Load balancing is one of the challenges associated with deploying renewable energy. Different energy sources like wind and sunlight are available to variable degrees at different times, and output might not correspond to energy demand. That is true both day-to-day and across the year. For instance, right now the dams in the Columbia river basin have an excessive amount of water due to melting snow and ice. As a result, output from wind farms is not needed and going unused:

BPA managers say near-flood conditions in the Columbia river—and strict laws protecting the river’s endangered salmon—give the agency no choice but to disconnect the windmills as it grapples with a large power surplus. Not making electricity is not an option on the river, the BPA argues, because only a limited amount of water can be kept out of turbines and spilled over federal dams. Too much spill dissolves too much nitrogen in the river, which can kill migrating salmon.

Dealing with the intermittence of energy output from renewable sources probably requires a suite of approaches: energy storage using pumped hydroelectric and multi-lagoon tidal facilities, management of demand to correspond to periods where renewable output is high, using different types of renewable energy to balance one another, linking different regional grids, and more.