that the MW rating should not be interpreted as a constant flow of electricity. In actuality, the rating is only potential---a maximum output that occurs for about one hour around noon on a sunny day.
A solar plant generates less than the megawatt rating the other 23 hours, and no power at all the 14 hours of no sun light.
As a result of the intermittent nature of solar plants, electric utilities must keep redundant fossil fuel-fired electric sources operating constantly to fill in immediately when solar power is disrupted by clouds, rain and nightfall.
Compounding the cost of generating electricity, the federal Public Utility Regulating Policies Act requires utilities to buy all commercial solar power generated, even if it is more expensive than energy from other sources such as nuclear, natural gas or hydro power.
According to the North Carolina State Solar House, the intermittent nature of solar energy generation, indicate that on mostly cloudy or raining days the house produced less than 10 percent of its maximum rating capacity.
A partly cloudy day recorded erratic fluctuations.
The variability of solar output would be the same regardless of a solar facility's size.
For example, the 60 MW generating plant in Currituck County, North Carolina running at full capacity for the full 8,760 hours in a year would produce 525,600 MWh.
However, the available usage is only 146,000 MWh or 27.7 percent of the full capacity since it generates only when the sun is shining.
COST OF SOLAR ENERGY PRODUCTION INCLUDES BACKUP GENERATION
Properly accounting for the cost of solar energy means including the cost of the backup generation that is required to accompany it.
Including these backup costs, the levelized cost of new solar plants is far more expensive than the levelized cost of existing power plants and nearly three times more expensive than the most efficient zero-emissions nuclear power plants.
An example of increased pollution due to solar power generation comes from a 2019 Duke Energy permit application.
Under its current permits in the heavily regulated market, Duke must completely shut down the backup combustion turbines when solar peaks under full sun, then restart them when the sun recedes.
Duke wants the N.C. Division of Environmental Quality to issue new permits allowing combustion turbines to throttle up and down from a “low load” idling operation instead of switching completely off and on as solar waxes and wanes.
In its permit applications, Duke said that would lower pollutant emissions and reduce stress on machines.
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About NOx
- NOx refers to both nitric oxide (NO) and nitrogen dioxide (NO2).
- NOx is a main constituent in the formation of ground-level ozone which causes severe respiratory problems.
- Along with sulfur oxides (SOx), NOx contributes to the formation of acid rain and causes a wide range of environmental concerns.
- NOx can deteriorate water quality by causing an overabundance of algae.
- NOx can form nitrous oxide (N2O), which is a greenhouse gas, and contributes to global warming.
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Without any solar power in the mix, “a typical combined cycle combustion turbine emits NOx at approximately 9-11 lb/hr., assuming 24 hours of ‘normal’ operation.
That is equivalent to 264 pounds of NOx emissions daily.
When those same plants are operated to supplement solar power facilities, daily emissions more than double to 624 pound a day, based on a table in Duke's application.
According to Duke's alternate operating scenario, a combustion turbine would emit 381 pounds of NOx daily, 44% more pollution than operating without any solar power on the grid.
Compounding the additional cost of backup energy generation is the fact that a solar farm requires 75 times more land than a conventional plant of the same capacity. These factors result in solar energy being an inefficient form of electrical generation.
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