The Need for Energy Storage

Impact Energy Storage and Snake Charming (this is a serious concept)

Aquifer Thermal Energy Storage (ATES)

The next step beyond this is the borehole system where many holes are drilled to tap warm groundwater. A working example is the Univeristy of Ontario Institute of Technology

Similiarly, rooftop systems are easy to install tho there are load bearing issues:

Pumped Hydroelectric Energy Storage:

Simple in concept use excess energy to pump water uphill pump from lower reservoir (natural or artifical) to upper reservoir.

Energy recovery depends on total volume of water and its height above the turbine

• need at least 100-meters this is a stringent limit on locations
• artificial lower reserviors can made via excavation can achieve higher energy density due to large vertical distance (up to 1000 feet!)
• facility does not impact free flowing stream
• sediment build-up at dam base is minimized
• Hydropower is 80% efficient (uphill or downhill). So to pump uphill and the get energy downhill, efficiency is 0.8x0.8 = 64%

Cost Issues:

Suppose a company has a coal fired plant which operates at 36% efficiency and uses excess power to pump water uphill. The overall efficiency of recovering that to deliver to the consumer is 0.36 x 0.64 = 0.23 (23%)

• So stored energy is more expensive what's the incentive?
• Need to balance this cost against the costs of building a power planet with capacity to meet some theoretical maximum demand but the rest of the time doesn't operate at this level

Real Life Facility in Michigan

• Use Lake Michigan as Lower Reservoir
• Upper reservoir is 75 meters higher
• Peak capacity is 2000 MW (!)
• Stored energy is 15 million KWH`

Of course, you can always just refill the lake in times of low demand

China now has the largest facility in Asia:

Specifications:

• Two storage reservoirs, 1 km apart
• Elevation is 590m
• Storage volume is 8 million cubic meters. This equates to 4 GWHs (gigawatt hours)
• Reservoir drainage: Two 7 meter diameter pipe branches into 3 3.2-m diameter pipes
• Each 3.2 m diameter pipe is connected to a 306 MW turbine.
• Total capcity is therefore 1.8 GW meaning the system can drain for about 2.5 hours to get 4 GWHS.
• Total project cost estimated to be 1.1 billion dollars so that's less than 1.1/1.8 dollars per watt (about 60 cents per watt).

Also the world's first seawater pumped storage facilty recently came on line. Height is 600 m above sea level; total capacity is 600 MW.

FLYWHEELS and ENERGY STORAGE

A flywheel, in essence is a mechanical battery - simply a mass rotating about an axis. Flywheels store energy mechanically in the form of kinetic energy. They take an electrical input to accelerate the rotor up to speed by using the built-in motor, and return the electrical energy by using this same motor as a generator.Flywheels are one of the most promising technologies for replacing conventional lead acid batteries as energy storage systems.

For off grid systems with wind energy, the flywheel storage equilibrates the continual fluctuations of the wind energy. 5 kWh storage capacity and 200kW peak power for 90 seconds. The Enercon flywheel storage runs in vacuum. About every 5 years, the bearings have to be replaced.

So, in other words. During times that your generating more power than you need, you can spin the fly wheel up, so to speak. When you need to recover that energy, you let the fly wheel spin down.

Example of Flywheel/Piston arrangement:
Inertia of the Flywheel helps keep the system going.

To optimize the energy-to-mass ratio the flywheel needs to spin at the maximum possible speed. This is because kinetic energy only increases linerarly with Mass but goes as the square of the rotation speed.

Rapidly rotating objects are subject to centrifugal forces that can rip them apart. Thus, while dense material can store more energy it is also subject to higher centrifugal force and thus fails at lower rotation speeds than low density material.

Tensile Strength is More important than density of material.

Long rundown times are also required frictionless bearings and a vacuum to minimize air resistance can result in rundown times of 6 months steady supply of energy

Flywheels are about 80% efficient (like hydro)

Flywheels do take up much less land than pumped hydro systems

Fused Silica Flywheels are possible: High tensile strength material allows it to be rotated very fast (100,000 rpm) without flying apart

The model with the small yellow disc tends to stop when the crank and connecting rod are in a straight line ('dead' spots) - because sliding the brass knob exerts no turning force on the shaft. In the model with the big yellow flywheel, it is easy to keep the disc turning, once it has started, due to the effect of the flywheel. The mass and the size of the big flywheel helps resist the slowing down of the model as it is turning.

Current Use of Flywheels; Frequency Regulation

Beacon Power - the Leader in Flywheel Technology

Compressed Air: