Performance of a greenhouse cum solar still for the climatic condition of Port Moresby

Thermal modelling, based on heat and mass transfer relations, of a greenhouse integrated with a solar still has been discussed in detail. The effect of the system (viz. heat capacity of plants/pot mixture, water mass, and orientation, etc.) as well as climatic parameters (solar insolation, ambient air temperature and ventilation due to wind, etc.) have been incorporated in the energy balance for various components of the system in order to validate the theoretical results. An experiment was carried out for a typical greenhouse in Port Moresby. The following observations were made: (i) there is a reasonable agreement between theoretical and experimental results, and (ii) the amount of distilled water obtained is sufficient to grow the plants inside the greenhouse.     

Transient analysis of a winter greenhouse integrated with solar still

The present work deals with a simple transient analysis of a winter greenhouse integrated with a solar still. Explicit expressions for the temperatures of still cover, brine (basin-water), basin of the still/roof of the greenhouse, greenhouse air, plants and floor of the greenhouse have been developed so as to study the transient thermal performance of the system. The effect of several parameters, namely relative humidity, ventilation/infiltration, heat capacity of basin water and plants, etc. has been incorporated in the analysis. On the basis of numerical calculations, some interesting conclusions have been made.     

Modeling the heat balance of a solar greenhouse with a passive heat accumulator

A model of heat balance of a solar greenhouse with a passive water accumulator in the system soil-plants-heat accumulator-air-fencing-atmosphere is presented. The heat of moisture evaporation from the soil surface and plants is defined using the Bowen-Penman method.     

Solar energy utilization by a greenhouse: General relations

Most of solar radiation incident on a greenhouse is absorbed by greenhouse components (i.e., the cover, humid air, plants and soil) and the remaining portion is lost to outside the greenhouse. It is essential to know the absorbed and lost energy terms for any thermal analysis of greenhouses. Existing greenhouse thermal models use the radiative properties of the greenhouse components to directly determine the absorbed energy terms. However, these models neglect the lost energy term and neglect the effects of the multiple reflections of solar radiation between the greenhouse components.The present study describes the general relations for estimating the amounts of solar energy absorbed by the greenhouse components and lost to outside the greenhouse. The relations take into consideration the interrelations as well as the multiple reflections of solar radiation between these components. Thus, the greenhouse system was treated as a solar collector having an absorber plate (i.e., the greenhouse soil) and a cover system consisting of three semi-transparent parallel layers (i.e., the greenhouse cover, the humid air, and the plants). Superposition theory and ray tracing technique were used for the analysis. The presented relations were applied to an experimental plastic-covered greenhouse with a floor area of 34 m². The greenhouse, located in Riyadh, Saudi Arabia, was planted with tomatoes with a leaf area index (LAI) of 3.0 and was cooled by a wet pad and fan system. Results of the presented relations were accurate and more realistic comparing to results of other relations reported in the literatures. Absorption of solar radiation by water vapor in the greenhouse was negligible. The presented relations can estimate the absorbed and lost energy terms for a greenhouse precisely with a max possible error of +1.8% on each term if the LAI was less than 1.5. The error is significantly decreased to less than +0.7% if the LAI in the greenhouse is increased to 5.     

An efficient greenhouse design for hot climates

Greenhouses are needed in hot climates to protect plants from excessive heat, which limits productivity, and to reduce the excessive energy and water requirements associated with controlled environment agriculture under such conditions. In Kuwait, where ambient air temperature can reach 50°C during the summer and where fresh water is scarce, a new approach to greenhouse design was used. This approach included passive, as well as active, energy conservation measures, which made the utilization of such a greenhouse economically feasible. A computer program is proposed here for greenhouse design in Kuwait, aimed mainly at reducing the cooling load in an arid climate. It takes into consideration the climate, the material and the geometry of the greenhouse. The concept is to reduce the amount of intense solar radiation received in Kuwait (infrared radiation) but to maximize the amount of the solar spectrum needed for plants, as well as control the other environmental factors.     

Performance and cost of wet and dry cooling systems for pulverized coal power plants with and without carbon capture and storage

Thermoelectric power plants require significant quantities of water, primarily for the purpose of cooling. Water also is becoming critically important for low-carbon power generation. To reduce greenhouse gas emissions from pulverized coal (PC) power plants, post-combustion carbon capture and storage (CCS) systems are receiving considerable attention. However, current CO₂ capture systems require a significant amount of cooling. This paper evaluates and quantifies the plant-level performance and cost of different cooling technologies for PC power plants with and without CO₂ capture. Included are recirculating systems with wet cooling towers and air-cooled condensers (ACCs) for dry cooling. We examine a range of key factors affecting cooling system performance, cost and plant water use, including the plant steam cycle design, coal type, carbon capture system design, and local ambient conditions. Options for reducing power plant water consumption also are presented.     

区域能源多能互补耦合系统在温室中的应用分析

针对典型温室,利用构建的优化配置模型,进行燃气轮机和内燃机两种区域能源多能互补耦合系统优化配置研究。从经济、能源利用率、环境影响等角度对提出的系统方案进行分析与评价,并与常规供能方案进行比较。结果表明:温室适合推广应用区域能源多能互补耦合供能技术;燃气轮机和内燃机系统均可行,燃气轮机合适的功率为4～4.5 MW,内燃机合适的功率为5～5.5 MW;燃气轮机系统的经济性更好,而内燃机系统在节能减排方面更具优势;在可再生能源利用方面,应优先选择河水、污水处理厂中水等浅表热能资源,其次再考虑地热资源。     

Comprehensive evaluation of coal-fired power plants based on grey relational analysis and analytic hierarchy process

In China, coal-fired power plants are the main supplier of electricity, as well as the largest consumer of coal and water resources and the biggest emitter of SO_x, NO_x, and greenhouse gases (GHGs). Therefore, it is important to establish a scientific, reasonable, and feasible comprehensive evaluation system for coal-fired power plants to guide them in achieving multi-optimisation of their thermal, environmental, and economic performance. This paper proposes a novel comprehensive evaluation method, which is based on a combination of the grey relational analysis (GRA) and the analytic hierarchy process (AHP), to assess the multi-objective performance of power plants. Unlike the traditional evaluation method that uses coal consumption as a basic indicator, the proposed evaluation method also takes water consumption and pollutant emissions as indicators. On the basis of the proposed evaluation method, a case study on typical 600 MW coal-fired power plants is carried out to determine the relevancy rules among factors including the coal consumption, water consumption, pollutant, and GHG emissions of power plants. This research offers new ideas and methods for the comprehensive performance evaluation of complex energy utilisation systems, and is beneficial to the synthesised consideration of resources, economy, and environment factors in system optimising and policy making.     

Effect of spectral quality on horticultural plant propagation in a greenhouse

A greenhouse of semi-circular shape was employed to study the effect of spectral light response on the stem-cutting propagation of horticultural plants. The number of days taken for the root formation were noted and it was observed that the stem cuttings showed earlier root formation under a red-tinged greenhouse followed by a blue-tinged greenhouse. The UV-stabilised sheet prolonged the formation of well-formed roots by an additional three days over that for the control system. The study shows that the temperature gradient is not only a minimum at canopy level but also negative throughout in blue cladded greenhouse and a maximum vertical heat flux of zero is noticed.     

Experimental study of the burning-cave hot water soil heating system in solar greenhouse

In the northern China areas, the traditional heating methods are widely used in solar greenhouse, for example: electric heating, hot air heating, hot water heating, burning-cave heating etc. If copying the assuring building indoor environment of constant heating ways into solar greenhouse, it will further increase building energy consumption, thus improving the efficiency of energy utilization, establishing appropriate growing environment, and realizing the agricultural waste recycling are important ways of consistent with the Chinese conditions, construction of sustainable development, improving the efficiency of the greenhouse production. To solve the problem of traditional heating method for high heating energy consumption, the inharmonious between greenhouse air temperature and soil temperature, uneven soil temperature, the research build the burning cave hot water soil heating system of solar greenhouse experimental platform in accordance with principle of energy cascade utilization. This experiment platform will transfer burning cave internal heat into soil heating system. The soil is evenly heated by system. Through testing the actual operation effect of the burning cave hot water soil heating system of new solar greenhouse, electric heating system, no taking any heating measures system, burning cave hot water soil heating system of solar greenhouse can improve the soil average temperature 5 ∼ 6 °C. This research provides experimental basis for practical applications and promotion.     

Mathematical modeling for greenhouse heating by using thermal curtain and geothermal energy

A thermal model has been developed for the heating of a greenhouse by using inner thermal curtain and natural flow of geothermal warm water through the polyethylene tube laid on its floor. The calculations were done for a typical production greenhouse with the climatic data in the central part of Argentina during winter period. From the energy conservations point of view, the greenhouse has been divided into three zones i.e., zone I (plants under thermal blanket), zone II (space under ceiling) and zone III (space between roof and ceiling). The model has been tested with the published experimental data of air temperatures in zone I and zone II of the greenhouse. From the results, it was observed that the temperatures of air surrounding the plant mass in zone I were maintained in the range of 14–23 °C during winter night and early morning resulting in the better growth of winter growing plants against the harmful freezing effects. The predicted values of air temperature both in zone I and zone II of the greenhouse obtained from the proposed model exhibited fair agreement with the published experimental values.     

Radiation and heat characteristics of plant leaves in a solar greenhouse

The paper considers spectral absorption characteristics of the middle leaf of agricultural plants. A model of heat balance in the plant-air-soil-fence leaf system in conditions of a greenhouse is given.     

GREENHOUSE GAS ANALYSIS OF SOLAR-THERMAL ELECTRICITY GENERATION

Solar-thermal electricity generation contributes to climate change because it incurs the emission of greenhouse gases during the provision of services and the production of materials needed for the construction and operation of solar power plants. These greenhouse gas costs (GGC) can be determined using either material inventories in physical units or monetary cost breakdowns. Solar-only plants employing parabolic troughs, central receivers or parabolic dishes exhibit GGC around 90 g CO₂-e/kWh_el. However, this figure varies with the plant size and also depends strongly on whether a fossil-fuelled backup or a heat storage system is utilised in order to increase the plant’s capacity factor.     

Climate change impacts in the energy supply of the Brazilian hydro-dominant power system

Over the past few years, there has been a growing global consensus related to the importance of renewable energy to minimize the emission of greenhouse gases. The solution is an increase in the number of renewable power plants but unfortunately, this leads to a high dependence on climate variables which are already affected by climate change. Brazil is one of the largest producers of electricity by renewables through its hydro-dominant power generation system. However, hydro-generation depends on water inflows that are directly affected by climate change that consequently affect the electricity production. Therefore, these changes need to be considered in the operation and planning of a hydro-dominant power system. In this paper, we present the effects of different climate scenarios in the water inflows produced by the regional Eta climate model. Normally, studies use an optimization model to make decisions in case of a hydro-thermal scheduling problem and use the assured energy to evaluate the hydro-production. In this analysis, water inflows used in the optimization process consider different trends according to its associated climate scenario. Our paper shows that climate change may drastically impact the system assured energy and consequently, the system's capability to supply load.     

Greenhouse solar heating in the Argentinian northwest

In the present paper a low cost solar active water heating system is proposed to increase the average night temperature and avoid freezing problems inside greenhouses. The system collects the excess of energy in the greenhouse during the day, and returns it at night. The most important part of the system is a plastic bag made of two thin polyethylene films vertically hung inside the greenhouse, that works as a solar collector during the day and as a heat exchanger at night.The films are soldered in such a way that the water introduced at the top of the bag falls by gravity following a zig-zag path. The warm water is stored in a pond directly built in the ground and waterproofed with a polyethylene film.The system has been designed taking into account the meteorological conditions in Salta where 12 freezing days are expected each year with minimum temperatures down to −8°C.A prototype was built in a 600 m² greenhouse covered with a single polyethylene film. It was located in the Province of Salta, Argentina, with a 24.5° South latitude and an altitude of 1200 m. Tests were performed for three years beginning at the 1992 winter, and a satisfactory thermal and operational behavior was obtained. With outside temperatures down to −6°C at the end of the night, the system was able to keep a temperature of 2°C inside the greenhouse.     

Exergoeconomic and environmental investigation of an innovative poly-generation plant driven by a solid oxide fuel cell for production of electricity,cooling, desalinated water,and hydrogen

Fuel cell and renewable-based poly-generation plants (PGPs) are proven as advanced technologies for multiple generation purposes. To limit the greenhouse gas emissions, an innovative PGP generating electricity, cooling, desalinated water, and hydrogen is proposed in the current study. The system consists of a solid oxide fuel cell as a prime mover integrated with a gas turbine, a biomass combustion chamber, an organic Rankine cycle, an ejector refrigeration cycle, a desalination unit, and a proton exchange membrane electrolyzer integrated with solar collectors. As the most effective tools for performance evaluation, exergoeconomic, and environmental analyses have been applied. The system produces electricity of 4.4 MW, refrigeration capacity of 0.16 MW, and desalinated water of 0.96 kg/s. The attained freshwater enters the electrolyzer during 12 daylight hours, leading to hydrogen and sanitary water generation with the values of 1.55 g/s and 0.94 kg/s, respectively. The cost per unit exergy and the total cost rate of the products are 11.28 $/GJ, 223 $/h, correspondingly. Carbon dioxide emission of the system is estimated to be 10.79 kmol/MWh. According to the evaluation, the total cost rate increases with increasing current density and fuel cell inlet temperature and decreasing fuel utilization factor.     

An option for solar thermal repowering of fossil fuel fired power plants

Global climate change urges immediate measures to be taken to limit greenhouse gas emission coming from the fossil fuel fired power plants. Solar thermal energy can be involved in different ways in existing power generation plants in order to replace heat produced by fossil fuels.Solar field feed water preheating is mainly discussed in this paper as an option for fast and feasible RES penetration. Rankine regenerative steam cycled power plant has been modelled with Thermoflow software. The plant model incorporates also a field with solar Fresnel collectors that directly heats boiler’s feed water. The proposed plant modification yields substantial fossil fuel input reduction. The best results can be obtained when the group of high pressure heaters is replaced and feed water temperature exceeds its original design value. The solar power generation share can reach up to 23% of the power plant capacity in this case, having efficiency higher than 39% for the best solar hour of the year.     

A study of a greenhouse concept on conventional biogas systems for enhancing biogas yield in winter months

A new concept is introduced of using a greenhouse for enhancing the biogas yield from a conventional biogas system in the winter months. If a conventional biogas system is glazed, the trapped solar energy can be used to raise the temperature of the slurry which normally goes low enough to reduce the gas yield appreciably. Numerical calculations have been performed corresponding to the meteorological data on a typical winter day, i.e. 19 January 1981, at New Delhi (India). A comparative study of the performances of conventional and solar-assisted biogas plants using the concept of a greenhouse indicates that the ambient temperature of the slurry can be raised from 18°C to about 37°C, the optimal temperature for anaerobic fermentation.     

Design and evaluation of PV-wind hybrid system with hydroelectric pumped storage on the National Power System of Egypt

National and international policies encourage increased penetration of solar and wind energy into electrical networks in order to reduce greenhouse gas emission. Solar radiation and wind speed variations complicate the integration of wind and solar generation into power systems and delay the transition of these sources from centralized to distributed energy sources. The increased penetration of nontraditional energy sources into the electric grid stimulates the demand for large capacities in the field of energy storage. A mathematical model, which describes the operation of a proposed hybrid system, including solar PV, wind energy, and a pumped storage hydroelectric power plant is developed in this paper. This hydropower plant utilizes seawater as a lower reservoir, and only a tank has to be built in order to reduce the installation cost of the storing system. The pumped storage power plant used for compensation of the variation of the output energy from the PV and wind power plants by discharging water from the upper reservoir, which is previously pumped in the case of surplus energy from PV and wind turbine power plants. The impact of the proposed system on the grid utility is investigated in accordance with the values of energy exchange (deficits and surpluses of energy) between the considered hybrid system and the grid. The optimum design is determined by the pump and turbine capacities, upper reservoir volume, and the volume of water left in the tank for emergencies. Different scenarios of the optimum operations are presented for analysis. The results obtained from the examined scenarios indicate the ability of such a hybrid energy system to reduce the exchange of energy with the grid. This paper indicates the technical feasibility of seawater pumped-storage hydropower plant for increasing the Egyptian national grid’s ability to accept high integration of renewable energy sources.     

Greenhouse heating and cooling using aquifer water

An aquifer coupled cavity flow heat exchanger system (ACCFHES) was designed using underground aquifer water for the heating as well as cooling of a composite climatic greenhouse. The performance of ACCFHES was experimentally evaluated for a full winter and a summer season. The ACCFHES makes use of constant temperature aquifer water (24 °C) available at an agricultural field through an irrigation tube well for heating in winter nights and cooling in summer days. The results showed that the average greenhouse room air temperature was maintained 7–9 °C above the outside air during extreme winter nights and 6–7 °C below the outside air in extreme summer days, and temperature fluctuations inside the greenhouse also decreased daily. The average relative humidity (RH) inside the greenhouse also decreased by 10–12% in the winter and increased by more than double in the extreme summer conditions as compared to the outside conditions. A comparison of economic feasibility of the ACCFHES coupled greenhouse was also conducted with conventional greenhouse and open field condition based on the yield of Capsicum annum. The ACCFHES was also compared economically with other existing heating/cooling technologies such as earth-to-air heat exchanger system (EAHES), ground air collector, evaporative cooling using foggers and fan & pad system in terms of net present worth (NPW) and pay back period. It was observed that the NPW of the ACCFHES coupled greenhouse was much higher as compared to the conventional greenhouse and open field condition. The payback period of the ACCFHES coupled greenhouse was the lowest among all other existing heating/cooling systems.