Science Nonfiction

• From March 2010 World Rivers Review  

The Future of Energy is Getting Greener (And Closer)

Renewables are booming around the world, but they still have a lot of catch-up to do. Installation of solar PV systems has been nearly doubling every two years in both the US and Europe. The cost of producing solar-generated energy fell by over half in just a decade and a half. Wind power capacity rose nearly a third last year, to a total power capacity of 157.9 gigawatts (China accounted for a third of that, doubling its wind capacity). Some 150 companies worldwide are working to commercialize algal biofuels, which could cleanly fuel cars, planes and other engines while feasting on the atmosphere's excess carbon dioxide.

It's been said there will be no silver bullet to fix our current dirty energy supply, but many hope that the "silver buckshot" approach could do the trick - in other words, try many different things at once, and see what works best. Here we look at some intriguing recent advancements in the world of green energy.

Beam Me Down, Scotty

While most of us think of space as a black void dotted with distant stars, some engineers see it as a great place to capture solar power. After all, our sun shines more intensely out there in our solar system. So why not take advantage of it to bring clean power on Earth?

That's exactly what Solaren is planning. Based in Manhattan Beach, California, the company signed a 15-year Power Purchase Agreement in December 2009 with California utility PG&E to provide 200 MW of power – 1,700 gigawatt hours (gWh) per year – beginning in June 2016. A 1-km-diameter concentrating mirror will beam solar waves at high-efficiency solar cells to create energy. A microwave converter will then beam the radio-frequency energy waves down to a receiver in central California, where it will enter the grid. Solaren says it expects to produce 1,000 MW of energy from this solar plant, but has not disclosed who would receive the remaining 800 MW of power.

Japan is also developing a solar power station, expected to produce 1GW of power and be in orbit by 2030. Their system would be massive: a 2.6 km x 2.4 km (1.6 miles x 1.5 miles) power generation/transmission panel tethered to a central bus system 10 km away. It's estimated cost is US$21 billion.

Space solar is a highly efficient and reliable source of energy. Compared to solar power produced on Earth, space solar isn't reduced by particulates or clouds in the atmosphere. And there's no "night" – space solar is 24-7. Additionally, radio frequency waves can be converted to electricity at a rate of about 90% efficiency (nuclear and coal plants operate at only about 33% efficiency).

One of the barriers to space solar is the high cost of launching the units into space. Solaren has been talking with Lockheed-Martin and Boeing about constructing both the solar plant and the rockets needed for transporting into space; they're also working on ways to decrease the weight of the plant, including using inflatable mirrors.

Still think this sounds like science fiction? Well, like so much of today's technology, it started out that way. Isaac Asimov was the first to propose space solar, in his 1941 book Reason. It's only taken 70 years for science to catch up with art this time.

Go Fly a Kite

Wind power takes to the skies.

California firm Joby Energy has created a new airborne wind turbine to harness the stronger, more consistent winds in the upper layers of our atmosphere. Each wind kite has multiple turbines connected to motor-generators that transmit electricity to the ground through a reinforced tether. The components are modular, so kites can easily be built to provide as much or as little energy as needed, and can be easily repaired in the event of a malfunction. The kites will fly over uninhabited areas, out of the path of airplanes, and eventually offshore, too.

Typical wind turbines today operate at about 100 meters above the ground; the wind kites fly on average at 400 meters. The faster winds found at these high altitudes allow the wind kites to produce nearly twice as much energy as their surface-based counterparts. And because they require about one-fortieth the construction materials, lower production costs could easily make them cost-competitive with our current unsustainable energy sources.

Scaling Up Fuel Cells

Hydrogen accounts for about 90% of the universe's atoms, so it's no wonder that people have been trying to find ways to turn it into fuel for a long time. However, one of the main drawbacks is that it takes more energy to produce hydrogen from water than it creates, so hydrogen is actually better as a form of energy storage than energy creation.

Fuel cells are seen by some as the next great energy source, but they've been slow to develop into a mass market. Some new breakthroughs may signal a change.

Horizon Fuel Cell Technologies just debuted their new desktop fuel cell called the Hydrofill, which extracts hydrogen from water and stores it in cartridges. To charge a cell phone, camera or other portable device, a cartridge is inserted into a pocket-sized unit that pulls the hydrogen from the cartridge and produces electricity. The company already has larger versions of the same hydrogen-creation technology. Both models need an energy source to initially create the hydrogen; it can be plugged into a wall outlet or a solar power system.

On the opposite end of the spectrum, industrial-scale fuel cells are now powering business giants such as Google, Ebay and WalMart. A California start-up called Bloom Energy has developed scaleable fuel-cell power plants that are being tested at these companies; the eventual goal is to develop a unit for home use that costs less than $3,000, and can compete with grid-based electricity. Unlike some earlier prototypes of home fuel cells, the Bloom Boxes (recently introduced to the public on the news show 60 Minutes) use low-cost materials, and can run on any fuel, not just pricey hydrogen. Some of the test units use natural gas, for example, and consume about half as much gas as a traditional power plant. A box about the size of a milk carton could power an entire US home (and one half that size, a European home).

One big unknown is whether this small, new company can achieve the economies of scale that will lead to truly affordable fuel cells for the home on a mass scale. If it can't, however, there are at least ten other companies globally that are chasing the same goal.

Storing the Wind

One of the big arguments against transitioning to a renewable energy supply is that many green energy sources aren't constant. The wind doesn't always blow, the sun doesn't always shine (on Earth at least – see "Beam Me Down Scotty"). Efficient ways to store intermittent energy for later use is the holy grail of renewable energy.

Compressed Air Energy Storage (CAES) works like this: off-peak electricity is used to pump air underground into a storage chamber. When energy demand is high, the compressed air is released, turning a turbine and generating electricity. CAES can usually supply about 100 MW of power for several hours at a time.

The system operates at only about 50% efficiency, and currently requires some burning of natural gas, negating some of the positive aspects of CAES.

While the geological formations needed for storage – old mines, depleted aquifers and salt caverns – exist all over the world, only two CAES plants are currently in operation: one in Alabama and another in Germany. In the US, several companies are considering CAES projects, but only one is in the design stage. The Iowa Stored Energy Park will have enough storage capacity to supply 270 MW for 16 hours a day.

The most exciting upgrade to CAES is the effort to increase its efficiency and decrease its environmental impact. General Electric and RWE Power, a German utility company, are developing an advanced system known as AA-CAES that captures waste heat from the compression process; this improvement alone bumps a system's efficiency up to 70%.

Another important way to green a CAES system is to use wind power as the initial energy source to pump and compress the air. Wind is one of the power sources being explored for the Iowa system. AA-CAES combined with wind power would produce an energy generation and storage system with zero carbon dioxide emissions.

These systems have more capacity and are cheaper to install than traditional energy storage methods, such as batteries and flywheels.

RWE and GE hope to have a 30 MW AA-CAES project ready in 2012, but their eventual goal is to create an AA-CAES facility able to generate 300 MW.

All That Glitters

New, tiny PV cells give new meaning to the term "glittering in the sun."

Sandia National Lab in New Mexico has come up with glitter-sized crystalline silicon PV cells that outperform today's photovoltaics in efficiency, reliability, cost, performance, and applicability. While today's conventional solar wafers are about six inches square, the new glitter PV cells are only 14-20 micrometers thick (a human hair is about 70 micrometers thick).

In terms of efficiency, the glitter cells use 100 times less silicon than today's PV to generate the same amount of electricity. Commercial cells today run between 13-20% efficiency; the glitter cells to date are 14.9% efficient, and they're still in the R&D stage. A big advantage to their size is that they can be embedded into flexible materials like cloth or plastic.

Some amazing applications can be envisioned – a shirt could charge a cell phone in Africa, an emergency tent in Haiti could provide electricity for light and a radio, or a backpack could charge a laptop in the Andes. Get ready for an energized fashion industry!

Just Kick It

Four Harvard students think solving the energy problems of poor nations should be child's play. The team has come up with a soccer ball that converts the energy used to kick it around into electricity. For each 15 minutes of play, the ball can store enough energy to illuminate a small LED light for three hours. The goal (!) is to reduce poor families' reliance on polluting kerosene, now widely used for indoor lighting, and to tap into a huge energy source – kids at play.

Their sOccket ball generates and stores electricity during normal game play. "Soccer is something you will find in every African country," one founder, Jessica Lin, told the New York Times' Green Inc blog. The team was inspired by dance floors that capture energy from the dancers' movements, and motivated by the huge need for clean, simple off-grid energy.

The idea is to sell the ball in Western markets and use the profits to subsidize the balls for sale at an affordable price in poor countries through organizations like Whizz Kids United, a South African NGO working to teach children about HIV/AIDS.

Tree Power

London-based start-up firm Solar Botanic is trying to create the world's first useful fake tree. The firm's solar tree combines three different energy-generation technologies – gathering electricity from visible sunlight, heat, and from movement from wind and rain – on a "nanoleaf." Each tree gets thousands of nanoleaves.

Each branch will be added independently, and individual leaves or entire branches can be replaced as needed. The inverters needed to turn the tree's electricity into usable alternating current will likely be located in the trunk.

The trunk will be of recycled tires and plastic bottles mixed with liquefied waste wood. This wood biomass can be molded to look, feel, and even smell like an actual tree.

Solar Botanic says that each tree could produce between 2,000 and 12,000 kilowatt hours (kWh) of electricity a year. With the average US person using about 12,000 kWh a year, you'll need at least one large tree per person.

Each solar tree will probably cost between $12,000 and $20,000. At about 120,000 kWh over a 20-year life span, each kilowatt-hour would cost about 13.5 cents, not much more than the 2009 US average of 12 cents per kWh.

The typical US family of four would need four trees at about $64,000. But said family already pays the electricity company more than $100,000 for 25 years of electricity (at current rates), then it's not too bad of an investment for non-toxic (and aesthetically pleasing) power.

It's going to be awhile before our urban forests become power plants, though: a working prototype probably won't be ready until 2012 or 2013.