Optimal control of a fuel cell/wind/PV/grid hybrid system with thermalheat pump loadSam Sichilalua, ⇑ , Henerica Tazvinga b , Xiaohua Xia aa Centre of New Energy Systems, Department of Electrical, Electronic and Computer Engineering, University of Pretoria, Pretoria 0002, South Africab Energy Centre, Council for Scientif i c and Industrial Research, P.O. Box 395, Pretoria 0001, South Africaa r t i c l e i n f oArticle history:Received 9 February 2016Received in revised form 15 May 2016Accepted 18 May 2016Available online 1 June 2016Keywords:Fuel cellHeat pump water heaterOptimal controlDispatch strategyWind generatorPhotovoltaicsElectrolyzerEnergy feed-ina b s t r a c tThis paper presents an optimal energy management strategy for a grid-tied photovoltaic–wind-fuel cellhybrid power supply system. The hybrid system meets the load demand consisting of an electrical loadand a heat pump water heater supplying thermal load. The objective is to minimize energy cost and max-imize fuel cell output, taking into account the time-of-use electricity tariff. The optimal control problemis solved using a mixed binary and real linear programming. The supply switch to the heat pump waterheater and the power from the grid, power to/from the inverter, electrolyzer hydrogen power and fuelcell power are the control variables. The temperature inside the water storage tank and the hydrogenin the storage tank are the state variables. The performance of the proposed control strategy is testedby simulating different operating scenarios, with and without renewable energy feed-in or rather exportto the grid, and the results conf i rm its effectiveness, as it increases the supply reliability of the system.? 2016 Elsevier Ltd. All rights reserved.1. IntroductionRising costs, depletion and environmental concerns about fossilfuel-based energy resources have led to signif i cant research effortin renewable and cleaner energy resources. Globally, governmentsare adopting policies to promote the development and applicationof various renewable energy (RE) technologies for generating elec-tricity. The main challenge associated with RE technologies such assolar and wind generator is their intermittent nature, which affectstheir ability to provide 100% supply reliability. Combining these REsources with battery storage and diesel generator systems hasbeen shown in various studies to be cost-effective (Hove andTazvinga, 2012; Dufo-Lopez et al., 2011; Tazvinga et al., 2015).Currently there are limitations to the fraction of RE (wind andsolar) that can be incorporated in the grid system because of theirintermittency and base load considerations. With the latest devel-opments pointing towards the feasibility of the hydrogen econ-omy, solar and wind power fractions can be safely extendedwithin the grid system by compensating for their intermittencywith an energy storage medium such as hydrogen. Interest inhydrogen is mainly driven by its ability to reduce carbon dioxideemissions, thereby helping to mitigate climate change, improvelocal air quality, improve energy security by reducing energyimports, increase energy supply options, reduce dependence onfossil fuels, and contribute to the introduction of advanced fuel cell(FC) technologies with high eff i ciency.FCs are promising sources of electricity that are environmen-tally friendly. Use of hydrogen FCs for power production is receiv-ing a lot of interest in many research communities, with industrialapplications in automobile industries and heat pumps (Ellis et al.,2001). FCs can serve as emergency sources of energy in the eventof a long-term power outage and in stand-alone applications. Theyare replacing battery systems and are increasingly being used indistributed generation systems. Hydrogen, once produced andstored, can generate power on demand. In order for photovoltaic(PV) and wind systems to meet demand completely, there is a needfor backup systems such as diesel generators (DGs), hydrogen FCsand battery storage in a hybrid system (Wang et al., 2016; Reihaniet al., 2016; Feng et al., 2015; Purvins and Sumner, 2013). Hybridenergy systems present a solution to the time correlation of inter-mittent RE sources (Ranaboldo et al., 2015; Tazvinga et al., 2013).RE-based power systems are being deployed globally to provideautonomous power for various remote applications and also ingrid-tied systems. Improvements in the performance of these sys-tems for both grid and off-grid applications continue globally inmany research communities (Bouzerdoum et al., 2013).http://dx.doi.org/10.1016/j.solener.2016.05.0280038-092X/? 2016 Elsevier Ltd. All rights reserved.⇑ Corresponding author.E-mail addresses: Sam.Sichilalu@up.ac.za, sichgroup@yahoo.com (S. Sichilalu).Solar Energy 135 (2016) 59–69Contents lists available at ScienceDirectSolar Energyjournal homepage: www.elsevier.com/locate/solener
