MIT Researchers Tip Their Cards

Energy is huge business at MIT, with a full 20% of its faculty involved in some kind of energy research. MIT Energy Initiative director Ernest Moniz said that the the goal of all MIT's energy research is to partner with the renewable energy and power industries to commercialize technology, because, unlike in IT, energy technologies can't go from an idea to commercialization in a garage.

Researchers at MIT have been particularly active in the solar energy sector, having already spun-out companies including 1366 Technologies, and the school is now home to one of 40 nation-wide Energy Frontier Research Centers that are funded by the U.S. Department of Energy with stimulus funds. The Center for EXcitonics is studying the application of excitons, quasiparticles consisting of a bound state of an electron and an imaginary particle called an electron hole in insulators and semiconductors, for solar lighting.

Excitons are the main mechanism for light emission in semiconductors and Dr. Marc Baldo, director of the center and professor of engineering, thinks they may be the way to offset the electricity demands of lighting, which makes up close to 30% of overall electricity usage.

In order to take advantage of these particles, Baldo and the rest of the team at the center are developing disordered materials, such as quantum dots, that can be sprayed on substrates. The example Baldo presented was called "luminescent solar concentrators," which are pieces of glass that concentrate light onto edges coated with the quantum dots.

When light is concentrated on the dots, excitons are formed. The advantage of this type of technology, Baldo said, is that disordered materials, unlike traditional crystalline materials that are used for solar energy technologies, are cheap and much easier to work with and produce.

"If we do solar right, it can be very, very, very cheap," Baldo said.

The center is still in the early stages of its research and the goal is to learn how to control the particles and movements to generate a charge. The ultimate end-game is to build thin-film, non-tracking solar cells with power efficiencies exceeding 30%.

Solar Thermoelectrics

While Baldo and the team working on excitons are looking at new ways to use the sun to generate electricity, engineering professor Dr. Gang Chen and the team at the Solid-State Solar Thermal Energy Conversion Center are looking at how plastics can replace copper parts in solar hot water systems, and be used to convert heat into electricity at CSP and possibly geothermal energy plants.

Chen's team is researching what it calls solar thermoelectrics. The technology involves using Fresnel lenses to concentrate light and in effect heat, onto a solid state converter made of plastics, which uses the heat differential on either side to create electricity. The same converter could also be used in what Chen referred to as thermophotovoltaics.

In this case, heat from any source could be exposed to one side of the converter, the other side would be used to create light which could then be focused on a photovoltaic panel, potentially allowing solar plants to produce electricity even when the sun isn't shining.

Energy Storage

If technologies like those being developed by Baldo and Chen, in addition to those already working in the field, are deployed at the scale that is necessary to reduce dependence on fossil fuel generating technologies, then large-scale storage will have to play a role. Dr. Luis Oritz from the materials science department said that not only are large scale storage solutions necessary for renewable energy deployment, but they're also important from a security vantage point.

Currently only 2.5% of the capacity of the U.S. grid is able to be stored, compared with 10% in Europe and 15% in Japan, which in the event of a grid failure could mean trouble for the U.S. Ortiz said that this is why his team, which is led by Professor Donald Sadoway, has received US $7 million from the U.S. Advanced Research Projects Agency for Energy (ARPA-E), $4 million from French oil company Total and support from the Defense Advanced Research Projects Agency (DARPA) and MIT.

The goal of Sadoway's research is to bring the cost of large scale energy storage facilities in line with the cost of natural gas plants. He said that in order to do this, incredibly large liquid metal batteries will need to be built and the facilities will need to be used in much the same way that flywheel storage plants are expected to be used, as frequency regulators that are capable of dispatching energy quickly in the event of an emergency. 

The basic principle behind the technology is to place three layers of liquid inside a container: Two different metal alloys, and one layer of a salt. The three materials are chosen so that they have different densities that allow them to separate naturally into three distinct layers, with the salt in the middle separating the two metal layers — like novelty drinks with different layers. 

The energy is stored in the liquid metals that want to react with one another but can do so only by transferring ions — electrically charged atoms of one of the metals — across the electrolyte, which results in the flow of electric current out of the battery.

When the battery is being charged, some ions migrate through the insulating salt layer to collect at one of the terminals. Then, when the power is being drained from the battery, those ions migrate back through the salt and collect at the opposite terminal. The whole device is kept at a high temperature, around 700°C, so that the layers remain molten.

While each of these technologies has a lot of lab work left before it's ready for field testing on a large scale, chemistry professor Dr. Dan Nocera and the company he helped found Sun Catalytix are working to commercialize a catalyst that can be used to split water.

The basis of Sun Catalytix's technology is a cobalt phosphate catalyst that Nocera said is more efficient at splitting water into hydrogen and oxygen than other materials. He said that the catalyst can work within normal ambient temperatures and with water sources as diverse as tap water and water straight out of the Charles River in Boston.

While commercial electrolyzers that split water to make hydrogen already exist, Nocera said that they're far too expensive and require a significant amount of energy to run. Sun Catalytix is in the process of testing an electroylzer that is built with its proprietary catalyst that can be manufactured using PVC plastic.

A completed 100-watt system would work like this: solar PV panels would power an electrolyzer, which would then produce hydrogen that would be stored in tanks and then used as fuel for a fuel cell for electricity or to power a hydrogen vehicle. Nocera said that three liters of water a day could power a home.

He said the ultimate goal of the Sun Catalytix system is use cheaper solar panels and fuel cells (still a stumbling block) to implement systems like this in the developing world where there is little-to-no electricity generating infrastructure in place and where three liters of even low-quality water per day could dramatically increase the quality of life of the people living there.

Development of the technology is being financed by more than $1 million from Polaris Venture Partners. Nocera said that he expects a working prototype to be completed in the next 5-8 years and that the company has already been approached by solar companies interested in having their panels used in the system.

While each of these technologies seem disparate, MIT Energy Initiative director Moniz emphasized that they all have one goal, to make renewable energy cheaper and easier to implement around the world, reducing reliance on carbon intensive sources of energy and helping to bring about a fundamental shift in the way the world produces and consumes electricity.