RGGI Transition Powerplants discussed the physical requirements of the renewable plus storage powerplants which would be required to replace existing conventional powerplants and add new generating capacity as the RGGI states continued their planned transition. This commentary will estimate the costs of these renewable plus storage powerplants and compare them with the costs of new conventional generation.

Nuclear generation, where available, is the primary choice for baseload generation. When nuclear generation is unavailable or the available nuclear capacity is inadequate to meet baseload demand, the typical choice has been coal-fired generation and more recently natural gas combined-cycle generation. Therefore, we will use the costs of new coal and natural gas powerplants as the basis for comparison of the costs of renewable plus storage powerplants.

The current estimated cost of a new 500 MW coal powerplant is approximately $2.5 billion. The current estimated installed cost of a new natural gas combined-cycle powerplant is approximately $550 million. The coal powerplant would require a land area of approximately 250 – 500 acres while the natural gas powerplant would require approximately 100 acres. Both plants would be capable of continuous operation with scheduled shutdowns during periods of low grid demand for routine maintenance.

The current estimated cost of a baseload solar plus storge generation facility capable of generating 500 MW continuously for one sunny day is shown below.

            Solar collectors:        $2 – 3 billion (4*500 MW @ 25% capacity factor)

            Storage batteries:     $1 billion (18 hrs.* 500 MWh * $125,000 per MWh)

Configuring this powerplant to operate for additional days without solar generation would require addition of:

            Storage batteries:     $1.3 billion (24 hrs. * 500 MWh * $125,000 per MWh)   

            Solar collectors:        $1 – 3 billion 

depending on the desired speed of recharge of the additional storage capacity. Configuring the powerplant to continue to power the grid for 10 consecutive days without significant solar generation, as was the case during and after winter storm Fern, would cost approximately $30 billion, or approximately 12 times the cost of a coal powerplant which could operate for far longer than 10 days and nearly 50 times the cost of a natural gas combined cycle powerplant of the same capacity.

The four 500 MW solar arrays would require a land area of 10,000 acres and the 9,000 MWh storage required for continuous single day operation would require approximately 200 acres.

The analysis above ignores several factors, including the acquisition cost of the required land area, the shorter useful lives of the solar collectors and batteries, the roundtrip efficiency of the storage system, seasonal variation in solar array outut and the cost of fuel for the coal and natural gas powerplants. Lithium batteries have a roundtrip efficiency of approximately 90% and are most suitable for short-duration storage. Pumped hydro systems are more suitable for intermediate-duration storage but have a roundtrip efficiency of approximately 75% and cost approximately $75 – 100 million for a 500 MWh system. The most commonly discussed approach to long-duration storage is the production and use of Green Hydrogen, which has a roundtrip efficiency of approximately 50% at a cost of $250 – 500 million for a 500 MWh system.

A solar plus storage electric grid is clearly not on the path to reduced electricity costs.