Heat and time take toll on solar panel performance

Solar arrays at NREL.
The widely held belief of solar systems is that once the initial cost is paid off, the rest is gravy.

Or more specifically, that the power harvested from the sun is free for those who own their systems. And that's true.

However, there's an important detail to consider, especially if the cost of materials and labor are financed over a long period.

"Numerous studies have shown that degradation rates for silicon modules are typically less than 1 percent per year," says analysis from the National Renewable Energy Laboratory in Golden, Colo.

That means power output diminishes minutely each year and could be significantly less for a system once the up-front costs are paid off after financing. That could mean a photovoltaic solar array produces 40 percent less power than the day it was installed once a 40-year loan is paid. A highly technical NREL study says declines could actually be less, ranging from .5 percent to .7 percent.

Of course degradation and performance rates depends on multiple factors, with some being solar intensity and temperature. Series resistance poses another interesting factor as does the system performing only as well as its worst cell. But that can be dealt with by connecting the panels in parallel or using other technical means.

On an NREL map of the United States outlining solar intensity, California's San Joaquin Valley sits in one of the optimal places. The region is sunny.

But with sun comes high temperatures, which also decrease electrical output somewhat. And that's something to consider in the Valley where many communities have more than 40 days of the year hotter than 100 degrees.

The reason for the heat-related performance decline has to do with conductivity, reducing the magnitude of the electric field and lowering voltage, according to "It should be noted that a higher temperature increases the mobility of electrons, which causes the flow of current to increase slightly," the site says. "This increase is however minor and insignificant compared to the decrease in voltage."

Simply put, "the solar radiation which produces solar electricity carries heat with it that will cause the components of your photovoltaic solar panel to become altered and less able to capture sunlight effectively," says

NREL has an outdoor test facility that's been operating about a decade testing all sorts of solar panels. As time marches on, more will be written about performance, maintenance and optimizing crystalline photovoltaic systems to extend their lifetimes.

I started looking into this concept after a colleague of mine who works with one of the counties I contract with mentioned solar performance issues. He said the county is likely to continue to pursue development of a significant solar project, but that it is also looking into other methods of boosting its clean energy footprint.

Net zero construction gains a foothold

A net-zero building consumes no more energy than it produces.

Cool idea but until recently was about as practical as living off the grid in a yurt. OK for some but hardly a sales feature Joe Sixpack would embrace.

The mere mention was limited to science fiction stories like "Logan's Run," in which the hero escapes with his life from a closed net-zero society of limited resources that could support only a limited population. In 2116, residents in the story who turn 21 are killed.

Net zero, however, has eclipsed such apocalyptic visions. In fact, it's arrived.

Rick Daysog of the Sacramento Bee reported that Pacific Housing Inc. plans to break ground this spring on a 34-home project in Sacramento, Calif. that produces as much energy as it uses. Daysog said Stockton, Calif.-based Sunverge Energy will install the $300,000 homes' solar systems.

And on the opposite side of the country in Fort Lauderdale, a company that last year decided to build all its new locations to the exacting Leadership in Energy and Environmental Design, or LEED, platinum standards decided to go a step further. TD Bank, which has more than 1,250 locations on the East Coast, is building a bank officials say will be the first registered in the U.S. Department of Energy's net-zero energy building, or NZEB, classification system.

The reason, said Jimmy Hernandez, a TD Bank spokesman based in New Jersey, is relatively simple.

"It just makes sense," he said.

Hernandez said bank officials learned that for a little more than what achieving LEED energy efficiency standards cost, they could add solar panels and actually produce more energy than they consume. And the solar panels will eventually pay for themselves, he said.

The bank will consume about 97,000 kilowatt hours of electricity a year to operate but produce at least 100,000 kWh.

Buildings consume about 40 percent of the overall energy and 70 percent of the electricity in the United States, according to the National Renewable Energy Laboratory. Many efforts are under way to reduce that and in the process lower production of greenhouse gases.

Those measures include sustainability policies from some of the largest publicly traded U.S. companies, measures by states to increase efficiency through building codes (California's new rules took effect Jan. 1), efforts by the U.S. Department of Energy to fund energy efficiency retrofits in municipal government buildings across the country, the whole house and passive house movements to increase efficiency in residential and commercial buildings and a number of others.

An NREL report, "Zero Energy Buildings," says "energy consumption in the commercial building sector will continue to increase until buildings can be designed to produce enough energy to offset the growing energy demand of these buildings."

To address that trend, the U.S. Department of Energy is seeking to develop the technology and a knowledge base for cost-effective zero-energy commercial buildings by 2025. NREL already has created a classification system for net-zero energy buildings to aid in the standardization process.

Buildings aren't the only target. A move is afoot in the San Joaquin Valley to bring solar to the region's farms and use untapped or marginal lands to produce energy. That effort remains in its infancy but could show big dividends and additional revenue streams to farmers, who are themselves big energy users.

Photo: TD Bank branch in Fort Lauderdale, Florida.