In mega (large-scale) solar power plant projects, one of the key points is the optimization of weed removal operations on the sites during the 20 years of operation.

Places suitable for solar power generation with abundant sunlight are also suitable for the fast growth of plants. If the weeds are not removed, they will have a negative effect on the power generation business, and, moreover, a rapid increase in insects will sometimes cause problems to the residents around the facilities.

Shade created by the weeds on solar panels will cause a decline in the amount of generated power. In addition, if crystalline silicon panels are used, ventilation under the arrays (unit of solar panels fixed on a mounting system) will deteriorate if weeds grow thickly, which will accelerate the increase in the panel temperature. As some have pointed out, such situation will pose the risk of lowering the conversion efficiency in summer, when the temperature is high.

If the ground surface is covered with asphalt or weed-proof sheets, the growth of weeds can be reduced substantially. However, these methods are not widely used because the initial investment will increase. Herbicide application is also normally avoided owing to the effect on the surrounding environment.

As such, the initial investments on measures against weeds used by many mega solar power plants are limited to covering the ground with crushed stones or clover plants, and cutting weeds several times a year from around June to August is included in the operation and maintenance.

The issue is the optimization in the efficiency of "weed cutting" operations. Workers have to walk from corner to corner on the site to cut weeds in summer, when the temperature is high, and the physical load on the workers is great. The number of workers increases in proportion to the size of the power plant, raising the operating cost.

To solve this, some mega solar power plants began to use riding grass cutters, aiming to reduce the load on workers and improve the operating efficiency (Fig. 1).

Fig. 1: Example of introduction by a mega solar power plant in Mie Prefecture. Used by Sanko Real Estate, which also handles O&M, to improve the efficiency of weed cutting. (Source: Sanko Real Estate)

The compact go-cart-like 4-wheel grass cutter has a weed cutting unit under the chair installed in the space surrounded by the four wheels. Weeds are cut by turning the blade in the unit. The worker can drive around the site just like riding a go-cart, and nearly all of the weeds on the site are cut down. The machine not only reduces the physical load on workers but also substantially reduces the operation time. Moreover, the operating efficiency tends to improve as the area increases.