Five types of storage systems are commonly in use today: batteries, fuel cells, thermal energy systems, compressed air energy systems, and flywheels.

Batteries
An early solution to the problem of storing energy for electrical purposes was the development of the battery as an electrochemical storage device. Batteries have previously been of limited use in electric power systems due to their relatively small capacity and high cost. However, since about the middle of the first decade of the 21st century, newer battery technologies have been developed that can now provide significant utility scale load-leveling capabilities.

There are two popular lead batteries used for solar and wind turbine installations:

• GEL batteries
• Absorbed Glass Mat (AGM) batteries

They have a number of advantages:

• Both store their charge very well.
• They do not degrade as easily as the common lead acid (wet cell) battery.
• Because of the type of material used as the electrolyte (GEL or Absorbed Glass Matt) there is very little chance of a hydrogen gas build up that can lead to an explosion.
• They do not corrode.
• They are very safe batteries.
• They are ideally suited to solar pv and wind turbine (remote power) installations.

In most cases AGM batteries are perfectly suitable for solar applications and are cheaper than GEL.

Fuel Cells
Fuel cells can be effectively used as both energy storage and as energy production equipment!

A fuel cell is a device that converts fuel into electricity through a chemical reaction with oxygen or another oxidizing agent. Hydrogen is the most common fuel, but hydrocarbons such as natural gas and biofuels (gases from food processing and wastewater treatment) are sometimes used. Fuel cells are different from batteries in that they require a constant source of fuel and oxygen to run, but they can produce electricity continually for as long as these inputs are supplied. The energy efficiency of a fuel cell is generally between 40-60%, or up to 85% efficient if waste heat is captured for use.

Many waste water treatment plants use anaerobic digestion to stabilize sludge generated during the treatment process. Microorganisms break down organic material, releasing biogas, a mixture composed of methane and carbon dioxide, trace gases, and water. Typically, the plants flare biogas to dispose of it, but this renewable fuel can be used in fuel cells to generate heat and electricity. This unique relationship between Direct FuelCells and anaerobic digesters results in the most efficient and environmentally friendly use of this energy source.

Manufacturers / Products / Links

Based in Danbury, CT, FuelCell Energy manufactures ultra-clean stationary fuel cell power plants that generate electricity with up to twice the efficiency of conventional fossil fuel plants – and with virtually no air pollution. With more than 30 years of experience, we are recognized as a global leader in the manufacture and commercialization of stationary electric power generation.

Ultra Electronics, AMI designs, tests and manufactures the future of portable power: solid oxide fuel cell technology. AMI is committed to providing dependable portable fuel cell power using readily accessible fuel that takes you into the wild or into combat. AMI's solid oxide fuel cell power systems have been proven reliable in field testing for military, leisure and emergency use.

ClearEdge, a manufacturer of fuel cells that run on natural gas, announced today that it has secured a $2.8 million grant from the U.S. Department of Energy. The grant will give ClearEdge working capital to produce and install fuel cells in 10 new businesses in Oregon and California. The funding came from the Department of Energy's Pacific Northwest National Laboratory (PNNL), which will monitor the fuel cells to see if they are producing the kind of energy savings expected for the businesses that purchase them. The fuel cells are connected to the Internet, which will let PNNL researchers monitor them in real-time.

Thermal Energy Systems
The most popular form of thermal energy storage for cooling is ice storage, since it can store more energy in less space than water storage and it is also less costly than energy recovered via fuel cells or flywheels.

It works by creating ice at night when electricity is usually less costly, and then using the ice to cool the air in buildings during the hotter daytime periods. Thermal storage has cost-effectively shifted gigawatts of power away from daytime peak usage periods, and in 2009 was used in over 3,300 buildings in over 35 countries.

Compressed Air Energy Systems
Compressed air energy systems use the energy from a wind farm to store air in an underground geologic structure during time periods of low customer electric demand and high wind. Then, during peak customer power demands and when the wind is not blowing, the stored air will be released, mixed with natural gas and used to power combustion turbines that produce environmentally friendly and economical electricity.

Of all the storage options, compressed air is the least developed and proven, particularly with regard to efficiency. Large projects underway will provide more data.

Flywheels
Primarily used by utilities, flywheel energy storage systems convert excess electrical power from the grid into spinning, rotational force. When electricity demand spikes, the energy from the massive, rotating flywheels is then converted back into electricity. The process is known as frequency regulation, and it reduces the need for additional generating sources. This type of storage system is designed for large users of electricity who also require precise voltage regulation.

Whether you're starting a system design or upgrading an existing one, MLC can help your town or school district develop an energy plan get you any of that includes the proper energy storage for any of these:

• BioEnergy
• Active Solar Systems
• Wind Microturbines
• Wind Generators
• Power Plant Improvements

Schools, Libraries and Other Public Buildings
For solar and wind projects, storage of energy is critical to making the system a success. Even with connectivity to the grid, the variations in power generated necessitate energy management. Make use of the rooftops of your school buildings with an array of solar panels, choosing PV technology that allows for both hot water and electricity production. Add an AGM battery backup system.

AGM batteries are sealed batteries that use "Absorbed Glass Mats", or AGM between the plates. Being rugged and maintenance free, AGM batteries are ideally suited for use in a grid-tied solar power system for a school. Because they are completely sealed they can't be spilled, do not need periodic watering, and emit no corrosive fumes. Perfect for a public building.

Schools are also great candidates for fuel cell systems, as they are large consumers of both heat and electricity. In addition, fuel cells are quiet.

Maintenance and Publics Works Facilities
Install a fuel cell system at your waste water treatment plant. Your public works department could build a system modelled after the Kings County plant in Renton, WA. (A primary goal of theirs was to build a plant everyone could copy.) Each year they take 30 million gallons of sewage and produce enough methane gas to run a 1 megawatt, fuel-cell power plant. The system can power 1,000 homes, but in this case all the electricity is going to help run the treatment plant, which needs about 7.5 MW per hour a day on average.

You can lease all the components of a fuel cell production plant, including

• A fuel cell with integrated fuel reforming,
• A gas processing unit including a dual set of carbon tanks,
• An air metering pump,
• A compressor.

Municipal Administration Offices
Install a thermal energy system in your municipal administration building to augment your wind or solar system. For example, install a microturbine array on the roof of your building. During the times when the wind produces more power than you can use, direct the overflow toward ice production. Municipal buildings are ideally suited to a thermal air conditioning system as they are generally not in use throughout the night.

Energy storage can be done in a variety of ways, but they all help attain the goals of increased efficiency and availability, and lowered cost:

A battery backup and storage system will make your solar and wind production more efficient:

• Smooth out transient fluctuations in wind energy supply.
• Use electricity when it is the least expensive, wherever it was generated.
• Guarantee performance of energy supply despite grid outages.
• Batteries are scalable and will help to manage growth-related pressures

There are many advantages to installing a Fuel Cell to your energy system:

• Fuel cell systems can make your landfill a profit center!
• They are a Lightweight/Long-lasting Battery Alternative
• Fuel cells convert chemical energy directly into electricity without the combustion process, and thus are highly efficient.
• Fuel cells can achieve high efficiencies in energy conversion terms, especially where the waste heat from the cell is utilized in cogeneration situation.
• A high power density allows fuel cells to be relatively compact source of electric power, beneficial in application with space constraints. In a fuel cell system, the fuel cell itself is nearly dwarfed by other components of the system such as the fuel reformer and power inverter.
• Fuel cells, due to their nature of operation, are extremely quiet in operation. This allows fuel cells to be used in residential or built-up areas where the noise pollution is undesirable.
• Low Emissions
• Modularity/Scalability/Flexible Siting
• Minimizes our reliance on petroleum products for energy.

Your school's HVAC system will be greatly improved with a Thermal Energy Storage system:

• Provides school administrators with a payback as little as one year, and improved cash flows for the life of the facility that can add up to millions.
• Energy storage is an important part of a high-performance, sustainable design.
• Provides a demand-responsive cooling system with fuel-source flexibility in an unregulated energy market.
• Aside from the economic benefits, energy storage also improves classroom comfort by lowering humidity levels.
• The savings can be invested toward further improving student education.

Thermal systems are great for building retrofit applications:

• Installed costs of a hybrid system can be comparable to conventional cooling while operating costs can be reduced up to 40 percent.
• Smaller chillers, cooling towers, and ancillary equipment can be used.
• Colder supply temperatures available from storage can help reduce pumping costs.
• Ideal for building expansions because instead of adding costly electrical and chiller capacity to cool the additional load from the new building space, ICEBANK tanks work in conjunction with the existing equipment to meet the increased cooling load.
• Hybrid cooling provides other benefits such as quantifiable return on investment and conservation of our valuable natural resources.