Category Solar Electric Power Generation – Photovoltaic Energy Systems

Summary

The drastic increase of humanity’s energy consumption results in an exponential rise in CO 2 emissions related to current predominant types of energy generation technology. The radiation exchange balance between the Earth’s surface and space has been altered by a significant increase in CO2 contents within the Earth’s atmosphere as observed over the last decades; now the balance occurs at higher surface temperatures. This is caused by the reduction of optical transmittance of the Earth’s atmosphere in the infrared range, at which thermal radiation from the Earth occurs, while the Sun’s solar spectrum reaching the ground remains relatively unchanged...

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Benefits of the I-SHS

• Ease of installation

• Significant reduction of system costs

• Increased efficiency via low cell temperature operations

• Increased reliability via pre-manufactured and pre-tested units

• Standard AC output (“Plug and Play”)

• Optional use of hot water as a by-product.

10.4.6.2 Further Development

The combination of all suggested improvements leads to a gain in electricity yields of 15-17%. At the same time systems costs could be reduced by 10-15% via pre-assembly and reduced installation costs. Ultimately the PV generation costs could be lowered by 28-38%. Construction can be environmentally sound: Recycling of all materials and components (glass, Si, PE) is entirely possible. Raw materials are available infinitely (glass, Si) or can be made of recycled materials (PE)...

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Balance of System Costs (BOS)

Since the foundation, support structure and mounting equipment are no longer required, significant reductions in installation costs and “turn-key” system costs are achieved. Together with improved aspects of maintenance and higher energy yields, PV electricity is becoming more available. Once the I-SHS has been placed at an appropriate site, it has just to be filled with water and is immediately ready to supply power to any AC device from its standard plug. The weight of the tank-container, without inverter and battery, is about seven kg, making transportation easy. When filled with water the container has a weight of more than 300 kg, thus making the system stable enough to withstand any storm without additional fixings...

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The Integrated Solar Home System (I-SHS)

10.4.6.1 Composition of the system

This project has been carried out by Fabian Ochs, a master student of the author, during 2001/02. Figure 10.25 shows the basic layout of the system: The PV generator consists of two parallel-connected, frameless 30 Wp modules. Located in the foundation structure are a maintenance-free lead-acid battery (12 V, 105 Ah) and a 200 W sine inverter (115 V, 60 Hz) with an integrated charge controller (6 A). A water tank cools all components. The output leads to a regular AC plug. All components are contained in a waterproof epoxy fiber glass tank. The prototype is 1.37 m long, 0.76 m high and 0.5 m deep and has a volume of 0.3 m3...

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Construction, Operation and Measurement of TEPVIS in Africa

In September 1995 a TEPVIS-tank was ordered at a locksmith’s shop in Harare (Zimbabwe). The material used for the construction was galvanized steel [21] (see Fig. 10.20).

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Fig. 10.20. Tank for reduction of cell temperature and serving as module mount/ foundation, manufactured in Harare (Zimbabwe) by galvanized sheet steel (without internal convection aid).

Two PQ 10/40 multi-crystalline PV modules (by Telefunken, now ASE – Schott/RWE) have been selected out of a series of twelve, according to similar short-circuit currents and open circuit voltages (see Fig. 10.21). To eliminate even small possible measurement errors, the modules were interchanged and retested after each day of measurement. The figures below are showing the average values of the measurements...

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Development of a Thermally Improved Prototype

The second prototype built in 1994 had a much larger water tank which served also as the module’s foundation, its stand and mounting structure (TEPVIS – Thermal Enhanced PV module with Integrated Standing). It was tested with an M55 in Berlin (see Figures 10.17, 10.18, and 10.19) and showed an energy gain of up to 12%, and with PQ 10/40 devices in Bulawayo, Zimbabwe and proved an increase of 9.5%. The gain in Zimbabwe was lower due to reduced water circulation and more stratification (the upper part of the tank got considerably warmer than the lower one). The inclination of the module plane in Zimbabwe was much lower (20 degrees, according to the latitude of Bulawayo), thus reducing the thermo-siphon effect...

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Preliminary Work for the Reduction of Temperatures in PV Modules

Research on an increase of PV-efficiency and electrical power output by means of a reduction in operating cell temperature has been carried out by the author since 1989 in a Ph. D. thesis (see Krauter 1993c).

The energy consumption of an active cooling system would not be compensated by the gain in increased energy generation, at least for small systems. Operational temperatures were kept at low levels by mounting the module on a water-filled tank. This allowed for an effective reduction in operating cell temperatures without spending any energy for refrigeration. The water virtually soaks up the heat flow generated by the module. Due to the high thermal capacity of the incorporated water (Cpwater= 1,254 kJ K-1) the temperature increases gradually (see also results below)...

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Thermal Enhancement of PV Modules

10.4.1 Real Operating Cell Temperatures Under Tropical Conditions

To know more about real operating behavior under tropical climatic conditions, specifically about cell temperatures and the output power (at MPP), a module (M55 from SSI) was tested at the PV Labs of the UFRJ in Rio de Janeiro (22°54’ S; 43°13’ W), Brazil during an equinox (9/22/1994). The components of irradiance (horizontal global, direct and diffuse) during that day have been recorded, as shown in Figure 10.14.

Подпись: Д-Д direct irradiance Э-О diffuse irradiance 0-0 global irradance

Fig. 10.14. Horizontal global, direct, and diffuse irradiance at Equinox (9/22/94) in Rio de Janeiro, Brazil (22°54’S; 43°13’W).

Figure 10.15 gives the measured temperature values at an M55 module during that day at almost no-wind conditions...

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