A battolyser combines the function of battery and electrolyser in one device, i.e. it provides both electrical energy storage and a means to produce hydrogen. A battolyser with lead-acid chemistry has recently been proposed, and this has potential as a particularly low-cost solution. Here, the battolyser is considered for the production of hydrogen as a cooking fuel ("hCooking") in sub-Saharan Africa, a region where cooking typically employs polluting fuels (firewood and charcoal). The more conventional approach for decarbonisation of cooking is the introduction of electric cookers (e.g. hotplate, induction hob, pressure cooker) which can be powered by PV and possibly battery storage; accordingly these electric cooking ("eCooking") systems are considered as the competing decarbonised technology. Multi-objective optimisation is used to design both battolyser and eCooking systems for a notional off-grid community, with solar PV as the main energy source. Objectives are the minimisation of net present cost and lifetime greenhouse gas emissions, and Pareto frontiers are produced to show the play-off between these. Results show that a battolyser system could eliminate 95.6 % of CO2 emissions when compared with a baseline using charcoal, at an annualised cost of $507 per household, over a system lifetime of 20 years. However, eCooking systems appear superior to the battolyser, with the cleanest battery + eCook system achieving 95.8 % emissions reduction at annualised cost $422/household. More generally, hCooking systems are nearly always Pareto dominated by eCooking systems, even under a realistic range of sensitivity scenarios. This result is due to the inherently higher energy intensity of cooking over a flame compared to the eCooking options. Priorities to make the battolyser a more viable solution include extending its lifetime as far as possible, cheaper PV systems, and improved hydrogen burner efficiencies. We also show that eCooking together with some continued use of charcoal may be the cheapest possible cooking solution, whilst simultaneously curtailing 60 % of lifetime greenhouse gas emissions.

A purpose built battolyser, using the combined technologies of a battery and an electrolyser, has been developed for energy storage and hydrogen production at a lower cost than current electrolysis technology. Various acidic conditions and electrode materials were used to evaluate the performance of each battolyser configuration. Only low-cost, abundant, low toxicity and low environmental hazard materials were selected. Performance was evaluated by durability and degradations tests and the results demonstrated that a vanadium redox flow battery configuration could achieve high hydrogen yields, good efficiency, and electrical storage compared to an iron flow cell and sodium-ion manganese hybrid cell. Materials deposited on the electrodes after cycling were characterized using power x-ray diffraction.

A battolyser is a combined battery electrolyser in one unit. It is based on flow battery technology and can be adapted to produce hydrogen at a lower efficiency than an electrolyser but without the need for rare and expensive materials. This paper presents a method of determining if a battolyser connected to a wind farm makes economic sense based on stochastic modelling. A range of cost data and operational scenarios are used to establish the impact on the NPV and LCOE of adding a battolyser to a wind farm. The results are compared to adding a battery or an electrolyser to a wind farm. Indications are that it makes economic sense to add a battolyser or battery to a wind farm to use any curtailed wind with calculated LCOE at £56/MWh to £58/MWh and positive NPV over a range of cost scenarios. However, electrolysers, are still too expensive to make economic sense.

Almost 800 million people currently lack access to reliable electricity, for many of whom solar microgrid systems are expected to be the most cost-effective solution. Quantifying current and future electricity demand is crucial for cost-effective design of reliable microgrids. However, electricity usage is connected to a wide range of social and economic factors alongside climatic conditions, making estimation of demand challenging. This paper presents a framework facilitating each stage of solar microgrid design from demand estimation through to cost-optimal sizing of the microgrid and its economic and environmental characterisation. Household demand is simulated based upon (1) climatic conditions, (2) appliance ratings and usage patterns, and (3) rates of growth in appliance ownership based upon the Multi-Tier Framework for measuring household electricity access. Microgrid demands are simulated based on the combination of these with (4) nondomestic demand based upon locally available data. The framework is demonstrated across four rates of domestic demand growth and two climatic conditions (‘tropical savanna’ and ‘humid subtropical’), alongside nondomestic demand based upon two operational microgrids (one rural and one peri-urban). When growth rates are high, newly introduced appliances tend to dominate, with differing impacts on the demand profile depending on power and usage times. Cooling represents a modest contribution to demand in the tropical savanna climate. However, in the hotter and more seasonally varying humid subtropical climate, cooling becomes the dominant driver of demand, increasing seasonality and proportion of demand at night. Nondomestic demand in the rural microgrid is primarily agricultural, and exhibits more seasonality and better alignment with daylight hours than demand in the peri-urban setting, which is more service-based. Across cases, increased seasonality and proportion of demand at night lead to poorer alignment with PV generation, increasing cost and GHG emissions per unit of electricity used in a cost-optimised microgrid system.

The lack of suitable membranes for nonaqueous electrolytes limits cell capacity and cycle lifetime in organic redox flow cells. Using soluble, stable materials, we sought to compare the best performance that could be achieved with commercially available microporous separators and ion-selective membranes. We use organic species with proven stability to avoid deconvoluting capacity fade due to crossover and/or cell imbalance from materials degradation. We found a trade-off between lifetime and coulombic efficiency: non-selective separators achieve more stable performance but suffer from low coulombic efficiencies, while ion-selective membranes achieve high coulombic efficiencies but experience capacity loss over time. When electrolytes are pre-mixed prior to cycling, coulombic efficiency remains high, but capacity is lost due to cell imbalance, which can be recovered by electrolyte rebalancing. The results of this study highlight the potential for gains in nonaqueous cell performance that may be enabled by suitable membranes.

Reducing the costs of cooking is one of the enablers to improve access to MECS (modern energy cooking services). Electric pressure cookers (EPCs) already compare favourably against conventional stoves, and very favourably against biomass cooking, in terms of energy consumption, but have evolved to satisfy wealthy consumers’ expectations which don’t necessarily match the needs of the global south. Choosing an EPC with an air-gapped lid provided the opportunity to replicate how a factory might install insulation, but displacing trapped-air insulation can be seen to provide limited benefit. This also demonstrates that improving something that is already high performing provides diminishing returns. In contrast, a poorly designed EPC may benefit to a greater degree.

In the context of the MECS project, the batteries are required to operate cooking appliances. In off-grid applications they are needed to store solar PV electricity. In weak-grid or mini-grid applications, batteries are needed to store electricity for later use, when grid electricity is more expensive, insufficiently powerful, or unavailable.All the batteries tested have a nominal capacity of 100Ah and a nominal voltage of 12V. In the case of lead-carbon, a single 100Ah battery was used. In the case of VRLA and LiFePO4, two 50Ah batteries of each were used to make a total of 100Ah when connected in parallel. Of the three battery chemistries tested, the lithium-iron-phosphate (LiFePO4) is clearly superior to the lead-acid and lead-carbon. It maintains a higher open-circuit voltage and can deliver much more energy at high power.

This paper describes the extension of CREST’s popular and open-source domestic energy demand model for UK households into one that can also model households in India. The model is based on a representation of individual appliances and their usage, dependent on ‘active occupancy’, meaning the times that people are both at home and awake. The model is well suited to the analysis of low-voltage networks and micro-grids, for which its ability to account for demand diversity is of critical importance. Energy consumption in households in India is quite different from that in the UK. Several functional extensions are required in order to represent features that are significant in India. The per-household ownership of appliances and lighting fixtures is currently much lower in India than in the UK. The model represents both urban and rural locations and the expected increase in appliance ownership in India. In India, the model shows that domestic demand profile is currently more heavily dominated by an evening peak of demand.

Economic considerations are a primary driver to the adoption of redox flow battery (RFB) technology for grid storage.1 Minimizing area-specific resistance of flow cells is critical to enabling efficient operation at high power, motivating research into redox electrolytes and cell designs.2,3 The ability to effectively test small quantities of materials is essential, as early prototypes will likely require down-selection and refinement to meet desired performance. Further, identifying the causes of device failure can be challenging as they may be related to either materials degradation (e.g., instability, insolubility, incompatibility) or shortcomings in cell design (e.g., crossover, membrane degradation, high resistance). While established methods exist for quantifying electrochemical and transport properties under well-defined conditions and in isolation, translating this knowledge to laboratory-scale flow cells (and beyond) is nontrivial as experimental conditions are complex and results are often convoluted by other processes within the system. To this end, decoupling molecular discovery and engineering science is key: demonstrations of new active materials and design improvements require dedicated toolkits and testing protocols that enable robust comparative evaluations.4 Thus, the development of broadly accessible research platforms, both hardware and software, may help advance scientific understanding and, ultimately, quicken technology growth. Here, we describe efforts to develop a small-scale (2.55 cm2), low-cost flow cell for screening of RFB component materials. Modeled on and validated against state-of-the-art vanadium RFB designs, the small volumes and chemical resistance of the prototype enables evaluation of a wide range of chemistries with minimal materials requirements (e.g., active materials, membranes). In this presentation, we will discuss the key features of this platform, highlight its utility via representative materials design campaigns, and propose future applications of potential scientific and technological value. Ultimately, the aim of this flow cell is to accelerate progress by enabling rapid turnaround (i.e., fail fast) and easing entry into the field of a diverse set of researchers with key subdomain expertise. In this spirit, detailed flow cell designs, bills of material, standard operating procedures, and validation sets are made freely available to the research community to enable internal assessment and potential adoption. References A. Z. Weber et al., J. Appl. Electrochem., 41, 1137–1164 (2011). M. Skyllas-Kazacos, M. H. Chakrabarti, S. A. Hajimolana, F. S. Mjalli, and M. Saleem, J. Electrochem. Soc., 158, R55 (2011). L. Su, J. A. Kowalski, K. J. Carroll, and F. R. Brushett, in Rechargeable Batteries, Green Energy and Technology. Z. Zhang and S. S. Zhang, Editors, p. 673–712, Springer International Publishing, Cham (2015) http://link.springer.com/10.1007/978-3-319-15458-9_24. J. D. Milshtein et al., Energy Environ. Sci., 9, 3531–3543 (2016).

Redox flow batteries (RFBs) are an emerging technology suitable for grid electricity storage. The vanadium redox flow battery (VRFB) has been one of the most widely researched and commercialized RFB systems because of its ability to recover lost capacity via electrolyte rebalancing, a result of both the device configuration as well as the symmetry of the redox chemistry. Despite broad acknowledgement of the benefits of this differentiating feature to system resilience and longevity, assessments of its economic value to the VRFB system have thus far been limited. Here we develop a techno-economic framework that incorporates a physical model of capacity fade and recovery from rebalancing and other servicing methods into a levelized cost of storage (LCOS) metric. We then evaluate the impacts of different contributing factors to the LCOS of a VRFB and identify opportunities for cost reduction through operating strategies (e.g., rebalancing schedule), performance improvements (e.g., reducing fade rates), design decisions (e.g., battery sizing), and investment approaches (e.g., electrolyte leasing). We anticipate this analysis will provide new insights into the cost-drivers for VRFBs and motivate further research efforts in understudied yet important areas.

Current redox flow battery (RFB) stack models are not particularly conducive to accurate yet high-throughput studies of stack operation and design. To facilitate system-level analysis, we have developed a one-dimensional RFB stack model through the combination of a one-dimensional Newman-type cell model and a resistor-network to evaluate contributions from shunt currents within the stack. Inclusion of hydraulic losses and membrane crossover enables constrained optimization of system performance and allows users to make recommendations for operating flow rate, current densities, and cell design given a subset of electrolyte and electrode properties. Over the range of experimental conditions explored, shunt current losses remain small, but mass-transfer losses quickly become prohibitive at high current densities. Attempting to offset mass-transfer losses with high flow rates reduces system efficiency due to the increase in pressure drop through the porous electrode. The development of this stack model application, along with the availability of the source MATLAB code, allows for facile approximation of the upper limits of performance with limited empiricism. This work primarily presents a readily adaptable tool to enable researchers to perform either front-end performance estimates based on fundamental material properties or to benchmark their experimental results.

This paper elaborates on the characterization of vanadium redox flow battery (VRFB) performance for energy arbitrage optimization based on the experimental data obtained in-house. Typical figures-of-merit used for evaluating VRFBs include coulombic, voltaic, and energy efficiencies. However, these metrics along with the deliverable power vary as a function of discharge/charge current during cycling. Thus, using a basic energy storage model with constant efficiency and fixed maximum power is not a rigorous approach for predicting the performance of VRFBs in applications with variable supply/demand of electricity. Moreover, optimization based on such an oversimplified treatment may result in inaccurate battery dispatch signal and may overestimate arbitrage profit. Here, we propose a more detailed VRFB model with dynamic efficiency and maximum power limits as a function of state of charge (SOC). These data were obtained using lab-scale VRFB cells over a range of operating conditions. The dynamic model's performance is compared to the basic model for various day-ahead electricity price profiles. Substantial difference between the predictions of two modeling approaches on the battery dispatch and profits was observed. The results indicate that the dynamic model provides more accurate predictions on the battery performance for applications with intermittent energy profile.

We report a class of perfunctionalized dodecaborate clusters that exhibit high stability towards high concentration electrochemical cycling. These boron clusters afford several degrees of freedom in material design to tailor properties including solubility and redox potential. The exceptional stability of these clusters was demonstrated using a symmetric flow cell setup for electrochemical cycling between two oxidation states for 45 days, with post-run analysis showing negligible decomposition of the active species (<0.1%). To further probe the limits of this system, a prototype redox flow battery with two different cluster materials was used to determine mutual compatibility. This work effectively illustrates the potential of bespoke boron clusters as robust material platform for electrochemical energy conversion and storage.

Due to their wider electrochemical windows of solvents and higher cell voltages, non-aqueous electrolytes containing organic active materials are of interest for use in redox flow batteries (RFBs) for grid energy storage.1 The main challenges to achieving high performance in a nonaqueous RFBs include (i) improving the solubility and stability of the active organic molecules, (ii) preventing the negolyte and posolyte molecules from crossing over separators or membranes, and (iii) to do so without also limiting charging rates due to high cell resistance.2 Using a range of commercially available membranes and separators, we sought to improve the performance of full flow cells containing two materials developed in our laboratory: N-[2-(2-methoxyethoxy)ethyl]phenothiazine (MEEPT)3 and bis[2-(2-methoxyethoxy)ethyl]viologen bis(trifluoromethanesulfonyl)imide (B(MEE)Vol-TFSI2). We first screened electrolyte salts …

Redox-active organic molecules (ROMs) are an attractive alternative to the inorganic, charge-storing compounds typically used in modern batteries as they exhibit potentially superior electrochemical properties, a wide materials design space, and an abundance of raw constituent materials, which, in turn, may open pathways to inexpensive energy storage. However, as most of these molecules are not produced on a commercial scale, assessing the cost proposition of new ROMs is a challenging but critical task for projecting the economic viability of incipient battery technologies. Here, we evaluate different cost estimation methods, explain their application, and determine their practicality for newly developed materials. For this purpose, we use anthraquinone disulfonic acid as a benchmark material, as this compound has been proposed for redox flow batteries and is already produced on an industrial scale. Our results show that simple cost estimation methods are easy to apply but ultimately fail to provide reliable cost information due to their limited accuracy. In contrast, more advanced methods offer more consistent and precise cost estimates but depend on detailed process knowledge rarely obtainable for new organic molecules. Furthermore, our cost analysis proves the feasibility of ROMs at the costs necessary to enable grid storage technologies that meet established cost targets.

Here, a model redox-active electrolyte (RAE) is fully characterized in terms of its transport properties, and subsequent flow cell polarization experiments enable extraction of mass-transfer coefficients. Specifically, experimental manipulation of flow rate and electrolyte viscosity are coupled with a 1-D polarization model in a flow cell to quantify the mass-transfer coefficients as a function of these material and operating parameters. Both flow-through and interdigitated flow fields are used to develop dimensionless correlations that describe mass-transfer rates as a function of RAE properties. Experimental results and fitted model parameters illustrate and quantify the changes in limiting current and mass-transfer coefficient as a function of electrolyte velocity and viscosity. The resulting power-law correlations for the Sherwood (Sh) number, in terms of the Péclet (Pe) and Schmidt (Sc) numbers, are Sh=0.0040Pe0.75Sc−0.24 and Sh=0.018Pe0.68Sc−0.18 for the flow-through and interdigitated flow fields, respectively. These correlations provide quantitative estimates of mass-transfer coefficients within high-performance flow cell architectures as a function of geometry and RAE properties, enabling front-end screening in future RAE development campaigns, as well as performance benchmarking for potential redox flow batteries (RFBs).

This paper explores the possible evolution of UK electricity demand as we move along three potential transition pathways to a low carbon economy in 2050. The shift away from fossil fuels through the electrification of demand is discussed, particularly through the uptake of heat pumps and electric vehicles in the domestic and passenger transport sectors. Developments in the way people and institutions may use energy along each of the pathways are also considered and provide a rationale for the quantification of future annual electricity demands in various broad sectors. The paper then presents detailed modelling of hourly balancing of these demands in the context of potential low carbon generation mixes associated with the three pathways. In all cases, hourly balancing is shown to be a significant challenge. To minimise the need for conventional generation to operate with very low capacity factors, a variety of demand side participation measures are modelled and shown to provide significant benefits. Lastly, projections of operational greenhouse gas emissions from the UK and the imports of fossil fuels to the UK for each of the three pathways are presented. & 2012 Elsevier Ltd. All rights reserved.

Redox flow batteries (RFBs) are promising candidates for grid storage, but current systems have not met the stringent cost and/or safety requirements needed for widespread implementation. Replacing vanadium with organic compounds may lower materials cost, and utilizing non-aqueous (aprotic) electrolyte solvents, in place of water, could enable a 2- to 3-fold increase in operating voltage. Both features make non-aqueous RFBs candidates for large-scale stationary storage. A limited number of organic compounds have been reported as stable electron donors and acceptors, with even fewer materials being studied as small molecule two-electron donors and/or two-electron acceptors. Our recent efforts have focused on the development of highly soluble electron donors and acceptors with stable oxidized and reduced states. This presentation will focus on design strategies utilized to increase molecular stability in all relevant states of charge as well as solubility. In particular, we highlight the design, synthesis, and electrochemical analysis of organic redox couples. Results will be presented on the cycling of phenothiazine and naphthoquinone derivatives in flowing full cell battery prototypes.

An hour-by-hour time-step analysis is presented of United Kingdom electricity grid balancing in low-carbon energy pathways from the DECC 2050 Calculator. The detailed modelling uses the future energy scenario assessment (FESA) tool, which uses real weather data and real electricity demand data from year 2001 to model future supply and demand profiles, suitably adjusted to reflect technology uptakes. The paper describes the linking of the DECC 2050 Calculator with FESA and many of the detailed considerations within the modelling. The calculation of net demand (total demand less intermittent renewables and inflexible portions of other electricity generation) reveals the magnitude and duration of peaks and troughs throughout the year and this allows quantification of required peaking plant, energy storage, demand response or a combination of these. The results indicate that the grid balancing challenge is much greater than is apparent from the DECC 2050 Calculator, with significant excess power from renewables and less flexible generators needing to be exported or curtailed, and, at other times of the year, a significant amount of additional conventional generation being required. FESA also indicates significantly lower capacity factors for despatchable generators than indicated in the DECC 2050 Calculator. The results underline the value of energy storage and flexible demand, particularly in the high-renewables pathways, but also that much of that storage and flexibility needs to be available for days or even weeks rather than hours.