Increasing renewable energy sources in island energy supply: case study Porto Santo

While the energy supply of most islands depends mainly on expensive oil derivatives’ importation, the others are linked by usually a weak electricity grid connection to the mainland. Due to high energy costs the islands are proving to be excellent test beds for the introduction of new technologies, and some islands are trying to become so-called renewable islands, to satisfy their energy demand mainly or entirely from indigenous and renewable sources, thus increasing the security of supply, and employment opportunities, without necessarily increasing the costs. Islands that have energy sources, such as hydro or geothermal energy, can easily integrate them into the power system, but those with mainly intermittent renewable energy sources are confronted with the necessity of energy storage. The most promising technologies are reversible hydro where geography allows, and storing hydrogen where it does not. The stored hydrogen can later be used for electricity production, and also for transport. This paper describes the H₂RES model for optimisation of integration of hydrogen usage with intermittent renewable energy sources on the example of an isolated island in the Madeira archipelago, Porto Santo. It shows that it is possible to significantly increase the penetration of renewable energy sources, albeit at a relatively high cost, with hydrogen storage technology. The H₂RES model, which includes reversible hydro and batteries as storage technologies, can serve as a valuable tool for island energy planning.     

A methodology for analysis of impacts of grid integration of renewable energy

Present electricity grids are predominantly thermal (coal, gas) and hydro based. Conventional power planning involves hydro-thermal scheduling and merit order dispatch. In the future, modern renewables (hydro, solar and biomass) are likely to have a significant share in the power sector. This paper presents a method to analyse the impacts of renewables in the electricity grid. A load duration curve based approach has been developed. Renewable energy sources have been treated as negative loads to obtain a modified load duration curve from which capacity savings in terms of base and peak load generation can be computed. The methodology is illustrated for solar, wind and biomass power for Tamil Nadu (a state in India). The trade-offs and interaction between renewable sources are analysed. The impacts on capacity savings by varying the wind regime have also been shown. Scenarios for 2021–22 have been constructed to illustrate the methodology proposed. This technique can be useful for power planners for an analysis of renewables in future electricity grids.     

Sustainable electricity generation fuel mix analysis using an integration of multicriteria decision-making and system dynamic approach

To achieve a national energy access target of 90% urban and 51% rural by 2035, combat climate change, and diversify the energy sector in the country, the Zambian government is planning to integrate other renewable energy resources (RESs) such as wind, solar, biomass, and geothermal into the existing hydro generation–based power system. However, to achieve such targets, it is essential for the government to identify suitable combination of the RESs (electricity generation fuel mix) that can provide the greatest sustainability benefit to the country. In this paper, a multicriteria decision-making framework based on analytic hierarchy process and system dynamics techniques is proposed to evaluate and identify the best electricity generation fuel mix for Zambia. The renewable energy generation technologies considered include wind, solar photovoltaic, biomass, and hydropower. The criteria used are categorized as technical, economic, environmental, social, and political. The proposed approach was applied to rank the electricity generation fuel mix based on nine sustainability aspects: land use, CO₂ emissions, job creation, policy promotion affordability, subsidy cost, air pollution reduction, RES electricity production, RES cumulative capacity, and RES initial capital cost. The results indicate that based on availability of RESs and sustainability aspects, in overall, the best future electricity generation mix option for Zambia is scenario with higher hydropower (40%) penetration, wind (30%), solar (20%), and lower biomass (10%) penetration in the overall electricity generation fuel mix, which is mainly due to environmental issues and availability of primary energy resources. The results further indicate that solar ranks first in most of the scenarios even after the penetration weights of RES are adjusted in the sensitivity analysis. The wind was ranked second in most of the scenarios followed by hydropower and last was biomass. These developed electricity generation fuel mix pathways would enable the country meeting the future electricity generation needs target at minimized environmental and social impacts by 2035. Therefore, this study is essential to assist in policy and decision making including planning at strategic level for sustainable energy diversification.     

储能与液流电池技术

大规模高效储能技术是解决可再生能源发电不连续、不稳定、不可控特性的重要途径,也是构建坚强智能电网的核心技术。本文对各种储能技术进行了综合分析,并对适用于大规模储能的抽水储能、压缩空气储能、钠硫电池、锂离子电池、铅酸电池和液流电池的技术特点、优劣势、发展前景进行了深入阐述;最后,对储能技术的发展思路进行了探讨,认为坚持技术开发与应用示范并重,进一步降低储能设备成本,提高其可靠性和稳定性并辅以一定的鼓励政策,是推进储能技术的产业化和实用化的重要途径。     

How the hydrogen production from RES could change energy and fuel markets: A review of recent literature

The goal that the international community has set itself is to reduce greenhouse gas (GHG) emissions in the short/medium-term, especially in Europe that committed itself to reducing GHG emissions to 80–95% below 1990 levels by 2050. Renewable energies play a fundamental role in achieving this objective. In this context, the policies of the main industrialized countries of the world are being oriented towards increasing the shares of electricity produced from renewable energy sources (RES).In recent years, the production of renewable energy has increased considerably, but given the availability of these sources, there is a mismatch between production and demand. This raises some issues as balancing the electricity grid and, in particular, the use of surplus energy, as well as the need to strengthen the electricity network.Among the various new solutions that are being evaluated, there are: the accumulation in batteries, the use of compressed air energy storage (CAES) and the production of hydrogen that appears to be the most suitable to associate with the water storage (pumped hydro). Concerning hydrogen, a recent study highlights that the efficiencies of hydrogen storage technologies are lower compared to advanced lead acid batteries on a DC-to-DC basis, but “in contrast […] the cost of hydrogen storage is competitive with batteries and could be competitive with CAES and pumped hydro in locations that are not favourable for these technologies” (Moliner et al., 2016) [1].This shows that, once the optimal efficiency rate is reached, the technologies concerning the production of hydrogen from renewable sources will be a viable and competitive solution. But, what will be the impact on the energy and fuel markets? The production of hydrogen through electrolysis will certainly have an important economic impact, especially in the transport sector, leading to the creation of a new market and a new supply chain that will change the physiognomy of the entire energy market.     

Analysis of the Cost per Kilowatt Hour to Store Electricity

This paper presents a cost analysis of grid-connected electric energy storage. Various energy storage technologies are considered in the analysis. Life-cycle cost analysis is used. The results are presented in terms of the cost added to electricity stored and discharged, in US dollar per kilowatt hour. Results are compared with wholesale and retail electricity costs and with the cost of conventional pumped hydro storage.     

Research and development aspects of pico-hydro power

Intensive explorations of different alternatives and renewable energy resources are currently being conducted worldwide. Pico-hydro power is at the forefront of these options because it is considered as the most cost-effective renewable energy option to provide electricity for rural areas, and to enable energy to be derived from extremely low head and flow streams of 1 m and 1 L/s, respectively. This review discusses the research and development aspects of pico-hydro and the factors influencing the success of the pico-hydro scheme in rural areas. These factors are also likely to increase the demand for pico in a rural energy market. This paper concurs with the view held by many researchers and experts that customs duty imposed on pico-hydro components is a major obstacle to the dissemination of renewable energy because it raises original cost by up to 40%. The future of the pico-hydro market looks prosperous because there is substantial availability of low head and flow hydroelectric sites in less developed countries. In the future, technology can play a crucial role in the lighting of houses in remote communities, with the energy source derived from domestic water supply.     

Size and power exchange optimization of a grid-connected diesel generator-photovoltaic-fuel cell hybrid energy system considering reliability,cost and renewability

In this paper, optimal size and power exchange of a grid-connected diesel generator-photovoltaic-fuel cell (diesel/PV/FC) hybrid energy system is investigated by multi-objective optimization for a community in Kerman, Iran. To optimally size hybrid system, number of system components (PV panels, diesel generators, electrolysers, FCs and hydrogen tanks) are considered as decision variables. In this paper, to optimize power exchange between the hybrid system and grid, two other decision variables are introduced: selling coefficient and purchase coefficient. Selling and purchase coefficients are defined to optimize the amount of electricity sold to the grid and the amount of electricity purchased from the grid, respectively. In order to optimally design the hybrid system, multi-objective optimization has been considered with respect to three objectives: levelized cost of energy (LCOE), loss of power supply probability (LPSP) and renewability. Based on simulation results, it can be drawn that when the hybrid system can sell/buy energy to/from the grid, (1) by decreasing non-renewable energy source usage, the value of LPSP increases, (2) by decrease of non-renewable energy usage, value of LCOE increases and (3) using FC system leads to increasing LCOE.     

Potential application of renewable energy for rural electrification in Malaysia

Energy poverty and lack of electricity in rural areas exacerbate the poverty of the developing countries. In Malaysia, 3.8% of the population lives below the poverty line and most of them are settled in rural areas. The electricity coverage in poor states is about 79% in comparison with 99.62% in Peninsular Malaysia. The renewable energy sources can be considered the best alternative to reduce the energy poverty of the rural areas where the grid extension through a difficult terrain and thick jungle is not possible or economic. In this study, the potential for applying renewable sources – solar, wind and hydropower – for rural electrification is investigated, especially in the poorest States. A comparative study on rural electrification policies, in order to have community approval, appropriate siting and financial benefits for the rural community, while considering the three categories of social, institutional and economic issues, is also examined. Finally, the Malaysian policies of rural electrification by applying renewable sources are explained. It is found that in Malaysia, with a maximum solar radiation of about 6.027 kWh/m² per day in Sabah and 5.303 kWh/m² per day in Sarawak, the potential for applying solar energy for electrification is too high. However, the potential for micro-hydropower in Sabah and Sarawak is found to be 3182 kW and 6317 kW through 18 and 22 sites, respectively.     

Feasibility of renewable energy storage using hydrogen in remote communities in Bhutan

This paper considers the technical and economic feasibility of using renewable energy with hydrogen as the energy storage medium for two remote communities in Bhutan, selected to illustrate two common scenarios presenting different challenges. The Royal Government of Bhutan has published plans to provide electricity to all households in the next 20 years, but the practical problems of extending the grid over long distances and mountainous terrain will make that target difficult and expensive to achieve. Consequently, the possibility of using natural energy and diversified generation is attractive. This paper examines the use of hydro power in one community and photovoltaics with wind power in another. Hydrogen is the proposed energy storage medium in both cases. Analysis suggests that it is technically possible to use renewable energy and hydrogen for diversified power supplies and that where, as here, the costs of grid extension are high, it may also be financially viable. Thus we argue that there is a good case for establishing a test and demonstration system near the capital Thimphu for further investigation prior to use in remote locations.     

储能技术在光伏并网发电系统中的应用分析

根据光伏并网发电系统的结构特点分析了不加储能装置的光伏并网发电系统对电网造成的不良影响,并分别从电网角度和用户角度提出了储能系统在光伏并网发电系统中的几种应用技术,最后提出了用于光伏并网发电系统的储能技术发展需求。     

National electricity planning in settings with low pre-existing grid coverage: Development of a spatial model and case study of Kenya

We develop a spatial electricity planning model to guide grid expansion in countries with low pre-existing electricity coverage. The model can be used to rapidly estimate connection costs and compare different regions and communities. Inputs that are modeled include electricity demand, costs, and geographic characteristics. The spatial nature of the model permits accurate representation of the existing electricity network and population distribution, which form the basis for future expansion decisions. The methodology and model assumptions are illustrated using country-specific data from Kenya. Results show that under most geographic conditions, extension of the national grid is less costly than off-grid options. Based on realistic penetration rates for Kenya, we estimate an average connection cost of $1900 per household, with lower-cost connection opportunities around major cities and in denser rural regions. In areas with an adequate pre-existing medium-voltage backbone, we estimate that over 30% of households could be connected for less than $1000 per connection through infilling. The penetration rate, an exogenous factor chosen by electricity planners, is found to have a large effect on household connection costs, often outweighing socio-economic and spatial factors such as inter-household distance, per-household demand, and proximity to the national grid.     

Parking the power: Strategies and physical limitations for bulk energy storage in supply–demand matching on a grid whose input power is provided by intermittent sources

It is shown that, in a sustainable energy future, energy for the electricity grid will probably be derived largely from the renewable sources of wind and solar radiation. Because both are intermittent, any infinite busbar grid supplying a metropolitan area must necessarily be buffered from these intermittencies by massive energy storage on the gigawatt-day level. It is then demonstrated that, under presently foreseeable scientific capabilities, only underground pumped hydro and advanced adiabatic compressed air energy storage appear capable of meeting anticipated technological and economic constraints. Neither has ever been constructed and tested; but even so it is predicted that underground pumped hydro ultimately will prove to be superior.     

A production-cost-simulation-based method for optimal planning of the grid interconnection between countries with rich hydro energy

Cross-border grid interconnection is a critical means to achieve wide-area share of hydro and other clean energy. Economic benefit assessment of cross-border grid interconnection projects should be carefully performed during early stage. In this paper, a method based on cost-benefit economic assessment for optimal planning of cross-border grid interconnection is proposed. An economic index for comprehensively assessing the cost of a transmission project and its resulting benefits of more usage of hydro energy is designed first. A chronological production cost simulation model considering hydro energy spillage due to transmission congestion and thermal operational limitation is then proposed to calculate the economic index. A case study is performed using the proposed method to determine the optimal capacity of a potential transmission link between Brazil and Argentina, which have rich and complementary hydro energy resources.     

Energy balance analysis of wind-based pumped hydro storage systems in remote island electrical networks

The introduction of pumped hydro storage (PHS) systems in isolated electrical grids, such as those found in island regions, appears to be a promising solution that is able to face both the high electricity production cost and the continuously increasing power demand encountered in these areas. In this context, the current work presents a methodology for the sizing of PHS systems that exploit the excess wind energy amounts produced by local wind farms, otherwise rejected due to imposed electrical grid limitations. The methodology is accordingly applied to the Greek island of Lesbos. Initially, a calculation of the wind power penetration ability to the local grid is carried out and the corresponding curtailments of existing and future wind farms are determined. An integrated computational algorithm is then presented which simulates the operation of the system during an entire year and gives in detail the hourly operational status as well as the various energy losses of the system main components. Based on the application results obtained, the ability of the wind energy to remarkably contribute to the electrification of the remote islands becomes evident.     

Model‐based approach for planning renewable energy transition in a resource‐constrained electricity system—A case study from India

Globally, electricity systems are going through transitions. The contributions from renewable energy‐based power generation, both in installed capacity and electricity generation, are moving from marginal to the mainstream. India is not an exception; it is aggressively pursuing this transition by fixing steep targets for renewable capacity additions. While the cost of renewable energy sources is expected to fast reach grid parity, the policy interventions play a critical role in ramping up the efforts to support the proposed investments in renewable capacity and renewable electricity generation. In this respect, this research attempts to analyze the effectiveness of renewable energy policies such as Renewable Purchase Obligation (RPO) and Renewable Energy Certificate mechanisms in tapping the renewable energy potential in India. We propose a mixed‐integer linear programming model‐based approach to evaluate the effectiveness of the above interventions in the Indian context. The model is developed and validated as a low carbon electricity planning tool to optimally meet the dynamic electricity demand and RPO targets as well as to manage the unmet total electricity demand and RPO targets. The Karnataka state electricity system (a state in south India) is chosen as a case study. The results suggest that Karnataka Electricity System is moving toward a sustainable renewable energy future even without any support from nonsolar Renewable Energy Certificate policy. However, policy interventions are critical for optimally utilizing the solar generation capacity.     

Decision-making between a grid extension and a rural renewable off-grid system with hydrogen generation

Most populations in rural Africa have no access to electricity, in this study, a comparative analysis between grid extension and the implementation of renewable off-grid hybrid power system is carried out. The objective of the study is to determine the best feasible option. Napier, a farming village in the Western Cape province of South Africa was selected as the site for the comparative analysis and HOMER PRO software was used to develop an optimal system using the wind and solar resources of the selected site. The load profile considered in the analysis includes lighting, cooking and hot water demands. The best feasible option is determined based on the Net Present Cost of each feasible scenario. Sensitivity analysis on the current cost and the projected cost of hydrogen storage w conducted to observe the impact of the cost of hydrogen storage on the renewable off-grid system cost of energy.     

Bulk energy storage potential in the USA, current developments and future prospects

Stored energy can provide electricity during periods of high demand, as currently demonstrated with bulk storage systems such as pumped hydro storage (PHS), which accounts for only 2.5% of the current installed base load in the USA. Sites for future developments have become less available, and environmental siting issues, as well as high costs have stopped further prospects. This paper looks at the potential beyond PHS, with bulk storage systems such as compressed air energy storage (CAES) flow-batteries and 1 MW flywheel systems that can provide system stability/support at the grid, substations and distributed level. Current developments in bulk energy storage will be reviewed as well as some storage project developments incorporating wind energy and the impact on base-loaded coal and natural gas fired GT combined cycle plants. The large potential and the economic benefits for energy storage in the US will be examined.     

Evaluation of the impact of access to electricity: A comparative analysis of South Africa,China, India and Brazil

Most developing countries include rural electrification programs in their efforts to improve social conditions. There are, however, several obstacles to the evaluation of such programs and therefore of their social, economic, environmental and energy impacts on the target population, particularly on impoverished communities located in remote areas. Evaluation of the efficacy of public policies aimed at rural electrification in South Africa, China, India and Brazil enables such actions to be quantified and re-considered so as to bolster the sustainability of their planning and implementation and also so as to enable comprehension of the significance of access to electricity in relation to other aspects of the drive to improve living standards. The provision of electric energy amounts to more than access to a public service and should be considered an essential right, in a context of social equity and justice, which permits social integration and the access to other equally essential services.     

The application potential of hydro power

Water is the only renewable energy source that has been exploited by man on a large scale and that has a well-developed technological base to support its continued exploitation. At present about 23% of the world's electricity supply is from hydro plants. Since all the new energy sources under development are mainly exploitable through electricity generation, it seems likely that the world will have to move increasingly to an electricity-based energy regime.To make an effective contribution to new energy supply patterns. hydro power could be exploited by the development of small generating units to meet local community needs, by the use of pumped storage to optimize operation of other energy sources, and by the development of the many remaining sites in remote areas and third world countries with high power potential including perhaps glacier-derived power. This last development could spawn a new energy trade which would require a transfer of manufacturing resources to the countries with hydro power.Political decisions and economic considerations will influence these developments. An effective electric power trade between countries requires an acceptable international code of practice. Ultimately the speed of development of these resources will depend upon the cost of energy delivered to the consumer compared with the cost of other energy sources closer to the load centre.