Getting Out of the Weeds: How To Control Vegetative Growth Under Solar Arrays

San Diego, Calif. It is officially summer. The sun is shining and the grass in your backyard is growing quickly. At home, mowing the lawn is one of summertime's most frequent chores and its no different for the solar industry.

Credit: Nihon Shokusei

Weed or vegetation management is particularly important for ground-mounted solar systems. Tall weeds growing around the installation can create shading, which can negatively impact system production. It can also cause hot spot heating if a part of the solar cell is shaded, the cell can heat up to such extreme temperatures that a module can burn out causing permanent damage.

After the feed-in tariff (FIT) program was launched in Japan a few years ago, many ground-mounted PV systems started popping up in the country where small residential roof-top solar systems used to dominate. System owners recognize that growing vegetation under and around PV systems must be minimized to protect their valuable investment.

There are several weed control methods used for PV ground-mount systems in Japan; mowing, spraying herbicide, grazing sheep/goats, and covering the area with weed control sheets, for example. Controlling weeds incurs additional operation and maintenance (O&M) expenses for PV system owners and the long-term costs and benefits need to be carefully examined.

Mowing is the most commonly used method in Japan at this point, but we are looking into other methods, said a project developer in Japan.

Mowing is very labor-intensive and needs to be repeated twice or three times a year. Besides hiring people or renting mowing equipment, there are fees for hauling and disposing the grass clippings. Another project developer commented that it costs between 100-200 yen (US $1-2) per square meter for a 2-MW system, which is typically about 40,000 square meters. Spraying herbicide is relatively inexpensive and requires a low initial investment. But spraying has to be done repeatedly over time and there are environmental concerns associated with certain chemicals in herbicides.

Herbivorous Animals to the Rescue

Last summer, Oita Sekiyu, a gasoline distributor and PV system reseller, built a 1.1-MW solar system on an old salt-pan site in Usa city, Oita prefecture. The company chose emu, the second largest bird in the world and native to Australia, to graze the vegetation growing under the solar system.

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Getting Out of the Weeds: How To Control Vegetative Growth Under Solar Arrays