Local City's 'RE100' Initiative Driven by Mega Solar Plant

Waste disposal site, reservoir, lease method utilized for solar power generation

2018/08/11 22:58
Kenji Kaneko, Nikkei BP Intelligence Group, CleanTech Labo

Tokorozawa City is in the southwest of Saitama Prefecture and has developed as a commuter town of Tokyo. It is noted as a verdant area with groves of mixed trees in the Musashino area and Sayama Hills as well as agriculture, with thriving Sayama Tea and outdoor-grown vegetables industries.

Local new power supplier with renewable energy ratio of 84%

On June 7, 2018, Mayor Masato Fujimoto of Tokorozawa City announced the city would start implementing "Tokorozawa-version RE100." "RE100" is an international initiative, in which enterprises advocate the goal of procuring 100% of the electricity needed for their business operation from renewable energy.

In Japan, many companies such as Ricoh Co Ltd, Fujitsu Ltd and Aeon Co Ltd have joined the initiative while the Foreign Affairs and Environment ministries have announced their commitment to RE100. Tokorozawa City seems to be the first municipality that has engaged with the concept of RE100. The city aims to derive electricity used at its main government building and other symbolic public facilities "100% from renewable energy."

Tokorozawa City has already steadily taken measures toward increased adoption and utilization of renewable energy.

On May 28, 2018, Tokorozawa City, JFE Engineering Corp (Chiyoda-ku, Tokyo), Hanno-Shinkin Bank and Tokorozawa Chamber of Commerce and Industry established s local new electric power company, Tokorozawa Future Electric Power Corp. Using such renewable energy as local solar and waste power generation as its primary power source, the company is slated to start supplying electricity to the city's public facilities and private consumers using high-voltage power in series from October 2018.

In the business plan, the new power company is planning to expand its supply scale from the initial 9.9MW in fiscal 2018 to 43MW by its fifth fiscal year of 2022.

The renewable energy-based power supply is expected to account for 84% of all its power supply in 2019 (including FIT-based power and unused energy). The breakdown is as follows: 5% by biomass in the city, 1% by solar in the city and 78% by biomass both inside and outside of the city. The remaining 16% will be procured from Japan Electric Power Exchange (JEPX). Biomass power generation is primarily associated with waste power generation (Fig. 1).

Fig. 1: Framework of Tokorozawa City's new electric power project (source: Tokorozawa City)

Renewable energy ratio in the city to be boosted to 15%

According to Tokorozawa City, it is not easy to further increase the ratio of renewable energy by reducing its procurements from JEPX with the view to maintaining the supply-demand balance. Therefore, the city will aim to further increase the ratio of the renewable energy-based power supply in the city from the initial 6%.

Two power generators with a rated capacity of 2.5MW have been set up at the city's Tobu Clean Center (waste incineration plant). Generating power through steam turbine power generators using the steam discharged when burning waste, the plant sells the excess power after consuming generated power within the facility. It will start supplying power to Tokorozawa Future Electric Power in October 2018.

At Tobu Clean Center, the amount of power for sale is expected to rise with excess power increasing as electric ash melting facilities will be abolished in the future.

Tokorozawa City has already set up and started operating "Mega Solar Tokorozawa" and the "Float Solar Tokorozawa" with an output of about 1MW and 385kW, respectively (Fig. 2 & 3). Both power plants leveraged idle property in the city and the comprehensive lease method. The goal to achieve "the renewable energy ratio of 6% within the city" in fiscal 2019 is counting on electricity generated at the Float Solar Tokorozawa and Tobu Clean Center.

Fig. 2: Mega Solar Tokorozawa with output of about 1MW (source: Tokorozawa City)

Fig. 3: Float Solar Tokorozawa with output of about 385kW (source: Tokorozawa City)

Mega Solar Tokorozawa has concluded a wholesale agreement with other electric retailers, but will reportedly provide its electricity to Tokorozawa Future Electric Power after the contract expires in fiscal 2021. As a result, including the increased power sales by waste power generation at Tobu Clean Center, the ratio of renewable energy-based electricity in the city is expected to reach about 15%.

Two-digit upswing in power generation

Mega Solar Tokorozawa started selling power in March 2014. It was constructed in Tokorozawa City's "Kitano General Waste Final Disposal Site." Its panel capacity is 1.053MW while the PV inverters' rated capacity is 1MW. This was reportedly Saitama Prefecture's first mega- (large-scale) solar power plant with an output of over 1MW. The unit price of power based on the feed-in tariff (FIT) scheme is 36 yen/kWh.

In its 20-year business plan, power sales are expected to total about 1 billion yen (approx US$9 million); expenses will be about 680 million yen, resulting in an overall profit of about 320 million yen. Tokorozawa City keeps the income from power sales as its "Eco Town Promotion Fund" separate from its general budget, and uses it for its environment-related subsidy system, for example.

Constructing a mega-solar plant on a landfill disposal site faces challenges such as weak ground, the risks of uneven subsidence and so forth.

Tokorozawa City adopted "FXT steel tube foundations," in which two steel tube pipes are driven into the ground diagonally, crisscrossing over each other, as a measure against weak ground. While limiting the panel angle to 10° to secure a mega-class capacity on the limited site, Tokorozawa City set up an observatory, electronic signage to display the amount of power generation and educational panels in view of the plant's use for environmental education (Fig. 4).

Fig. 4: FXT steel tube foundations adopted as measure against weak ground source: Nikkei BP)

A total of 4,298 polycrystalline silicon panels (245W/unit) of Sharp Corp and two 500kW-output PV inverters of Toshiba Mitsubishi-Electric Industrial Systems Corp (TMEIC) were adopted. A standalone battery (2.5kWh) of Eliiy Power Co Ltd and two more solar panels are provided so the battery system can autonomously operate and charge power in an emergency for the use of information devices and others (Fig. 5).

Fig. 5: Sharp solar panels and TMEIC PV inverters (source: Nikkei BP)

The amount of power generation has outperformed the business plan, marking a 13.4% upswing to about 1,278,000kW and roughly 53 million yen in fiscal year 2017, compared with the 1,120,000kW and 43 million yen estimates, respectively (Fig. 6).

Fig. 6: The power generation amount is released to the public on the city's website. Above are the amounts of power generation in 2017. (source: Tokorozawa City)

Towa Arcs supplies float mounting systems

The Float Solar Tokorozawa is a floating solar plant that started generating power in March 2017. Solar panels with a total output of 385.56kW were arrayed on the surface of "Matsugaoka reservoir" in Matsugaoka, Tokorozawa City. This reservoir was constructed in the wake of a large-scale housing development. And 1,224 solar panels float on about 4,296m2 of the approximately 11,616m2 total surface area when it is full.

Towa Arcs Co Ltd supplied its floating mounting systems in which steel mounting systems to attach panels are built on polyethylene floats.

Panels are attached to mounting systems made of highly corrosion-resistant alloy steel; these are assembled on the ground and built on the floats. The floats are stabilized against the wind and waves, being tied with the foundations at the bottom of the reservoir by a mooring system using ropes and chains (Fig. 7)

Fig. 7: Towa Arcs "floating mounting system" (source: Nikkei BP)

When developing the Float Solar Tokorozawa, the city listened to requests from residents in meetings. As a result, the city decided to give consideration to many waterfowl that use the reservoir, despite it being artificial. The water surface area covered by the panels was reduced to about a third of the entire surface. And "green artificial islands," on which trees were planted, were floated on the water (Fig. 8).

Fig. 8: Number of panels reduced in consideration of waterfowl (source: Nikkei BP)

Facility overview