Renewable Electricity Grid Research Articles

Reimagining renewable electricity grid management with dispatchable generation to stabilize energy storage

With the expansion of intermittent renewable energy sources, and the development of economical and scalable energy storage technologies, the management of the electrical grid has the potential to fundamentally change. Under the current grid management paradigm, balancing and stabilizing a grid with a large penetration of intermittent renewables tends to require that those balancing resources ramp power output up and down more rapidly and more frequently to compensate for output variations of intermittent resources, as well as those of load. This paper describes a strategy of combined wind, solar, and in-stream tidal intermittent generation with energy storage. The new control strategy operates dispatchable generation with the objective of keeping the energy storage at a neutral state of charge in preparation for unpredicted upcoming imbalances between intermittent generation output and system load, while limiting power ramp rates within an acceptable envelope. A case study in Nova Scotia, Canada is examined. The model reveals that approximately 4 h of storage is sufficient to permit up to 70% intermittent generation contribution to the grid at a cost about 50% higher than that of the least cost renewable generation alone.

Electricity generation and demand flexibility in wastewater treatment plants: Benefits for 100% renewable electricity grids

In future, the low carbon electricity grid will need an additional potential of energetic flexibility to compensate the variable renewable supply. Wastewater treatment plants have the potential to provide electricity demand and generation flexibility. A novel approach of utilising the energetic flexibility in wastewater treatment plants to optimize the installed capacity of a fully renewable electricity grid in Australia is presented. In this hourly electricity supply simulation, both the electricity generation and demand of wastewater treatment plants are shifted for reducing the required size of 100% renewable electricity grid and achieving perfect supply-demand matching. The electricity demand and dispatchable electricity generation capacity of cogeneration systems in wastewater treatment plants are modelled on a 90×110 raster grid. For a 6-hour shift in wastewater treatment plant’s electricity demand and it’s electricity generation limited to five times the current capacity, a 100% renewable electricity grid would need an installed capacity of around 149 GW to meet the existing reliability standard (6–8 h of power outages per year). The electricity generation cost is around 16 ¢/kWh with a capacity factor of 28% and spilt electricity of less than 21%. The electricity generated from sewage methane in wastewater treatment plants is only 1% of the total generation and is utilised along with biomass power plants to plug demand-supply gaps. Our results indicate that a 2% reduction in installed capacity and 11% reduction in levelized cost of electricity is achieved by utilizing the energetic flexibility of wastewater treatment plants.

GIS-based modelling of electric-vehicle–grid integration in a 100% renewable electricity grid

We examine the spatio-temporal interactions of widespread electric vehicle (EV) charging with a future, 100% renewable electricity system in Australia. More specifically, we use a GIS-based electricity supply-demand model simulating an hourly competitive-bidding process over an entire year. We obtain least-cost grid configurations that include both renewable energy (RE) generators and EVs, the latter under both uncontrolled and controlled charging, and adoption rates between 0 and 100%. We characterise the vehicle-to-grid interaction in terms of overall installed capacity, hourly generation and spillage, levelized cost of electricity (LCOE), as well as transmission network expansion topology. We show that supplying 100% renewable electricity to cover current electricity needs in Australia, as well as powering all Australian passenger vehicles as controlled-charged EVs, requires 205 GW of installed capacity at an LCOE of 14.7 AUD¢/kWh. This 100% RE supply with EV charging leads to an additional electricity cost of 1710 AUD/capita annually, comparing to the current annual expenditure for electricity and conventional vehicle fuel.

Beyond 100 % renewable: Policy and practical pathways to 24/7 renewable energy procurement

Corporations are increasingly shaping the future of the electric grid by pursuing 100 % renewable energy goals that seek to match their annual energy consumption with an equal volume of renewable energy. The challenge of achieving a 100 % renewable electricity grid, however, is not only a question of how much renewable energy is built, but rather whether renewables can supply electricity when it is needed. One emerging approach to address this challenge is “24/7" renewable energy, which requires matching a corporation’s hourly energy demand with renewable energy produced in the same region and hour. This paper explores the evolution of voluntary renewable energy procurement goals, presents a practical framework for 24/7 renewable energy procurement, and suggests policy developments that would support wider adoption of a time-matched renewables procurement approach.

Attractiveness of Using Photovoltaic Panels in a Building Connected to a Mainly Renewable Electricity Grid

Photovoltaic (PV) panels contribute to overall building’s loads, but generally have their impacts offset at the operational stage. For increasingly renewable electricity grids, PV’s contribution to lowering non-renewable energy becomes less significant. This paper aims at investigating the non-renewable cumulative energy demand (CEDnren) and global warming potential (GWP) payback times associated to onsite PV generation in the highly renewable Brazilian grid, considering a 50-year building service life. Operational energy consumption was simulated in Energy Plus. CEDnren and GWP were calculated through the CED method and CML-IA, respectively. SimaPro 7.3 and Ecoinvent 2.2 supported performed LCAs. Different PV settings were analyzed to rank the most effective technological options. Amorphous and single-Si panels performed worst (around 17 years of non-renewable CED payback time, whilst for GWP the payback time was much shorter for all technologies). PV’s production and replacement loads played a significant role, therefore technological investments to increase panels’ durability and improve manufacturing efficiency could ensure its attractiveness.

Thermodynamic Analysis of a Hybrid Power System Combining Kalina Cycle with Liquid Air Energy Storage.

Liquid air energy storage (LAES) is a promising energy storage technology in consuming renewable energy and electricity grid management. In the baseline LAES (B-LAES), the compression heat is only utilized in heating the inlet air of turbines, and a large amount of compression heat is surplus, leading to a low round-trip efficiency (RTE). In this paper, an integrated energy system based on LAES and the Kalina cycle (KC), called KC-LAES, is proposed and analyzed. In the proposed system, the surplus compression heat is utilized to drive a KC system to generate additional electricity in the discharging process. An energetic model is developed to evaluate the performance of the KC and the KC-LAES. In the analysis of the KC subsystem, the calculation results show that the evaporating temperature has less influence on the performance of the KC-LAES system than the B-LAES system, and the optimal working fluid concentration and operating pressure are 85% and 12 MPa, respectively. For the KC-LAES, the calculation results indicate that the introduction of the KC notably improves the compression heat utilization ratio of the LAES, thereby improving the RTE. With a liquefaction pressure value of eight MPa and an expansion pressure value of four MPa, the RTE of the KC-LAES is 57.18%, while that of the B-LAES is 52.16%.

Agricultural demand response for decarbonizing the electricity grid

Historically, the focus of the agricultural industry has been increasing profit through maximizing crop yield. Costs for energy and water are small compared to equipment and personnel, and are thus often overlooked. However, energy costs for irrigation are increasing and could be exacerbated with declining water levels in many Western states. This trend has motivated many farmers to explore sustainable irrigation water and energy management practices. Much of this new focus has been directed towards the adoption of new agricultural technologies with a misplaced assumption that technology alone will inherently bring all the benefits. On one hand, farms are going through a paradigm shift, and are turning into net electricity generators, and on the other, higher penetration of intermittent renewable sources into the electricity grid, require dynamic loads to help the grid balance its intra-hour variability and short duration ramps. The agricultural industry could be restructured to utilize larger amounts of renewable energy such as wind and solar and provide a great deal of flexibility to the grid. As emerging producers of clean energy, farmers are required to learn and speak the complex language of the electricity grid in order to monetize their energy generation while making the renewable electricity grid more resilient and reliable. In this paper, we develop a foundational approach for understanding and connecting three important concepts that can help the agricultural industry during this critical transition period. Those three concepts are: (a) current and future needs of the electricity grid, (b) available electricity market mechanisms through which farms can provide services to the grid, and (c) understanding electricity consuming/generating equipment on farms. Defining these concepts and condensing them into a standardized framework, can remove a significant barrier for enabling farms to provide services to the electricity grid while improving their bottom line.

Prioritizing among the end uses of excess renewable energy for cost-effective greenhouse gas emission reductions

Preventing the curtailment of excess renewable generation, caused by mismatches between variable renewable electricity generation and the electric load, is a key strategy for maximizing greenhouse gas emissions reductions by integrating renewable resources into the electric grid. Strategies to harness excess renewable generation for useful purposes exist, but it is unclear which of these end uses provides the most effective use of available excess generation to maximize greenhouse gas emissions reductions in a cost-effective manner. This study investigates and compares three end-use strategies for utilizing excess renewable generation – storage in electrical energy storage systems, production of transportation fuel or vehicle charging, or production of renewable gas – and their diverse technology pathways on the bases of their greenhouse gas emissions reduction potential and the impacts of their implementation on the cost of energy services. This is accomplished by modeling the integration of 46 different technology pathways for using excess renewable generation in a 70% renewable and an 80% renewable electric grid configuration during the year 2050 in California using the Holistic Grid Resource Integration and Deployment (HiGRID) platform, which is a temporally-resolved resource dispatch model of the electricity system. Technology and cost characteristics for batteries, hydrogen energy storage systems, vehicle fueling or charging, and renewable gas production technologies are collected from multiple sources and their effect on reducing greenhouse gas emissions and affecting the Levelized Cost of Energy (LCOE) services in the HiGRID platform are examined. It was discovered that using excess renewable generation to produce transportation fuel for hydrogen vehicles or to charge electric vehicles provided the largest total greenhouse gas emissions reductions and lowest per-ton cost of greenhouse gas reduction. Use in grid energy storage and production of renewable gas provided similar but relatively lower total greenhouse gas reductions than transportation, with the latter imposing lower per-ton costs of greenhouse gas reduction. More generally, greenhouse gas reduction potential of these end uses depended on the intensity of the fuel being displaced by renewables, while LCOE effects depended on the temporal flexibility of the technologies associated with this end use. Overall, this study provides insight into a priority order for directing the use of excess renewable generation towards end uses to achieve greenhouse gas reduction goals such as those in California in a cost-minimal manner, and investigates the sensitivities that influence the effectiveness of these end uses.

Can electric vehicles significantly reduce our dependence on non-renewable energy? Scenarios of compact vehicles in the UK as a case in point

Electric vehicles (EVs) are increasingly regarded as the way forward to deliver a much-needed improvement in the transport sector's sustainability profile, and the UK is embarking on a major transition towards them. While previous studies focused mainly on greenhouse gas (GHG) emissions, this article assesses the extent to which EVs may contribute to reducing the UK's dependence on (mostly imported) non-renewable primary energy. The study combines a life-cycle model of a compact battery electric vehicle (BEV) with a prospective energy analysis of a range of electricity supply alternatives for the vehicle's use phase. The key metric analysed is the non-renewable cumulative energy demand (nr-CED). Results show that, already under current conditions, the nr-CED of a compact BEV in the UK is lower by approximately 34% with respect to that of an otherwise similar internal combustion engine vehicle (ICEV). Such reduction is then expected to improve further under all future scenarios, indicating that a transition to EVs is indeed a recommendable option to reduce the UK's demand for non-renewable energy, especially if this is accompanied by a shift to a more renewable electric grid.

Shifting air‐conditioner load in residential buildings: benefits for low‐carbon integrated power grids

This study presents a simulation of low-carbon electricity supply for Australia, contributing new knowledge by demonstrating the benefits of load shifting in residential buildings for downsizing renewable electricity grids comprising wind, hydro, biomass, and solar resources. The load-shifting potential for the whole of Australia is estimated, based on air-conditioner load data and an insulation model for residential buildings. Load shifting is applied to enable transferring residential air-conditioner load from peak to off-peak periods, assuming that air-conditioners can be turned-on a few hours ahead of need, during periods where demand is low and renewable resource availability is high, and turned-off during periods of high demand and low resource availability. Thus, load shifting can effectively reduce installed capacity requirements in renewable electricity grids. For 1 h load shifting of residential air-conditioners, Australian electricity demand can be met at the current reliability standards by 130 GW installed capacity, at cost around 12.5 ⊄/kWh, and a capacity factor of 32%. The installed capacity can be further reduced by increasing the number of hours that loads can be shifted. The findings suggest that the application of load shifting in residential buildings can play a significant role for power networks with high renewable energy penetration.

Best Practices for Recovering Rural Abandoned Towers through the Installation of Small-Scale Biogas Plants

The massive and continuous development of renewable energy systems is making it possible to achieve the European goals regarding environment and sustainability. On the other hand, it leads to the progression of significant problems such as low renewable energy density (i), social acceptability (ii), and non-programmability of renewable energy sources (iii). The rural architecture, which is largely present in the countryside of central Italy, is generally equipped with several annexes such as dovecotes (i), grain stores (ii), and tobacco drying kilns (iii). Nowadays, those towers appear in decay because of the decline of agricultural activities, although they are classed as Environmental and Historical Heritage sites. The present work aims to propose a methodology for improving the energy grid in the countryside, while reusing abandoned buildings by modifying their function and maintaining their aspect as much as possible. The proposed workflow was applied to a rural silo, which has fallen into disuse, in Sant’Apollinare (Marsciano, Perugia) by converting it into a mini-biogas plant. The function of the annex which was chosen as the case study changes from agricultural use to energy production: it becomes an on-site renewable energy-based electric grid that can produce clean energy from agricultural and forestry residues. The project turns out to be sustainable not only in terms of energy and the environment, but also from an economic point of view as a result of the recent regulations and incentives for renewable energy production.

Energy‐aware resource allocation for OFDMA wireless networks with hybrid energy supplies

In this study, the authors investigate the resource allocation for orthogonal frequency-division multiple access (OFDMA) wireless networks, where the base station is powered by renewable energy and electric grid. To fully exploit the renewable energy, the authors propose an energy-aware resource allocation (EARA) algorithm to maximise the network utility, which captures the tradeoff between the system throughput and the grid energy consumption. Specifically, the EARA algorithm only has to track the current system states (e.g. channel and queueing conditions) without requiring a relevant priori distribution knowledge, making it applicable for practical OFDMA wireless networks with unpredictable channel dynamics, renewable energy arrivals and stochastic traffics. Moreover, the performance achieved by the EARA algorithm is theoretically characterised. Most importantly, the authors develop an implementation architecture to take the EARA algorithm into practice, and also analyse the low implementation costs (e.g. low computational complexity, trivial signalling overhead etc.). Finally, simulation results verify the theoretical analysis and also demonstrate the advantages of the EARA algorithm.

Basis for Fluoride Salt–Cooled High-Temperature Reactors with Nuclear Air-Brayton Combined Cycles and Firebrick Resistance-Heated Energy Storage

The fluoride salt–cooled high-temperature reactor (FHR) with a nuclear air-Brayton combined cycle (NACC) and firebrick resistance-heated energy storage (FIRES) is a new reactor and plant concept. The development of a new reactor is a large undertaking that requires a strong commercial case and a strong basis for government support to enable commercialization. The goals are (1) increase plant revenue by 50% to 100% relative to base-load nuclear plants with capital costs similar to light water reactors, (2) enable a zero-carbon nuclear renewable electricity grid, (3) no potential for major fuel failure and thus no potential for major radionuclide off-site releases in a beyond-design-basis accident, and (4) offer a pathway to more advanced energy systems. The approaches to achieve those goals are described herein.The FHR uses liquid-salt coolants originally developed for molten salt reactors (MSRs) where the fuel is dissolved in the coolant. However, in the FHR the fuel is not dissolved in the coolant. Instead, the FHR uses graphite-based high-temperature gas-cooled reactor (HTGR) coated-particle fuel. This combination enables delivering heat to the power cycle between 600°C and 700°C that, in turn, enables the FHR to couple to NACC. Using an air-Brayton power cycle enables the FHR to operate as a base-load reactor and produce added electricity in a peaking mode with the addition of auxiliary heat (natural gas, stored heat, or hydrogen). The auxiliary heat-to-electricity production is a thermodynamic topping cycle with efficiencies of 66%. Because an FHR with NACC is more efficient in converting natural gas into peak electricity than a stand-alone natural gas plant (60%), it can economically compete with a natural gas plant for peak electricity production because it uses less fuel. NACC can also incorporate FIRES heat storage that enables buying electricity at low prices to later sell electricity at high prices. For every 100 MW(electric) of base-load capacity, the station output can vary from minus several hundred megawatts to +242 MW(electric) because of the capabilities of the NACC with FIRES. The FHR can be built in different sizes.The use of high-temperature liquid-salt cooling and coated-particle fuel enables near-term reactor designs where large-scale fuel failure cannot occur, and thus, large-scale off-site releases of radionuclides cannot occur. Under extreme accident conditions decay heat can be passively conducted to the environment at temperatures below fuel failure temperatures and thus avoid the potential for large-scale radionuclide releases.The FHR is the gateway technology to several advanced salt-cooled reactor systems that have additional capabilities. The MSR can be designed to enable breeding and actinide waste burning. New high-magnetic-field fusion systems may require liquid-salt cooling. The FHR would provide the required salt and power cycle technology for these advanced reactors. There are significant development challenges. The United States has a competitive advantage in developing the FHR because it leads in gas turbine technology, high-temperature materials, and HTGR fuels.

Energy storage against interconnection as a balancing mechanism for a 100% renewable UK electricity grid

This study considers generation and demand challenges of a 100% renewable UK electricity grid and how this could be addressed with interconnection or energy storage. Hourly demand and electricity generation profiles for a year have been constructed: Business as Usual (BAU) with a yearly demand of 540 TWh and Green Plus (GP) with a demand of 390 TWh, Two further scenarios based on the above have been considered with electrification of heating (ASHP) and electric vehicle transportation (EV). The resultant hourly imbalances have been used to calculate the interconnection and energy storage requirements. This paper discusses the findings of the BAU scenario. The calculated interconnector capacity required was found to be 60 GW and cost £58 billion. Energy storage capacity requirements vary depending on the selected technology. Rated capacity was estimated to be 14 GW with storage capacity of 3 TWh for pumped storage, 11 GW and 2.3 TWh for liquid air, and 65 GW and 13.6 TWh for hydrogen storage, at a cost of £65, £76 and £45 billion respectively. This paper indicates that storing hydrogen in underground caverns would offer the cheapest solution. However, whilst these technological solutions can address generation and demand imbalance in a fully renewable electricity grid, there clearly remain barriers to each technology.

Energy Management and Cross Layer Optimization for Wireless Sensor Network Powered by Heterogeneous Energy Sources

Recently, utilizing renewable energy for wireless system has attracted extensive attention. However, due to the instable energy supply and the limited battery capacity, renewable energy cannot guarantee to provide the perpetual operation for wireless sensor networks (WSN). The coexistence of renewable energy and electricity grid is expected as a promising energy supply manner to remain function for a potentially infinite lifetime. In this paper, we propose a new system model suitable for WSN, taking into account multiple energy consumptions due to sensing, transmission and reception, heterogeneous energy supplies from renewable energy, electricity grid and mixed energy, and multidimension stochastic natures due to energy harvesting profile, electricity price and channel condition. A discrete-time stochastic cross-layer optimization problem is formulated to achieve the optimal trade-off between the time-average rate utility and electricity cost subject to the data and energy queuing stability constraints. The Lyapunov drift-plus-penalty with perturbation technique and block coordinate descent method is applied to obtain a fully distributed and low-complexity cross-layer algorithm only requiring knowledge of the instantaneous system state. The explicit trade-off between the optimization objective and queue backlog is theoretically proven. Finally, the extensive simulations verify the theoretic claims.

Molten-Salt Power Towers: Newly Commercial Concentrating Solar Storage

Molten-salt storage is already commercially available for concentrating solar power (CSP) plants, allowing solar power to be produced on demand and to “backup” variable renewable sources such as wind and photovoltaics. The first CSP plants to operate commercially with molten-salt storage utilized parabolic trough concentrators, for example, the Andasol-1 plant. A new type of storage plant has now reached commercial status, with the 19.9-MWe Torresol Gemasolar power tower, featuring 15 h of molten-salt storage, having come online in Spain in May 2011. Advantages of the power tower storage system include the elimination of heat transfer oil and associated heat exchangers, a lower salt requirement, higher steam cycle efficiency, better compatibility with air cooling, improved winter performance, and simplified piping schemes. Near-term advances in molten-salt power tower technology include planned up-scaling, with SolarReserve due to begin constructing a 110-MWe plant in Nevada by August 2011. Other advances include improvements to the thermal properties of molten salts and the development of storage solutions in a single tank. With these developments at hand, CSP will continue to provide dispatchable solar power, with the capacity to provide energy storage for 100% renewable electricity grids in sun-belt countries.