We started our series on solar energy at a small scale. This time, we are going big -- the Al Kharsaah Solar Plant in Qatar is one of the largest solar farms in the world. In this episode, we're going to take a closer look at solar at scale—exploring the limits to scaling up this seemingly unlimited energy source, and the innovations underway today that could define what the solar industry looks like in the future, both in solar photovoltaics like in Qatar, as well as concentrating solar thermal.

People: Puskar Thapaliya

Places: Al Kharsaah Solar Plant, Qatar; Ivanpah Solar Electric Generating System, California

Technology/Concepts: Concentrated Solar Power, Project Hail Mary Closing the Gap is hosted by Gwen Holdmann and edited by Jennifer Pemberton. This episode was produced by Liz Smith and Tony Williams. Music is from Blue Dot Sessions.

This is the first episode in a series about solar energy, and we're starting really small. In Germany, Gwen learned about these compact personal solar kits you can install yourself -- right out of the box. There, they call it balkonkraftwerk, or balcony solar. Of course she had to buy one when she got back from Europe and try it out on her roof in Fairbanks. But is the grid ready for this kind of DIY power generation?

People: Mariana Low, Alaska Center for Energy and Power; Dan McIntosh, Golden Valley Electric Association

Places: Germany; Fairbanks, Alaska

Technology/Concepts: Origins of solar panels, photovoltaics, Solar One house, balcony solar, plug-in solar

Closing the Gap is hosted by Gwen Holdmann and edited by Jennifer Pemberton. This episode was produced by Liz Smith. Music is from Blue Dot Sessions.

You don't need super high temperatures to harness geothermal energy. Under the right circumstances, a much smaller thermal gradient can be used as well. If we start digging, we're guaranteed to find heat. It's getting that heat to the surface where we can use it without spending more energy than we can actually get out of it -- that's the tricky part. We visit South Africa, Denmark, and upstate New York to learn about the not-so-hot geothermal resource that's beneath our feet all over the world.

People: Morten Hansen, Project Services Lead, Innargi; Jeff Tester, Professor of Sustainable Energy Systems at Cornell University

Places: Mponeng Mine, South Africa; Aarhus, Denmark; Cornell University Bore Hole Observatory

Technology/Concepts: ground source heat pump, low temperature geothermal, district heating

Closing the Gap is hosted by Gwen Holdmann and edited by Jennifer Pemberton. This episode was produced by Liz Smith. Music is from Blue Dot Sessions.

A look at the extreme edges of geothermal energy. We'll start with the super hot -- actual liquid magma -- chatting with a couple of visionary Icelanders that have some big ideas about the future of geothermal.

People: Hjalti Páll Ingólfsson, Director, GEORG (Geothermal Research Cluster); Eli Gudleifsson, Alaska Center for Energy and Power; Björn Þór Guðmundsson, CEO Krafla Magma Testbed; John Eichelberger, Alaska Volcano Observatory; Paul Craig and Anthony Pennino, co-founders of GeoAlaska

Places: Krafla Volcano, Iceland; Mt. Augustine, Alaska

Technology/Concepts: Super hot geothermal energy; drilling magma; volcano energy

Closing the Gap is hosted by Gwen Holdmann and edited by Jennifer Pemberton. This episode was produced by Tony Williams. Music is from Blue Dot Sessions.

We cover the basics of geothermal energy before diving in to the more extreme versions of the technology in the next few episodes. And where better to kick off an episode on geothermal than with a mini-tour of Iceland — a country that has arguably made better use of geothermal than anywhere else on earth? In this episode, we'll visit three sites in the southwest near the capital of Reykjavik before winding up in my own backyard in Alaska.

People: Viktoría Gísladóttir, Wind and Hydro Project Manager, Orkuveitan (Reykjavik Energy); Arni Hrannar Haroldsson, CEO Orka Natturunnar; Eli Gudleifsson, Alaska Center for Energy and Power;

Places: Hvammvik, Iceland; Hellisheidi Geothermal Power Plant; Grindavik, Iceland; Chena Hot Springs

Technology/Concepts: Geothermal power; geothermal district heating

Closing the Gap is hosted by Gwen Holdmann and edited by Jennifer Pemberton. This episode was produced by Tony Williams. Music is from Blue Dot Sessions.

Before our towns and homes were lit by electricity, we relied on something called town gas for everything from reading lights to cooking. Eventually, town gas in most places was replaced by natural gas, which burned cleaner. But the switch from town gas to natural gas was not a one to one replacement, and it was not trivial. Because town gas, unlike natural gas, is mostly hydrogen.

People: Tony Izzo, CEO Matanuska Electric Association; Laurent Nassif, Alaska Center for Energy and Power

Places: Honolulu, Hawaii; Chena Hot Springs

Technology/Concepts: hydrogen blending, town gas, syngas, natural gas

Closing the Gap is hosted by Gwen Holdmann and produced by Jennifer Pemberton. Music is from Blue Dot Sessions.

Hydrogen is the most abundant element in the universe and is the energy source powering our sun. The idea of a hydrogen economy has been promoted for decades. So what's holding us back? In this episode, I learn how to fill up a hydrogen vehicle in Hawaii and share the amazing story behind the discovery of naturally occuring hydrogen gas reserves in Africa that have energy wildcatters scouring the earth for more.

People: Aaron Miyashiro, Service Manager, Servco Toyota in Honolulu, Hawaii; Erin Whitney, Director, U.S. Arctic Energy Office; Geoffrey Ellis, U.S. Geological Survey

Places: Honolulu, Hawaii; Mali

Technology/Concepts: hydrogen powered cars, geologic hydrogen Closing the Gap is hosted by Gwen Holdmann and produced by Jennifer Pemberton. Music is from Blue Dot Sessions.

We explore two carbon capture technologies that are exploiting natural geologic processes. But the companies working on these solutions are taking those natural processes and speeding them up a bit -- giving mother nature a little extra push in order to try and slow down climate change. The first is a company called Carbfix in Iceland, which is turning carbon dioxide into stone and storing it underground. The other is using rock flour ground up by glaciers in Greenland as a carbon sink.

People: Katrina Hoffman, Prince William Science Center; Ólafur Teitur Guðnason, Communications Director at Carbfix; Minik Rosing, Professor of Geology, University of Copenhagen

Places: Cordova, Alaska; Reykjavik, Iceland; Greenland; Ghana; Denmark

Technology/Concepts: carbon sequestration, plate techtonics,

Closing the Gap is hosted by Gwen Holdmann. Jennifer Pemberton is our producer. Music is from Blue Dot Sessions.

Special thanks to Jess Larson, a volcanologist at the Geophysical Institute at the University of Alaska Fairbanks for helping me understand some of the concepts we shared here. And additional thanks to Wendy Ranney, the owner of Orca Lodge in Cordova for narrating our hike to the Sheridan Glacier.

See Bjork's Carbfix shoes.

Not every place has the right geologic settings for long-term carbon storage. But Alaska is one – in fact, Cook Inlet is the best tidewater location for storage on the entire west coast of North America. North Dakota is another. And for North Dakota this isn't necessarily so much about mitigating climate change, it's about building a new niche market to offer a service that others are willing to pay them for.

People: Kevin Connors, University of North Dakota Energy and Environmental Research Center; Adam Dunlap, Chief Development Officer, at Harvestone Low Carbon Partners; John Reiten, Senior Energy Policy Advisor, North Dakota Office of the Governor; Stacy Tschider, President, Rainbow Energy; Haley Paine, Deputy Director, Alaska's Division of Oil and Gas

Places: Bismark, North Dakota; Blue Flint Ethanol Plant;

Technology/Concepts: carbon capture and sequestration Special thanks to Alaska Department of Natural Resources for allowing me to tag along on their tour to North Dakota and to Charlene Crocker and Scott Ayash from the UND for transporting their permeability fish tank display halfway across North Dakota at my request so we would get the chance to play with it.

Closing the Gap is hosted by Gwen Holdmann. Jennifer Pemberton is our producer. Music is from Blue Dot Sessions.

Like much of rural Alaska, the town of Nome relies heavily on imported fuels for heating and power. The cost of heating oil here is well over $7/gallon. That's what incentivizes a lot of Alaska communities to pursue new energy technologies, often well before they are part of the mainstream. Nome was the first community in Alaska to have a commercial solar array, and first to enter into an agreement to purchase power from a privately owned wind farm. If nuclear micro nuclear reactors are going to be feasible anywhere, Nome seems like a pretty good candidate.

People: Ken Morton, Nome Joint Utility System manager; Michael Valore, Senior Director of Advanced Reactor Commercialization, Westinghouse; John Hanlon, Mayor of Nome

Places: Nome, Alaska

Technology/Concepts: Nuclear microreactor

Closing the Gap is hosted by Gwen Holdmann and produced by Jennifer Pemberton. Music is from Blue Dot Sessions.