Optimal control of renewable energy/grid hybrid systems with heat pump load

Abstract

The rising costs, power deficit and environmental concerns about fossil fuel-based energy resources have led to significant research effort in renewable and cleaner energy resources. Globally, governments are adopting policies to promote the development and application of various renewable energy (RE) technologies for generating electricity. The main challenge associated with RE technologies such as solar and wind generation is their intermittent nature, which affects their ability to provide 100% supply reliability. Combining these RE sources with energy storage systems such as battery storage and hydrogen can be cost-effective. Currently there are limitations to the fraction of RE that can be incorporated in the grid system because of their intermittency and base load considerations. The major challenge is the escalating power demand, far above the installed capacity in most countries. This requires urgent mitigation of demand side management(DSM), in order to stabilize the imbalance in the short, medium and long term. Energy efficiency and optimal integration could provide one of the most effective technological solutions, with the usage of energy-efficient devices such as heat pump water heaters (HPWH). These collective efforts at energy saving should involve proper selection of an appropriate technology, application of optimal control (OC) in RE, usage of energy-efficient equipment, green building materials and an effective energy policy. The proper integration of these sources and the use of HPWH could reduce the power utility?s maximum demand and improve the security of the supply. Most countries at policy level are beginning to introduce attractive feed-in tariffs, dynamic energy pricing (time-of-use) and rebate systems for using greener energy and energy-efficient load such as HPWHs. Hence, this thesis provides the first practical attempt to integrate various distributed energy resources (DRE) effectively into the grid, using HPWHs for the generation of the required thermal energy. This multi-directional approach in this work has proven that OC strategy could significantly reduce the cost of energy and provide an opportunity for power trade-off/feed-in in the electricity market. This thesis developed four main models that meet both the technical and operational constraints of DSM and optimal integration of DREs. Solar energy is abundant in Africa, its exploitation in addition to other REs is a priority in this work. The first model is an optimal scheduling strategy of a gridtied/ battery/PV system supplying HPWH. Secondly, an optimal energy management model with a diesel generator back-up system is developed that minimizes the fuel cost, while maximizing the utilization of renewable energy with a HPWH. Thirdly, in OC model of a HPWH, the thermal output is state variable. It is supplied by the second abundant wind energy hybrid resources. An economic analysis is done in this model to assess the break-even period, which is important to every investor. Finally, the future green energy hydrogen fuel cell hybrid system is modeled. Hydrogen has attracted attention in modern research owing to its ability to reduce carbon dioxide emissions, thus helping to mitigate climate change, improve local air quality, improve energy security by reducing energy imports, increase energy supply options and reduce dependence on fossil fuels. These models are suitable for application in both urban and rural areas where the electrical power power supply is intermittent. These models have several advantages for building owners intending to turn their dwelling into zero/positive energy buildings and enter electricity market. However, engineering solutions alone cannot yield much success on DSM, sensitization and education on energy savings at individual level and how these are intertwined with climate change are of the utmost importance.

Die stygende koste, kragtekort en besorgdheid oor die uitwerking van fossielgebaseerde energie op die omgewing het tot beduidende navorsingspogings rakende hernubare en skoner energiebronne gelei. W?reldwyd aanvaar regerings beleid om die ontwikkeling en aanwending van verskeie hernubare energietegnologie? vir die opwekking van elektrisiteit te bevorder. Die hoofuitdaging in verband met hiedie tegnologie?, soos sonkrag- en windopwekking, is hulle wisselvallige aard, wat ?n invloed het op hulle vermo? om volledige betroubaarheid van voorsiening te verseker. ?n Kombinasie van hierdie hernubare energiebronne met energiebergingsisteme soos batteryberging en waterstof kan kosteeffektief wees. Daar is tans beperkings op die gedeelte van die hernubare energie wat in die netwerk ingesluit kan word, omrede hulle wisselvalligheid en basisladingoorwegings. Die hoofuitdaging is die groeiende aanvraag vir krag, ver meer as die ge?nstalleerde kapasiteit in die meeste lande. Gevolglik is dringende ingryping deur aanvraagkantbestuur nodig om die wanbalans in die kort, medium en lang termyn te stabiliseer. Energiedoeltreffendheid en optimale integrasie kan een van die mees effektiewe tegnologiese oplossings verskaf, deur die gebruik van energie-effektiewe toestelle soos hittepompwaterverhitters. Hierdie kollektiewe pogings om energie te bespaar behoort ?n toepaslike keuse van geskikte tenologie, aanwending van optimale kontrole in hernubare energie, gebruik van energie-doeltreffende toerusting, groen boumateriale en ?n effektiewe energiebeleid in te sluit. Die behoorlike integrasie van hierdie bronne en die gebruik van hittepompwaterverwarmers mag die maksimunaanvraag van die energievoorsiener verminder en die sekuriteit van voorsiening verbeter. Op beleidsvlak begin die meeste lande aanloklike invoertariewe, dimamiese energieprysbepaling (tyd-van-gebruik) en kortingsisteme invoer om die gebruik van groener energie en energie-doeltreffende belading soos hittepompwaterverhitters te bewerkstellig. Hierdie tesis bied die eerste praktiese poging om verskeie verspreide energiebronne in die netwerk te integreer deur die gebruik van hittepompwaterverhitters vir die opwekking van die vereiste hitte-energie. Die multi-gerigte benadering in hierdie werk het bewys dat optimale kontrolestrategie die koste van energie beduidend kan verminder en die geleentheid bied vir kragruil/krag-invoer in die elektrisiteitsmark. Hierdie tesis het vier hoofmodelle ontwikkel wat sowel die tegniese en operasionele beperkings van aanvraagkantbestuur en optimale integrasie van verspreide energiebronne kan hanteer. Sonkrag-energie is oorvloedig beskikbaar in Afrika en die benutting daarvan saam met ander hernubare energiebronne is ?n prioriteit in hierdie werk. Die eerste model is ?n optimale skeduleringstrategie van ?n netwerkgebonde/ battery/fotovolta?ese sisteem wat krag voorsien aan ?n hittepompwaterverhitter. Tweedens word ?n optimale energiebestuurmodel met ?n dieselgeneratorrugsteunsisteem ontwikkel wat die brandstofkoste minimeer, terwyl dit die gebruik van hernubare energie met ?n hittepompwaterverhitter maksimeer. Derdens is die hitte-uitset in ?n optimale-kontrolemodel van ?n hittepompwaterverhitter veranderlik volgens toestand. Dit word verskaf deur die tweede oorvloedige hibridiese bron, windenergie. ?n Ekonomiese analise word in hierdie model gedoen om die gelykopuitkomsperiode te bepaal, wat vir alle beleggers belangrik is. Laastens word die toekomstige groen-energie waterstofbrandstofselhibriedsisteem gemodelleer. Waterstof het in moderne navorsing aandag getrek deur sy vermo? om koolstofdioksieduitlatings te verminder en sodoende te help om klimaatverandering te beperk, plaaslike lugkwaliteit te verbeter, energiesekuriteit te verbeter deur energie-invoer te verminder, energievoorsieningopsies te vermeerder en afhanklikheid van fossielbrandstowwe te verminder. Hierdie modelle is geskik vir aanwending in sowel stedelike as landelike gebiede waar kragvoorsiening ongereeld is. Hulle het verskeie voordele, byvoorbeeld vir eienaars van geboue wat hulle woonplekke wil omskep in zero/positiewe energiegeboue en die elektrisiteitsmark wil betree. Desnieteenstaande kan ingenieursoplossings op hulle eie nie veel sukses behaal met aanvraagkantbestuur nie; sensitering en opvoeding oor energiebesparing op persoonlike vlak en bewustheid van hoe dit vervleg is met klimaatverandering is van die uiterste belang.