Energy analysis of solar blind system concept using energy system modelling

摘要

Energy conservation in the horticultural industry is one of the main challenging points regarding to the sustainable development. Commercial greenhouse is known as the most energy consuming and simultaneously the most effective cultivation method which promises 10 times more production yield than open field horticultural methods. Supplementary heating demand, electrical energy demand for artificial lighting system as well as active cooling systems are the main parameters which have to be reduced in order to have more energy efficient system. Usually, in the conventional greenhouse the solar radiation will blocked using a thermal screen to avoid the overheating problem and reduce the cooling demand. In this method, a large portion of solar irradiation will reflected and absorbed by curtain without any useful utilization. By introducing the solar blind system, the excess solar radiation will absorb and convert into useful thermal energy as well as electrical energy. As a matter of fact, the solar blind system consists of a series of thermal photovoltaic modules. The solar blind system will operate based on the defined set point temperature. By exceeding the greenhouse indoor temperature than set point temperature the solar blind thermal photovoltaic modules rotate over their axis to cover the greenhouse roof and block the solar radiation and it keeps blocking the solar irradiation until the indoor temperature drops below the set point. Therefore, the cooling demand will reduce considerably while the absorbed heat and electricity gain though the thermal photovoltaic cells can be utilized later to cover a part of the greenhouse thermal and electrical demand. The main aim of this paper is to assess the solar blind system performance for various set point temperatures. Therefore an energy model has to be developed and TRNSYS is used for this purpose. The results show that by considering 18 degrees C as the set point temperature, the highest thermal and electrical energy performance can be reached. The maximum thermal energy performance of the system is about 86% while the minimum that is corresponded to the highest set point temperature is 38%. By considering the solar blind system operated at 18 degrees C as the set point temperature, the cooling demand in the greenhouse can be almost covered totally, which is the main aim of this concept. However, the electrical demand is reduced almost by 73%. Additionally, by applying the solar blind system concept, the irradiation level inside the greenhouse kept in the optimal level that leads to more uniform cultivation during the whole year. (C) 2016 Elsevier Ltd. All rights reserved.