There are millions of U.S. rooftops waiting for someone to install solar panels. If these surfaces were generating electricity today, we could cover at least half of the country’s electricity demand, say researchers .

But today’s solar panels, despite shattering growth projections and plunging in price, are still too expensive and fragile to replace asphalt shingles and the other materials that cover roofs today.

Sustainability involves developing technology that can be productive over the long term.

Finding cheap materials to withstand the rigors of roofing while generating cost-effective electricity is the next frontier for solar. Dow has already introduced its PowerHouse Solar Shingle, a thin-film photovoltaic cell that acts like traditional roofing and lasts the life of your roof. While the shingles are cheap (the company claims you’ll earn $4 in energy savings for every $1 you invest), they still cost more than conventional materials and rely on exotic metals such as copper indium gallium diselenide–both expensive and controlled almost entirely by China.

Now, researchers are using everyday materials for solar power generation to dramatically cut costs of new solar devices. Speaking at the annual meeting of the American Chemical Society, physicst Harry Atwater of the California Institute of Technology and James Stevens with Dow Chemical, announced that new zinc and copper devices are breaking records for electrical current and voltage achieved in thin-film solar energy devices. Their goal is to ditch rare, expensive metals for common materials and achieve very high efficiencies for electricity generation at a cost approaching today’s coal-fired power plants, a milestone that could come within 20 years, said Atwater.

“Sustainability involves developing technology that can be productive over the long term, using resources in ways that meet today’s needs without jeopardizing the ability of future generations to meet their needs,” said Atwater at ACS. “That’s exactly what we are doing with these new solar-energy conversion devices.”

There’s no doubt that market-ready technologies will start to change the equation in the future, but today’s solar shingles aren’t adding up just yet. The German company Energy Conversion Devices, which touted its own shingle technology, is now up for auction after its share value peaked earlier this year. The bankrupt company sold its solar assets for “future manufacturing of USO’s proprietary Uni-Solar brand thin-film solar laminates” in June. Any other takers?