Magnetism is the force typically utilized to create the electricity that powers your home. A usual generator at a power plant contains a very large magnet that spins inside a ring wrapped in a huge quantity of wire.

When the magnet rotates, its magnetic field knocks loose electrons. This creates electric current in each section of the wire as it passes. All these small currents add up to a sizable one.

The magnet is turned by a turbine that rotates due to the force of something pushing on its fins. In most power plants, the turbines are turned by steam.

This is created by heating water with a fuel such as coal, natural gas, or nuclear fuel. At hydroelectric plants, the rush of water turns the turbines. Other forms of energy, such as wind and solar power, can generate electricity as well.

Electricity flows out to its destination under pressure, along what is called a hot wire, (energise wire) and returns without pressure along a neutral wire. Overhead or underground wires bring electricity to houses.

The house also has a grounding system, which is a path for carrying wayward electricity safely to the ground. Each circuit, and each point along that circuit where electricity is used, has a ground wire, which is usually either bare copper or covered with green insulation. All those wires lead back to the house's main ground wire. The main ground wire is sunk deep into the earth, typically connected to a rod or a cold water pipe.

Energy efficiency

Green Power is electricity generated from clean, renewable energy (RES) such as solar energy, wind power, biomass, and hydropower. All these have an unlimited supply and provide significant benefits in reducing greenhouse gas emissions by the reduction in fossil fuel consumption for power generation.

The cost of installing renewable energy can also be paid off over a few years by the provision of reduced power bills (the balance of power generated in free to the household).

Figure 1 Generation of power using renewable energy

a) Photovoltaic Cells (PV Cells) integrated in Solar Panels and Solar Hot Water

How Works PV Cells:

1. Solar panels convert sunlight instantly into DC electric power
2. Inverter converts DC power into standard household AC power and synchronizes with the utility, making your meter in reverse during times of excess production.
3. An optional battery back-up module could be added to the installation, but it is not a part of this grid-inertia only system description.
4. Utility meter spins backwards when solar power generation exceeds house demand, generating a credit against what you will consume during the night and less sunny periods throughout the year.

Define terms:

Simply put, a solar panel is a assemblage of photovoltaic cells. They function collectively to provide electrical energy for varied utilizations. A single photovoltaic cell doesn't have the capability for generating a lot of electrical energy so multiple photovoltaic cells are joined together to increment the capacity. The number of photovoltaic cells depends on the amount of necessitated electrical energy. Solar panels are configured to convert light into electricity. The operation of extracting electrical energy from light is named Photovoltaic (PV). The Photovoltaic operation converts solar power directly into electrical energy.

A photovoltaic cell, as well known as a self-generating barrier layer cell, is a photovoltaic detector that converts radiant flux straight into an electrical current. It consists of a thin silver film, on a semiconductor layer, deposited on an iron substrate. There are no dangerous emissions from photovoltaic equipment and its operations are literally noise free, which makes it environmentally superior to alternative forms of electrical energy generation.

Solar Hot Water

The biggest energy cost to nearly all houses is the production of hot water. The utilize of solar hot water heating system is the basic utilization of renewable energy.

These systems can be aggregated with gas hot water to guarantee a uninterrupted hot water supply even during cloudy days. The heated water is stored in a tank. It utilizes the Sun’s energy to directly heat the water or a heat transfer fluid like water glycol antifreeze.

A flat-plate collector is the most frequent of 3 types of collectors. It's a weatherproof and insulated box that has a dark absorber plate under at least one see-through cover. A different collector is the evacuated-tube, which consist of rows of parallel glass tubes.

The tubes comprise a glass outer tube and an inner tube covered with a special coating that assimilates solar power while inhibiting radioactive heat loss. The system forms a vacuum by withdrawing air from the space between the tubes, thuseliminating conductive and convective heat loss.

The last collector is the concentrating collector. Generally, these are parabolic troughs utilizing reflected surfaces to focalize the energy from the Sun onto an absorber tube. It contain a heat-transfer fluid. The absorber tube is occasionally named a receiver.

Solar water-heaters are of two types: active or passive. An active system utilizes electric pumps, contollers, and valves to distribute water or extra heat-transfer fluids through the collectors. Differently, a passive system doesn't have a pump

The water’s temperature depends on many variables, namely the following ones: the amount of sunshine; ambient air temperature; the amount of insulation used; the supply water’s temperature, as well as the hot water demand.

Possible configurations could include few different renewable energy sources (RES) working together in house (Wroclaw Division of Electro technical Institute 2004).

Figure 2 A complete solar system used in house (present the entire optimal variant) that could by used in house in order to save energy

Focusing on solar sources, they design a system that functions as follows: The power controller combines the two different solar sources: PV and hot water.

The energy produced is used directly for supplying the household elements; if excessive, the energy is stored by the hydrogen and oxygen generated in the electrolysis process. If the needed energy in house is more that the produced one, two alternatives are possible: burning the stored combustible (H2, O2) or consuming the power from the traditional power network.

b) Wind-generated electrical power

Wind power is a form of solar energy produced by the uneven heating of the earth's surface. It is a highly variable source of energy. Yet, wind power is an energy source that is almost impossible to regulate. It is also a clean technology, emitting no pollutants as it transforms wind into electrical power. Furthermore, it is the cheapest energy technology we have today.

Principle: A turbine converts the wind into electrical power. It consists of propeller like blades (the rotor) and a generator. The rotor is what captures the energy of the wind and converts it into motion to drive the generator. A properly designed rotor turns the generator fast enough to produce maximum power, but not so fast that it presents a danger to the system.

Since the wind does not always blow when you want to listen to your stereo, an "off-grid" system typically includes turbine-charged batteries so that electricity is available at any time throughout the day, plus a regulator to protect the batteries from overcharging. A battery system will usually also has an inverter to change the DC electricity from the turbine and batteries into AC electricity that most of our appliances consume.

Another important factor in the amount of possible power is the rotor’s area. A larger rotor will intercept a larger area of wind, thus providing more power. Although we do have control over what size rotor we use, we do not have control over the wind speed. So it is essential to know how much wind is necessary for a wind system to be practical.

c) Biomass power

Biomass means organic matter - biomass energy (or "bio fuels") comes from natural material, such as wood products, municipal solid waste, agricultural crops, and even landfill gases. If you burn wood in a fireplace, you are producing biomass energy; if you put ethanol gasoline in your car, you are consuming biomass energy.

Biomass energy provides substantial environmental advantages: it doesn't contain sulphur, so it doesn't lead to acid rain; it saves space in landfills by recycling waste products; and it contributes no new CO2 to the atmosphere as any carbon dioxide emitted during electricity generation is reabsorbed by new plant material.

In plus, growing agricultural crops for energy production helps stabilize the soil, reduces erosion and chemical runoff, controls flooding and enhances the wildlife habitat.
Farms’ agricultural waste can be processed and converted to fuel (methane) to generate electricity reduce odor and minimize groundwater problems.

d) Hydroelectric power plant

Hydro Power in common is produced from the movement of a mass of water: streams, rising and falling of tides through lunar (and solar) gravitation, wave energy, energy of sea currents. There are two types of hydroelectric power plants:

1. A high-head plant takes advantage of the force of falling water and is built along major rivers to create reservoirs; the utility controls the flow of water through the dam in response to the demand for electricity.
2. A low-head plant is use for convert small falling water in energy. Reactive turbine, like Francis turbine can be used to convert the water power in electric energy
3. A run of the river plant relies on the flow of the river to spin the turbines.

The hydroelectric generator includes an electronic control system that adapts the parameter of electric energy to the level of power network. The commutation devices can generate some commutation noise in the power network. The block diagram of electronic part is presented in figure 3:

Figure 3 Elements of a hydro-turbine: Francis turbine (reactive turbine); the inferior and superior bearings that reduce the slipping between the hub and the turbine support; electrical generator.

In the case of hydropower plant is necessary to prepare adequately the place that host the hydro generator (build a dam, realize the deviation of water stream) that increase the price of plant.

The benefits of hydropower are many: no hazardous emissions or solid waste, no fuel costs and it is entirely sustainable. Hydro plants are reliable, have low maintenance costs and provide flood control.

Figure 3.1 Block diagram of electronic control device used to manage the power provided by the hydropower plat

In all situations electric power generators such as: PV cells, Wind power plants and micro-hydro power plants need a storage element. The role of this is to better adapt the generation of power to the consumers’ demands.

We want to emphasize the role that the hydrogen has as transporting and storage vectors of energy.  There are two processes involving hydrogen. The first process represent the separation of hydrogen that is stored in order to be used when is necessary. In the second process, the hydrogen is oxidized into fuel cells, generating electrical energy when is necessary.

Wind power plants

The wind power plants include the following elements:

• Nacelle, including the gearbox and the electrical generator of wind power plant.
• Rotor blades, capturing the wind power. The number of blades could differ: one, two, three or more blades. The modern turbines are three-bladed designed with the rotor position maintained upwind. Installing position and axis of turbine can be horizontal or vertical.

Figure 3.2 Wind power plats

• Hub, assuring the transmission of movement from turbine to the generator. The speed turbine domain is: 19 to 30 rotations/minute, and could be modified.
• Gearbox, increasing the rotational speed of hub, adapting the speed to the electrical generator characteristics
• Generator, being a synchronous or asynchronous induction machine. On a modern wind turbine the maximum electric power is usually between 600 and 3000 kilowatts.
• Mechanical brake being used to break the turbine, acting on the hub of turbine that is equipped with an emergency mechanical disc brake. The mechanical brake is used in case of failure of the aerodynamic brake, or when the turbine is being serviced.
• Yaw mechanism, using electrical motors to turn the nacelle with the rotor against the wind. The electronic controller that senses the wind direction using the wind vane operates the yaw mechanism. Normally, the turbine will yaw only a few degrees at a time, when the wind changes its direction electronic controller, hydraulics system, cooling unit, tower, and anemometer and wind vane.
• Electronic controller, implementing the control low for the wind power plant adjusting the functioning parameters of generator function of wind speed and needs of electrical distribution system. The system can inject switching noise in the network, result of power electric commutation.
• Cooling unit, assuring the cooling of power plant generator. This cooling unit could use air or water as thermal transfer agent.
• Tower, representing the support of wind power plant, the nacelle with the turbine and generator being placed on top of the tower.. In the function of power and type of turbine are chosen the corresponding heights.   
• Anemometer, being a device that measures the direction and speed of the wind: It drives the electronic controller in order to orient the turbine in the direction of wind.

Short summary of regulations that are in development for wind turbine and power plants

1. IEC 61400-1 Wind Turbine Safety and Design
2. IEC 61400-1 Ed2 Wind Turbine Safety and Design Revision
3. IEC 61400-2 Small Wind Turbine Safety

They explain the safety philosophy, quality assurance and engineering integrity, and specify requirements for the safety of Wind Turbine Generator Systems (WTGS), including design, installation, maintenance, and operation under specified environmental conditions.

1. IEC 61400-12 Power Performance
2. IEC 61400-11 Noise Measurement

They present sound measurement procedures that enable noise emissions of the wind turbine to be characterized. This involves using measurement methods appropriate to noise emission assessment at locations close to the machine, in order to avoid errors due to sound propagation, but far enough away to allow for the finite source size. The procedures described are different in some respects from those that would be adopted for noise assessment in community noise studies.

1. IEC 61400-13 Mechanical Load Measurements
2. IEC 61400-23 Blade Structural Testing

These standards could be used as a guideline for full scale testing of rotor blades of a WTGS. It could be a possible part of a final design verification of the blade structural integrity . The tests included are fatigue tests, static tests, and modal tests.

1. IEC 61400-22 Wind Turbine Certification
2. IEC 61400-21 Power Quality

They prepare a standard for determining the characteristics of wind turbine output, with respect to the impact on the power quality in the public supply system, while securing proper operation of the wind turbine.

PV cells

The sunrays emergent at the surface of Si layer will generate pair of electrons and hole that move freely in the Si layer.  The efficiency of generation is related to the incident photon energy, so only a small part of solar radiation will generate free charges. In order to use the energy of separately charges is needed to collect them using electrodes, which are implemented on the surface of Si layer. In the figure bellow we present such a structure.

Figure 3.3 Structure of a PV cell

The crystalline silicon technology has dominated the market (market share more than 95%) and there is no doubt that this technology will also be dominant during the next couple of years. In the production of multi crystalline silicon, cell efficiency of between 13 and 16% is achieved.

In the laboratory, the current efficiency is between 17% and 20%. Efficiency of mono crystalline silicon is slightly higher (20% and just under 25% in laboratory).

Technologies use to produce silicon PV cells are: thin film technology on the basis of various cell materials, like amorphous silicon, CIS or CIGS solar cells, CdTe solar cells and wafer technology realized in crystalline Si wafers with thicknesses up to 50 µm. Chemical vapor deposition of Si in thin film, or in injection cell or organic cell are possible too.

Solar cells are not normally operated on an individual basis, due to their low voltage, and to the fact that in PV modules, cells are mostly connected in series.

Figure 3.4 Close-up of a PV cell

The current PV cells production situation is shown in table 1:

Table Volume of PV cell type production

Cell type	Rate of global production
Mono crystalline Si	30-35 %
Multi/Poly crystalline Si	50-55 %
Amorphous Silicon	5-7  %
Ribbon/sheet c-Si	< 5 %
CdTe	< 1 %
CuInSe2	< 0.5 %

By using serial connections of PV cells is obtained a medium voltage value for the group of cells. Electronic inverters convert this voltage to the voltage level of power lines that supply the building. Thus, the energy produced by PV cells group can supply the individual building needs or it can be injected in the network. In Germany, for example, more that 100.000 roofs were covered with PV cell panels. (Year 2004)