Several firms in Japan have started replacing aluminum and steel PV racks with wooden ones made of thinned cypress or cedar trees for solar plant installation.
For Japan, these two resources are abundant and help to inspire local economies and reduce imports.
Wooden PV racking was developed in order to expand usage of local woods and utilizing the domestic woods promotes proper forest management, said, Naomi Urakami, representative, Sun Forest, which started marketing PV racks made of thinned wood in 2013.
The company is a wholly owned subsidiary of Forest Owners Cooperative Associations representing Hyogo prefecture. So far, the largest system the company developed is a 5-MW system in Hyogo prefecture.
Thinned woods are used for PV racking. The Forestry Agency promotes thinning activities and usage of thinned wood with subsidies under the Thinning Promotion Special Law. Between 2007 and 2011, 3.8 million hectares of forests were thinned in Japan.
In addition, these thinned woods are pressure-treated with copper azole, water-borne preservatives, ensuring a long life. Studies concluded that the pressure-treated wood lasts at least 20 years, which is the duration of the current feed-in tariff (FIT) policy.
Wooden racking systems offer a number of benefits. Wood can prevent PV systems from losing efficiency due to rising temperatures and they will not corrode or rust.
According to Kanematsu Nissan, a wooden PV rack maker, lease of installation is another benefit, helping to assemble the racks easily without nails. Compared to steel racks, wooden racks are much lighter and easier for workers to carry and construct. It takes 21 minutes for 2 people to assemble a wooden racking system for a 0.9-kW PV system.
Another benefit to using wood as PV racking is that they can be used further, after its life as PV racking. At the end of its useful life, these wooden PV racks can be recycled as biomass energy. Sun Forest is planning to recycle used wood as biomass after its 20-year lifespan.
However, wooden racking systems are a bit more costly. For a 50-kW system, the average cost of a wooden rack is ¥35,000/kW (US $325/kW), compared to ¥20,000/kW (US $127/kW) for steel and ¥30,000/kW (US $281/kW) for aluminum.
Wooden products need solid concrete footing to anchor the rack to the ground. This adds extra cost to wood over steel or aluminum, confirm company officials.
If the cost of dismantling are concerned, these products are cost competitive. The customer’s choice boils down to cost or environment-friendliness as priority.
Japan is blessed with vast forests and the domestic market is saturated with low-cost, imported timber, reducing the self-sufficiency for lumber from 98 percent in 1950 to 26 percent in 2011, according to the Japan Forestry Agency.
However, Japan is poor in natural resources and relies on import of fossil fuel making solar a prime choice as an alternative energy source.
At the end of April, Japan had over 68 GW worth of reserved PV capacity under the FIT program.