Photovoltaic Solar Energy

You've seen the panels on rooftops and mirrors in the desert. But how much do you really know about the technology needed to capture the tremendous power of the sun?

1. What is photovoltaic solar energy?

   ‘Photovoltaic’ is an amalgam made of two words: photo - photon which means ‘light’ and voltaic from Volt which is the unit used to measure electric potential at a given point.

   Photovoltaic systems use cells to convert sunlight into electricity. PV cells can be made from various so-called semiconductor materials. Today, silicon is the most widely used material, but other, usually compound (made from two or more elements) semiconductors are also used. PV cells are silent and non-polluting and utilize a source of energy that is practically inexhaustible.

2. What difference is there between thermal solar energy and photovoltaic solar energy?

   A photovoltaic solar energy system converts sunlight directly into electric power to run lighting or electric appliances. A photovoltaic system requires only daylight (indirect sunlight) to generate electricity.

   The solar thermal energy system converts direct sunlight into heat. This thermal energy can be used to heat water or air in buildings and in many other applications.

   Both technologies use the irradiance of the sun even if they are quite different.

    

3. What is a photovoltaic (PV) system?

   A photovoltaic (PV) system is a system that uses solar cells to convert light into electricity.

   A PV system consists of multiple components, including cells, electrical connections, mountings and means that regulate and/or modify the electrical output. Due to the low voltage of an individual solar cell (typically ca. 0.5V), several cells need to be combined into photovoltaic modules which are then connected together in an array.

   PV systems can be used for homes, offices, public buildings or remote sites where grid connection is either unavailable or too expensive. PV systems can be mounted on roofs, integrated in building façades or operate as stand-alone systems. The innovative PV array technology and mounting systems mean that PV can be retrofitted on existing roofs or easily incorporated as part of the building envelope at the construction stage. Modern PV technology has advanced rapidly and PV is no longer restricted to square and flat panel arrays but can be curved, flexible and shaped according to the building design.

   Photovoltaic cells are equally used in many daily electrical appliances, including watches, calculators, toys, battery chargers, professional sun roofs for automobiles. Other applications include power for services such as water sprinklers, road signs, traffic signals, remote lighting and security phones.

   PV systems can be either grid connected or off-grid.

   “Grid connected” means that the system is connected to the electricity grid. Connection to the local electricity network allows any excess power produced to feed into the electricity grid and to sell it to the utility, depending on local feed-in regulations.

   Such a PV system is designed to meet all or a portion of the daily energy needs. Typical on-grid applications are roof top systems on private houses.

   The diagram shows how electricity generated by solar cells in roof-mounted PV modules is transformed by an inverter into AC power suitable for export to the grid network. The owner then has two options: either to sell all the output to the local power utility (if a FiT is available) or to use the solar electricity to meet demand in the house itself, and sell any surplus to the utility.

   “Off-grid systems” have no connection to an electricity grid. Off-grid systems are contributing to rural electrification in many developing countries. PV is also used for many industrial applications where grid connection is not possible e.g. telecommunications, especially to link remote rural areas to the rest of the country.

   

4. What is a PV system composed of?

   Elements of a grid-connected PV system are: PV modules - converting sunlight into electric power, an inverter that converts direct current into alternating current, sub-construction -consisting of the mounting system, cabling and components used for electrical protection and a meter to record the amount of electric energy fed into the grid.

   Off-grid (stand-alone) systems on the other hand, use a charge controller to charge a storage battery used for providing the electric energy when there is no sunlight, e.g. during night hours.

5. What is an inverter?

   Solar cells produce direct current (DC). However, most of the electrical devices we commonly use work with a standard alternating current (AC) power supply. An inverter converts the DC from the solar cells into a useable form of AC.

   An inverter is moreover necessary to connect a PV system to the grid.

6. What is net metering?

   Under a self consumption scheme, the consumer primarily uses the electricity generated by his PV system in his own home or office and sends any surplus energy to the utility grid for use by others.

   A bidirectional meter counts both the outgoing and the incoming energy flow. If the home or office requires more or less electricity than can be produced by the PV system, the balance is provided by the grid or the excess electricity is sold to the grid.

   With a net metering scheme, the utility company only charges the difference between the consumed energy and the produced surplus energy. In some countries, the surplus energy remains available for consumption for a limited amount of time and cannot be sold (you can’t have a ‘negative’ energy bill).

   In many countries the utility company purchases all PV electricity generated at a higher rate (FiT) than the tariff applied for consumed electricity. In this case, a dedicated metering exists for ‘PV generation’ and a second metering for ‘power taken from the grid’, applying a different tariff to each.

7. What is the Feed-in Tariff (FIT) and how does it work?

   Utility companies are legally obliged to buy electricity from renewable energy producers at a premium rate, usually over a guaranteed period, ensuring a reasonable rate of return for the producer. The extra cost is shared among all energy users, thereby reducing it to a barely noticeable level. In addition, FiTs often include ‘tariff degression’, a mechanism according to which the price (or tariff) ratchets down over time.

   FiTs have been empirically proven to generate the fastest, lowest-cost deployment of renewable energy. This way PV significantly contributes to combating climate change securing energy supply, not to mention creating jobs and competitiveness.
   
   The FiT system means that the pay-back time for PV is reduced significantly. Germany has a good example of a FiT in place, and the country is world leader in installed PV power.

   This financing model has now been taken up widely around the world, as the table below shows:
   
   Countries, states and provinces that have adopted FITs
   Year Cumulative number Countries/states/provinces added that year

   1978	1	United States
   1990	2	Germany
   1991	3	Switzerland
   1992	4	Italy
   1993	3	Denmark, India
   1994	8	Spain
   1997	9	Sri Lanka
   1998	10	Sweden
   1999	13	Portugal, Norway, Slovenia
   2000	14	Thailand
   2001	16	France, Latvia
   2002	20	Austria, Brazil, Czech Republic, Indonesia, Lithuania
   2003	27	Cyprus, Estonia, Hungary, Korea, Slovak Republic, Maharashtra, (India)
   2004	33	Italy, Israel, Nicaragua, Prince Edward Island (Canada), Andhra, Pradesh and Madhya Pradesh (India)
   2005	40	Turkey, Washington (US), Ireland, China, India, (Karnataka, Uttaranchal, Uttar Pradesh)
   2006	41	Ontario (Canada)
   2007	56	South Australia (Australia), Albania, Bulgaria, Croatia, Dominican Republic, Finland, Macedonia, Moldova, Mongolia, Uganda
   2008	69	Queensland (Australia); California (USA); Chattisgarh, Gujarat, Haryana, Punjab, Rajasthan, Tamil Nadu, and West Bengal (India); Kenya; the Philippines; Tanzania; Ukraine
   2009	80	Australian Capital Territory, New South Wales and Victoria (Australia); Hawaii, Oregon, and Vermont (USA); Japan; Kazakhstan; Serbia; South Africa; Taiwan
   2010	84	Bosnia and Herzegovina, Malaysia, Malta, United Kingdom

   Source: REN21, 2011FiTs can be shaped according to a country’s RE resources, its electricity distribution system and its RE targets.

8. Does PV technology need bright sunshine to work properly?

   A PV system needs daylight but not direct sunlight to work properly, however the power output is smaller. In fact, if a PV module is exposed to an artificial light source, it will also produce electricity.

   The light of the sun consists of both direct and indirect or diffuse light (which is the light that has been scattered by dust and water particles in the atmosphere). PV cells not only use the direct component of the light, but also produce electricity when the sky is overcast. It is a common misconception that PV only operates in direct sunshine and is therefore not suitable for use in temperate climates. This is incorrect: PV makes use of diffuse solar radiation as well as direct sunlight.
   
   The amount of useful electricity generated by a PV module is proportional to the intensity of light energy that falls onto the conversion area. The greater the available solar resource, the higher the electricity generation potential.

   Because the electrical output of a PV module is dependent on the light intensity to which it is exposed, it is certain that PV modules will tend to generate more electricity on bright days than when skies are overcast. Nevertheless, PV systems do not need direct sunlight to work, so even on overcast days a PV module will generate some electricity.

9. How much electricity can a PV system produce?

   The electricity production of a PV system depends on external (environmental conditions) and internal (technology, layout of the system) parameters.

   The production of a PV system depends on:

   • The power of the PV system
   • Orientation towards the sun
   • Geographic location
   • The tilt angle or inclination of the roof. For European countries, the average optimal inclination is 30°-35°
   • The irradiance (light intensity) value on site
   • The climate zone
   • The way how BIPV is structurally integrated in the building shell (ventilated/ non-ventilated)

   Shadows on the modules (even if they appear only at certain times of day) can reduce the gain of the whole system and should be avoided if possible.

   The map below represents the yearly sum of irradiation (‘raw’ solar energy) on a horizontal surface.
   Alternatively, the maps represent solar electricity (kWh) generated by a 1kWp system per year with horizontal (or inclined) modules.

   

   Source: http://re.jrc.ec.europa.eu/pvgis/countries/europe.htm

10. What does grid parity mean?

    In light of decreasing solar electricity generation costs and increasing price for conventional electricity, solar power systems will equally become increasingly economic during the coming years. Over the next 10 years solar electricity will become cheaper than retail electricity (depending on location and electricity prices) for end electricity consumers.

    A considerable advantage of solar electricity is that it is mainly produced around midday when conventional electricity is particularly expensive. Solar electricity largely replaces expensive peak-load electricity at preferential customer prices, which is why it would be wrong to compare it with cheap base-load electricity.
    
    Grid parity (competitiveness with retail electricity prices) will be reached progressively from 2013 onwards in several European markets. Countries with the highest solar irradiation and higher electricity prices, such as Italy and Spain, have the potential to reach grid parity starting in 2013 and 2015 respectively. Grid parity is likely to be reached in Germany and France in 2015 as well and cover progressively most other EU countries up until 2020.
    
    Grid parity is defined as the moment at which, in a particular market segment in a specific country, the net earnings  of the electricity supply from a PV installation is equal to the long-term cost of receiving traditionally produced and supplied power over the grid. In other words, Grid parity is the moment at which it is equivalently profitable for an end consumer to buy a PV System and produce his own electricity without any direct incentives (FIT or net metering) than buying electricity from the grid over 25 years.

11. Do PV modules lose efficiency each year?

    The degeneration of PV modules varies according to the type of PV modules installed. The loss of power production during a life cycle of 20 to 25 years is estimated to be 10 to 20% for crystalline PV modules.

12. What is the carbon footprint of a PV system?

    When measuring the environmental impact of a product, it is important to take the direct and indirect impacts throughout the entire product life-cycle, from material sourcing, through manufacturing, transportation, construction, operation, dismantling and to product collection and recycling into account.

    PV systems have a very light carbon footprint; they have no direct CO2 emissions into air during operation. Small, indirect emissions are mainly linked to the energy required during the manufacturing process of the PV module. This depends on the amount of energy consumed during manufacturing and on the electricity mix (i.e. gas, fuel, nuclear, hydro) at the production sites. Other small indirect emissions are connected to the technical greenhouse gases used as process gases when manufacturing the PV module, its components or the manufacturing equipment.

    The carbon footprint (g CO2eq/kWh) will depend on the lifetime and the conversion efficiency of the PV system, the system design and its orientation, in addition to the solar irradiation where the relevant system is installed. Annual solar horizontal irradiation varies from approximately 800 kWh/m2 in Northern Germany to approximately 1700 kWh/m2 in Southern Italy and even up to 2500 kWh/m² (II) in the “Sunbelt area” resulting in higher electricity output for the same initial carbon input.

    The carbon footprint of PV systems - assuming a location in southern Europe - ranges from 16 to 32 gCO2 eq. per kWh compared to between 300 and 1000 g CO2 eq. per kWh when produced from fossil fuels.

    

13. Is it worthwhile using solar energy in Europe?

    Definitely! In Germany, for example, the average of the annual solar irradiation is 1000 kWh per square meter. With efficient solar power systems, this is sufficient to generate a considerable volume of electricity and heat from solar power.

    Unlike other electricity generation technologies, solar is a highly modular electricity generating technology, scalable to powers suited for a single household up to large-scale ground-mounted installations.
    
    Small-scale PV electricity in central Europe is up to twice as costly as large-scale PV electricity in southern Europe due to the combined benefits of economies of scale of large systems and higher irradiation in the South. Nevertheless, small-scale domestic 'northern' PV is today as cost-effective as large-scale 'southern' PV when incorporating the cost to deliver it to the domestic consumer.
    
    PV will become soon a competitive solution where it is needed (i.e where electricity is consumed).
    
    Hence it is worthwhile producing solar energy in Europe, not least because this makes Europe less dependent on energy imports but also because:

    • The fuel is free
    • It produces no noise, harmful emissions or polluting gases
    • PV systems are very safe and highly reliable
    • It brings electricity to remote rural areas
    • The energy pay-back time of a module is constantly decreasing
    • It creates thousands of jobs
    • It contributes to improving the security of Europe’s energy supply

14. Can renewable energy sources guarantee a secure power supply despite their dependence on the weather?

    Can renewable energy sources guarantee a secure energy supply despite their dependence on the weather?

    The best way forward to ensure a secure energy supply for the future is an energy mix of renewable energy sources and intelligent load management (smart grids) in combination with energy storage. This will enable renewable energy sources to ensure a secure, climate-friendly and sustainable energy supply.
    
    Solar power is particularly available during periods of peak load demand (midday and in summer) and is excellently complemented by wind power, where peak values are principally reached in winter. Further to this, biomass, hydropower and geothermal energy are continually available and counterbalance deficits.

15. What is the lifetime of a PV system?

    The estimated lifetime of a PV module is 30 years. Furthermore, the modules’ performance is very high providing over 80% of the initial power after 25 years which makes photovoltaic a very reliable technology in the long term.

    Most manufacturers in general propose performance guarantees on the modules after 20 years of 80% of the initial output power. As regards the electronic components and accessories (inverters), the guarantee usually does not exceed 10 years.

    But this doesn’t mean that PV systems do not produce energy after 20 – 25 years.

    Most PV systems installed more than 25 years ago still produce energy today!

16. What if there is a problem with the PV system?

    If a PV module has a defect, no longer produces electricity or produces much less electricity than before, it is generally covered by the manufacturer’s performance guarantee against a drop in efficiency of more than 20%.

    Most manufacturers indeed propose performance guarantees on modules of 20 and 25 years for 80% of the initial output power. On the electronic components and accessories (inverters), the guarantee usually does not exceed 10 years, although longer inverter insurances can be arranged.

17. Is solar energy more expensive than conventional energy?

    In the light of decreasing solar power generation costs and increasing costs for conventional electricity (due to oil and gas prices), solar power systems will become increasingly economic during the coming years.

    A considerable advantage of solar power is that it is mainly produced during the day when the demand is high and therefore conventional electricity is particularly expensive. Another important feature is that PV is normally produced close to demand; therefore, a high investment on extending the electricity infrastructure is not required.

    In the long term solar energy will be much cheaper than conventional energy. Nowadays, like all energy production technologies (coal, gas, nuclear etc.) in the past and present, solar energy still needs financial support to further develop the technology and thus reduce prices to become competitive.

    However, solar energy is already well on the way: whereas the costs for conventionally generated energy have constantly increased in recent years and – faced with finite resources – will continue to increase by a considerable extent, increasing mass production has enabled the cost of solar energy to drop by an average of more than 10% per year.

18. What contribution can solar electricity play world-wide with regard to total energy consumption?

    The solar PV market has been booming over the last years despite a dip in 2009. By the end of 2010 the global cumulative capacity was about 69.4 GWp, with 29.4 GWp added just in 2011.

    In the long term it is estimated that solar power could contribute to an increasing share of total energy consumption. With appropriate policies both in developed and developing countries, the European Photovoltaic Industry Association (EPIA) and Greenpeace have devised that in a joint scenario photovoltaic systems could produce enough energy to supply electricity to 3.7 million people globally by 2030.

    The Solar Generation report published by Greenpeace and EPIA in February 2011 concludes that solar electricity can contribute largely to the energy needs of two-thirds of the world’s population - including those in remote areas - by 2030.

    The report confirms the impressive growth of the solar energy sector and demonstrates its potential of becoming a global energy contributor. It estimates that over 1800 GW of photovoltaic systems will have been installed worldwide by 2030, which represents over 2600 TWh of electricity produced per year or 14% of global electricity demand.

    In theory, every country could provide for its own energy needs from local renewable energy sources many times over.

19. Can the solar industry also grow without government subsidies?

    Public incentives will no longer be required to help the development of energy produced by photovoltaic means in the long run/

    The solar industry will be capable of generating a high degree of growth without government subsidies in the foreseeable future.

    With increasing sales leading to economies of scale and efforts realized by producers to reduce the cost of photovoltaic products, it is expected that costs for photovoltaic energy will be competitive with electricity prices in southern Europe by 2015 and in most of Europe by 2020.

    Until then, the market introduction of solar energy is dependent on statutory frameworks if it is to become competitive and survive in the global market. The industry will require investment security for developing solar power manufacturing plants and for their high development input and, until then, consumers will require legally secure incentives to invest in installing solar systems. The cost reduction can be achieved through research development and large-scale implementation with cost-effective financing instruments.

20. What are Green Certificates?

    Green Certificate, also known as Renewable Energy Certificate (REC), is a tradable commodity certifying that a certain amount of electricity (normally sold to the customer) is generated using renewable energy sources. The following sources are considered as renewable: wind, solar, wave, tidal, geothermal, hydro and biomass Typically, one certificate represents the generation of 1 MWh of electric energy.

    Green Certificates represent the environmental value of the renewable energy generated. The certificates can be traded separately from the energy produced. Several countries use Green Certificates as a means to bring the support of green electricity generation closer to market economy instead of more bureaucratic investment support and FiTs. Such national trading schemes are in use for PV in e.g. Poland, Sweden, Belgium (Wallonia and Flanders), and some US states.

    In practice, producers, wholesalers, retailers or consumers (depending on who is obliged) can be obliged to supply or consume a certain percentage from renewable electricity sources. For each unit of renewable electricity (e.g. MWh), a certificate is granted to the producer.

    This certificate serves as proof that renewable electricity was delivered into the grid.

    The graph below shows the costs per MWh versus the certificate value. Some technologies will be excluded from a Green Certificate market, while mature technologies are stimulated (only fictitious values are used to show the impact).

    Unlike the FiT, specific for each technology, a Green Certificate has no technology-specific price.

    Instead of compensating specific generation costs of the technology, a number of technologies will generate windfall profits, meaning that the compensation is higher than their actual generation costs.

    

21. How long will the development of PV depend on FiTs?

    The major challenge for the renewable energy industry in general has been to make the cost of clean energy competitive with conventional energy. Householders or energy companies who wanted to install wind turbines or solar panels have been faced with lengthy pay-back times.
    Without increased consumer demand and political measures to facilitate access to the market, manufacturers of solar photovoltaic (PV) panels cannot produce the unit volumes that would be needed to bring prices down and drive technological innovation.

    The FiT has proven to be the most effective policy instrument in overcoming these barriers.
    The FiT allows the pay-back time for PV to be only years instead of decades (see also Q.7).
    In 2011, the majority of installed PV systems benefited from well-designed grant support, in particular the FiT mechanism. This provides fair remuneration to the investor and rewards the effort made in investing in a clean energy source. Solar energy is becoming more economically viable and should become cost-competitive with conventional energy by 2015 in southern European countries and by 2020 across most of Europe.

    Increasing customer’s demand and costs for conventional electricity, together with decreasing installation costs will make solar power systems increasingly economic during the coming years. During the next 5-10 years solar power will become cheaper (depending on location and electricity prices) for private households than conventional electricity. Thus solar power will become independent of subsidies much earlier than might be deemed at first glance.

    With stand-alone systems remote from the electricity grid, it is already worthwhile using solar technology today.

    The Renewable Energy Sources Directive reinforces the current legal framework and could facilitate the implementation of the FiT schemes throughout Europe.

    CCRES special thanks to

     ManagEnergy.net http://www.managenergy.net/actors/5074 

     EU Commission   http://ec.europa.eu/index_en.htm

     EU Sustainable Energy   http://www.eusew.eu/index.php?option=com_see_eventview&view=see_eventdetail&index=1&countryID=55&sort=-1&pageNum=0&eventid=3405

     European Photovoltaic Technology Platform http://www.eupvplatform.org

    Croatian Center of Renewable Energy Sources (CCRES)

Solar pv CCRES

solar pv

how does pv work

‘Photovoltaic’ is a marriage of two words: ‘photo’, from Greek roots, meaning light, and ‘voltaic’, from ‘volt’, which is the unit used to measure electric potential at a given point.

Photovoltaic systems use cells to convert solar radiation into electricity. The cell consists of one or two layers of a semi-conducting material. When light shines on the cell it creates an electric field across the layers, causing electricity to flow. The greater the intensity of the light, the greater the flow of electricity is.

The most common semi conductor material used in photovoltaic cells is silicon, an element most commonly found in sand. There is no limitation to its availability as a raw material; silicon is the second most abundant material in the earth’s mass.

A photovoltaic system therefore does not need bright sunlight in order to operate. It can also generate electricity on cloudy days.

PV Technologies: Cells and Modules

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.

Crystalline silicon technology:

Crystalline silicon cells are made from thin slices cut from a single crystal of silicon (monocrystalline) or from a block of silicon crystals (polycrystalline), their efficiency ranges between 11% and 19%. This is the most common technology representing about 90% of the market today.

Three main types of crystalline cells can be distinguished:

• Monocrystalline (Mono c-Si)
• Polycrystalline (or Multicrystalline) (multi c-Si)
• Ribbon sheets (ribbon-sheet c-Si)

Thin Film technology:

Thin film modules are constructed by depositing extremely thin layers of photosensitive materials onto a low-cost backing such as glass, stainless steel or plastic.

Thin Film manufacturing processes result in lower production costs compared to the more material-intensive crystalline technology, a price advantage which is counterbalanced by lower efficiency rates (from 4% to 11%). However, this is an average value and all Thin Film technologies do not have the same efficiency.

Four types of thin film modules (depending on the active material used) are commercially available at the moment:

• Amorphous silicon (a-Si)
• Cadmium telluride (CdTe)
• Copper Indium/gallium Diselenide/disulphide (CIS, CIGS)
• Multi junction cells (a-Si/m-Si)

Other cell types:

There are several other types of photovoltaic technologies developed today starting to be commercialised or still at the research level, the main ones are:

• Concentrated photovoltaic:
  Some solar cells are designed to operate with concentrated sunlight. These cells are built into concentrating collectors that use a lens to focus the sunlight onto the cells. The main idea is to use very little of the expensive semiconducting PV material while collecting as much sunlight as possible. Efficiencies are in the range of 20 to 30%.
  
• Flexible cells:
  Based on a similar production process to thin film cells, when the active material is deposited in a thin plastic, the cell can be flexible. This opens the range of applications, especially for Building integration (roofs-tiles) and end-consumer applications.

PV Applications

The Photovoltaic technology can be used in several types of applications:

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 equipments.

Grid-Connected power plants

These systems, also grid-connected, produce a large quantity of photovoltaic electricity in a single point. The size of these plants range 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.

Off-grid systems for rural electrification

Where no mains electricity is available, the system is connected to a battery via a charge controller. An inverter can be used to provide AC power, enabling the use of normal electrical appliances. Typical off-grid applications are used to bring access to electricity to remote areas (mountain huts, developing countries). Rural electrification means either small solar home system covering basic electricity needs in a single household, or larger solar mini-grids, which provide enough power for several homes. More information is available on CCRES.

Off-grid industrial applications

Uses for solar electricity for remote applications are very frequent in the telecommunications field, especially to link remote rural areas to the rest of the country. Repeater stations for mobile telephones powered by PV or hybrid systems also have a large potential. Other applications include traffic signals, marine navigation aids, security phones, remote lighting, highway signs and waste water treatment plants. These applications are cost competitive today as they enable to bring power in areas far away from electric mains, avoiding the high cost of installing cabled networks.

Consumer goods

Photovoltaic cells are used in many daily electrical appliances, including watches, calculators, toys, battery chargers, professional sun roofs for automobiles. Other applications include power for services such as water sprinklers, road signs, lighting and phone boxes.

Environmental impact

Climate protection

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.

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)

10 good reasons to switch to solar photovoltaic electricity

Photovoltaic is emerging as a major power source due to its numerous environmental and economic benefits and proven reliability:

1

The fuel is free.
The sun is the only resource needed to power solar panels. And the sun will keep shining until the world's end. Also, most photovoltaic cells are made from silicon, and silicon is an abundant and non-toxic element (the second most abundant material in the earth's mass).

2

It produces no noise, harmful emissions or polluting gases.
The burning of natural resources for energy can create smoke, cause acid rain, pollute water and pollute the air. Carbon dioxide or CO2, a leading greenhouse gas, is also produced. Solar power uses only the power of the sun as its fuel. It creates no harmful by-product and contributes actively to reduce the global warming.

From : Externe project, 2003; Kim and Dale, 2005; Fthenakis and Kim, 2006; Fthenakis and Kim, 2007; Fthenakis and Alsema, 2006.

3

PV systems are very safe and highly reliable.
The estimated lifetime of a PV module is 30 years. Furthermore, the modules' performance is very high providing over 80% of the initial power after 25 years which makes photovoltaics a very reliable technology in the long term. In addition, very high quality standards are set at a European level which guarantees that consumers buy reliable products.

4

The energy pay-back time of a module is constantly decreasing.
This means that the time required for a PV module to produce as much energy as it needs to be manufactured is very short, it varies between 1,5 years to 3 years. This is between 6 to 18 times more energy than the energy needed to be manufactured (depending on the technology, the type of system and the location).

5

PV Modules can be recycled and therefore the materials used in the production process (silicon, glass, aluminium, etc.) can be reused.
Recycling is not only beneficial for the environment but also for helping to reduce the energy needed to produce those materials and therefore the cost of fabrication. More information is available on the following website: CCRES.

6

It requires low maintenance.
Solar modules are almost maintenance-free and offer an easy installation.

7

It brings electricity to remote rural areas.
Solar systems give an added value to rural areas (especially in developing countries where electricity is not available). House lighting, hospital refrigeration systems and water pumping are some of the many applications for off-grid systems. Telecommunication systems in remote areas are also well-known users of PV systems.

8

It can be aesthetically integrated in buildings (BIPV).
Systems can cover roofs and façades contributing to reduce the energy buildings consume. They don't produce noise and can be integrated in very aesthetic ways. .European building legislations have been and are being reviewed to make renewable energies as a required energy source in public and residential buildings. This fact is accelerating the development of ecobuildings and positive energy buildings (E+ Buildings) which opens up many opportunities for a better integration of PV systems in the built environment. More information is available on CCRES.

9

It creates thousands of jobs.
The PV sector, with an average annual growth of 40% during the past years is increasingly contributing to the creation of thousands of jobs in Europe and worldwide.

10

It contributes to improving the security of Europe's energy supply.
In order to cover 100% of the electricity demand in Europe, only the 0.7% of the total land of Europe would be needed to be covered by PV modules. Therefore Photovoltaics can play an important role in improving the security of Europe's energy supply.

More info about RES & EE on solarserdar@gmail.com

Croatian Center of Renewable Energy Sources (CCRES)