Feasibility Study of Solar Adsorption Technologies for Automobile Air-Conditioning

An adsorption system driven by solar heat or waste heat can help to eliminate the use of ozone depletion substances, such as chlorofluorocarbons (CFCs) and hydro-chlorofluorocarbons (HCFCs). In recent years, adsorption system has witnessed an increasing interest in many fields due to the fact that this system is quiet, long lasting, cheap to maintain and environmentally benign. Although adsorption system is not commonly used for automobile air conditioning, adsorption-cooled mini-refrigerators have been marketed for recreational transports (motor homes, boats, etc). Hence, there exists a need for a creative design and innovation to allow adsorption technology to be practical for air conditioning in automobile. The objective of this paper is to present a comprehensive review on the past efforts in the field of solar adsorption refrigeration systems and also the feasibility study of this technology for automobile airconditioning purpose. It is a particularly an attractive application for solar energy because of the near coincidence of peak cooling loads with the available of solar power.

An Adaptive Perturb and Observe Maximum Power Point Tracking System for Photovoltaic Arrays

This paper presents a maximum power point (MPP) hardware tracking system based on an adaptive Perturb and Observe (PAO) algorithm. Under a given solar and temperature condition the search for the MPP starts with a large perturbation step. When a drop in the delivered power is detected, the size of the step is halved and the direction of duty cycle change is reversed. Eventually the MPP will be tracked by small perturbation step (e.g. 1/ 255). When tracking at a maximum and a sudden change occurs in the atmospheric conditions, the system will try to reach the new MPP, with an adaptive perturbation step size that is allowed to increase after 4 consecutive increases or decrease in the duty cycle leading to increase in power delivery. This adaptive PAO algorithm forces the system to respond fairly quickly to any changes in the solar radiation or temperature level irrespective of where the previous operating point MPP was and without deteriorating the tracking efficiency. A tracking efficiency of about 96% was achieved using a very simple controller.

Transient Analysis and Performance Prediction of a Solid Adsorption Solar Refrigerator

The transient analysis and performance prediction of a solid adsorption solar refrigerator, using activated carbon/methanol adsorbent/adsorbate pair are presented. The mathematical model is based on the thermodynamics of the adsorption process, heat transfer in the collector plate/tube arrangement, and heat and mass transfers within the adsorbent/adsorbate pair. Its numerical model developed from finite element transformation of the resulting equations computes the collector plate and tube temperatures to within 5°C. The condensate yield and coefficient of performance, COP were predicted to within 5% and 9%, respectively. The resulting evaporator water temperature was also predicted to within 4%. Thus the model is considered a useful design tool for the refrigerator to avoid costly experimentation.

Evaluation of a High-Performance Solar Home in Loveland, Colorado

Building America (BA) partner McStain Neighborhoods built the Discovery House in Loveland, Colorado, with an extensive package of energy-efficient features, including a high-performance envelope, efficient mechanical systems, a solar water heater integrated with the space-heating system, a heat-recovery ventilator (HRV), and ENERGY STAR™ appliances. The National Renewable Energy Laboratory (NREL) and Building Science Consortium (BSC) conducted short-term field-testing and building energy simulations to evaluate the performance of the house. These evaluations are utilized by BA to improve future prototype designs and to identify critical research needs. The Discovery House building envelope and ducts were very tight under normal operating conditions. The HRV provided fresh air at a rate of about 75 cfm (35 l/s), consistent with the recommendations of ASHRAE Standard 62.2. The solar hot water system is expected to meet the bulk of the domestic hot water (DHW) load (>83%), but only about 12% of the space-heating load. DOE-2.2 simulations predict whole-house source energy savings of 54% compared to the BA Benchmark [1]. The largest contributors to energy savings beyond McStain’s standard practice are the solar water heater, HRV, improved air distribution, high-efficiency boiler, and compact fluorescent lighting package.

Improved Design Parameters for a Liquid Desiccant Dehumidifier in Confined Spaces

Investigations of a desiccant dehumidifier system have been performed for humidity control application in confined spaces. A previous study revealed that the base dehumidifier system can reduce moisture condensation by 22% over a conventional exhaust ventilation system. The current study aims to develop improved design requirements for a desiccant dehumidifier. The energy consumption of an exhaust ventilation system and an improved dehumidifier system was compared. To investigate the improved desiccant dehumidification system, numerical simulations were conducted and an objective function was established. This paper presents simulated results for an existing desiccant dehumidification system and an improved system, in which improved parameters are used. Use of the improved design parameters can reduce moisture condensation by 26.6% over a base dehumidifier system and shorten the dehumidifier performance period by 14%. Energy consumption with the sole use of an exhaust system is compared with that of the improved dehumidifier system under the same conditions. The results show that energy consumption can be substantially reduced, by 63%, in the improved dehumidifier system with the same amount of moisture condensation on surfaces of the confined space.

Use of Solar Desiccant Air-Conditioning Systems in Commercial Buildings

Desiccant air conditioning systems provide an environmentally friendly alternative to the traditional methods of conditioning a building’s internal environment. Whilst conventional air conditioning systems rely on electrical energy to drive the cooling cycle, desiccant cooling is a heat driven cycle. As such, desiccant cooling provides an opportunity to be coupled with solar thermal collectors to reduce energy demands. This paper discusses the potential for a desiccant cooling cycle utilising solar thermal energy as the sole source of heat for regeneration of the desiccant. The study demonstrates that under the assumed design conditions this system will theoretically not require a regeneration heater. Installation of such a system in a commercial building would be extremely beneficial in reducing building’s energy consumption and therefore greenhouse gas emission.

Storage Options and Sizing for Utility Scale Integration of Wind Energy Plants

Electric energy storage has been discussed as an option for increasing the marketability of wind energy facilities by reducing output variation. Utility scale wind plants face economic exposure to tariff charges for output variation as well as depending on volatile market prices for success. Wind speed variability and associated changes in wind plant output raise specific challenges to design engineers sizing electric energy storage systems. Evaluation of prospective Wind/Storage applications depends on the characteristics of individual wind plant output and the choice of storage technology. Energy storage options range from traditional lead acid batteries and pumped hydro storage to recently commercialized electrochemical flow battery systems. Selection and sizing of energy storage for wind plants vary with the time frame for each application. Different time frames correspond with the utility definitions of regulation, load shaping and load factoring. Results from a storage system model are presented that differentiate appropriate storage system sizes for these applications.

Some Environmental Considerations of Electrical Power Generation From Ocean Currents in the Straits of Florida

Ocean currents contain a remarkable amount of kinetic energy and have potential worldwide capability. Initial tests to harness current power focus on the Straits of Florida where the Florida Current has a total flow capacity of about 30 × 106 m3 s−1. Generation of clean electricity from ocean currents off southeast Florida is based on a power extractor comprised by open-center turbine technology. This innovative turbine provides safe passage for fish and other aquatic species. The water-column array of energy production units (EPUs) will have a 350 km2 footprint, based on a 600 m (10 rotor diameters) downstream separation distance between EPUs with a lateral separation of 400 m. Water depths for the EPU field are in the range of 100 to 500 m. With such a large area of water column and benthic habitat utilized, environmental concerns must be overcome, including routing of transmission lines to shore. Risks and vulnerabilities of the proposed ocean current generated electricity include failure of individual EPUs and damage to sensitive coastal marine environments during installation.

Operation and Maintenance Field Experience With Photovoltaic Water Pumping Systems

This paper presents an assessment of the failure modes, operation and maintenance (O&M) costs, and system lifecycle costs for 77 photovoltaic (PV) water pumping systems installed during a fourteen year period from 1990 to 2004. These systems were supplied, installed, operated and maintained through a customer lease program by two rural utilities, Northwest Rural Public Power District in Nebraska and Verendrye Electric Cooperative in North Dakota. Field records have been tracked and analyzed to capture maintenance events, component failure experience, repair/replacement costs and installation cost histories. The results of these analyses including annual O&M cost, failure rates, and economic comparisons with grid extension options are presented and discussed.

Energy Demand, Availability in Nepal and Present PV Cost Analysis

This paper describes the Photovoltaic solar electricity generating capacity in Nepal. Although Nepal is rich in hydropower, currently only about 17% of the total population has access of electricity. The majority of the population who are living in the rural mountainous parts of Nepal is still deprived of electricity. The relatively high insulation throughout the year and geographical situation encourage for the development of PV energy in the country. The monthly mean solar radiation analysis shows that April and January receive the highest and the lowest solar radiation respectively. The PV installation rate has increased dramatically in the last five years due to relative decrease in PV module cost and government subsidy. PV technology is reliable because of its simplicity, extremely low maintenance cost and point-of-use installation possibility. The widespread use of PV will help to reduce CO2 emission and consequently contributes towards better environment.