The city of Fukuoka in Kyushu, Japan has announced a project designed to produce electricity from osmosis, a process involving two liquids with different concentrations of dissolved substances (“Japanese Power Plant Turns Saltwater Into Electricity—and It’s a Glimpse Into the Future“, Gizmodo, 2025-08-26). Water will seep through a permeable membrane from the less salty to the more briny side, creating a pressure difference that can drive a turbine and a generator. Here is a PDF of the Fukuoka area waterworks agency that describes it in detail.

In the case of this plant, on one side it uses clean treated sewage water from a nearby sewage treatment plant. On the other side, it uses salty brines from a reverse osmosis plant that extracts freshwater from sea water using pressure created by electric pumps — the exact opposite process of the osmosis power plant.

The osmosis power plant has an output of 110 kW. Working 24 hours a day, 365 days a year and with a conversion efficiency of 91%, this yields 880,000 kWh per year. This is the typical annual power consumption of 290 households. Sounds impressive? Let’s compare it to an alternative.

Looking at the building on Google Maps, the roof area of that plant measures 100 m by 160 m, or 16,000 m2. Covered with standard solar panels (1.4m x 1m, 280 Wp per module), a rooftop solar setup at that location would, according to the National Renewable Energy Laboratory solar calculator, produce 3,450,000 kWh per year, enough for about 1200 households vs. the 290 quoted in this article.

And that is before you take into account the energy losses for pumping brine and reclaimed cleaned sewage water that the osmosis plant will require for operation.

What this demonstrates is just how extremely mature a technology solar power is by now. There are no moving parts, no filters to clean, no pipes to replace, etc. You just install it and harvest electricity, year after year after year, for 25 years and more.