Getting Started Guide
for
HOMER Version 2.1
April 2005
National Renewable Energy Laboratory
1617 Cole Boulevard, Golden, Colorado 80401-3393
303-275-3000 • www.nrel.gov
Operated for the U.S. Department of Energy
Office of Energy Efficiency and Renewable Energy
by Midwest Research Institute • Battelle
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About this Getting Started Guide
This Getting Started guide introduces you to HOMER by walking you through eleven steps.
You will start by providing HOMER with information, or inputs, about power system designs
that you want to consider. HOMER will simulate system configurations, create a list of
feasible system designs, and sort the list by cost-effectiveness. In the final step, you will
use HOMER to perform a sensitivity analysis. By going through each step in the guide, you
should become familiar with the software, and develop enough experience to start using the
model on your own.
It should take about an hour to complete this exercise.
The online version of this guide
You can open an online version of this guide by choosing Getting Started on HOMER's Help
menu.
Checking your work as you go
Throughout the guide are illustrations that show how HOMER should look as you use the
software. Be sure to compare what appears on your computer screen to the illustrations to
make sure that you have correctly completed each step.
About Tips and Notes:
Throughout this guide, tips and notes provide additional information to help you better
understand how HOMER works. A note is important information that you should read to
better understand the step of the exercise that you are completing. A tip is supplementary
information that you may find useful for your future work with HOMER, but is not essential
to understand to complete the exercise.
Table of Contents
Welcome to HOMER........................................................................................... 3
Step one: Formulate a question that HOMER can help answer .......................... 5
Step two: Create a new HOMER file................................................................... 6
Step three: Build the schematic ........................................................................ 7
Step four: Enter load details ............................................................................. 9
Step five: Enter component details ................................................................. 11
Step six: Enter resource details ...................................................................... 15
Step seven: Check inputs and correct errors................................................... 17
Step eight: Examine optimization results........................................................ 20
Step nine: Refine the system design ............................................................... 22
Step ten: Add sensitivity variables .................................................................. 25
Step eleven: Examine sensitivity analysis results ........................................... 27
Getting Started Guide summary ...................................................................... 29
Contacts.......................................................................................................... 30
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Welcome to HOMER
What is HOMER?
HOMER, the micropower optimization model, simplifies the task of evaluating designs of
both off-grid and grid-connected power systems for a variety of applications. When you
design a power system, you must make many decisions about the configuration of the
system: What components does it make sense to include in the system design? How many
and what size of each component should you use? The large number of technology options
and the variation in technology costs and availability of energy resources make these
decisions difficult. HOMER's optimization and sensitivity analysis algorithms make it easier
to evaluate the many possible system configurations.
How do I use HOMER?
To use HOMER, you provide the model with inputs, which describe technology options,
component costs, and resource availability. HOMER uses these inputs to simulate different
system configurations, or combinations of components, and generates results that you can
view as a list of feasible configurations sorted by net present cost. HOMER also displays
simulation results in a wide variety of tables and graphs that help you compare
configurations and evaluate them on their economic and technical merits. You can export
the tables and graphs for use in reports and presentations.
When you want to explore the effect that changes in factors such as resource availability
and economic conditions might have on the cost-effectiveness of different system
configurations, you can use the model to perform sensitivity analyses. To perform a
sensitivity analysis, you provide HOMER with sensitivity values that describe a range of
resource availability and component costs. HOMER simulates each system configuration
over the range of values. You can use the results of a sensitivity analysis to identify the
factors that have the greatest impact on the design and operation of a power system. You
can also use HOMER sensitivity analysis results to answer general questions about
technology options to inform planning and policy decisions.
How does HOMER work?
Simulation
HOMER simulates the operation of a system by making energy balance calculations for each
of the 8,760 hours in a year. For each hour, HOMER compares the electric and thermal
demand in the hour to the energy that the system can supply in that hour, and calculates
the flows of energy to and from each component of the system. For systems that include
batteries or fuel-powered generators, HOMER also decides for each hour how to operate the
generators and whether to charge or discharge the batteries.
HOMER performs these energy balance calculations for each system configuration that you
want to consider. It then determines whether a configuration is feasible, i.e., whether it can
meet the electric demand under the conditions that you specify, and estimates the cost of
installing and operating the system over the lifetime of the project. The system cost
calculations account for costs such as capital, replacement, operation and maintenance,
fuel, and interest.
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Optimization
After simulating all of the possible system configurations, HOMER displays a list of
configurations, sorted by net present cost (sometimes called lifecycle cost), that you can
use to compare system design options.
Sensitivity Analysis
When you define sensitivity variables as inputs, HOMER repeats the optimization process for
each sensitivity variable that you specify. For example, if you define wind speed as a
sensitivity variable, HOMER will simulate system configurations for the range of wind speeds
that you specify.
HOMER on the Internet
The HOMER Web site, www.nrel.gov/homer, contains the latest information on the model,
as well as sample files, resource data, and contact information.
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Step one: Formulate a question that HOMER can help answer
HOMER can answer a wide range of questions about the design of small power systems. It is
useful to have a clear idea of a question that you want HOMER to help answer before you
begin working with HOMER. Examples of the kinds of questions that HOMER can answer are:
• Is it cost-effective to add a wind turbine to the diesel generator in my system?
• How much will the cost of diesel fuel need to increase to make photovoltaics cost
effective?
• Will my design meet a growing electric demand?
• Is it cost-effective to install a microturbine to produce electricity and heat for my
grid-connected facility?
For this exercise, let us assume that diesel generators typically serve small loads in a
remote area, and that we want to use HOMER to find out whether it makes sense to add
wind turbines to such systems. The question we will use HOMER to help answer is: How do
changes in average wind speed and fuel price affect the feasibility of adding wind turbines to
a diesel-only system design?
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