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EE535: Renewable Energy: Systems, Technology & Economics. Solar Plant Engineering. Solar Power Plants. The output of a solar power plant (SPP) may be Thermal Energy for direct use in heat processes Electricity for use in an autonomous network or fed into a utility grid
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EE535: Renewable Energy: Systems, Technology & Economics Solar Plant Engineering
Solar Power Plants • The output of a solar power plant (SPP) may be • Thermal Energy for direct use in heat processes • Electricity for use in an autonomous network or fed into a utility grid • Electricity may be generated : • Directly from solar radiation using photovoltaic modules in photovoltaic power plants • Via intermediate thermomechanical conversion in thermal solar power plants
Conventional power plant Input to conventional plants is combustible matter (coal, oil, gas, biomass) or nuclear Needs to be extracted from geological deposits Becomes an article of commerce Needs to be transported to location of plant Stock of primary raw material can be stored and utilized as required Solar Power Plant The primary energy input to the SPP (radiation) has no raw material form & is dilute Terrestrially accessible only available during daylight hours Availability depends on latitude, season, time, topography of location, meteorological conditions Cannot be stored directly for later use Not usually abundant in places where bulk energy is required Free, indigenous, renewable Free from toxins or radioactivity Inherently very low risk SPP vs Conventional power plant Nature, quality and availability of input energy to a SPP differs significantly from a conventional power plant
Site Requirements • Engineering (‘mining’) and supply functions must be carried out at the site of a SPP • Power rating of the plant is directly proportional to the effective collector surface area • Consequently SPP’s require more on-site land area than conventional power plants • No off-site land is needed for energy raw materials mining, processing, handling and transport, disposal of (sometimes hazardous) residues
State of the Art • Technology for producing electricity from solar energy is technically proven for PV and solar thermal • 354 MW solar thermal plants using trough technology have been operational in the US since the 1980’s • Large PV plants (circa 50MW) are now in operation
Solar Plant Design Parameters • Design Point: • Provides basis for sizing of SPP, in combination with specification of output power capacity under rated conditions. • Conventional power plant facility usually sized based on nominal (nameplate) output conditions. Operation at these conditions may be maintained for extended time periods (base load supply) • Solar energy is fluctuating – need to specify conditions on a certain day, time, etc – design point • Rated power capacity of a SPP is usually stated in terms of Design Point. • Performance: • Actual performance will differ from design point and must be calculated be calculated temporally. • Key factors impacting performance include meteorological conditions (irradiation), plant parasitics and losses. • Performance can often be enhanced by use of an auxillary energy source.
Solar Plant Design Parameters • Solar Multiple: • ratio of collector subsystem output power at design point conditions to that needed by the Power Control Unit for generating nominal output. • Necessary to obtain better performance on ‘average irradiation days’ • With SM > 1, excess energy can be stored (e.g. charge thermal storage) • Capacity Factor: • Plants never operate at rated capacity over a full year due to maintenance, service or costs, etc. • Main factors affecting CP are: location-specific irradiation conditions, the SPP type and configuration, operating reliability • Field-receiver ratio: • to increase number of hours at which receiver can operate at its design point rating, the converter may be oversized at the design point by 10 – 15%
Semiconductor materials need to be of high quality and consistent properties Mass production with high levels of precision Final product lifetime > 20years in hostile environment -30C to + 200C No contact corrosion Redundancy included in design to mitigate against system failure Solar modules are usually composed of several individual cells Individual cells can be connected in series or parallel Each cell generates its own emf and current density J Arrangement A produces a higher output voltage – usually about 3V needed above battery voltage for charging Arrangement B lower voltage but higher current Cell Design Criteria A B
3 Generations of Solar Cells • First generation solar cells are the larger, silicon-based, photovoltaic cells that have, and still do, dominate the solar panel market. These solar cells, using silicon wafers, account for 86% of the solar cell market. They are dominant due to their high efficiency. This despite their high manufacturing costs; a problem that second generation cells hope to remedy. • Second generation cells, also called thin-film solar cells, are significantly cheaper to produce than first generation cells but have lower efficiencies. The great advantage of second generation, thin-film solar cells, along with low cost, is their flexibility. Thin-film technology has spurred lightweight, aesthetically pleasing solar innovations such as solar shingles and solar panels that can be rolled out onto a roof or other surface. It has been predicted that second generation cells will dominate the residential solar market as new, higher-efficiency cells are researched and produced. • Third generation solar cells are the cutting edge of solar technology. Still in the research phase, third generation cells have moved well beyond silicon-based cells. Generally, third generation cells include solar cells that do not need the p-n junction necessary in traditional semiconductor, silicon-based cells. Third generation contains a wide range of potential solar innovations including polymer solar cells, nanocrystalline cells, and dye-sensitized solar cells. If and when these technologies are developed and produced, the third generation seems likely to be divided into separate categories. http://solar.calfinder.com/blog/solar-information/solar-genealogy-on-three-generations-of-solar-cells/
Costs Wim C Turkenburg, Utrecht Scenario: Module Price = 3€/Wp Infrastructure Price = 2€/Wp System Price = 5€/Wp UNEP Energy Technology Factsheet
Table showing average cost in cents/kWh over 20 years for solar power panels http://en.wikipedia.org/wiki/Photovoltaics
Economics • Cost of solar PV has reduced dramatically over the past number of years – but is still relatively uncompetitive • Reduction in cost due to improvements in manufacturing technology and high volume manufacturing & better conversion efficiency • Insolation is a major variable determining the economic value of a solar project • For remote locations (far from the grid) the economics of solar can be much more attractive
Economics • In grid-connected systems, the excess energy generated during the day can be exported to the grid, or stored • Equally, in grid-connected systems, any shortfall can be imported from the grid or a storage device • Government subsidies an tariffs and have a major impact on solar PV economics (e.g. Germany)
Grid Connected vs Stand-Alone Grid PV Panels DC/AC Grid Connect PV System user Storage PV Panels Regulator Stand-alone PV System user
Increase conversion efficiency Reduce materials usage Mass production of PV components Reduction of balance of system costs (e.g. multifunctional use of PV functional area) Long term Aims: efficiency ~ 40% system cost < 1€/Wp No hazardous or scarce materials Long term stability (>40years) Options to Reduce PV Costs
Question • The capital cost of installing an array of solar panels that will produce 1kWp is €8000. • The annual solar energy density in the location where the panels are to be installed is 2000 kWh/m2. • The lifetime of the solar panels is estimated to be 50 years. • Assuming a discount rate of 6%, calculate the cost of electricity per kWh.
Solution Loan repayment factor: A = (1 – 1/(1+r)n) / r NPV = EAC x A = Capital Cost = €8000 A = (1 - 1/(1 + 0.06)30) / 0.06 = 13.764 EAC = NPV/ A = 8000 / 13.764 = €581 Cost of Electricity = Celec = Net Present Value of Costs (cent) / Net Present Value of Output (kWh) Celec = 581 / 2000 = € 0.29 / kWh
An efficient solar conversion technique involves placing a Stirling Engine at the focal point of a solar concentrator / collecting dish The dish focuses the light onto the hot side of the engine – resulting in up to 30% efficiency. Engine usually contains sealed hydrogen gas. Stirling is very quiet, reliable, safe, has a high thermal efficiency, has a completely external heat supply, has no emissions The gasses used inside a Stirling engine never leave the engine. There are no exhaust valves that vent high-pressure gasses, as in a gasoline or diesel engine, and there are no explosions taking place. Because of this, Stirling engines are very quiet. The Stirling cycle uses an external heat source, which could be anything from gasoline to solar energy to the heat produced by decaying plants. No combustion takes place inside the cylinders of the engine. Solar Conversion : Solar Stirling
Stirling Engine Cysle (1) a→b process, working fluid absorbs heat and raise temperature with constant volume; (2) b→c process, working fluid absorbs heat and expands at constant temperature; (3) c→d process, working fluid cools and lower temperature with constant volume; (4) d→a process, working fluid cools and contracts at constant temperature.
