The footprint will vary from project to project. Almost the entirety of the footprint consists of the reservoirs; everything else, except transmission, is below ground. For some of our typical sites, reservoirs are typically 60-120 acres each in surface area. So let's say 250 total acres, compact. Tanks with volumes of thousands of acre-feet, required to match the scale of a pumped storage plant and provide 8+ hours of storage, using normally available heads, would be too expensive and generally not necessary. There was one such project proposed in California, some time ago. Ideally one finds sites with topography that minimizes the construction involved in reservoir creation. Occasionally there are unusual opportunites like the newly proposed Maysville Pumped Storage project in Kentucky, which would use existing excavated mine space 1,000' below the surface as the lower reservoir. This dramatically lowers the cost of the project.
As this need grows, and it looks like it certainly will with advances in alternative energies, I would imagine there could be public/private pumped hydro projects. Certainly a lake would serve the public in many ways.
As correctly stated, pumped storage has been the number one option for large-scale storage. It remains the number one option. There are today 75 applications for new pumped storage projects in the United States, most concentrated in the west but some in the east. Only the best of these are developable, and those best represent quite a few thousands of megawatts. The scale of these projects - from 280 MW to over 1,000 MW - is large, but so is the scale of renewable energy and the need for new firm capacity toward the end of the decade. Cost per kW varies widely from site to site, but the best will be under $2,000/kW, and some under $1,200/kW. That, combined with storage durations exceeding 12 hours and lifetimes of 75+ years, give pumped storage the lowest capital cost per kWh (with the exception of conventional CAES - see below).
As for the article's note on siting difficulty - that is not a new issue; quite a few pumped storage projects from the olden days never got built due to poor siting choices, environmental concerns, etc. Today, however, a new generation of closed-loop projects are under development, many of which avoid similar issues.
On Mr. Murray's comment - the cost of pumped hydro is not much related to the price of land because its footprint is pretty small.
As for Compressed Air Energy Storage - the only rival to pumped storage at large scale. More modular (generally, units of 135 MW); no FERC licensing required; and somewhat lower capex. CAES also has the lowest cost per kWh of duration of any storage technology - if using salt caverns. Where such geology is available, it's relatively easy to expand storage capacity to levels allowing for semi-weekly storage. The newer CAES technologies have only marginal advantages over existing CAES in areas of suitable geology. While they would eliminate the natural gas component, fuel use for existing CAES is already extremely low, and the round-trip electrical efficiency would be about the same. Using pipes for storage will also certainly be more expensive than using caverns, so while pipes would allow for wider geographic siting options, the advantage of long duration storage would likely be compromised. CAES without natural gas also shifts the economics such that it becomes more dependent on off-peak/peak price spread, which has been shrinking, rather than on moderate amount of natural gas, which will be inexpensive for some time.
I don't know about the economic feasibility of pumped hydro versus batteries, Rob, largely because so much of pumped hydro's cost is dependent on the price of the land. In terms of system technology, pumped hydro has a big advantage over the acres of batteries that would otherwise be used (and would later need to be replaced). But for pumped hydro, it's always going to come back to land availability and cost.
I can understand that, Chuck. I'm curious, though, as to the economic feasibility of pumped hydro compared with alternatives. I would think that once the lake is in place, the system for pumping and retrieving power via that downhill stream would be relatively inexpensive. As for the lake -- seems every community could stand an extra lake.
Rob, pumped hydro (i.e., the lake on the hill) is still our biggest source of storage today. But as commenter ehunt has so succinctly stated below, pumped hydro "has not seen wider implementation due to geological, environmental and capital constraints."
The Lux report does indeed reinforce the need for large-scale energy storage solutions as renewable energy deployments continue. Other researchers (Pike, Frost and Sullivan, EPRI) have reported much the same thing. The only two proven viable (efficient and economic) methods thus far for storing hundreds of MW for hours - pumped hydro and compressed air energy storage, or CAES - have not seen wider implementation due to geological, environmental and capital constraints. Indeed, no CAES system has been built for more than 20 years (and there are only two in the world).
A new method for compressing large volumes of air to store energy at low cost exists and is being developed by several companies, my own included. Isothermal CAES compresses air but does so in a way that maintains near-constant temperature, thus avoiding the inefficiencies of conventional CAES. ICAES also allows site-anywhere storage using pipes, rather than relying on caverns. Even better, because it retains most of the heat produced during compression, ICAES does not need a natural gas turbine to reheat the air during decompression, thus avoiding emissions and fossil fuel consumption. It's a truly sustainable solution that will be deployed on a MW scale in 2013.
One note about Lux's reference to flywheels: they are not considered a bulk storage technology and are not able to provide MWs for hours as is needed for diurnal renewable energy storage. Flywheels are fast-responding devices that are very good at delivering short bursts of energy for minutes (and absorbing the same), in order to provide grid ancillary services like frequency regulation. This is considered a power application, where the demands to inject or absorb energy are instantaneous and durations relatively brief, but with many cycles each day. As renewable use expands and brings all of its intermittencies with it, short-duration fast-response storage systems will also be needed to smooth out the irregularities and maintain stability. But they will not compete with ICAES, large battery systems, or other emerging methods of providing bulk storage.
Full disclosure: I work for SustainX, one of the ICAES developers.
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