Alternative Sources of Energy In this chapter you will find a brief introduction on various alternative sources of energy available in the world. 11.1 Passive solar Passive solar refers to using solar energy without involving mechanical and electrical devices. In building designs, all the structure is designed to collect, store and distribute solar energy in the form of heat in the winter and reject this heat in the summer. It can be used also as a collection of light to reduce electrical light during the day. In Malta we don t have harsh cold winters, but the insulation of the envelope is essential to reduce using heaters or fire places to heat the surrounding air. In summer temperature above 25 o is normal. During this period, air-conditioners and fans are widely used to try to maintain an adequate temperature. So, according to the Maltese climate it is better to try to build in a way to let heat outside the building frame. This can be done in various ways. First one has to consider what type of building material is best to be used. The obvious choice would go to material which offers the most resistance to the passage of heat. In fact, in Malta we build the exterior wall with a double wall of globigerina limestone with an air cavity inside it. According to A.Abela 1, a Maltese university lecturer, a double limestone wall with an air cavity inside doesn t offer sufficient thermal insulation, but filling the air cavity with some for of insulation such as glass wool is sufficient to lower the thermal transmittance to acceptable values. The same result is shown with brickwork. Another important thing to consider is to use at least double glazing windows, with thermal breaks and shades in summer periods. Other aspects to consider while building regard where to place the rooms according to room type and to consider a substantial amount of 1 (Abela, 2006) Lecturer: Mr J.Agius Page 1
ventilation in rooms such as bedrooms. Orienting the building to face the equator to capture the morning sun and extending the building along the east/west axis if possible. Windows should be sized to face the midday sun in winter times and be shaded or protected with a shade in summer periods. Protecting the roof in summer periods with shades or overhanging plants that absorb the energy of the sun. In this way the energy received on the roof will be minimized and during the night the radiant energy will be less. To note that although it is relatively easy to build up a house according to these standards, it is also possible to make arrangements in already build houses to try to reduce heat flow through the fabric. Some other forms of passive systems use a small amount of conventional energy to control dampers, shutters, night insulation, shades, lighting systems, and other devices that enhance solar energy collection, storage, use, and reduce undesirable heat transfer. Water heating is considered one of the best applications for passive solar energy. There exits two types of solar heating systems. Liquid based systems that heat water or liquid antifreeze in a hydronic collector such as flat plate collector and evacuated tube collector. Both systems collect and absorb solar radiation, which is transferred to the interior or to a storage system such as a water tank. If the circulation of water is left to circulate on natural convection, then this system is considered to be passive solar heating. Benefits regarding passive solar are due to the performance of the building fabric. If a building is properly insulated, it is possible to reduce the amount of electrical consumption since heaters won t be needed during winter times and the operating time of air-conditioner can be decreased in summer times. Moreover, due to the collection of solar energy in water containers, water will be heated with this energy instead of using electrical water heaters. If the amount of solar energy is not sufficient, then a back-up system can be used. But this also means that the amount of electricity consumed can be reduced by such system. Limitations of such system, is that solar energy is only used during the daylight. To heat the water from solar energy, one has to wait for a certain amount of time before using it. Orientation of the building is also considered as a limitation. It is not always Lecturer: Mr J.Agius Page 2
possible to build along the east/west axis especially in Malta where the areas are overpopulated with houses. Not all houses have the potential of installing solar heaters. For example, apartments have to rely entirely on the building fabric to reduce electricity consumption especially those living at ground floor level. Such persons don t have enough space to install solar water heaters. On the other hand, those living in the top floor have all the space to install solar heaters, but they have to protect the building fabric more than the others during summer periods, since the heat absorbed by the fabric during the day is released during the night. The following table shows how much passive solar is reliable according to the type of fabric and production. ommercial Status T E H N O L O G Y S U P P L I E R S O S T Implementation Issues F I N A N I N G A E P T A N E R E G U L A T O R Y Operable Windows Thermal Mass Passive Solar Design Wing Walls Thermal himney Satisfactory Satisfactory in most conditions Satisfactory in Limited onditions 2 Unsatisfactory or Difficult 2 Table taken from (Sustainable Sources. 17 years of online Green Building information) Lecturer: Mr J.Agius Page 3
11.2 Active solar Active solar technologies usually consist of a solar collecting device that is designed to capture the sun s energy to store it or transfer it as heat energy in water or air. Unlike passive solar technologies, active solar technologies involve mechanical and electrical devices. This in general is achieved by using pumps. For example, using a pump to circulate the water will increase the system s efficiency but with additional capital cost requirements for the pump and associated controls. Active solar technologies work by heating the cold mains water to the required temperature by using solar collectors such as flat-plate collectors or evacuated tube collectors. These collectors are securely installed on the roofs, facing south, towards the sun with an inclination between 10 o to 60 o. This inclination will depend according to the latitude of the country. In Malta, solar collectors are installed at an angle of 45 o, but studies conducted by local distributers are concluding that an angle between 55 o and 60 o gives better performance during winter times. A flat plate collector is an insulated water proofed box that contains a dark absorber plate under a glass cover. The absorber plate collects sun energy and transfers the heat into the pipes which run through the absorber plate. The water runs through pipes under the absorber plate and the heat from the sunlight is transferred via the absorber to the water as it flows through the pipes. Figure 1: Flat Plate collector 3 3 (Active Solar Technology) Lecturer: Mr J.Agius Page 4
Evacuated tube collectors consist of a number of transparent glass tubes. Each tube consists of two glass tubes made from very strong glass. The outer tube is transparent allowing light rays to pass through with minimal reflection. The inner tube is coated with a special coating which has excellent solar radiation absorption and minimal reflection properties. The tops of the two tubes are fused together and the air contained in the space between the two layers of glass is pumped out while exposing the tube to high temperatures. This "evacuation" of the gasses forms a vacuum, which is an important factor in the performance of the evacuated tubes. Figure 2: Evacuated tube collector 4 Benefits of such installations are due to carbon savings. Such technology generates more heat energy than passive solar. All the stored energy can be used at a later time during the day. Such technology can save electricity consumption up to 90% on the Maltese islands. Payback will be subject to local electrical costs, but these in general are within the first 5 years. In order to attract more buyers, the Malta Resources Authority has issued a number of support schemes, the latest one being a grant of 40% up to 400 on the equipment purchased. Advantages of such technology include silent operation. Since there are no machines involved, this technology operates silently. 4 (Active Solar Technology) Lecturer: Mr J.Agius Page 5
Limitations to such technologies include operation time restrict during the day. Shades and clouds limit the performance of such devices and visual impact. Their size is relatively big. They take a substantial amount of roof space, and their view from the sky is not so much attractive. Application of such technologies is restricted to the amount of light falling on the building. To note that such systems can be used in combination with other forms of energy such as biomass or ground source heat pumps. 11.3 Wind Wind energy has been used for hundreds of years. During those times, windmills were used to pump water or grind the grain or other types of fruit. Today wind energy is being utilised to generate electricity. This electricity can be generated in two ways. Either by constructing wind farms, like the proposed project at Sikka l-bajda that forms a grid capable of generating 100MW, or by stand-alone applications with battery back-up for home use like the one found on the roof of Tip-Top shop at Fgura. Figure 3: A 4kW turbine installed in Xewkija, Malta 5 In order to generate worthwhile quantities of electricity, average wind speeds of more than 5-6 m/s are typically required. There are two basic kinds of wind turbines: horizontal axis and vertical axis. Horizontal axis turbines are generally more efficient. These comprise a central hub 5 (Wind Farm Wars, 2011) Lecturer: Mr J.Agius Page 6
supported on a tower with evenly spaced blades, and rotate at an almost fixed rate, regardless of wind speed. Vertical axis systems can be installed without the need for a tower, and may be easier to integrate with a building s structure. The power output of a wind turbine depends on two key factors: the swept area of the rotor and the wind speed. So this alternative source of power does not rely on sunlight like passive and active solar power does. The best locations for wind turbines are away from obstructions which affect air flow. Wins speeds increase with heights, thus ideal sites for wind turbine installations would be near hill tops and the coast. The design of the wind turbine will depend on the type of wind speed. So before installing a wind turbine, one must assess what are the normal wind speeds of the region. Since the energy generated from wind turbines does not involve any type of fossil burns, this energy is considered to be a carbon saving technology. According to the records, the installation of a grid of turbines at Sikka l-bajda will cater for 10% of the total energy needed on the Maltese islands. This means that carbon emission form the power plants will be reduced by 10%, if such installation would occur. Wind turbines are widely considered to be one of the most financially viable of the renewable energy technologies. For small scale, building applications, payback period will be within 20 years time without grant. Limitations of such technology are space and noise. Installation of such turbines occupies space, and not every householder in Malta can apply to erect a wind turbine on his roof. Local regulations of height above the ground of common dwellings don t leave enough space to mount a wind turbine. Noise levels are generally low and can be masked by the sound of the wind but turbines tend to generate vibrations. onsiderations should be taken during the design stage to mount dampers to reduce vibrations. Safety is another issue to take into consideration. Enough space must be ensured to leave the blades rotate without hitting other objects. Lecturer: Mr J.Agius Page 7
Figure 4: Horizontal Wind turbine for home use Figure 5: Vertical wind turbine for home use 11.4 Bio-Fuels Biofuel is a product from biomass. Energy from biomass is produced by burning organic matter such as trees, crops or animal dunk. This heat energy can drive engines to generate electricity. Biofuel is considered carbon neutral, as the biomass absorbs roughly the same amount of carbon dioxide during growth, as when burnt. For this reason, this fuel is considered much cleaner than petrol or diesel alternatives. But in order to create biofuel, large areas of forests are sacrificed to make space for the plantation of biofuel suitable crops. The main types of biomass can be divided into three categories; Woody biomass: this includes all types of trees that grows fast such as willow, hazel and poplar, miscanthus (elephant glass) and wood waste used in the industry or in construction. Biofuel: this is created from cellulose and vegetable oil crops such as palm oil. This type of fuel is also used to move cars. Animal residue: cattle, chicken and pig waste can be converted to gas or other fuel types. Lecturer: Mr J.Agius Page 8
Some biofuels currently in use are: Biobutanol Biodiesel Bioethanol Biogas Vegetable Oil It could be argued that biofuel is a product of solar energy, since plants needs substantial amount of solar energy to grow. arbon savings attributed to this form of energy are very significant. Power plants using this type of energy reduce carbon emissions substantially since this type of fuel produce a net zero carbon. All other types of fuel although, generated from plants and animal remains long time ago, their energy is being used almost immediately compared with the amount of time it took to change to fuel form. This type of energy is not cost effective since the machines needed to transform this fuel to electricity cost more than conventional machines used to burn diesel, petrol or gas. Emissions, noise, vibration and visual are similar to conventional plant using petrol, diesel or gas engines. Such emissions can be controlled by appropriate filters. Limitations of such fuel are that, crops needs time to grow and to be changed to fuel. Moreover, one needs to consider the space where to store such fuel and cost of transport if such fuel is not in the vicinity of the plant. For example, in Malta it is not possible to create biofuel, since space to harvest such crops is very limited and such space is more conveniently used to harvest food. So, in our case, this fuel needs to be transported from other countries. Moreover, it is not possible to rely only to this type of energy since to provide biofuel only for any type of transport across the globe would require a colossal amount of space to be used for plantation of crops which is practically impossible. Lecturer: Mr J.Agius Page 9
11.5 ombined Heat and Power ombined heat and power, also known as cogeneration refers to the use of heat engine or power plant that simultaneously generates electricity and useful heat in the form of hot water or steam. All power plants emit a certain amount of heat during electricity generation. For example, in Malta, the power plants work by heating the water to create steam which is then channelled in tubes that pass directly into turbines which rotates due to the pressure exerted by the steam. In general all this heat is released into the natural environment through cooling towers and flue gas. Such energy is lost. If on the other hand this heat energy is used to heat nearby places during winter times, then the efficiency of the plant rises since now more energy is being produced from the same amount of fuel burnt. The overall efficiency of a combined heat and power (HP) plant can be more than 80% if correctly used. This amount is at least twice the amount that the power plants in Malta are capable to generate. HP is most appropriate to buildings which require all year round demands for heat such as hospitals, hotels and leisure centres with heated swimming pools. HP can significantly reduce primary energy consumption and carbon emissions with respect to conventional power plants. This does not mean that using such technology will eliminate all the problems present such as cost of fuel and cleaner air. To commission such power plant will require more money than any conventional power plant, but payback of such plant which operates for more than 4500 hours each year will be within 5 to 10 years. Emissions, noise, vibration and visual are similar to conventional plant using petrol, diesel or gas engines. Such emissions are lower than those produced from conventional power plants which can also be controlled by appropriate filters. Noise can be solved by proper installation of noise acoustic enclosures and vibration can be reduced with anti-vibration mountings. Lecturer: Mr J.Agius Page 10
11.6 omparison between various types of alternative energy sources The following table shows a comparison between various types of alternative energy sources described in the previous sections. omparison includes efficacy, carbon dioxide savings, and costs of installations, payback period, and limitations. Such comparison will be directed to what is being installed or already exists on the Maltese islands and what effects will it have on the energy produced by the power plants present. The efficiency will represent the amount of energy generated by such installation which is needed on the Maltese Islands. Technology Passive solar Active solar Wind Bio-fuels O 2 reductions Efficiency osts of installation Payback period Limitations Noise Vibration Low Low High Undefined Depends upon the orientation of the house ompletely silent NA Low in general. Medium if considered as a household installation. Low in general High 5-10 years Depends on availability of grants Operate only during the day ompletely silent Pump vibrations only Visual Impact Attractive Unattractive Medium 10% One of the most financially viable of the renewable energy technologies 20 years Requires space Low, often masked by wind-generated noise Low but can be controlled Highly visible and unattractive High, carbon released during combustion is equivalent to the amount absorbed by the crop Same as conventional plants but can increase is HP is considered. Higher than conventional systems Depends upon where the fuel is generated, transport and storage costs Requires time to be produced, storage and drying facilities Associated with production and transport Associated with production and transport Similar to conventional plants ombined Heat and Power Reduction of 0.6 tonnes for every 1kW of electrical capacity provided Twice as much as conventional power plants Higher than normal plants 5-10 years Depends on fossil fuels or biofuels which still produce O 2 emissions Medium-high Medium-high Unattractive and takes an amount of space Lecturer: Mr J.Agius Page 11