Both Kill-A-Watt and Bob2 are correct. Viewed nationally, the wind is blowing and/or sun shining somewhere nearly all the time. But we don't have a national grid, and 'blowing/shining somewhere' doesn't necessarily match the need at any given time and place. OTOH, the relative inconstancy doesn't mean we shouldn't do it and keep on burning coal etc. because there are ways around it.

Hit the Back button now to avoid another rant.

The real issue is that to work with renewables effectively means having a grid that isn't one-way, and that can accept and dispatch a wide variety of power sources at a wide variety of locations in real time. What we have now is mostly one-way, designed to use a relatively small number of large "utility-scale" power sources that are controlled in anticipation of demand. There alway has to be more generation online than demand, but some percentage to cover short-term changes that the control system can't work with. Then, most 'utility-scale' power facilities (including renewables) are NIMBY-incompatible, so they're a long distance from the demand resulting in power-line losses of some consequence. Renewables usually (not always - see solar in the desert and wind in West Texas for instance) tend to be smaller plants, and may or may not be a long distance from the load (depends on the physical character of the source - hydro & geothermal for instance, at least in the US, tend to be some distance from urban areas, while small solar is potentially scattered over all the rooftops in town).

Most utilities (especially some municipal utilities, which tend to be smaller "islands" in regional grids) are working on dealing with this, which becomes a serious computing and data storage/use problem, and requires in some cases rewiring parts of the grid to handle higher power as rooftop solar, for instance, becomes more widespread. Storage of various kinds is also needed - not so much as a Final Solution for nighttime power but as a balancing tool allowing each power source to be used most effectively. It's all expensive, so our bills will go up faster than inflation to cover it. Sorry about that. Then of course there are the utilities that appear to be using a prevent defense on solar and other renewables - some of them will eventually go bankrupt trying.

Unfortunately for coal, power plants burning it tend to be among the least flexible in terms of power output variation and response. To the extent that coal remains part of the mix, it'll be a smaller proportion, and the plants probably will become smaller because they will be covering mainly the true base load - whatever the renewables and storage don't handle. From a *coal trains!* standpoint, that's not a good omen, but from a GHG/watt standpoint (and feasibility of carbon capture and sequestration) standpoint a smaller, more modern unit is good. I don't think natural gas will totally wipe out coal-fired power production, either; you need to have the n.g. available, and if there's no pipeline it's hard to get enough btus/train with n.g. compared to coal. Plus, in either case, you're burning a fossil fuel which needs to be minimized. Seems more likely, though, that the old "mine-mouth" power plant concept will be used where possible; that avoids long-distance coal transport, and the extra transmission lines will be needed for renewables anyway.

Happy Friday! ;)