Browsing by Author "Bot, G."

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Greenhouse with a CPV system and NIR reflecting lamellae
Janssen, H.J.J. ; Tuijl, E.A. van ; Swinkels, Gert-Jan ; Sonneveld, P.J. ; Bot, G.
2012, Article / Letter to editor (Acta Horticulturae, iss. 927, (2012), pp. 43)In previous research a new type of greenhouse with an integrated concentrated photovoltaic system (CPV) was developed based on a circular covering geometry and an integrated filter for reflecting the near infrared radiation (NIR) of the greenhouse and exploiting this radiation in a solar energy system. The performance of the system was promising. In this study further optimalisation of the CPV system is made to avoid the large construction for solar tracing and the high investment. Hereto all parts for the solar concentrating system will be integrated into the greenhouse. The NIR-reflector material is carried out as a NIR-reflective lamellae system and the CPV-module is mounted into the ridge. In this paper the results of the optimization process of the CPV system based on NIR reflecting lamellae is presented. The optimization process is based on a maximal total annual electricity production and is performed with a ray tracing model and actual radiation data. Results show that the optimization of the lamellae greenhouse can be seen from a theoretical and a practical point of view. Theoretically, the number of lamellae for the investigated concept must be high (>100) and focus with a generic focal length of 3.5 m and glazing bars must be avoided. Then the maximal annual electricity output can be over 26 kWh/m2. In practice, mechanical restrictions, plant conditions and costs will determine the implementation. The proposed CPV-system has positive side-effects like reducing the heat load (and the need for cooling) during summer and blocking of the direct radiation which can be harmful for some crops. With this, the feasibility of the system depends greatly on local conditions which require a tailor-made economic analysis.
Energy performance of a concentrated photovoltaic energy system with static linear Fresnel lenses integrated in a greenhouse
Tuijl, E.A. van ; Sonneveld, P.J. ; Campen, J. van ; Swinkels, Gert-Jan ; Janssen, H.J.J. ; Bot, G.
2011, Article / Letter to editor (Solar Energy, vol. 2011, iss. 85, (2011), pp. 432-442)A new type of greenhouse with linear Fresnel lenses in the cover performing as a concentrated photovoltaic (CPV) system is presented. The CPV system retains all direct solar radiation, while diffuse solar radiation passes through and enters into the greenhouse cultivation system. The removal of all direct radiation will block up to 77% of the solar energy from entering the greenhouse in summer, reducing the required cooling capacity by about a factor 4. This drastically reduce the need for cooling in the summer and reduce the use of screens or lime coating to reflect or block radiation. All of the direct radiation is concentrated by a factor of 25 on a photovoltaic/thermal (PV/T) module and converted to electrical and thermal (hot water) energy. The PV/T module is kept in position by a tracking system based on two electric motors and steel cables. The energy consumption of the tracking system, ca. 0.51 W m-2, is less than 2% of the generated electric power yield. A peak power of 38 W m-2 electrical output was measured at 792 W m-2 incoming radiation and a peak power of 170 W m-2 thermal output was measured at 630 W m-2 incoming radiation of. Incoming direct radiation resulted in a thermal yield of 56% and an electric yield of 11%: a combined efficiency of 67%. The annual electrical energy production of the prototype system is estimated to be 29 kW h m-2 and the thermal yield at 518 MJ m-2. The collected thermal energy can be stored and used for winter heating. The generated electrical energy can be supplied to the grid, extra cooling with a pad and fan system and/or a desalination system. The obtained results show a promising system for the lighting and temperature control of a greenhouse system and building roofs, providing simultaneous electricity and heat. It is shown that the energy contribution is sufficient for the heating demand of well-isolated greenhouses located in north European countries.
Feasibility study for combining cooling and high grade energy production in a solar greenhouse
Flamand, G. ; Bot, G. ; Swinkels, Gert-Jan ; Sonneveld, P.J.
2010, Article / Letter to editor (Biosystems Engineering, iss. 105, (2010), pp. 51-58)Throughout the world greenhouse horticulture is expanding and intensifying. The expansion is driven by the much higher production levels that are achieved in greenhouses compared to open fields. This provides increased income for farmers and a positive effect on rural development. Intensification is driven by the demand for better control of the production process resulting in higher yield but, more importantly, higher product quality. As a result products can meet the standards of the fast expanding consumer market for high quality fresh products, driven by the booming new economies. However greenhouse horticulture also faces major problems. In northern countries, with cold winter climates, greenhouses have to be heated for optimal growing conditions so energy supply is an important issue. In the southern countries with the combination of high global radiation and high outdoor temperatures during summer, cooling of greenhouses is needed during this period. Solutions for energy supply in winter and cooling in summer can be combined applying seasonal storage of excess solar energy and exploiting this for heating in winter. The advantage of this system is cheaper cooling, and energy savings of about 35% compared to heating by furnace. The disadvantage is that the excess solar energy is converted to low grade thermal energy which is stored at a temperature level of about 18 °C. This can only be exploited for heating in winter by a heat pump, driven by high grade energy such as electricity. Here, the feasibility of a novel approach is investigated of a greenhouse design combining cooling with energy supply in such a way that excess solar energy is directly converted to high grade electric energy. A prototype greenhouse according to this design is under construction. In a following paper the experimental results of this prototype greenhouse will be presented.
Measurements on a solar greenhouse combining cooling and electrical energy production
Tuijl, E.A. van ; Sonneveld, P.J. ; Janssen, H.J.J. ; Campen, J. van ; Bot, G. ; Swinkels, Gert-Jan
2010, Article / Letter to editor (Biosystems Engineering, iss. 106, (2010), pp. 48-57)Performance results are given of a new type of greenhouse, which combines reflection of near infrared radiation (NIR) with electrical power generation using hybrid photovoltaic cell/thermal collector modules. Besides the generation of electrical and thermal energy, the reflection of the NIR will result in improved climate conditions in the greenhouse. In a previous paper (Sonneveld, P. J., Swinkels, G. L. A. M., Bot, G. P. A., & Flamand, G. (2010). Feasibility study for combining cooling and high grade energy production in a solar greenhouse. Biosystems Engineering, 105, 51–58) a design and feasibility study of this electricity-producing greenhouse was presented. After the description of the construction of this greenhouse, the peak power for Dutch climate circumstances is determined based on the amount of electrical and thermal energy (hot water) produced. The typical yearly yield of this greenhouse system is determined as a total electrical energy of 20 kW h m-2 and a thermal energy of 160 kW h m-2. Improvements are possible in the spectral range of the NIR film and in the focusing unit of the system. In future the improved electricity-producing greenhouse system could generate 31 kW h m-2 of electrical energy and 270 kW h m-2 of thermal energy, so it could operate independent of fossil fuels.
Design of a Solar Greenhouse with Energy Delivery by the Conversion of Near Infrared Radiation - Part 1 Optics and PV-cells
Swinkels, Gert-Jan ; Sonneveld, P.J. ; Bot, G.
2009, Article / Letter to editor (Acta Horticulturae, iss. 807, (2009), pp. 47-53)In this paper the design and development of a new type of greenhouse with an integrated filter for reflecting near infrared radiation (NIR) and a solar energy delivery system is described. Especially the optical parts as the spectral selective film, the properties of the circular reflector and the efficiencies of photo voltaic cells are studied. As a first measure, the spectral selective cover material, which prevents the entrance of NIR radiation, is investigated. It has to block up to 35% of the solar energy outside the greenhouse, which will reduce the needed cooling capacity. The second measure is the integration with a solar energy system. When the NIR reflecting coating is designed as a circular shaped reflector integrated in the greenhouse, the reflected solar energy of a PhotoVoltaic (PV) cell in the focus point delivers electric energy. With a ray tracing computer program the optimal geometry of the reflector was designed with respect to the collecting efficiency. The PV cells mounted in the focal point require cooling due to the high heat load of the concentrated radiation (geometric concentration factor of 30). The properties of different PV materials were investigated to find the optimal cell for this application. Cooled greenhouses are an important issue to cope with the combination of high global radiation and high outdoor temperatures. All parts are integrated in a 100m2 prototype greenhouse which will be applied for the proof of principle.

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Browsing by Author "Bot, G."

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