There are three types of electricity – baseload, dispatchable, and variable.
Lots of confusion out there over the last day on what this all means, so this is a short little diary o' definitions.
Baseload is a word that is used to describe both the minimum level of power required to keep a system going and the type of generation that provides it. Coal and nuclear are the classic examples here – they're slow to warm up but once they're moving they're kept at a certain operating range for months on end. You may also hear 'spinning reserves' – this is a baseload type generating facility that is 'spun up' but unloaded, running in reserve for demand peaks. Hydroelectric can also be considered baseload generating capacity if it's got a steady flow of water behind it.
Dispatchable is a word used to describe generating sources that are quick to react to new requirements. Natural gas generating using 'peaker' plants is the classic example. These systems maybe only run for a week total out of ever year but electric rates are such that they're profitable when servicing demand spikes. Hydroelectric power is also counted as dispatchable – simply open the gate, the turbine spins up, and power begins to flow.
Intermittent sources produce irregularly (wind) or periodically (solar). Natural gas or hydroelectric dispatchable power coupled with these renewables can make for a smooth, trustworthy flow of power.
Deferred hydroelectric production has great value. If you've got an impoundment driving a dam that isn't getting the rain/snow fall needed to refill it that's a potential problem. If you've got wind turbines nearby you can defer hydro production by using their output, keeping water levels up.
A larger, smarter grid decreases the need for backing wind with fossil fuel or hydroelectric generation. The larger the pool of wind sites the more likely the wind is blowing for at least some of them. Denmark started doing wind in sites as small as a single turbine and they prove out this concept – the naturally diverse footprint of their wind plant means it's much smooth, megawatt per megawatt, than our system of large farms of utility scale turbines here.w
The long term picture for how to cover our electric need while reducing greenhouse gases is this.
Conserve the hell out of the supply. We use double with Japan and France do per capita. That has to change.
Coal is an immediately dirty baseload while nuclear has long term waste problems. The possibility of long term waste problems which can be remediated is vastly preferable to the immediate, guaranteed global warming, mercury emissions, and acid rain problems associated with coal.
Wind and dispatchable power such as natural gas and hydro are natural friends that support each other. If you have a good way to make renewable ammonia it can be used as natural gas is. This allows for wind plants to produce their own carbon free backing fuel during the less busy overnight hours.
OK, very tired after long trip to DC, had a good conference, and I'm signing out for bed. As this is going to be a definition collection I'm asking for comments here – did I miss anything? Do I need to clarify any particular point?
(UPDATE: I expected like six comments and instead you guys go nuts! Here are some answers to questions raised by some of the responses below.
It is possible to get energy from tides but these may be analyzed in the same fashion as solar - diurnal variable power source.
The Iowa Stored Energy Park chooses to try to firm renewables, in that case wind, by storing compressed air underground. It's a possible solution, but it's situational - don't have the right geology under the wind farm, don't get to use this method.
Last year I published the National Renewable Ammonia Architecture. Inside you will find a map of the 643 largest hydroelectric facilities in the U.S. Some have impoundments while others are 'run of river' - that's the 'slow flow' hydro mentioned below.
Niagara Falls has a 1,900 acre pumped hydro storage impoundment a few miles east of the falls. I think the whole idea is that it lets them take turbines offline for maintenance without powering down. Kossack Nb41 lives there and will likely chime in with a detailed response when he notices this.
Some people mentioned biomass. The engineer in my cringes - this works in places like Massachusetts, where trees grow like weeds, but the mass balance calculation indicates the hilltowns can get 170 megawatts sustainably ... if no one is gathering too much wood for heating ... which everyone does in New England. We have to use more than biology as we tumble down fossil fuel mountain on our way back to the solar max for this planet.
Again someone fails to understand the issue at hand and brings up the nuclear waste issue. If we don't get our heads around what it means to run out of recoverable oil and natural gas ... well ... fretting over nuclear waste stored in ponds that are going to dry out due to climate change will be a ways down the list of worries humans have. Kossack wondering if has a nice response on this point.
the major long term waste issue is actually potential fuel, unused because of policy decisions in regards to weapons proliferation that rejected fuel reprocessing.
Reprocessing the spent fuel reduces the volume of waste by about 95%, leaving you with 1/20 as much to deal with.
It also removes much of the "hundreds of generations" aspect. After the actinides are removed, the big problem isotopes have halflifes on the order of 30 years, meaning that they will not be a problem in 3 centuries - add an extra century or two (10 to 100 times further reduction).
Also consider that there are several newer reactor designs that effectively do the reprocessing internally, so that their spent fuel has much less of the troublesome actinides in it and reducing the waste problem proportionally. Besides that, there are several proposals for systems in which reactor farms would include a subset of reactors or other device that would 'burn' the waste radioisotopes to stable ones, in theory eliminating the issue and in practicality greatly reducing it. However while based on known processes, they have not been implemented in a test case.
Someone asked if there was no mention of solar - YES, Steven Chu (I think) was talking about the flexible printed circuit style panels and replacing all roofs in the southwest with that material. That's from memory, don't quote me, so solar did get some play, but I can't be everywhere at once :-)
OK, this is making my eyes cross. One more and then I wait for DailyKos university followups. Wind will be improved by having a better grid - the larger the total footprint, the more stable output; the wind doesn't stop everywhere all at once. I forget exactly where he keeps it but I think Paul Gipe has done a study regarding how Denmark's "small wind" has achieved a more steady output than our Stalinist sized wind farms.