**Optimal Design of an Hybrid Wind-Diesel System with Compressed Air Energy Storage for Canadian Remote Areas**

Younes Rafic1, Basbous Tammam2 and Ilinca Adrian3 *1Lebanese University, Faculty of Engineering, Beirut, 2LREE, University of Quebec in Chicoutimi, Chicoutimi, 3LREE, Quebec University in Rimouski, Rimouski, 1Lebanon 2,3Canada* 

#### **1. Introduction**

#### **1.1 Context**

268 Modeling and Optimization of Renewable Energy Systems

[18] M. Wilk, M. Inger, J. Kruk, A. Gołębiowski, R. Jancewicz, B. Szczepaniak, *Przem. Chem.,*

[8] M. Wilk, J. Nieścioruk, M. Inger, E. Rój, *Sprawozdanie INS*, nr 3009, Puławy, 2005. [9] M. Wilk, J. Nieścioruk, M. Inger, E. Rój, *Sprawozdanie INS*, nr 3190, Puławy, 2007.

[10] *N2O abatement project at nitric acid plant of ZAT, Poland*, nr 0091, 2006. [11] J. Nieścioruk, M. Wilk, E. Rój, *Sprawozdanie INS*, nr 2997, Puławy, 2005. [12] J. Nieścioruk, M. Wilk, E. Rój, *Sprawozdanie INS*, nr 3000, Puławy, 2005. [13] M. Wilk, M. Inger, J. Nieścioruk, *Sprawozdanie INS*, nr 3008, Puławy, 2006. [14] J. Nieścioruk, E. Rój, M. Wilk, *Sprawozdanie INS*, nr 3178, Puławy, 2007. [15] J. Nieścioruk, M. Wilk, M. Inger, *Sprawozdanie INS*, nr 3276, Puławy, 2008. [16] J. Nieścioruk, M. Wilk, E. Rój, *Sprawozdanie INS*, nr 3275, Puławy, 2008. [17] *N2O emissions reduction project at Zakłady Azotowe Anwil SA,* 2006.

[7] M. Wilk, J. Nieścioruk, *Projekt INS*, Puławy, 2003.

2009, t. 88, 6, 730.

Most of the remote and isolated communities or technical installations (communication relays, meteorological systems, tourist facilities, farms, etc.) which are not connected to national electric distribution grids rely on Diesel engines to generate electricity [1]. Dieselgenerated electricity is more expensive in itself than large electric production plants (gas, hydro, nuclear, wind) and, on top of that, should be added the transport and environmental cost associated with this type of energy.

In Canada, approximately 200,000 people live in more than 300 remote communities (Yukon, TNO, Nunavut, islands) and are using Diesel-generated electricity, responsible for the emission of 1.2 million tons of greenhouse gases (GHG) annually [2]. In Quebec province, there are over 14,000 subscribers distributed in about forty communities not connected to the main grid. Each community constitutes an autonomous network that uses Diesel generators.

In Quebec, the total production of Diesel power generating units is approximately 300 GWh per year. In the mean time, the exploitation of the Diesel generators is extremely expensive due to the oil price increase and transportation costs. Indeed, as the fuel should be delivered to remote locations, some of them reachable only during summer periods by barge, the cost of electricity produced by Diesel generators reached in 2007 more than 50 cent/kWh in some communities, while the price for selling the electricity is established, as in the rest of Quebec, at approximately 6 cent/kWh [3].

The deficit is spread among all Quebec population as the total consumption of the autonomous grids is far from being negligible. In 2004, the autonomous networks represented 144 MW of installed power, and the consumption was established at 300 GWh. Hydro-Quebec, the provincial utility, estimated at approximately 133 millions CAD\$ the annual loss, resulting from the difference between the Diesel electricity production cost and the uniform selling price of electricity [3].

Optimal Design of an Hybrid Wind-Diesel System with

Fig. 1. Wind -Diesel system with dump load.

Compressed Air Energy Storage for Canadian Remote Areas 271

Fig. 2. Variation of wind and diesel power with wind speed for a high-penetration WDS [16].

Moreover, the electricity production by the Diesel is ineffective, presents significant environmental risks (spilling), contaminates the local air and largely contributes to GHG emission. In all, we estimate at 140,000 tons annual GHG emission resulting from the use of Diesel generators for the subscribers of the autonomous networks in Quebec. This is equivalent to GHG emitted by 35,000 cars during one year.

The Diesel power generating units, while requiring relatively little investment, are generally expensive to exploit and maintain, particularly when are functioning regularly at partial load [4]. The use of Diesel power generators under weak operating factors accelerates wear increases fuel consumption [5]. Therefore, the use of hybrid systems, which combine renewable sources and Diesel generators, allows reducing the total Diesel consumption, improving the operation cost and environmental benefits.

#### **1.2 Wind-Diesel systems**

Among all renewable energies, the wind energy experiences the fastest growing rate, at more than 30% annually for the last 5 years [7,8]. Presently, wind energy offers cost effective solutions for isolated grids when coupled with Diesel generators. The "Wind-Diesel hybrid system" (WDS) represent a technique of generation of electrical energy by using in parallel one or several wind turbines with one or several Diesel groups. This approach is at present used in Nordic communities in Yukon [9], Nunavut [10] and in Alaska [11].

The "penetration rate" is used in reference to the rated capacity of the installed wind turbines compared to the maximum and minimum loads. A strict definition of a "low-penetration" system is one when the maximum rated capacity of the wind component of the system does not exceed the minimum load of the community. In practical terms however, a lowpenetration system is one where the wind turbines are sized so as not to interfere with the Diesel generators' ability to set the voltage and frequency on the grid. In effect, the windgenerated electricity is "seen" by the Diesel plant as a negative load to the overall system. It is important to note however that because such a system needs to be designed for the peak capacity of the wind generator it will typically operate with an average annual output of 20- 35% of its rated power, such that while low-penetration systems will have noticeable fuel and emissions savings they will be fairly minor [12,2]. In many cases it is likely that similar savings could be achieved through energy efficiency upgrades for similar capital costs.

A "high-penetration" system without storage [13], as illustrated in Figure 1, is one where the output from the wind generators frequently exceeds the maximum load for extended periods of time (10 min to several hours), such that the Diesel generators can be shut off completely when there is significant wind. The variation of wind and Diesel-generated power according to the wind speed and considering a constant load is illustrated at Figure 2. The Diesel generators therefore are required only during periods of low winds and/or to meet peak demands. The advantage of such systems are that very significant fuel savings can be achieved reducing import and storage costs, but also will extend the life and servicing frequency of the Diesel generators as they will log less hours. Such systems can also benefit from economies of scale for construction and maintenance, but require much more significant and expensive control systems [14,15] to regulate the grid frequency and voltage while the Diesel generators are turned off. A dump load is required during periods when the power from the wind turbines exceeds the demand in order to maintain system frequency and voltage [11].

Moreover, the electricity production by the Diesel is ineffective, presents significant environmental risks (spilling), contaminates the local air and largely contributes to GHG emission. In all, we estimate at 140,000 tons annual GHG emission resulting from the use of Diesel generators for the subscribers of the autonomous networks in Quebec. This is

The Diesel power generating units, while requiring relatively little investment, are generally expensive to exploit and maintain, particularly when are functioning regularly at partial load [4]. The use of Diesel power generators under weak operating factors accelerates wear increases fuel consumption [5]. Therefore, the use of hybrid systems, which combine renewable sources and Diesel generators, allows reducing the total Diesel consumption,

Among all renewable energies, the wind energy experiences the fastest growing rate, at more than 30% annually for the last 5 years [7,8]. Presently, wind energy offers cost effective solutions for isolated grids when coupled with Diesel generators. The "Wind-Diesel hybrid system" (WDS) represent a technique of generation of electrical energy by using in parallel one or several wind turbines with one or several Diesel groups. This approach is at present

The "penetration rate" is used in reference to the rated capacity of the installed wind turbines compared to the maximum and minimum loads. A strict definition of a "low-penetration" system is one when the maximum rated capacity of the wind component of the system does not exceed the minimum load of the community. In practical terms however, a lowpenetration system is one where the wind turbines are sized so as not to interfere with the Diesel generators' ability to set the voltage and frequency on the grid. In effect, the windgenerated electricity is "seen" by the Diesel plant as a negative load to the overall system. It is important to note however that because such a system needs to be designed for the peak capacity of the wind generator it will typically operate with an average annual output of 20- 35% of its rated power, such that while low-penetration systems will have noticeable fuel and emissions savings they will be fairly minor [12,2]. In many cases it is likely that similar savings

A "high-penetration" system without storage [13], as illustrated in Figure 1, is one where the output from the wind generators frequently exceeds the maximum load for extended periods of time (10 min to several hours), such that the Diesel generators can be shut off completely when there is significant wind. The variation of wind and Diesel-generated power according to the wind speed and considering a constant load is illustrated at Figure 2. The Diesel generators therefore are required only during periods of low winds and/or to meet peak demands. The advantage of such systems are that very significant fuel savings can be achieved reducing import and storage costs, but also will extend the life and servicing frequency of the Diesel generators as they will log less hours. Such systems can also benefit from economies of scale for construction and maintenance, but require much more significant and expensive control systems [14,15] to regulate the grid frequency and voltage while the Diesel generators are turned off. A dump load is required during periods when the power from the wind

used in Nordic communities in Yukon [9], Nunavut [10] and in Alaska [11].

could be achieved through energy efficiency upgrades for similar capital costs.

turbines exceeds the demand in order to maintain system frequency and voltage [11].

equivalent to GHG emitted by 35,000 cars during one year.

improving the operation cost and environmental benefits.

**1.2 Wind-Diesel systems** 

Fig. 1. Wind -Diesel system with dump load.

Fig. 2. Variation of wind and diesel power with wind speed for a high-penetration WDS [16].

Optimal Design of an Hybrid Wind-Diesel System with

Fig. 3. Wind-Diesel system with compressed air energy storage

Diesel generators [21,22].

Compressed Air Energy Storage for Canadian Remote Areas 273

problem of strong stochastic fluctuations of the wind power because it offers a high efficiency conversion (60-70% for a complete charge-discharge cycle), uses conventional materials which are easy to recycle and is able to make an almost unlimited number of cycles [18,19].The compressed air energy storage can more specifically, be used to overcharge the Diesel engines and ensure maximum efficiency over all functioning regimes. In this paper we analyze the technical and economical performances of a Diesel engine overcharged with compressed produced from wind energy surpluses. However, the advantage of a hybrid system compared to a wind alone system, depends on many fundamental factors: the form and the type of the load, the regime and speed of the wind, the cost and the availability of energy, the relative cost of the wind machine, the storage system and other efficiency determining factors [20]. The capital cost of the wind turbine and the CAES system is considerably damped by the reduction of the operating costs of

A medium-penetration system refers to a system in between the low- and highpenetration configurations. A medium-penetration system will have periods of time when the wind-generated electricity dominates the Diesel-generated electricity and may also be able to meet the system load for brief periods of time (30 s - 5 min). When wind speeds are high and/or the community demand is very low, the Diesel generators may not be required at all, but are not shut off, rather they are left to idle to be able to respond quickly to load demands. A medium-penetration system is potentially subjected to both the benefits and the drawbacks of low- and high penetration configurations. Beyond a certain penetration, the obligation to maintain idle the Diesel at any time, generally around 25-30% of its nominal output power, forces the system to function at a very inefficient regime. Indeed, for low- and medium-penetration systems, the Diesel consumes, even without load, approximately 50% of the fuel at nominal power output. These systems are easier to implant but their economic and environmental benefits are marginal [12]. The use of high-penetration systems allows the stop of the thermal groups, ideally as soon as the wind power equals the instantaneous charge, to maximize the fuel savings. However, considering the Diesel starting time as well as the instantaneous charge and wind speed fluctuations, the thermal production must be available (Diesel group to minimal regime) from the moment when the over-production passes under a threshold, named power reserve, considered as security to answer to the instantaneous requested power. The value of this reserve should be chosen so that it insures the reliability of the system and has a direct effect on the fuel consumption and the exploitation and maintenance costs of the Diesel generators. In other words, the Diesels must still idle to compensate for a sudden wind power decrease under the level of the charge and a greater the value of the power reserve leads to longer periods of time during which the Diesels are functioning at inefficient regimes.

During time intervals when the excess of wind energy over the charge is considerable the Diesel engine must still be maintained on standby so that it can quickly respond to a wind speed reduction (reduce the time of starting up and consequent heating of the engine). This is an important source of over consumption because the engine could turn during hours without supplying any useful energy. Assuming optimum exploitation conditions [17,2] the use of energy storage with wind-Diesel systems can lead to better economic and environmental results, allows reduction of the overall cost of energy supply and increase the wind energy penetration rate (i.e., the proportion of wind energy as the total energy consumption on an annual basis) [2].

Presently, the excess wind energy is stored either as thermal potential (hot water), an inefficient way to store electricity as it cannot be transformed back in electricity when needed or in batteries which are expensive, difficult to recycle, a source of pollution (leadacid) and limited in power and lifecycle. The fuel cells propose a viable alternative but due to their technical complexity, their prohibitive price and their weak efficiency, their appreciation in the market is still in an early phase. The required storage system should be easily adaptable to the hybrid system, available in real time and offer smooth power fluctuations. For this reason we examine the use of compressed air energy storage (CAES) with the wind-Diesel hybrid system (WDCAS), illustrated in Figure 3. The energy storage in the form of compressed air (CAES) is adaptable for the two sources of electricity production (wind energy and Diesel). Moreover, the CAES is an interesting solution to the

A medium-penetration system refers to a system in between the low- and highpenetration configurations. A medium-penetration system will have periods of time when the wind-generated electricity dominates the Diesel-generated electricity and may also be able to meet the system load for brief periods of time (30 s - 5 min). When wind speeds are high and/or the community demand is very low, the Diesel generators may not be required at all, but are not shut off, rather they are left to idle to be able to respond quickly to load demands. A medium-penetration system is potentially subjected to both the benefits and the drawbacks of low- and high penetration configurations. Beyond a certain penetration, the obligation to maintain idle the Diesel at any time, generally around 25-30% of its nominal output power, forces the system to function at a very inefficient regime. Indeed, for low- and medium-penetration systems, the Diesel consumes, even without load, approximately 50% of the fuel at nominal power output. These systems are easier to implant but their economic and environmental benefits are marginal [12]. The use of high-penetration systems allows the stop of the thermal groups, ideally as soon as the wind power equals the instantaneous charge, to maximize the fuel savings. However, considering the Diesel starting time as well as the instantaneous charge and wind speed fluctuations, the thermal production must be available (Diesel group to minimal regime) from the moment when the over-production passes under a threshold, named power reserve, considered as security to answer to the instantaneous requested power. The value of this reserve should be chosen so that it insures the reliability of the system and has a direct effect on the fuel consumption and the exploitation and maintenance costs of the Diesel generators. In other words, the Diesels must still idle to compensate for a sudden wind power decrease under the level of the charge and a greater the value of the power reserve leads to longer periods of time during which the Diesels

During time intervals when the excess of wind energy over the charge is considerable the Diesel engine must still be maintained on standby so that it can quickly respond to a wind speed reduction (reduce the time of starting up and consequent heating of the engine). This is an important source of over consumption because the engine could turn during hours without supplying any useful energy. Assuming optimum exploitation conditions [17,2] the use of energy storage with wind-Diesel systems can lead to better economic and environmental results, allows reduction of the overall cost of energy supply and increase the wind energy penetration rate (i.e., the proportion of wind energy as the total energy

Presently, the excess wind energy is stored either as thermal potential (hot water), an inefficient way to store electricity as it cannot be transformed back in electricity when needed or in batteries which are expensive, difficult to recycle, a source of pollution (leadacid) and limited in power and lifecycle. The fuel cells propose a viable alternative but due to their technical complexity, their prohibitive price and their weak efficiency, their appreciation in the market is still in an early phase. The required storage system should be easily adaptable to the hybrid system, available in real time and offer smooth power fluctuations. For this reason we examine the use of compressed air energy storage (CAES) with the wind-Diesel hybrid system (WDCAS), illustrated in Figure 3. The energy storage in the form of compressed air (CAES) is adaptable for the two sources of electricity production (wind energy and Diesel). Moreover, the CAES is an interesting solution to the

are functioning at inefficient regimes.

consumption on an annual basis) [2].

problem of strong stochastic fluctuations of the wind power because it offers a high efficiency conversion (60-70% for a complete charge-discharge cycle), uses conventional materials which are easy to recycle and is able to make an almost unlimited number of cycles [18,19].The compressed air energy storage can more specifically, be used to overcharge the Diesel engines and ensure maximum efficiency over all functioning regimes. In this paper we analyze the technical and economical performances of a Diesel engine overcharged with compressed produced from wind energy surpluses. However, the advantage of a hybrid system compared to a wind alone system, depends on many fundamental factors: the form and the type of the load, the regime and speed of the wind, the cost and the availability of energy, the relative cost of the wind machine, the storage system and other efficiency determining factors [20]. The capital cost of the wind turbine and the CAES system is considerably damped by the reduction of the operating costs of Diesel generators [21,22].

Fig. 3. Wind-Diesel system with compressed air energy storage

Optimal Design of an Hybrid Wind-Diesel System with

Fig. 4. Variation of indicated efficiency with the air/fuel ratio [39]

Fig. 5. Admission of CAES at the compressor intake.

Fig. 6. Admission of CAES at the engine intake

Compressed Air Energy Storage for Canadian Remote Areas 275
