Appropriate solar spectrum usage : the novel design of a photovoltaic thermal system

Abstract: The path towards zero energy buildings is fraught with many challenges, the onsite renewable energy production to drive consumer appliances that are not low or zero energy is an important challenge. Therefore, developing the energy production such that the production mode is matched to the usage mode is the simplest manner to improve efficiency. As such, energy consumption for lighting could be significantly reduced by optimizing the building`s design to maximize direct daylight usage, similarly cooking using solar stoves, or water heating using solar geysers eliminates the need for PV cells to generate electricity. The most important energy consumption in most buildings is HVAC (accounting for approximately 40% of a building`s energy consumption) which can be addressed with the use of a solar power absorption chiller. This article introduces the design of a novel solar concentrated photovoltaic thermal (CPVT) system that produces electricity and thermal energy simultaneously from the same surface area. The goal of the proposed system is to provide sufficient heat for an absorption cooling system, water heating as well as to produce electricity in a cost effective way. The CPVT system is designed to operate over a wide spectrum (400nm upward contains around 90% of the incident solar radiation spectrum). In the proposed system, solar irradiation is highly concentrated (to the equivalent intensity of approximately 100 suns) onto a single point, using a dual axis sun tracking concentrator with a Fresnel lens. A filter then separates the infrared (IR) from the visible light (VL) components using an imaging lens (viz. a hot mirror which has approximately a 98% filter efficiency). The IR is then utilized for heating while the VL components power the PV cell. The efficiency of the electricity generation in the PV cell improves when the IR component is removed from the incident solar irradiance. High-temperature high pressure water, at approximately 95-120oC (203–248oF), is generated by the IR and serves as a heat source for the absorption cooling system (lithium bromide water / ammonia-water). The proposed system is expected to deliver electricity at the rate of 0.08 W/cm2 (0.2032 W/in2) of PV cell area, and around 0.04W/cm2 (0.1.016 W/in2) collector area. Given that the ratio of collector area to PV cell area is ±9:1 this allows us to design the relative size to suit the building requirements

Light filtered concentrated photovoltaic thermal system

Abstract: PV cells generate electricity, but the electrical output is only one component of the total energy produced by a photovoltaic array. A typical PV module has an ideal conversion efficiency of around ±15%, with the remaining energy generated as heat. This heat can raise the temperature by as much as 50°C above ambient temperature, resulting in two concerns: possible structural damage; and PV cell efficiency decreases as temperature increases. Crystalline cells are affected by temperature and their performance drops as cell temperature rises. In the case of combined photovoltaic thermal cells it has been shown that for each 1°C increase in temperature, the power output drops by approximately 0.5% which results in limiting the harvested energy This article aims to introduce the concept of a concentrated Photovoltaic thermal system using an optical filtering technique. To this end concentrated sunlight is filtered into its major components and then utilised in a more appropriate way. The visible light is directed onto a standard PV surface while infrared is filtered before striking the PV surface and directed to a water column for heating purposes

High rise buildings energy assessment towards near net-zero energy consumption

M.Eng. (Engineering Management)The residential and commercial urban sprawl towards green future is governed by the ability to overcome the challenges facing the high rise buildings sustainability. This research is dedicated to assess the high rise buildings’ energy towards near net-zero energy consumption from the point of view of production (the on-site energy generation via renewable technologies) and consumption (the usage of low consumption products). The features of the high rise buildings limit the on-site renewable energy production to solar energy, therefore the integration of solar application in the building’s facade plays a major role in the on-site energy production. Since, the relative roof area compared to the height of the high rise buildings is much less than the single family houses. Therefore, the use of the facade in high rise buildings for clean energy production becomes a major element towards its sustainability. There are several solar energy production techniques of which the most feasible and effective one is the combined electricity generation and heat collection via integrating PV and thermal collector system this system is denoted as solar Photovoltaic and Thermal (PVT) system. PVT system produces both electricity and heat at a higher efficiency from one integrated system on the same surface area exposed to the sun. For instance, PVT system produces approximately 43% more primary energy than a conventional solar thermal collector per unit surface area, and even around 96% more than a conventional Photovoltaic PV system (PVTwins, n.d). The concept of the PVT system was generated based on the fact that Photovoltaic (PV) system has typically 14-17% efficiency, so the rest of more than 80% is a lost energy; this lost energy goes in a form of heat. This heat could reach as high as 50oC above the ambient temperature resulting in structural damage as well as reducing the system efficiency by 25%. Recovering this harmful heat could reach up to five times thermal energy more than electricity from PV array (Hollick, 2011). From the energy consumption perspective, the air conditioning and ventilation system (HVAC) is considered as one of the highest energy consumer in the overall high rise buildings energy consumption (around 40%). This makes it an essential part of any high rise buildings energy solution therefore several low energy consumption HVAC systems has been developed recently. As such, absorption chiller presents one of the greenest HVAC system whereby it has no moving part, no electricity required, thermal driven system (use heat to produce cold) and could be operated by solar thermal energy. In this sense, the enterprise should respond to the increasing demand of the high efficiency buildings mainly by developing new solutions that enhance the latest green technologies and overcome the recent energy challenges