Optimisation of hybrid off-grid energy systems by linear programming
Fabian Huneke
0
Johannes Henkel
0
Jairo Alberto Benavides Gonzlez
1
Georg Erdmann
0
0
Department of Energy Systems, Technische Universitt Berlin
, Einsteinufer 25 (TA8),
Berlin
, 10587,
Germany
1
Equitel Organization, Av. Ciudad de Cali No. 11-22, Bogot,
Colombia
Background: In this study, a general model of a hybrid off-grid energy system is developed, which can be adjusted to reflect real conditions in order to achieve economical and ecological optimisation of off-grid energy systems. Methods: Using linear programming methods in the General Algebraic Modeling System (GAMS) environment, the optimal configuration of the electrical power supply system following characteristic restrictions as well as hourly weather and demand data is found. From this model, the optimal mix of solar- and wind-based power generators combined with storage devices and a diesel generator set is formed. Results: The operation of this model was tested in two real off-grid energy systems, a cluster of villages in India and Titumate in Colombia. Both optimisation processes resulted in hybrid energy systems, utilising photovoltaics (PV), lead-acid batteries and a diesel generator as a load-balancing facility. Conclusions: With respect to small off-grid energy systems, it was found that renewable energy in combination with electrical storage devices help to reduce the cost of energy compared to stand-alone diesel generator sets. The optimal solutions strongly depend on the particular load demand curve. As both PV and wind energy benefit from energy storage, the costs of the battery can be shared and the two technologies complement each other. Finally, although the optimised capacity of the diesel generator remains nearly constant, its contribution to the total power generation is being substituted by renewable energy sources, which serve as fuel-saving technologies.
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Background
One major issue associated with the challenge of the
worlds increasing demand for energy is the electrification
for approximately two billion people [1] in developing
countries that do not currently have access to electricity.
The worlds population is expected to reach nine billion
people in 2050. Most of this expected population growth
will take place in developing countries and emerging
nations [1]. Additionally, policies in emerging nations are
concerned with increasing the supply of energy, as energy
consumption per capita has become one of the major
indicators for the developmental progress of a country. These
two factors mainly determine the growth in energy
demand.
Many of the places with limited or no connection to
the national grid are rural communities. The question is
how to provide these off-grid energy systems. A
common solution for off-grid power supply in small and
medium-sized energy systems is a fuel generator set [2];
however, the following current developments have
sought to improve the competitiveness and desirability
of alternative off-grid energy systems:
Steeply decreasing production costs of renewable
energy technologies like solar, wind and biomass
caused a boom in the respective technologies in
developed countries,
Expanding research in electric storage devices
sparked by the plans of several countries to use
electric vehicles in the future,
Increasing environmental concerns and awareness
of climate change provoked by CO2 emissions
produced by the combustion of fossil fuels and
Increasing operation costs for fuel generator sets
due to rising oil prices.
The following section provides a review of literature on
the topic, leading to the presentation of the research
questions. In [1], integrated energy farms, which aim to bring
power and food to rural communities, are discussed. The
supply of electricity is integrated in an independent and
decentralised energy supply concept under consideration
of sustainable development of remote areas by
empowering the residents to take care of their own needs. The
study of Nfah et al. [3] is concerned with the optimisation
of off-grid energy systems at rural communities in
Cameroon focussing on hydro and solar resources. Another
more general steady-state modelling approach is done in
[4] under consideration of hybrid energy systems
consisting of a micro-hydro, a biogas, a biomass, a back-up diesel
generator and a photovoltaic (PV) array. The optimal
dispatch strategy, as well as the optimal sizing, especially of
the PV array is calculated simultaneously by linear
programming. The performance of another type of hybrid
energy system is investigated in [5]. Here, the interaction
between an existing wind/diesel energy system and a
leadacid battery bank is examined. The optimal sizing of such
a wind-diesel hybrid energy system is discussed in [6]
under consideration of the minimum long-term electricity
production cost. In [7], the life cycle costs of stand-alone
diesel generator sets and PV battery systems are
compared. The benefit from linking different solar home
systems by installing an off-grid (...truncated)