1. Solar Energy Lecture

2. Future energy mix

3. 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.

4. Breakdown of incoming solar energy

5. 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.

11. Solar Cells Background
French physicist A. E. Becquerel first recognized the photovoltaic effect.
Photo+voltaic = convert light to electricity
first solar cell built, by Charles Fritts, coated semiconductor selenium with an extremely thin layer of gold to form the junctions.
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%.
First spacecraft to use solar panels was US satellite Vanguard 1

12. 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

13. 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.

14. 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.

15. 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 % efficiency
Multi-crystal silicon % efficiency
Silicon Cell Average Efficiency
and Solar Generation V Report Sept 08

16. 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.
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.
Wurth Solar commercialized its CIGS technology producing 15 MW.
Nanosolar commercialized its CIGS technology in 2007 with a production capacity of 430 MW for 2008 in the USA and Germany.
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
and Solar Generation V Report Sept 08

17. 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)
and Solar Generation V Report Sept 08

18. Global Cumulative PV Power

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

20. Global Annual PV Market Outlook

21. 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 $
EPIA Solar Generation V Report Sept 08

22. Cumulative installed solar electric power by 2007
1st Germany GW
2nd Japan GW
3rd US MW
4th Spain MW

23. 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

24. 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

25. Olmedilla Solar Park
60 MWp photovoltaic park installed by Nobesol with modules from Silikin

26. Waldpolenz Solar Park

27. Waldpolenz Solar Park

28. Nellis AFB Solar panels

29. GM installs world's biggest rooftop solar panels
9 July 2008

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

31. 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).

32. 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.

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

34. 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 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.

35. 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

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

37. 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.

38. 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.

39. Power Towers
Power tower in Barstow, California.

40. 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.

41. 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.

42. 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

43. 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.

44. 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

45. 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.

46. 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

47. Cost Trends - Photovoltaics
100 80 60 40 20
COE cents/kWh

48. 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

49. 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

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

51. 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

52. 2.1. RADIATION PROPERTIES OF THE ATMOSPHERE

53. Solar spectrum Natural Dye Absorption

54. Solar Energy Spectrum
Power reaching earth 1.37 KW/m2

55. 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