The U.S. is experiencing diminished reliance on electricity generated from fossil fuels (coal, petroleum and natural gas generation) and an increase in reliance on renewables (wind, tide, geothermal, hydroelectric, solar and nuclear).  Coal now accounts for just 30% of electric generation.  While use of renewables has increases dramatically, only in one state has a renewable become the top source (hydroelectric in Vermont).  Renewables for electric generation may not be a top source, but in aggregate they are a huge part of overall power generation.

A review of state-by-state energy in 2017 shows coal is still the largest electric generation source in 18 states.  Natural gas was the dominant generation source in 16 states.  Nuclear provided the bulk of generation in 9 states.  Hydroelectricity leads in six states and petroleum was the major generation source only in Hawaii.

The U.S. has built one sixth of the global 539,291 megawatts of wind generating capacity.  Wind generated 6.3% of electricity for the U.S. in 2017 and by 2019, it’s expected to provide 6.9%, surpassing hydroelectric generation.  U.S. offshore turbines are expected to grow 600% by 2030 and their generation will top out at 24,135 megawatts, then about a quarter of U.S. capacity.   From a recent standing start, the U.S. now has enough offshore turbine capacity to power more than 17,000 homes. In four states (Iowa, Oklahoma, Kansas and South Dakota), onshore wind contributed 30% to 37% percent of each state’s entire electricity generation.

The costs ascribed to renewable power generation can include capital cost plus the costs of decommissioning the facilities that renewables would replace.  Another complicating factor for renewables is the cost of technologies that would “cover” the periods of time when insufficient sunlight, wind or water flow is available to generate power to serve the demand that renewables are supposed to fill.  Those intermittent lapses in output are usually covered by batteries, or by electricity from adjacent interconnected networks.  There is a limit to “borrowing” electricity from adjacent grids if those grids are also fueled by renewables and subject to intermittency.

Bloomberg New Energy estimates $55 per megawatt hour as the onshore wind farm “levelized cost” (a variant of net present value). The levelized cost for solar generated power is $70 per megawatt hour, similar to coal ($68 per megawatt hour), but much cheaper than combined-cycle natural gas ($93 per megawatt hour). On the other hand, Xcel received 11 bids for a new 450 megawatt wind power facility with a median bid of just $21 per megawatt hour including batteries to handle some predictable intermittency. The Xcel bids were reliant on a 30% federal tax credit.

Most discussion of batteries focuses on chemical storage batteries such as the Lithium ion technology or Cobalt batteries used in wireless phones and electric cars.  Currently the wholesale price for such batteries is near $200 per kilowatt hour, but it is expected to drop to $105 per kilowatt hour (i.e., $105,000 per megawatt hour).

An alternate battery contender is the “flow technology” battery. Flow technology can be scaled at a level suitable for electric grids.  In that technology, liquid electrolytes are made flow in opposite directions on opposite sides of membrane, causing electric charges to pass between them.  Reversing the flow will recharge the flow battery. The high cost of a flow battery is a challenge to its viability.

The migration away from coal-powered generation is well underway, but there is no single solution to providing clean power.  The least costly source for generation is wind-power (onshore or offshore), but it suffers from intermittency that requires a separate source of generation handle periods of inadequate wind.  Further research may provide a cost breakthrough on flow batteries that will accelerate the migration to wind and solar.  Thankfully, it does not appear that more federal tax credits are required to promote wind power.