From the utility grid perspective, a fundamental problem with wind and solar is intermittency.
In the US, wind has a median capacity factor of 31%. In California’s Mohave Desert,
solar PV has a capacity factor of 23%. To make up the electricity supply difference
during the rest of the time, grids must either add otherwise unnecessary backup generation,
or flex base load generation (dropping below optimum output so the grid can accept
the intermittent renewable input). At a minimum, flexing results in costly capital
inefficiency. Otherwise unnecessary backup generation is even more costly.
The higher the renewable penetration, the greater this intermittency burden becomes.
For Texas’ ERCOT grid with 10.6% wind, the additional costs are ~$19/MWh for generation
plus ~$6.50/MWh for transmission. It is now so expensive in Germany (26% renewable
generation) that its largest utility, RWE, took a €3.3 billion impairment charge
1Q2014. The second largest, E.ON, took a €4.5 billion impairment charge 4Q2014, and
announced it was spinning its conventional generating assets off into an unprofitable
separate company. E.ON will also be shutting Irsching 4 and 5, large efficient CCGT
units completed in 2010 and 2011! Irsching simply is not viable without being compensated
for the forced Energiewende flexing it endures, while selling its electricity against
the subsidized renewables with which it is also forced to compete.
So renewables advocates hope for major advances in grid storage to offset wind and
solar intermittency. This guest post surveys what might be possible in the future
given what is presently known. The focus is on utility scale, but takes an irresistible
detour through TESLA’s newly hyped residential Powerwall. Sandia has a more detailed
(albeit somewhat dated and hopefully slanted) utility storage analysis than this
post, for CE denizens interested in digging deeper.
There are in principle only five ways that generated electricity can be subsequently
‘stored’: potential energy (e.g. pumped hydro), kinetic energy (e.g. flywheels),
electrostatic energy (capacitors), electrochemical energy (batteries), and chemical
energy (e.g. water hydrolysis). Anyone inventing another is in line for an automatic
Nobel Prize (probably two, physics or chemistry plus peace).