Photovoltaic Systems


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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?

Published in: Technology, Business

Photovoltaic Systems

  1. 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. 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. 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. 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. 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. 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. 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. 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. 9. Photovoltaic (PV) systems Minute Lectures Operating principle of the silicon system (2/2)
  10. 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. 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. 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. 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. 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. 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. 16. Photovoltaic (PV) systems Minute Lectures Further information • PV Technology Platform • IEA Photovoltaics Power Systems Programme • DTI Good Practice Guide