Silicon solar cells built on a nanostructured substrate (top left) have a surface patterned with nanoscale domes (top right). The scale bar in both electron-microscope images is 500 nanometers. The diagram shows the layers of the device, from bottom to top: a quartz substrate, a reflective layer of silver, a transparent conducting oxide, the active layer of amorphous silicon, and another oxide layer. Credit: ACS/Nano Letters

The accumulation of dust on the surface of a solar cell can block light and cut into cell efficiency. Researchers at Stanford have demonstrated that solar cells patterned at the nanoscale with domed structures absorb more light and, as a bonus, are self-cleaning.

The nanoscale patterning is not just on the surface of the cell but is applied to every layer. The cells are built on a substrate patterned with nanoscale cones. The bottom layer is a film of silver 100 nanometers thick that acts as an electrical contact and a light reflector; atop this is a film of amorphous silicon sandwiched between transparent conducting layers. Though the substrate is jagged, the accumulation of layers results in domed structures that happen to resemble the mushroom-like structures other researchers have been developing for self-cleaning surfaces. An added layer of hydrophobic molecules makes the cells nearly superhydrophobic: water droplets roll along the surface, pulling dust away with them.

These nanodome structures not only repel water, but help trap light. Because they're so small--about 500 nanometers in diameter--the nanodomes interact with light in a cool way, absorbing 94 percent of all light from the infrared to the ultraviolet. A flat solar cell made from the same materials absorbs only 65 percent of light in the same broad spectrum. So far the overall power conversion efficiency of the cells is 5.9 percent. The lead researcher, Stanford materials science professor Yi Cui, says these patterning techniques could be applied to other solar materials. This work is described online in the journal Nano Letters.

Solar companies presenting business plans to investors at a National Renewable Energy Laboratory (NREL) conference this week devoted particular attention to how they hope to compete with Chinese manufacturers. The audience at the NREL Industry Growth Forum in Denver consisted largely of venture capitalists and partners from private equity firms.

Stellaris, a company that assembles solar modules in Lowell, MA, has already received $6.1 million in funding to develop techniques for packaging silicon and thin-film cells. The company, represented at the conference by CEO James Paull, is seeking further financing in 2010.

Paull said that while European companies' cell-to-module costs are 70 cents per watt, China's are half that. "Solar modules have become a commodity, and China is dominating," he said. Like most of the other presenters, Paull didn't reveal too much about his company's technology. But he said that Stellaris hopes to save costs by adding passive plastic concentrators to silicon and thin-film cells and by reducing cell sizes.

An executive from a large European solar company expressed skepticism, however, that the US will ever be able to catch up with Chinese solar manufacturers. The executive, who manages his company's operations in China, said his company had explored manufacturing in California and Texas but that the labor costs were much too high. That said, he was at the conference looking for new solar technologies to buy up--an area where the US does still have an edge.

Today President Obama announced what the White House is calling "the largest single energy-grid modernization investment in U.S. history." It's actually anything but "single"--it's $3.4 billion in stimulus funds to help pay for a collection of projects scattered around different utilities and companies. (The White House managed to give something to projects in 49 out of 50 states.) The money will pay for, among other things, several million so-called "smart meters" that allow customers to manage their electricity use. Consumers will be able, for example, to take advantage of dynamic pricing and trim consumption at expensive peak times. They can save money while helping utilities make the grid more efficient and reduce emissions.

The move should prod utilities to finally start offering the dynamic pricing -- cheapest at night, with differing prices at various times of day -- needed to make the most use of the technology. "By giving electric utility systems across the country the tools that allow them to realize billions of benefits from dynamic pricing, they are hoping to induce the states to modernize their retail pricing policies," Peter Fox-Penner, principal with the Brattle Group, a consultancy in Cambridge, MA, told me. "There are signs this inducement will cause a historic shift in retail utility pricing policies, but the outcome is not fully visible yet."

The stimulus dole-out is surely going to be very helpful, as far as it goes. The White House says that the expenditures will, taken together, "reduce peak electricity demand by more than 1,400 [megawatts], which is the equivalent of several larger power plants, and can save ratepayers more than $1.5 billion in capital costs and help lower utility bills." If true, this is a remarkable testament to the power of investing in smart grid and other energy-efficiency technologies. (You can find a good example of such an installation in Boulder, CO, here, a good recent analysis of the issues here, as well as a longer piece about building a green grid here.)

But there are a couple of caveats.

First, the White House move does not change the fundamental rationale behind most utility investments. Today it's often too easy for utilities to make a business case for building new power plants to burn more energy in support of wasteful consumption, rather than installing software and smart meters and control systems geared towards saving a similar amount of energy--even though it is very possible for them to make such a case. If this thinking had really changed--meaning, if efficiency-mindedness was really top-of-mind in utility boardrooms and state regulatory agencies--no federal stimulus money would be needed to install these kinds of technologies. Instead, utilities would already be installing them--based on the documented energy and dollar savings they'd be projected to realize.

The second caveat is that, structural issues aside, $3.4 billion is not very much money (even if, as the White House says, the $3.4 billion is being matched by $4.7 billion in private investment). In fact, this total sum ($8.1 billion) is still only about two percent of where we need to be--that is, if you believe Obama's fellow Nobel Peace Prize laureate, Al Gore. Just last summer, Gore made a fairly sensible call for a unified national smart grid that would move power from remote, renewable sources of wind and solar power and, in particular, increase the efficiency of electricity use through smart meters and other technologies installed across the nation, to move beyond today's scattered projects. The analysis by Gore's people put the tab for such a grid at $400 billion.

"We're on the cusp of a new energy future," Obama said today. True enough, but the operative word is still "cusp."