HOMER Energy is now part of UL

You may have heard about the recent  acquisition of HOMER Energy by UL. This is a truly great milestone and a good opportunity to review the history of the HOMER software.  It all started with the Earth summit in Rio de Janeiro in 1992 where the US government offered to help developing nations provide clean renewable electricity to the billions of people who had no access to any power at all. At the US Department of Energy National Renewable Energy Laboratory (NREL), we responded by creating the Village Power Program (VPP).

In 1992, solar photovoltaics were still extremely expensive, lithium batteries did not exist, and the only alternatives to grid extensions other than some small wind generators were diesel generators.  Although we didn’t call them microgrids at the time, those of us in the VPP recognized that hybrid systems combining renewable power with diesel generators and batteries would be a solution to the electrification problem. To do this, however, we needed a software model that would allow us to simulate the performance of different designs and optimize those designs for minimum cost.  I jumped at the chance to use the optimization knowledge I had recently acquired at Stanford along with experience with developing distributed generation projects through my internship with International Power Technology.

HOMER was first created to inform the design of early hybrid energy systems

We created the first version of HOMER using specialized optimization software called GAMS that had been originally developed at the World Bank. GAMS was expensive software without a real user interface, so the original version of HOMER could only be used by 1-2 researchers at NREL. One of the first things we learned was that linear programming was not adequate for what we were trying to do, since the optimization of hybrid systems is inherently non-linear.

In 1996, Tom Lambert, who is now also the developer of UL’s Windographer software, was a graduate student at Colorado State University interning at NREL. He suggested porting HOMER to a C++/Windows application. Although this sounded overly ambitious at the time, he succeeded. This allowed us to put HOMER on this new thing called the internet and let other people download and use it.

The early 2000’s were a difficult time for HOMER, as NREL disbanded the VPP in response to shifting political winds.  We received some internal funding from NREL to expand HOMER’s capabilities to larger systems with multiple generators, including combined heat and power (CHP) and limited modeling of grid connections. This allowed us to get more involved with island power systems that could be over 100 MWs and were burning diesel fuel 24/7. We also kept our program  alive with “Work for Others”, what NREL calls funding from outside of the Department of Energy.

HOMER software moves out of the laboratory to design island power systems

Both the Government of Anguilla and the Bermuda Electric Light Company wanted to understand the role that renewable power could play on their islands. These contracts would have been very difficult to get through the Department of Energy’s approval process, so in March of 2007 I took a sabbatical to work on them. Shortly thereafter I started negotiating a commercialization license for HOMER through NREL’s Technology Transfer Office. In late 2008, I created HOMER Energy, LLC, and I finalized the license with NREL in January of 2009.

The next big milestone came in 2010 with a Small Business Innovative Research grant from the National Science Foundation. Also in 2010, Dr. Marilyn Walker came on board as COO with a broad range of modeling and small business and e-commerce experience.  HOMER Energy combined revenue from its consulting business with the NSF/SBIR funds to create a completely re-architected HOMER Pro for public release in 2014.

In 2016, HOMER Energy received its first (and only) outside private financing from Factor[e] Ventures. We used this funding to create a new version of HOMER for grid-connected projects, HOMER Grid, and a set of APIs. HOMER’s user base continued to grow at a steady rate, matching the growth of microgrids and distributed generation markets more broadly. That growth is now accelerating, so the UL acquisition comes at an excellent time.

UL and HOMER Energy: Why we are a good fit

UL has been promoting safety and engineering standards for 125 years. Renewable energy and sustainability in general is a logical extension of the traditional UL commitment to safety. Among many other renewable energy acquisitions, UL acquired AWS TruePower in 2016 and are now a leader in resource assessment and due diligence of renewable energy projects. The company’s approach to standards and quality assurance will increase public trust and improve the prospects for financing of microgrids.  

HOMER Energy, our people, and our software, will continue as before, but now with more resources and growth opportunities. In the short term, there will be few changes, but over time you will see greater support and services for our global user base and more integration with other software. We are thrilled to be part of a much larger team and such a well-respected organization.

To our existing customers and users – thank you for helping us get here and for working with us to help the world with clean, reliable, and affordable power. To everyone interested in microgrids and distributed generation – we are excited about 2020 and all the good we can do as a global community dedicated to a more sustainable world.


  1. i signed up and paid for Homer training that’s supposed to happen but haven’t heard back from anyone. Can somebody help that process along.

  2. Hm, too bad. This makes Homer less usable for technical Consultants in the RE field (other than UL) since it now belongs to the competition. No more indenpence…. 🙁

  3. Am happy to learn how Homer Software has been developed over time and the challenges the developers have faced in the development process. It has shown high level of commitment and I also hope they will achieve more in 2020.

    1. Hi Andrew,
      Many thanks for your kind comment. We do expect to grow our achievements in 2020 and beyond!

      We wish you you all the best,

  4. Peter, I remember very fondly my years working on HOMER with you, and I’m pleased as punch to be working with you again. Here’s to a bright (and clean) future!

    1. Hi Tom,
      Thanks so much! Your – and Peter’s – hard work on the original HOMER software is at the root of many terrific projects all over the world. May there be many more.

      All the best,

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