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Contenu archivé le 2022-12-27

USE OF PARABOLIC TROUGH SOLAR COLLECTORS TO PROVIDE SPACE HEATING AND INDUSTRIAL PROCESSES

Objectif

To use parabolic trough solar collectors for the conversion of solar, into 90 deg.C - 130 deg.C thermal energy, to be used for winter space heating, low temperature industrial processes and, in summer to feed an absorption heater. It is also intended to accurately assess the cost of mounting and maintaining such an installation.
Annual fuels saving which can be obtained on the basis of annual available energy output (expressed in fuel oil equivalent) is +/- 14,000 gas oil litres/y, assuming a receiver efficiency of 0.7 and specific heat of 10,000 Kcal/kg.
After problems with the temperature regulators it was decided to equip the plant with a shunted action system controlled by a sun radiation sensor. Some difficulties also arose in the tracking control system due to strongly variable insolation (cloudy skies and sudden reappearance of sunlight), causing unpredictable tracker performance. This drawback was eliminated by fitting an additional inhibiting sensor preventing the motors from running below a minimum radiation threshold.
As to the operation of the solar part of the overall automation and monitoring system, this performed well.
Tests have demonstrated that the parabolic trough collectors used in this plant are appropriate for 100 deg.C - 130 deg.C operation but unsuitable for plants requiring temperatures between 150 deg.C - 200 deg.C when their efficiency becomes too low, and would require modification of the tube diameter of the receiver, to increase the diameter of the tubular receiver to increase the actual concentrationrate.
During trials it was found that the plant was practically unserviceable before 8.00 and after 16.00 hours due to reciprocally collector generated shadows. It was also observed that after 16.00 hours and prior to 8.00 hours the reflected insolation suddently decreases, due to reciprocal shadows. This has led to the conclusion that parabolic trough collector systems may be used for not more than 8 hours of the day in any single period throughout the year. However, heat can be stored also during the hours in which the collectors are partially in shadow, although storage temperature will be lower.
Based on updated data, the available energy output of the plant is 81 000 000 Kcal/y (340 000 MJ/y), which is +/- 20 less than the preliminary assessed output.
The main factors causing this reduction are:
- soiling of mirror surfaces (+/-10%)
- greater influence of the reciprocal collector shadows (due to limitation of the installation site in comparison with the orginally planned area)
- less direct sun radiation measured with respect to the total available sun radiation (persisting mist and haze, even on bright days)
- negative effect of Pyrex tube failure protecting the tubular receivers
While the efficiency of individual collectors met design expectations, the efficiency of the total solar plant in real conditions is well below the average measured on separate collectors.
The 48 parabolic trough solar collectors mounted on the roof of the industrial hall and their thermohydraulic equipment are essentially for the production of thermal energy.
The plant consists of a collector field, heat storage and thermal solar system. The collector field is divided into four groups of 12 collectors in series connection. These in turn are connected in parallel. Each collector has a working reflective area of 3.5 m2 and a total collecting surface of 168 m2. Each collecotr group is fitted with an automatic photovoltaic tracking system and two way motor driven valve for adjustment of the heat transfer fluid (water and glycol). Heat output is conveyed to users at 90 deg.C for use in various systems such as heating and low temperature industrial uses. In summer, the solar plant produces hot water for sanitary facilities and supplies the absorption refrigeration system for office air conditioning.
Solar energy is trapped by parabolic trough solar collectors with tubular absorber, installed on a polar mounting. These collectors have a thin, silvered reflecting surface and are constartly moved to track the sun. Using a hydraulic circuit and heat exchanger, thermal energy is transferred to a heat storage tank and/or to the users. Main thermohydraulic circuits collect the heat transfer fluid previously heated in the solar collectors for transfer to the solar heating plant located in the building. The primary fluid is pumped through a plate type heat exchanger to heat secondary fluid in one or two (2 m2 capacity) short-term buffer storage tanks.
All circuits are equipped with hydraulic fittings, temperature probes and flow meters for data collection. Regulation is achieved by mixing heat exchanger hot fluid outlet, with cold fluid returning from the users.
Two hydraulic lines convey secondary fluid (temperature regulated by a three-way motor driven valve with heat gauge one to the unit heaters provided the fluid is of sufficiently high temperature (otherwise it has to be conveyed to the two parallel connected boilers, each of 300,000 Kcal/h cpapcity). The other line goes to the absorption (75 deg.C - 100 deg.C) refrigerator, although, as an alternative, it can be supplied with fluid from the combined 80,000 Kcal/h capacity boiler. The absorption refrigerator's cooling circuit is provided by an 88,000 Kcal/h. forced draft evaporator tower.
The plant may also be operated in 10 main alternative configuration eg. for operation at +100 deg.C temperatures.

Thème(s)

Appel à propositions

Data not available

Régime de financement

DEM - Demonstration contracts

Coordinateur

Ansaldo Impianti SpA
Contribution de l’UE
Aucune donnée
Adresse
Via Gabriele d'Annunzio 113
16121 Genova
Italie

Voir sur la carte

Coût total
Aucune donnée