Документ взят из кэша поисковой машины. Адрес
оригинального документа
: http://zebu.uoregon.edu/1999/ph162/l8.html
Дата изменения: Thu Apr 22 19:36:49 1999 Дата индексирования: Tue Oct 2 00:04:10 2012 Кодировка: Поисковые слова: п п п п п п п п п п п р п р п р п р п р п р п р п р п р п р п р п р п р п р п р п р п р п р п р п р п р п р п р п р п р п р п р п |
But first to finish up with electric vehicles:
![]() Credit: Michael Goodman KEY COMPONENTS of an electric vehicle are energy storage cells, a power controller and motors. Transmission of energy in electrical form eliminates the need for a mechanical drivetrain. Regenerative braking (inset) uses the motor as a generator, feeding energy back to the storage system each time the brakes are used. |
The Key of course is marketing
people have to buy the product
California Mandate:
Some Prototypes:
Energy Density of Some Materials (KHW/kg)
Energy density storage drives the choices that can be made:
At the turn of the century electric vehicles were commonplace (using basically lead-acid batteries). Since gasoline has much higher energy density it quickly dominated the way vehicles were propelled.
In fact, gasoline has one of the highest energy density storage capacities known. This makes it very difficult to duplicate the convenience that gasoline has traditionally provided (e.g. 350 kg of batteries is equivalent to 1 kg of gasoline !).
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
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%)
Real Life Facility in Michigan
Inertial constants for different shapes:
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. Centrifugal force for a rotating object goes as:
MRw2
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
Some Network Resources Related to Flywheels
Consider a solid disc flywheel of radius 50 cm and mass 140 kg. How fast would it have to spin to have a store the equivalent amount of energy that is stored in just 10 kg of gasoline when burned in an internal combustion engine:
= pi2MR2* w(RPS)2
Compressed Air:
Has high energy storage capacity compared to the alternatives. About 10 times higher per cubic meter than water.
One example (in Germany) to date: