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29-31 Solar Power Generation System Energy Payback Period

Author: Source: Datetime: 2016-12-26 09:47:35
Solar power generation system Energy Payback Period (EPT)

Photovoltaic power generation, as a renewable energy source, is widely regarded as a more promising "green" energy source, mainly because of its focus on solving environmental problems on Earth. To determine the indicators of renewable energy, one is acceptable costs, and second, the potential of greenhouse gas emissions. The former is no longer controversial, the world's photovoltaic power generation in many developed countries have achieved parity Internet access. Here to first introduce the concept of energy recovery period, and then clarify the potential of CO2 emissions.

Photovoltaic power generation systems, including solar cell components and system balance components, also consume energy in the manufacturing process, but also produce greenhouse gases. And this part of the energy generated by their own recycling. The recovery time is called the energy payback period (Energy Payback Time, EPT). Assuming that the energy produced by a device each year is multiplied by its life-cycle, the energy produced by the device in its lifetime can be obtained. If this energy is less than the energy consumed to manufacture the device, the device can not be used as energy.

Photovoltaic system EPT depends on a series of complex factors. The input energy is related to many factors, such as the type of solar cells (monocrystalline silicon, polycrystalline silicon, amorphous silicon or other thin-film cells, etc.), process, packaging materials and methods, matrix and support structures, (BOS) materials and manufacturing processes. If the system with energy storage device, we must consider the battery. In addition, consider the installation, operation and life after the end of the demolition and waste treatment and other energy consumption.

The output energy of the PV system is also related to many factors, such as whether the system design is optimized, the equipment configuration is reasonable, whether the installation is improper, the operation and maintenance can be in place, the service life and performance and efficiency of the solar cell module and auxiliary components, Geographical and meteorological conditions. In addition, there are indirect factors that are not related to the power generation system itself.

Despite the complexity of the factors affecting the EPT, still can be through theoretical research and practical investigation to sort out, grasp the main factors, a comprehensive analysis. Since the 20th century, 90 years, many European and American scholars have made a detailed study related to the analysis of Table 2-3 lists some of the findings.

Table 2-3 summarizes some of the results of the PV energy recovery time


Low estimate / year

Low estimation of critical conditions

High Estimate / Year

High estimation of critical conditions



Roof mounted membrane modules


Roof-mounted polysilicon components

Alsema & Nieuwlaar(2000)


Film components


Polysilicon components

Battisti & Corrado (2005)


Thermal photovoltaic hybrid components


Tilt roof polycrystalline silicon components

Jester (2002)


150W polysilicon components


55W polysilicon components



not consider the heat of the polysilicon components


Consider the heat of the single-crystal silicon components

Kato,Hibino,Komoto,Ihara,Yamamoto & Fujihara(2001)


Annual production of 100MW of amorphous silicon components (including supporting components)


Annual output of 10MW of polysilicon components (including parts and components)

Kato,Murata & Sakuta (1997)


Not using micro-electronics industry production process of single-crystal silicon components
Not using micro-


use of micro-electronics industry production process of single-crystal silicon components

Kato,Murata & Sakuta (1998)


Not using micro-electronics industry production process of amorphous silicon components


use of micro-electronics production process of polycrystalline silicon components

Knapp & Jester (2001)


Film module products


Before the pilot in the thin-film components

Lewis & Keoleian (1996)


37.6 kWh / year borders a  Si module installed in Bordeaux, Colorado


22.3 kWh / year frameed a Si module installed in Detroit, Michigan

Meijer,Huijbregts,Schermer & Reijnders (2003)


Polysilicon components


Film components

Pearce & Lau (2002)


Amorphous silicon components


Single crystal silicon components

Peharz & Dimroth (2005)


All glass Fresnel lens Front and rear condenser cell irradiation conditions 1900kWh (m2 years)


All-glass Fresnel lens Front and rear condenser cell Irradiation conditions 1000kWh (m2years)

Raugei,Bargigli & Ulgiati (2005)


CdTe components (including supporting components)


Polycrystalline silicon components (including supporting components)

Schaefer & Hagedorn (1992)


2.5MW amorphous silicon components


2.5MW monocrystalline silicon components

Tripanagnostopoulos,Souliotis,Battisti & Corrado (2005)


Thermal photovoltaic hybrid glass components


Thermal photovoltaic hybrid non-glass components

It is worth mentioning that the University of Utrecht, the Netherlands Alsema EA is one of the most famous researchers in the field of photovoltaic power generation efficiency, he published in July 1998 Energy Paybak of Photovoltaic Energy Systems: Present Status Prospects paper, A number of published more than 10 published literature that is reasonable, pointed out that some of the literature for the manufacture of components required for different energy, polysilicon 2400 ~ 7600KJ /m2, monocrystalline silicon in the 5300 ~ 16500KJ / m2, in part because of the production process parameters Different, such as silicon thickness and slice loss and so on. Alsema established the "best estimate of the energy required for polysilicon, monocrystalline silicon, thin-film battery components and associated components." In 2000, he analyzed different types of components, suggesting that polysilicon cells and thin-film batteries contain aluminum borders, support structures and Inverters and other required energy, the system's energy repayment time were 3.2 years and 2.7 years respectively. Solar battery life is estimated to be 25 to 30 years, so the energy of these components; repayment time is only 1 / 10.Alsema was estimated , Due to technological progress, by 2010 can be reduced to 1 to 2 years, has been achieved in China by 2020 will be even lower.

Since 2009, the Chinese government has paid more attention to the domestic application of photovoltaic energy, and has formulated a series of policies and measures. Grid-connected photovoltaic power generation system has been developing rapidly. Especially, the distributed roof-connected grid-connected PV system using polysilicon components is very common . The issue of energy payback in this regard is a matter of concern, so a special reference to the IEA Joint Report is here.

IEA-PVPS and EPTP: Jointly published in May 2006 Compared Assessment of Selected Environmental Indicators of Photovoltaic Electri-cities in the OECD Cities, based on a worldwide survey of photovoltaic technology (IEA-PVPS) and the European Photovoltaic Industry Association (EPTP) The current study on the energy input of PV systems provides a report on the energy reimbursement time for all PV systems (not only components, but also ancillary components, connecting cables and electronics, etc.) depending on local solar irradiance For 26 41 major cities in the OECD countries were analyzed and calculated. The annual PV power output, energy recovery factor and PV unit power of these cities are listed in detail as the annual reductions in CO2 emissions. The conclusion is that the energy recovery time for roof-mounted grid-connected PV system is 1.6-3.3 years, and 2.7-7.7 years for vertical installation to the equator.

Gaiddon B., et al., Published an article on Environmental Benefits of PV Systems in OECD Cities, and explained the basis and method of analysis. It was pointed out that the above conclusions were mainly directed against the use of standard polysilicon components and inverters
Grid-connected PV system.

Since the orientation and inclination of the photovoltaic array have a significant effect on the amount of electricity generated by the grid-connected PV system, the following two common scenarios are considered, taking into account the specific situation in the city for PV and building integration applications.
(1) Install a roofing grid-connected PV system with an inclination of 30 ° towards the equator and square.

(2) PV array installed perpendicular to the equator, that is, the angle of 90 °, such as as a curtain wall.

Then, according to the local solar radiation data, calculate the unit power (1kW) polysilicon grid-connected photovoltaic power system per year.

In the entire photovoltaic system processing, manufacturing and installation process, must consume energy, according to Europe and the United States nine modern photovoltaic factory statistics, network polysilicon photovoltaic system power consumption shown in Table 2-4.

At last, we calculate the energy reimbursement time of 41 cities, and get the range of energy repayment in OECD countries.

Table 2-4 Grid-connected polysilicon PV system power consumption


Consumption of electricity



Consumption of electricity




Supporting components




Total System


Table 2-5 Energy Repayment Time Range of OECD Photovoltaic System


Maximum / year

Minimum / year

Roof-mounted photovoltaic system



Vertical installation of photovoltaic systems



In the production process, different types of solar modules, the unit power consumption is not the same power, and different processes, the scale of production also have an impact. For the polysilicon grid-connected PV system, the average power consumption per unit of power as shown in Table 2-4, that per kilowatt polysilicon grid-connected photovoltaic system power consumption is 2525kWh.

To assess the environmental benefits of grid-connected PV systems, Prof. Yang Jinhuan was analyzed and calculated according to the above-mentioned technical indexes for 28 major cities in China. The solar radiation in the local horizontal plane is averaged according to the measurement data of 1981 ~ 2000 published by National Meteorological Center, and calculated according to Klein.SA and Theilacker.JC. The average solar irradiance on the surface is compared and the maximum solar radiation amount H1 can be received in the whole year. The corresponding inclination is the best dip angle of grid-connected photovoltaic array, and it can also be determined that the vertical solar radiation is perpendicular to the equator The time of energy recovery of the grid-connected PV system in some cities in China is shown in Table 2-6.

Table 2-6 Energy recovery time of grid-connected PV systems in some Chinese cities
Table 2-6 Energy recovery time of grid-connected PV systems in some Chinese cities
In some major cities in China, the shortest energy recovery time is in Lhasa, which is 1.57 years and 2.5 years, respectively, in the direction of the equator, in accordance with the best dip angle installation and vertical installation of grid-connected PV systems. The external input energy required for the removal, installation, operation and end of the final life cycle, removal of the system and disposal of waste is not included in the calculation. According to the analysis, the energy per unit power (W) allocated to the solar cells has little effect on the energy recovery. Of course, for monocrystalline silicon cells, the energy repayment time increased slightly, while the thin-film batteries are reduced.

In short, the PV system in the entire life cycle (now 25 to 30 years, the future is expected to increase to 35 years), the energy generated is far greater than its manufacturing, transportation, installation, operation and other stages of all input energy, and with the With the development of technology, the energy consumed during the manufacture and installation of photovoltaic systems will be reduced and the time for energy repayment will be further reduced. Photovoltaic power generation is indeed a clean "green" energy that is worth popularizing.

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