Since diving into the deep end when it comes to energy issues, almost every day sees new fascinating concepts, approaches, and technologies. Fascinating … exciting … even hope inspiring at times. And, as well, as the passion builds, so many of these are truly Energy COOL.
A critical challenge for some renewable power systems is providing backup power or power storage. Better power storage will foster adoption of intermittent renewable power sources (and to help shift base load to peak load requirements). One of the best, ‘all renewable’ options has been pumped hydro storage. which enables reliable power supplies using intermittent power sources (like wind). But, hydro storage has been mainly limited to places with existing (or easily created) hydroelectric power systems (dams).
Several options are emerging that could be game changing in hydro storage and open up new vistas for renewable power integration into power grids.
Energy Storage is a major challenge, whether batteries for Plug-In Hybrid Electric Vehicles or a means for saving power from wind power when there isn’t any wind. As to the second, there are some interesting developments in pumped hydro storage that merit Energy COOL.
TUNNELING FOR HYDRO STORAGE
Hydro power storage, basically using damns, works well. (International Hydropower Association Pumped Storage Database)However, it is constrained as a storage device to where the water (the dams) exist and where there is adequate water for using the hydro-system as a storage unit. These are greatly constraining requirements.
Consider for a moment the type of tunneling device used to make the Chunnel. Think about all the oil wells around the world. Truth be told, humanity has gotten extremely good at drilling holes in the earth.
As per an Energy Pulse discussion,
with advanced tunneling technology, it may be practical to expand hydroelectric resources without building any large dams.
As far as power generation is concerned, a dam is nothing more than a way to get water from the reservoir inlet to the power turbine without losing head. A smooth-walled tunnel would serve just as well, as long as it was large enough to allow the water to move relatively slowly. So instead of building a giant dam and flooding hundreds of square miles of river valley, one could have only two small reservoirs, connected by tunnel. A portion of the river’s flow would continue in its natural course, but the larger portion would be diverted through the tunnel for power generation.
Or, well, one wouldn’t necessarily have to have this associated with a river. This could, for example, use the ocean as the bottom reservoir, with a tunnel going up inside a mountain/cliff, and a reservoir hollowed out of mountain. The reservoir might not ever need to see the light of day.
But, what might the power storage potential and at what cost?
Near Chicago, for example, underground reservoirs help control sewage run-off during storms.
A recently completed segment included 8.1 miles of concrete-lined tunnel bored through bedrock. The cost for the finished project came to roughly $1.00 per gallon of holding capacity, or $265 per cubic meter. If a deep reservoir for pumped hydroelectric storage could be built for the same cost, would it be a feasible solution for energy storage?
One cubic meter of water dropping 100 meters in elevation releases just under a megajoule. If the average tunnel grade were 10%–100 meters per kilometer–then 31 cubic meters per second flowing through the tunnel would represent about 30 megawatts per kilometer. At a cost of slightly under $10 million / kilometer, the tunnel’s contribution to power cost, in round numbers, would be $300 per kilowatt. The turbines and generators and other “balance of system” items would up that figure, but it’s still in the ballpark for the cost of dispatchable gas-fired capacity, and well under the $1500 / kilowatt “rule of thumb” for new coal-fired plants.
Writ large, the Energy Pulse article suggested a 0.8 cents per kilowatt hour premium for this large-scale energy storage option.
Hmmm … for less than one penny per kilowatt, a utility could provide a path from moving from intermittent wind power, to a 24/7, 365 days/year electrical power system.
incorporates a new concept in pumped hydro storage — an inverse offshore pump accumulation station (IOPAC).
On the Energy Island when there is a surplus of wind energy, the excess energy is used to pump seawater out of the interior “subsurface-lake” into the surrounding sea. When there is a shortage of wind power, seawater is allowed to flow back into the interior “lake” through commercially available generators to produce energy.
Ok, pumped hydro storage … ho-hum … Sure, it works well. (Pumped storage works well with wind power, storing at roughly an 70%-85% efficiency of excess power to be released for power when the wind isn’t blowing (or there is excess/peak demand.) And, well, there is a lot of it. (Oover 90 GW of pumped storage in operation world wide, which is about three percent of global generation capacity.) This is great stuff, but, well, what is Energy COOL about this Energy Island?
Well, there is something new and innovative here. KEMA, Lievenseand the Das brothers have designed an artificial island that would, in essence, be somewhat like a Pacific atoll, but the inner water surrounded by the outer ring would be sealed off from the larger ocean. The interior reservoir would be 50 meters deep, enabled by the mud of the seas off the Netherlands. And the island (the dikes/outer ring) would be made from the materials dredged to create the reservoir.
On that outer ring, a long line of wind turbines for sending power ashore. When producing excess power, sea water would be pumped out of the enclosed lake into the surrounding sea. When there is greater demand, sea water flows back into the ‘lake’, driving generators.
Here is how the Environmental News Network discussed this:
Imagine you’re looking for treasure on a small island in the middle of an ocean. …. you dig a hole where the tattered map says the treasure should be. Dig, dig and dig you go, and soon you’re way over your head and all you can see is the blue sky above, and the walls of sand and dirt around you.
No treasure to be found.
Suddenly you have a revelation. The hole you’ve dug is deeper than the surface of the ocean around your little island. Should the skies turn cloudy and a storm come in, the ocean could come pouring into your hole. You’d be in deep trouble in your hole in the middle of the ocean.
But you have a second revelation, you’ve invented an energy storage device. What if you dug a large and deep hole in an island – on an ocean or big lake – and purposely allowed the surrounding body of water to flow in, but at your discretion and through pipes and hydroelectric turbines. As the water flowed you be generating power. When filled your deep hole, or reservoir, would be pumped out into the surrounding ocean by another source of energy, perhaps wind turbines or excess capacity on the shore-side power grid. In effect you be storing the energy from those sources.
Your little island with a deep lake in the middle is your energy storage device, your energy island. In the long term it could provide more revenue than the chest of gold you never found.
“More revenue than the chest of gold you never found.” Yet another indication that one can make some serious green by Going Green. Here is another path where an upfront, smart investment could foster a lower long-term, total ownership cost.
The analysis to date suggests a 12-hour power delivery at 1.5 gigawatts (roughly equal to three coal-fired plants). The KEMA analysis suggests a total annual storage capacity of 20 GWh or “enough energy to offset 500 to 840 kilotons of CO2 emissions.”
The Energy Island seems like a real potential for making offshore wind power a 24/7 electrical power source.
Note that the Energy Island truly does seem to be an island of energy. Not only the wind mills and electrical generators from sea water, but as well a chemical plant (better far from an urban area) and a liquid natural gas (LNG) terminal.
Compressed Air Energy Storage is another pumping process for storing power.
“Utilities can use off-peak [or excess renewable power] electricity to compress air and store it in airtight underground caverns. When the air is released from storage, it expands through a combustion turbine to create electricity.”
CAES is in use. For example, the 110-MW McIntosh, Alabama, CAES went into operation in 1991.
The system uses an underground cavern to store compressed air. The cavern was formed by “solution mining” a salt deposit — pumping water into and out of it to dissolve the salt and form the cavern. The cavern is 220 feet in diameter and 1000 feet tall, for a total volume of 10 million cubic feet. At full charge, the cavern is pressurized to 1100 psi, and it is discharged down to 650 psi. During discharge, 340 pounds of air flow out of the cavern each second. The cavern can discharge for 26 hours.
The compressed air feeds a 100-MW gas-fired combustion turbine. Compared to conventional combustion turbines, the CAES-fed system can start up in 15 minutes rather than 30 minutes, uses only 30% to 40% of the natural gas, and operates efficiently down to low loads (about 25% of full load).
Note that CAES is not a fully-renewable system, as currently run. It significantly reduces natural gas requirements as compressing the air
But, CAES might soon face a major expansion, specifically linked to wind power. The Iowa Stored Energy Park (ISEP):
ISEP will use the energy from a large wind power facility located in Iowa where there are good wind resources. This wind energy will be used to store air in an underground geologic structure. During peak power demands, the stored air will be released, mixed with a fuel and used to power combustion turbines that produce environmentally friendly and economical electricity.
Thus, a path for a major reduction in natural gas requirements for natural gas backup to cover wind intermittency. Not quite ‘all renewable’, but a major reduction in CO2 emissions (especially compared to coal electricity).
There is no (NO) single Silver Bullet solution to our energy challenges, to deal with global warming. There are, however, critical paths and critical opportunities for moving toward a better energy future, for becoming Energy Smart. There are Silver BBs that we must pursue. Energy Efficiency. Renewable Power. And, well, power storage to enable that renewable power. These are two options for that power storage, two approaches to pumped hydro storage that truly merit the moniker, Energy COOL!
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* For a very interesting, related discussion, see Energy from Wind: A Discussion of the EROI Research at The Oil Drum. * The Energy Island is a separate concept for a modular approach to OTEC power systems that would “bring together on a single floating structure a variety of renewable energy conversion systems to maximise the energy production available from the diverse sources available”. This is a potential topic for a separate Energy COOL discussion.