Renewables-Only Grid

How Much Does It Take?

26 March 2023

Meredith Angwin, author of Shorting the Grid, estimated the generation requirements for a renewables-only grid, one powered only by wind, solar, and batteries. She summed capacities:

• peak load to supply the grid

• another peak load  to charge the batteries

• plus sufficient battery storage to supply peak load for a week or two.

See note [1] for definitions of technical terms.

In this essay, I analyze German data to investigate her claim. Germany has reported results of its real-life experiment in creating a largely renewables grid. This data is complete enough to confirm Angwin’s estimate and to conclude that Germany should shut down its wind and solar generators.

The German Data

Jack Devanney has extracted the following information from German data [2]. His essay investigated the flaw in electricity that is often overlooked by enthusiastic amateurs, but I will use his data to refine Angwin’s estimate and draw some conclusions.

No country has more strongly committed to intermittents Germany. German power demand averages about 57 GW. Currently, Germany is supporting both an intermittent grid, and a dispatchable grid as Table 1 shows. The total, 226 gigawatts, is 2.7 times the peak hourly load, 83 GW, in the 2016 to 2023 period.

Let’s translate this data into a form suitable for analysis. The following table shows the ratio of capacity to demand derived from Devanney’s data. The four demand levels range from the lowest load power to the highest. On a typical grid, the lowest demand is called the baseload, It is required every hour of every day and averages more than half the peak. I estimate the German baseload at 45 GW. Reserve capacity is typically 15% of peak demand. Other than these two estimates, all the numbers are derived from German data in Devanney’s essay.

In December 2016, there was a 100-hour dunkelflaute, a "dark calm", cloudy with little wind.  Renewable generators supply the least amount of power during a dunkelflaute, so I include  a column of ratios that adjust the nameplate capacities by the 2% capacity factor observed in 2016 [3]. This column represents the minimum contribution of renewables to grid demand, while the nameplate column represents their maximum contribution.

The table shows how small a fraction of the demand, from 3% to 6%, was delivered by renewables during a dunkelflaute. Such conditions are unusual but not rare, so the grid must be able to handle them without interrupting power to users. This requires that grid operators be able to dispatch generators having capacity totaling just under peak + reserve.

The German grid has nameplate renewable generation more than twice the average demand, and its dispatchable generators have enough capacity to back them up. Thus Germany’s renewable capacity exceeds Angwin’s estimate of nameplate renewables to supply current demand for power plus demand for charging batteries. If they installed sufficient batteries to back up peak load, there would be no need for the current dispatchable generators. I conclude that the German data confirms Angwin’s estimate of one peak load for each component of the renewables-only grid.

Implications For the German Grid

It is not worth discussing the 10,000 GWh of battery storage required to back up the German grid for a week-long dunkelflaute. Nobody has any idea where they would acquire the materials and money for such a massive project. Entrepreneurs are investigating other technologies for back-up, but right now the only available technologies for carbon-free backup are nuclear fission, pumped storage in some situations, and batteries.

What if we remove the requirement for battery back up? Then diapatchable generators must supply 94 to 97 percent of the load in a dunkelflaute. At all demand levels, many dispatchable generators are idle but must be ready to supply power at the request of the grid operator. This operational mode increases maintenance costs, increases fuel consumption, and reduces the useful life of machinery. Furthermore, while renewable generators are producing significant power, the dispatchable generators are not being paid for their primary product.

If Germany stopped building wind and solar generation immediately, they would save money on construction and its attendant environmental destruction. In fact, the grid operators might as well permanently shut down all existing renewables thereby saving costs, reducing environmental degradation, and improving grid stability.

Notes

[1] Some terms used in the electric power industry need definition.

Power is the rate electric energy is supplied to the grid or used by customers.

Load, or demand, is the power being demanded by customers.

GW is a measurement unit of grid power. One GW equals one billion watts, and a typical household demands an average of one thousand watts.

GWh describes the energy of one GW supplied or used during one hour. A 168 GWh battery can supply an average of 1 GW for a week. One cannot store power.

Capacity is the power a generator can supply to the grid.

A dispatchable generator can supply electric power when the grid operator requests it to supply demand. Fossil, hydroelectric, battery, and nuclear are dispatchable generators; wind and solar are not.

[2] Jack Devanney, "Electricity's Fundamental Flaw", Gordian Knot News (substack), 21 March 2023.

[3] Heiner Flassbeck, "The End of the Energiewende?", energypost.eu (website), 10 January 2017.