Advantages and Disadvantages of Solar Energy - Essay Example

Assignment Solar Energy Contents P Introduction 2. Advantages and disadvantages of the system 2 3. Solar collection 6 4. Solarcollector types 11 5. Case study 14 6. Conclusion 17 7. References 18 1. Introduction Solar energy is one of the most significant renewable energies. It is environment friendly and no green house emissions. Solar energy can be transformed to be utilized for diverse purposes that require energy. In order to enhance the efficiency of the solar energy harvesting systems, researchers have been consistently trying to develop and design the technologies to effectively convert the energy into some usable form like converting it to electrical current with the use of solar panels. The most reliable method to evaluate the efficiency of the solar energy converting system is to analyze the solar energy verses the energy converted by the system from the solar energy. In general, solar photovoltaic panels are efficient enough to convert only 15% of the incident solar energy. However, with the help of continuous research in the area helped develop the solar photovoltaic panels that can attain a maximum efficiency of more than 40%. It means that these solar PV panels and solar thermal pannels are capable of converting 40% of the incident solar energy into a usable form of electrical current. Arrays of solar Panels are stacked to derive enough current to power a residential unit or an even an industrial unit. 2. Advantages and disadvantages of the system While comparing the solar energy with respective other renewable and non-renewable energy resources, solar energy remains advantageous in most situations. Non-renewable energy resources like coal and oil, solar energy is not only cheaper but environment friendly too. Solar energy is free from hazardous emissions that are mostly associated with the fossil fuel resources. Some of the perspective advantages of the solar energy are given below. 2.1 Advantage: 2.1.1 Predictable Solar energy remains predictable as solar thermal power generation units remain functional throughout the day without any influence of external resource or fossil fuel resource. In daytime, in the presence of sun, solar energy directly converts the thermal content of the solar energy into electrical energy, while some content of this thermal energy is used to enhance the temperature of molten salt that remains hot for longer terns and used to generate electrical energy during night. 2.1.2 No Pollution and it save the eco-systems and livelihoods Solar energy is free from emission that are associated with the fossil fuel resources that solar energy is environment friendly and preserves the biodiversity of the planet by maintain the healthy environment for the humans and for the earthly creatures. 2.1.3 Using Existing Industrial Base Solar thermal power generation units are thermal power generation units which require the thermal energy o change the water to super saturated stream for the generation of energy through turbines. Solar thermal energy requires no extra equipment in the power generation process. The lenses are made for other purposes too. However, solar tubes are made specifically for the power generation units. 2.1.4 No Fuel Cost Solar Thermal Energy does not need any fuel for transportation like different sourcs of energy such as fossil fuels. Oil prices are increasing as well as electricity prices are also increasing rapidly in most parts of the world much but it can be seen that there are no increases in the cost of using solar power once it has been installed. In other words, after the installation of the solar equipment, it can be observed that the use of solar energy becomes free. Solar does not require expensive and ongoing raw materials like oil or coal and its maintenance costs are also very low. Solar energy does not need to be transported to the plant and can be accessible from any place. The life expectancy of solar panels varies among the companies that manufactur them and some even have life expectancies of up to 40 years. 2.2 Disadvantages of solar energy 2.2.1 Solar doesn’t work at night The main disadvantage of solar energy is that it is not always constant as a result of the fact that solar power can only be produced when there is sufficient sunlight. Energy must be stored in batteries and the main problem is that the storage capacity may not last the whole night. Solar production decreases during winter periods when the sun radiation is less intense. 2.2.2 Financing It is very expensive to build huge solar projects for small industrial purposes. 2.2.3 High Costs Solar Thermal Energy costs at least Euro 3.5/watt and these costs are too high as Solar PV already costs Euro 2.5/watt. These need to be reduced. 2.2.4 Solar panels are bulky Solar panels are too big especially the higher-efficiency, silicon crystalline wafer solar modules that are in mosted cases covered in glass. The new technology thin-film solar modules are much less bulky but the disadvantage is that the thin-film solar device is currently less efficient than crystalline wafer solar. 2.2.5 Long Gestation Time Leading to Cost Overruns The gestation period which involves aspects such as financing as well as drilling take long periods such as seven years to build a solar thermal power plant that is concentrated. On the other hand, a PV plant requires about three months only to construct. 3. Solar Collection The energy from the sun can be used directly by converting it to either electricity or heat using PV (photo-voltaic) or ST (solar thermal) technologies. 3.1 PV (Photo-Voltaic) PV converts energy from sunlight into electric current using a semiconductor material and this is silicon in most cases. When the light is absorbed within the semiconductor, electrons are allowed to flow and this result in electric current being produced.  PV panels absorb light from the sun and this is converted from direct current to alternating current using an inveter. This power is then channeled into the supply grid for different dommestic or commercial purposes.  The PV panels can operate directly other gadets that use DC power and some of these include lights, calculators as well as portable radios among others. These devices also have batteries that can store power to be used in future. Standard PV solar panels are capable of converting direct sunlight into electric current at the efficiency rate of about 15% while some other panels can operate as much as 20%.  It is significant to observe that a solar panel that normally has the rate of 200Watts will not provide that 200Watts of electricity at a constant rate throughout the day.  The rate of 200 Watts is mainly based on the maximum radiation of the sun in summer gauged to be 1000W/m2 ( 317.1Btu/ft2) at a temperature of 25oC / 77oF.  Therefore, on a clear summer day, a 200Watt panel can provide around 0.7 - 0.8kWh of electrical energy. 3.2 ST (Solar Thermal) Solar thermal panels have different names including Solar Water Heater, Solar Hot Water Panel, Solar Thermal Panel, Solar Hot Water Collector, or Solar Thermal Collector.  Solar water heaters mainly work by absorbing sunlight and converting it into usable heat.  Solar water heaters work through absorbing heat and converting it into energy that can heat water for domestic purposes. For instance, high quality absorber coatings mainly used by Apricus products can absorb up to 95% of the energy in sunlight the day.  A good example can be drawn from Tinox which manufactures quality absorber material for coating and it can absorb about 95% of sunlight available and only emits about 4% as heat from the same absorbed energy.  The key areas to look at include the yellow patches which represent solar radiation and the light blue shows the amount of sunlight that is absorbed by the coating.  Solar water heaters like the AP evacuated tube solar collectors by Apricus can reach solar collector efficiency of 70% and these are based on the dimension of the aperture and over 80% in the event that the surface area of the absorber is black. Basically, solar water heaters can reach efficiencies that are more than four times higher than PV panels for a specific place. 3.3 Solar Thermal & Photovoltaic Working Together Solar Thermal and PV should not be seen as competing technologies given that they have different functions and can work together as a system that is balanced in as far as provision of solar energy is concerned.  Electricity generated from the solar system can be used for any application such as water heating. This constitutes the bulk amount of heat required for any household use.  4. Solar collector types The most common solar collector types include evacuated tubular collectors (ETC) and flat plate collectors (FPC) without a vacuum. 4.1 Flat plate collectors FPCs can have convection barriers between the cover glass and absorber and in some instances they may not have this. The convection barrier is made of a thin plastic foil that is placed between the absorber and the glass covers. The gap between the absorber and cover glass is very important since it helps to reduce the heat lost due to conduction as well as convection. A minimum distance between the absorber and the convection barrier is also essential. The thermal expansion of the thin plastic foil should be considered since this foil should not get into contact with the absorber. In that situation, it decreases the total energy transmitted and does not act as a convection barrier. Figure A-- Flat plate collector The convection barrier is shown in figure A and it helps to reduce the circulation of air between the hot absorber and the cold glass cover. This helps to minimize the heat lost from convection. Since the convection barrier is not 100 % transparent, it helps to reduce the radiance on the absorber slightly. This entails that there is a certain temperature limit which helps to distinguish if there is an advantage to include a convection barrier or not with regards to the aspect of efficiency. In order to make the choice of collector type costs, the convection barrier should be compared with the extra annual energy output. 4.2 Evacuated tubular collectors ETCs are made in different ways they all use vacuum to insulate the absorber. An example of an ETC-unit is shown in figure B. Figure B- Evacuated tubular collector unit In ETCs, the heat can either be absorbed through the use of solar collector fluid flowing through the absorber or it can be collected via heat pipe principle where little fluid is sealed inside each evacuated tube. The energy transfer occurs in four different steps: 1. Evaporation of the fluid takes place through solar radiation process. 2. The vapor moves upwards where it meets a colder pipe and some liquid flows through it. 3. Condensation of the vapor takes place. 4. The condensed fluid moves to the bottom triggering the start of the process again. ETCs can also be made as “U-pipe” to replace solar thermal panel to enable heat to flow through one single pipe. The concave mirrors are put behind the collectors to make sure that heat radiation that may slip between the collector tubes will be driven back from behind into the tubes. The reflectors can be made from cheap material such as polished aluminum. The back side of the absorber should have a selective surface just like the front in order for it to be efficient. 5. Case study Case study 1: Hong Kong International Terminals Limited (HIT) Hong Kong International Terminals Limited (HIT) switched on its new solar panel installation to add it to its latest addition to its green energy programme. HIT installed 129 solar photovoltaic (PV) panels above the Terminal 4 gatehouse and this has made it the fifth largest solar PV system installation in Hong Kong from the private sector. The panels have been designed to produce about 19,200 kWh of electricity a year and this is enough to supply power to a household comprising of four people in Hong Kong for about three years. The solar PV panels will be used to provide power to the canopy floodlights, gatehouse office lighting and Security Office equipment. Unlike previous solar installations at HIT, these panels are directly connected to the CLP grid to generate power instead of heat thereby allowing the lights and equipment to automatically switch back to CLP power if there is not enough solar power that can sustain such kind of operations. Case study 2: HK Electric HK Electric which has Hong Kongs largest photovoltaic installation has recently completed the expansion of its solar power system in Lamma Power Station. This has doubled its capacity and the output capacity has risen from 550 kW to the current 1 MW. More advanced amorphous/microcrystalline silicon tandem junction thin-film photovoltaic (PV) modules which have better electricity-generating capacity were mainly used for this particular project. The new modules which are similar can generate forty percent extra electricity than those initially installed. With the addition of more than 3,000 such modules, the whole solar power system is now comprised of 8,662 PV modules. These have been placed on rooftops and other surrounding areas at Lamma Power Station which covers about 13,000 square meters. When the solar power system was first used in July 2010, it generated 2.26 million units of green electricity and this helped to save about 1,880 tonnes of carbon dioxide and this is also equal to planting more than 81,000 trees. When the plant was completed in 2011, this meant that more than 1.1 million units of green electricity could be produced per year which means that about 915 tonnes of carbon dioxide emissions would have been reduced or equal to planting 39,000 trees. 6. Conclusion Solar energy has many advantages in Hong Kong since there is abundant sunlight. High-rise and high-density urban environment often create difficulties for solar energy applications. The other issue is that the current business practices do not favor renewable energy and the Governments role is critical for stimulating the market for solar power. Although current applications are limited in number, they can still provide valuable data and enlighten people about the new technology. There have been interesting results derived from using solar systems in the area. For instance, wind and solar energy have been proposed to be used in the "Hong Kong Disneyland."It has also been proposed that solar power can be used to provide lighting in tunnels and other areas in Hong Kong. More research and innovation are however needed to examine and identify the suitable design options. Thus, partnership between Hong Kong and mainland China will open up a new era for achieving sustainable energy development in these countries. 7. References Boxwell, M, 2010, Solar Electricity Handbook, Edition: A Simple. Foley, E, 2012, Solar Panels On the Move. Garg, HP 1990,Solar Energy:Fundamentals And Applications(1ST REV ) Parida, B, Iniyan, S &and Goicm R 2011, “A review of solar photovoltaic technologies,” Renewable and Sustainable Energy Reviews, 15 (3): 1625-1636. Practical Guide to Solar Energy n.d., Designing and Installing Photovoltaic Solar Electric Systems Rashid, M 2007 , Solar Power Conversion, Power Electronics Handbook Sailor, DJ, Wamser, C & Rosenstiel, T 2011) “Solar PV and green roof integration --performance and design considerations,” An invited presentation at the 8th Annual Green Roof & Wall Conference – Cities Alive, Vancouver, Canada. Chen, CJ 2011, Physics of Solar energy http://www.hit.com.hk/cn/Corporate-Social-Responsibility/Sustainability/Major-Achievements-Environmental-Protection.html http://www.hkelectric.com/web/Index_en.htm Read More