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First, a clarification: Last week’s headline said we can expect 100% solar and wind energy on the grid in the future. Although that’s likely to become feasible within the next 20-30 years, I don’t think it’ll happen in Washington. We are, however, likely to have 100% renewable energy by 2050. Solar and wind will be prominent, but hydroelectric generation will still be used and geothermal energy may even be developed. Iceland and New Zealand have 100% renewable electric systems already because both are rich in hydroelectric and geothermal resources.

Hydroelectric power is the most prevelant renewable generation source other than solar and wind. Water acts as the source of energy to turn the generators.

Run-of-river hydro power, with running water diverted through mechanical devices, was used long before electricity, for grain mills powered by water wheels. River hydro power has been used since the earliest days of commercial electricity. Hawaiian King David Kalakaua put electricity into the royal palace in Honolulu in 1886, powered by the Nu’uanu river. Run-of-river hydro generation is still in use, although, like solar and wind power, it is intermittent and seasonal.

Today, most hydro power is generated by capturing water at a high elevation behind a dam and choosing when the water falls through a turbine, turning it and producing power. Hydroelectric generation supplies over half of this state’s electricity.

Dam-based hydro isn’t just renewable; it is advantageous in two other major ways. First, water can be released to produce power on demand. Dam-based hydro isn’t dependent on the sun being up or the wind blowing. Second, water can be pumped back above the dam when electricity demand is low, enabling more generation when demand is high. This is called “pumped storage.” Although batteries are making progress, pumped storage is the largest-scale, lowest-cost form of electric storage in existence. The combination of hydroelectric generation and pumped hydro storage has kept Washington’s electric rates among the lowest and most stable in the U.S. for decades.

R&D is being done on tidal energy, wave energy and the thermal differences between surface and deep ocean water. Tide and wave energy have been obvious potential sources of electricity for decades. Recent developments in deep-water construction and in materials science (for corrosion and biofouling resistance) are improving their economics and reliability. Tide and wave power are approaching commercial viability.

Geothermal generation turns a turbine using the expansion of a fluid into a gas (usually, liquid water into steam). The energy to boil the liquid is supplied by the heat of the deep earth itself. In areas in which volcanic activity is high, rocks are porous (to store water) and permeable (so that water can run through them) and there is enough underground water, the earth itself provides enough steam to run power plants.

Geothermal plants have been in use for decades. They take very little space and run continuously, with shutdowns mostly for scheduled maintenance. However, they require specific geologic conditions that don’t exist everywhere.

In Washington, Mt. Baker and Mt. Rainier are potential sources of geothermal energy, but their underground geology is complex and no one has yet located the particular combination of heat and water that would enable generation at either of them.