(July 17, 2015) Solar
panels are an investment—not only in terms of money, but also energy. It takes
energy to mine, process and purify raw materials, and then to manufacture and
install the final product.
Silicon-based panels, which dominate the market for solar
power, usually need about two years to return this energy investment. But for
technology made with perovskites—a class of materials causing quite a buzz in
the solar research community—the energy payback time could be as quick as two
to three months.
By this metric, perovskite modules are better than any solar
technology that is commercially available today.
These are the findings of a study by scientists at
Northwestern University and the U.S. Department of Energy’s Argonne National
Laboratory. The study took a broad perspective in evaluating solar technology:
In what’s called a cradle-to-grave life cycle assessment, scientists traced a
product from the mining of its raw materials until its retirement in a
landfill. They determined the ecological impacts of making a solar panel and
calculated how long it would take to recover the energy invested.
Perovskite technology has yet to be commercialized, but
researchers everywhere are excited about the materials. Most projects, however,
have been narrowly focused on conversion efficiency—how effectively the
technology transforms sunlight into useable energy.
“People see 11 percent efficiency and assume it’s a better
product than something that’s 9 percent efficient,” said Fengqi You,
corresponding author on the paper and assistant professor of chemical and
biological engineering at Northwestern. “But that’s not necessarily true.”
A more comprehensive way to compare solar technology is the
energy payback time, which also considers the energy that went into creating
the product.
This study looked at the energy inputs and outputs of two
perovskite modules. A solar panel consists of many parts, and the module is the
piece directly involved in converting energy from one form into
another—sunlight into electricity.