1. Solar Energy: The Ultimate Renewable Resource

2. 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).

3. How much solar energy?
The surface receives about 47% of the total solar energy that reaches the Earth. Only this amount is usable.

4. 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.

5. 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.

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

7. 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.
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.

8. 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

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

10. Heating Living Spaces
A passively heated home uses about 60-75% of the solar energy that hits its walls and windows.
It is estimated 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.

11. 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.

12. Power Towers
Power tower in Barstow, California.

13. 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.
The more recent facilities converted a remarkable 22% of sunlight into electricity.

14. 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.

15. 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

16. Direct Conversion into Electricity
Photovoltaic cells are capable of directly converting sunlight into electricity.
A simple wafer of silicon with wires attached to the layers. Current is produced based on types of silicon (n- and p-types) used for the layers. Each cell=0.5 volts.
Battery needed as storage
No moving partsdo no wear out, but because they are exposed to the weather, their lifespan is about 20 years.

17. Single-Crystal Silicon Cell Construction
The majority of PV cells in use are the single-crystal silicon type.
Silica (SiO2) is the compound used to make the cells. It is first refined and purified, then melted down and re-solidified so that it can be arranged in perfect wafers for electric conduction. These wafers are very thin.
The wafers then have either Phosphorous or Boron added to make each wafer either a negative type layer or a positive type layer respectively. Used together these two types treated of crystalline silicon form the p-n junction which is the heart of the solar– electrical reaction.
Many of these types of cells are joined together to make arrays, the size of each array is dependant upon the amount of sunlight in a given area.

18. How Does A Cell Become A Module?
A solar cell is the basic building block of a PV system.
A typical cell produces .5 to 1V of electricity.
Solar cells are combined together to become modules or if large enough, known as an array.
A structure to point the modules towards the sun is necessary, as well as electricity converters, which convert DC power to AC.
All of these components allow the system to power a water pump, appliances, commercial sites, or even a whole community.

19. The Photovoltaic Effect
The photovoltaic effect relies on the principle that whenever light strikes the surface of certain metals electrons are released.
In the p-n junction the n-type wafer treated with phosphorus has extra electrons which flow into the holes in the p-type layer that has been treated with boron.
Connected by an external circuit electrons flow from the n-side to create electricity and end up in the p-side.

20. A picture of an typical silicon PV cell
Photovoltaic Effect
                                                                                                                                      
A picture of an typical silicon PV cell

21. Sunlight is the catalyst of the reaction.
The output current of this reaction is DC (direct) and the amount of energy produced is directly proportional to the amount of sunlight put in.
Cells only have an average efficiency of 30%

22. 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

23. 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

24. 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)

25. 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

26. Waldpolenz Solar Park
The Waldpolenz Solar Park is built on a surface area equivalent to 200 soccer fields, the solar park will be capable of feeding 40 megawatts into the power grid when fully operational in 2009.
In the start-up phase, the 130-million-euro ($201 million) plant it will have a capacity of 24 megawatts, according to the Juwi group, which operates the installation.
The facility, located east of Leipzig, uses state-of-the-art, thin-film technology. Some 550,000 thin-film modules will be used, of which 350,000 have already been installed. The direct current produced in the PV solar modules will be converted into alternating current and fed completely into the power grid.
After just a year the solar power station will have produced the energy needed to build it, according to the Juwi group.

27. Waldpolenz Solar Park

28. 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 (Idaho Power Co.).
Largest solar plant in US, sponsored by the DOE, served the Sacramento area, producing 2195 MWh of electric energy, making it cost competitive with fossil fuel plants.

29. World's Biggest Rooftop Solar Panels
The largest rooftop solar power station in the world is being built in Spain. With a capacity of 12 MW of power, the station is made up of 85,000 lightweight panels covering an area of two million SqFt.
Manufactured in rolls, rather like carpet, the photovoltaic panels are to be installed on the roof of a General Motors car factory in Zaragoza, Spain.
General Motors, which plans to install solar panels at another 11 plants across Europe, unveiled the €50M ($68M) project yesterday. The power station should be producing energy by September.
The panels will produce an expected annual output of 15.1 million kilowatt hours (kWh) - enough to meet the needs of 4,600 households with an average consumption of 3,300kWh, or power a third of the GM factory. The solar energy produced should cut CO2 emissions by 6,700 tons a year.
Energy Conversion Devices who makes the panels, said it would be the largest rooftop solar array in the world.

30. World's Biggest Rooftop Solar Panels

31. BREAKDOWN
PV systems are like any other electrical power generating systems, except the equipment used to generate the power is different.
Specific components required, and may include major components such as a DC-AC power inverter, batteries, auxiliary energy sources, sometimes the specified electrical load (appliances), wiring, surge protection and other hardware.
Batteries are often used in PV systems for the purpose of storing energy produced by the PV array during the day, and to supply it to electrical loads as needed (during the night and periods of cloudy weather). Also to keep the system at full operational power

32. Grid-connected or Utility-Connected
Grid-connected or utility-interactive PV systems are designed to operate in parallel with and interconnected with the electric utility grid.
These system contain an inverter, called a power conditioning unit (PCU) which converts the DC power produced by the PV array into AC power consistent with the voltage and power quality requirements of the utility grid.
A bi-directional interface allows the AC power produced by the PV system to either supply personal electrical loads, or return power back to the grid when the PV system output is greater than the personal demand.

34. Stand-Alone PV Systems
Stand-alone PV systems are designed to operate independent of the electric utility grid
Supply DC and/or AC electrical loads
The simplest type of stand-alone PV system is a direct-coupled system, where the DC output of a PV module or array is directly connected to a DC load
Since there are no batteries involved in direct load systems, stand-alone PV systems are suitable for such processes as heating and pumping water, ventilation fans, etc…Although they can only work in the day.
Stand-Alone systems may also power AC loads such as batteries. Like the AC adapter which powers your laptop.

35. 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%.
Cost of electricity from coal-burning plants is anywhere b/w cents/kWh, while photovoltaic power generation is anywhere b/w $0.50-1/kWh.
Does not reflect the true costs of burning coal and its emissions to the nonpolluting method of the latter.
Underlying problem is weighing efficiency against cost.
Crystalline silicon-more efficient, more expensive to manufacture
Amorphous silicon-half as efficient, less expensive to produce.

36. Final Thought
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.
Goal is to decrease our dependence on fossil fuels.
Currently, 75% of our electrical power is generated by coal-burning and nuclear power plants.
Mitigates the effects of acid rain, carbon dioxide, and other impacts of burning coal and counters risks associated with nuclear energy.
pollution free, indefinitely sustainable.

37. Advantages and Disadvantages
All chemical and radioactive polluting byproducts of the thermonuclear reactions remain behind on the sun, while only pure radiant energy reaches the Earth.
Energy reaching the earth is incredible. By one calculation, 30 days of sunshine striking the Earth have the energy equivalent of the total of all the planet’s fossil fuels, both used and unused!
Disadvantages
Sun does not shine consistently.
Solar energy is a diffuse source. To harness it, we must concentrate it into an amount and form that we can use, such as heat and electricity.
Addressed by approaching the problem through:
1) collection, 2) conversion, 3) storage.

38. The End