Introduction to renewable energies

    The use of renewable energy sources, such as solar, wind and hydraulic energies, is very old; they have been used since many centuries before our time and their applications continued throughout history and until the "industrial revolution", at which time, due to the low price of petroleum, they were abandoned.

     During recent years, due to the increase in fossil fuel prices and the environmental problems caused by the use of conventional fuels, we are reverting back to renewable energy sources.

    Renewable energies are inexhaustible, clean and they can be used in a decentralised way (they can be used in the same place as they are produced). Also, they have the additional advantage of being complimentary, the integration between them being favorable. For example, solar photovoltaic energy supplies electricity on sunny days (in general with low wind) while on cold and windy days, which are frequently cloudy, the wind generators are in position to supply more electric energy.

 


    How to procure electricity from the sun, wind and water.

I. From the sun: SOLAR PHOTOVOLTAIC ENERGY


Fig. 1: Solar tracker with 44 PV modules  (SOLÉNER)

    An easy method to collect the sun's energy is photovoltaic conversion, this consists of the transformation of solar energy to electric energy using solar cells. Solar cells are manufactured  from pure silicon with some impurities of other chemical elements, and they are each able to generate from 2 to 4 Amps, at a voltage of 0.46 to 0.48 V, using solar radiation as the source. They capture both direct and diffuse radiation, this means that energy can be generated even on cloudy days. The cells are mounted in series to form PV modules in order to reach a suitable voltage for electrical applications; the PV modules collect the solar energy transforming it directly in electric energy as direct current, which, in isolated applications, it is necessary to store in batteries in order that it may be used during periods of the day in which there is no sunlight.

 

II. From the wind: WIND ENERGY

    Another alternative to produce electricity is wind energy: the supplied by the wind. The device able to perform this conversion is called wind generator, this consists of a mechanical system of rotation which is powered by blades as in old windmills. This rotary system is connected to an electric generator whose axis joined to the driving system. In this way the wind, forcing the blades to turn, drives the electric generator which can be either a dynamo or an alternator (the alternator, in comparison to the dynamo, presents the advantage of a higher efficiency, supplying energy at a lower speed, and supplying more energy at higher speed).

 
Fig. 2: Wind generator Vélter II

        As in the case of solar energy, we should have batteries to store the energy in windy periods.

 

III. From the water: HYDRAULIC ENERGY

    One interesting application for small installations near water jumps is mini-hydroelectricity, with a power range of between 100 W and 5 kW it can be combined with other energy sources.

 

Fig. 3: Pelton turbine (SOLÉNER)

        The applications are enormous, more than three quarters of humanity does not have electrical energy to obtain drinkable water, lighting, electric powered tools, food conservation or audiovisual media. At this moment this kind of system constitutes the most promising direct help for the third world (NGO).

 


    Advantages

    - Once installed and paid for (initial cost investment), no additional costs are originated; the electrical energy consumed is free.

    - Installations using photovoltaic modules are (as the name suggests) modular; if energy needs increase, the number of modules can be increased without the intervention of specialized personnel.

    - These sources do not use fuels, thus avoiding the inconveniences of supply and the dangers that arise through their storage.

    - The electricity produced is in the form of direct current and generally of low voltage, avoiding the risk of dangerous accidents which can become problematic with the use of conventional power lines.

    - Solar energy is produced in the same place as it is consumed: transformers, underground cables and distribution networks through the streets are not required.

    - No environmental impact: solar energy does not produce wastes, fumes,  powders, vapors, noises or smells. As it is the only natural energy and the origin of all the other sources, it does not pollute nature, nor affect the countryside with pylons or electrical lines.

    - The ability to withstand adverse climatologic conditions: rain, snow, wind, ice balls.

    - No maintenance is required: the photovoltaic modules have no mobile pieces and are cleaned by the rain.

    - It is possible to use conventional electrical installations through the use of inverters which supply AC current at 220V.

     - The size of the PV modules is very reduced, they can be easily installed on home roofs, with the only condition that they could collect the solar radiation directly and without shadows throughout the day.

    - Both solar and wind energies present the advantage of being self-complimentary. Solar photovoltaic energy supplies electricity on sunny days (in general with low wind) whilst on cold and windy days, which are frequently cloudy, the wind generators are able to counteract the lack of sunlight.

 


    Components of a installation

 - Generator: is the fundamental component of the installation. It consists of a group of photovoltaic modules, or wind generators, or a mixture of both, that collect the energy from the sun and/or from the wind, and transform it into direct current at a low voltage (usually 12 or 24 V). An example of the characteristics of a photovoltaic module can be seen here.


Fig. 4: A hybrid wind-photovoltaic installation

 - Battery: The electrical energy produced by photovoltaic modules or by a wind generator can be used in two ways: consumed at the time of generation or stored. In order to use this energy at times other than daylight hours or on days without wind, it is necessary to install batteries whose function it is to store the energy produced by the generator and to maintain the voltage of the installation at a reasonably constant level.

 
Fig. 5: Battery room in a installation of  200 kW (Senegal)

    The battery system consists of a group of battery elements, generally lead-acid, each of which produces a voltage of 2 Volts. This means that for 12 Volts installation, a 6 cell battery will be required, connected in series; while if 24 Volts are required, the battery will consist of 12 cells in series.

    The amount of energy that a battery can store depends on its capacity, this is measured in Amp hours (for example: if 100% efficiency is supposed a 100 Ah battery can deliver 1 Amp for 100 hours or 2 Amps for 50 hours, or 5 Amps for 20 hours).

    The number of days that a battery can supply the load in an installation without receiving charge from the generator (number of days of autonomy) will depend on its capacity. The more Amp hours it can store, the higher the number of days available with a single charge. Thus, the battery should be sized in such a way that, without being highly expensive, it can supply the load for the desired number of days of autonomy.

 
Fig. 6: Digital charge controller manufactured by SOLÉNER (OEM version)

 - Charge controller: the regulation system has basically three functions:

   * To avoid battery overcharges which can cause irreversible damage to the battery.
   * To avoid the battery discharging through the PV modules when there is no incident solar radiation.
   * To make the system operate at its point of maximum efficiency.

    The charge controller is one of the most important elements in a photovoltaic system, the battery life depends totally on its correct operation.


Fig. 7: High efficiency electronic lamp (SOLÉNER)

 - Lighting systems: The lighting systems should be of high efficiency and low consumption: electronic lamps, fluorescent tubes, sodium vapour lamps, etc. This type of lamp also withstands supply voltage variations (a voltage variation of 20% can destroy an incandescent lamp, while fluorescent tubes withstand these variations).
 


Fig. 8: High efficiency refrigerators

     -Electric appliances: This devices must be energy efficient, especially when they consume energy over many hours. In the image above we can see three energy efficient refrigerators.

 

Fig. 9: SOLÉNER sinewave inverter

    - Inverter: Most appliances require alternating current at 220 Volts and frequency of 50 Hz. In order to produce this kind of current, a DC/AC (from DC current to AC current) inverter is necessary to transform the DC current from the battery (12 or 24 Volts), into AC current at 220 Volts and 50 Hz.

    The kind of inverter to be used depends on the application. For example, if we want AC current to operate a TV or a computer and some small appliances, a square wave inverter can be used. But if the application is to provide energy to appliances such as washing machines, refrigerators, or some AC motors - loads that require a sinusoidal wave form source for their correct operation - a sinewave inverter must be used.

      Soluciones Energéticas produces modified square wave inverters that, apart from producing a wave form suitable for all these applications, have a very high efficiency (higher than 95%), thus minimizing the losses in the DC to AC conversion. In this way, it is possible to have AC current at 220 Volts and 50 Hz to supply the whole installation - appliances and illumination alike - the general efficiency of the system is thereby improved because the voltage drop in 220 Volts lines is much lower than in 12 or 24 Volts.

    We also produce a wide range of sinewave inverters of high efficiency controlled by microprocessors and programmable by the user by means of a display. This display also continuously shows information about the state of the system, including the energy consumed.

 
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