construct a reservoir above a source of H₂O.
in times of slack demand, use electricity to pump water to the reservoir.
when you need electricity, run water through turbines to generate it.
can be used to increase base load, decrease peak load....is this good?
base costs to pump water ~$0.03-0.05/kWh.

Pumped water storage is used in:

Can also do this for air at about 90% efficiency. In 2000 the US had about 20GW of pumped storage capability.

In load management the utility starts and stops home electrical storage water heaters by radio or timer. This uses the consumers own consumption of electricity to flatten out the load curve. These include:

What is a superconductor?

Why superconductors?

Joule losses (I²R)! True workable room temperature superconductors would revolutionize technology.

Effciency of electric generators
-Conventional electric generators are 98.6% eff.
-Superconducting generators will be ~99.5% eff.

Is this gain worth it?

-Not for refrigerators, etc.
-Room-temperature superconducting transmission lines would save
10-15% for short-distance transmission
2% for long-distance transmission.

What does this mean?

-1% improvement in transmission $1 billion in savings.

Type II superconductors

Do not lose their superconducting properties in a magnetic field.
These are used for making large magnets...which could be used to store energy since currents would circulate with no loss.
This technology is developing rapidly and such devices will probably exist in your lifetime!
Other uses: computers, magnetic trains.

Flywheels are an old technology. Storing energy in a slow moving heavy object has been around for a long time.

So what is new about flywheels?....

It is the material....strong plastics and epoxy allow edge speed of 1400 m/s!

It is now feasible to create cars which store energy in flywheels ...these could be powered by electricity, natural gas, etc.

The presently available flywheels for cars rotate at 30,000 rpm and can deliver 0.55 kWh_e. These may be considered flywheel batteries. The Prius uses flywheels to store energy!

The oldest electrical storage device is the battery. The lead-acid battery in your car is capable of producing 50-100W/kg for a total stored energy of 25-35 Wh/kg.

However lead is expensive. Other alternatives include:

But cars need fast recharge:

Recall: latent heat of fusion of water=333kJ/kg at 0°C. In sodium sulfate it is 213 kJ/kg at 31°C. The idea here is to store excess energy in the material by changing its phase (solid to liquid) and then get it back later by using the liquid to run a generator.

70-80% of Municipal waste is combustible.
Unprocessed solid waste can produce 10-15 MJ/kg compared to 23 MJ/kg coal.
Garbage produces methane at a rate of 250 m³/tonne.
NYC alone sends 20,000 tonnes of garbage into landfills each day.
Incinerators can reduce the volume by about a factor of 2-4.

A typical plant uses 10% coal with the garbage.

See Energy for a description of the Columbus trash burning facility and its fate....in particular:

plastics if not burned completely at high enough temperature, (>1000°C), produce dioxin....
if the temperature is too high they produce nitrogen oxides.

Hydrogen can be

Need metal hydrides which "soak up" hydrogen at 20 times atmospheric pressure and release it at 5 times atmospheric pressure. These also "clean" the hydrogen.

Hydrogen can also be used in fuel cells and run electric cars.

When a pesticide is applied to cropland, the target pest population sometimes increases while the predator population that has been controlling the pest declines. How do we understand this?

If the pesticide attacks the pest population and reduces it, the predator population might be reduced. That in turn would relieve the pressure on the pest population allowing it to grow back. But then wouldn’t the predator population recover as well?

How would we model this?

Note that if the pesticide attacks the prey then a’ will decrease which will reduce the predator population...not the ultimate prey population!

Note also if the pesticide also increases the death rate of the predator then a’ will decrease and a will increase...the effect of this is to decrease the steady state predator population and increase the steady state prey population!

The equations which describe this model are: