Water is not the only material that can be stored and harnessed to be used for energy storage. Air can also be used as an energy storage medium with what is known as Compressed Air Energy Storage (CAES). Several different methods are being explored to use this type of energy storage, although the earliest examples have been in place for decades.

Using underground caves to store compressed air is a technology that dates back to the 1970s in Huntorf, Germany, where a 290 megawatt facility was built using a salt dome. A similar, though smaller (110 megawatt) facility was built in Alabama in the early 1990s. These facilities are both still in operation, but very little was done with the technology for many years.

One of the problems that compressed air storage faces is a thermodynamic effect where a gas heats up as it is compressed, which makes it increasingly difficult to store additional compressed air.

Although the storage conversion efficiency of CAES can be fairly high, the compressed air needs to be air as it is released, which typically requires an outside fuel source. The McIntosh plant in Alabama ends up burning an amount of natural gas to reheat the compressed air equal to about 1/3 of what it would use for direct combustion power generation. This makes CAES far less environmentally friendly than many other storage options. Overall, the efficiency of compressed air systems is also lower than many other storage systems, ranging from 45-70 percent.

Underground CAES systems also are reliant on location, much like pumped hydro systems. Suitable geological formations are necessary to have underground caverns that can be used to contain the pressurized air. However, it turns out these same formations are also desirable for natural gas storage, and, in the last decade, developers who were interested in setting up new CAES facilities often found that the gas industry was already using the available underground structures. Competition for access to suitable sites has also been a hindrance to development of CAES systems. But not all CAES systems are dependent upon locations with suitable geology.

Another compressed-air system being developed by a company called SustainX uses proprietary technology for isothermal compression (ICAES), which avoids the high temperatures and thermal losses. SustainX claims far lower costs than “conventional” compressed air storage, as well as almost 95 percent storage efficiency.

Instead of using caverns or geological formations, the SustainX method uses conventional, industrial, high-pressure bottles to store the compressed air. This enables the SustainX system to be installed anywhere, rather than relying on locations with salt domes or other usable geological formations. Because the process is isothermal, the air does not need to be heated or cooled, and, most importantly, there is no need to burn natural gas, which makes this approach preferable, particularly when it comes to storing power from clean, renewable sources. As yet, there are no installations of the ICAES system, but SustainX plans construction of a demonstration pilot plant to be completed in 2013.

Another especially interesting version of compressed air storage is the Energy Bag. Whereas in most instances, high pressure vessels or rock formations are used to contain the air under high pressure, the energy bag is a lightweight (75 kilograms or 165 pounds) bag that can store pressurized air sufficient to provide 70 megawatt hours of storage. The trick is that it does so deep underwater, where water pressure from the surrounding ocean provides the containment.

A 20-meter (65.6-foot) diameter Energy Bag at a depth of 600 meters (2,000 feet) needs no additional structure to withstand the great pressure of air stored within. The greatest drawback to the Energy Bag is that its application is limited to locations with ready access to fairly deep water, making it best suited for use with off-shore wind turbines. However, there may be some near-shore wave and tidal power generating applications that could also take advantage of this system, as well.

Like SustainX, the Energy Bag is a developmental system still going through testing. An initial investigation was begun off the coast of Scotland in the summer of 2011. Initial studies indicate that the Energy Bag offers a potential storage efficiency of more than 85 percent.

Main photo: Energy Bag, credit Thin Red Line Aerospace
Secondary images: CAES-Huntorf, credit U.S. Dept. of Energy; CAES diagram, credit Sandia National Labs

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Some methods of power storage use chemicals to store an electric charge. Others use various ways of applying physics to create potential energy storage that can be tapped to produce power when it is needed. One of the most intriguing methods of potential energy power storage is flywheel power storage.

Other potential energy storage systems use static potential energy — in which the physical medium essentially sits still, waiting to be released — like the body of water in a pumped hydro system waiting to be released through the turbines to produce electricity. But in flywheel power storage, the energy is in a carefully balanced flywheel spinning at many thousand revolutions per minute. A flywheel can almost instantaneously be tapped to release power when it is needed.

Flywheel power storage units are large cylinders roughly the size of a small car, 7 feet (2.13 meters) in diameter and weighing roughly one and a half tons (1360 kilograms). The flywheels are sealed inside a vacuum chamber and are supported on frictionless magnetic bearings, so that there are virtually no losses once the flywheels are spinning. They spin at up to 16,000 RPM, meaning the outer rim of the flywheel is moving at about 1,500 miles per hour (2,400 kilometers per hour). The magnetic bearings allow the flywheel to float inside its enclosure without any physical contact or wear, leaving the flywheel with a life expectancy of at least 20 years.

A single flywheel unit is able to store and deliver 25 kWh of extractable energy, and can operate through thousands of charging and discharging cycles. The sealed vacuum and frictionless environment makes flywheel storage systems low-maintenance and long-lasting, and the system does not require the use of potentially hazardous chemicals.

Because flywheel power storage is a rather industrial system, it does not require any particular location characteristics, and is well suited for urban and rural installations. The flywheels are typically installed with the cylinders buried in the ground to provide additional protection in the case of a possible mechanical failure, which could result in shrapnel from a disintegrating flywheel shooting off in all directions at high speeds.

As a segment of the energy storage market, flywheel storage suffered a significant setback when Beacon Power, one of the leaders in the field, was forced to file for bankruptcy near the end of 2011. Despite this setback, Beacon was acquired by another company and is continuing to develop additional power storage facilities using their flywheel technology.

The system efficiency of a flywheel energy storage system is around 85 percent. This efficiency, combined with its fast response time, also makes flywheels an excellent system for providing uninterruptible power supply for locations with power-critical needs like data centers and hospitals. Although the initial capital costs for these systems are higher than other battery systems, the flywheels take up less space and need much less maintenance than battery systems, which makes them cost-effective over their lifespan.

The largest flywheel storage facility is a 20 megawatt plant at Stephentown, New York which is connected to the New York state grid.

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Many people are not familiar with flow batteries, which are a type of chemical battery well suited for large-scale power storage. Though the technology is fairly new, flow batteries currently offer a conversion efficiency between 65 and 75 percent, with the potential for increased efficiency as the technology develops.

Most batteries contain chemicals that react with one another to produce a charge, which is the source of electron flow. However, as reactions take place and the chemicals become depleted, it becomes harder and harder for a battery to provide the same level of energy. This wear signals a need for single-use batteries to be replaced and rechargeable batteries to be charged.

While some batteries can be drained fairly far and then recharged (known as deep-cycle batteries), depleting a battery too far tends to cause chemical reactions among the constituent materials that cannot be undone by recharging. Depletion can cause chemical crystallization, resulting in lessened battery capacity over time.

Batteries tend to lose some capacity as soon as they are put to use, because chemicals remain even after they react and become inactive. The inactive chemicals take up space in the battery and prevent some remaining active chemicals from interacting, thereby lessening capacity.

Now, imagine if you were able to connect a battery to a big tank full of reaction-producing chemicals, and that you could flush out depleted material and replace it with fresh material as the battery was being discharged. That, in essence, is how a flow battery operates. Rather than wrapping up all the material in cells, fresh material can flow into the battery cell as depleted chemicals flow out. When recharging the battery, the pumps are reversed. In this way, flow batteries are much like pumped hydroelectric systems; however, flow batteries function with chemicals in a compact space rather than using potential energy of water behind a dam.

Considering most of the flow battery chemicals sit in an inert tank, and are not in contact with any of the active parts of the battery, a flow battery can remain sitting without losing any of its charge. Likewise, flow batteries can be fully discharged and remain in that state for a long period of time without suffering damage when it is eventually recharged. Because the capacity of the battery is driven by the volume of its tanks, rather than needing to construct more complicated battery assemblies, it is relatively easy to add capacity to a system by increasing the size or number of tanks for the system.

At present, the most common form of flow batteries use vanadium in different oxide forms. Vanadium is a rare earth metal primarily used in industrial applications as an alloying element for strengthening steel. By using different oxides of vanadium with different charge states, the battery chemistry in vanadium flow batteries is simplified and does not suffer any long-term degradation or contamination of the electrolyte, since vanadium and vanadium oxides are the only chemicals in the system.

Non-vanadium flow batteries also exist, and some of those have the potential to provide increases in power density. As with other technologies that rely on scarce minerals, the global vanadium supply could play a role in further development of flow batteries, and whether or not they can be cost-effective in the future. The first mine in the United States to extract vanadium is under development in Nevada and is expected to begin production later this decade. The company behind this project is focusing on the battery market.

Flow batteries are a relatively new technology. Although originally dating back to the mid-1950s, most of the research leading to their development was carried out by NASA in the 1970s and by scientists at the University of New South Wales in the 1980s, where the contemporary, vanadium-based version was patented. The largest flow battery installation is a 1.5 megawatt facility at a semiconductor factory in Japan.

The technology offers relatively low energy density in terms of energy storage per pound of material–even compared to heavy storage systems like lead-acid batteries–which does not make them good candidates for mobile applications. For stationary power storage purposes, however, this is far less a critical factor than it is for vehicles or for portable electronics. Flow batteries’ high level of rechargeability and relative safety (compared to lead-acid batteries, which release dangerous hydrogen gas) and stability make them potentially well suited for further development for moderate-scale power storage systems.

Flow batteries are also useful as large-scale backup power supplies because of their ability to quickly respond (within fractions of a millisecond) to demand for power. Because of their long life expectancy, they would also do extremely well for load-shifting, where electricity is used to charge the battery during off-peak hours when rates are low, and then provide power back to a facility from the batteries instead of paying the premium, peak electricity rates.

Main image credit: University of New South Wales

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Batteries are the first thing most people think of when it comes to power storage, because that is what we are most familiar with in our day-to-day lives. Batteries are packages that store energy in chemical form until it is needed.

At the consumer level, some batteries are single-use, and cannot be easily recharged after they have been depleted due to the kinds of chemical reactions they rely on to provide power. Single-use batteries may be convenient for consumers, but they are not viable for significant power storage. At grid scale, batteries must be able to be charged when there is extra electrical production and discharged when there is extra demand.

One problem that most kinds of rechargeable batteries suffer over time is a loss of capacity. The repeated charging and discharging of the battery will lead to some of the chemicals crystallizing, and thereby losing the ability to store power, which leads to battery degradation over time.

Even if there is no demand on the battery, there will be a gradual discharge of the battery over time. Monitoring of the charge level of the battery can aid in keeping it kept fully charged until its power is needed. Typically, the stored power will be used within a few days and then the battery will be recharged again.

Unlike the batteries in your cell phone or laptop computer, the batteries for grid-level power storage use different kinds of chemical combinations for more efficient power storage. Chemical batteries such as sodium-sulfur batteries offer large-scale methods for storing power. Flow batteries are another specialized type of chemical battery that offer some unique features that can make them attractive in some cases. (We will take a look at flow batteries in a separate, forthcoming article.)

Sodium-sulfur batteries are one kind of liquid metal chemical battery that is used in large scale power storage. The properties of sodium-sulfur batteries make them unsuitable for most uses other than industrial level uses. Sodium metal is a hazardous material that will spontaneously burn if it comes into contact with any moisture, so it particularly needs to be kept in a contained environment.

Sodium-sulfur batteries also need to be kept hot, and have an operating temperature of 300-350 degrees C (572-662 degrees F). This makes them unsuited for more mobile applications, but larger scale installations can be thermally efficient and can work better than smaller sized batteries. The process of charging and discharging the battery generates a fair amount of heat, so that, once it is in operation, a sodium-sulfur battery does not usually require external heat to keep it at its working temperature.

The relatively low cost of materials needed for sodium-sulfur batteries makes them affordable, particularly in comparison with other types of batteries using rare and exotic materials that can be expensive to obtain. Sodium-sulfur batteries also have a good energy density, so a large amount of storage is able to be contained in a small space.

Sodium-sulfur batteries have an efficiency of around 90 percent, which makes them particularly effective for power storage. The largest sodium-sulfur battery installation is a 34 MW installation at Futamata wind farm in northern Japan.

Other kinds of battery grid-storage systems are also beginning to be used, as well. Manufacturers such as A123, which is a manufacturer of batteries for vehicles (BMW, Fisker, VIA Motors, etc.), also manufacture grid storage units with a number of installations throughout the world providing several megawatt-hours of power storage capacity. An installation at the Laurel Mountain wind farm in West Virginia is similar in size (32 MW) to the Futamata wind farm.

Other types of battery chemistries are also being explored for other cost-effective ways of storing electricity, though pumped hydro is still overwhelmingly the most common method for power storage. At the high tech end, some of the most advanced battery research is going on in the automotive industry, where battery manufacturers are looking to extend the range and performance of electric vehicles. Those developments are likely to find applications in other power storage systems, as well. At the other end, scientists are developing solutions for power storage using materials as basic as iron and air (essentially using the process of rust for power storage).

Main photo: Minwind battery storage in Luverne, Minn. Credit: Four Peaks Technologies

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Renewable energy systems produce electrical power. One of the most frequent objections to the use of these systems is that they don’t always produce power when it is needed.

“Solar power arrays can’t produce power at night.” “Wind power only generates electricity when the wind is blowing.” — These, and other complaints, highlight what is one of the key benefits of fossil fuel, namely that it is stored energy.

A sail ship can move only when the wind is blowing, but a steam ship could move as long as it had coal to fire its boilers. Stored energy systems allowed the directed application of energy to whatever purpose it was needed for at the time and place of the user’s choosing.

Modern life has made us accustomed to this convenience. In the developed world, the supply of gas and electricity to our buildings are utilities, basic services so ubiquitous that they are provided to all.

But a number of systems are under development or are already in place to allow the clean energy generated from wind, solar, and other renewable sources to be effectively stored until needed.

One of the oldest and most widely used systems for storing power is pumped hydro. The first pumped hydro installations were built in the 1890s in the Swiss Alps and Italy, where narrow valleys could be easily dammed to create the higher reservoirs needed for a pumped hydro installation.

Pumped hydro uses flowing water to turn turbines that generate electricity. But where conventional hydropower uses a flowing watercourse like a river to run its turbines, pumped hydro uses a lake or other reservoir to collect and store the water until electricity is needed. Using simple physics, potential energy is stored by pumping water to a higher elevation and storing it until power is needed. Then the water is allowed to flow out through the turbines to produce the needed electricity.

The generating turbines at a pumped hydro facility are usually also used to pump water up into the storage pond, which helps lower capital equipment requirements.

Diagram of a pumped hydro system

Pumped storage facilities are fairly economical to build and to operate because they do not require hazardous chemicals or especially complex industrial systems for their operation. When natural geography provides the proper conditions, a pumped hydro facility can be built without a great deal of additional infrastructure. They do well when located next to natural bodies of water, which can serve as lower ponds.

Because pumped storage facilities require a large area of land (the storage pond at the Ludington, Mich., facility covers 1.3 square miles, or 3.4 square kilometers), they are not well suited for proximity to urban centers, so they require access to high capacity electrical transmission. However, this proximity also makes it possible for them to be used to store excess power from whatever source is producing excess electricity.

Some of the largest pumped hydro facilities are able to supply thousands of megawatts of power for several hours, if needed. The largest pumped storage facility in the world is the Bath County Pumped Storage Station in northern Virginia, which has a maximum capacity of 3 gigawatts (3,000 megawatts). Because they can begin generating additional power very quickly, pumped hydro facilities are a very good option instead of gas-fired peaker plants for responding to changing power demand.

Ocean shore pumped hydro systems are possible, particularly in locations with high cliffs which permit the storage pond to be higher above sea level (and thereby creating a greater potential difference for the stored water). A potential drawback to these systems is that salt water is more corrosive and typically requires more maintenance for the equipment than freshwater systems. However, seashore locations are particularly good for wind farms, and there is a good synergy to be had from the pairing of a coastal wind farm with a pumped storage facility. One proposed alternative energy system, called Searaser would use a fleet of offshore ocean buoys equipped with pistons to pump water up to an onshore storage pond

As with every mode of energy conversion, there are losses from using pumped hydro to store energy. Pumped hydro has an average system efficiency in the range of 70-80 percent. Pumped hydro can also suffer from evaporative losses during a period of drought (though it also gains “free” energy from rainfall and other runoff that feeds into the storage pond).

Image credits: Ludington MI Pumped Storage Consumers Power; diagram funjoker23/Wikimedia Commons

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Walmart tops the list in terms of total capacity (installed kW) and in number of locations with solar facilities. This information only counts on-site solar, so companies that buy renewable energy credits or otherwise support solar (or other alternative energy programs, for that matter) that are off-site are not included as part of the survey.

This does mean that companies with bigfoot buildings are high on the list. It is not surprising, then, that the top five, in terms of capacity, are all retailers (Walmart, Costco, Kohl’s, IKEA and Macy’s). General Motors is the No. 1 automaker on the list and is ranked in 13th place overall, making it one of the highest ranked manufacturers (surpassed only by Johnson & Johnson and Campbell’s Soup) on the list.

Use of solar energy isn’t limited to just the sunny southwest, either. As the report notes, “Many corporations have solar energy systems in diverse states including Michigan, Wisconsin and Massachusetts, which is a strong indication that solar energy can make business sense in all U.S. climates.” IKEA leads the list as the most widespread user of solar power, with installations in 16 states, followed by REI and Kohl’s, both of which have solar installations at facilities in 10 states.

Main image credit: General Motors Co.

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The array of sensors and computers needed to operate these vehicles means that there is a lot of data available about the car. The dashboards of these vehicles typically have much more information available to the driver about the power generating state (whether the car is charging or not), momentary and overall efficiency, and a range of other data, but that is just a small fraction of the information that is collected about the vehicle.

Connecting cars to the electronic world we inhabit was one of the major trends at this past year’s North American International Auto Show. Many manufacturers are developing applications for smartphones and finding ways of integrating the car and the driver’s lifestyle. Along with this, more and more data about the vehicle is available to both the owner and the manufacturer. Car owners can access some of this data through subscriptions, like a monthly email report from OnStar for owners of the Chevrolet Volt.

The manufacturers of several electric vehicles not only offer data to the car owners, but also are using this data internally. Although the various manufacturer programs are strict about privacy concerns and do not share the data with others, their engineers are certainly using this collected data about vehicle performance to learn more about how these relatively new vehicles are performing in the real world. There have even been cases where a problem with a vehicle was identified through anomalous readings, enabling the manufacturer to contact the car owner in order to fix the problem before it became a more serious issue.

As with software that sends the developer a crash report when it fails, to allow it to be improved and debugged, automotive engineers are also able to learn from the data that is reported from these vehicles. This information will assist with both the maintenance of existing vehicles as well as providing a better profile about vehicle use that will be helpful in improving new models of electric vehicles and learning how to make improvements in range and performance for subsequent models of these cars.

Main photo credit: rudisillart and Mariordo/Wikimedia Commons

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While pent up artificial lakes are easy to turn into massive power plants, the environmental devastation that comes from the flooding of millions of acres of land, and the disruption of the ecosystem of the river make large-scale hydropower a second-class form of green power, at best. From a carbon perspective, hydropower is certainly preferable to burning fossil fuels. But the associated damages caused by building large-scale hydropower plants — including turning flowing water into lakes and blocking the migration of fish — is such that new dams for generating electrical power are mostly off the table.There are alternatives to creating an enormous lake in order to constantly feed the turbines.

Small-scale turbines that can sit in flowing bodies of water and generate electricity could now be poised to bring a new face to hydropower. These turbines are greener since they don’t require the blockage of waterways and the destruction and flooding of land in order to be able to produce power. Hydrodynamic power works with the energy in moving water, rather than closing off waterways to build up huge reserves of potential energy stored in the water held behind giant dams. Developmental systems from several companies are now exploring the production of more modest amounts of power, but with far lower cost and with much less environmental destruction than that from the creation of dammed hydropower. Companies such as Hydrovolts Inc., Free Flow Power and Verdant Power have different systems to make use of this power, which they are testing in different parts of the country. There are also researchers who are working on other systems that can potentially take advantage of more energy available in slower moving water.

The federal government in the United States has identified this as an as-yet untapped source of power. The existing water infrastructure of the American West offers a great deal of hydropower potential, with the greatest amount found in the states of Colorado, Oregon and Wyoming. A study by the U.S. Department of the Interior’s Bureau of Reclamation found that 1.5 million megawatt-hours of renewable energy could be generated through hydropower without needing to construct new — and environmentally questionable — large-scale dams. Instead, existing waterways and reservoirs can be used to provide electricity in addition to serving water needs of the region. (For comparison, the Hoover Dam power station produces about 4 million megawatt-hours of electricity annually. Think of this as another one-third of a Hoover Dam spread out through the existing water infrastructure.)

Aqueducts and canals represent an available source of power for additional electrical generation. Particularly in the western U.S., where water management is carried out through an extensive infrastructure of constructed canals and waterways, it may be possible to provide power for tens of thousands of additional homes. Existing dams that were built for water management rather than for power generation may be able to be tapped for power production as well, through the installation of smaller scale equipment that can efficiently and cost-effectively produce power from dams that may have previously been thought too small to be useful for power generation.

To make use of this hydrodynamic power, small, in-line turbines can be installed that generate electricity from the flow of water through aqueducts and canals. The turbine sits directly in the waterway, without a dam, which means that the negative impacts to the environment, as well as the infrastructure costs to install this equipment, are greatly reduced.

Because these waterways already constrict the flow of water moving through them, a greater proportion of the energy from the water flow can be captured with this equipment. In a canal, where most of the water flow must go through the turbine, the efficiency can be as high as 60 percent. Depending on the size of the waterway and the flow rate of the water moving through it, turbines can provide electrical output ranging from 1.5 kW to 30 kW. Because many of these waterways have continuous flows of water moving through them, they are well suited to provide additional, continuous power generation for the grid.

The Bureau of Reclamation has over 47,000 miles of canals, laterals, drains, pipelines and tunnels. To find places with hydropower potential, the government study identified those locations where there was at least a 5-foot drop and where the waterway was in operation for at least four months out of the year and where the power generation potential was at least 50 kW (based upon flow rate of canal and the drop height).

One manufacturer producing turbines for in-line uses is Hydrovolts, Inc. These are reasonably small pieces of equipment. Turbines for canals and waterways are about the size of a car or small truck. Waterfall turbines can be even smaller, and will still produce a significant amount of power. They are also fairly inexpensive, with the cost of the smallest portable model starting at just $2,000. The canal-sized turbines cost from $20,000 to $40,000. While wholesale electrical rates are not great, since their output will be fairly consistent, these turbines can potentially repay their investment cost in just a few years. Initial tests of the Hydrovolts turbine were carried out in the Roza Canal in Washington State earlier this year.

(Quick back-of-the-napkin math: A turbine costing $40,000 and generating an average of 25kW over a year of operation will produce almost 220 MWh of power and earn over $10,000 at a wholesale electrical rate of $0.05/kWh. That could mean that the equipment could be paid off in four years.)

Hydrovolts turbine in the Roza Canal in Washington State:

Hydrovolts turbines also can be outfitted with different kinds of blades, depending on the flow rate of the water. This makes the system more versatile, and the same equipment can be used in different locations, with just a change of blades in order to produce the optimal yield from a given location.

While many of these channels being discussed for use are artificial waterways used for irrigation, the same technology can be used in open water rivers and streams with a sufficient flow rate. In those cases, having the waterway open to fish migration and movement is another benefit from this technology.

While the Hydrovolts turbines are being developed for very small waterways, the opposite end of the hydrokinetic power scale is also being explored with a project set in the world’s largest river. Free Flow Power is a company that is developing river flow turbines to be placed along a length of the lower part of the Mississippi River.

The Free Flow Power turbine is a 3-meter diameter multi-bladed propeller inside a housing that makes it look very much like a large jet engine. The turbine has a 40 kW rating. The first array of these turbines will be installed at a total of 25 locations along the Mississippi River and will provide a total generating capacity of 3,303 MW. Given the size of the river and the volume of water that flows through it, there is a great potential for much more energy production if this technology turns out to be effective and cost-competitive.

Unlike wind farms, these turbines are out of sight below the surface of the water. Despite their size, since these turbines will be installed below the water’s surface, they will present very little obstacle to navigation, so that the Mississippi will also continue to serve as an efficient highway for barge traffic moving goods up and down the river. This project may be just the beginning for harnessing the vast power of so much water moving through the middle of the country.

In New York City’s East River, the Roosevelt Island Tidal Energy Project (RITE) being run by Verdant Power Inc. will eventually have 30 turbines installed underwater and generating as much as 1,050 kW of electricity when the pilot project is fully installed in 2015. These turbines are considerably larger than the Hydrovolts equipment. Rather than drawing power from the narrow flow of water in a channel, these units are instead powered by the tidal flows from the ocean.

Verdant Power has another project that builds on some of the work done for the RITE project. The Cornwall Ontario River Energy Project (CORE) is installing turbines in the St. Lawrence River near Cornwall, Ontario to study how the turbines work in a river flow situation.

The turbines Verdant is developing are three-bladed, without an enclosure, and look quite similar to the now familiar three-bladed wind turbines, except for their comparatively much smaller size. The Verdant turbines are larger than those being developed by Free Flow Power; for the CORE project they are using turbines with a blade diameter of 5 meters and with a generating capacity of 60-80 kilowatts. These turbines, too, would sit out of the way of surface vessels on the bottom of the waterway. An animation from Verdant shows what a large-scale farm of these turbines might look like.

Along with these developmental systems, researchers are working on other low-velocity technologies for hydrokinetic power generation. One system, being explored by researchers at the University of Michigan is called VIVACE, which stands for Vortex Induced Vibrations for Aquatic Clean Energy. VIVACE is especially interesting because it promises to work with slow moving river flows as slow as 2 knots. Most river currents in the United States are slower than 3 knots.

The VIVACE system works with horizontal cylinders placed across the flow of the water to create a vortex as the water flows past the cylinder. “Vortex Induced Vibration (VIV) is an extensively studied phenomenon where vortices are formed and shed on the downstream side of bluff bodies (rounded objects) in a fluid current. The vortex shedding alternates from one side of a body to the other, thereby creating a pressure imbalance resulting in an oscillatory lift.” This motion of the cylinder can, in turn, be used to move a magnetic field in order to produce electricity.

The turning blades of hydrokinetic turbines are a potential concern, just as wind turbines are with birds. Part of the reporting being done with these early projects is to study potential problems with this kind of equipment. Although its development is lagging behind some of the other systems, VIVACE may turn out to be a preferable technology because it has less impact on marine wildlife. The cylinders used in this system are very slow moving (only about 1 cycle per second), and the risk of harm to any fish is therefore extremely low.

Hydrokinetic projects are appealing because the power generation is more constant than some other sustainable systems. Waterway flows can be more regular and dependable than intermittent sources like wind. Hydrokinetic power is presently an underutilized resource, but as these companies develop their technology, it is likely to become another part of the energy mix.

Main, second and third photo credits: Hydrovolts Inc.

Video credit: Hydrovolts Inc.

Fourth photo credit: Free Flow Power

Fifth photo credit: Kris Unger/Verdant Power, Inc.

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Renewable energy developers target their projects for locations where the energy sources they seek to tap are plentiful. This is why solar power plants are abundant in the southwest and many wind farms are found on the Great Plains. Many islands in the Pacific are volcanic in origin, which makes the use of geothermal energy a similarly smart move. The Palinpinon Geothermal Power Plant in the Philippines (above) is one example.

Most of the electricity for Vanuatu presently comes from diesel generators. This makes for a volatile pricing market, and electrical tariffs are revised each month. The average cost for electricity is 60 cents per kWh.

The geothermal project, which is being run by KUTh Energy, an Australian energy company, looks to develop and install an 8 MW geothermal plant and also to improve and extend the electrical infrastructure for the nation’s major island, Efate.

The project has been endorsed by the World Bank, and KUTh Energy is looking for funding to move the project forward. Cost for the entire project is estimated to be as much as $120 million, but half of that is expected to come from development bank loans.

Current estimates are that the first phase of the project would be complete in 2015, with the second phase being completed in 2019.

Photo credit: Mike Gonzalez/Wikimedia

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