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4.2.7.2 Optimization
HOMER displays a list of feasible systems, after simulating all possible system con-
figurations, and sort them by lifecycle cost. One can easily identify the system with
the lowest cost at the top of the list. It would also be possible to scan the list for other
feasible systems as per requirements.

4.2.7.3 Sensitivity Analysis
With HOMER one can study the effect of changing input conditions on system design.
HOMER can perform a sensitivity analysis on almost any input by assigning more
than one value to each input of interest. It would repeat the optimisation process for
each value of the input so that it can be examined that how they can affect the results.
One can specify as many sensitivity variables as possible, and the results can be ana-
lysed using HOMER’s powerful graphing capabilities. HOMER uses hourly simula-
tions to arrive the optimum target. It is a time-step simulator that uses hourly load and
environmental data inputs for renewable energy system assessment. it facilitates the
optimization of renewable energy systems based on Net Present Cost for a given set
of constraints and sensitivity variables.
HOMER has been used extensively by researchers in various RES case studies
[74,102–104] and in renewable energy system validation tests [69]. The operation
of HOMER is simple and straightforward. However, depending upon the numbers
of sensitivity variable used, the simulations can take a long time. Moreover, the
program’s limitation is that it does not allow the user to intuitively select the appro-
priate components for a system, as algorithms and calculations are not visible or
accessible.
The software HYBRID2 was developed by the Renewable Energy Research
Laboratory (RERL) of the University of Massachusetts. It is hybrid system simula-
tion software, with a very precise simulation which can define time intervals from
10 min to 1 h. National Renewable Energy Laboratory recommends optimizing the
system with HOMER and then, once the optimum system is obtained, improving the
design using HYBRID2 [65].
iHOGA (improved Hybrid Optimization by Genetic Algorithms) is a software
developed in C++ by researchers of the University of Zaragoza (Spain) for the simu-
lation and optimization of Hybrid Stand-alone Systems of Electric Power Generation
based on Renewable Energies [105]. The software can model systems with electri-
cal energy with AC/DC load, and/or Hydrogen, as well as consumption of water
from tank or reservoir previously pumped. This software is used to optimally size
the system components of an energy system that includes photovoltaic generator,
wind turbines, hydroelectric turbine, auxiliary generator (diesel, gasoline), inverter
or inverter-charger, batteries (lead acid or lithium), charger and batteries charge con-
troller as well as components of hydrogen (electrolyser, hydrogen tank and fuel cell).
It is capable of simulating and optimizing systems of any size which is either grid-
connected or standalone. The software includes the options of mono objective/ multi-
objective optimization, simulation in time steps of up to 1 minute, sensitivity analysis,
probability analysis, etc. Very detailed models of the components are used in this
software, resulting very precise estimates of the operation of the system designed.