Physics and PV Solar

Physics and PV Solar

PV solar has fundamental limitations that won’t go away, even though solar energy is abundant.

According to the Energy Information Administration (EIA) “solar energy is the most abundant energy resource on earth … More than 10,000 times the world’s total energy use.”

From this has evolved efforts to use PV solar by utilities, and by homeowners and businesses with rooftop installations.

While PV solar can theoretically supply all the electricity the world needs, it can’t do so economically or without interruption.

The fear of climate change has caused governments to promote and subsidize PV solar installations.

Remove the fear of CO2 causing climate change, and PV solar becomes a boondoggle, with limitations that can’t be avoided.

PV rooftop solar with electrical connection. Photo by D. Dears
PV rooftop solar with electrical connection. Photo by D. Dears

A PV solar installation using mono-crystalline silicon has an efficiency of 15% to 18%, while a thin film installation will have an efficiency of around 8%… and these efficiencies can’t be improved very much.

While the maximum theoretical limit for monocrystalline silicon is 44%, there are other unavoidable factors that preclude getting above 18% by any significant amount in a usable configuration. An article by Tom Murphy, Don’t Be An Efficiency Snob, explains these facts and is worth reading.

He rightly points out that the average American home only needs 1/6 of its roof area to generate all the electricity the homeowner needs. But, as he also points out, costs may not warrant the homeowner installing a PV rooftop system.

What he doesn’t point out is that solar can’t generate electricity at night or when there are cloudy days.

The amount of required roof area also varies from state to state based on the amount of electricity used by homeowners in each state.

  • As reported by Inside Energy using EIA data, the average homeowner in the U.S. uses 911 kWh per month: The homeowner in Hawaii uses the least amount of electricity at 506 kWh per month, while the homeowner in Louisiana uses the most at 1291 kWh per month.

In addition, the PV solar installation must point due south, otherwise output is significantly reduced.

Basically, at 15% efficiency, one square meter of a PV solar installation delivers 0.75 kWh of energy to the homeowner when the installation is pointed due south.

However, the amount of electricity generated depends on the amount of sunlight received in any specific area. The number of sunny days varies widely around the country, and around the world.

Yuma, Arizona has around 242 sunny days, while New York City has around 107.

Whether an installation is worth the investment also depends on how much the homeowner is paying for electricity.

According to the EIA, the homeowner in Florida is paying around 11.6 cents per kWh, while the homeowner in Connecticut is paying around 20.9 cents per kWh.

It takes longer to recover an investment when the rate being paid for electricity is lower, which is one reason why it could take 11 years to recover an investment in Florida. With a rate nearly twice as high in Connecticut, it also takes around 11 years to recover the investment in a PV rooftop system.

Payoff tables by state are listed in Nothing to Fear.

It’s theoretically possible to use PV solar to provide the world with electricity, but it may not be economical to do so, and it can’t do it without interruption.

Businesses frequently require a payback of two years or less for an investment. Homeowners may also worry about any payback longer than two years since they may move and not be able to recover their investment when selling their home.


  • Only Hawaii in the United States provides for an acceptable rate of return, of around three years without subsidies.

The Federal subsidy is currently 30% of the investment.

  • Southern California has a return of around 8 years, while most states have a return on investment of well over 12 years without subsidies.
  • Some states would see a payback period longer than the life of the solar panels.
  • Solar cannot provide an uninterruptible supply of electricity without expensive storage that may not be practical for homeowners. Trying to provide storage for when there are several cloudy days would add substantially to the investment and may not be possible. Storage can easily double the required investment and payback periods.
  • The laws of physics won’t allow the efficiency of PV solar to be improved very much beyond 18%.

While some costs may come down, such as for the inverter, it is doubtful that paybacks will get below an acceptable level anytime in the near future for most areas of the United States, even with subsidies … And for the world.

Burdening average Americans with debt by providing taxpayer funded subsidies for PV rooftop installations is bad for the United States … And unnecessary.

Wasting valuable financial resources on an unnecessary activity is bad for all Americans.

Remove the fear of CO2 causing climate change, and PV solar becomes a boondoggle, with limitations that can’t be avoided.


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