Q&A：FITがあと5年、蓄電池を導入するタイミングがわかりません

Today, I'd like to answer a question I received in the comments section of my video. Today's question is, "I currently have about 5 years left on my FIT (Feed-in Tariff) contract, but I'm unsure about the timing of installing a battery storage system." More specifically, the question was, "I'm considering installing a battery storage system, but I still have 5 years left on my FIT. Considering that I won't be able to use my air conditioner during summer power outages, it seems like it would be better to install a battery storage system using subsidies, but I'm unsure about the timing." So, as usual, please refer to my whiteboard notes while I explain this. First, let's clarify the premise of this person's situation: they already have solar panels installed. However, we don't know how many kilowatts they have. Knowing that would give us a more concrete picture, but assuming it was installed about 5 years ago, I imagine it's around 4 or 5 kilowatts. And they have 5 years left on their FIT contract. FIT is a system where, for 10 years after installing solar panels, the electricity generated is purchased at a fixed price. Even looking at it from May 2026, when this video is being filmed, the purchase price per kilowatt-hour was likely high back then, which I think is the source of the concern. Furthermore, this person is worried about power outages during disasters, especially in the summer. They're worried it will be too hot to live in, and they'll have trouble sleeping, so they want to be able to run the air conditioner. That's why they're wondering whether they should install it now, including considering subsidies. To put it simply, if you have 5 years left on your FIT (Feed-in Tariff), it's often more economically advantageous to sell the electricity. If you installed it around 2019, the selling price was probably around 24 yen per kilowatt-hour. Now it's around 16 yen, so it was high. On the other hand, in some areas, buying electricity costs around 35 to 45 yen. Considering that, it seems more profitable to sell the electricity you can and buy electricity optimally only at night. However, deciding on a battery storage system isn't simply a matter of "will I get my money's worth?" There are three perspectives to consider: firstly, economic rationality; secondly, peace of mind during power outages, in other words, disaster preparedness. The third point is future strategy after the FIT (Feed-in Tariff) period ends. In this person's case, the decision will likely depend on how much importance they place on disaster preparedness. They want to avoid unpleasant experiences during disasters and protect their young children and elderly family members. These feelings are important and cannot be measured solely by economic rationality. So, how much would a battery storage system cost? Based on current market prices, a 5-kilowatt-hour battery would cost around 900,000 to 1,400,000 yen, a 10-kilowatt-hour battery would cost nearly 2,000,000 yen, and even with subsidies, it might still cost around 1,500,000 yen. A 15-kilowatt-hour battery would cost around 3,000,000 yen. That's quite a lot of money. Practically speaking, around 10 kilowatt-hours seems about right, but even with 10 kilowatts, only about 80% is actually usable, around 8 kilowatt-hours. A 6-tatami mat size air conditioner used for cooling in the summer uses approximately 300-800 watts. Roughly assuming 0.5 kilowatt-hours per hour, 8 kilowatt-hours would last about 16 hours. In other words, you might be able to manage for about two nights by enduring the heat. However, this is only considering the air conditioner. If you also consider the refrigerator, lighting, Wi-Fi, standby power for the water heater, ventilation, etc., the entire house might not even last a single night. Winter heating uses even more energy, so a battery alone isn't enough; you'll probably need other backups like a kerosene fan heater. Therefore, if you seriously want to improve your disaster preparedness, you'll want a larger capacity. But if you're spending around 3 million yen, I think it's better to study a bit more and imagine your future lifestyle before making a purchase, rather than rushing into a decision now. However, if you absolutely can't stand the idea of ​​the air conditioner not working in the summer, there's the option of a portable power supply. There are now models like EcoFlow with decent capacity available. Some can be bought for a few hundred thousand yen, so you can at least take refuge in the bedroom, huddle together as a family, and get through one or two nights. It's not just for disasters that could strike at any time; it can also be used for camping, barbecues, and using electric pots outdoors, so I think it's worth trying it out as a small battery first. And the most important thing to consider is what happens after the FIT (Feed-in Tariff) program ends in five years. From now on, I believe we'll move further into an era where we consume the electr...