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Content archived on 2022-12-27

SOLAR GREENHOUSE FOR THE PRODUCTION OF "PLEUROTE" MUSHROOMS

Objective

To demonstrate that solar energy is an economic source of energy for high value crops; in this case short term inter seasonal storage systems will also be demonstrated in combination with a solar mushroom house. Expected energy production is 1.7 TOE/yr giving a payback of 4 years.
Since the beginning of the project the mist system was changed. The pump, which was too fragile, was replaced by one used in the "Fog System" of DUTRY PLANT SA and which is designed for intensive use. However after having tested this sytem's distribution bus-bass, it was decided to keep the original oil burner type bass as they blocked up less frequently and are easier to clean. The hydrostats were also changed and placed 2 metres away from the air and mist ventilation duct exit. The whole system is satisfactory having a short response time and operating cycle (30 secs operation and 60 secs at rest at 80% humidity)
As far as energy savings are concerned, measurements taken have shown that for the month of February 1987 when mushrooms were growing in the greenhouse with continual air changes, there was a saving of 27% on the total requirement of 5774 kWh. 48% come from the solar air collectors and 52% from storage corresponding to forecasts. Over the whole heating season, the efficiency of the solar collectors is about 30%, and the greenhouse heat loss coefficient is 1.2 W/m3.K.
On the other hand the greenhouses cannot be used in July and August due to the impossibility of maintaining internal temperatures below 20 deg C.
The negative aspect of the project is that it has not been possible to obtain the good yield from the culture required to ensure the cost effectinveness of the farm.
There are various reasons for this :
- impossible to control the substrate culture
-what has been cultivated the most had to be withdrawn from the market because of degeneration.
- the incubation phase, which is the most delicate and has probably been underestimated, should be carried out in a perfectly conditioned nearby room.
INRA who was consulted about the substrate advised on the preparation of the substrate by the contractor in order to control its composition and notably the level of mushroom spores.
Unfortunately due to the size of the farm which is between artisan and industrial scale, this was not possible.
Pleurote mushrooms were still a short time ago a rarety only found in woods; it is only recently that large scale production techniques have been perfected. This project, using an innovative mushroom house design, shows how solar energy can be used as an energy source.
These mushrooms are grown in two distinct phases: an incubation period lasting 15 days during which time substrate is kept in the dark, in conditions of humidity (95%), excess CO2 and warmth (25 deg C), growth during which time much light, 100 lux. low CO2 concentration, 80% relative humidity and temperatures of 8-20 deg C are required. These requirements indicated that a well insulated building was necessary. The design chosen is a semi-cylindrical structure, built from galvanised steel supports, orientated east-west. On the south facing side, air solar collectors are integrated into the structure. The collectors are covered with polyethylene and the absorber is in galvanised steel covered with a black paint. Beneath the absorber is an 8 cm layer of insulating material. The total area of the absorbers is 30 x m2.
The remainder of the building is covered with 10 cm of insulating material between two sheets of polyethylene. The heat is recovered by simple conduction by forced air circulation.
The remainder of the installation is traditional: humidity levels being maintained by water misters.
Excess solar energy is stored by passing warm air through five concrete channels 1.2 m below the surface of the mushroom house.

Call for proposal

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Coordinator

UNIVERSITE DE NICE
EU contribution
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Address
LAB. THERMO EXPERIMENTAL PARC VALROSE
06034 NICE CEDEX
France

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Total cost
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