Building-integrated solar photovoltaic systems—a hybrid solar cooled ventilation technique for hot

Building-integrated solar photovoltaic systemsÐa hybrid solar cooled ventilation technique for hot climate applicationsA.M.Sharaf,M.M.AboulNaga*,R.El DiastyCollege of Engineering,UAE University,PO Box 17555,Al-Ain,United Arab EmiratesAbstractThe paper presents two low-cost photovoltaic utilization schemes (1±50kW)for ventilation and air conditioning loads.Both schemes can be controlled by novel dynamic on-line power tracking regulator.This ensures maximum power utilization and energy e ciency under varying conditions of solar insolation levels.The system could be used to conserve electric energy through the decrease of electric demand particularly in developing countries.In addition,the system o ers bene®ts in other areas such as indoor enhanced air quality.#1999Elsevier Science Ltd.All rights reserved.Keywords:Solar electrical systems;Solar energy;Photovoltaic systems;Hot climates;Cooling venti-lation1.IntroductionConventional fossil fuel energy sources such as coal,oil,gas,nuclear,geothermal and others are either dwindling,pose serious environmental hazard or scarce in nature,location and volume.This gives rise in renewed interest in renewable,alternative and abundant non conventional sources of energy such as photovoltaics,wind and fuel cells.These renewable energy sources particularly 0960-1481/00/$-see front matter #1999Elsevier Science Ltd.All rights reserved.PII:S 0960-1481(99)00021-XRenewable Energy 19(2000)91±/locate/renene*Corresponding author.Tel.:+971-3-622-318;fax:+971-3-636925/632382.E-mail address:m.naga@uaeu.ac.ae (M.M.AboulNaga)photovoltaics are proven to be both clean and economical [1,2]due to new advanced technological and e cient cells.Photovoltaic solar powered industrial applications include water pumping,air conditioning,electric-vehicles and ventilation systems [3,4].The essential problem facing photovoltaic utilization as a renewable energy source is solar array sizing,load matching and economic utilization via maximum solar energy tracking controllers and power tapping at all times [5±8].Matching problems such as motor starting performance,energy transfer,starting Torque,etc.,are the key to successful,e cient,and economical selection of PV-energy utilization schemes.The growing interest in alternative renewable energy systems is propelled by environmental concerns as well as economical bene®ts.The technological advances in photovoltaic (PV)systems,namely thin ®lm and low-cost PV-array-amorphous en-capsulation promises competitive electricity generation at a cost below that generated from fossil fuel resources [9].One of the most economic PV application in buildings is a dispersed electric generation integrated with PV renewable energy sources.The PV-array,cost per kW-peak output,is now about US$1500±3000with energy cost in the range of US$0.05±0.08kWh.This range is expected to drop further in the next decade [10,11].PV electricity is most suitable for ventilation and air conditioning applications mainly due to the matching of the supply and demand loads with time of day.The advantages of PV systems have led to a rapid implementation of the `Solar Electric Building Concept'.This is a result of the recent drop in the initial cost of PV and the possible integration into buildings.In the early 1990s,the application of building-integrated solar electrical systems were considered expensive due to the high initial cost of the PV cells [9,10].This paper focuses on a building-integrated hybrid solar electrical system for hot climates.Energy conservation and the decrease of electric demands,particularly in developing countries,are the main goals of this system.In addition,the system o ers bene®ts in other areas such as indoor air quality.2.ObjectivesThe paper aims at regulating solar panel (Volt-Ampere)maximum power operation to ensure maximum tracking for available solar energy utilization under varying solar insolation levels.The economical PV scheme can be utilized as standalone or electrical grid interconnections.3.System descriptionBoth schemes utilize novel e cient DC/DC and CD/AC interface converters to ensure maximum solar energy utilization and minimum impact on the host electrical grid system in terms of supply security,reliability and solar energy e cient utilization.The schemes are low-cost systems and most suitable forA.M.Sharaf et al./Renewable Energy 19(2000)91±9692ventilation and air conditioning applications in buildings and malls.The proposed PV schemes provide an e ective way to utilize renewable energy sources to reduce consumption via demand side-energy management.The two PV interface schemes presented are:1.PV-Battery-permanent magnet motor drive for air conditioning mechanical unit suitable as a standalone (1±15kW),and it is highly suitable for residential and small commercial buildings (Fig.1).2.PV-DC-AC solid-state inverter,driving a three phase induction motor for ventilation and air conditioning loads.The scheme has economic rating of (15±50kW),and is reasonably suitable for large commercial buildings and small industrial electricity generation (Fig.2).Fig.1.PV-PMDC utilization scheme(1).Fig.2.PV±AC link scheme (2).A.M.Sharaf et al./Renewable Energy 19(2000)91±96934.Digital simulation resultsThe uni®ed PV-permanent magnet motor drive was digitally simulated using the MatLab Simulation Software.The novel dynamic regulator,shown in Fig.3,was used to ensure on-line maximum power energy utilization under varying insolation levels.Fig.4depicts the PV scheme tracking and system dynamic states.The (V g ÀI g )characteristics presents the mean-maximum power tracking as the motor load tracks available energy from the Sun.5.ConclusionThe paper presents two low-cost PV utilization schemes (DC and AC).The two schemes are controlled by a similar dynamic maximum energy utilization regulator under varying solar insolation levels,(extract available solar power).The proposed system can be utilized as a standalone or electric grid interconnected.The two schemes are most suitable for ventilation,air-conditioning applications in buildings as well as water pumping.The proposed PV schemes provide an e ective way to utilize abundant renewable energy sources and enhance demand side-energy management especially in the developing countries.Cost is comparable to traditional diesel-generators (US$2±3/W peak).AcknowledgementsThe authors acknowledge the ®nancial support of UAE University,the Scienti®c Research Council,College ofEngineering.Fig.3.Two-loop dynamic nonlinear tracking controller..PWM circuit control (a D)for scheme (1)or (V m )for scheme (2).A.M.Sharaf et al./Renewable Energy 19(2000)91±9694References[1]Buresch M.Photovoltaic energy systems design and installation.McGraw-Hill,Inc,1983.[2]Pulfrey DL.Photovoltaic power generation.Van Nostrand Reinhold Company,1978.[3]Mahmoud AMA,Kandil EA.The feasibility of self sustained remote station for the cultivation of barren land.Cairo International 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