Two years after it was first unveiled, Breakthrough Energy Ventures -- a billion-dollar fund to finance breakthroughs in energy technology -- is finally pulling back curtain a little bit.

Speaking this week at the One Planet Summit in Paris, Bill Gates, the de facto leader of the group, detailed five areas that the team will look to invest in. The sectors are some of the most challenging, and most important, in energy, including energy storage, liquid fuels, off-grid microgrids, low-carbon building materials and geothermal.

We’ve also been able to glean a few more details on the BEV leadership team. While the website lists multiple high-profile cleantech experts, a source close to the group specified that the fund is being led by former Duke professor and ARPA-E Program Director Eric Toone on the science side, and entrepreneur and investor Carmichael Roberts on the business side. Rodi Guidero, who works as part of Gates’ private office, will serve as executive director and primary liaison to the board.

This new information provides the first glimpse at just how this major experimental effort, backed by 21 high-profile investors, will look to conduct investments and try to find breakthrough energy technologies.

Investors in the fund include Gates, Silicon Valley investors Vinod Khosla and John Doerr, as well as some big tech heavyweights like Alibaba founder Jack Ma, Amazon founder Jeff Bezos, and SoftBank founder Masayoshi Son. 

The five areas that the team will focus on probably won’t surprise anyone that’s familiar with the Valley’s tumultuous cleantech history. The sectors are some that Gates and Khosla -- both board members -- have already invested considerable time and money in.

The board sets BEV's investing strategy, while the management team has the independence to make investment decisions, sources say.

"Incredibly cheap grid-scale storage"

The first topic that Breakthrough plans to focus on is the one on virtually everyone’s minds in the energy business: energy storage. The company says on its website that it wants to invest in “incredibly cheap grid-scale storage with a very long calendar life.”

Gates has long been interested in energy storage and has personally invested in a handful of next-gen battery startups like Aquion, which declared bankruptcy, and Ambri. He’s even backed some more unusual energy storage ideas like Energy Cache, which was described as offering “buckets of gravel on a ski lift” and is no longer in business.

Khosla has also funded a variety of battery companies like Seeo and Sakti3, which were both acquired, as well as energy storage startup LightSail Energy.

As lithium-ion batteries get cheaper, funding new chemistries to store energy has been getting harder. Many startups have gone bankrupt attempting to scale up new forms of batteries.

BEV believes lithium-ion batteries may be getting cheap enough to “meet the demand for extra energy at peak times,” but that other forms of energy storage will be needed to turn intermittent energy into baseload power.

These alternative forms of energy storage will be incredibly difficult to fund and grow successfully. The companies that have successfully built businesses off of energy storage these days are mostly piggy-backing off of low-cost lithium-ion batteries, like Tesla, Stem and AES Energy Storage.

BEV leaders say they're looking at storing energy as heat and compression and through next-gen batteries, which means the team has their work cut out for them.

Inspired by solar fuels

The second topic that the firm is looking to invest in is another one near and dear to the heart of Khosla and Gates: liquid fuels. Khosla, in particular, has invested millions into biofuels (with few successes) and Gates has sometimes invested in companies alongside him.

Biofuels represent another extremely challenging sector. The cost of liquid fuels needs to be as cheap, or cheaper, than gasoline to compete at scale. However, most companies have found that the cost of collecting biomass and processing it into a fuel is far more expensive than the cost to produce gasoline.

BEV isn't just looking at projects that convert biomass into fuels, but also at other alternative ways to make liquid fuels like capturing carbon from the air and converting it using the sun. 

Bill Gates has been particularly interested in this approach, which he and others call “solar fuels.” Caltech chemistry professor Nathan Lewis has been working on solar fuels in his lab, which Gates recently visited and called “inspiring.”

On BEV's website, the group says: “Electric cars hold great promise, but there aren’t enough companies making them and it takes too long to extract lithium to manufacture the batteries at the necessary scale. It is incredibly difficult to electrify air travel and long-haul shipping across oceans. The future of transportation will almost certainly require liquid fuel.”

The EV industry and Elon Musk would likely disagree. Musk often says that all transportation, other than rocket ships, will eventually go electric.

Developing global microgrids

The third topic that BEV intends to tackle is one that’s a break from the Gates/Khosla cleantech investing strategy, although it is one that the Bill & Melinda Gates Foundation is likely interested in.

BEV wants to invest in projects that build microgrids and mini-grids across the developing world like rural Africa and India. Such microgrids would presumably require low-cost solar and low-cost energy storage, but could also rely on cellular networks.

The market for such devices and projects is actually starting to garner some serious investment and attention from entrepreneurs. Companies focused on microgrids in sub-Saharan Africa and rural India include Off-Grid Electric, M-Kopa, and d.light. All of these companies have raised substantial capital from investors.

Unlike with new forms of energy storage or new types of liquid fuels, building microgrids will rely on technology that’s already been developed and is becoming cheaper. This is an area where BEV could invest growth capital and, if done right, make a return.

Zero-carbon building materials

Creating startups to develop new building materials is another tricky issue. BEV says it's interested in “zero-carbon ways of producing concrete and steel,” “engineered wood,” “mass timber” and “fiber-reinforced composites.”

Companies like Serious Materials tried to make low-carbon building materials and struggled. As with biofuels, it’s hard to produce these commodity products in a sufficiently low-cost manner to compete with the current ones already available.

Other companies like LanzaTech, which Khosla invested in, can take waste gases, like carbon, and inject them into building materials. Turning carbon waste into a product that someone will pay for is a growing area of interest for startups.

Geothermal

The final sector is (no surprise) another really difficult one. Khosla is one of the few investors who has invested any money into new geothermal energy technologies.

AltaRock Energy, backed by Khosla, Kleiner Perkins, and others including Google.org, has been trying to develop next-gen geothermal technologies and has made some progress, but also struggled. At one point, Google.org was interested in geothermal tech, but that went by the wayside when it shut down its RE<C project.

BEV believes recent advances in drilling technology present interesting new opportunities for geothermal, however. "Techniques like horizontal drilling, multilateral drilling, extended reach drilling, complex path drilling, and hydraulic fracturing, or fracking, all developed to extract fossil resources, offer interesting possibilities for geothermal energy," according to the website. 

A broader coalition

In addition to unveiling BEV's investment focus, Gates announced an expansion of the Breakthrough Energy Coalition, which connects transformative, government-funded research to interested investors in an attempt to get clean energy innovation to market faster.

This week, BEC unveiled 15 new coalition members, including Engie, National Grid, Energy Impact Partners, General Electric and Total. Furthermore, BEC is now piloting public-private collaborations with five  Mission Innovation members: Canada, the European Commission, France, Mexico and the United Kingdom.

“Energy transitions take a long time, but there’s more urgency than ever to prevent the worst impacts of climate change," said Gates, in a statement. "We need new models of investment and new partnerships between governments and a broad network of investors, companies, and energy customers. Breakthrough Energy is designed to help facilitate those partnerships and bring more energy products from the lab to the market more quickly.”