Product: HOMER Grid 1.1 and HOMER Pro 3.11

This article provides users with tips to make HOMER calculations run faster and explains why some calculations may run slower.

In terms of hardware, the most important piece would be the processor speed and the number of cores. For example an i7 processor that has 4 cores, means that it can run four sensitivity analysis optimizations in parallel at 3.4 GHz. However, if there are other applications open and depending upon the operating system, this can slow the processing time. Shutting down other applications allows HOMER to run even faster, dependent on how many CPU resources those are taking.

In terms of RAM, once you click calculate, HOMER will store the system results in memory for quick retrieval and processing. HOMER software is intelligent and will not re-calculate systems that it has previously simulated. You can increase the amount of cached systems in the Settings page of HOMER, but the primary limitation is the hardware.

So to summarize computer hardware tips: faster processors, more processing cores, and more RAM all make HOMER provide results faster.

Here are some other considerations to make HOMER Grid calculations run faster:

- Model hourly time steps. This may be less precise, but can be a good way to speed things up, particularly in initial design runs when you are simulating a lot of design options. Keep in mind that many utilities use a 15-minute demand averaging window; you many want to use shorter time steps once you've narrowed down your options, if you have good enough load data.
- Add an upper limit to the PV array size in HOMER Optimizer. One common approach that users use is make just a little larger than your peak load.
- If you can limit the number of sizes you'd like to consider, use the search space instead of the HOMER Optimizer. If you plan to use a lot of entries in the search space, the HOMER Optimizer will likely be faster.
- Limit the number of sensitivity analyses, or use just one or two sensitivity variables at a time.
- Modeling a CHP or generator in HOMER Grid makes the simulation run a bit slower. If you can rule out a CHP or generator, or create a design without it, you will get results quicker.

Here are some considerations to make HOMER Pro calculations run faster:

- Model hourly time steps.
- Add an upper limit to the PV array size in HOMER Optimizer. One common approach is to make it just a little larger than your peak load.
- If you can limit the number of sizes you'd like to consider, use the search space instead of the HOMER Optimizer. If you plan to use a lot of entries in the search space, the HOMER Optimizer will likely be faster.
- Limit the number of sensitivity analyses, or use just one or two sensitivity variables at a time.
- Limit the number of generators. Many controllers slow down significantly when you have a lot of generators. If you want to model a lot of generators, consider using the HOMER Generator Order controller.
- Limit the number of components you are comparing, and try to keep the search space limited to options you'd like to consider.
- Use the Multi-Year analysis after you have performed initial modeling with a Single-Year simulation. Multi-Year analyses take much longer than Single-Year analyses. You can often refine the design with single-year analysis, and then polish your results by running Multi-Year analysis on a much smaller set of component options.
- Limit the number of controllers in your model.

The time for a calculation has to do with the complexity of the system you model. Here are some examples:

- Changing the time step from one minute to hourly can speed up your calculation by a factor of 60, since there are then 60 fewer energy balance calculations.
- A model with three sensitivity variables will increase the calculation time by the multiple of the number of sensitivity values in each. For example, let’s say that you have three numbers for the diesel fuel price, three discount rates, and three installed PV prices (you can set these using the PV capital multipliers). That is a total of 3 × 3 × 3 = 27 sensitivity possible combinations, which means 27 total sensitivity cases that HOMER will optimize. If each optimization has 25,000 simulations, 25,000 × 27 = 675,000 total system simulations. If you are running an hourly simulation, this would be about 6 billion hourly energy balance calculations. If your computer has 4 cores, then it can run 4 optimizations simultaneously, so you'll be able to run the 6 billion calculations four times faster than if they were run serially.