Evaluating the impact of adding energy storage on the performance
of a hybrid power system
Headley Jacobus
a,b
, Baochuan Lin
a
, David Henry Jimmy
c
, Rashid Ansumana
c
,
Anthony P. Malanoski
a
, David Stenger
a,
⇑
a
Center for Bio/Molecular Science & Engineering, Naval Research Laboratory, Code 6900, 4555 Overlook Avenue, S.W., Washington, DC 20375, USA
b
Nova Research Incorporated, 1900 Elkin Street, Suite 230, Alexandria, VA 22308, USA
c
Mercy Hospital Research Laboratory, Kulanda Town, Bo, Sierra Leone
article info
Article history:
Received 19 July 2010
Accepted 29 January 2011
Available online 24 March 2011
Keywords:
Hybrid power
Diesel-only generator
Load profile
Battery bank
Generation cost
Operation and maintenance
abstract
Hybrid power systems have the capability to incorporate significant renewable energy penetration for a
small autonomous system while still maintaining reliable grid stability. While there are many papers
covering the optimization of component size and dispatch strategy, far fewer papers contain experimen-
tal performance data from hybrid systems. Mercy Hospital in Bo, Sierra Leone is converting their power
system into a photovoltaic (PV)–diesel hybrid system, thus providing an opportunity to examine the
change in system performance before, during, and after the conversion. Due to the seasonal availability
of electric power in Sierra Leone, two datasets representing two distinct load profiles are analyzed: Wet
Season and Dry Season. The difference in generation efficiency, cost per kW h, generator runtime, and fuel
consumption are calculated between a diesel-only generation baseline and the recorded hybrid system
performance. The results indicated that the hybrid system significantly reduces operation costs; approx-
imately 37% less during Dry Season and 64% reduction in the Wet Season than a diesel-only generator
serving the same load.
Published by Elsevier Ltd.
1. Introduction
A hybrid power system is an autonomous power system that
incorporates two or more unique power generation technologies
to produce power at lower costs and/or higher reliability than a
singular power system. The system takes advantage of different
power production technologies that complement each other and
provides inventive energy usage and production schemes through
which renewable energy can be maximized while excess energy is
minimized. There are several hybrid systems described in the liter-
ature, such as photovoltaic (PV)/Diesel generator power systems
[1], PV/Battery/Diesel [2–4], PV/Wind Turbine/Battery/Diesel [5],
PV/Wind only [6], and PV/Wind/Diesel/Microhydroelectric turbine
[7]. In reality, designing a hybrid system is a two-part optimiza-
tion: the component sizing which dictates how much electricity
is available to be utilized by the load and the energy dispatch
strategy which describes the set points when electricity producers
start production, what power level do they produce at, utilization
of excess energy, and load shedding. Both aspects of system design
are important in predicting total system cost. The component siz-
ing of the system dictates the capital cost while the dispatch strat-
egy dictates the operation costs of the system [8]. To make
optimization process more complicated, the optimum of both the
component sizing and the dispatch strategy are dependent on
one another.
Many studies have looked to optimize the component size of a
system without variation of the distribution strategy [9–13]. How-
ever, few studies discussed the optimization of the dispatch strat-
egy of a hybrid system because it is such a large multi-variable
problem. Those that are willing to tackle optimization of both com-
ponent size and dispatch strategy usually employ genetic algo-
rithms to reduce the computation time [8,14,15]. Although
useful, all the papers described above propose new and different
models to describe the performance of a hybrid system and out
of necessity all models are only approximations of reality. There
is very little literature documenting the performance of installed
systems. Nayar et al. built and tested a PV–diesel hybrid system
and described the system’s ability to act as an uninterruptible
Power Supply [16]. Phuangpornpitak and Kumar examined the
economic benefit (or lack of benefit) of 10 Solar/Wind/Diesel
0196-8904/$ - see front matter Published by Elsevier Ltd.
doi:10.1016/j.enconman.2011.01.015
Abbreviations: PV, photovoltaic; O&M, operation and maintenance; BKPS,
bo-kenema power supply.
⇑
Corresponding author. Tel.: +1 202 404 6035; fax: +1 202 404 8897.
E-mail addresses: jacobush@gmail.com (H. Jacobus), baochuan.lin@nrl.navy.mil
(B. Lin), dave_jimmy07@yahoo.co.uk (D.H. Jimmy), rashidansumana@gmail.com
(R. Ansumana), Anthony.malanoski@nrl.navy.mil (A.P. Malanoski), david.stenger@
nrl.navy.mil (D. Stenger).
Energy Conversion and Management 52 (2011) 2604–2610
Contents lists available at ScienceDirect
Energy Conversion and Management
journal homepage: www.elsevier.com/locate/enconman