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strike the Earths surface. Solar energy is thus the primary energy source on our planets surface

and exceeds 8,000 times our primary energy supply. Fulfilling global energy needs as projected

for 2030 would require covering about 0.6% of emerged lands with 10% net efficient solar

conversion systems.

Another indication of the abundance of solar energy is, somewhat paradoxically, thethreat of climate change itself. The increases in the atmospheric concentrations of well-mixed

greenhouse gases from the pre-industrial to present time result mainly from the combustion of

fossil fuels for energy purposes (Figure 1). Solar energy has the potential to help solve this

problem it creates.

Figure 1. US Energy Diagram from LLNL 2009

Photovoltaic System

A photovoltaic system (or PV system) is a system, which uses one or more solar panels to

convert sunlight into electricity. It consists of multiple components, including the photovoltaic

modules, mechanical and electrical connections and mountings and means of regulating and/or

modifying the electrical output.

Solar cell/panel/array

Solar cell

When photons in sunlight hit the solar panel and are absorbed by semiconducting

materials, such as silicon, the electrons are knocked loose from their atoms, causing anelectric potential difference. Current starts flowing though the material to cancel the

potential and this electricity is captured. Due to the special composition of solar cells, the

electrons are only allowed to move in a single direction.


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Solar panelThe majority of solar panel modules use wafer-based crystalline silicon cells or

thin-film cells based on cadmium telluride or silicon. The cells must be connected

electrically to one another and to the rest of the system. Cells must also be protected frommechanical damage and moisture. Most solar panels are rigid, but semi-flexible ones are

available, based on thin-film cells. Electrical connections are made in series to achieve adesired output voltage and/or in parallel to provide a desired current capability. Separatediodes may be needed to avoid reverse currents, in case of partial or total shading, and at

night. Reverse currents waste power and can also lead to overheating of shaded cells.

Solar cells become less efficient at higher temperatures and installers try to provide good

ventilation behind solar panels.

Solar arrayConnecting solar panels in series or parallel forms a solar array, in order to match

up with the battery system, parallel voltages and polarities must match, blocking diodes

are included in the panel by the manufacture.

Grid tied inverter

Grid tie inverter (GTI) converts direct current electricity into alternating current

electricity and feeds it into an existing electrical grid. GTI is often used to convert direct current

produced by many renewable energy sources, such as solar panels or small wind turbines, into

alternating current used to power homes and businesses.

Developments in solar thermal and PV

Government-controlled Chinese solar industry has been unusually vitriolic recently.

These Chinese companies dumpingsolar panels into the United States at prices, aided bygovernment subsidies, lower than the cost of making and distributing them.

Building-9 rooftop solar thermal system at Cal Poly Pomona

The building-9 rooftop solar thermal system at Cal Poly has three 24V-208 Watt sharp

panels in series (Figure 2) with one Enphase 240 VAC MPP microinverter (Figure 3).


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Figure 2. Rooftop solar thermal system Figure 3.Enphase 240 VAC MPP microinverter

This system includes a grid tied inverter (Figure 4) to converts direct current electricity

produced by the solar panel into alternating current electricity.

Figure 4. Grid tied inverter

Another important component of this roof top solar thermal system is the single axis sun

light tracking system. It includes a sunlight sensor (Figure 5) and a drive actuator (figure 6). It is

used to minimize theangle of incidencebetween the incoming light and the solar panels. This

increases the amount of energy produced from a fixed amount of installed power generating
http://en.wikipedia.org/wiki/Angle_of_incidencehttp://en.wikipedia.org/wiki/Angle_of_incidence


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capacity. What worth mentioning is the stand off and drive actuator was remolded from a

discarded satellite receiver, which made the whole system much more cost efficient.

Figure 5. Sun light sensor Figure 6. Single axis tracking system