Article
Design of a Hybrid Energy System with Energy Storage for
Standalone DC Microgrid Application
Mwaka I. Juma
1,2,
*, Bakari M. M. Mwinyiwiwa
1
, Consalva J. Msigwa
2
and Aviti T. Mushi
1
Citation: Juma, M.I.; Mwinyiwiwa,
B.M.M.; Msigwa, C.J.; Mushi, A.T.
Design of a Hybrid Energy System
with Energy Storage for Standalone
DC Microgrid Application. Energies
2021, 14, 5994. https://doi.org/
10.3390/en14185994
Academic Editors: Pierluigi Siano
and Adalgisa Sinicropi
Received: 11 August 2021
Accepted: 14 September 2021
Published: 21 September 2021
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
published maps and institutional affil-
iations.
Copyright: © 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
1
Electrical Engineering Department, University of Dar es Salaam, Dar es Salaam P.O. Box 35131, Tanzania;
bakari1mwinyiwiwa@gmail.com (B.M.M.M.); aviti.thadei@udsm.ac.tz (A.T.M.)
2
Electrical Engineering Department, Dar es Salaam Insititute of Technology,
Dar es Salaam P.O. Box 2958, Tanzania; msigwaj34@gmail.com
* Correspondence: jumamwaka@gmail.com
Abstract:
This paper presents microgrid-distributed energy resources (DERs) for a rural standalone
system. It is made up of a solar photovoltaic (solar PV) system, battery energy storage system (BESS),
and a wind turbine coupled to a permanent magnet synchronous generator (WT-PMSG). The DERs
are controlled by maximum power point tracking (MPPT)-based proportional integral (PI) controllers
for both maximum power tracking and error feedback compensation. The MPPT uses the perturb
and observe (P&O) algorithm for tracking the maximum power point of the DERs. The PI gains
are tuned using the Ziegler–Nichols method. The developed system was built and simulated in
MATLAB/Simulink under two conditions—constant load, and step-load changes. The controllers
enabled the BESS to charge even during conditions of varying load and other environmental factors
such as change of irradiance and wind speed. The reference was tracked extremely well by the output
voltage of the DC microgrid. This is useful research for electrifying the rural islanded areas which
are too far from the grid.
Keywords:
solar photovoltaic (PV); wind turbine coupled to permanent magnet synchronous gener-
ator (WT-PMSG); battery energy storage system (BESS); maximum power point tracking (MPPT);
DC/DC converters
1. Introduction
Recent research has shown that in Tanzania, the access to electricity is limited to 35.6%
of the total 56.32 million population as of 2018 [
1
]. One location, a village called Luxmanda,
is not connected to the grid, but survives on the available DC microgrid which provides
power to some few loads [
2
]. This problem of limited access to electricity can be reduced
not only by grid expansions, but rather by utilizing distributed renewable energy sources
(RES). These systems, such as solar home systems (SHS) and micro- and mini-solar plants,
are increasingly being used as sources of electric energy in rural areas worldwide and in
Tanzania. They are designed for use at the demand of small households, usually in power
ranging by few kilowatts, thereby causing limitations for enterprise and other potentially
larger users of electricity within rural areas. However, if these hybrid RES are deployed
in villages or remote locations, they result to least net present cost and reduced emission
of carbon dioxide [
3
,
4
] by paying extra attention to their optimal sizing design as was
carried out in Palestine [
5
]. These microgrids can be highly efficient in delivering energy to
local loads [6].
Solar photovoltaic (PV) plants and wind energy need big power storage (such as
batteries) to provide voltage regulation, and reduce the effects of the energy source inter-
mittency, which adds to the cost of the installation. For example, in India [
6
], a solar PV
plant was able to supply 55.1% of the required electricity. This, however, still leaves the
locale dependent on the grid. To reduce the cost of battery, it has been proposed to integrate
several RES to form a hybrid power system [
7
]. Therefore, there exists a need to manage the
Energies 2021, 14, 5994. https://doi.org/10.3390/en14185994 https://www.mdpi.com/journal/energies
