January 1, 2015

Energy Beyond Fossil Fuels

Renewables can power the post-carbon fuel energy age—if we can improve energy storage. 

As the middle class swells around the world, energy demands are increasing exponentially. China passed the United States in absolute energy use after nearly doubling its electrical power capacity between 2005 and 2010, and a similar trend is taking place in India and elsewhere. Countries that provide their citizens with a particular level of electricity attain a high score on the U.N.’s Human Development Index (HDI), as Alan Pasternak of the Department of Energy’s Lawrence Livermore National Laboratory observed in 2000. Pasternak’s breakthrough research showed that countries attain a 0.9 HDI—approximately the level of Spain—when citizens consume 4,000 kilowatt hours of electricity per year.

At Singularity University, we have examined how much additional electricity-generating capacity would be required to provide this “Pasternak level” of power to everyone in the world. It would take about five times what the present U.S. electrical power system produces. That is a lot—but it is achievable.

Meeting growing power needs would, of course, accelerate the use of our planet’s finite supply of fossil fuels. The vast majority of civilization’s energy still comes from burning coal, natural gas, oil, wood and biomass. The remaining supply comes from nuclear fission of radioactive materials left over from the formation of the solar system and thermonuclear fusion that takes place inside the sun. This latter activity is responsible for direct solar photovoltaic energy (light) and direct solar thermal energy (heat). Indirectly, sunlight is also responsible for wind energy (the sun drives wind currents) and hydro energy (it causes water to evaporate, which then comes down as rain or snow). Hydropower accounts for more electricity generation than all other renewables combined. A significant reason for that is hydropower’s intrinsic storage capability.

So with a finite amount of fossil fuels to supply an exponentially increasing global demand, the question becomes: What will it take to change the energy equation so that the majority of our energy comes from direct and indirect solar energy?

Renewables will become truly viable only when the cost of renewable energy, plus storage of that energy, equals the cost of getting energy from traditional fuels.

First, it will require a significant decrease in the cost of converting solar energy into usable forms of energy such as electricity. Fortunately, the cost of solar cells has been steadily declining since Bell Labs showcased the first solar batteries more than 60 years ago. But future renewable energy systems must resolve another fundamental issue: intermittency. We have to be able to provide energy when users require it, not when nature offers it. This essential challenge of solar energy can be overcome in two ways: energy networks and energy storage.

Improved energy networks would enable a greater penetration of renewables into the energy mix, since they would allow energy to be transported from where wind is blowing or the sun is shining to where it is not. The author and inventor Buckminster Fuller famously proposed an enormous (and expensive) global energy network that would enable intercontinental power sharing. NASA has demonstrated technologies that enable us to send electricity wirelessly from high Earth orbit (where the sun always shines) to cities and megacities with high energy needs. While such systems would be economical if the space components were built from materials already in space, such as lunar and asteroid materials, it will be some time before we see the large-scale use of solar power satellites.  

I believe, however, that the most important developments in energy in our lifetime will involve improved energy storage. The main reason that we use fuel-based energy like gasoline is that such fuel allows us to unlock energy at will. Renewables will become truly viable only when the cost of renewable energy, plus storage of that energy, equals the cost of getting energy from traditional fuels. The following energy storage methods are both cost-effective and scalable.

Pumped hydro. While demand for energy is low at night, water is pumped uphill into reservoirs. Then, during peak demand periods, water is allowed to run back downhill through turbines, pumping the reservoirs dry and generating electricity. Pumped hydro storage is presently the only grid-scale storage method in widespread use. The primary challenge of this technique is that it’s entirely terrain-dependent—it wouldn’t work in places like Illinois, which is relatively flat. However, in equally flat Ontario, Canada, this method is achieved by using disused mine shafts that are pumped dry at night.

Compressed air energy storage (CAES). In this technique, air is compressed using off-peak energy and released to drive turbines during periods of peak energy need. Berkeley, California-based LightSail Energy and Quebec-based Sigma Energy Storage, among others, are experimenting with ways to store and reuse the heat that results from the compression cycle. Some tests have used underground formations to hold the compressed air, but automated manufacturing of tanks made from composite materials (such as carbon fiber, which allow the tanks to be strong and light) could make these systems independent of special geology.

Thermal storage. This method heats up inexpensive materials, such as salts, in insulated tanks. The heat can come from concentrated solar energy, or from off-peak electricity such as that produced by wind farms at night. Heat is extracted during periods of high electricity demand using steam turbines or other conventional heat engines. An example: Emeryville, California-based Halotechnics develops molten salt and glass products that can store thermal energy at temperatures as high as 1,200 degrees Celsius.

We have to be able to provide energy when users require it, not when nature offers it. This essential challenge of solar energy can be overcome in two ways: energy networks and energy storage.

Liquid metal batteries. Traditional batteries, including the lithium batteries in your laptop or electric car, are still too expensive for home, microgrid (a neighborhood) or grid-scale (a whole city or region) storage. The liquid metal battery, credited to Donald Sadoway and David Bradwell of MIT, uses cheap, earth-abundant materials and doesn’t require special geological features. The two metals involved (which are currently proprietary to Ambri, the company Sadoway and Bradwell founded) have different densities that allow them to stack up and maintain their relative positions inside a vat, with the heavier metal on the bottom, molten salt as the electrolyte in the middle and the lighter metal on top. Ambri’s battery is in the prototype stage and not yet in use commercially.

Most of the popular scientific and energy news outlets are still focused on details of energy generation. However, what we really need most to boost the percentage of usable renewable energy is improvement in low-cost energy storage.

Gregg Maryniak is the chairman of the energy and environmental systems track at Singularity University, a Silicon Valley-based business education institution.