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.
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.
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.
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.
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.
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.
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.
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.
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 power of the PV system
Orientation towards the sun
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)
The production of a PV system depends on:
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.
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.
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.
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.
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.
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!
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.
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.
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.
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.
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.
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.
Where can I learn more about photovoltaic solar energy?
Where can I learn more about PV solar energy?
Some very useful information about photovoltaic solar energy can be found on the following websites: