This document summarizes information about photovoltaic (PV) solar energy and wind energy. It discusses how PV cells convert sunlight into electricity and how they are arranged in modules and arrays. It also describes how wind turbines convert kinetic wind energy into electrical energy using blades and generators. The document notes that both PV and wind power capacities have grown significantly in recent decades and that renewable resources like these could potentially meet 100% of energy needs in the future as technologies advance.

1. PV AND WIND
Renewable Energy Resources
Prepared by Engineer:
Ahmed Amin Hassan Hefny

2. Introduction:
Solar cells convert sunlight directly into electricity. Solar cells are often used to power
calculators and watches. They are made of semiconducting materials similar to those used in
computer chips. When sunlight is absorbed by these materials, the solar energy knocks
electrons loose from their atoms, allowing the electrons to flow through the material to
produce electricity. This process of converting light (photons) to electricity (voltage) is called
the photovoltaic (PV) effect.
It is typically combined into modules that hold about 40 cells; a number of these modules
are mounted in PV arrays that can measure up to several meters on a side. These flat-plate
PV arrays can be mounted at a fixed angle facing south, or they can be mounted on a tracking
device that follows the sun, allowing them to capture the most sunlight over the course of a
day. Several connected PV arrays can provide enough power for a household; for large
electric utility or industrial applications, hundreds of arrays can be interconnected to form a
single, large PV system. Figure.1 and 2 show installing of PV in different places and ranges
of output power.
Fig. 1 PV cells over roofs of homes with different scale

3. Fig. 1 PV cells over roofs of garage and large buildings
Some solar cells are designed to operate with concentrated sunlight. These cells are built
into concentrating collectors that use a lens to focus the sunlight onto the cells. This approach
has both advantages and disadvantages compared with flat-plate PV arrays. The main idea
is to use very little of the expensive semiconducting PV material while collecting as much
sunlight as possible. But because the lenses must be pointed at the sun, the use of
concentrating collectors is limited to the sunniest parts of the country. Some concentrating
collectors are designed to be mounted on simple tracking devices, but most require
sophisticated tracking devices, which further limit their use to electric utilities, industries, and
large buildings.
The performance of a solar cell is measured in terms of its efficiency at turning sunlight
into electricity. Only sunlight of certain energies will work efficiently to create electricity, and
much of it is reflected or absorbed by the material that make up the cell. Because of this, a
typical commercial solar cell has an efficiency of 15%-about one-sixth of the sunlight striking
the cell generates electricity. Low efficiencies mean that larger arrays are needed, and that
means higher cost. Improving solar cell efficiencies while holding down the cost per cell is
an important goal of the PV industry.

4. We have been harnessing the wind's energy for hundreds of years. From old Holland to
farms in the United States, windmills have been used for pumping water or grinding grain.
Today, the windmill's modern equivalent - a wind turbine - can use the wind's energy to
generate electricity.
Wind turbines, like windmills, are mounted on a tower to capture the most energy. At 100
feet (30 meters) or more aboveground, they can take advantage of the faster and less
turbulent wind. Turbines catch the wind's energy with their propeller-like blades. Usually, two
or three blades are mounted on a shaft to form a rotor. Figure.3 shows the different between
the past and present wind turbine in height and generated power.
Fig. 3 the past and the present wind turbine

5. A blade acts much like an airplane wing. When the wind blows, a pocket of low-pressure
air forms on the downwind side of the blade. The low-pressure air pocket then pulls the blade
toward it, causing the rotor to turn. This is called lift. The force of the lift is actually much
stronger than the wind's force against the front side of the blade, which is called drag. The
combination of lift and drag causes the rotor to spin like a propeller, and the turning shaft
spins a generator to make electricity.
Wind turbines can be used as stand-alone applications shown in figure 4, or they can be
connected to the utility power grid or even combined with a photovoltaic (solar cell) system
shown in figure 5. For utility-scale sources of wind energy, a large number of wind turbines
are usually built close together to form a wind plant. Several electricity providers today use
wind plants to supply power to their customers.
Stand-alone wind turbines are typically used for water pumping or communications.
However, homeowners, farmers, and ranchers in windy areas can also use wind turbines as
a way to cut their electric bills.
Small wind systems also have potential as distributed energy resources. Distributed
energy resources refer to a variety of small, modular power-generating technologies that can
be combined to improve the operation of the electricity delivery system.
Fig. 4 Stand-alone wind turbines

6. Fig. 5 Wind turbine and PV connected to the utility power grid
Photovoltaic development:
It is a fast-growing technology doubling its worldwide installed capacity every couple of
years. PV systems range from small, residential and commercial rooftop or building
integrated installations, to large utility-scale photovoltaic power station. The predominant PV
technology is crystalline silicon, while thin-film solar cell technology accounts for about 10
percent of global photovoltaic deployment. In recent years, PV technology has improved its
electricity generating efficiency, reduced the installation cost per watt as well as its energy
payback time, and has reached grid parity in at least 30 different markets by 2014. Financial
institutions are predicting a second solar "gold rush" in the near future.
At the end of 2014, worldwide PV capacity reached at least 177,000 megawatts.
Photovoltaic grew fastest in China, followed by Japan and the United States,
while Germany remains the world's largest overall producer of photovoltaic power,
contributing about 7.0 percent to the overall electricity generation. Italy meets 7.9 percent of

7. its electricity demands with photovoltaic power—the highest share worldwide. For 2015,
global cumulative capacity is forecasted to increase by more than 50 gigawatts (GW). By
2018, worldwide capacity is projected to reach as much as 430 gigawatts. This corresponds
to a tripling within five years. Solar power is forecasted to become the world's largest source
of electricity by 2050, with solar photovoltaic and concentrated solar power contributing 16%
and 11%, respectively. This requires an increase of installed PV capacity to 4,600 GW, of
which more than half is expected to be deployed in China and India. Figure 6 show the world
wide growth of photovoltaic capacity in megawatts.
Fig. 6 Worldwide growth of photovoltaic capacity in megawatts

8. Wind power development:
Modern utility-scale wind turbines range from around 600 kW to 5 MW of rated power,
although turbines with rated output of 1.5–3 MW have become the most common for
commercial use; the power available from the wind is a function of the cube of the wind speed,
so as wind speed increases, power output increases up to the maximum output for the
particular turbine. Areas where winds are stronger and more constant, such as offshore and
high altitude sites, are preferred locations for wind farms. Typically full load hours of wind
turbines vary between 16 and 57 percent annually, but might be higher in particularly
favorable offshore sites.
Globally, the long-term technical potential of wind energy is believed to be five times total
current global energy production, or 40 times current electricity demand, assuming all
practical barriers needed were overcome. This would require wind turbines to be installed
over large areas, particularly in areas of higher wind resources, such as offshore. As offshore
wind speeds average ~90% greater than that of land, so offshore resources can contribute
substantially more energy than land stationed turbines. In 2013 wind generated almost 3% of
the world’s total electricity. Figure 7 shows the worldwide growth of wind capacity in gigawatts.
Fig. 7 the worldwide growth of wind capacity in gigawatts

9. Hope of 100 % renewable energy resources:
Renewable energy use has grown much faster than even advocates had
anticipated. Wind turbines generate 39 percent of Danish electricity, and Denmark has many
biogas digesters and waste-to-energy plants as well. Together, wind and biomass provide
44% of the electricity consumed by the country's six million inhabitants. In 2010, Portugal’s
10 million people produced more than half their electricity from indigenous renewable energy
resources. Spain’s 40 million inhabitants meet one-third of their electrical needs from
renewables.
Renewable energy has a history of strong public support. In America, for example, a
2013 Gallup survey showed that two in three Americans want the U.S. to increase domestic
energy production using solar power (76%), wind power (71%), and natural gas (65%). Far
fewer want more petroleum production (46%) and more nuclear power (37%). Least favored
is coal, with about one in three Americans favoring it. Figure 8 illustrates the total world energy
consumption with respect to the source.
Fig. 8 Total world energy consumption by source