If the official definitions of renewable energy were logical, renewable energy would be defined as energy that does not emit CO2 and that is not using a resource in danger of running out anytime soon.  But the definitions written into the laws of many states are not logical.  Hydroelectric energy is mostly banned because the environmental movement hates dams.  Nuclear is banned because a hysterical fear of nuclear energy was created by environmental groups.  Both nuclear and hydro don't emit CO2.  Hydro doesn't need fuel.  Nuclear fuel is cheap and plentiful.  A large number of prominent global warming activists, such as James Hansen, Michael Shellenberger, and Stewart Brand have declared that nuclear is the only solution for the crisis that they imagine is approaching.

For those of us who don't take global warming seriously, there is nothing wrong with using coal and natural gas to generate electricity.  The CO2 emitted helps plants to grow better with less water, a great help to agriculture.

In approximately thirty states that mandate renewable energy, the only scalable forms of renewable energy allowed are wind and solar.  California mandates that 60% of its electricity come from renewable energy by 2030.  Nevada mandates 50% by 2030.  There are other types of official renewable energy, but they can't be easily scaled up.  Examples are geothermal energy, wave energy, and garbage dump methane.

Wind and solar are erratic sources of energy.  The output depends on the weather.  Solar doesn't work at night.  Because they are erratic, there have to be backup plants, generally natural gas plants, that balance the erratic flow of electricity from wind or solar.  The backup plants increase output when renewable energy output declines and vice versa.  Because both wind and solar are subjected to periods of near zero output, the backup system has to be able to carry the entire load of the electric grid without the wind or solar.  Neither wind nor solar can replace conventional plants.  If you hear that a utility is replacing fossil fuel plants with wind or solar, that can't happen.  The most that can happen is that the fossil fuel plants will use less fuel when the wind or solar is generating electricity.  For a natural gas plant, the gas to generate a megawatt-hour of electricity costs about $20.  That $20 is the economic value of each megawatt-hour generated by wind or solar.  Unsubsidized, wind or solar electricity, either one, costs about $80 a megawatt-hour to generate.  The difference between $80 and $20 is the subsidy that has to be paid in order to use wind or solar.

As long as the percentage of electricity that comes from wind or solar is small, the grid can handle the erratic nature of that electricity.  But if the penetration becomes large, severe problems start to emerge.  Solar power is strongest in the middle of the day and weakens toward the end of the day.  But the late afternoon and early evening, when solar is dying, are when power usage peaks in many locations.  The graph below shows how the sun's strength varied in Las Vegas for July 2018.

The output of wind farms varies rapidly.  The graph below is for the Texas wind system, with thousands of wind turbines.  In one hour, the output can change by more than 3,000 megawatts.

The problem with increasing the penetration of wind or solar to 50% or 60% of electricity generation is that there will be periods when there is too much electricity from wind or solar.  In that case, the grid operator will order that the wind or solar power be curtailed.  If you cut the output of a wind or solar plant, the power not generated is lost forever.  Further, curtailing the renewable energy works against meeting the mandate of 50% or 60% renewable energy.  For various technical reasons, it is increasingly difficult to utilize erratic renewable energy as the penetration increases.  Backup fossil fuel plants have trouble rapidly changing their output.  The geographical distribution of sources of generation impacts the capability of the transmission network.  The network has to have spinning reserve capability so that the sudden failure of a plant doesn't create a blackout.

In Nevada, the Gemini project is in the approval process.  It is a 700-megawatt (nameplate) solar plant with an associated battery system that can store 1,400 megawatt-hours of electricity, allowing electricity to be moved from midday, when there may be too much solar electricity, to the late afternoon, early evening, when it is needed.  The problem is that batteries are very costly for moving electricity.  A megawatt-hour of solar electricity that costs, unsubsidized, $80 during the day ends up costing $270 when moved to the early evening via a battery, based on costs from the National Renewable Energy Laboratory.  The $270 includes the cost of replacing the battery every five years.  The batteries have to be air-conditioned; otherwise, they will wear out even faster than in five years.  If the day is cloudy, there will be no solar energy, and the battery can't be charged.  Backup plants will take care of supplying electricity on cloudy days.  Use of batteries with wind is more difficult because there are long periods with too much or not enough electricity.

The renewable energy industry is asking its friends in Congress to extend subsidies for another five years and to add new subsidies for energy storage (batteries).  Producing CO2-free electricity for $270 a megawatt-hour that needs a duplicate set of backup plants makes no sense because nuclear could supply CO2-free electricity for $80 without needing backup plants.  Battery electricity demands large subsidies.

Another side-effect of increasing the penetration of wind and solar is that backup natural gas generating plants generate only half as much electricity if the penetration of renewables is increased to 50%.  The cost of electricity from a natural gas plant mainly consists of the capital cost of the plant spread over the megawatt-hours generated during the life of the plant and the cost of the fuel to generate each megawatt-hour.  Typical combined cycle natural gas plants operate at a capacity factor of about 50%.  That means they generate 50% of what they could generate if they ran at full power 100% all the time.  At 50%, the cost of the electricity is about half capital cost and half fuel cost.  If the capacity factor is cut in half, the capital cost doubles, increasing the cost of the electricity from underutilized plants.  Roughly, the cost of gas electricity will increase from $50 to $70 per megawatt-hour if renewable penetration increases to 50%.

Wind and solar are basically a waste of money.  The subsidies can be justified only as a payment for reducing CO2 emissions.  But wind and solar are expensive devices for reducing emissions.  It cost about $140 in subsidies per metric ton of CO2 emissions avoided.  Using nuclear or buying carbon offsets is a much cheaper solution.

Norman Rogers writes often about energy.  He has a website: Nevada Solar Scam.  He is the author of the book Dumb Energy: A Critique of Wind and Solar Energy.