Making solar energy affordable, efficient and user-friendly
Shocked by the low efficiency and high cost of solar-energy systems, many potential buyers decide to wait till new materials or photovoltaic (PV) technology improve the affordability. Consumers dont realize that with a better power conditioning system, even todays technology can be more affordable, according to Jason Lai, director of ECEs Future Energy Electronics Center (FEEC).
You buy your panel and power electronics separately, Lai explains. The panels typically run $2 per watt, so the manufacturers try to sell the cheapest control system, typically between 50 cents and $1 per watt. These systems are not designed for efficiency and create much of the operating problems with solar PV systems, he says.
The problems can be significant. Currently, most commercial PV cells are connected in series to get the necessary voltage. So if one cell shuts down, the entire panel shuts off. Shade, clouds, and even bird droppings covering any part of a PV cell can turn off an entire array.
If power generation suddenly spiked or dropped, because, for example, a cloud passed overhead, it could disrupt some of the existing systems, explains graduate student Chris Hutchens, who works in the FEEC. Youd be out on a beautiful sunny day and the whole thing would be down. Its as if you flipped on the light switch at your house and caused a blackout in your town, he says.
Lai and his team at the FEEC are trying to solve these problems and capture more energy for the same panel cost by improving the power electronics system. He and Kathleen Meehan, an associate professor of ECE, were recently awarded a $3.2 million grant from the U.S. Department of Energys High Penetration Solar Deployment effort. The programs goal is to increase widespread commercialization of grid-tied solar PV systems. The grant is part of the Green Jobs initiative and aims not just at commercializing solar technology, but also at creating domestic jobs.
In order to connect to the 240V grid, a PV system must produce 400V peak. Single solar panels typically produce an average of 20V. Conventional lower-cost systems today stack a number of 20V panels in series to reach the 400V maximum, then use a dc-ac inverter to match the electrical grid. A number of companies are solving this problem by using micro-inverters on each panel to convert from 20V dc to 240V ac, and connecting them in parallel. These systems solve a lot of the problems, Lai says, but at a higher cost. He estimates the cost at more than $1 per watt.
The FEEC solution is to install dc-dc converters directly on each 20V panel and then connect the outputs in parallel to a 400V dc bus. Then, just one high-power dc-ac inverter is needed for the entire house to connect to the grid. The result is efficient system operation at a currently estimated cost of 20 cents per watt. My goal, however, is 10 cents per watt, Lai says.
A high switching frequency enables Lais group to integrate PV panels with a small module that eliminates the need for electrolytic capacitors. Electronics used with commercial solar panels today use electrolytic capacitors for smoothing the dc power. The capacitors, however, are short lived and require expensive maintenance.
The Virginia Tech team is not only lowering purchasing and operating costs, but also providing a solar system for the future. There is no need to convert to ac at all for most modern appliances, Lai says. With each conversion, you waste energy. His system will give the option for modern homes to access dc power directly. He predicts that ac will be obsolete in 100 years, but expects that the first step will be buildings with both ac and dc options.
The team will demonstrate a proof-of-concept in 2011 and is working on IC design and low-cost production. They are also making systems that are consumer-friendly. We had another project a while back where we told a corporate partner that our system worked, recalls Hutchens. They came over, switched the power switch on and off really fast for a few minutes and it exploded. Now the FEEC designs everything to withstand significant abuse to make it absolutely hassle-free.
You should be able to install it in your car or house and it will work for 20 years without any fuel costs and very low maintenance, says Hutchens.
Thats good news for consumers.