If we want a shot at transitioning to renewable energy, we’ll need one crucial thing: technologies that can convert electricity from wind and sun into a chemical fuel for storage and vice versa. Commercial devices that do this exist, but most are costly and perform only half of the equation. Now, researchers have created lab-scale gadgets that do both jobs. If larger versions work as well, they would help make it possible—or at least more affordable—to run the world on renewables.

The market for such technologies has grown along with renewables: In 2007, solar and wind provided just 0.8% of all power in the United States; in 2017, that number was 8%, according to the U.S. Energy Information Administration. But the demand for electricity often doesn’t match the supply from solar and wind. In sunny California, for example, solar panels regularly produce more power than needed in the middle of the day, but none at night, after most workers and students return home.

Some utilities are beginning to install massive banks of batteries in hopes of storing excess energy and evening out the balance sheet. But batteries are costly and store only enough energy to back up the grid for a few hours at most. Another option is to store the energy by converting it into hydrogen fuel. Devices called electrolyzers do this by using electricity—ideally from solar and wind power—to split water into oxygen and hydrogen gas, a carbon-free fuel. A second set of devices called fuel cells can then convert that hydrogen back to electricity to power cars, trucks, and buses, or to feed it to the grid.

If the goals of the “Green New Deal” are a political minefield, so, too, are the most likely strategies for reaching its target of very high national levels of renewable energy output.

A shelf of authoritative studies under the Department of Energy’s sponsorship dating back to George W. Bush’s presidency define how to take a big step in that direction. Their answer — build a network of long-distance, ultra-high-voltage transmission lines to widely share wind and solar power across the continent’s time zones.

But the strategy has faced overpowering headwinds of not-in-my-backyard opposition from residents and not-through-my-state political pushback. It’s also been rare for Congress to put aside partisan politics and pass major legislation facilitating transmission corridors.

“If you’re going to do a 100 percent clean energy portfolio — that is really 70 to 80 percent of electric power from renewables — I don’t know how you avoid huge transmission builds,” said Richard Sedano, president of the Regulatory Assistance Project, a nonprofit, nonpartisan think tank advocating a clean energy future. “It’s either that or overbuilding the system so much with surplus renewables and batteries” that consumers will be hammered.

“I don’t see how you have a national clean energy standard without significant federally mandated or incented transmission build cutting across regions of the country,” added Travis Kavulla, a former Montana utility commissioner and president of the National Association of Regulatory Utility Commissioners, now with the R Street Institute in Washington, D.C.

DOE’s National Renewable Energy Laboratory (NREL) issued the Eastern Wind Integration and Transmission Study in 2010, with strategies to provide 20 percent of the electricity supply east of the Rocky Mountains from wind energy by 2024. It counseled: “The integration of 20 percent wind energy is technically feasible, but will require significant expansion of the transmission infrastructure and system operational changes.”

The most detailed of the analyses is NREL’s ongoing Interconnections Seam Study based on massive computer simulations of power flows. It outlined one scenario with three ultra-high-voltage direct-current lines spanning the Rocky Mountains to the Mississippi River, with other new lines moving western power eastward.

Because grid operators can control the direction of power flows on direct-current lines, surplus afternoon solar power from the Southwest could stream into Southeastern states at dusk. Other lines could ship unused wind energy from the Great Plains into major cities in the Great Lakes and East Coast regions, or the other way into California.

By linking time zones, the variability of wind and solar power at different times of day becomes a strength, not a weakness, explained project leader Aaron Bloom.

It wasn’t that long ago that solar power and wind power were labeled as marginal, ‘green’ electricity, but in the last five years or so they have become much more affordable and economically more feasible than conventional sources like coal and nuclear.

What supported solar along the way partly was the emergence of energy storage in the form of battery systems. Electricity can now be made by solar power systems and the excess can be stored for usage at night or on less sunny days. At least, solar power has been paired successfully with energy storage, and it is catching up with solar power. The cost of this newish technology is dropping, “The overall estimated cost fell 32% in 2015 and 2016, according to the 2017 GTM Reseach utility-scale storage report. That will slow over the next five years, GTM reported. But battery storage is — in certain places and applications — on its way to cost-competitiveness.”

According to Lazard, it could drop another 36% between 2018 and 2022. The UC-Berkeley research study, “Energy Storage Deployment and Innovation for the Clean Energy Transition,” predicted lithium-ion batteries could hit the $100 per kilowatt-hour mark in 2018.

FERC Order 845, from this April, made conditions more favorable for wind energy storage, “FERC Order 845 is more important for wind developers because it changes the interconnection rules. A developer with underused interconnection capacity can now add storage without a new interconnection, allowing the wind developer to profit from underused interconnection capacity in a way that was not possible before,” said RES Group Chief Technology Officer Andrew Oliver.

It isn’t only lithium-ion batteries that have potential to back up wind power systems, as flow batteries might work too, “Due to its scalable energy capacity the Vanadium redox battery is a highly promising option to support our advanced technology offers for isolated and grid connected systems,” said Antonio de la Torre, SGRE’s chief technology officer.

The notion of cost-competitiveness can be a strange one, because the costs of fossil fuels go far beyond extraction, processing and shipping. What is the cost of burning oil and coal on human health and the planet? Fossil fuels have always had much higher costs than have been acknowledged, so comparing them directly with those of solar and wind is quite misleading.

COPENHAGEN (Reuters) – The world’s largest wind turbine maker Vestas (VWS.CO) is tapping into experience from the car battery industry to try to address the challenge of using erratic wind and solar energy to meet a growing share of power demand.

Energy storage is becoming increasingly important as production of renewable energy rises, because the wind might not blow or the sun shine during the peak hours when most consumers turns on their lights and appliances.

In order to bring down cost of renewable energy and help grid operators balance intermittent output, Vestas last year said it would work to combine wind, solar and battery storage technology.

As part of this, it invested 10 million euros ($12 million) in battery manufacturer Northvolt, which aims to build Europe’s biggest battery cell plant with the backing of investors such as Volkswagen-owned (VOWG_p.DE) truckmaker Scania.

“We can piggyback on all the research they do with batteries for cars and get an excellent industry battery at the same time,” Vestas chairman Bert Nordberg told Reuters.

Vestas is partnering with Sweden’s Northvolt, headed by former Tesla executive Peter Carlsson, to develop a lithium-ion battery for power plants of the future.

Battery costs have traditionally been high, but the technology is becoming increasingly viable as automakers such as BMW (BMWG.DE), Daimler (DAIGn.DE), Volkswagen and Volvo Car Group (0175.HK) ramp up electric car production.

The spectacular falls in the cost of wind and solar energy continued in 2017, dropping another 18 per cent across the globe, according to the latest report from Bloomberg New Energy Finance.

The report also highlights the falling cost and growing uptake of battery storage, which together are mounting an unprecedented challenge to fossil fuel power, particularly as batteries start to encroach on the flexibility and peaking revenues enjoyed by those fossil fuel plants.

The new report from BNEF highlights Australia as one of the key countries to have led the cost reductions in both wind and solar. India is also cited for both wind and solar.

“Coal and gas are facing a mounting threat to their position in the world’s electricity generation mix, as a result of the spectacular reductions in cost not just for wind and solar technologies, but also for batteries,” the BNEF report says.

It notes that the cost of solar has fallen by 77 per cent to a benchmark global average of $70/MWh over the last seven years, while the cost of wind has fallen 38 per cent to a benchmark global average of $US55/MWh.

The benchmark price for lithium-ion batteries has also fallen nearly 80 per cent from $US1,000 per kWh in 2010 to $US209/kWh in 2017.

To be sure, there are countries where the cost of wind and solar is significantly cheaper than this, but it is interesting to note that these correspond roughly to the cost of wind and solar in Australia – if the $A was substituted for the $US calculation.

“Our team has looked closely at the impact of the 79 per cent decrease seen in lithium-ion battery costs since 2010 on the economics of this storage technology in different parts of the electricity system,” says Elena Giannakopoulou, head of energy economics at BNEF.

“Some existing coal and gas power stations, with sunk capital costs, will continue to have a role for many years, doing a combination of bulk generation and balancing, as wind and solar penetration increase.

“But the economic case for building new coal and gas capacity is crumbling, as batteries start to encroach on the flexibility and peaking revenues enjoyed by fossil fuel plants.”

The BNEF report says that fossil fuel power is now facing an unprecedented challenge in all three roles it performs in the energy mix – the supply of ‘bulk generation’, the supply of ‘dispatchable generation’, and the provision of ‘flexibility’.

In bulk generation, as energy authorities in Australia have long recognised, the threat comes from wind and solar photovoltaics, both of which have reduced their LCOEs further in the last year, thanks to falling capital costs, improving efficiency and the spread of competitive auctions around the world.