Study Of A Renewable Energy Of Photovoltaic System Engineering Essay

Besides, the guidelines to Account for and Report on Greenhouse Gas Emissions and Removals for Buildings (Commercial, Residential or Institutional Purposes) in Hong Kong 2010 Edition of EMSD and EPD report that climate change has become a challenge to the international community. The Government of the Hong Kong Special Administrative Region is committed to working closely with the international community in formulating measures to reduce greenhouse gas (GHG) emissions.

Being a service economy without any major energy-intensive industries, electricity generation is the major source of GHG emissions in Hong Kong, accounting for over 60% of the total local emissions. The second largest GHG emission source is transport sector (16%), followed by waste (12%). Among various end uses of electricity, buildings account for some 89% in Hong Kong. Therefore, red ucing electricity consumption for building operations is instrumental in bringing down our GHG emissions. It will also have the co-benefits of reducing operational costs and improving the local and regional air quality.

GHG emissions associated with the electricity purchased based on a territory-wide default value of 0.7kg/kWh in Hong Kong and these specific emission factors are available from the 2 nos. of electric companies (CLP – The China Light & Power Company Ltd. & HEC – The Hong Kong Electric Company Ltd.) from years 2002 to years 2007 in Hong Kong as following:

Photovoltaic System

More renewable energy sources may help containing fossil fuel use, thereby reducing greenhouse gas (GHG) emissions. Solar energy is one of the renewable energy being widely used over the world mainly due to its clean and emission free properties. Solar energy can be used in many ways which can provide the heat energy, mechanical power and electrical power. One of the most common methods is to convert solar radiation into electricity through the use of photovoltaic (PV) technology. The sunlight will converted to electricity using photovoltaic solar cells. The photovoltaic cells are usually bundled together in panels and modules to produce the increased power. The PV panel advantages are no pollution, quiet operation and require a little maintenance. Over the past few years, photovoltaic technologies have been developed rapidly.

To promote greater adoption of renewable energy technologies in Hong Kong, the Energy Efficiency Office (EEO) of the Electrical and Mechanical Services Department (EMSD) always seeks opportunity to promote the use of new renewable energy technologies. Attention is now being paid to the flexible amorphous thin-film technology in view of the increasing popularity for applications in overseas countries

Renewable energy is ready to be inexhaustible, harnessed and more importantly is a clean alternative to fossil fuels. Photovoltaic System is the type of the renewable energy in Hong Kong and aim to have 1 and 2% of Hong Kong’s total electricity supply met by power generated by the year 2012. The world population of 10 billion by the year 2050, the world’s fossil fuel resources will advance more depletion rapidly according to the increasing global energy demand at the world.

Photovoltaic is a method of generating electrical power by converting solar radiation into direct current electricity using semiconductors that exhibit the photovoltaic effect. The photovoltaic power generation employs solar panels composed of a number of solar cells containing a photovoltaic material. Photovoltaic device directly and silently convert light energy to electricity. No-post installation energy input other than the light source virtually. The sun is required normally. Materials presently used for photovoltaic include monocrystalline silicon, polycrystalline silicon, amorphous silicon, and cadmium telluride and copper indium gallium selenide/sulfide. Due to the growing demand for renewable energy sources, the manufacturing of solar cells and photovoltaic arrays has advanced considerably in recent years.

Many solar photovoltaic power stations have been built which mainly in Europe region.

As of December 2011, the largest photovoltaic power plants in the world are the Golmud Solar Park (China, 200MV), Sarnia Photovoltaic Power Plant (Canada, 97MV), Montalto di Castro Photovoltaic Power Station (Italy, 84.2 MW),Finsterwalde Solar Park (Germany, 80.7 MW), Ohotnikovo Solar Park (Ukraine, 80 MW), Lieberose Photovoltaic Park (Germany, 71.8 MW), Rovigo Photovoltaic Power Plant (Italy, 70 MW),Olmedilla Photovoltaic Park (Spain, 60 MW) and the Strasskirchen Solar Park (Germany, 54 MW)

Advantages of Photovoltaic System

For the renewable energy, solar power is pollution free during use. Production end wastes and emissions are manageable using existing pollution controls. End of user recycling technologies are under development and policies are being produced that encourage recycling from producers. PV installations can operate for many years with little maintenance or intervention after their initial set up. So that, after the initial capital cost of building any solar power plant, operating costs are extremely low compared to existing power technologies. Grid-connecting solar electricity can be used locally thus reducing transmission and distribution losses. Compared to fossil and nuclear energy sources, Very little research money has been invested in the development of solar cells, so there is considerable room for improvement. Nevertheless, experimental high efficiency solar cells already have efficiencies of over 40% in case of concentrating photovoltaic cells and efficiencies are rapidly rising while mass production costs area rapidly falling.

1.5 Environmental Impact of PV System

The most important feature of solar PV systems is that there are no emissions of carbon dioxide – the main gas responsible for global climate change – during their operation. Although indirect emissions of CO2 occur at other stages of the lifecycle, these are significantly lower than the avoided emissions. PV does not involve any other polluting emissions or the type of environmental safety concerns associated with conventional generation technologies. There is no pollution in the form of exhaust fumes or noise.

Decommissioning a system is unproblematic. Although there are no CO2 emissions during operation, a small amount does result from the production stage. PV only emits 21,65 grams CO2/kWh, however, depending on the PV technology. The average emissions for thermal power in Europe, on the other hand, are 900g CO2/kWh. By substituting PV for thermal power, a saving of 835879 g/kWh is achieved.

The benefit to be obtained from carbon dioxide reductions in a country’s energy mix is dependent on which other generation method, or energy use, solar power is replacing. Where off-grid systems replace diesel generators, they will achieve CO2 savings of about 1 kg per kilowatt-hour. Due to their tremendous inefficiency, the replacement of a kerosene lamp will lead to even larger savings, of up to 350 kg per year from a single 40 Wp module, equal to 25kg CO2/kWh. For consumer applications and remote industrial markets, on the other hand, it is very difficult to identify exact CO2 savings per kilowatt-hour.

Recycling of PV modules is possible and raw materials can be reused. As a result, the energy input associated with PV will be further reduced.

If governments adopt a wider use of PV in their national energy generation, solar power can therefore make a substantial contribution towards international commitments to reduce emissions of greenhouse gases and their contribution to climate change.

By 2030, according to the EPIA-Greenpeace Solar Generation Advanced Scenario, solar PV would have reduced annual global CO2 emissions by just over 1,6 billion tonnes. This reduction is equivalent to the output from 450 coal-fired power plants (average size 750 MW).

Cumulative CO2 savings from solar electricity generation between 2005 and 2030 will have reached a level of 9 billion tonnes.

Carbon dioxide is responsible for more than 50% of the man-made greenhouse effect, making it the most important contributor to climate change. It is produced mainly by the burning of fossil fuels. Natural gas is the most environmentally sound of the fossil fuels, because it produces roughly half as much carbon dioxide as coal, and less of other polluting gases. Nuclear power produces very little CO2, but has other major safety, security, proliferation and pollution problems associated with its operation and waste products.

1.6 Energy Payback

A popular belief still persists that PV systems cannot “pay back” their energy investment within the expected lifetime of a solar generator – about 25 years. This is because the energy expended, especially during the production of solar cells, is seen to outweigh the energy eventually generated.

Data from recent studies shows, however, that present-day systems already have an energy payback time (EPBT) – the time taken for power generation to compensate for the energy used in production – of 1 to 3.5 years, well below their expected lifetime. With increased cell efficiency and a decrease in cell thickness, as well as optimized production procedures, it is anticipated that the EPBT for grid-connected PV will decrease further.

The figure hereafter shows energy payback times for different solar cell technologies (thin film, ribbon, multicrystalline and monocrystalline) at different locations (southern and northern Europe). The energy input into a PV system is made up of a number of elements, including the frame, module assembly, cell production, ingot and wafer production and the silicon feedstock. The energy payback time for thin film systems is already less than a year in southern Europe. PV systems with monocrystalline modules in northern Europe, on the other hand, will pay back their input energy within 3.5 years.

Figure – Energy payback times for range of PV systems (rooftop system, irrad. 1700 resp. 1000 kWh/m2/year)

1.7 Future Markets of PV System

International Energy Agency Photovoltaics Power Systems Programme (IEA PVPS) newsletter issue35, 2011/09/01, Page 6 report that The PV market continues to grow faster than expected and prospects for the future remain strong – as long as policymakers encourage a stable and sustainable approach to market development.

The global PV growth trend in recent years has been astonishing. In 2010, growth was higher than 100%, with capacity additions close to 17 gigawatts (GW) from 7.2 GW installed in 2009. At the start of 2011 the total installed world capacity was close to 40 GW, producing some 50 terawatt-hours (TWh) of electrical power every year. Most of that increase was due to the rapid growth of the German (7.4 GW) and Italian markets (2.3 GW), though other countries also showed significant development.

However in many countries the rapid price decreases have led PV close to competitiveness. With PV system prices down in certain market segments to around €2/ Wp ($2.8), the cost of generation of electricity from PV went down in sunny countries to less than €0.15/ kWh. There are few doubts about the ability of PV prices to drop significantly and bring electricity costs below 10 eurocents ($0.14) in the five coming years.

Chapter 2 Literature Review

This part of the thesis summaries the related work by other researchers. The focus is on those researches that the related to my own area directly which is the study of the photovoltaic system.

2.1 PV Technology

Photovoltaic technology is the direct conversion of the electricity from the sun light. The first PV cells, it was only realized in year 1954 after the development of material science and manufacturing of solid state devices. Nowadays, it is extensively accepted as a good technology to generate electricity directly from sun light with minimal environment pollution and as one of the possible alternatives to fossil fuel energy sources.

At photovoltaic system, it has many ways to apply the PV to obtain the solar energy. Solar electricity, year 2004, Markvart. T. report that in the development of semi-conducting devices manufacturing, it mainly consist of silicon, the development of PV cells from the by-products of semi-conductor industry lower the cost and made civil application of PV feasible.

Throughout the history of development of PV, its dominating applications have long been the stand -alone applications. In a stand-alone photovoltaic system, PV is the only way and source of energy powering the electrical load. It has not other external electrical power sources. To supply for the demand when there is no sunlight such as deep in the night. The PV system has not enough sun light to transform into the electricity. It requires some kinds of energy storage such as battery, fuel cells, and water tanks and so on. These types of systems are widely used for the rural area and the faraway area which power network is not more maturity. IEA PVPS trends in photovoltaic application, survey report of selected IEA countries between 1992 and 2010, T1-20:2011 show that these stand alone photovoltaic system fell below about 4% of total world-wide photovoltaic installations. Nowadays, the dominating type of photovoltaic application is the grid connecting photovoltaic system producing the clean power for supporting the electricity grid. From year 2000 to 2010, the percentages of gird connected in the reporting countries are from about 55% to 95%.

IEA PVPS T1-20:2010, percentages of grid-connected and off-grid PV power in the reporting countries.

The operational principle of the grid-connecting photovoltaic system is used the cells to convert the solar radiation into electricity. When the light shines on the cell it creates an electric field across the layers, causing electricity to flow. The direct current (DC) electricity from the PV modules to alternating current (AC) with sophisticated power electronic devices and then supplies the power to the loads in conjunction with the utility grid. It services as a supplementary power source to main stream generation with fossil fuel, nuclear or other conventional means from the utility. Effectively the grid-connecting photovoltaic systems use the grid power as the storage and also the complementary source. It would supply the loads together with the gird when there is not enough from the sun, and would generate excess power into the grid when the PV system could provide more than the loads is needed. This is the fastest uptake type of PV application and became the dominant type by the end of 1999 (IEA PVPS T1-11:2002, P4). Luther et al. (2003, p.98) argued that this type of PV system will be contributing to the main-stream power production towards the reduction of CO2 emission in industrialized countries. Hence the course of change in PV application indicates a development of its role in supplying power to remote areas where no other means of electricity could be easily available and then to supporting the modern society in reducing the adverse effect of burning fossil fuels.

The grid-connecting photovoltaic system is the most popular type of solar PV system for homes and businesses in developed areas. Connection to the local electricity network allows any excess power produced to feed the electricity grid and to sell it to the utility. Electricity is then imported from the network when there is no sun.  An inverter is used to convert the direct current power produced by the system to alternative power for running normal electrical equipment.

2.1.1 Grid-Connected Domestic Systems

This is the most popular type of solar PV system for homes and businesses in developed areas. Connection to the local electricity network allows any excess power produced to feed the electricity grid and to sell it to the utility. Electricity is then imported from the network when there is no sun.  An inverter is used to convert the direct current power produced by the system to alternative power for running normal electrical equipment

2.1.2 Grid-Connected Power Plants

These systems are also grid-connected, produce a large quantity of photovoltaic electricity in a single point. The size of these plants range is from several hundred kilowatts to several megawatts. Some of these applications are located on large industrial buildings such as airport terminals or railways stations. This type of large application makes use of already available space and compensates a part of the electricity produced by these energy-intensive consumers.

2.2 Crystalline Silicon

Crystalline Silicon is the most mature photovoltaic industry technology. It has been developed since the 1950s which had the relatively high conversion efficiency of about 11% to 15% at Standard Test Conditions. Standard Test Conditions (STC) is the convention adopted by the photovoltaic industry benchmark for the performance of a PV cell under the particular testing circumstances. This way of characterization of PV modules has its limitations. Crystalline silicon is still dominating the PV market and is expected to do so for the near future. Meanwhile, in its crystalline form, pure silicon has a grey color and a metallic luster. Like a germanium, silicon is rather strong, very brittle and prone to chipping. The crystal structure of the silicon is resembles the diamond cubic crystal structure. The structure is very stable and less susceptible to degradation due to the heat and light. It also used in a high efficiency photovoltaic applications. In terms of charge conduction, silicon is an intrinsic semiconductor which means that unlike metals it conducts electron holes and electrons which may be released from atoms within the crystal by heat and thus increase silicon’s electrical conductance with higher temperatures. This particular property enables crystalline silicon PV to last for over 20 years and remain functional. Some of the PV manufactures are offering the warranty of over 20 years.

Crystalline silicon can subdivided into 2 types. It is mono-crystalline silicon (m-Si) and poly-crystalline silicon (p-Si). On the mono-crystalline silicon, it is the earliest commercialized technology for applications. It requires the high energy input to produce the raw materials for m-Si cell by single crystal growth. A less energy demanding casting procedure of Silicon crystal was therefore developed to lower the production cost. IEA PVPS trends in photovoltaic application, survey report of selected IEA countries between 1992 and 2010, T1-20:2011 show that due to its lower module price, the p-Si of photovoltaic system is becoming popular gradually. These two manufacturing technologies dominate the market of PV system and in year 2003 accounted for over 85% market share.

The thickness of crystalline silicon PV cells is from 0.13mm to 0.3mm. It needs the suitable protection for the relevant mechanical reason. So, to provide the relevant mechanical protection, the most common method of the PV modules for crystalline Si is the cells embedded in the glass layers. This enables a natural integration with building since glass is one of the most widely deployed building materials.

The manufacture process of the Crystalline Silicon photovoltaic cell

(Picture from EPIA – European Photovoltaic Industry Association)

2.3 Amorphous Silicon

Amorphous is the term describing the characteristics of silicon atoms grouped together forming the PV cell. The amorphous literally means formless. The structure contrasts with its crystalline counterpart which is much more stable and high efficiency. One of the main reasons for developing amorphous silicon (a-Si) PV technology is the lower production cost. The lower production cost is brought about by the lower energy input for the deposition of silicon layer onto the substrate instead of high temperature crystal formation (Luther et al., 2003, p55) and the significantly less amount of silicon required for the cell production (Deng and Schiff, 2003, p.508). The thickness of silicon coating on the substrate is usually in the range of about 0.001mm. That is less than one-hundredth of that of crystalline silicon PV cells. The significant decrease in raw material used enable a-Si module to be sold at a much lower price per unit area than that of crystalline silicon modules especially at the time of ever increasing price of silicon due to the competition between manufacturing of computer chips and PV modules.

In its amorphous state, the photo-electric property of silicon is subjected to light-induced degradation. The effect was reported by Staebler and Wronski, therefore known as the Stabler-Wronski effect (Goetzberger and Hoffmann, 2005, p.60). After an initial degradation of about 10% – 20% decrease in conversion efficiency, the electrical properties of the a-Si cells will be stabilized. It is now a common practice for the manufacturers to publish the stabilized efficiency. The stabilized STC efficiencies of commercial a-Si PV modules are around 4% – 8%. In order to improve the conversion efficiency of the a-Si modules, some manufacturers stack layers of Si depositions to capture more photons. Although with lower efficiency, a-Si PV cells are widely applied in indoor applications for small electronic appliances attributing to its better response to weak light. It is the third most widespread type of PV technology after crystalline silicon the a-Si has been used as a photovoltaic solar cell material for devices which require very little power such as pocket calculators and toys.

Since the thin layer of a-Si can be deposited onto various types of substrate. This enables the form of PV modules made of a-Si having a much greater variety. Furthermore, silicon in its amorphous form does not have the limitations of thickness or mechanical strength as in crystalline form. These special properties facilitate its application in a flexible form. This is very suitable for producing PV modules for building applications. Together with its performance being less affected by the heat built up in the modules, it can be a good candidate for applications in hot climates. The a-Si PV modules area commercially available for installation onto the roofs of buildings either applied onto the finished roof or integrated into the roof covering. The advantage over traditional PV panels is that they are very low in weight. It is not subject to wind lifting and can be walked on. The comparable disadvantages are increased cost and reduced efficiency.

Flexible a-Si PV modules can made as roofing material

2.4 Other Thin-Film Technologies

Thin-film is the general term for PV cells produced other than those thick layers of crystalline silicon. Amorphous silicon is the earliest commercialize thin-film technology. Its development was mainly from the drive to lower production costs by using significantly less rea material and energy input during the manufacturing process. Other new comers comprise Copper Indium Diselenide (CIS), Cadmium Telluride (CdTe) and so on.

In 1975, a Copper Indium Diselenide (CIS) cell of 12% efficiency was successfully demonstrated at the USA’s Bell Labs and work at the National Renewable Energy Laboratory (NREL) developed the technology under the US department of Energy’s thin film program during the 1980’s, consolidating the technology’s promise (Zweibel, 1990, pp.161-180). Due to the collapse of research funding in the US it was almost another 10 years before Siemens Solar Industries (SSI) produced the first commercially CIS modules in late 1990s. A family of similar compounds has also been developed such as CuInSe2, CuGaSe2, CuInS2, Cu2 and so on. the coating of thin film CIS onto substrate was found to be more flexible and easily manipulated (Goetzberger and Hoffmann, 2005, p.65). Therefore CIS is the major material used within this family of compounds.

Similar to a-Si, CIS can be coated into many types of substrate. The choices of CIS modules are wider. For example, flexible CIS modules and modules on polymer back sheets can be found on the PV market. However, due to the rapidly evolving technology, the manufacturing process and even the compound used for CIS modules are ever changing. Second generation CIS modules was reported by Palm et al. (2004) and more development is imminent. With the flexibility in manufacturing the modules, CIS can be one of the candidates for building integration.

These can further be divided into ordinary Building-Integrated Photovoltaic (BIPV) system and Photovoltaic (PV) systems and the solar cells in the market can be classified into two main categories: Crystalline Silicon Cells and Thin-Film Cells. PV cells are generally made either from crystalline silicon, sliced from ingots or castings, from grown ribbons or thin film, deposited in thin layers on a low-cost backing.

The performance of a solar cell is measured in terms of its efficiency at turning sunlight into electricity. A typical commercial solar cell has an efficiency of 15% about one-sixth of the sunlight striking the cell generates electricity. Improving solar cell efficiencies while holding down the cost per cell is an important goal of the PV industry.

Cadmium Telluride (CdTe) has a similar long history in the whole group of thin-film PV modules. Due to its tolerance to defects and grain boundaries, simple and easy to handle deposition process is possible for this material (Luther et al. 2003, p.70). Technology wise this type of material should have been booming. The major hurdle now is the market acceptance since both Cadmium and Telluride are toxic materials although CdTe itself is stable and harmless to the environment. Furthermore, different countries have different regulations regarding Cadmium containing materials (Deb, 2002). This uncertainty might increase the risk factor in investing production plant for CdTe and BP Solar was reported to have closed their CdTe plant (Luther et al. 2003, p.72).

Synergising with the technology advancement in device handling and manufacturing process in semi-conductor industry, there are emerging technologies for thin film PV cell (Sopori, 2003, p.308). These include crystalline silicon thin film (m-SiTF), micro-crystalline silicon (μm-Si) and so on. However, they are still new technology and even not yet commercialized.

Due to the longer history of development, crystalline silicon PV modules are still the more common to apply for the building envelope nowadays. But due to the PV modules brittleness, it have to be well protected by the glass layer and backing. It is this intrinsic nature of crystalline silicon that determines the formation and hence limits its applications on buildings. On the other hand, the thin film photovoltaic technology can be applied on many more substrate and the flexible film modules are available for thin film besides glass-glass modules and glass film modules that are common in crystalline silicon technology. The different size, form, material used can apply to the different building design. Hence, the applications of thin film photovoltaic modules are better than the crystalline silicon nowadays.

2.5 Electrical Characteristics and Performance

PV modules can serve as the building envelope to keep out the weather and control heat gain. To analysis the electrical performance of a PV module, both the instantaneous power output and the energy yield over the time period under investigation has been considered. Instantaneous power has been normalized to per unit power under Standard Test Condition (STC) for easy comparison between different types of technology. Each PV panel is rated under industrial STC of solar irradiance of 1,000W/m2 with zero angle of incidence, solar spectrum of 1.5 air mass and 25℃ cell temperature. Electrical characteristics from manufacturers include maximum rated power, open circuit voltage, short circuit current, maximum power voltage, maximum power current and the temperature coefficients .Also, the energy yield has been normalized in a similar manner. The methodology of evaluation of performance has been based on the Standard IEC 61724 (1998).

2.6 Photovoltaic Simulation

In the photovoltaic system simulation, the prediction of the PV module performance is the core part of the simulator. Normally, the modeling is based on the physical characteristics of the photo electric effect at the semi-conductor. The simulation is calculated the photo-current generated by a certain amount of the irradiance at the surface of the semi-conductor at specific physical conditions. Nowadays, the most of the commercial photovoltaic system simulation programs is the temporal series of data being simulated such as RETSCREEN, PVPSYST, PVSOL, PV-Design Pro, Hybird2 HOMER and so on.

2.6.1 RETSCREEN

The RETScreen software is a program developed by Natural Resources Canada for evaluating both financial and environmental costs and benefits for many different renewable energy technologies. RETScreen has a specific Photovoltaic Project Model that can model PV array performance for many locations around the worldncludes a climatic database including average measurements for 4’700 ground stations, compiled from over 20 different sources, and covering the period 1961-1990. These data are presented as a unique coherent database, and present numerous parameters including Irradiation, air temperature and wind velocities.

2.6.2 PVSYST

PVsyst software has been developed at the University of Geneva in Switzwerland. This is an excellent package for design and analysis of a solar photovoltaic system. It is widely used due to the many parameters available for the user to modify. This software is oriented towards architects, engineers, researchers and holds very helpful tools for education. Both stand-alone and grid-connected PV as well as solar water pumping system could be designed by using PVsyst.

2.6.3 PVSOL

The PVSol program is photovoltaic system analysis software developed by Valentin

Energy Software in Germany with an English language version distributed by the Solar

Design Company based in the UK. The first version of PVSol was released in 1998.

2.6.4 PV-Design Pro

PVDesignPro software is a commercially available software model developed by the Maui Solar Energy Software Corporation (MSESC) and SNL for photovoltaic systems modeling. The software incorporates algorithms from both of SNL’s PV array and inverter performance models as well as SNL’s database of PV module and inverter parameters. NIST uses a custom version of PVDesignPro for comparing different PV technologies and predicting PV module performance for BIPV applications. The program uses an hourly time-step for modeling system performance.

2.6.5 Hybird2

Hybrid2 is described as a probabilistic time series computer model for evaluating the performance and economics of hybrid electricity generating systems. It was developed by the Renewable Energy Research Laboratory (RERL) at the University of Massachusetts Amherst with support from NREL. This program is an engineering design model for hybrid systems consisting of PV, wind, generators and battery storage for both on-grid and off-grid systems

2.5.6 HOMER

HOMER is a hybrid system model developed at NREL in 1993 for both on-grid and offgrid systems. A unique capability that HOMER offers is the ability to find the optimal configuration based on price estimates as well as perform sensitivity analysis to help understand tradeoffs between different technologies and economic considerations. The software has the ability to compare multiple system configurations as well as different battery types. HOMER uses the KiBaM code for battery life modeling as described below in Section 4.2.1. The model can incorporate the following components: PV, wind, hydro, fossil fuel generator, battery, AC/DC converter, electrolyzer, hydrogen tank and reformer. The loads that it can simulate include primary, deferrable, thermal and hydrogen.

Sania National Laboratories Report SAND2009-8258 show that the different in capabilities of both PV and hybrid system models as followings,

Type of Model

POA Radiation Modle

Array Performance

PV-SOL

System

Hay and Davies

Based on irradiance and module voltage at STC and efficiency characteristic curve. Linear or dynamic temperature model. Incident angle modifier.

PVSYST

System

Hay, Perez et al.

One diode equivalent circuit. Modified one diode for stabilized aSi, CiS and CdTe thin-film modules. Also, Incident angle modifier and air mass correction

Hybird2

Hybrid system

HDKR

5-parameter array performance model.

PV-Design Pro

System

HDKR, Perez et al.

Sandia PV Array Performance Model.

HOMER

Hybrid system

HDKR

Power calculated as a function of incident radiation, derating, rated array capacity and PV cell temperature.

Modeled PV Technologies

Weather and Insolation

Economics /

Financing

PV-SOL

cSi, μc-Si, Ribbon, HIT, TF(CdTe, CiS, aSi)

MeteoSyn, Meteonorm, OVGIS, NASA SSE, SWERA, custom locations

Economic efficiency for cash value factor, capital value, amortization period and electricity production costs.

PVSYST

cSi, μc-Si, HIT, TF(CdTe, CiS, aSi)

Meteonorm, Satellight, TMY 2, ISM-EMPA, Helioclim-1 and 3, NASA-SSE, WRDC, PVGIS-ESRA, RETScreen

System financing, feed-in tariffs, annual and used energy costs

Hybird2

cSi, TF(CdTe, CiS, aSi)

Unk

Lifecycle cost, cash flow, NPV, payback, IRR, tax credits, tradeoffs between different hybrid configurations.

PV-Design Pro

cSi, CPV, mj-CPV, TF(CdTe, CiS, aSi)

TMY 2/3, METEONORM, custom locations

Financial analysis including lifecycle and energy costs.

HOMER

Uses some input data form module manufacturer and other available data.

Scaled data in a text file. User can select locations in software, use TMY 2 data or input custom data.

Inputs include annual real interest rate, project lifetime, system fixed capital costs and O&M costs and capacity shortage penalty. Main outputs include total Net Present Cost (NPC), and LCOE.

The contrast of photovoltaic simulation software by IEA-PVPS

Chapter 3 Case Study

The chapter describes the methodology and the process of the building techniques developed. The simulation calculation data is compared and verified with the real data collected by the BMS from a case study. The following sections will outline the information and details of the case study.

3.1 Case study – Hong Kong Customs Headquarters Tower.

The photovoltaic project is located at Hong Kong Customs Headquarters Tower, North Point which is commenced on July 2007 and completed on December 2010. It has approximate 41,000m2 covered areas and 34-storey. The owner of the building is the Architectural Services Department (ASD) of Hong Kong Government.

3.2 Background of the Project

For the new developed building, Hong Kong Government wants to increase more green features gradually. So that Hong Kong Customs Headquarters Tower will embrace a host of related controls on environmental qualities and energy efficiency. This project specific features aiming to create a sustainable and environmental- friendly building achieving the highest platinum class under the Building Environmental Assessment Method (BEAM) are four-fold: Energy-efficient Curtain Wall, Green Podium Roof, employment of Energy-efficient Air Conditioning and Lighting Installation and Use of Renewable Energy. One of the renewable energy is the photovoltaic system.

The photovoltaic system is installed at Roof Floor. The Grid-Connected System is used for the above buildings which are connected to grid indirectly. The output or renewable power connects to the electrical distribution system of the site and the PV system operates in parallel with the electricity supply from the grid to meet the electricity consumption of the building. The comprehensive monitoring system can acquire the data automatically at every 30 minutes. Photovoltaic panel system is served as renewable energy source. The photovoltaic panel system will supply electricity of 15kW and arrange in connecting to the power grid of HKE.

The photovoltaic collection panel will be located at the roof of the building. The photovoltaic panel system will equip with two power conversion system (PCS) with operation in a duty/ standby configuration. In case one PCS fails, the other PCS will maintain the output with continuity of operation automatically without affecting the overall operation.

The photovoltaic panel system is able to interface with the central control and monitoring system via high-level interface, such that the central control and monitoring system is able to undertake real time management without direct access to the photovoltaic panel system terminal.

3.3 Specification of PV System

Referring to the captioned project, the employer’s requirements document has list the general requirements of the photovoltaic system for the project. The international system of unit (SI) shall be used for the work and the works shall be designed and installed in compliance with the latest editions of the standards and specifications.

General specification for Building, issued by Architectural Services Department

General specification for electrical installation in Government Buildings, 2002 Edition, issued by Building Services Branch of Architectural Services Department

General specification for air conditioning, refrigeration, ventilation and central monitoring and control system installation in Government Buildings by Building Services Branch of Architectural Services Department, 2001 Edition.

General specification for Fire Services Installation in Government Buildings by Building Services Branch of Architectural Services Department, 2001 Edition.

Testing and Commissioning Procedures No. 2 for Electrical Installation, 2002 Edition, issued by the Building Services Branch of Architectural Services Department,

Construction site safety manual issued by the Works Bureau.

Code of Practice for the Electricity (Wiring) Regulations issued by Electrical and Mechanical Services Department (EMSD).

General requirement for electronic contracts specification no. ESG01 issued by Electronics Division, Electrical and Mechanical Services Department.

Supply Rules, Guide to connection of supply and other technical requirements of the Hong Kong Electric Co. Ltd.

BS6651: Code of Practice for Protection of Structure Against Lightning

EN50081-1: Generic Emissions (Residential, Commercial and Light Industrial)

IEC 60891: Procedures for temperature and irradiance corrections to measured I-V characteristics of crystalline silicon photovoltaic devices.

IEC 60904-1: Photovoltaic devices. Part 1: Measurement of photovoltaic current-voltage characteristics.

IEC 60904-2: Photovoltaic devices. Part 2: Requirements for reference solar cells.

IEC 60904-3: Photovoltaic devices. Part 3: Measurement principles for terrestrial photovoltaic (PV) solar devices with reference spectral irradiance data.

IEC 60904-5: Photovoltaic devices. Part 5: Determination of the equivalent cell temperature (ECT) of photovoltaic (PV) devices by the open circuit voltage method.

IEC 60904-6: Photovoltaic devices. Part 6: Requirements for reference solar modules.

IEC 60904-7: Photovoltaic devices. Part 7: Computation of spectral mismatch error introduced in the testing of a photovoltaic device.

IEC 60904-8: Photovoltaic devices. Part 8: Measurement of spectral response of a photovoltaic (PV) device.

IEC 60904-9: Photovoltaic devices. Part 9: Solar simulator performance requirement.

IEC 60904-10: Photovoltaic devices. Part 10: Methods of linearity measurement.

IEC 61215: Crystalline silicon terrestrial photovoltaic (PV) modules – Design qualification and type approval.

IEC 61345: UV test for photovoltaic (PV) modules

IEC 61683: Photovoltaic system – Power conditioners – Procedure for measuring efficiency.

IEC 61724: Photovoltaic system performance monitoring – Guidelines for measurement, data exchange and analysis.

IEC 61829: Crystalline silicon photovoltaic (PV) array – On-site measurement of I-V characteristics.

IEC 61701: Salt mist corrosion testing of photovoltaic (PV) modules.

IEC 61721: Susceptibility of a photovoltaic (PV) module to accidental impact damage (resistance to impact test)

IEC 61173: Overvoltage protection for photovoltaic (PV) power generating system – Guide.

IEC 61277: Terrestrial photovoltaic (PV) power generating systems – General and guide.

IEC 61646: thin-film terrestrial photovoltaic (PV) modules – Design qualification and type approval.

IEC 61725: Analytical expression for daily solar profiles.

IEC 61727: Photovoltaic (PV) system – Characteristics of the utility interface

IEC / TR2 61836: Solar photovoltaic energy systems – Terms and symbols.

IEC62116: Testing procedure – Islanding prevention measures for power conditioners used in grid connected photovoltaic (PV) power generation systems.

Engineering Recommendations and Technical Reports issued by the Electricity Association of the United Kingdom as follows:

G5/4 – Planning levels for harmonic voltage distortion & the connection of non-linear equipment to transmission systems & distribution networks in the United Kingdom.

G59/1 – Recommendations for the connection of embedded generating plant to the Public Electricity Suppliers distribution systems.

G74 – Procedure to meet the requirements of IEC 909 for the calculation of short-circuit currents in three phase AC power systems.

G75 – Recommendations for the connection of embedded generating plant to Public Electricity Supplies distribution systems above 20kV or with outputs over 5MW.

G77 – Recommendation for the connection of Inverter-Connected Single Phase Photovoltaic (PV) Generators up to 5KVA to Public Distribution Networks.

ETR113 – Notes of guidance for the protection of embedded generating plant up to 5MW for operation in parallel with Public Electricity Suppliers Distribution Systems (Revision 1).

All PV panels shall be rated at efficiency specifications are at standard test condition (STC) of 1,000 W/m2 solar irradiant, 25℃ cell temperature and solar spectral irradiant per ASTME89. The efficiency of PV cells under this standard condition shall not be less than 15%.

3.4 Model of Photovoltaic System

In this project, Siemens Ltd. is our photovoltaic subcontractor which has a longer history and good experience of the PV system manufacture and installation. The project has total 60 nos. of the SunTech ltd. high efficiency PV module and the model no is STP260S-24/Vb. On this model, the open circuit voltage (VOC) is 44.3V, optimum operating voltage (Vmp) is 35V, Short-circuit current (Isc) is 8.04A, optimum operating current (Imp) is 7.43A, Maximum power STC (Pmax) is 260Wp, the operating temperature is from -40℃ to +85℃, he maximum system voltage is 1000V DC and No. of cells and connections is 72.

The PV cell efficiency of PV module can be calculated base on the data of manufacturer.

For PV cell of STP260-24/Vb

Efficiency = (Pmax / (PV cells area x Input light power)) x 100%

= (3.61 / (0.156 x 0.156m x 1,000W/m2)) x 100%

= 15%

Pmax = the output of each PV module / no. of cells in each PV module

= 260W / 72pcs

= 3.61Watt

SunTech PV Modules Catalogue

3.5 Simulation of the Photovoltaic System

In this project, it used the simulation software for the photovoltaic system is RETSceen, Clean Energy Project Analysis Software which is a clean energy awareness, decision support and capacity building tool. The core of the tool consists of standardized and integrated clean energy project analysis software that can be used world-wide to evaluate the energy production, lift-cycle costs and greenhouse gas emission reductions for various types of energy efficient and renewable energy technologies. The benefits of using the RETScreen software are that it facilitates the project evaluation process for decision-makers. The financial summary worksheet, with its financial parameters input items and its calculated financial feasibility output items, allows the project decision-marker to consider various financial parameters with relative ease.

In the simulation, the climate date location of site reference conditions is King’s Park which had the Meteorological Station. The King’s Park Meteorological Station is used to observation the air temperature, relative humidity, grass temperature, rainfall, wind, MSL pressure and the solar radiation. The solar radiation data of King’s Park Meteorological Station is suitable for our simulation of photovoltaic system in Hong Kong.

On the project location, the latitude and longitude is follow the meteorological system which are 22.3° and 114.2°. The elevation of the building is 65m. For the technology data, it assumed that the slope of photovoltaic panel is 15°. After the calculation, the annual electricity exported to grid is 18.181MWh. The details as following,

Heating design temperature – 10.6℃

Cooling design temperature – 31.6℃

Earth temperature amplitude – 9.5℃

Month

Air Temperature

℃

Relative Humidity

%

Daily Solar Radiation

kWh/m2/d

Atmospheric pressure kPa

January

16.0

73.0%

2.83

101.2

February

16.2

78.5%

2.61

101.1

March

18.8

82.0%

2.53

100.8

April

22.5

83.4%

2.97

100.5

May

26.2

83.4%

3.89

100.1

June

28.0

82.7%

4.14

99.8

July

29.0

81.3%

5.03

99.8

August

28.7

81.6%

4.44

99.7

September

27.8

78.6%

4.17

100.1

October

25.4

73.5%

4.03

100.6

November

21.6

70.2%

3.33

101.0

December

17.8

67.5%

3.00

101.3

Annual

23.2

78.0%

3.59

100.5

Month

Wind Speed

m/s

Earth Temperature

℃

Heating Degree-Day

℃-d

Cooling Degree-days

℃-d

January

2.9

17.2

62

186

February

3.2

18.4

50

174

March

3.4

21.1

273

April

3.3

24.0

375

May

3.0

26.2

502

June

3.0

27.5

540

July

2.7

28.0

589

August

2.4

27.9

580

September

2.6

26.7

534

October

3.4

24.9

477

November

2.9

22.0

348

December

2.7

18.3

6

242

Annual

3.0

23.5

118

4,820

Month

Daily Solar Radiation

Horizontal kWh/m2/d

Daily Solar Radiation

Tilted kWh/m2/d

Electricity Export Rate $/MWh

Electricity exported to Grid MWh

January

2.83

3.17

1.376

February

2.61

2.75

1.083

March

2.53

2.60

1.123

April

2.97

2.96

1.217

May

3.89

3.79

1.574

June

4.14

3.98

1.586

July

5.03

4.83

1.982

August

4.44

4.38

1.786

September

4.17

4.26

1.688

October

4.03

4.34

1.788

November

3.33

3.72

1.516

December

3.00

3.45

1.482

Annual

3.59

3.69

0.00

18.181

Meanwhile, The RETSceen software also simulates the Emission Reduction for the project. In the emission reduction analysis, the calculation is based on the Hong Kong GHG emission factor which is 0.685 tCO2/MWh. As the photovoltaic electricity result, it is 18.181MWh. So the net annual GHG emission reduction is 12.6 tCO2.

3.6 Installation Details of Photovoltaic System

Referring to the captioned project, the total 60 nos. photovoltaic system rated at 15kW peak (PV type) is gird-connecting to the electric company, The Hong Kong Electric Co. Ltd. (HEC) power network. 20 nos. of strings in parallel is supply for the phase power. The irradiance sensor and surface temperature sensor are installed at the PV frame bracket to measure the relevant data immediately. 2.5mm sq. XLPE LSOH armoured cable will connect from PV panel to array combiner box. The anti-islanding protection of the photovoltaic system will be tripped within 0.2 sec if the grid supply is interrupted. Before the power on the system and connect to HEC power grid, the owner should be submitted the application form to HEC include the schematic wiring diagram, summation meter scheme and grid connection of photovoltaic system submission. Before the inspecting and testing by HEC, the relevant system had applied to power on and the HEC will issue the permit for the relevant photovoltaic system accordingly.

Schematic Wiring Diagram for Photovoltaic System

The photovoltaic panels are installed at roof floor and installed on the PV frame bracket which are facing south with inclined angle of 15℃.. The DC/AC inverter and the array combiner box are installed at the PV plant room. The data will collect together and transmit to the CCMS for the monitoring and controlling at CCMS Room. The relevant data will display for public and update at 15 minutes at the G/F Main Lobby.

Photovoltaic panel installed at Roof Floor

Chapter 4 Results and Discussion

The chapter describes the collection results of the photovoltaic system. The data compare with the simulation report. Meanwhile, it describes the feasibility and suitability of the photovoltaic system development in Hong Kong

4.1 Collection Data of Photovoltaic System

In the case study, Hong Kong Customs Headquarters Tower, we recorded the relevant photovoltaic system data by CCMS such as PV system amp, volt, and power factor, total, kW, total kVA, frequency, output power and so on from 1 July 2011 to 1 July 2012 which stored on the server. According to the collection data, the photovoltaic system was produced the electric about 19.78MWh in this time.

4.2 Cost Study of Photovoltaic System

Item

Qty

Unit Price HK$

Amount HK$

PV Module

60 Nos.

12,310.00

738,600.00

Array Combiner Box

3 Nos.

5,000.00

15,000.00

DC to AC Inverter

4 Nos.

36,410.00

145,640.00

SMA Interface Controller

1 No.

14,890.00

14,890.00

PV Graphic Base Management System

1 No.

11,430.00

11,430.00

Anti-Islanding Protection Circuit

1 No.

28,580.00

28,580.00

Dual Redundant PLC Controller

1 No.

98,370.00

98,370.00

High Level Integration

1 No.

42,600.00

42,600.00

Engineering Work for Design, Submission, Approval, Project Management and T&C work

1 Lot

179,420.00

179,420.00

Electrical Installation of PV Module with Solar Cable Installation Labour Work

1 Lot

186,670.00

186,670.00

Supporting Framework

1 Lot

245,000.00

245,000.00

Budget Cost for the Employment of RSE for Structure Calculation

1 Lot

37,500.00

37,500.00

Total

1,743,700.00

Based on the final account record; the total cost of photovoltaic system is HK$1,743,700.00 for the building and the electric tariff for the building is refer to the HEC commercial, Industrial & Miscellaneous Tariff which is shown on HEC website. The net rate is 144.6 cents/unit. The unit is mean the kilowatt hour for this situation. From our collection data, the deduction of the photovoltaic system is amount to 19.78MWh which is HK$28,681.88 per year.

Consumption

Basic Charge

(Cents/Unit)

FCA

(Cents/Unit)

Net Rate

(Cents/Unit)

For each of the first 1,500unit

94.6

37.0

131.6

For each of the next 18,500 unit

105.1

37.0

142.1

From 20,001 units and above

107.6

37.0

144.6

“Unit” means kilowatt hours, “FCA” means Fuel Clause Adjustment

Commercial, Industrial & Miscellaneous Tariff by HEC

As a result, the payback period should be needed about 61 years in the building exclude any maintenance and repair cost.

4.3 Discussion of Photovoltaic System

Essentially, the photovoltaic system is the good renewable energy source and it also can improve the air pollution. But, as our case study result reflect that it need a very long payback period and don’t more efficiency in Hong Kong.

My point of view is that the urban area of Hong Kong has the highest population and employment density in the world. Some areas may have population densities of more than 500,000 people per square kilometer. The high price of land in Hong Kong also contributes to its high density development. Meanwhile, Hong Kong is developed a major commercial and financial centre in Asia. It has increased through new buildings on reclaimed land and the redevelopment of old buildings into new office blocks. Although there is an increase in employment density. The photovoltaic system also can install at roof floor only. But the cross section area of the roof floor is very restricted. It only can install about 60-100 nos. of photovoltaic panel normally. For this reason, many commercial companies are not willing install the photovoltaic system in their buildings because of the long payback period and low efficiency of the photovoltaic system. They will not pay the huge cost to install the system.

Therefore, the photovoltaic systems are also installed on the government building recently. It is because the Hong Kong Government has obligation to improve the air pollution and implement the environmental policy such as the renewable power source.

So that the new building will also contain at least 2 nos. of renewable energy system such as photovoltaic system, solar water system, winds power and so on.

Finally, the photovoltaic system is good renewable system at the world, but it is not suitable for Hong Kong and other high density countries. It is because these countries have not the enough land to install many photovoltaic panels.