1. Energy and Environment
Renewable Energy
Solar Energy

2. Introduction
An appropriate lead-in to the renewable energy sources (solar energy) is to explain the advantages and disadvantages of solar power.
The advantages include:
1- Solar energy is free, although there is a cost in the building of ‘collectors’ and other equipment that is required to convert solar energy into electricity or hot water.
2- Solar energy does not cause pollution. However, solar collectors and other associated equipment/machines are manufactured in factories that do generate some pollutants during the manufacturing process.

3. Introduction
3- Solar energy can be used in remote areas where it is too expensive to extend the electricity power grid, such as mountainous areas or in poorer nations lacking such infrastructure.
4- Many everyday items such as calculators and other low power consuming devices can be effectively powered by solar energy.
5- It is estimated that the world’s oil reserves will last for 30 to 40 years at the current rates of consumption and discovery. On the other hand, solar energy is infinite (as long as the sun is burning).

4. Introduction The disadvantages include:
1- Appreciable amounts of solar energy can only be harnessed when it is daytime and sunny.
2- Solar collectors, panels and cells are relatively expensive to manufacture, although prices are falling rapidly.
3- Solar power stations can be built, but they do not match the power output of similar sized conventional power stations; i.e. the large solar-thermal power plant only produces 10 MW, while a “normal” size coal-fired plant is around 1000 MW. Solar power stations are also very expensive.

5. Introduction The disadvantages include:
4- Unreliable climate means that solar energy is also unreliable as a source of energy. Cloudy skies reduce the effectiveness of solar power generation.
5- Large areas of land are required to capture the suns energy. Collectors are usually arranged together, especially when electricity is to be produced and used in the same location.
6- Solar power is used to charge batteries so that devices can be used at night. However, the batteries are large, heavy, and need storage space. They also need replacing from time to time.

6. A Flat Plate Collector System
The flat plate collector is the most common type of solar thermal collector.
Flat plate collectors do well in almost any environment and climate.
Can heat water to 160 or 180 degrees Fahrenheit.

7. A Flat Plate Collector System

8. A Flat Plate Collector System

9. Home Space Heating

10. A Flat Plate Collector System
Example
Estimate the collector surface area needed to heat 100 gallons of water a day from 500F to 1200F when the daily insolation is 1000 Btu/ft2. assume an efficiency of 50%.

11. Passive Solar
Passive Solar technologies use sunlight for useful energy without use of active mechanical systems (like pumps, motors, tracking units, etc). These technologies convert sunlight into usable heat (water, air, thermal mass), cause air-movement for ventilating, or future use, with little use of other energy sources.

12. Passive Solar
Passive solar technologies include direct and indirect solar gain for space heating, solar water heating systems based on the thermo siphon, use of thermal mass and phase-change materials for slowing indoor air temperature swings, solar cookers, the solar chimney for enhancing natural ventilation, and earth sheltering.

13. Passive Solar

14. Passive Solar
Example
a)Calculate the amount of of solar energy in Btu that would come in a double glazed window of 100 ft Btu per square feet will be incident on the window that day. Assume 75% of the incident light is transmitted.
b)If the conductive heat loss from inside to outside that day is 480 Btu per square feet. How many Btu are lost by conduction that day.
c)Find the net solar gain

15. Concentrating Solar Power (CSP)
There are many kinds of high-temperature commercial solar thermal systems. These systems take solar heat and use it to make electricity.
Parabolic Trough
Power Tower
Dish Designs

16. Parabolic Trough

17. Parabolic Trough

18. Parabolic Trough
The parabolic trough was developed in the late 1800s and patented in 1907.
Parabolic Trough power plants use a curved trough which reflects the direct solar radiation onto a pipe containing a fluid (also called a receiver, absorber or collector) running the length of the trough, above the reflectors.
These troughs track the sun on a single axis, from east to west.

19. Parabolic Trough
The receiver may be enclosed in a glass vacuum chamber. The vacuum significantly reduces convective heat loss.
A fluid (also called heat transfer fluid) passes through the receiver and becomes very hot (around 400 degrees F). Common fluids are synthetic oil, molten salt and pressurized steam. The fluid containing the heat is transported to a heat engine where about a third of the heat is converted to electricity.

20. Parabolic Trough

21. Parabolic Trough

22. Power Tower

23. Power Tower

24. Power Tower
Power Towers (also known as 'central tower' power plants or 'heliostat' power plants) use an array of flat, moveable mirrors (called heliostats) to focus the sun's rays upon a collector tower (the receiver).

25. Power Tower

26. Power Tower
The advantage of this design above the parabolic trough design is the higher temperature. Thermal energy at higher temperatures can be converted to electricity more efficiently and can be more cheaply stored for later use.
The disadvantage is that each mirror must have its own dual-axis control, while in the parabolic trough design one axis can be shared for a large array of mirrors.

27. Power Tower

28. Power Tower

29. Power Tower

30. Dish Designs

31. Dish Designs
A dish system uses a large, reflective, parabolic dish (shaped like a satellite television dish). It focuses all the sunlight that strikes the dish up onto to a single point above the dish, where a receiver captures the heat and transforms it into a useful form. Typically the dish is coupled with a Stirling engine in a Dish-Stirling System. From there the energy is converted into electricity.

32. Dish Design
The advantage of a dish system is that it can achieve much higher temperatures because of the higher concentration of light (like the tower designs). Higher temperatures leads to better conversion to electricity.

33. Dish Design There are two main disadvantages:
Heat to electricity conversion requires moving parts and that results in maintenance.
The heavy engine is part of the moving structure, which requires a rigid frame and strong tracking system, which adds to the cost.

34. 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.

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%.

36. Efficiency and Disadvantages
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.

37. 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.