Gas turbines, not batteries, may provide the easiest path forward for renewables

Source: Umair Irfan, E&E • Posted: Tuesday, September 29, 2015

For ramping up renewables, storing electrons may not be the gatekeeper as some policymakers presume, a new study has found.

Clouds passing overhead and lulls in the wind make turbines and photovoltaics waver in power output. This can destabilize the grid and create energy shortfalls, forcing another electricity source to fill the gaps to keep the lights on.

Using a battery, a compressed air cavern or flywheel to soak up excess power when it’s available and dish it out when needed is an attractive prospect, but many of the technologies aren’t mature enough to deploy at the scales needed to keep up with renewables hitting double-digit penetration rates in some markets.

This is no cause for alarm, according to a report published last week in the journal Energy & Environmental Science.

It turns out that current natural gas turbines, nuclear reactors and hydroelectric dams could help renewables drastically displace dirtier fossil fuels on the grid, thereby lowering the carbon intensity of electricity generation.

“If you allow for some dispatchable power, you really don’t need much storage,” said David Keith, a co-author of the study and a professor of applied physics at Harvard University.

Keith reached this conclusion after modeling the economics of bulk electricity storage systems, devices that can hang onto power for several hours on the grid. The model accounted for performance, capital costs and fuel prices, with the aim of cutting carbon dioxide emissions.

“The novelty of this paper is that it’s doing a careful and clean job of energy system analysis that’s transparent and simple,” said Keith.

An overestimated need for storage?

It turned out that energy storage loses economically compared to natural gas turbines or dispatchable zero-carbon generators. This means that the low-carbon grid of the future can run on much of the technology that exists today rather than waiting for a hypothetical battery that’s cheap and easy to scale.

The findings run contrary to conventional wisdom that suggests that renewables need storage to compensate for intermittency before they catch on, though Keith noted that some other studies had also suggested that the purported need for energy storage is overstated.

“You could take wind from 4 percent to 40 percent and still not use much storage,” he said.

This is further supported by some real-world examples. In Germany, renewables are approaching one-third of the country’s energy supply, with a big chunk coming from intermittent wind and solar. However, the country has negligible energy storage but maintains one of the most stable electric grids in Europe using dispatchable power and energy trading.

The insistence on storage stems from “energy idealism” that aims to bring carbon emissions down to zero from generators, instead of using renewables and cleaner fossil fuels to displace dirtier energy sources — even though the latter approach is more economically viable, according to Keith. Opponents of renewable energy mandates also cite inadequate storage as a reason for blocking requirements for cleaner energy.

Jay Apt, a professor of engineering and public policy at Carnegie Mellon University who was not involved in this research, praised the new study. “It’s a very rigorous look at a future where energy storage is not required,” he said.

“None of this means that storage isn’t useful in smaller applications,” Apt added. “There will be off-grid applications, microgrid applications and emergency power applications where storage is extremely valuable.”