Last week, Greentech Media hosted a conference focused on generating and delivering power in efficient and environmentally-friendly ways. Most of those presenting were involved in private companies that had received enough venture capital to develop a functioning product, but they weren't ready to start widespread sales or deployments of that product. Their presentations should be viewed with a degree of caution—there was no shortage of self-promotion involved—but the fact that these companies generally had working demonstrations of their technology suggests that the self-promotion wasn't pure hype.

The session on power generation was especially intriguing because it provided three very different takes on ways to produce power without relying on fossil fuels. Although these technologies may not actually make it in the wider market place or may end up occupying only a small niche, they still provide a window into the sort of innovative approaches that are possible in an already crowded field.

Here, we'll profile the three approaches that were described at the meeting.

Converting construction waste to hydrogen: Bill Davis of Ze-Gen described his company's approach to the problem of municipal waste. Each year, the US produces about four billion metric tons of waste that, thanks to the various hydrocarbons in it, actually has about half the energy content as the same weight of coal. Most of that material gets put in landfills, where some of it winds up metabolized into methane, a potent greenhouse gas. Ze-Gen has found a way to liberate hydrogen gas from that waste.

Using technology from the steel industry, where oxides and carbon contamination are a largely solved problem, Ze-Gen is taking the wood from construction waste and dumping it into liquid iron in an oxygen-free environment. It gets out a mixture of carbon monoxide and hydrogen gas. Although there's a significant energy cost here, Davis quipped that "keeping iron molten doesn't take as much energy as you'd think."

The technique can be translated, with lower efficiencies, to household waste. There's a chance that this could provide a secondary revenue stream for landfills and dumps, although Davis emphasized that the company hopes to ensure that the process pays for itself purely in energy terms.

On the environmental front, this winds up being being carbon-neutral, since the original source of the hydrocarbons is typically a tree. Keeping waste out of landfills also has some obvious benefits, although getting everything to a Ze-Gen plant may entail burning some energy that shipping to landfills doesn't. The other notable aspect of this approach is that Ze-Gen may wind up competing for waste material with other green technologies, like wood recycling and landfill methane production. The fact that there will be winners and losers as these technologies mature is overlooked far too often.

The nuclear option: Hyperion Power was represented by Deborah Dean Blackwell, who described the company's product as an outgrowth of work by the staff of Los Alamos National Labs. In a lot of ways, however, the technology is secondary to the regulatory environment for nuclear power in the US. With large facilities facing a complex regulatory maze and lots of local opposition, Hyperion offers an alternative: a small, completely self-contained product that uses basic chemistry to control the rate of nuclear decay. The reactors remain sealed for their five year lifespan, after which they're returned to the factory for recycling.

The chemistry behind this involves uranium hydride, or UH 3 , which forms at higher temperatures. If the reactor heats up, more of the UH 3 is formed, and the concentration of uranium is reduced. The reactor contains a reservoir for the hydrogen and a heat exchanger, which can warm an external source of water. Aside from the piping into the heat exchanger, the entire reactor can be encased in concrete. One of these modules can produce 27MW of electricity and 70MW of thermal energy at about two-thirds of what it would cost to produce that in a large commercial plant; Hyperion is hoping for a 2013 deployment.

Hyperion would still face issues related to the fact that the US has no clear strategy for long-term storage of nuclear wastes and a public that's not prone to carefully evaluating the safety of anything that contains the word "nuclear"—see, for example, debates over the safety of irradiated food and NASA's radioisotope thermoelectric generators.

Perhaps in recognition of this, Hyperion is (ironically) promoting its reactors as ideal for powering remote sites involved in the production of petroleum products, which often need both electricity and steam.

Forget green, solar goes Bloo: Right now, there are many competing approaches to photovoltaic technology, but only one of them made an appearance at the meeting: Bloo Solar, which is working on what it calls a third-generation solar brush. Larry Bowden, the company's CEO, described it as a solution to two of the biggest inefficiencies in solar power: photons that don't get absorbed and electrons that don't get transferred to the conducting portions of the device, where they're put to use.

Bowden actually described the manufacturing process for the device. Photolithography is used to drill an array of micron-scale holes in a mold material. That mold is then used to create a complementary array of pegs—the brushes—from a conducting material. The conductor is then coated with a thin layer of photovoltaic material; the company says it can use just about anything, but favors CadTel, a material based on cadmium and tellurium.

The final brushes are 5.5 microns apart, 2 microns wide, and 9 microns high, with about 30 million of them packed into each square centimeter. Right now, the company is able to make wafers that are eight inches on a side.

The arrangement of pillars means that, if incident light initially gets reflected rather than absorbed, it tends to ping-pong within the grid until it is absorbed. The thin film of CadTel, in addition to requiring far less raw material, means that electrons liberated by this light don't have far to travel, on average, before they reach the conductor. Far more of them go into producing power, and far fewer get reabsorbed in a way that produces waste heat.

According to Bowden, the main challenge Bloo faces is managing the current produced. He expects that power yields will be in the neighborhood of 30 percent by the time the company is ready to market these devices, with a cost of $0.06-0.09/kWhr.

Again, it's not yet clear that any of these technologies will reach the broader market, much less achieve a dominant position if they do. But they do provide an indication of some of the creative solutions that are easing out of the research labs and closer to production.