HAWI, Hawai’i Down a dirt road on America’s southernmost island, 16 windmills tilt their sleek blades toward the ocean, as dependent on the whims of Hawai’i’s tropical breeze as residents are on the electricity they help produce.

The Hawi wind farm on the Big Island makes clean and affordable energy, but the 100-foot-tall wind turbines stop when the air is still.

Most forms of renewable energy face a similar difficulty nationwide they’re cleaner than oil and coal but fall short on reliability and convenience. […]