This new minute lecture gives an introduction to photovoltaic (PV) systems for residential use, providing an answer to following questions: * How does a PV system work? * What can be expected from a PV system? * What types of systems are available? * How is technology expected to evolve?

1. Photovoltaic (PV) systems
Minute Lectures
A PV system converts sunlight directly
into electrical energy
It produces direct current
A PV system consists of:
• Photovoltaic cells connected into
modules and encapsulated
• Modules grouped into panels
• Panels groups into arrays
• A power conditioning unit
• Batteries
What is a Photovoltaic system?
Picture Pete Beverly; source NREL Picture library

2. Photovoltaic (PV) systems
Minute Lectures
…but production is significantly smaller when cloudy.
Also functions without direct sunlight
Blue sky, no clouds
Weather condition
Solar radiation and its diffusion during various weather conditions
Power of radiation
(W/m2)
Percentage of this power
originating from diffuse
radiation (%)
600 - 1,000 10 - 20
200 - 400 20 - 80
50 - 150 80 - 100
Overcast or cloudy, sun
visible as a yellow disc

3. Photovoltaic (PV) systems
Minute Lectures
What can be expected from PV systems?
Annual output [kWh/kWp]
Location Roof-top Façade
Australia, Perth 1,587 932
Denmark, Copenhagen 850 613
Germany, Munich 960 660
Greece, Athens 1,278 774
Japan, Tokyo 955 631
Netherlands, Amsterdam 886 611
UK, London 788 544
Source: IEA Photovoltaic Power Systems Programme

4. Photovoltaic (PV) systems
Minute Lectures
Advantages
• Environmental performance: emission-free in use
• “Fuel” delivered free, by nature
• Easy to install, modular technology
• install as small or as large as needed
• More modules can be added later on
• Low maintenance
• Long life span
Disadvantages
• Off-grid system needs to be combined with a back-
up or storage system to secure supply
• High initial investment cost
• Substantial surface required

5. Photovoltaic (PV) systems
Minute Lectures
Off-grid systems
• For modest consumption or where connection to the grid is difficult
• Battery needed for storage
• Over 80% of PV systems in Mexico, Norway, Israel, Canada,
Sweden, Australia, …
• Also used for calculators, emergency telephones, space
technology,…
Grid coupled system:
• Surplus electricity is put on the grid
• Converter is needed to transform direct current into 230V
alternating current
• Over 80% of systems in Germany, Japan, UK, Netherlands,
Denmark, …
Two current practices

6. Photovoltaic (PV) systems
Minute Lectures
Two main installation methods
Mounted systems
• E.g.
• Stand-off mounted, roof-top
• Ground-mounted, rack or pole
• Patio cover
• Advantages for lower cost, more flexibility in
modules and easier to replace
Integrated systems
• E.g.
• Roof integrated PV products or roof slates
• Façade integrated
• Low visual impact

7. Photovoltaic (PV) systems
Minute Lectures
Two main technologies
Silicon
• Higher efficiency
• Expensive raw material
• Energy intensive process
• 93% of today’s market
Thin film
• Lower efficiency, so larger
surface needed
• Lower production cost
• Large future potential
• 7% of today’s market

8. Photovoltaic (PV) systems
Minute Lectures
Operating principle of the silicon system (1/2)
PV arrays are made out of coupled solar cells
• small sheets of silicon with metal contact strips
• protected by vacuum behind glass
When sunlight strikes, light particles (“photons”) knock
electrons free from silicon atoms
• Internal electrical field pushes electrons out of the cell
• one surface becomes negatively charged, opposite surface
becomes positive
An electrical current is created by connecting the positive
and negative sides

9. Photovoltaic (PV) systems
Minute Lectures
Operating principle of the silicon system (2/2)

10. Photovoltaic (PV) systems
Minute Lectures
Efficiency…
… is determined by percentage of solar energy converted
into electrical energy.
Depends on the type of silicon:
• Mono-crystalline: 12 – 16%
most expensive, life span > 20 years
• Polycrystalline: 11 – 15%
easier to produce, life span > 20 years
• Amorphous: 6 – 8%
shorter life span, used for watches and calculators
Cell efficiency also depends on temperature
Further losses occur in wires, inverter and storage systems

11. Photovoltaic (PV) systems
Minute Lectures
Some typical figures
Annual horizontal irradiation: 1000-2000 kWh/m2
per year
Annual PV electricity production: 100-200 kWh/m2
panel
surface
Annual electricity consumption: 3500 to 4000 kWh per
family
Just a family’s domestic electric demand already requires a
surface of 17 to 40 m2
But:
• PV produces about 30 times more energy per square
meter than bioenergy (source)

12. Photovoltaic (PV) systems
Minute Lectures
Current potential for installers
PV systems have large potential
Sales increase by approximately 35% each year
Strong incentives promote PV deployment
Not yet widely adopted

13. Photovoltaic (PV) systems
Minute Lectures
Prospects
Investment costs have reduced by a factor 2 during past
10 years (due to decreasing manufacturing costs
through volume production)
Increasing performance of silicon cells
European Technology Platform has ambitious objectives
for 2030
Significant investment in thin film R&D

14. Photovoltaic (PV) systems
Minute Lectures
Requirements for PV system of the future
According to PV-TRAC (Photovoltaic Technology Research
Advisory Council of the European Commission):
• Efficiency of 25%
• Life span of 40 years
• Pay back period of less than one year
• Build with abundantly available, non-toxic materials
Since silicon is scarce, research on thin film technology is
the best option
(but silicon cells are growing thinner as well, and new
production methods for silicon are being explored)

15. Photovoltaic (PV) systems
Minute Lectures
Round-up
• Converts sunlight into electrical energy
• Produces direct current
• Surplus electricity can be put on the grid for the time being
• Investment cost is still high
• Strong incentives are available
• High potential, provided technology development can
significantly reduce costs

16. Photovoltaic (PV) systems
Minute Lectures
Further information
• PV Technology Platform
• IEA Photovoltaics Power Systems
Programme
• DTI Good Practice Guide