Japan Solar: Sotsu-FIT & Asset Strategy
公開日：2026-08-12
The Sotsu-FIT Crossroads: What Changes After 2026
If your solar plant in Japan was certified under the Feed-in Tariff (FIT) scheme before 2019, you are approaching a critical inflection point known as *sotsu-FIT* (卒FIT). This term refers to the "graduation" from the fixed-price purchase period, which typically lasts 10 years for commercial and industrial solar. For most plants commissioned between 2012 and 2015, the guaranteed purchase price from utilities like TEPCO, Kansai, or Chubu expires between 2022 and 2026. After this date, your plant no longer sells electricity at the guaranteed tariff—you must either sell on the wholesale market, sign a new corporate PPA (power purchase agreement), or find an aggregator.
The financial impact is stark. A typical 10 kW to 50 kW plant that enjoyed a ¥40–¥42 per kWh tariff might now face market prices of ¥7–¥12 per kWh, depending on region and time of day. However, this is not inherently a loss scenario. The key is that your plant's value moves from a "fixed income" model to an "asset optimization" model. Many owners are surprised to learn that their plant can still generate stable revenue if the operation and maintenance (O&M) costs are controlled and the system is performing near its nameplate capacity. The decision you make now—whether to continue operating, sell the asset, or repower—will define your return on investment for the next decade.
Output Decline: The Hidden Leak in Your Revenue
One of the most common misconceptions among non-Japanese owners is that solar panels last 25–30 years with minimal degradation. While the physical panels do last, the *system* output declines faster than many expect. In Japan's humid, typhoon-prone climate, degradation rates average 0.5% to 1.0% per year, but this can accelerate to 1.5% if the plant suffers from PID (Potential Induced Degradation) or micro-cracks from snow loads or thermal cycling. By year 10, a plant that originally produced 100 MWh annually may now produce only 90–92 MWh—a revenue loss that becomes critical when the FIT tariff drops.
More concerning is *soiling and vegetation* impact. Japanese landscapes often have dense tree lines, and unmanaged vegetation can shade modules for 2–3 hours per day, reducing output by 15–25%. Many owners only notice this when their monthly monitoring data shows a sudden drop, but by then, the cumulative loss is already significant. To address output decline, you must first establish a baseline: compare your actual annual kWh production against the *estimated* production from the original design simulation (e.g., PVsyst). If your plant is below 80% of the theoretical output, it is not a "market" problem—it is a technical problem that can often be fixed with string-level monitoring, module cleaning, or replacing a faulty inverter.
The 10-Year Inspection: Not Optional, But Strategic
Under Japan's Electrical Equipment and Materials Safety Act (電気用品安全法) and the Fire Service Act, all commercial solar plants must undergo a mandatory inspection at the 10-year mark. This is not a bureaucratic formality—it is a legal requirement that can lead to fines or forced shutdown if ignored. The inspection covers three main areas: electrical safety (wiring, breakers, grounding), structural integrity (mounting frames, roof attachments), and fire risk (DC isolators, junction boxes). For ground-mounted plants, soil settlement and corrosion of galvanized steel are also checked.
For asset owners, this inspection is a strategic opportunity, not just a compliance cost. The inspection report provides a documented condition assessment that is critical for two purposes: (1) negotiating a higher sale price if you choose to divest, and (2) identifying early-stage failures that would become expensive later. For example, a common finding is degraded DC connectors (MC4) that have overheated due to moisture ingress. Replacing these connectors costs ¥100,000–¥300,000 per site, but if left untreated, they can cause a string failure or even a fire. Many Japanese O&M providers bundle the 10-year inspection with a "recommissioning" service, which includes thermal imaging (drone-based), IV curve tracing, and insulation resistance testing. Budget for this: typically ¥200,000–¥500,000 for a 50 kW plant, but the cost is tax-deductible and often extends the plant's useful life by 5–10 years.
Asset Sale: Timing, Valuation, and Buyer Expectations
If you are considering selling your sotsu-FIT plant, the market has matured significantly since 2020. Japanese infrastructure funds, regional banks, and even foreign private equity firms are actively acquiring operating solar assets. However, the valuation methodology has shifted. During the FIT period, buyers used a "yield-based" approach (e.g., 4–6% unlevered IRR). Post-FIT, buyers discount more heavily for merchant price risk, and they scrutinize the 10-year inspection report and O&M history. A plant with a clean inspection report and a solid PPA (even at ¥8/kWh) can fetch 1.5–2.0x the price of a plant with unresolved technical issues.
The key mistake we see is that owners try to sell *before* the sotsu-FIT date, assuming the FIT contract adds value. In reality, the FIT contract's remaining term is often less valuable than a well-structured corporate PPA with a local utility or a retailer like Eneos or Idemitsu. Buyers are also wary of "land lease" issues—if your land lease expires within 5 years, the buyer will discount heavily. To maximize sale value, consider these steps: (1) complete the 10-year inspection and fix all "C" and "B" grade findings, (2) secure a 3–5 year PPA with a creditworthy off-taker, and (3) provide a transparent O&M log showing monthly output data. A broker can help, but be aware that brokerage fees in Japan are typically 3–5% of the sale price, which is negotiable.
Practical Steps: From Data to Decision
The most rational approach to your sotsu-FIT decision is not based on emotion or a single electricity price forecast. It is based on your plant's *specific* condition. Start by pulling your last 12 months of inverter data and comparing it to the first 12 months. Calculate the annual degradation rate. Then, request a quote for a "diagnostic audit" from a third-party engineer (not your current O&M provider). This audit should include a drone thermal scan, an IV curve test on at least 10% of strings, and a review of your grid connection agreement (連系契約) to see if your capacity is still appropriate.
Once you have this data, you can model three scenarios: (1) Continue operating with optimized O&M (e.g., switching to a TPO or performance-based O&M contract), (2) Sell the asset after a minor capex injection, or (3) Repower—replace inverters and add DC capacity if your grid connection allows. For most plants, scenario 1 is the default, but scenario 2 is increasingly attractive for owners who want to exit Japan's complex administrative environment. Regardless of your choice, do not delay. The sotsu-FIT transition is a one-time event, and the quality of your decision depends entirely on the accuracy of your plant's condition data. Start with accurately understanding your plant's condition—measure, inspect, and document. Only then can you negotiate from strength, whether with a buyer, a utility, or your own O&M contractor.