Role of Internal Combustion Generators (ICG) in Standalone Hybrid Energy Systems (HES)

Recently HES were introduced as an alternative to ICG systems in order to reduce the fuel consumption and life cycle cost. At the same time Hybrid Renewable Energy Systems (HRES) which consists of renewable energy sources such as wind, Solar PV (SPV) and energy storage such as battery bank, Hydrogen Storage where system does not include ICG were also discussed. This makes it important to investigate role of ICG as a dispatchable energy source in standalone systems.

When it comes to as ICG it is capable of absorbing the seasonal variation of renewable energy sources. More importantly, when compared to battery banks and other energy storage techniques ICG can be used to absorb long-term fluctuations of renewable energy sources. Therefore, ICG capacity is plays a major role when it comes to lifecycle cost and power supply reliability. With the increase of power supply reliability ICG plays a dominant role. Hence, combining renewable energy sources to ICG systems are more economical compared to HRESs.     

 

Design and controlling of multiple boiler systems

With increasing energy demands optimal design and operation of multiple boiler system (Fig. 1) has become vital. When it comes to initial designing of multiple boiler systems it is important to figure out the best combination of boilers considering capacity, fuel type etc and dispatch of boilers when catering time varying steam demand. It is a difficult process to come up with optimum system configuration and operation strategy as it involved intricate objective functions. At the same time modeling should have to b coupled with simulation in order to come up with certain objective functions.

Due to these reasons design and control has not taken into consideration in most of the publications though controlling depends upon initial system design. During last few months our research team in University of Moratuwa, studied the capability of using a Fuzzy-Evolutionary hybrid algorithm to come up with this problem. A fuzzy controller was developed using fuzzy Mamdani rules. Basic energy flow and life cycle cash flow was modeled which can be used to optimize both system configuration and operation strategy. Currently group is working on exergy flow through the basic components.

Hybrid Renewable Energy System Designing and Optimization

Standalone Hybrid Energy Systems (HES) have become an interesting area of study due to its versatile applicability in producing electricity where extending existing electricity grid is not viable and expensive. At the same time HESs produce less Green House Gasses (GHG), consume lesser amount of fuel and cost effective compared to Internal Combustion Generator (ICG) s. Due to the above mentioned advantages a number of researches has been focused on different configurations of HES systems.
Even though the prime concern of HES at the late nineties were rural electrification, recently plenty of other applications were also been considered such as desert agriculture, tourism industry, desalination plant operation, telecommunication etc. At the same time plenty of work being focuses on converting existing centralized ICG systems into HES through methods like decentralized energy production which reduces both cost and pollutant emission. Grid connected HES is also an emerging area, which reduces large amount of Wasted Renewable Energy produced and system over sizing. Present plenty of work is taking place in order to expand the application of HES, which makes it important carry out in depth analyze of HESs.

Importance of Hybrid Energy Systems

Hybrid Energy system is a combination of energy sources of different characteristics and an energy storage medium. When it comes to stand-alone applications depending on hybrid energy system is a challenging process due to number of reasons such as determining the best combination, which reduces the initial capital investment, maintaining power supply reliability, reducing the maintenance of system components etc.

Combination of energy sources having different characteristics reduces the impact of time varying energy potential of renewable energy sources. Simply Solar PV (SPV) energy is available in the daytime but when it comes to night, you need to fine some other alternative or store some SPV energy during daytime. When it comes to wind energy, it is also having similar qualities but generally with a much chaotic variation. Time varying nature of the renewable energy potential makes it essential to incorporate energy storage and dispatchable energy sources.

 Fig 1: Schematic diagram of a stand alone hybrid energy system

Moving from stand-alone to grid connected

With time, most of the stand-alone systems need to be adjusted to increasing load demand and grid integration. The time taken for this will depend on the development of the energy infrastructure (especially in rural electrification projects), expansion of the main grid etc. Selecting optimum system configuration considering a later expansion or grid integration is a difficult task where more research work needs to be focused on.

At present, mainly there are two types of grid connected energy systems.

Category 1: Main intention of the grid connected energy system is to supply the local demand and additional energy produced will be sent to the existing main grid.

Category 2: Main intention of the grid connected energy system is power generation for the grid and small fraction of it is taken for the local demand.

Fig.2 Grid connected energy system at Ambewela, Sri Lanka

It is prudent that existing methods cannot be used with advanced technologies such as smart metering where factors such as hourly Cost Of Energy (COE), hourly variation of the local demand, selling price of energy unit etc needs to be considered when selecting the operation strategy. Further, this delineate the importance of energy storage mechanism which can be used to store energy either the energy production is high or the COE of the grid is low so that it can be used later when the COE of the grid is high.

Bibliography:   

[1] D. P. Kaundinya, P. Balachandra, and N. Ravindranath, “Grid-connected versus stand-alone energy systems for decentralized power—A review of literature,” Renewable and Sustainable Energy Reviews, vol. 13, pp. 2041-2050, Apr. 2010.

[2] J. L. Bernal-Agustin and R. Dufo-Lopez, “Hourly energy management for grid-connected wind-hydrogen systems,” International Journal of Hydrogen Energy, vol. 33, no. 22, pp. 6401-6413, Nov. 2008.

Modeling of energy components

Modeling of HESs mainly comprised of energy flow modeling and life-cycle cost modeling. Power supply reliability and pollutant emitted has been also considered as objectives to be modeled specially with the introduction of multi objective optimization.

Energy flow modeling
Among those components energy flow modeling becomes vital as its directly linked with system sizing ultimately combined with system life-cycle cost which is the main factor considered when designing HESs. General Energy Flow of a HES comprised of three components

1. Renewable energy component (wind, solar, pico/micro hydro etc)
2. Dispatchable energy component (ICG modeling)
3. Energy storage mechanism  (battery bank/fuel cell modeling)