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Facing the Operational Challenges of Mini-grids

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Overview

The following article details the proceedings of the Micro Perspectives for Decentralized Energy Supply Conference - 2013.


Analyzing Drivers and Barriers for Renewable Energy Integration to Small Islands Power Generation – Tapping a Huge Market Potential

Introduction and Motivation

Findings on how socio-economic and natural factors have influenced the introduction of renewable energies to island electricity grids: Financial, market, policy and natural factors are studied in order to analyze which of them could be drivers or barriers for successful technology specific renewable energy implementation to islands. The existence of a regulatory framework, using e.g. a feed-in tariff, is the most important for the large-scale implementation of young renewable energy technologies as PV and wind energy. Furthermore a spatial Geographic Information System analysis of global islands is carried out to describe area, location and population of the islands.[1]


Methodology

There is a special remark on the market potential of global islands as well as on the socio-economic factors. Until now, island grids are mostly supplied by diesel generators which results in both high CO2 emissions and high electricity tariffs. The renewable energy resources on islands are very good even in some pacific islands geothermal energy could be used.


Indonesia and the Philippines have the densest population, while on less than 10,000 islands live less than 10,000 inhabitants.

The analysis took into consideration:

  • Independent and semi-autonomous island states
  • No base load power plants
  • No grid connection
  • Highest population < 3 Mio. Inhabitants
  • Max. 2 GW installed capacity


Considering the socio/economic factors: GDP, competition, ownership (private or not), regulatory framework, energy vision), analyses were carried out for the specific scenarios (only PV, only hydro, only wind, all RE, only new RE) were developed and analyzed.


Results

  • Each scenario has (at least) one very good determinant
  • There is a big spread of variation
  • Feed-in tariff programs are highly recommended
  • 87,000 islands with 11,300 inhabitants were examined
  • Hydro is not affected so much by socio/economic factors


A Community Managed Micro-Hydro Connected Mini-grid in Nepal

Introduction

Despite Nepal having a high hydropower potential and enough Renewable Energy sources, there are still many people in rural areas that do not have access to electricity. This presentation focused on Micro-hydropower systems (MH) and on the innovative concept of a community managed micro hydro system connected as mini-grid, which was established as a pilot project in Baglung, Nepal. The current technology allows to run parallel six Micro hydropower plants (MHP). A cooperative has been created for the sustainable management of the system.[2]


Motivation

The investigated region is located between China and India. The potential of hydro-power in this region comes up to 83MW, of which only 1% is used. Nowadays, there is still a high dependency on oil and other traditional energy sources. 56% of the population has access to electrification. The Ministry of Energy responsible for the grid extension does not have rural electrification as a priority. Different organizations such as AEPC (Alternative Energy Promotion Centre) have provided support to off-grid-systems.


10% of the population was connected to the grid thanks to the RERL-Program (Renewable Energy for Rural Livelihood) that was founded in 1996, covering 31 out of 75 districts. The parsed households are far away from the grid or neighborhood.

Hydropower plants with less than 100 kW are categorized as micro hydro and deploy in regions with available water resources and suitable terrain, accounting with an installed capacity of 22MW.


Challenges

Main Problem: The energy supply was not reliable during supply period. Lighting is, in many cases, the only use of electricity. A threat to the micro hydro plants is the expansion of the grid, which implies a waste of resources as the MHP are likely to be abandoned as soon as the grid reaches the region.


Results

An interconnection between the mini-grid and the national grid was established, by offering a sizable load to the NEA (Nepal Electricity Authority). The surplus electricity of one/more MHP is balanced with the deficit electricity of other MHP. In order to assure system sustainability, the revenues of the MHPs are increased from the high use/sale of electricity.


In the Baglung Mini-Grid Project, 6 MHP are connected to each other, with a total capacity of 107kW providing services to 1200 households. The management of the plants is community based, while MHP functional groups out of community organizations are present, making the project financially viable. A microprocessor based control system synchronizes various MHPs and manages the connection to the national grid.


The use of the MHP brought a sense of unity to the community and a high sense of confidence to own and manage bigger projects by having not only technical and social advantages, but also economical.


Overcoming Grid Instability in Micro-grids by Using a Flywheel Energy Storage System While Operating a PV/diesel Hybrid System

Introduction and Motivation

The so called Marble bar hybrid system is installed in a remote Australian area. Australia has a regulatory framework which obligates the utilities to provide the same quality of power with no exception between urban or remote areas.

The need of stable power was a huge challenge. Thanks to a lot of space available, a 300 kW PV system with single axis tracker was installed and combined with 4 x 320 kW diesel generators and a 1 x 500 kW PowerStoreTM grid stabilization device (flywheel energy storage).[3]


Challenges of the System

  • The system is used on a daily basis providing utility grade power 24/7
  • The combination of PV and Diesel requires limiting the power of the PV system.
  • The surplus of the PV plant has to be limited in order to operate the diesel generators in safe conditions. Not limiting the load would potentially drive the generators as motors.
  • Thermal plants in hybrid mode have lower fuel efficiency if renewable fluctuations are imposed on the generators
  • Necessity of back-up for the case of cloud-covering (no power from PV).
  • During operation, frequency and voltage are measured in order to assure stability through the PowerStoreTM. The flywheel storage system can switch in 5 ms from 100% energy absorption to 100% energy rejection, balancing any frequency fluctuations.


Results

  • PV-systems are not a stable source of power, even in sunny days. There have been cases, where there was no cloud coverage at all, but the PV-power was not maximum due to air-particles that cannot be seen by humans.
  • The nature of the generators demands their operation within 15-30% of their total power at least, which implies that the PV-system can never be used to 100% capacity, if the load is not big enough. A hybrid system therefore always has to be designed, not only looking at the renewables but also at the thermal power plant criteria.
  • The frequency is constantly changing; it can fluctuate around off-grid systems without stabilization aroundaround 50 +/-2.0 Hz. With a PowerStoreTM this variation can be kept within acceptable limits of +/-0.1 Hz.


Further Information


References

  1. Presentation: By Enrico Howe - Reiner Lemoine Institut
  2. Presentation: By Bhupendra Shakya - Renewable Energy for Rural Livelihood Programme AEPC
  3. Presentation: By Martin Baart - ABB, The third presentation was cancelled and Mr. Martin Baart from ABB held a spontaneous presentation.