1. Photovoltaics
Photovoltaic system 'tree' in Styria, Austria
Photovoltaic system (or PV) is the field of technology and research related to the
application of solar cells for energy by converting solar energy (sunlight, including ultra
violet radiation) directly into electricity. Due to the growing demand for clean sources of
energy, the manufacture of solar cells and photovoltaic arrays has expanded dramatically
in recent years.[1][2][3]
Photovoltaic production has been doubling every 2 years, increasing by an average of 48
percent each year since 2002, making it the world’s fastest-growing energy technology.[4]
At the end of 2008, the cumulative global PV installations reached 15,200 megawatts, a
94% annual increase.[5][6] Roughly 90% of this generating capacity consists of grid-tied
electrical systems. Such installations may be ground-mounted (and sometimes integrated
with farming and grazing) [7] or built into the roof or walls of a building, known as
Building Integrated Photovoltaics or BIPV for short.[8]
Net metering and financial incentives, such as preferential feed-in tariffs for solar-
generated electricity, have supported solar PV installations in many countries including
Australia, Germany, Israel,[9] Japan, and the United States.[1]

2. Contents
[hide]
• 1 Overview
• 2 Current development
• 3 Worldwide installed totals
• 4 Applications
o 4.1 Power stations
o 4.2 In buildings
o 4.3 In transport
o 4.4 Standalone devices
o 4.5 Rural electrification
o 4.6 Solar roadways
• 5 Performance
o 5.1 Temperature
o 5.2 Optimum Orientation of Solar Panels
• 6 Economics
o 6.1 Power costs
o 6.2 Grid parity
o 6.3 Financial incentives
o 6.4 Investment
• 7 Environmental impacts
o 7.1 Greenhouse gases
o 7.2 Cadmium
o 7.3 Energy payback time and energy returned on energy invested
• 8 Advantages
• 9 Disadvantages
• 10 Photovoltaics companies
• 11 See also
• 12 References
• 13 External links
o 13.1 Photovoltaic industry associations
o 13.2 Photovoltaics research institutes
o 13.3 Live data
o 13.4 Others

3. [edit] Overview
Photovoltaic cells produce electricity directly from sunlight
Photovoltaics are best known as a method for generating electric power by using solar
cells to convert energy from the sun into electricity. The photovoltaic effect refers to
photons of light knocking electrons into a higher state of energy to create electricity. The
term photovoltaic denotes the unbiased operating mode of a photodiode in which current
through the device is entirely due to the transduced light energy. Virtually all photovoltaic
devices are some type of photodiode.
Solar cells produce direct current electricity from light, which can be used to power
equipment or to recharge a battery. The first practical application of photovoltaics was to
power orbiting satellites and other spacecraft, but today the majority of photovoltaic
modules are used for grid connected power generation. In this case an inverter is required
to convert the DC to AC. There is a smaller market for off grid power for remote
dwellings, roadside emergency telephones, remote sensing, and cathodic protection of
pipelines.
Average solar irradiance, watts per square metre. Note that this is for a horizontal surface,
whereas solar panels are normally propped up at an angle and receive more energy per
unit area. The small black dots show the area of solar panels needed to generate all of the
world's energy using 8% efficient photovoltaics.
Cells require protection from the environment and are usually packaged tightly behind a
glass sheet. When more power is required than a single cell can deliver, cells are
electrically connected together to form photovoltaic modules, or solar panels. A single
module is enough to power an emergency telephone, but for a house or a power plant the
modules must be arranged in multiples as arrays. Although the selling price of modules is
still too high to compete with grid electricity in most places, significant financial
incentives in Japan and then Germany, Italy and France triggered a huge growth in
demand, followed quickly by production. In 2008, Spain installed 45% of all
photovoltaics, but a change in law limiting the Feed-in Tariff is expected to cause a
precipitous drop in installations there, from 2500 MW in 2008 to 375 MW in 2009.[10]
Perhaps not unexpectedly, a significant market has emerged in off-grid locations for
solar-power-charged storage-battery based solutions. These often provide the only
electricity available.[11]
The EPIA/Greenpeace Advanced Scenario shows that by the year 2030, PV systems
could be generating approximately 1,864 GW of electricity around the world. This means
that, assuming a serious commitment is made to energy efficiency, enough solar power

4. would be produced globally in twenty-five years’ time to satisfy the electricity needs of
almost 14% of the world’s population.[12]
[edit] Current development
Map of solar electricity potential in Europe
The most important issue with solar panels is capital cost (installation and materials).
Newer alternatives to standard crystalline silicon modules including casting wafers
instead of sawing,[13] thin film (CdTe[14] CIGS,[15] amorphous Si,[16] microcrystalline Si),
concentrator modules, 'Sliver' cells, and continuous printing processes. Due to economies
of scale solar panels get less costly as people use and buy more — as manufacturers
increase production to meet demand, the cost and price is expected to drop in the years to
come. By early 2006, the average cost per installed watt for a residential sized system
was about USD 7.50 to USD 9.50, including panels, inverters, mounts, and electrical
items.[17]
In 2006 investors began offering free solar panel installation in return for a 25 year
contract, or Power Purchase Agreement, to purchase electricity at a fixed price, normally
set at or below current electric rates.[18][19] It is expected that by 2009 over 90% of
commercial photovoltaics installed in the United States will be installed using a power
purchase agreement.[20] An innovative financing arrangement is being tested in Berkeley,
California, which adds an amount to the property assessment to allow the city to pay for
the installed panels up front, which the homeowner pays for over a 20 year period at a
rate equal to the annual electric bill savings, thus allowing free installation for the
homeowner at no cost to the city.[21]
The current market leader in solar panel efficiency (measured by energy conversion ratio)
is SunPower, a San Jose based company. Sunpower's cells have a conversion ratio of
23.4%, well above the market average of 12-18%. However, advances past this efficiency
mark are being pursued in academia and R&D labs with efficiencies of 42% achieved at
the University of Delaware in conjunction with DuPont.[22]

5. [edit] Worldwide installed totals
This section may stray from the topic of the article into the topic of another article,
Deployment of solar power to energy grids. Please help improve this section or discuss
this issue on the talk page.
See also: Deployment of solar power to energy grids and History of photovoltaics
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World solar photovoltaic (PV) installations were 2.826 gigawatts peak (GWp) in 2007,
and 5.95 gigawatts in 2008, a 110% increase.[23][24] The three leading countries (Germany,
Japan and the US) represent nearly 89% of the total worldwide PV installed capacity.
Germany was the fastest growing major PV market in the world from 2006 to 2007. By
2008, 5.337 GWp of PV was installed, or 35% of the world total.[6] The German PV
industry generates over 10,000 jobs in production, distribution and installation. By the
end of 2006, nearly 88% of all solar PV installations in the EU were in grid-tied
applications in Germany.[1] Photovoltaic power capacity is measured as maximum power
output under standardized test conditions (STC) in "Wp" (Watts peak).[25] The actual
power output at a particular point in time may be less than or greater than this
standardized, or "rated," value, depending on geographical location, time of day, weather
conditions, and other factors.[26] Solar photovoltaic array capacity factors are typically
under 25%, which is lower than many other industrial sources of electricity.[27] Therefore
the 2008 installed base peak output would have provided an average output of 3.04 GW
(assuming 20% × 15,200 MWp). This represented 0.15 percent of global demand at the
time.[28]
Produced, Installed & Total Photovoltaic Peak Power Capacity (MWp) as of the end of 2007
Feed-in
off on Installed off on Total Wp/capita Module kW·h/kWp·yr
Country or Region Tariff
grid grid 2007 grid grid 2007 Total Price Insolation
Report Nat. Int. EU¢/kW·h
Δ Δ Σ Σ €/Wp
Germany[29][30] 35 1,100 1,135 35 3,827 3,862 46.8 4.0–5.3 1,000–1,300[31] 51.8–56.8
Japan[30][32] 1.562 208.8 210.4 90.15 1,829 1,919 15 2.96 1,200–1,600 Ended(2005)
1.2–
United States[30][33] 55 151.5 206.5 325 505.5 830.5 2.8 2.98 900–2,150[31]
31.04(CA)
Spain ?[30] 22 490 512 29.8 625.2 655 15.1 3.0–4.5 1,600–2,200 18.38–44.04
Italy[30][34] 0.3 69.9 70.2 13.1 107.1 120.2 2.1 3.2–3.6 1,400–2,200 36.0–49.0
0–
Australia[30][35] 5.91 6.28 12.19 66.45 16.04 82.49 4.1 4.5–5.4 1,450–2,902[36]
26.4(SA'08)
South Korea[30][37] 0 42.87 42.87 5.943 71.66 77.60 1.6 3.50– 1,500–1,600 56.5–59.3

6. 3.84
[30][38]
France 0.993 30.31 31.30 22.55 52.68 75.23 1.2 3.2–5.1 1,100–2,000 30.0–55.0
Netherlands[30][39] 0.582 1.023 1.605 5.3 48 53.3 3.3 3.3–4.5 1,000–1,200 1.21–9.7
3.18–
Switzerland[30][40] 0.2 6.3 6.5 3.6 32.6 36.2 4.9 1,200–2,000 9.53–50.8
3.30
Austria ?[30] 0.055 2.061 2.116 3.224 24.48 27.70 3.4 3.6–4.3 1,200–2,000 >0
Canada[30][41] 3.888 1.403 5.291 22.86 2.911 25.78 0.8 3.76 900–1,750 0–29.48(ON)
5.44–
Mexico ?[30] 0.869 0.15 1.019 20.45 0.3 20.75 0.2 1,700–2,600 None
6.42
United 3.67– 0–
0.16 3.65 3.81 1.47 16.62 18.09 0.3 900–1,300
Kingdom[30][42] 5.72 11.74(exprt)
Portugal ?[43] 0.2 14.25 14.45 2.841 15.03 17.87 1.7 1,600–2,200
Norway[30][44] 0.32 0.004 0.324 7.86 0.132 7.992 1.7 11.2 800–950 None
3.24–
Sweden[30][45] 0.271 1.121 1.392 4.566 1.676 6.242 0.7 900–1,050 None
7.02
5.36–
Denmark[30][46] 0.05 0.125 0.175 0.385 2.69 3.075 0.6 900–1,100 None
8.04
Israel[30][47] 0.5 0 0.5 1.794 0.025 1.819 0.3 4.3
2,200–2,400 13.13–16.40
World
(Total of countries 127.9 2,130 2,258 662.3 7,178 7,841 2.5–11.2 800–2,902 0–59.3
listed)
off on off on Module Feed-in
Country or Region Installed Total Wp/capita kW·h/kWp·yr
grid grid grid grid Price Tariff
Report Nat. Int. 2007 2007 Total Insolation
Δ Δ Σ Σ €/Wp EU¢/kW·h
Notes: Off grid refers to photovoltaics which are not grid connected. On grid means connected to the local
electricity grid. Δ means the amount installed during the previous year. Σ means the total amount installed.
Wp/capita refers to the ratio of total installed capacity divided by total population, or total installed Wp per
person. Module price is average installed price, in Euros. kW·h/kWp·yr indicates the range of insolation to
be expected. While National Report(s) may be cited as source(s) within an International Report, any
contradictions in data are resolved by using only the most recent report's data. Exchange rates represent the
2006 annual average of daily rates (OECD Main Economic Indicators June 2007).
Module Price: Lowest:2.5 EUR/Wp[30] (2.83 USD/Wp[48]) in Germany 2003. Uncited insolation data is from
maps dating 1991-1995.
PV Power (2007-June)[43][49] IEA PVPS website.
[edit] Applications
Main article: Photovoltaic system
[edit] Power stations
Main article: List of photovoltaic power stations

7. Solar array at Nellis Air Force Base. These panels track the sun in one axis.
As of April 2009, the largest photovoltaic (PV) power plants in the world are the
Olmedilla Photovoltaic Park (Spain, 60 MW), the Puertollano Photovoltaic Park (Spain,
50 MW), the Moura photovoltaic power station (Portugal, 46 MW), and the Waldpolenz
Solar Park (Germany, 40 MW).[50]
The 14 MW Nellis Solar Power Plant is the largest solar photovoltaic system in North
America,[51] and is located within Nellis Air Force Base in Clark County, Nevada, on the
northeast side of Las Vegas. The Nellis solar energy system will generate in excess of
25 million kilowatt-hours of electricity annually and supply more than 25 percent of the
power used at the base.[52]
World's largest photovoltaic (PV) power plants (30 MW or larger)[50]
DC
Name of PV power Peak GW·h Capacity
Country Notes
plant Power /year factor
(MW)
Olmedilla Completed September
Spain 60 85 0.16
Photovoltaic Park 2008
Puertollano
Spain 50 2008
Photovoltaic Park
Moura photovoltaic Completed December
Portugal 46 93 0.16
power station [53] 2008
550,000 First Solar thin-
Waldpolenz Solar film CdTe modules.
Germany 40 40 0.11
Park[54][55] Completed December
2008
Arnedo Solar Plant Spain 34 Completed October 2008
Merida/Don Alvaro Completed September
Spain 30
Solar Park 2008
Planta Solar La
Magascona & La Spain 30
Magasquila
Planta Solar Ose de
Spain 30
la Vega

8. Topaz Solar Farm is a proposed 550 MW solar photovoltaic power plant which is to be
built northwest of California Valley in the US at a cost of over $1 billion.[56] Built on
9.5 square miles (25 km2) of ranchland,[57] the project would utilize thin-film PV panels
designed and manufactured by OptiSolar in Hayward and Sacramento. The project would
deliver approximately 1,100 gigawatt-hours (GW·h) annually of renewable energy. The
project is expected to begin construction in 2010,[57] begin power delivery in 2011, and be
fully operational by 2013.[58]
High Plains Ranch is a proposed 250 MW solar photovoltaic power plant which is to be
built by SunPower in the Carrizo Plain, northwest of California Valley.[58]
[edit] In buildings
Main article: Building-integrated photovoltaics
Photovoltaic solar panels on a house roof.
Building-integrated photovoltaics (BIPV) are increasingly incorporated into new
domestic and industrial buildings as a principal or ancillary source of electrical power,[59]
and are one of the fastest growing segments of the photovoltaic industry.[60] Typically, an
array is incorporated into the roof or walls of a building, and roof tiles with integrated PV
cells can now be purchased. Arrays can also be retrofitted into existing buildings; in this
case they are usually fitted on top of the existing roof structure. Alternatively, an array
can be located separately from the building but connected by cable to supply power for
the building.
Where a building is at a considerable distance from the public electricity supply (or grid)
- in remote or mountainous areas – PV may be the preferred possibility for generating
electricity, or PV may be used together with wind, diesel generators and/or hydroelectric
power. In such off-grid circumstances batteries are usually used to store the electric
power.
In locations near the grid, however, feeding the grid using PV panels is more practical,
and leads to optimum use of the investment in the photovoltaic system. This requires both
regulatory and commercial preparation, including net-metering and feed-in agreements.
To provide for possible power failure, some grid tied systems are set up to allow local use

9. disconnected from the grid. Most photovoltaics are grid connected. In the event the grid
fails, the local system must not feed the grid to prevent the possible creation of dangerous
islanding.
The power output of photovoltaic systems for installation in buildings is usually
described in kilowatt-peak units (kWp).
[edit] In transport
Main article: Photovoltaics in transport
PV has traditionally been used for auxiliary power in space. PV is rarely used to provide
motive power in transport applications, but is being used increasingly to provide auxiliary
power in boats and cars. Recent advances in solar race cars, however, have produced cars
that with little changes could be used for transportation.[61]
[edit] Standalone devices
Solar parking meter.
Until a decade or so ago, PV was used frequently to power calculators and novelty
devices. Improvements in integrated circuits and low power LCD displays make it
possible to power such devices for several years between battery changes, making PV use
less common. In contrast, solar powered remote fixed devices have seen increasing use
recently in locations where significant connection cost makes grid power prohibitively
expensive. Such applications include parking meters,[62] emergency telephones,[63]
temporary traffic signs, and remote guard posts & signals.
[edit] Rural electrification
Developing countries where many villages are often more than five kilometers away from
grid power have begun using photovoltaics. In remote locations in India a rural lighting
program has been providing solar powered LED lighting to replace kerosene lamps. The
solar powered lamps were sold at about the cost of a few month's supply of

10. kerosene.[64][65] Cuba is working to provide solar power for areas that are off grid.[66] These
are areas where the social costs and benefits offer an excellent case for going solar though
the lack of profitability could relegate such endeavors to humanitarian goals.
[edit] Solar roadways
Main article: Solar roadway
A 45 mi (72 km) section of roadway in Idaho is being used to test the possibility of
installing solar panels into the road surface, as roads are generally unobstructed to the sun
and represent about the percentage of land area needed to replace other energy sources
with solar power.[67]
[edit] Performance
[edit] Temperature
Generally, temperatures above room temperature reduce the performance of
photovoltaics.[68]
[edit] Optimum Orientation of Solar Panels
For best performance, PV systems aim to maximize the time they face the sun. Solar
trackers aim to achieve this by moving PV panels to follow the sun. The increase can be
by as much as 20% in winter and by as much as 50% in summer. Static mounted systems
can be optimized by analysis of the Sun path. Panels are often set to latitude tilt, an angle
equal to the latitude, but performance can be improved by adjusting the angle for summer
and winter.
[edit] Economics
This section may stray from the topic of the article into the topic of another article,
Renewable energy commercialization. Please help improve this section or discuss this
issue on the talk page.
This section may contain original research or unverified claims. Please improve the
article by adding references. See the talk page for details. (September 2007)
See also: Renewable energy commercialization

11. US average daily solar energy insolation received by a latitude tilt photovoltaic cell.
In photovoltaics, the solar value added chain is the set of steps from sand or raw silicon
to the completed solar module and photovoltaic system completion and installation[69].
[edit] Power costs
The PV industry is beginning to adopt levelized cost of energy (LCOE) as the unit of
cost. For a 10 MW plant in Phoenix, AZ, the LCOE is estimated at $0.15 to 0.22/kWh in
2005.[70]
The table below is a pure mathematical calculation. It illustrates the calculated total cost
in US cents per kilowatt-hour of electricity generated by a photovoltaic system as
function of the investment cost and the efficiency, assuming some accounting parameters
such as cost of capital and depreciation period. The row headings on the left show the
total cost, per peak kilowatt (kWp), of a photovoltaic installation. The column headings
across the top refer to the annual energy output in kilowatt-hours expected from each
installed peak kilowatt. This varies by geographic region because the average insolation
depends on the average cloudiness and the thickness of atmosphere traversed by the
sunlight. It also depends on the path of the sun relative to the panel and the horizon.
Panels can be mounted at an angle based on latitude,[71] or solar tracking can be utilized to
access even more perpendicular sunlight, thereby raising the total energy output. The
calculated values in the table reflect the total cost in cents per kilowatt-hour produced.
They assume a 10% total capital cost (for instance 4% interest rate, 1% operating and
maintenance cost, and depreciation of the capital outlay over 20 years).
Table showing average cost in cents/kWh over 20 years for solar power panels
Insolation
Cost 2400 2200 2000 1800 1600 1400 1200 1000 800
kWh/kWp•y kWh/kWp•y kWh/kWp•y kWh/kWp•y kWh/kWp•y kWh/kWp•y kWh/kWp•y kWh/kWp•y kWh/kWp•y
200
$/kW 0.8 0.9 1.0 1.1 1.3 1.4 1.7 2.0 2.5
p
600 2.5 2.7 3.0 3.3 3.8 4.3 5.0 6.0 7.5
$/kW

12. p
1000
$/kW 4.2 4.5 5.0 5.6 6.3 7.1 8.3 10.0 12.5
p
1400
$/kW 5.8 6.4 7.0 7.8 8.8 10.0 11.7 14.0 17.5
p
1800
$/kW 7.5 8.2 9.0 10.0 11.3 12.9 15.0 18.0 22.5
p
2200
$/kW 9.2 10.0 11.0 12.2 13.8 15.7 18.3 22.0 27.5
p
2600
$/kW 10.8 11.8 13.0 14.4 16.3 18.6 21.7 26.0 32.5
p
3000
$/kW 12.5 13.6 15.0 16.7 18.8 21.4 25.0 30.0 37.5
p
3400
$/kW 14.2 15.5 17.0 18.9 21.3 24.3 28.3 34.0 42.5
p
3800
$/kW 15.8 17.3 19.0 21.1 23.8 27.1 31.7 38.0 47.5
p
4200
$/kW 17.5 19.1 21.0 23.3 26.3 30.0 35.0 42.0 52.5
p

13. 4600
$/kW 19.2 20.9 23.0 25.6 28.8 32.9 38.3 46.0 57.5
p
5000
$/kW 20.8 22.7 25.0 27.8 31.3 35.7 41.7 50.0 62.5
p
Physicists have claimed that recent technological developments bring the cost of solar
energy more in parity with that of fossil fuels. In 2007, David Faiman, the director of the
Ben-Gurion National Solar Energy Center of Israel, announced that the Center had
entered into a project with Zenith Solar to create a home solar energy system that uses a
10 square meter reflector dish.[72] In testing, the concentrated solar technology proved to
be up to five times more cost effective than standard flat photovoltaic silicon panels,
which would make it almost the same cost as oil and natural gas.[73] A prototype ready for
commercialization achieved a concentration of solar energy that was more than 1,000
times greater than standard flat panels.[74]
[edit] Grid parity
Further information: Low-cost solar cell and Solar America Initiative
Grid parity, the point at which photovoltaic electricity is equal to or cheaper than grid
power, is achieved first in areas with abundant sun and high costs for electricity such as
in California and Japan.[75]
Grid parity has been reached in Hawaii and other islands that otherwise use fossil fuel
(diesel fuel) to produce electricity, and most of the US is expected to reach grid parity by
2015.[76][77]
General Electric's Chief Engineer predicts grid parity without subsidies in sunny parts of
the United States by around 2015. Other companies predict an earlier date:[78] the cost of
solar power will be below grid parity for more than half of residential customers and 10%
of commercial customers in the OECD, as long as grid electricity prices do not decrease
through 2010.[79]
The fully-loaded cost (cost not price) of solar electricity is $0.25/kWh or less in most of
the OECD countries. By late 2011, the fully-loaded cost is likely to fall below $0.15/kWh
for most of the OECD and reach $0.10/kWh in sunnier regions. These cost levels are
driving three emerging trends:[79]
1. vertical integration of the supply chain;
2. origination of power purchase agreements (PPAs) by solar power companies;

14. 3. unexpected risk for traditional power generation companies, grid operators and
wind turbine manufacturers.
Abengoa Solar has announced the award of two R&D projects in the field of
Concentrating Solar Power (CSP) by the US Department of Energy that total over $14
million. The goal of the DOE R&D program, working in collaboration with partners such
as Abengoa Solar, is to develop CSP technologies that are competitive with conventional
energy sources (grid parity) by 2015.[80] Concentrating photovoltaics (CPV) could reach
grid parity in 2011.
[edit] Financial incentives
Main article: PV financial incentives
How do we become number one in the world in terms of solar power generation? In
order to achieve this, we must put an end to the following vicious cycle: costs are high
because of lack of demand, and demand remains stagnant due to high costs. Above all
else, I think a strong political will to create 'demand through policies,' is necessary. -
Japanese Prime Minister Taro Aso
The political purpose of incentive policies for PV is to facilitate an initial small-scale
deployment to begin to grow the industry, even where the cost of PV is significantly
above grid parity, to allow the industry to achieve the economies of scale necessary to
reach grid parity. The policies are implemented to promote national energy independence,
high tech job creation and reduction of CO2 emissions.
Three incentive mechanisms are used (often in combination):
• investment subsidies: the authorities refund part of the cost of installation of the
system,
• Feed-in Tariffs (FIT)/Net metering: the electricity utility buys PV electricity from
the producer under a multiyear contract at a guaranteed rate.
• Renewable Energy Certificates ("RECs")
With investment subsidies, the financial burden falls upon the taxpayer, while with feed-
in tariffs the extra cost is distributed across the utilities' customer bases. While the
investment subsidy may be simpler to administer, the main argument in favour of feed-in
tariffs is the encouragement of quality. Investment subsidies are paid out as a function of
the nameplate capacity of the installed system and are independent of its actual power
yield over time, thus rewarding the overstatement of power and tolerating poor durability
and maintenance. Some electric companies offer rebates to their customers, such as
Austin Energy in Texas, which offers $4.50/watt installed up to $13,500.[81]
With feed-in tariffs, the financial burden falls upon the consumer. They reward the
number of kilowatt-hours produced over a long period of time, but because the rate is set
by the authorities, it may result in perceived overpayment. The price paid per kilowatt-

15. hour under a feed-in tariff exceeds the price of grid electricity. Net metering refers to the
case where the price paid by the utility is the same as the price charged. Net metering is
particularly important because it can be done with no changes to standard electricity
meters, which accurately measure power in both directions and automatically report the
difference, and because it allows homeowners and businesses to generate electricity at a
different time from consumption, effectively using the grid as a giant storage battery. As
more photovoltaics are used ultimately storage will need to be provided, normally in the
form of pumped hydro-storage. Normally with net metering deficits are billed each
month, while surpluses are rolled over to the following month and paid annually.
Where price setting by supply and demand is preferred, RECs can be used. In this
mechanism, a renewable energy production or consumption target is set, and the
consumer or producer is obliged to purchase renewable energy from whoever provides it
the most competitively. The producer is paid via an REC. In principle this system delivers
the cheapest renewable energy, since the lowest bidder will win. However, uncertainties
about the future value of energy produced are a brake on investment in capacity, and the
higher risk increases the cost of capital borrowed.
The Japanese government through its Ministry of International Trade and Industry ran a
successful programme of subsidies from 1994 to 2003. By the end of 2004, Japan led the
world in installed PV capacity with over 1.1 GW.[82]
In 2004, the German government introduced the first large-scale feed-in tariff system,
under a law known as the 'EEG' (Erneuerbare Energien Gesetz) which resulted in
explosive growth of PV installations in Germany. At the outset the FIT was over 3x the
retail price or 8x the industrial price. The principle behind the German system is a 20 year
flat rate contract. The value of new contracts is programmed to decrease each year, in
order to encourage the industry to pass on lower costs to the end users. The programme
has been more successful than expected with over 1GW installed in 2006, and political
pressure is mounting to decrease the tariff to lessen the future burden on consumers.
Subsequently Spain, Italy, Greece (who enjoyed an early success with domestic solar-
thermal installations for hot water needs) and France introduced feed-in tariffs. None
have replicated the programmed decrease of FIT in new contracts though, making the
German incentive relatively less and less attractive compared to other countries. The
French and Greek FIT offer a high premium (EUR 0.55/kWh) for building integrated
systems. California, Greece, France and Italy have 30-50% more insolation than
Germany making them financially more attractive. The Greek domestic "solar roof"
programme (adopted in June 2009 for installations up to 10 kW) has internal rates of
return of 10-15% at current commercial installation costs, which, furthermore, is tax free.
In 2006 California approved the 'California Solar Initiative', offering a choice of
investment subsidies or FIT for small and medium systems and a FIT for large systems.
The small-system FIT of $0.39 per kWh (far less than EU countries) expires in just 5
years, and the alternate "EPBB" residential investment incentive is modest, averaging

16. perhaps 20% of cost. All California incentives are scheduled to decrease in the future
depending as a function of the amount of PV capacity installed.
At the end of 2006, the Ontario Power Authority (Canada) began its Standard Offer
Program, the first in North America for small renewable projects (10MW or less). This
guarantees a fixed price of $0.42 CDN per kWh over a period of twenty years. Unlike net
metering, all the electricity produced is sold to the OPA at the SOP rate. The generator
then purchases any needed electricity at the current prevailing rate (e.g., $0.055 per
kWh). The difference should cover all the costs of installation and operation over the life
of the contract.
The price per kilowatt hour or per peak kilowatt of the FIT or investment subsidies is
only one of three factors that stimulate the installation of PV. The other two factors are
insolation (the more sunshine, the less capital is needed for a given power output) and
administrative ease of obtaining permits and contracts.
Unfortunately the complexity of approvals in California, Spain and Italy has prevented
comparable growth to Germany even though the return on investment is better.
In some countries, additional incentives are offered for BIPV compared to stand alone
PV.
• France + EUR 0.25/kWh (EUR 0.30 + 0.25 = 0.55/kWh total)
• Italy + EUR 0.04-0.09 kWh
• Germany + EUR 0.05/kWh (facades only)
[edit] Investment
There is an International Conference on Solar Photovoltaic Investments organized by
EPIA.[83]
[edit] Environmental impacts
This section may stray from the topic of the article into the topic of another article,
Solar power. Please help improve this section or discuss this issue on the talk page.
Unlike fossil fuel based technologies, solar power does not lead to any harmful emissions
during operation, but the production of the panels leads to some amount of pollution. This
is often referred to as the energy input to output ratio. In some analysis, if the energy
input to produce it is higher than the output it produces it can be considered
environmentally more harmful than beneficial. Also, placement of photovoltaics affects
the environment. If they are located where photosynthesizing plants would normally
grow, they simply substitute one potentially renewable resource (biomass) for another. It
should be noted, however, that the biomass cycle converts solar radiation energy to
chemical energy ( with significantly less efficiency than photovoltaic cells alone). And if

17. they are placed on the sides of buildings (such as in Manchester) or fences, or rooftops
(as long as plants would not normally be placed there), or in the desert they are purely
additive to the renewable power base.[citations needed]
[edit] Greenhouse gases
Life cycle greenhouse gas emissions are now in the range of 25-32 g/kWh and this could
decrease to 15 g/kWh in the future.[84] For comparison, a combined cycle gas-fired power
plant emits some 400 g/kWh and a coal-fired power plant 915 g/kWh and with carbon
capture and storage some 200 g/kWh. Only nuclear power and wind are better, emitting
6-25 g/kWh and 11 g/kWh on average. Using renewable energy sources in manufacturing
and transportation would further drop carbon emissions. BP Solar owns two factories
built by Solarex (one in Maryland, the other in Virginia) in which all of the energy used
to manufacture solar panels is produced by solar panels.
[edit] Cadmium
One issue that has often raised concerns is the use of cadmium in cadmium telluride solar
cells (CdTe is only used in a few types of PV panels). Cadmium in its metallic form is a
toxic substance that has the tendency to accumulate in ecological food chains. The
amount of cadmium used in thin-film PV modules is relatively small (5-10 g/m²) and
with proper emission control techniques in place the cadmium emissions from module
production can be almost zero. Current PV technologies lead to cadmium emissions of
0.3-0.9 microgram/kWh over the whole life-cycle.[84] Most of these emissions actually
arise through the use of coal power for the manufacturing of the modules, and coal and
lignite combustion leads to much higher emissions of cadmium. Life-cycle cadmium
emissions from coal is 3.1 microgram/kWh, lignite 6.2, and natural gas 0.2
microgram/kWh.
Note that if electricity produced by photovoltaic panels were used to manufacture the
modules instead of electricity from burning coal, cadmium emissions from coal power
usage in the manufacturing process could be entirely eliminated.
[edit] Energy payback time and energy returned on energy invested
The energy payback time is the time required to produce an amount of energy as great as
what was consumed during production. The energy payback time is determined from a
life cycle analysis of energy.
Another key indicator of environmental performance, tightly related to the energy
payback time, is the ratio of electricity generated divided by the energy required to build
and maintain the equipment. This ratio is called the energy returned on energy invested
(EROEI). Of course, little is gained if it takes as much energy to produce the modules as
they produce in their lifetimes. This should not be confused with the economic return on
investment, which varies according to local energy prices, subsidies available and
metering techniques.

18. Life-cycle analyses show that the energy intensity of typical solar photovoltaic
technologies is rapidly evolving. In 2000 the energy payback time was estimated as 8 to
11 years[85], but more recent studies suggest that technological progress has reduced this
to 1.5 to 3.5 years for crystalline silicon PV systems [84].
Thin film technologies now have energy pay-back times in the range of 1-1.5 years
(S.Europe).[84] With lifetimes of such systems of at least 30 years, the EROEI is in the
range of 10 to 30. They thus generate enough energy over their lifetimes to reproduce
themselves many times (6-31 reproductions, the EROEI is a bit lower) depending on
what type of material, balance of system (or BOS), and the geographic location of the
system.[86]
[edit] Advantages
The 89 petawatts of sunlight reaching the Earth's surface is plentiful - almost 6,000 times
more than the 15 terawatts of average electrical power consumed by humans.[87]
Additionally, solar electric generation has the highest power density (global mean of 170
W/m²) among renewable energies.[87]
Solar power is pollution-free during use. Production end-wastes and emissions are
manageable using existing pollution controls. End-of-use recycling technologies are
under development.[88]
PV installations can operate for many years with little maintenance or intervention after
their initial set-up, so after the initial capital cost of building any solar power plant,
operating costs are extremely low compared to existing power technologies.
Solar electric generation is economically superior where grid connection or fuel transport
is difficult, costly or impossible. Long-standing examples include satellites, island
communities, remote locations and ocean vessels.
When grid-connected, solar electric generation replaces some or all of the highest-cost
electricity used during times of peak demand (in most climatic regions). This can reduce
grid loading, and can eliminate the need for local battery power to provide for use in
times of darkness. These features are enabled by net metering. Time-of-use net metering
can be highly favorable, but requires newer electronic metering, which may still be
impractical for some users.
Grid-connected solar electricity can be used locally thus reducing
transmission/distribution losses (transmission losses in the US were approximately 7.2%
in 1995).[89]
Compared to fossil and nuclear energy sources, very little research money has been
invested in the development of solar cells, so there is considerable room for
improvement. Nevertheless, experimental high efficiency solar cells already have

19. efficiencies of over 40% and efficiencies are rapidly rising while mass-production costs
are rapidly falling.[90]
[edit] Disadvantages
A major drawback is the area of land required for solar power generation. The 550MW
California plant that is planned requires 9.5 square miles. Many areas of the world could
not find this amount of unused land for this type of project.[citation needed] At the same time,
photovoltaics take up no land at all when installed on existing rooftops or on land not
otherwise used, such as decommissioned coal pits or in deserts.
Depending on the cost of the installation and local electric rates the payback can be 14–
20 years.[citation needed] While the modules are often warranted for upwards of 20 years, an
investment in a home-mounted system is mostly lost if you move. The city of Berkeley
has come up with an innovative financing method to remove this limitation, by adding a
tax assessment that is transferred with the home to pay for the solar panels.[91]
Solar electricity is seen to be expensive. Once a PV system is installed it will produce
electricity for no further cost until the inverter needs replacing (about 12 years[citation needed]).
Current utility rates have increased every year for the past 20 years[citation needed] and with the
increasing pressure on carbon reduction the rate will increase more aggressively[citation
needed]
. This increase will (in the long run) easily offset the increased cost at installation but
the timetable for payback is too long for most.
Solar electricity is not available at night and is less available in cloudy weather conditions
from conventional silicon based-technologies. Therefore, a storage or complementary
power system is required. However, the use of germanium in amorphous silicon-
germanium thin-film solar cells provides residual power generating capacity at night due
to background infrared radiation.[citation needed] Fortunately, most power consumption is
during the day, so solar does not need to be stored at all as long to the extent that it offsets
peak and "shoulder" consumption.[citation needed]
Apart from their own efficiency figures, PV systems work within the limited power
density of their location's insolation. Average daily insolation (output of a flat plate
collector at latitude tilt) in the contiguous US is 3-7 kilowatt·h/m²[92][93][94][95] and on
average lower in Europe.
Solar cells produce DC which must be converted to AC (using a grid tie inverter) when
used in current existing distribution grids. This incurs an energy loss of 4-12%.[96]
[edit] Photovoltaics companies
Main article: List of photovoltaics companies
[edit] See also

20. Energy portal
Environment portal
Sustainable development portal
• Active solar
• American Solar Energy Society
• Carbon nanotubes in photovoltaics
• Clean Energy Bank
• Concentrator photovoltaics
• Deployment of solar power to energy grids
• Distributed Energy Resources
• Distributed generation
• Electranet
• Green technology
• Grid-tied electrical system
• High efficiency solar cells
• History of photovoltaics
• Infrared
• Islanding
• Investment fund
• Maximum power point tracker
• Microgeneration
• Microgeneration Certification Scheme
• Photoelectrochemical cell
• Photovoltaic and renewable energy engineering in Australia
• Photovoltaics in transport
• Renewable energy
• Renewable energy in the European Union
• Solar vehicle
• Solar thermal energy
• Solar Today
• Solar energy
• Solar cell
• Solar panel
• Solar air conditioning
• Thin-film solar cell
• World Council for Renewable Energy