Deployment of Hybrid Renewable Energy Systems in Minigrids

• Verlag: Asian Development Bank
• Jahr: 2017
• ISBN:
  9789292579807
• Thema: Technology & Engineering
• Thema: Renewable Power Resources

Despite significant economic growth in Asia in recent decades, millions of people in rural Asia still lack access to electricity. In response, the Asian Development Bank is working to foster universal access to energy by developing small hybrid renewable energy systems in rural Asian areas. This publication highlights the experiences of ADB's pilot projects to achieve access to electricity and energy efficiency in five developing countries in Asia. It provides technical guidance and recommendations for the effective deployment of similar systems in minigrids in remote rural locations and small isolated islands.

1 INTRODUCTION

1.1 Background and Context

1. Lack of access to electricity is one of the major barriers to human development, as we need it to power lighting, refrigeration, and other basic home appliances. Economic growth cannot be conceived without access to electricity. The percentage of population with access to electricity is undeniably one of the clearest indicators of the level of development of a country. According to the World Energy Outlook 2016 [1] by the International Energy Agency, an estimated 1.2 billion people, which represents more than 16% of the world population, do not have access to electricity. Most of them are living in countries of Sub-Saharan Africa and developing Asia, mainly in rural or remote areas. Moreover, most rural communities with access to electricity have it at the expense of huge funds spent on subsidies for fossil fuels, which hampers the deployment of more sustainable energy sources. There are several institutions and initiatives worldwide working toward universal energy access with a special focus on developing renewable energy (RE) and energy efficiency. Among them, the United Nations’ initiative Sustainable Energy for All [2], to which 102 countries have signed up as partners, seeks to achieve universal electricity access by 2030. The Asian Development Bank (ADB) is one of the leading regional development organizations that play a pivotal role in fighting poverty and fostering universal energy access.

2. There are several technical approaches to supply electricity to remote or isolated areas [3]. The first approach is to expand the national electricity grid, or connect to a continental grid in the case of island states. In many cases, the high cost of expanding the distribution power lines usually leads to economically unfeasible projects. The challenging geography in certain remote locations highly impacts distribution line expansion costs. Islands and areas with difficult logistics necessitate extra time and resources to deploy distribution power lines because, in the case of the islands, this usually involves submarine cables. Likewise, the magnitude of the demand determines the cost per kilowatt-hour (kWh) of grid expansion. A certain minimum level of consumed energy is necessary for project viability. Remote areas and small isolated islands have usually a small energy demand per connection, so the national authorities and/or utilities are less inclined to connect these communities to the electricity network. Moreover, security of supply and power quality issues are major concerns that utilities usually face in developing countries. Consumers may only have power during limited hours per day, and outages are quite common. Electricity network expansion usually comes with a demand load growth. However, if there is no resource capacity adequacy, connecting new consumers to the electricity network will just exacerbate the situation and decrease the quality of the electricity supply service.

3. The International Energy Agency estimates a threshold of about 100 kWh of electricity per person per year as a reasonable level of energy access. Solar lanterns, as well as stand-alone solar home systems, are crucial elements to provide energy for basic lighting, cellular phone charging and, in some cases, television. However, other more energy-intensive demands, such as workshop tools, refrigerators, rice mills, or irrigation pumps, are usually associated to higher economic and social developments. Minigrids are certainly an alternative that can provide such progress.

4. The second approach relates to installation of electricity home systems. Such energy systems are becoming more and more popular. They usually provide energy to an individual household or a small number of households, and are a technically robust solution, relatively inexpensive, simple to maintain, and easily accessible. The dispersed and distributed nature of remote settlements is a perfect setting for electricity home systems, particularly with RE sources, which is usually competitive in the remote areas. In most cases, remote and isolated locations can benefit from a single or a combination of solar photovoltaic (PV) systems, solar home systems, mini- or micro-hydropower plants, or even wind home systems. In these cases, the generation sources are often deployed close to the demand, avoiding distribution expansion costs.

5. The third approach is based on electricity minigrids or microgrids that can supply electricity at the local level through village-wide electricity distribution networks. Minigrids—with a 100% RE mix or hybridized with other technologies (i.e., diesel generators)—are fast to deploy, easy to scale up to meet future energy demand, and could be connected to a central grid when it becomes reachable.

6. Minigrids play an essential role in fostering rural electrification. They may use fossil fuel-based generation sources (in most cases diesel generators). Alternatively, they can also integrate indigenous RE sources. Since diesel generation sets usually require reduced up-front costs, they are still very popular. However, some RE technologies are already competitive in terms of levelized costs of energy (LCOE).¹

7. A minigrid can be supplied by different types of energy resources and power plants. However, in this report, we will concentrate on the minigrids that are supplied by hybrid RE systems with solar PV and/or wind sources backed with a battery electric storage system (BESS). Such hybrid minigrids allow generation sources to meet demand by synchronizing RE technologies with existing diesel generators. The bidirectional nature of the power flow on the BESS can charge an electrical battery storage system whenever excess energy is available from a renewable source or using a diesel generator. It can act as a direct current–alternating current (DC–AC) converter whenever energy is required from the battery. The inverter can also supply “peak shaving” services [4], as part of a control strategy, at the time the demand load exceeds the supply capacity of the diesel generator.

8. A hybrid minigrid usually provides an energy supply service with high quality standards, which can be even better than the service provided to customers connected to a central grid in some regions. Such minigrids supply enough power to meet domestic needs (lighting, refrigeration, communication, and water supply), public services (health facilities and schools) requirements, and to enable development of small businesses and services in local communities.

9. Due to their modularity, hybrid minigrids show an important advantage: generation adapts to demand growth since generation technologies can be easily scaled up.

10. Therefore, this kind of energy solution is a credible alternative to the existing diesel-powered minigrids. There is a multitude of diesel-based isolated grids with the total capacity measured in gigawatts that could be retrofitted with RE technologies. This is particularly the case of many remote rural villages and isolated islands in South Asia.

11. In a minigrid, electricity is distributed at a local level without requiring access to the main network. The minigrid is normally managed by an operator that may have different legal forms to provide energy services to end users. Usually, the minigrid will operate under AC low voltage, although DC is also feasible, especially for very small minigrids. Minigrids have installed capacity ranging from 10 kilowatts (kW) to 1 megawatt, even though larger systems exist.

12. On the other hand, sharing limited energy resources among customers in a minigrid or microgrid requires a tariff structure that ensures the sustainability of the system, enforcing a rational use of the available resources.

1.2 Scope and General Objective

13. Many technical, financial, and socioeconomic factors come into play in the design of a hybrid RE minigrid. Efforts to adapt the design to the natural, present, and expected socioeconomic conditions of each location, in contrast to trying to standardize system designs, will pay off in terms of efficiency, user satisfaction, and sustainability of the system.

14. This publication aims to present state-of-the-art guidelines and recommendations for deployment of solar PV–wind–diesel hybrid RE systems with a battery energy storage system in minigrids, and to provide some insights on technical and implementation aspects of such systems.

15. The topics covered by the guidelines range from data collection to operation and maintenance (O&M) issues with a special focus on technical design aspects. A couple of illustrative pilot projects are also described in this report.

2 SUSTAINABLE HYBRID RENEWABLE ENERGY PROJECT DEPLOYMENT

16. A series of implementation stages are required for the successful deployment of a hybrid RE minigrid project. They are summarized in .

Figure 1.2-1: Steps for the Deployment of Minigrid Projects

Source: Jose Antonio Aguado (Effergy Energia).

17. These implementation stages include the following:

(i) Data collection. To come up with a design that optimally adapts to particular conditions of each location, it is fundamental that present and future electricity demand, natural resources, existing infrastructure, and socioeconomic conditions are properly assessed.

(ii) Business models analysis. The financial sustainability of a minigrid project depends on the suitability of a business model chosen for the project. Different public or private agents can assume the different responsibilities in the deployment and O&M of a minigrid. The specific features of each location will determine the most sustainable model. Tariffs and subsidies need to be adequately adapted to the economic conditions to achieve a balance between affordability for customers and being able to cover O&M costs.

(iii) Technical design. The technical design process includes determining the optimal mix of generation and storage technologies, the best location for components, control architecture, and distribution infrastructure. This stage needs to be based on optimization studies using contrasted data for each specific project, as the best design is dependent on the particular conditions of each place (demand profile, natural resources, etc.).

(iv) Capacity building and training. Training electricity users and local staff in at least minor routine maintenance tasks is important for the proper functioning and maintenance of a minigrid, and should be carried out before and during the implementation of the minigrid project.

(v) Operation, maintenance, and management. Many minigrids fail prematurely after only a few years due to lack of proper maintenance. The different components of the minigrid should be inspected regularly, and maintenance planning should be agreed between different agents involved in the project.

(vi) Monitoring and project evaluation. For the sustainability of the project, it is crucial to monitor key performance indexes. Project evaluation will allow the project team to benchmark the system and provide actions to improve the project performance.

18. Lessons learned from previous projects point that, beyond technology barriers, many failures come from a lack of clear standards to operate and maintain the systems. Poor estimations of electric demand growth, incorrect understanding of customer behaviors, poor design of the tariff structure, and the lack of well-defined business models are the main reasons for minigrid failures.

3 DATA COLLECTION IN MINIGRIDS

19. Different minigrids will have different technical and socioeconomic needs, as well as different resources to supply them. Collecting enough reliable data is essential for a correct design. Failing to collect reliable data on the present and future needs, natural conditions and resources, and socioeconomic situation of the community, in which a minigrid is to be deployed, will most likely result in unsatisfactory and suboptimal designs.

3.1 Electric Demand Assessment

20. Demand assessment and load forecast in the planning stage is critical in optimizing the design of a hybrid minigrid. Oversizing the generation and/or storage capacity will result in poor cost-effectiveness of the proposed minigrid solution, while undersizing will result in inability to supply all demands and in customer dissatisfaction.

21. For a correct design of a hybrid RE minigrid, the following demand data should be collected:

(i) Average daily energy demand (in kilowatt-hour). The average amount of energy that is consumed in a day gives an idea of the necessary generation and storage capacity, but it is not enough by itself for a proper design.

(ii) Annual peak power (in kilowatt). The maximum expected level of power consumption needs to be quantified, as it sets the minimum generation capacity required to serve all demand.

(iii) Daily load profiles. This data corresponds to the hourly power consumption over 1 day in a minigrid. To Figure out the energy sources installation and to analyze demand-side management (DSM) measures, it is of great importance to know at what hours of the day high and low demand periods take place.

(iv) Seasonal variations. Winter and summer electricity demand profiles can be quite different in some places due to the use of air conditioners and radiators, difference in ...