As the old saying goes, two heads are better than one. The same is true when it comes to solar cells working in tandem. Researchers at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) have prepared a roadmap on how to move tandem solar cells—particularly those that mesh different photovoltaic technologies—closer to commercialization.

As the researchers pointed out in an article in the journal Joule, considerably more solar power must be added globally beyond the currently installed 1 terawatt of capacity. Because of the growing population and increased electrification of all energy sectors, experts are predicting the world will need 75 terawatts of photovoltaics (PV) by 2050.

The vast majority of solar modules in use today rely on a single junction, which is able to absorb only a fraction of the solar spectrum and thus are limited to how efficient they can be. Tandem solar cells, which consist of two or more junctions, hold the potential to reach much higher efficiencies. Because tandems are stacked on top of each other, the total area a module requires decreases—in turn, raising the efficiency and potentially lowering the total system cost.

It’s the “duck curve” problem. Solar power is providing huge amounts of energy during the day, creating a headache for grid operators.

Now that we can generate clean, renewable energy from the wind and sun, one of the most pressing questions facing the clean energy transition is how to effectively store that energy for future use. For one city in Finland, the answer is a giant underground cavern.

Vantaan Energia has announced that it will construct a massive underground seasonal thermal energy storage facility for the city of Vantaa, the country’s fourth-most-populous municipality. The facility will be twice the size of Madison Square Garden, New Atlas reported.

“The world is undergoing a huge energy transition,” Vantaan Energia CEO Jukka Toivonen said. “Wind and solar power have become vital technologies in the transition from fossil fuels to clean energy. The biggest challenge of the energy transition so far has been the inability to store these intermittent forms of energy for later use. Unfortunately, small-scale storage solutions, such as batteries or accumulators, are not sufficient; large, industrial-scale storage solutions are needed.”

A couple of solar-sector manufacturers have a powerhouse agreement that reaches a unique benchmark. Thanks to a $400 million, three-year deal between Heliene and Suniva, solar panels and cells will be entirely made in the U.S., a unique combination until now.

Electrek reports that to this point, solar cells — the contraption that turns sunlight into electricity — were imported.

“Heliene is proud to embark on this historic partnership with Suniva at a time when the U.S. is poised to capture a greater share of the global solar market by bolstering domestic manufacturing and onshoring of supply,” Heliene CEO Martin Pochtaruk said in a press release.

Scientists developed a device that combines wind and solar to harvest clean energy more efficiently and create a self-cleaning solar panel.