Photovoltaics

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 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.

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.

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]

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]

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.

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 power plants generate more than 1,000 MW.

**World's largest PV power plants ^[3]**
DC Peak Power	Location	Description	MW·h/year
12 MW	Gut Erlase, Germany	1408 SOLON mover	14,000 MW·h
11 MW*	Serpa, Portugal	52,000 solar modules	Press Release
10 MW	Pocking, Germany	57,912 solar modules	11,500 MW·h
6.3 MW	Mühlhausen, Germany	57,600 solar modules	6,750 MW·h
5 MW	Bürstadt, Germany	30,000 BP solar modules	4,200 MW·h
5 MW	Espenhain, Germany	33,500 Shell solar modules	5,000 MW·h
4.59 MW	Springerville, AZ, USA	34,980 BP solar modules	7,750 MW·h
4 MW	Geiseltalsee, Merseburg, Germany	25,000 BP solar modules	3,400 MW·h
4 MW	Gottelborn, Germany	50,000 solar modules (when completed)	8,200 MW·h (when completed)
4 MW	Hemau, Germany	32,740 solar modules	3,900 MW·h
3.9 MW	Rancho Seco, CA, USA	n.a.	n.a.
3.3 MW	Dingolfing, Germany	Solara, Sharp and Kyocera solar modules	3,050 MW·h
3.3 MW	Serre, Italy	60,000 solar modules	n.a.

* Under construction, as of July 2006.Press Release

World solar power production

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).

**Installed PV Power as of the end of 2004 ^[4]**
Country	PV Capacity
	Cumulative			Installed in 2004
	Off-grid PV [KW]	Grid-connected [KW]	Total [KW]	Total [KW]	Grid-tied [KW]
Japan	84,245	1,047,746	1,131,991	272,368	267,016
Germany	26,000	768,000	794,000	363,000	360,000
United States	189,600	175,600	365,200	90,000	62,000
Australia	48,640	6,760	52,300	6,670	780
Netherlands	4,769	44,310	49,079	3,162	3,071
Spain	14,000	23,000	37,000	10,000	8,460
Italy	12,000	18,700	30,700	4,700	4,400
France	18,300	8,000	26,300	5,228	4,183
Switzerland	3,100	20,000	23,100	2,100	2,000
Austria	2,687	16,493	19,180	2,347	1,833
Mexico	18,172	10	18,182	1,041	0
Canada	13,372	512	13,884	2,054	107
Korea	5,359	4,533	9,892	3,454	3,106
United Kingdom	776	7,386	8,164	2,261	2,197
Norway	6,813	75	6,888	273	0

Deployment of solar power to energy grids

A view of the deployments of solar power of all types is given at Deployment of solar power to energy grids.

PV power costs

In the table below, the labels on the left show various total costs, per peak kilowatt (kW_p), of a photovoltaic installation. The headings across the top refer to the annual energy output expected from each installed kW_p. This varies by geographic region and according to efficiency, etc. The calculated values reflect the total cost in cents per kWh produced, including a 4% cost of capital, 1% operating and maintenance cost, and depreciating 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	2200 kWh	2000 kWh	1800 kWh	1600 kWh	1400 kWh	1200 kWh	1000 kWh	800 kWh
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 a year

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

Equipment prices

Polycrystalline modules (manufacturing): ~$2,000 / kW_p
Polycrystalline modules (commerce): 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

Grid parity

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

Photovoltaics research institutes

There are many research institutions and departments at universities around the world who are active in photovoltaics research. Countries which are particularly active include Germany, Spain, Japan, Australia, China, and the USA.

Some universities and institutes which have a photovoltaics research department.