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PV Solar Energy Generation and Utilization

2014

 

TOPICS: 2.2 - PV Technology Background, 3 – Design strategies, 4.1- The principal types of PV installation options to the building, 6- Advantages and Disadvantages in Relation to other Renewable Energy Sources, 7- Price, Market and Manufacturers, 8-  Conclusion

1-Introduction

 

Solar radiation as a renewable energy source has one of the highest energy potential compared to wind power, biomass, geothermal energy and oceanic energy water power. (7) Because of the exposed abundance of free unlimited energy source, photovoltaic (PV) has great importance to convert this source of energy into our electricity demand.

 

This particular report starts with the overview of photovoltaics, including the explanation of types of solar cells within the years. Afterwards, the design concept for PV in construction will be examined. The main parts of PV system, the types of installation methods and the PV installation options for building will be highlighted. The report will be followed by the information of required maintenance works for PV, the key advantages and disadvantages in relation to other renewable energy sources and the current market and manufacturers.

 

2 - Features of Photovoltaics

 

PV is a technique of generating electricity by transforming solar radiation into direct current electricity. PV power generation consists of solar panels with solar cells which comprised of semiconductors that display photovoltaic effect. And, PV as a sustainable energy source is a fast growing sector, which has increased its power capacity %36 in 2013. It equals a total of 136 GW worldwide. (1)

 

2.1 - How a PV system works

 

Silicon material as a semiconductor element can be used to generate energy. However, pure silicon is not a conductive material, through the addition of “other elements to its crystalline structure” can become conductive material as known as ‘“n-type” or “p-type”’ silicon. (2) (Figure 1)

 

As shown in Figure 1, every phosphorous nucleus contains extra electron in its lattice. This electron can move in its boundary independently and therefore carries an electric charge. Conversely, in boron nucleus, there is a hole in every boron atom in its lattice. Electrons from adjacent atoms can move and fill the hole from one to another atom in its lattice. (3) 

  Crystalline Silicon cells: Solar cells are produced from crystalline silicon. And approximately %85 of solar cells is being used around the world market. However, silicon is as an element after oxygen is the second most abundant source on the Earth; it is not in pure form in the nature. The silicon was obtained from semiconductor industry waste for a long time. But, the increasing demand and search in advanced quality in solar cell can no longer meet by the industrial waste. Therefore, the solar cell industry has developed and established its own production units. Accordingly, monocrystalline and polycrystalline types of silicon due to the different methods have become useful to manufacture solar cells, which have in individual 0.2 mm thickness and 150-156 mm length. (3)(7)

 

Thin-film solar cells:  This type of cells technology is called as the “second generation of solar cells.” The main differences between crystalline silicon cells and thin-film cells can be noted as the thickness is much more smaller, the manufacture process requires less material and energy (lower cost), larger design potential and utilization of variety of compound 

in the production such as amorphous silicon (a-Si), cadmium telluride (CdTe) and compound of  copper (Cu), indium (In), selenium (Se) or sulphur (S) and in some circumstances gallium (Ga). (7) However, the typical module efficiency of thin-film solar cells are around %5-11 require 9-20 m2 area per kilowatt peak power(kWp) in comparison with the efficiency of silicon cells varies between %11-18 and require 6-10 m2/kWp according to the research before 2009. (12) 

 

Nano-solar cells: The Biomimicry of natural process on the basis of observing energy through sunlight in other word photosynthesis underpins the nano-solar cell production ideology. Simultaneously, the aim of “solar paint” can turn all around the façade of building into the energy generation unit. However, one of the problems is that long-lasting binding of the “electrolytes” has to be tackled. Nevertheless, the first marketable product is introduced and centred on the ink with copper indium selenide (CIS) nano particles are printed onto a largely conductive aluminium foil through roll-to-roll procedure. (7) 

 

After the p-n type silicon are combined together as shown in Figure 2,  if this combination (solar cell) is exposed to the light, the electrons in the N-type silicon atom absorb the energy of light. Hence, the gained energy from the light breaks the electrons bond in the N-type silicon. The flow of the released electrons from N type silicon to the P type silicon creates electricity through the connection of circuit and an inverter. This process, in whole, is also called as the photovoltaic effect. (3)

 

2.2 - PV Technology Background

 

The development behind PV technology has gradually increased and become complex since Alexandre-Edmund Becquerel discovered the photovoltaic effect at the first time in 1839. The history and the recent expectations towards PV technology after 1960 can be divided into four stages. And each stage covers around 20 years. (5)

 

1960 – 1980: PV technology has been placed to the satellites in the beginning of 1960s. The companies from USA, Germany and Japan are respectively Tecstar, AEG and Sharp that were the primary PV panel production companies in this area. The Solar Energy Research Institute (SERI) later as National Energy Laboratory (NREL) was opened in 1977 in the USA to conduct research. (5)

 

1980 – 2000: With the aim of PV technology utilization for land use, enormous research, development and investment has been delivered at this stage. To manufacture solar cells and modules, experimental developments were examined. For example, “6 MW Carrisa Plains plant” in the USA has set up in the beginning of 1980s.  Afterwards, commercial actions on PV technology has increased at first in the USA, and then followed by Germany and Japan. The total installed PV power in the world has reached over 1 GW energy generation capacity in 1999. (5)

 

2000-2020: This stage can be called as “transition” stage. The increasing awareness of PV technology and the

prior political regulations, has accelerated the PV “cost effectiveness” in all marketable sector. With the main contributor markets in Germany, USA, Japan and Spain, new markets from Asia and other countries of Europe and America will appear to be the part of this development. (5)

 

2020 – 2040: In this last stage, generation of electricity by PV systems, in the end will be recognized throughout the world market. As a result of global supplement and hence decreasing prices, energy generation through PV systems will become as reasonable as the major conventional energy sources. (5)

 

2.3 - Developments in Solar cell

 

At the same time, the development regarding to the solar cells has been increased since the 20th century.  As the technology towards solar cells continues to improve, the studies and enhancement move forward. As a result of the developments, solar cells are improved due to the efficiency, size and cost. (6) The solar cells can be classified into three groups. (Figure 3) In principal, cell types are divided into two groups as: the conventional crystalline silicon cells and the newer thin-film solar cells. However, nano solar cells can be included in this classification upon recent progressive advancements. (7)

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3 – Design strategies

 

The variety of design strategies for building-fixed PV technology is available in the market. And the examples of the structures can be seen around the world. There should be noted that the integration of architecture and construction are totally different terms. But, the adoption of energy generation to this structure will create a functional overall effect to the aspect of building. (7)

 

Balance of system equipment (BOS): The system involves “installing systems and wiring systems” that provides to place the solar panels to the structure and electrical systems of the house. In general, wiring systems cover “direct current (DC) - alternating current (AC) inverter, ground-fault protection and overcurrent protection for the solar modules.” (16)

 

DC-AC Inverter: This device basically converts the DC power received from PV panels to the AC power in order to use the power in the house. (16)

Maximum Power Point Tracking (MPPT): Is an electronic typically digital tracking. It examines the obtained output of PV and battery voltage automatically. Accordingly, it converts the power into the best voltage that can deliver maximum Amperage (AMPS) to the battery, which improves the efficiency.  (17)

Metering: Indicates the system performance and the house energy consumption. (16)

The battery backup system has additional devices in relation to absorb the generated surplus energy. (Figure 5) The PV system can work more self-sufficient through battery adopted PV system. Because, during daylight hours, PV can supply the required energy both for house demand and battery charge. During the night, the charged battery can supply the house energy demand as long as the capacity of the battery permits. (16)

 

c) Off-grid installations: rooftop-mounted and/or small-scale solar farms (remote communities): The term of off-grid system can be called as “stand-alone systems (SHS)” that enables electricity without dependence on the grid. (18) The type of PV with battery backup system is required.

d) Off-grid installations: Low-maintenance lighting and communications (e.g. Road signage, path marking): The variety of PV system applications is possible to use in a daily life.  For instance; in transportation as solar vehicles, standalone devices such as parking meters and in rural electrification as solar lantern. (19)

 

4.1- The principal types of PV installation options to the building:

 

The PV systems can be installed in the structure element roof, façade and sunshade. The design and the placement of the PV system to the building can vary regarding the architectural prospect.

Façade installation: By the PV technological development against energy generation in the building, the façade surface is available to generate energy rather than providing passive solar gain to the house. In the northern hemisphere, south facing cold façade is convenient for PV installation. The cold façade surface can be enabled with the ventilation cavity which contributes to the higher energy generation of PV system since the increase in temperature reduces solar cells’ efficiency. The decision of installation of PV to the façade should be considered at the design stage of building to organize this with the layout of the building. The manufacturers can offer a range of colour for solar cell production, according to the architectural view. However, this process may increase the cost of the construction budget. (7)

 

 

Sunshade installation: Sun shading and PV elements have a great combination. Shading primary property is to keep away the direct sunlight. At the same time, the placement of PV as sunshade can generate the energy while it protects the house from direct sunlight and overheating. Sunshade installations are divided into two groups: fixed systems and movable systems as shown in Figure 6. However, the mixture of both systems in the same building is also applicable. Movable systems compared to the fixed systems have greater advantage that enable to take solar power better through adjusting its slope of sunshade PV systems according to the elevation of the sun throughout the year.  (7) 

 

5- Maintenance of PV systems

 

Since each device of the PV system connected to each other to transfer convenient electricity, the maintenance of each element has the same importance on the basis of optimum and safe energy generation. At the same time, the maintenance cost is considerably lower compared to the existing power stations. (1) The main components of a PV system: Battery, solar panels, charge controller, inverter, wiring and connections maintenance shortly: (23)

 

 - Battery Maintenance:

 

  1. Checking and frequent cleaning

  2. The level of electrolyte controlling (not necessary if Gel Batteries)

  3. Maintain at a high level of charge (23)

 

- Solar panels Maintenance:

 

  1. The panel should be cleaned with water. If there is dirt on the surface should be used a sponge, without using metal brush and detergents

  2. During a visual inspection, if there is an apparent defect found, the position should be noted in the “system logbook” for further investigation in the future.

  3. The assembling elements of PV panels should be checked if rusted or in good condition. (23)

 

- Inverter and wiring and connections Maintenance:

 

  1. Minimizing the dust on these components and keep these components clean through a dry cloth.

  2. All the indicators for instance “LED lights” and also the length of wires should be checked if it is loose.

  3. If the charge controller does not show the system is charged during the sunny day then, should be contacted to the “installer”. (23) 

6- Advantages and Disadvantages in Relation to other Renewable Energy Sources

 

The advantages:

  • After primary “capital cost” of the construction of the PV panel system, operational cost is substantially low, which can generate free unlimited source of energy for 100 years or even more. (19) In comparison with other renewable energy sources, since wind turbines have mechanical moving parts, it has greater cost for maintenance. (24)

  • PV panels have large potential to be the leading renewable energy power in the future since the cost of solar panels decreases as well as the efficiency of solar cells improved up to %44. 4. (24) (Appendix B) At the same time, “the thermal efficiency of geothermal electric plants” is low as around 10-23%. (25) And according to the Betz’ law the maximum feasible “extraction of wind power by a wind turbine as 59% of the total kinetic energy of the air flowing through the turbine.” (26) 

  • The installation of PV system can be thought on a massive scale as construction of giant solar power stations; on the other hand, it can be applied on a small scale and variety of ways, such as, calculator, street lighting and vehicles without noise, which makes solar power flexible, practical and easily adaptable to the existing environment. On the basis of adaptation to the environment, solar panels are virtually more acceptable compared to wind turbines.

 

The disadvantages:

  • The necessity of land is important for large PV systems. More energy generation can be possible simply with more land occupation with PV panels. Because of this, the land cannot be used for any other purposes. (24) Conversely, in wind power station, the land can be still used for example; for agriculture.

  • The necessity of additional tools (inverters) to convert the generated electricity from DC to AC. (24) This may cause to establish a more complex system and result less energy efficiency.

  • There is no possibility to generate constant energy because of night time as well as cloudy or rainy days. Therefore, energy generation is periodically in PV systems. (24) In contrast, wind or geothermal energy sources have no related problem.

Subjugation: The aim of this type of concept is to purely generate electricity without considering any architectural appearance of the structure. The installation can be placed on or in front of a building and can be detached and transport for the same reason to another structure. (7)

Domination: The construction design is affected and combined fully with PV systems that largely influence the appearance of the building in this “domination” type of design concept. Therefore, PV systems in this concept have an indicative function on the appearance of structure on the basis of colour, shape, size and planning. (7) The location, orientation and the tilt of the roof are the major factors determining the rate of energy absorption from the sun that should be analysed well at the design stage of the structure.

Integration: PV systems and the structure are in harmony and they are the parts of the “symbiotic system”. The function of solar panel is not only providing required electricity, but also it fulfils the architectural expectation and other purposes of the building framework. For example, sun shading and roof protection. (7)

Subordination: The embedded solar cells into the structure that makes the electrical system hardly visible. This type of concept brings the possibility of electricity generation without changing the original appearance of the structure. Because of this reason, the concept application can be more useful for the ancient and historical structures since it does not affect the characteristic view of those structures. (7)

Imitation: The imitation concept aims at finding ways to copy the conventional role of construction. The replacement of the existing units with the new types will provide renewable energy rather than only constructional function. (7)

 

4- Types of Installation

 

The type of installation of PV system can be divided into four, according to the connection to the grid and the utilization area. (13)

a) Grid-connected PV systems: These systems are linked to the “utility grid” and comprises of “PV panels, maximum power point tracking (MPPT), solar inverters, power conditioning units and grid connection equipment.” For example: Solar power stations. (14) One of the biggest solar power stations is in the USA, Topaz Solar Farm with its 300 MW power capacity. (15)

 

b) Grid-connected, installed on domestic and industrial rooftops: The solar energy benefit in a small scale can be obtained. During the extensive generation of solar energy, the surplus electricity is transferred to the grid, conversely, during the cloudy day; the required energy can be delivered from the grid. Therefore, the maximum efficiency and minimum waste of energy balance can be reached through this type of installation. (14)

 

In addition, there are typically two types of PV systems are used for houses: Grid-connected without battery backup and with battery backup. The sequence of both system designs can be seen below Figure 5. (16)

 

The main system components:

PV Array: consist of solar cells, which are placed on to the PV modules. Generally, the PV module has 5-25 square feet (0.15 – 0.75 m2) in size and around 3-4 lbs/ft2 (4.5 – 6 kg/m2) weight. These modules are usually placed together and connected to each other, which creates solar panel. (16) 

Roof installation: If the PV installation fixed above the existing building without any function for the structural load or building envelope, it is classified as stand-off systems. In contrast, in the integrated system, the PV panels take place the roof element completely. Because of this reason, the system has to ensure both energy generation and stability and strength in order to transfer or carry the load. (7)

 

Basically, in the northern hemisphere, south-facing and 30° angle is the ideal method for installation of PV for the solar energy generation effectively throughout the year. However, the efficiency changes approximately %10 between horizontal installation and ideal orientation with the angle. (7)

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9-References

 

  1. Wikipedia, the free encyclopedia. (2014). Photovoltaics. Available: http://en.wikipedia.org/wiki/Photovoltaic. Last accessed 08/05/2014.

  2. From Computer Desktop Encyclopedia TechBites Interactive. (2008). n-type silicon. Available: http://www.answers.com/topic/p-type-silicon. Last accessed 08/05/2014.

  3. The German Energy Society (2008). Planning & Installing Photovoltaic Systems. 2nd ed. London: Earthscan. p20- 21, 23.

  4. Eco2solar. (n.d.). How does Solar PV work. Available: http://eco2solar.co.uk/solar-electricity/how-does-solar-pv-work/. Last accessed 08/05/2014.

  5. Petrova-Koch, V., Hezel, R. and Goetzberger, A. (2009). High-Efficient Low-Cost Photovoltaics. Berlin: Springer-Verlag. p18-19, 42.

  6. Shahan, Z.. (n.d.). Solar Panel Efficiency Has Come A Long Way (Infographic). Available: http://cleantechnica.com/2014/02/06/technological-advancements-drove-solar-panel-prices/ . Last accessed 08/05/2014.

  7. Weller, B., Hemmerle, C., Jakubetz, S. and Unnewehr, S. (2010). Photovoltaics Technology Architecture Installation. Munich: 1st ed. Detail. p7, 14-17, 40-41, 50, 55, 62, 66-67.

  8. Sidhu,R. and Carlson, E. D.. (2010). Crystalline Silicon Solar Cell Technology. p13. Available: http://www.lesker.com/newweb/news/jpg/bpsolarsidhu_4-13-2010.pdf. Last accessed 08/05/2014.

  9. tradeindia.com. (n.d.). 144W Thin Film Amorphous Silicon Flexible Solar Panels. Available: http://www.tradeindia.com/fp882650/144W-Thin-Film-Amorphous-Silicon-Flexible-Solar-Panels.html. Last accessed 08/05/2014.

  10. CdTe-solar module (Empa). (2011). Efficiency record for flexible CdTe solar cell due to novel polyimide film. Available: http://phys.org/news/2011-06-efficiency-flexible-cdte-solar-cell.html. Last accessed 08/05/2014.

  11. Nano.gov. (n.d.). Nanotechnology & You - Benefits and Applications. Available: http://www.nano.gov/you/nanotechnology-benefits. Last accessed 08/05/2014.

  12. Roberts, S. and Guariento, N. (2009). Building Integrated Photovoltaics. Basel, Boston, Berlin: Part of Springer Business Media. p21.

  13. Reynolds, S.. (n.d.). Photovoltaic Technologies., University of Dundee. p7.

  14. Wikipedia, the free encyclopedia. (2014). Grid-connected photovoltaic power system. Available: http://en.wikipedia.org/wiki/Grid-connected_photovoltaic_power_system. Last accessed 08/05/2014.

  15. Wikipedia, the free encyclopedia. (2014). List of photovoltaic power stations. Available: http://en.wikipedia.org/wiki/List_of_photovoltaic_power_stations.  Last accessed 08/05/2014.

  16. Endecon Engineering 347 Norris Court San Ramon, California 94583 and Regional Economic Research, Inc. 1104 Main Street, Suite 630 Vancouver, Washington 98660 . (2001). A GUIDE TO PHOTOVOLTAIC (PV) SYSTEM DESIGN AND INSTALLATION - CONSULTANT REPORT. p5-6. Available: http://pdf.wholesalesolar.com/guide.pv.installation.pdf.  Last accessed 08/05/2014.

  17. Northern Arizona Wind & Sun - Electricity. (n.d.). ALL ABOUT MAXIMUM POWER POINT TRACKING (MPPT) SOLAR CHARGE CONTROLLERS. Available: http://www.solar-electric.com/mppt-solar-charge-controllers.html.  Last accessed 08/05/2014.

  18. Wikipedia, the free encyclopedia. (2014). Stand-alone power system. Available: http://en.wikipedia.org/wiki/Stand-alone_power_system. Last accessed 08/05/2014

  19. Wikipedia, the free encyclopedia. (2014). Photovoltaics. Available: http://en.wikipedia.org/wiki/Solar_photovoltaic_panels#Applications.  Last accessed 08/05/2014.

  20. The Telegraph. (n.d.). BP: a history in pictures. Available: http://www.telegraph.co.uk/finance/newsbysector/energy/oilandgas/5933200/BP-a-history-in-pictures.html?image=15.  Last accessed 08/05/2014.

  21. ET18/November 2008. (2008). Peter Kulka Architektur: Fire station, Heidelberg, Germany.. Available: http://www.architecturetoday.co.uk/?p=5018.  Last accessed 08/05/2014.

  22. DAMS Incorporated - Architectural Metals. (n.d.). Utah State University College of Agriculture – Photovoltaic Sunshades. Available: http://www.damsinc.com/portfolio/usu-via-bipv/.  Last accessed 08/05/2014.

  23. Tetra Tech Inc.. (2013). SOLAR PV SYSTEM MAINTENANCE GUIDE . Available: http://www.poweringhealth.org/Pubs/Guyana_Solar_PV_Systems_Maintenance_Guide.pdf.  Last accessed 08/05/2014.

  24. Green, D. . (2012). Advantages and disadvantages of Solar Photovoltaic – Quick Pros and Cons of Solar PV. Available: http://www.renewableenergyworld.com/rea/blog/post/2012/12/advantages-and-disadvantages-of-solar-photovoltaic-quick-pros-and-cons-of-solar-pv.  Last accessed 08/05/2014.

  25. Wikipedia, the free encyclopedia. (2014). Geothermal energy. Available: http://en.wikipedia.org/wiki/Geothermal_energy. Last accessed 08/05/2014.

  26. Wikipedia, the free encyclopedia. (2014). Wind turbine. Available: http://en.wikipedia.org/wiki/Wind_turbine#cite_note-14.  Last accessed 08/05/2014.

  27. Schachinger, M.. (2014). Module price index April 2014: Little movement. Available: http://www.pv-magazine.com/investors/module-price-index/#axzz315BQ2iii. Last accessed 08/05/2014.

  28. Jäger-Waldau, A.. (2013). JRC SCIENTIFIC AND POLICY REPORT - PV Status Report 2013. p7. Available: http://iet.jrc.ec.europa.eu/remea/sites/remea/files/pv_status_report_2013.pdf. Last accessed 08/05/2014.

  29. Lian, R.. (2014). Top 10 PV module suppliers in 2013. Available: http://www.pv-tech.org/guest_blog/top_10_pv_module_suppliers_in_2013.  Last accessed 08/05/2014.

 

7- Price, Market and Manufacturers

 

The price of crystalline silicon solar cell has decreased from 76.7 $/W to an average 0.74 $/W between 1977 and 2013.  At the same time, the price of PV modules per MW has dropped by %60 from 2008 and 2011. (1) However, on a country basis over the last year, there are slight changes, according to the price of PV modules in the countries which are the most significant manufacturers of PV in the world.

 

According to the Figure 11, Germany is competing with the Korea and Japan in the last few months. However, the price of China, South and Southeast Asia are still cheaper than Europe and Germany PV modules. But, in overall, the price is very high to increase the demand of solar power. (27)

 

Figure 12 also indicates the obvious investment in PV manufacture across the world. China covers the main percentage of the production and it follows by Taiwan, Japan and Europe relatively. There is also a slight reduction in the production of PV in Europe from 2011 to 2012.  (28)

 

The first 10 PV module manufacturers in the world market in 2013:

 

- Yingli Green Energy (China)

- Trina Solar (China)

- Sharp Solar (Japan)

- Canadian Solar (Canadian)

- Jinko Solar (China)

- ReneSola (China)

- First Solar (USA)

- Hanwha SolarOne (Korea)

- Kyocera (Japan)

- JA Solar (China) (29)

 

8- Conclusion

 

Since the first generation and utilization of electricity from solar power, the development towards solar technology has been growing in particular, in the efficiency of solar cell, manufacturing in lower price and maintaining the harvested renewable energy from advanced batteries. At the same time, especially in recent years, the governments with their policies and regulations are also encouraging the utilization of renewable energies in order to minimize carbon emissions and climate change. And, solar energy generation is a promising technology that can be used in every area of life. Especially in the building, there are many varieties of installation methods of solar cells. But also, solar cells can be used in transportation and street lighting. As a result, the enhancement in solar power technologies will be boosted and become more widespread throughout the world.

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