Solar Energy Lecture

Future energy mix

Energy from the Sun About half the incoming solar energy reaches the Earth's surface. The Earth receives 174 petawatts (PW) (1015 watts) of incoming solar radiation at the upper atmosphere. Approximately 30% is reflected back to space while the rest is absorbed by clouds, oceans and land masses. Earth's land surface, oceans and atmosphere absorb solar radiation, and this raises their temperature. Sunlight absorbed by the oceans and land masses keeps the surface at an average temperature of 14 °C. By photosynthesis green plants convert solar energy into chemical energy, which produces food, wood and the biomass from which fossil fuels are derived. http://en.wikipedia.org/wiki/Solar_energy

Breakdown of incoming solar energy http://en.wikipedia.org/wiki/File:Breakdown_of_the_incoming_solar_energy.svg

Energy from the Sun Yearly Solar fluxes & Human Energy Consumption The total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 3,850,000 exajoules (EJ) (1018 joules) per year. (70% of incoming sunlight) (1 Joule = energy required to heat one gram of dry, cool air by 1˚ C) Primary energy use (2005) 487 EJ (0.0126%) Electricity (2005) 56.7 EJ (0.0015%) Therefore a good target 2002, more energy in one hour than the world used in the year. Photosynthesis captures approximately 3,000 EJ per year in biomass. The amount of solar energy reaching the surface of the planet is so vast that in one year it is about twice as much as will ever be obtained from all of the Earth's non-renewable resources of coal, oil, natural gas, and mined uranium combined. As intermittent resources, solar and wind raise issues. http://en.wikipedia.org/wiki/Solar_energy

Solar Cells Background 1839 - French physicist A. E. Becquerel first recognized the photovoltaic effect. Photo+voltaic = convert light to electricity 1883 - first solar cell built, by Charles Fritts, coated semiconductor selenium with an extremely thin layer of gold to form the junctions. 1954 - Bell Laboratories, experimenting with semiconductors, accidentally found that silicon doped with certain impurities was very sensitive to light. Daryl Chapin, Calvin Fuller and Gerald Pearson, invented the first practical device for converting sunlight into useful electrical power. Resulted in the production of the first practical solar cells with a sunlight energy conversion efficiency of around 6%. 1958 - First spacecraft to use solar panels was US satellite Vanguard 1 http://en.wikipedia.org/wiki/Solar_cell

PV Solar for Electricity Photovoltaics For the 2 billion people without access to electricity, it would be cheaper to install solar panels than to extend the electrical grid. (The Fund for Renewable Energy Everywhere) Providing power for villages in developing countries is a fast-growing market for photovoltaics. The United Nations estimates that more than 2 million villages worldwide are without electric power for water supply, refrigeration, lighting, and other basic needs, and the cost of extending the utility grids is prohibitive, $23,000 to $46,000 per kilometer in 1988. A one kilowatt PV system* each month: prevents 70kg. of coal from being mined prevents 140kg. of CO2 from entering the atmosphere keeps 105 gallons of water from being consumed keeps NO and SO2 from being released into the environment http://www.solarenergy.org/resources/energyfacts.html

How Solar Cells Work Photons in sunlight hit the solar panel and are absorbed by semiconducting materials, such as silicon. Electrons (negatively charged) are knocked loose from their atoms, allowing them to flow through the material to produce electricity. An array of solar cells converts solar energy into a usable amount of direct current (DC) electricity. http://en.wikipedia.org/wiki/File:Silicon_Solar_cell_structure_and_mechanism.svg

Solar Cells Background Three generations of solar cells Solar Cells are classified into three generations which indicates the order of which each became important. At present there is concurrent research into all three generations while the first generation technologies are most highly represented in commercial production, accounting for 89.6% of 2007 production. http://en.wikipedia.org/wiki/Solar_cell

Solar Cells Background First Generation – Single Junction Silicon Cells 89.6% of 2007 Production 45.2% Single Crystal Si 42.2% Multi-crystal SI Large-area, high quality and single junction devices. High energy and labor inputs which limit significant progress in reducing production costs. Single junction silicon devices are approaching theoretical limit efficiency of 33%. Achieve cost parity with fossil fuel energy generation after a payback period of 5–7 years. (3.5 yr in Europe) Single crystal silicon - 16-19% efficiency Multi-crystal silicon - 14-15% efficiency Silicon Cell Average Efficiency http://en.wikipedia.org/wiki/Solar_cell and www.epia.org Solar Generation V Report Sept 08

Solar Cells Background Second Generation – Thin Film Cells CdTe 4.7% & CIGS 0.5% of 2007 Production New materials and processes to improve efficiency and reduce cost. As manufacturing techniques evolve, production costs will be dominated by constituent material requirements, whether this be a silicon substrate, or glass cover. Thin film cells use about 1% of the expensive semiconductors compared to First Generation cells. The most successful second generation materials have been cadmium telluride (CdTe), copper indium gallium selenide (CIGS), amorphous silicon and micromorphous silicon. Trend toward second gen., but commercialization has proven difficult. 2007 - First Solar produced 200 MW of CdTe solar cells, 5th largest producer in 2007 and the first to reach top 10 from of second generation technologies alone. 2007 - Wurth Solar commercialized its CIGS technology producing 15 MW. 2007 - Nanosolar commercialized its CIGS technology in 2007 with a production . capacity of 430 MW for 2008 in the USA and Germany. 2008 - Honda began to commercialize their CIGS base solar panel. CdTe – 8 – 11% efficiency (18% demonstrated) CIGS – 7-11% efficiency (20% demonstrated) Payback time < 1 year in Europe http://en.wikipedia.org/wiki/Solar_cell and www.epia.org Solar Generation V Report Sept 08

Solar Cells Background Third Generation – Multi-junction Cells Third generation technologies aim to enhance poor electrical performance of second generation (thin-film technologies) while maintaining very low production costs. Current research is targeting conversion efficiencies of 30-60% while retaining low cost materials and manufacturing techniques. They can exceed the theoretical solar conversion efficiency limit for a single energy threshold material, 31% under 1 sun illumination and 40.8% under the maximal artificial concentration of sunlight (46,200 suns). Approaches to achieving these high efficiencies including the use of multijunction photovoltaic cells, concentration of the incident spectrum, the use of thermal generation by UV light to enhance voltage or carrier collection, or the use of the infrared spectrum for night-time operation. Typically use fresnel lens (3M) or other concentrators, but cannot use diffuse sunlight and require sun tracking hardware Multi-junction cells – 30% efficiency (40-43% demonstrated) http://en.wikipedia.org/wiki/Solar_cell and www.epia.org Solar Generation V Report Sept 08

Global Cumulative PV Power http://www.epia.org/fileadmin/EPIA_docs/publications/epia/Global_Market_Outlook_Until_2013.pdf

Solar Cell Market Estimate -- First Generation -- -- Second Generation -- - Third Gen - SEMI PV Group March 2009 from source Yole Development

Global Annual PV Market Outlook http://www.epia.org/fileadmin/EPIA_docs/publications/epia/Global_Market_Outlook_Until_2013.pdf

Cost Projections $/kWh “Grid parity’ where PV cost are equal to residential electricity costs is expected to be achieved first in southern European countries and then to move north $1.35 $1.07 $0.81 $0.54 $0.27 $0.13 --- www.epia.org EPIA Solar Generation V Report Sept 08

Cumulative installed solar electric power by 2007 1st Germany 3.8 GW 2nd Japan 1.9 GW 3rd US 814 MW 4th Spain 632 MW

World's largest photovoltaic (PV) power plants (12 MW or larger) 1] World's largest photovoltaic (PV) power plants (12 MW or larger) Name of PV power plant     Country      DC Peak Power (MW) GW·h /year       Notes       Olmedilla Photovoltaic Park Spain 60 85 Completed September 2008 Puertollano Photovoltaic Park 50 2008 Moura photovoltaic power station Portugal 46 93 Completed December 2008 Waldpolenz Solar Park Germany 40 550,000 First Solar thin-film CdTe modules. Completed Dec 2008 Arnedo Solar Plant 34 Completed October 2008 Merida/Don Alvaro Solar Park 30 17 more 2 more Korea Avg 20 Koethen 14.75 13 200,000 First Solar thin-film CdTe modules. Completed Dec 2008 Nellis Solar Power Plant USA 14.02 70,000 solar panels Planta Solar de Salamanca 6 more Spain, 1 US, 1 Germany 13.8 Avg 12 n.a. 70,000 Kyocera panels http://en.wikipedia.org/wiki/Photovoltaic_power_stations

Large systems in planning or under construction Name of Plant    Country DC Peak Power (MW) GW·h /year   Notes       Rancho Cielo Solar Farm USA 600 Thin film silicon from Signet Solar** Topaz Solar Farm 550 1,100 Thin film silicon from OptiSolar ** High Plains Ranch 250 Monocrystaline silicon from SunPower with tracking ** Mildura Solar concentrator power station Australia 154 270 Heliostat concentrator using GaAs cells from Spectrolab** KCRD Solar Farm 80 Scheduled to be completed in 2012 ** DeSoto County, Florida 25 To be constructed by SunPower for FPL Energy, completion date 2009.* Davidson County solar farm 21.5 36 individual structures** Cádiz solar power plant Spain 20.1 36 * Kennedy Space Center, Florida 10 To be constructed by SunPower for FPL Energy, completion date 2010.** * Under construction; ** Proposed http://en.wikipedia.org/wiki/Photovoltaic_power_stations

Olmedilla Solar Park 60 MWp photovoltaic park installed by Nobesol with modules from Silikin http://www.siliken.com/clientes_proyectos/instalaciones/ficha?contentId=572

Waldpolenz Solar Park http://www.dw-world.de/dw/article/0,2144,3430319,00.html

Waldpolenz Solar Park http://lumbergusa.com/main/Bild/sp_pv_07/Brandis-Waldpolenz-Fotomont.jpg

Nellis AFB Solar panels http://en.wikipedia.org/wiki/File:Nellis_AFB_Solar_panels.jpg

GM installs world's biggest rooftop solar panels http://www.guardian.co.uk/environment/2008/jul/09/solarpower.renewableenergy 9 July 2008

Top 10 PV Cell Producers Until recently BP Solar was dominant supplier. New Top 10 produce 53% of world total Q-Cells, SolarWorld - Germany Sharp, Kyocera, Sharp, Sanyo – Japan Suntech, Yingli, JA Solar – China Motech - Taiwan

What is Solar Energy? Originates with the thermonuclear fusion reactions occurring in the sun. Represents the entire electromagnetic radiation (visible light, infrared, ultraviolet, x-rays, and radio waves).

Putting Solar Energy to Use: Heating Water Two methods of heating water: passive (no moving parts) and active (pumps). In both, a flat-plate collector is used to absorb the sun’s energy to heat the water. The water circulates throughout the closed system due to convection currents. Tanks of hot water are used as storage.

Heating Water: Active System Active System uses antifreeze so that the liquid does not freeze if outside temp. drops below freezing.

Heating Water—Last Thoughts Efficiency of solar heating system is always less than 100% because: % transmitted depends on angle of incidence, Number of glass sheets (single glass sheet transmits 90-95%), and Composition of the glass Solar water heating saves approx. 1000 megawatts of energy a yr, equivalent to eliminating the emissions from two medium sized coal burning power plants. By using solar water heating over gas water heater, a family will save 1200 pounds of pollution each year. Market for flat plate collectors grew in 1980s because of increasing fossil fuels prices and federal tax credits. But by 1985, when these credits were removed and fossil fuel prices were low, the demand for flat plate collectors shrunk quickly. While solar water heating is relatively low in the US, in other parts of the world such as Cyprus (90%) and Israel (65%), it proves to be the predominate form of water heating.

Heating Living Spaces Best design of a building is for it to act as a solar collector and storage unit. This is achieved through three elements: insulation, collection, and storage. Efficient heating starts with proper insulation on external walls, roof, and the floors. The doors, windows, and vents must be designed to minimize heat loss. Collection: south-facing windows and appropriate landscaping. Storage: Thermal mass—holds heat. Water= 62 BTU per cubic foot per degree F. Iron=54, Wood (oak) =29, Brick=25, concrete=22, and loose stone=20

Heating Living Spaces Passive Solar Trombe Wall Passively heated home in Colorado

Heating Living Spaces A passively heated home uses about 60-75% of the solar energy that hits its walls and windows. The Center for Renewable Resources estimates that in almost any climate, a well-designed passive solar home can reduce energy bills by 75% with an added construction cost of only 5-10%. About 25% of energy is used for water and space heating. Major factor discouraging solar heating is low energy prices.

Solar-Thermal Electricity: Power Towers General idea is to collect the light from many reflectors spread over a large area at one central point to achieve high temperature. Example is the 10-MW solar power plant in Barstow, CA. 1900 heliostats, each 20 ft by 20 ft a central 295 ft tower An energy storage system allows it to generate 7 MW of electric power without sunlight. Capital cost is greater than coal fired power plant, despite the no cost for fuel, ash disposal, and stack emissions. Capital costs are expected to decline as more and more power towers are built with greater technological advances. One way to reduce cost is to use the waste steam from the turbine for space heating or other industrial processes.

Power Towers Power tower in Barstow, California.

Solar-Thermal Electricity: Parabolic Dishes and Troughs Focus sunlight on a smaller receiver for each device; the heated liquid drives a steam engine to generate electricity. Output was 13.8 MW; cost was $6,000/peak kW and overall efficiency was 25%. Through federal and state tax credits, Luz was able to build more SEGS, and improved reduced costs to $3,000/peak kW and the cost of electricity from 25 cents to 8 cents per kWh, barely more than the cost of nuclear or coal-fired facilities. The more recent facilities converted a remarkable 22% of sunlight into electricity.

Parabolic Dishes and Troughs Collectors in southern CA. Because they work best under direct sunlight, parabolic dishes and troughs must be steered throughout the day in the direction of the sun.

Solar Panels in Use Because of their current costs, only rural and other customers far away from power lines use solar panels because it is more cost effective than extending power lines. Note that utility companies are already purchasing, installing, and maintaining PV-home systems

Efficiency and Disadvantages Efficiency is far lass than the 77% of solar spectrum with usable wavelengths. 43% of photon energy is used to warm the crystal. Efficiency drops as temperature increases (from 24% at 0°C to 14% at 100°C.) Light is reflected off the front face and internal electrical resistance are other factors. Overall, the efficiency is about 10-14%. Underlying problem is weighing efficiency against cost. Crystalline silicon-more efficient, more expensive to manufacture Amorphous silicon-half as efficient, less expensive to produce.

Spring 2010 Photovoltaics Solar’s Disadvantage It may come as a surprise, but the sun is not always up A consumer base that expects energy availability at all times is not fully compatible with direct solar power Therefore, large-scale solar implementation must confront energy storage techniques to be useful at small scale, can easily feed into grid, and other power plants take up slack by varying their output Spring 2010 Lecture 11

Solar’s Disadvantage…. Methods of storage (all present challenges): conventional batteries (lead-acid) exotic batteries (need development) hydrogen fuel (could power fleet of cars) global electricity grid (always sunny somewhere) pumped water storage (not much capacity) Argument that sun provides power only during the day is countered by the fact that 70% of energy demand is during daytime hours. At night, traditional methods can be used to generate the electricity.

On the Grid, or Off..? Most residential homes using PV technology are still linked to the Utilities power grid Other option is storing excess generated energy in battery unit -No alternate source available then

Cost Trends - Photovoltaics 100 80 60 40 20 COE cents/kWh 1980 1990 2000 2010 2020

Production and Disposal Concerns Production - Worker Health and Safety ･Amorphous silicon ﾑ Silane, an explosive gas, is used in making amorphous silicon. Toxic gases such as phosphine and diborane are used to electronically "dope" the material. 
 ･Copper indium diselenide ﾑ Toxic hydrogen selenide is sometimes used to make copper indium diselenide, a thin-film PV material. 
 ･Cadmium telluride ﾑ Cadmium and its compounds, which are used in making cadmium telluride PV cells, can be toxic at high levels of lung exposure. Disposal ･Module lifespan typically around 30 years ･Some material classified as hazardous waste ･Recycling process not yet perfected

Large Scale Solar Power PV-generated electricity still costs more than electricity generated by conventional plants in most places, and regulatory agencies require most utilities to supply the lowest-cost electricity. Output dependent on weather Mostly used in Southwest 150 MW solar power facility in California – the world’s largest Dish collector focuses heat to drive generator Solar furnace project in California

The PV Value Chain (multi-crystalline) Polysilicon Wafer Solar Cell Solar Module Chemical Process (purification) Casting Cutting Surface Treatment Assembly Systems Installation Operation

Photosynthetic Process Operationally Sunlight is trapped by chloroplasts Water is transported from soil to leaf Carbon dioxide enters through stomata Water and light combine to form chemical energy Chemical energy and carbon dioxide rearrange to form carbohydrates and oxygen Sugar is stored in plant and oxygen is released through stomata

2.1. RADIATION PROPERTIES OF THE ATMOSPHERE

Solar spectrum Natural Dye Absorption

Solar Energy Spectrum Power reaching earth 1.37 KW/m2

2.3. SOLAR SPECTRAL IRRADIANCE P=1.367kWm-2 - the solar constant – solar radiation power outside the Earth’s atmosphere Taken from: S. M. SZE; Physics of Semiconductor Devices; Second Edition; John Wiley & Sons;New York; 1981