Pairing wind and solar

I've talked before about an Ozzie combined wind and solar farm, the Kennedy Energy Park, which because wind and solar are complementary (wind blows at night when the sun doesn't shine, wind blows more in winter when there's less insolation and less in summer when the daylight hours are longer) produces quasi-baseload output.  However, it was clear that there is a gap which opens up as wind speeds die down in the afternoon and the sun moves lower in the sky, a gap which is exacerbated by the rise in demand between 3 pm and 8 or 9 pm.  That gap could be filled either with gas, or with storage (pumped hydro or batteries).  This concept has now spread to the USA.

Along a country road east of Lima, Ohio, a company is preparing to build one of the world's largest renewable energy projects that pairs wind and solar to create a hybrid power source. It's a rare combination now, but one that's expected to become more common because of its potential to cut costs while providing a more consistent flow of clean energy.

Invenergy is starting with a 175 megawatt wind farm. Within the wind farm, it plans to build a 150 megawatt solar farm. Together, they would produce enough electricity for about 175,000 homes.

The wind and solar energy complement each other. They hit their peaks at different times of day and night, allowing them to provide a steadier output together than if each was alone. And they save money because they can share equipment, power lines and workers.

The consistency is increasingly important as renewable energy replaces coal-fired plants, which can provide 24-7 power but that also create pollution and contribute to climate change.

[Read more here]

The GIF below gives a similar perspective to the Australian experience.  Note how strong wind is at night, making up for the absence of sunlight.  And note how wind tails off during the day, when solar is increasing.  Yet we get the same problem as the Kennedy Energy Park in Australia has to deal with: the gap which opens up between demand and supply in the late afternoon.  Wind speeds are dying down, the sun is lower in the sky and then sets, but demand is peaking.  Right now, US utilities are using gas to bridge that gap.  But gas still produces CO2, though less than coal, but because it's used only for part of the day, total emissions are much lower than with coal.  US utilities seem to be moving towards what I call the 1/3rd solution: 1/3rd wind, 1/3rd solar, 1/3rd gas.  This will produce only 1/6th of the CO2 that coal does.  Adding some storage--more each year as prices drop--will reduce those even further. 

(Source: Inside Climate News)