HOMER software is a tool that is used to design a HRES by combining different renewable and non-renewable sources such as WT, PV, DG, hydro generator, fuel cells, inverter and energy battery for all sector such as villages, islands and campuses. It was created by National Renewable Energy Laboratory/USA. The input data that the HOMER needs to optimize the system are the system variables, which are the types and sizes of the component with the prices of them and the meteorological data which are wind speed, solar irradiance and ambient temperature.

It can model on-grid and off-grid systems and provide different configuration to get the optimal system with the least COE. HOMER can handle three tasks which are simulation, optimization and sensitivity analysis.

In simulation, HOMER performs calculations on all the proposed options for the system based on the type of loads required and renewable sources such as solar energy and available wind energy. It compares the energy that the system can provide to the electrical load demand in every hour of the year and calculate the direction of generated energy between the components. The number of these possibilities may be hundreds or even thousands.

In optimization, optimal solution or optimal design of the system is found among all the available design options that the program reached, and the optimal here is to express the economic aspect because HOMER is essentially an economic model for choosing the best model. For example, the program offers the option that achieves the largest savings of spent fuel for DG if it was approved as a source to cover the load that the system was designed for.

HOMER is also considered the best option in the sensitivity analysis. The word sensitivity here is related to economic operations. It analyses the effect of changing one factor on the performance of the system. For example, it performs the changing of solar radiation or wind speed on the amount of fuel consumed with keeping constant the rest of the factors. Figure .1 shows the HOMER flowchart.

HOMER flowchart

Economic Parameters in HOMER

HOMERΒ  software is applied for design, optimization and sensitivity analysis in this study. It provides sensitivity analysis option to understand changes that impact on NPC of the particular system. The other economic indicators used for this study is explained in subsection below.

Initial Capital Cost

The initial capital cost represents total amount of component at the beginning of the project including equipment and installation cost. In the hybrid systems, civil work, installation cost, and electric connections and testing are the components of the initial capital cost.

Replacement Cost

The replacement cost means that if a component completes economic life, the new one is replaced. It differs from initial capital cost as only some part of the component may require replacement. It may differ from initial capital cost in terms of some reasons:

  • Some component of the hybrid system may not require replacement at the end of their life.
  • The initial cost may be decreased or minimized by subvention while replacement cost may not be reduced.

Operation and Maintenance Cost

Operation and Maintenance (O&M) cost is the overall scheduled cost for life time operation and maintenance of the facility. O&M cost is mainly entered as an annual amount but some component is in hourly basis such as generators. O&M cost for the grid is annual power purchase from grid minus revenue from the sell electricity to the national grid. System fixed O&M cost, and penalties including emission and capacity shortage is classified as the other O&M costs in HOMER. Other O&M cost can be calculated as using equation (3.1) :

πΆπ‘œπ‘š,π‘œπ‘‘β„Žπ‘’π‘Ÿ = πΆπ‘œπ‘š,𝑓𝑖π‘₯𝑒𝑑 + 𝐢𝑐𝑠 + πΆπ‘’π‘šπ‘–π‘ π‘ π‘–π‘œπ‘›π‘ 

πΆπ‘œπ‘š,π‘œπ‘‘β„Žπ‘’π‘Ÿ ($/yr) is the hybrid system fixed O&M cost, 𝐢𝑐𝑠 capacity shortage penalty ($/yr) and πΆπ‘’π‘šπ‘–π‘ π‘ π‘–π‘œπ‘›π‘  ($/yr) is emission penalty per year.

Salvage Value

This value represents remainder in a part of the energy system at the end of the project lifetime. HOMER presume that the salvage value which is calculated in equation (3.2) only subjects to replacement cost.

HOMER Software

Hybrid optimization model for multiple energy resources (HOMER) program was initially established by national renewable energy laboratory (NREL) in the USA but now it is operated by Homer energy. It simulates a standalone and grid interactive energy system based on user inputs such as load profile, renewable sources, the component’s technical and economic details. The program runs the simulations of all possible combinations and gives the results according to the most cost-effective ones which can meet the load demand by arranging them in terms of their NPC in ascending order. The system with the lowest NPC is the optimal hybrid configuration.

The HOMER program uses mathematical calculation for simulation. The software simulates several numbers of situations. For example, integrating traditional energy sources with the renewables to satisfy load demand. Investigations can be either as grid integrated or standalone and their emissions levels studies. HOMER enables the user to make inputs of renewables according to their demand. This will let the user to investigate the potential of small-scale power systems before the final application. Also, it permits comparing several diverse configurations according to their technical and economic benefits.

HOMER designs hybrid energy system’s physical components and the lifecycle cost, in turn lets the user to compare many diverse design selections, according to their technical and economic benefits. Also, the program helps in understanding the effects of uncertainty based on in the user inputs. The program chooses whether or not the renewable energy can supply the load demand. If the renewable sources are inadequate, it ensures that other sources such as generator or the grid operates and satisfy the demand.

HOMER performs three main tasks:

Simulation, optimization and sensitivity analysis. Simulation: HOMER simulates the performance of a specific hybrid system to identify the technical feasibility and economical cost for each hour of the year. The software also simulates the operations of a hybrid energy system for a whole year, in time steps from one minute to one hour.

Optimization: HOMER program simulates various system configurations at lowest cost. Also, it calculates the ideal value of the variables for which the user has control over, for example system’s component size.

Sensitivity analysis: HOMER performs numerous optimizations under series of inputs to measure the effects of uncertainty. So, sensitivity study helps to establish the effect of uncertainty over which the program designer has no power to control, such as wind speed, solar insulation, price of fuels. Finally, the most economical hybrid configuration can be recognized based on the optimization result.

Figure 2. shows the connection between simulation, optimization & sensitivity analysis. optimization may contain one simulation or multiple simulation. While the sensitivity analysis also can contain multiple optimizations but for any given system, only one sensitivity analysis is likely. So, in this study, mixtures of renewable energy, diesel generator, battery and the grid are adopted to come up with the most optimal hybrid system design.

Correlation between simulation optimization and sensitivity analysis

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