Photovoltaics

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Photovoltaics, or PV for short, is a solar power technology that uses solar photovoltaic arrays or solar cells to provide electricity for human activities. Photovoltaics is also the field of study relating to this technology.

solar atlas

Solar cells produce direct current electricity from the sun’s rays, which can be used to power equipment or to recharge a battery. Many pocket calculators incorporate a solar cell.

When more power is required than a single cell can deliver, cells are generally grouped together to form “PV modules” that may in turn be arranged in “solar arrays” which are sometimes ambiguously referred to as solar panels. Such solar arrays have been used to power orbiting satellites and other spacecraft and in remote areas as a source of power for applications such as roadside emergency telephones, remote sensing, and cathodic protection of pipelines. The continual decline of manufacturing costs (dropping at 3 to 5% a year in recent years) is expanding the range of cost-effective uses including roadsigns, home power generation and even grid-connected electricity generation.

Large-scale incentive programs, offering financial incentives like the ability to sell excess electricity back to the public grid ("feed-in"), have greatly accelerated the pace of solar PV installations in Spain, Germany, Japan, the United States, Australia, South Korea, Italy, Greece, France, China and other countries.

1 Current development
2 PV in buildings
- 2.1 Example of PV in building
3 Solar-powered vehicles
4 PV power stations
5 Worldwide installed photovoltaic totals
6 PV power costs
7 Energy return on investment
8 Grid parity
9 Financial incentives
10 Photovoltaics research institutes
11 References
12 See also

[edit] Current development

Many corporations and institutions are currently developing ways to increase the practicality of solar power. While private companies conduct much of the research and development on solar energy, colleges and universities also work on solar-powered devices.

The most important issue with solar panels is cost. Because of much increased demand, the price of silicon used for most panels is now experiencing upward pressure. This has caused developers to start using other materials and thinner silicon to keep cost down. Due to economies of scale solar panels get less costly as people use and buy more — as manufacturers increase production, the cost is expected to continue to drop in the years to come. As of early 2006, the average cost per installed watt was about $6.50 to $7.50, including panels, inverters, mounts, and electrical items.

Grid-tied systems represented the largest growth area. In the USA, with incentives from state governments, power companies and (in 2006 and 2007) from the federal government, growth is expected to climb. Net metering programs are one type of incentive driving growth in solar panel use. Net metering allows electricity customers to get credit for any extra power they send back into the grid. This would cause role reversal, as the utility company would be the buyer, and the solar panel owner would be the seller of electricity. To spur growth of their renewable energy market, Germany has adopted an extreme form of net metering, whereby customers get paid 8 times what the power company charges them for any surplus they supply back to the grid. That large premium has made a huge demand in solar panels for that area.

[edit] PV in buildings

Solar arrays are increasingly incorporated into new domestic and industrial buildings as a principal or ancillary source of electrical power. Typically, an array is incorporated into the roof or walls of a building, roof tiles can now even be purchased with an integrated PV cell. 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 only possibility for generating electricity, or PV may be used together with wind and/or hydroelectric power. In such off-grid circumstances batteries are usually used to store the electric power. However, the largest installations are grid-connected systems (see table below). These systems are connected to the utility grid through a direct current to alternating current (DC-AC) inverter. When the load required in the building is more than that supplied by the PV array then electricity will be drawn from the grid; conversely when the PV array is generating more power than is needed in the building then electricity will be exported to the grid. Batteries are not required and standard AC electrical equipment may be used. The average lowest retail cost of a large PV module declined from $7.50 to $4 per watt between 1990 and 2004. However, prices have gone up 15-20% in 2005-2006 due to increased demand (mainly due to increased incentives and subsidies) and silicon shortages. The silicon shortage is expected to persist until at least 2008. With many jurisdictions now giving tax and rebate incentives, and/or net metering solar electric power can now pay for itself in ten to twenty years in a few places.

In August 2006 there was widespread news coverage in the United Kingdom of the major high street electrical retailer’s (Currys) decision to stock PV modules, manufactured by Sharp, at a cost of one thousand pounds sterling per module. The retailer also provides an installation service. The agency that administers UK government grants for domestic solar power systems estimates that an installation for an average-sized house would cost between £8,000 and £18,000, and yield annual savings between £75 and £125. ^[1]

[edit] Example of PV in building

In the United Kingdom, the second tallest building in Manchester, the CIS Tower, was clad in PV panels at a cost of £5.5 million and started feeding electricity to the national grid in November 2005. ^[2]

[edit] Solar-powered vehicles

There is intensive research interest in solar-powered vehicles and the technology is developing rapidly. Solar-powered cars have commonly appeared at solar races such as the World Solar Challenge and at car and technology shows. Solar boats are a new application of the technology. Solar Boats from colleges and universities compete in the Solar Splash^[1] competition in North America, and the Frisian Nuon Solar Challenge^[2] in Europe.

[edit] PV power stations

Deployment of solar power depends largely upon local conditions and requirements. But as all industrialised nations share a need for electricity, it is clear that solar power will increasingly be used to supply a cheap, reliable electricity supply. In 2004 the worldwide production of solar cells increased by 60% but silicon shortages reduced growth afterwards.

The list below shows the largest photovoltaic plants in the world. For comparison, the largest solar plant, the solar trough-based SEGS in California produces 350 MW and the largest nuclear reactors generate more than 1,000 MW. A plant in Australia, which will not come into service until 2008, is expected to be 154 MW when it is completed by 2013.[3]

**World's largest PV power plants ^[3]**
DC Peak Power	Location	Description	MW·h/year	Coordinates
12 MW	Gut Erlasse, Germany^[4]	1408 SOLON mover	14,000 MW·h	n.a.
11 MW*	Serpa, Portugal	52,000 solar modules	Press Release	n.a.
10 MW	Pocking, Germany	57,912 solar modules	11,500 MW·h	n.a.
6.3 MW	Mühlhausen, Germany^[5]	57,600 solar modules	6,750 MW·h	49°09′29″N, 11°25′59″E
5.2 MW	Kameyama, Japan	47,000 square meters on Sharp LCD factory roof	n.a.	34°52′15″N, 136°24′19″E
5 MW	Bürstadt, Germany	30,000 BP solar modules	4,200 MW·h	n.a.
5 MW	Espenhain, Germany	33,500 Shell solar modules	5,000 MW·h	n.a.
4.59 MW	Springerville, AZ, USA	34,980 BP solar modules	7,750 MW·h	n.a.
4 MW	Geiseltalsee, Merseburg, Germany	25,000 BP solar modules	3,400 MW·h	n.a.
4 MW	Gottelborn, Germany	50,000 solar modules (when completed)	8,200 MW·h (when completed)	n.a.
4 MW	Hemau, Germany	32,740 solar modules	3,900 MW·h	n.a.
3.9 MW	Rancho Seco, CA, USA	n.a.	n.a.	n.a.
3.3 MW	Dingolfing, Germany	Solara, Sharp and Kyocera solar modules	3,050 MW·h	n.a.
3.3 MW	Serre, Italy	60,000 solar modules	n.a.	n.a.

* Under construction, as of July 2006.Press Release

[edit] Worldwide installed photovoltaic totals

Total peak power of installed solar panels is around 5,300 MW as of the end of 2005. (IEA statistics appear to be under-reported: they report 2,600 MW as of 2004, which with 1,700 installed in 2005 would be a cumulative total of 4,300 for 2005). The three leading countries (Japan, Germany and the USA) represent 90% of the total worldwide PV installations. A view of the deployments of solar power of all types is given at Deployment of solar power to energy grids.

**Installed PV Power as of the end of 2005 ^[6]**
Country	PV Capacity
	Cumulative			Installed in 2005
	Off-grid PV [kW]	Grid-connected [kW]	Total [kW]	Total [kW]	Grid-tied [kW]
Japan	87,057	1,334,851	1,421,908	289,917	287,105
Germany	29,000	1,400,000	1,429,000	635,000	632,000
United States	233,000	246,000	479,000	103,000	70,000
Australia	41,841	8,740	60,581	8,280	1,980
Spain	15,800	41,600	57,400	20,400	18,600
Netherlands	4,919	45,857	50,776	1,697	1,547
Italy	12,300	15,200	37,500*	6,800	6,500

* Original source gives these individual numbers and totals them to 37,500 KW. The 2004 reported total was 30,700 KW.^[7] With new installations of 6,800 KW, this would give the reported 37,500 KW.

[edit] PV power costs

The table below shows the total cost in US cents per kWh of electricity generated by a photovoltaic system. The row headings on the left show the total cost, per peak kilowatt (kW_p), of a photovoltaic installation. The column headings across the top refer to the annual energy output in kWh expected from each installed kW_p. This varies by geographic region because of different levels of insolation and it also depends on the overall efficiency of the PV system. The calculated values within the table reflect the total cost in cents per kWh produced. They assume a 4% cost of capital, 1% operating and maintenance cost, and depreciation of the capital outlay over 20 years. (Normally, photovoltaic modules have 25 years' warranty, but they should be fully functional even after 30-40 years.)

20 years	2400 kWh/kW_p	2200 kWh/kW_p	2000 kWh/kW_p	1800 kWh/kW_p	1600 kWh/kW_p	1400 kWh/kW_p	1200 kWh/kW_p	1000 kWh/kW_p	800 kWh/kW_p
200 $/kW_p	0.8	0.9	1.0	1.1	1.3	1.4	1.7	2.0	2.5
600 $/kW_p	2.5	2.7	3.0	3.3	3.8	4.3	5.0	6.0	7.5
1000 $/kW_p	4.2	4.5	5.0	5.6	6.3	7.1	8.3	10.0	12.5
1400 $/kW_p	5.8	6.4	7.0	7.8	8.8	10.0	11.7	14.0	17.5
1800 $/kW_p	7.5	8.2	9.0	10.0	11.3	12.9	15.0	18.0	22.5
2200 $/kW_p	9.2	10.0	11.0	12.2	13.8	15.7	18.3	22.0	27.5
2600 $/kW_p	10.8	11.8	13.0	14.4	16.3	18.6	21.7	26.0	32.5
3000 $/kW_p	12.5	13.6	15.0	16.7	18.8	21.4	25.0	30.0	37.5
3400 $/kW_p	14.2	15.5	17.0	18.9	21.3	24.3	28.3	34.0	42.5
3800 $/kW_p	15.8	17.3	19.0	21.1	23.8	27.1	31.7	38.0	47.5
4200 $/kW_p	17.5	19.1	21.0	23.3	26.3	30.0	35.0	42.0	52.5
4600 $/kW_p	19.2	20.9	23.0	25.6	28.8	32.9	38.3	46.0	57.5
5000 $/kW_p	20.8	22.7	25.0	27.8	31.3	35.7	41.7	50.0	62.5

Kilowatt-hours per peak kilowatts per year at various locations

South Germany: ~900-1,130 kWh/kW_p
Italy, Sicily: ~1,800 kWh/kW_p
South Spain: ~1,800 kWh/kW_p
China, Takla Makan: ~1,840 kWh/kW_p
U.S.A., Great Basin: ~1,930 kWh/kW_p
Spain, Canary Islands: ~2,000 kWh/kW_p
U.S.A., Hawaii: ~2,100 kWh/kW_p
Africa, Sahara: ~2,270 kWh/kW_p
Australia, Great Sandy: ~2,320 kWh/kW_p
Middle-East, Arabian: ~2,360 kWh/kW_p
South America, Atacama: ~2,410 kWh/kW_p

Equipment prices

Polycrystalline modules (manufacturing costs): ~$2,000 / kW_p
Polycrystalline modules (commercial prices): from $3,490 up to $5,100 / kW_p (8 m²/kW_p)
Installation: from $600 up to $2,000 / kW_p (self-construction: from $100 up to $400 / kW_p)
Inverter for grid feed-in: ~$400 /kW_p

[edit] Energy return on investment

The energy return on investment (EROI) for photovoltaic installations is equal to the electricity generated divided by the energy required to build and maintain the equipment. Currently the energy payback-time of a polycrystalline PV system is at least as low as 1.7 years while the lifetime of such systems is at least 30 years giving it an EROI higher than 17. Because of large scale manufacturing and new technological development it is likely that polycrystalline PV-systems will reach an energy payback time of close to 1 year and a corresponding EROI of close to 30 in the forseable future. However one is expected to get an energy payback-time in the order of months for thin-film PV systems by manufacturers such as nanosolar, this would give an EROI in the 50+ range.

The EROI for photovoltaics currently ranges from from about 4 for the worst performing systems to at least 17 for the best ones. [4]

[edit] Grid parity

Grid parity is already reached in some regions. This means photovoltaic power is equal to or cheaper than grid power. Grid parity has been reached in Hawaii and many other islands that use diesel fuel to produce electricity.

[edit] Financial incentives

The most significant incentives given by governments of European countries are listed here.

[edit] Germany

Situation as of 2006. [5]

The legal framework is the German Renewable Energy Sources Act (Erneuerbare-Energien-Gesetz – EEG), amended version in force since 1 August 2004.