Getting the electricity from the plant to the light switch Not a place for wireless technology-or is it?

Wireless is not out of the question Wireless transmission of electricity was actually pioneered by Nikola Tesla in late 19 th century Wireless power transmission is known as the Tesla effect Based on inductive power transfer

Tesla’s ideas

Tesla envisioned a world wide electricity network

Inductive power transfer An electric toothbrush recharges through three simple steps. First, a current from the wall outlet is directed into the charger and into the base coil via an electric wire. When the current flows through the base coil, the coil generates a magnetic field which in turn induces a current to flow to the coil in the toothbrush handle. This charges the toothbrush battery.

Inductive power transfer But the objects have to be in contact, what about over a distance? Problem is the magnetic field decreases over distance, so the magnetic field generated in the base has to be large, but this reduces efficiency Using ideas of magnetic resonance(a radio signal is use to align the electron spins in their highest magnetic energy states), the distance can be greatly increased. Over large distances and high powers, lasers, radio and microwaves can be used. – Many technology demonstrations of this have already occurred and it is the subject of much research

Heat Pumps In a heat engine, heat is converted to mechanical energy by taking advantage of the fact that heat flows from hot to cold. The heat is taken from a source, some of it turned into mechanical energy and the rest sent to a heat sink, which is at a lower T than the source. Could we reverse this process?

Heat pumps A compressor compresses a gas (Freon) to raise its Temperature and pressure. It flows through a heat exchanger in which the gas is cooled by room temp air and it condenses. The heat it gives up in condensing goes to heat the inside air around the heat exchanger. The gas then passes through a valve to a region of lower pressure where it expands and becomes very cold. It next passes through a heat exchanger exposed to outside air. The outside air warms the gas and it returns to the compressor and starts the cycle all over again. Reverse the process for cooling

Heat pumps

Effectiveness measured by the Coefficient of Performance C.O.P. = T h /(T h -T c ) This comes from the Carnot Efficiency As the outside air gets colder, T h -T c gets larger to C.O.P decreases. This means heat pumps are less efficient in very cold weather and very cold climates. Usually this occurs when the outside T falls below 15 F.

Peltier effect Peltier was experimenting with electricity Connected a bismuth and copper wire together and hooked them to a battery. Found one side became hot and the other cold as the current flowed! Basis for modern thermoelectric cooling/heating Modern devices use semi-conductors (more efficient). Not efficient enough for large scale heating or cooling Creates a lot of excess heat

Peltier Effect Right hand junction is heated-electrical energy is converted to heat Left hand junction is cooled-heat energy is converted to electrical energy.

Peltier effect

Cogeneration Power plants generate lots of waste heat Modern coal fired plants convert 38% of the energy in the coal to electricity, the other 62% is waste! Usually shed off into the environment (air, cooling pond, river, lake etc) Can have environmental consequences Can it be put to use?

Cogeneration Problem arises when the power plant is located far away from population centers- cannot effectively transport the heat over long distances In principle, the waste heat could be used to heat a boiler and provide steam for space heating and cooling. Or it could be recycled to drive turbines to produce additional electricity

Types of cogeneration plants Topping cycle plants - produce electricity from a steam turbine. The exhausted steam is then condensed, and the low temperature heat released from this condensation is utilized for heating. Bottoming cycle plants- produce high temperature heat for industrial processes, then a waste heat recovery boiler feeds an electrical plant. Need a high initial source of heat-metal manufacturing plants.

Examples The New York City steam system - district heating system which carries steam from central power stations under the streets of Manhattan to heat, cool, or supply power to high rise buildings and businesses. Another example is in use at the University of Colorado, Boulder - Total efficiency is 70% Possibility of explosions due to pipe failures exists

Example of Explosions The July 18, 2007 New York City steam explosion sent a geyser of hot steam up from beneath a busy intersection, with a 40-story-high shower of mud and flying debris raining down on the crowded streets of Midtown Manhattan It was caused by the failure of a Consolidated Edison 24- inch underground steam pipe installed in 1924

Possibilities Outside the U.S., energy recycling is more common. Denmark is probably the most active energy recycler, obtaining about 55% of its energy from cogeneration and waste heat recovery. In the US about 8% of its electricity is produced via cogeneration

Solar Power Power derived directly from sunlight Seen elsewhere in nature (plants) We are tapping electromagnetic energy and want to use it for heating or convert it to a useful form, usually electricity Renewable-we won’t run out of sunlight (in its current form) for another billion years

Solar Energy Sun derives its energy from nuclear fusion deep in its core In the core Hydrogen atoms are combining (fusing) to produce helium and energy. Physicists refer to this as Hydrogen burning, though be careful, it is not burning in the usual (chemical) sense. The supply of H in the sun’s core is sufficient to sustain its current rate of H burning for another billion years

Solar Energy The energy is released in the H burning deep in the sun in the form of photons. Here we use the particle description of light, where light is considered a packet of energy called a photon. Photons have energy E=hν or E =hc/λ where ν is the frequency of the light, λ is the wavelength of the light, c is the speed of light (c=3.00x10 8 m/s) and h is Planck’s constant (h= × m 2 kg / s)

Solar energy The photons take a long time to reach the surface of the sun, about 1 million years. Why? Deep in the sun, the density is very high. The photons travel a very short distance before they are absorbed by an electron in an atom. Normally in an atom, the electrons occupy specific positions relative to the nucleus called energy levels. When the electrons are in the lowest energy levels possible, they are said to be in the ground state. When an electron in an atom absorbs a photon, it gains more energy and moves to a new (higher) energy level. It can only gain a photon with the correct energy to change energy levels. The photon energy must equal the energy difference between two energy levels in the atom.

Solar energy But electrons don’t like to be in these higher energy states, so they will emit energy in the form of a photon to drop to a lower energy level.

Solar energy So in the sun, the photons emitted by the H burning travel a short distance before they are absorbed by an atom. The atom quickly re-emits the photon, but not necessarily in the same direction it came from. The atom can re-emit the photon in any direction. The photon follows a random looking path on its way out of the sun, called a random walk.

Random walk So the photons take this random walk form the core to the surface of the sun. On average, it takes 1 million years before a photon generated in the core leave the surface of the sun. It then takes another 9 minutes to reach the Earth