Solar cells – tapping into a renewable energy resource

Photovoltaic (PV) cellsPhoto – lightVoltaic - volts

OregonDOT@Flickr

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Energy transformations in solar cells

Light energy is transmitted in ‘parcels’ called photons. Silicon-based solar cells are less than 20% efficient. This means they transform less than 20 % of the incoming light energy into electrical energy. The rest of the light energy is transformed into heat energy.

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Silicon-based solar cells contain thin layers of two different materials, each of which is mostly made from silicon.

When photons (bundles of light energy) of sufficient energy enter one of these materials, their energy is transferred to electrons on the surface of some of the atoms, which causes them to move out and along the junction between the layers. This causes a movement of electrons around the electrical circuit.

How do silicon-based solar cells work?

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• A typical silicon-based solar cell delivers 0.65 V. The current delivered is a direct current (DC) – a current that flows in just one direction.

• A solar panel consists of many solar cells connected together. The greater the total area of solar cells, the greater the amount of electrical power they deliver.

• If 2 solar cells were connected in series, the voltage delivered would be double that of one solar cell.

• If 2 solar cells were connected in parallel, the voltage will be the same as for one solar cell.

• In commercial solar panels, the solar cells are connected in series and parallel to deliver the desired voltage and power.

What voltage is delivered?

A solar panel

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Factors affecting the amount of electrical energy produced by solar panels include:

•The total area of the solar panel

•The intensity of light shining on the panel

•The type of solar cells being used

• How the solar cells are connected

•The angle of the panel to the direction of the light

•Clouds and shadows

•Dirt or other deposits

•The temperature of the panel

What affects the amount of electrical energy produced?

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Advantages of solar cells include:•Solar cells convert solar energy directly into electrical energy.

•They have no moving parts that can wear out.

•They do not produce greenhouse gases or other pollution when operating.

•They provide electrical energy for over 50 years.

•They can be used in remote areas.

•Excess electrical energy can be stored in batteries for later use or fed back into the grid.

•Many places receive a lot of solar energy.

Advantages of solar cells

Source: ANU Fenner School of Environment & Society

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Disadvantages of solar cells include:•Variable light intensity due to:

• Cycle between day and night• Clouds• Shadows• Changing angle of the incoming sunlight to

the face of the panel, due to the changing position of the Sun in the sky

• Dirt, pollution or other obstructions

This means they cannot produce a steady amount of electrical power.

• Expensive (?)• They have a low energy efficiency, so a large

area is required.• It can be expensive to connect solar farms into

a statewide electricity grid, due to the distances involved.

Disadvantages of solar cells

myuibe@Flickr

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• A typical household rooftop installation will have a capacity of 1.0 kW - 1.5 kW. Each solar panel consists of cells connected in series and parallel to give a desired output - 12 V or 24 V (DC).

• An inverter is placed into the circuit to change the DC voltage from the solar panels to 240 V AC for running household appliances.

Advantages include:• Excess electrical energy can be sold back into the

electricity grid.

• Solar panels have a life span of up to 50 years.

• Solar panels do not produce greenhouse gases when they are operating.

House or school solar systems

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The circuit for house or school solar systems

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In Australia

Wizard Power Solar Farm

See STELR Case Study

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In Australia

Sydney Town Hall

See STELR Case Study “Green Cities”

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Emerging technologies include: •Printable PV for flexible uses such as backpacks•Building-integrated PV for use in roofing and window materials•Dye-sensitised solar cells imitate photosynthesis to produce electrical energy.

Emerging Technologies

Source:Dyesol

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Example Early Stage Career Opportunities

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Sci

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Development Approval OperationsConstruction

Project Development Stage

Solar Power Researcher

Development Engineer

Development Officer

Ecologists

Design Engineer

Heritage Monitors

Solar Design

Engineer

Construction Manager

Community Engagement

Officer

Plant Optimisation

Engineer

Electrical Engineer

Solar Cell Installer

Careers

See STELR Career Profiles

Career Profiles

Name: Nicole Kuepper

Job: Solar Cell Researcher

Employer: UNSW

•Researches new solar cell designs that are more efficient and less expensive

•Read Nicole’s career profile on the STELR website.

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Revision Questions

• What energy transformations occur when a solar cell operates?

• What factors affect the amount of energy ‘captured’ by a solar panel?

• How efficient are silicon-based solar cells?

• Which direction should fixed solar panels face in Australia?

• How can you connect solar cells to get a bigger voltage?

• What are three disadvantages of using solar panels to produce electrical energy?

• List two issues that scientists and engineers need to consider when developing a solar energy power station.

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