Maybe storage isn’t the ultimate key to a renewable energy future.
The question of how to integrate more variable renewable energy – solar and wind – onto the grid has typically focused on balancing generation capacity and load, an approach that tended to require expensive energy storage (or dramatic storage breakthroughs) to make it all work. But a new study out of Delaware went at the question from a new angle, and came up with results that suggest that a nearly complete switch to clean power sources might be more viable than previously thought.
The researchers, from the University of Delaware and Delaware Technical Community College, found that by aiming to achieve high levels of renewable energy integration at the lowest cost possible – even if it means at times generating vastly more power than necessary – it could be possible to meet 90 percent of demand with renewables at electric costs below today’s. Even 99.9 percent renewables, while not quite as cost-effective, could be achieved at comparable costs, the researchers said.
“The least cost solutions yield seemingly excessive generation capacity – at times, almost three times the electricity needed to meet electrical load,” the researchers wrote in their study. “This is because diverse renewable generation and the excess capacity together meet electric load with less storage, lowering total system cost.”
In doing this analysis, the researchers built a model that used actual weather conditions and demand from the PJM Interconnection, the 13-state regional grid that stretches from Illinois to New jersey and serves nearly a fifth of the nation’s electricity needs. The study employed what the authors suggest are conservative estimates of technology costs in 2030 – no remarkable breakthroughs, no government subsidies. It did incorporate external costs when measuring the full toll for fossil fuels, but didn’t factor in how things like scarcity or pollution control requirements might drive up such costs.
The researchers then ran some 28 billion combinations of wind, solar and storage at 30, 90 or 99.9 percent renewables over those 35,040 hours of shifting PJM demand. These calculations revealed that building a lot of geographically dispersed wind power – both onshore and offshore – and in some circumstances solar power, with a relatively modest amount of energy storage, could be a relatively cheap way to meet electricity needs. This is a departure from earlier researcher. The authors write:
Our model … cares not about over-generation, it simply makes load at minimum cost…. Since our model is cost optimizing, it demonstrates that matching generation to load via more storage (per Markvart, Denholm and others) would lead to higher cost of energy than our model’s selected mix. Thus, one conclusion of our study is that over-generation is preferred over more storage because excess generation is more cost-effective.
How much renewables are we talking about here? At the 90 percent level, which offered the lowest electricity prices at 2030 technology cost, offshore wind would offer 14.4 gigawatts of capacity; inland wind 126 GW; fossil fuels 56.9 GW; and energy storage 69.2 GW. At the 99.9 percent renewables level, the mix becomes more diverse, adding solar PV (16.2 GW) in with offshore wind (89.7 GW), inland wind (124 GW), fossil fuels (28.3 GW) and storage (51.9 GW) – but wind is still the big player, at least for the PJM grid.
To put all that in perspective, at the end of 2011, the entire country had 47 GW of installed wind capacity. Or, thought of another way, assuming 2.5 megawatts per land-based wind turbine – pretty common these days – it would take around 50,000 turbines to pull off the 90 percent renewables scenario.
One last thing: There’s the matter of all that excess energy that would at times be produced.. The authors didn’t formally factor it into their cost models. As they write, “(O)ver-generation is cost-effective at 2030 technology costs even when all excess is spilled.” But what if it wasn’t spilled, but instead was put to use? “If excess generation displaces heating fuels, the cost is lowered even further,” they write.