If 90 percent of the electric grid was powered with renewable energy sources like solar and wind, it would halve the cost of electricity by 2030, according to a new study released by the University of Delaware.

“There was a lot of stuff going on in this research that we didn’t expect,” said Willett Kempton, a professor in the School of Marine Science and Policy.

“We found that it is possible to have a reliable electric system with a very high percentage of renewable penetration,” Kempton said. “That’s definitely not something that was believed to be the case.”

Kempton and his co-authors created a computer model that tested 28 billion combinations of renewable energy sources and storage mechanisms using data from the PJM Interconnection, which serves 13 states from New Jersey to Illinois and represents one-fifth of the United State’s power grid.

Kempton said he has worked in the power industry in the past and was able to pull out some of the most surprising data and highlight in the report.

The study found that the best way for renewable energy generation to replace fossil fuel power without intermittency issues would be to overproduce it. Rather than storing energy, which is costly, utilities could produce more than twice what they need at peak demand periods using diverse renewable energy generation technologies that produce most at different times of the day.

That mix is key, Kempton said.

“A really high penetration you need solar because it’s the only one that reliably produces every single day and often at peak times,” Kempton said.

But you can’t just have solar. Wind can provide power at night.

As for energy storage, batteries are costly and unlikely to compete, Kempton said. Hydrogen storage is an option.

“The cheapest option was to use the batteries in electric vehicles when they weren’t in use,” Kempton said.

The research team used current projections for costs of existing renewable energy and stripped away all subsidies in calculating their costs. Kempton said that was incredibly conservative because it’s extremely unlikely that new technologies will not emerge in the next 17 years that will bring renewable energy costs even lower.

The team also factored in the real cost of fossil fuel power generation, including health and environmental expenses not usually assumed by the utilities.

As states begin charging power producers for carbon emissions, Kempton said he expects the University’s model to look increasingly realistic.