Lack of energy storage is a key issue in the development of renewable energy sources. Most renewables, especially solar and wind, when used alone, cannot sustain a reliably constant power output over an extended period of time. These sources generally generate variable amounts of power intermittently, therefore, an efficient electrical energy storage (EES) method is required to better temporally balance power generation to power consumption. One of the more promising methods of electrical energy storage is the unitized regenerative fuel cell (UFRC.) UFRCs are fuel cells that can operate in a charge-discharge cycle, similar to a battery, to store and then to subsequently release power. Power is stored by means of electrolysis while the products of this electrolysis reaction can be recombined as in a normal fuel cell to release the stored power. A major advantage of UFRCs over batteries is that storage capacity can be decoupled from cell power, thus reducing the potential cost and weight of the cell unit. Here we investigate UFRCs based on hydrogen-halogen systems, specifically hydrogen-bromine, which has potential for improved electrode reaction kinetics and hence cheaper catalysts and higher efficiency and energy density. A mathematical model has been developed to analyze this system and determine cell behavior and cycle efficiency under various conditions. The conventional H2-Br2 URFCs, however also so far have utilized Pt catalysts and Nafion membranes. Consequently, a goal of this work was to explore alternate schemes and materials for the H2-Br2 URFC. Thus, three generations of test cells have been created. The first two cells were designed to use a molten bromide salt, ionic liquid or anion exchange membrane as the ion exchange electrolyte with the liquids supported on a porous membrane. This type of system provides the potential to reduce the amount of precious metal catalyst required, or possibly eliminate it altogether. Each cell showed improvement over the previous generation, although the results are preliminary. The final set of results are promising for anion exchange membranes on a cost basis compared Nafion. Another promising energy storage solution involves liquid methanol as an intermediate or as a hydrogen carrier. An alternative to storing high-pressure hydrogen is to produce it on-board/on-site on demand via a methanol electrocatalytic reformer (eCRef), a PEM electrolyzer in which methanol-water coelectrolysis takes place. Methanol handling, storage, and transportation is much easier than that for hydrogen. The hydrogen produced via methanol eCref may then be used in any number of applications, including for energy storage and generation in a standard H2-O2 PEM fuel cell. The mathematical modeling and analysis for an eCref is very similar to that of the HBr URFC. In this work, a comprehensive model for the coelectrolysis of methanol and water into hydrogen is created and compared with experimental data. The performance of the methanol electrolyzer coupled with a H2-O2 fuel cell is then compared for efficiency to that of a direct methanol fuel cell data and was found to be superior. The results suggest that an efficient and small paired eCRef-fuel cell system is potentially be a cheaper and more viable alternative to the standard direct methanol fuel cell. Both the H2-Br2 URFC and the methanol eCref in combination with a H2-O2 fuel cell have significant potential to provide higher energy efficiency and energy density for EES purposes.

The project Austerland Energi at the eastern tip of the island of Gotland called Östergarnslandet was started as a response to the larger project Omställning Gotland funded by the Swedish government as an effort for a pilot project to convert to renewable energy to reach zero CO2-emissions for the country in 2045. The current plan for the Austerland energy system is a solar PV and wind production base with energy storage in the form of batteries and hydrogen which also can be used as vehicle fuel. The system will also continue to be connected to the grid and the annual electricity consumption for the area is 3.4 GWh, including both households and agricultural activities. The energy system has been modeled by Energenious, a company based in Berlin, Germany, who recommended a battery storage and electrically driven vehicles. The total investment cost of which was 30.099 MSEK and the operation and maintenance cost was 2,780 kSEK/year and the emission rate was 138 ton/year.  The yearly global horizontal irradiance is approximately 1,060 kWh/m2 at the location, the average wind speed is 7.5-8.5 m/s at 100 m hub height, but the wind turbine would have to be lower because of the Östergarnslandet being a protected area for the beautiful scenery. The heat production is mostly individual for each household or farm with either heat pumps or biomass boilers. There are no options for hydropower at the location and there is a desalination plant and a water treatment facility which provides the households and farms with drinking and irrigation water. The alternative energy storage solutions investigated in this thesis includes Flywheel, Redox flow battery, Pumped hydro, Deep Sea pumped hydro, Supercapacitors, Compressed air energy storage and Thermal energy storage. The first three of which were included in the models of the system. For the Future scenario changes of the energy consumption, the patterns of change for the households were based on national and regional trends the last 25 years.  The Austerland energy system was modeled using the software Homer Pro, where the base case of using batteries and batteries together with hydrogen storage was analyzed. The batteries were then switched to flywheels, a redox flow battery and a pumped hydro system respectively and analyzed with and without the hydrogen storage. The results showed that the recommended storage solution was still the batteries since the flywheel storage has too short storage duration, the flow battery storage is more expensive, and the pumped hydro storage has a complicated installation process. However, the recommended size of the batteries was half that of the recommended size provided by the Energenious models and the results also showed that the system would be suitable for a future change of the consumption patterns.  Lastly, the sustainability analysis showed that all the alternative energy storage devices have a slightly less CO2-emission rate, but none of the systems had a emission rate as low as that calculated by Energenious. However, when considering any of the components in an energy system, a more thorough investigation of environmental and social issues of the production process should be made. The investigation should include studying working conditions, wages, suspicions about child labour, process waste streams and other emissions streams and ethical values at the production company. / Projektet Austerland Energi är lokaliserat på ön Gotlands östra spets kallat Östergarnslandet. Projektet startades som ett efterfrågat initiativ genom det större projektet Omställning Gotland vilket är finansierat av den svenska regeringen. Omställning Gotland är för ett pilotprojekt för att ställa om till förnybar energi i landet och för att nå netto noll CO2-utsläpp i landet år 2045. Den nuvarande planen för Östergarns energisystem är en solcells- och vind produktions bas med energilagring i form av batterier och vätgas vilket också kan användas som fordonsbränsle. Systemet kommer även fortsättningsvis att vara anslutet till det lokala elnätet och den årliga elförbrukningen för området är 3.4 GWh inklusive både hushåll och lantbruksverksamhet. Energisystemet har modellerats av Energenious, ett företag baserat i Berlin, Tyskland, som rekommenderade batterilagring och elfordon snarare än att använda vätgas. Den totala investeringskostnaden var beräknad till 30,099 MSEK och drift- och underhållskostnaden var 2,780 kSEK/år och CO2-utsläppen var 138 ton/år.  Den årliga solinstrålningen på Östergarn är cirka 1,060 kWh/m2, medelvindhastigheten är 7.5-8.5 m/s vid 100 m navhöjd, men vindkraftverket måste vara lägre än så eftersom Östergarnslandet är ett skyddat område på grund av det vackra landskapet. Värme förses mestadels individuellt för varje hushåll eller gård med hjälp av antingen värmepumpar eller värmepannor som använder biomassa. Det finns ingen möjlighet för vattenkraft på denna del av Gotland men det finns en avsaltningsanläggning och en vattenreningsanläggning som förser hushållen och gårdarna med dricksvatten och vatten för bevattnings. De alternativa energilagrings lösningar som undersöks i denna avhandling inkluderar svänghjul, redox flödesbatteri, ett pumpkraftverk antingen på land eller till havs, superkondensatorer, trycklufts lagring och lagring av termisk energi. De tre förstnämnda alternativen ingick i modelleringen utförd i detta arbete. För undersökningen av framtida energiförbruknings förändringar, undersöktes utvecklingen för hushållen på nationella och regional nivå under de senaste 25 åren. Austerlands energisystem modellerades med hjälp av programvaran Homer Pro, där originalmodellen med endast eller batterier tillsammans med vätgaslagring analyserades. Batterierna byttes sedan till svänghjul, ett redox flödesbatteri respektive ett pumpkraftverk och analyserades med och utan vätgaslagringen. Resultaten visade att den rekommenderade lagringslösningen fortfarande var batterierna eftersom svänghjulet har för kort lagringstid, flödesbatteriet är för dyrt och pumpkraftverket har en mycket mer komplicerad installationsprocess. Den rekommenderade storleken på batterierna visade sig dock vara hälften av den rekommenderade storleken från Energenious-modellerna och resultaten visade också att systemet kommer vara lämpligt för den beräknade framtida konsumtionen. Slutligen visade hållbarhetsanalysen att alla alternativa energi lagringstyper har en något lägre koldioxidutsläpp, men inget av systemen hade en så lågt utsläpp som beräknat av Energenious. När någon av komponenterna i ett energisystem övervägs bör dock en mer grundlig undersökning av miljömässiga och sociala frågor i produktionsprocessen göras. Undersökningen bör omfatta arbetsvillkor, löner, misstankar om barnarbete, avfallshantering och andra utsläpp under produktionsprocessen och etiska värderingar hos produktionsföretaget.

Redox Flow Batteries are chemical based energy storage systems that accumulate energy in liquid electrolytes. Dissolved redox active substances undergo redox reactions in an electrochemical cell and so charge and discharge a battery. Recently, the introduction of organic materials as electrolytes raised research interest. Electrolytes that operate with the bromine/bromide redox couple are interesting due to their high energy density and fast reversible kinetics. They are used in combination with several anodic chemistries (e.g. Zinc, Hydrogen, Quinone), including organic materials.Due to the corrosive and volatile nature of bromine, practical electrolytes use Bromine Complexing Agents (BCAs) in order to bind bromine in a less volatile form and deal with safety issues. These additives have a strong influence on the battery’s operation by influencing the concentration of redox active species, the cell voltage and the electrolyte conductivity. Nevertheless, very little is known about the real properties of aqueous acidic bromine electrolytes, both in pure dilution and in presence of BCAs, which influence on the electrolyte is not predictable so far. The aim of this PhD project is to provide a comprehensive understanding of the behavior of an electrolyte based on bromine and bromide, with particular reference to the one used in semi-organic flow batteries. Along this work an analysis on the performance of a AQDS-Bromine flow battery cell was executed and an extensive study on the physico-chemical behavior of the positive electrolyte was developed. A review of the flow battery technology and of the metrics and methods available for diagnostics was firstly performed as a basis to define macro characteristics,such as State of Charge (SoC) and State of Health (SoH). The cycling behavior of an AQDS-Bromine flow battery was investigated by cell tests and possible degradation mechanisms have been highlighted and explained by interpretation of electrochemical measurements. Following, a broad characterization of the bromine-based electrolyte was performed, producing extended experimental data on physico-chemical properties and a modeling framework for the prediction of the electrolyte behavior.

The objective of the first part of master’s thesis is mapping the potential of various types of renewable sources in Europe and Czech Republic, especially solar energy, wind energy, water energy and biomass. There are described principals and ways of energy generation from these sources, brief overview of current technologies, and also their advantages and limitations. An important part is electric supply continuity from renewable sources, there are large differences and the resulting to restrictions on construction and connecting the units to the power system. In this work there are mentioned some impacts on network and rates of change of supply, some sources are also evaluated in terms of maximum power, that can be connected to the power system in our country. The conclusion of the first part is dedicated to energy storage technologies, which are suitable and usable for renewable sources, there are described their principals, properties, status of development and types of aplications, in which these technologies are used. This chapter also focusses on the price level of each technology. The second part of the thesis deals with 1 MWp on-grid photovoltaic power plant design. This design includes also the redox flow batteries accumulation, the first variant calculates on 24-hour steady energy supply, the second optimalized variant calculates on daily energy supply. There are the accumulation system costs estimated and also the payback period for the both variants. Additionally there is also determined minimum penalization for cost-effective operation. The last part is dedicated to changes of impact on the local grid and changes of system impacts, after the accumulation system is installed.