Best Practices for Sizing and Installing Off-Grid Solar Systems

Solar power, when done correctly, is one of the most cost-effective, low-maintenance, and reliable solutions for powering remote electronics in today’s connected world.

However, many solar power solutions fail due to being improperly sized and installed. A poorly designed system can experience significant outages and a shorter life.

To properly size a solar system, it is important to consider these five factors:

1. Solar resource varies a great deal based on local weather patterns and the system’s location relative to the equator. The closer to the equator, the more daylight hours and greater solar potential. The key is to base the system design on winter sun hours, not on year-round averages. That way, shorter winter days, cold temperatures, and overcast skies do not affect operations.
2. Supported Loads. When sizing a system one of the most important factors to know is the average operating load that will be supported. Ideally, this load should be a measured operating load, and not based on component spec sheet information. Spec sheet information is typically worst-case scenario, resulting in an oversized, needlessly expensive system.
3. Battery Life. Battery bank sizing is the most important consideration when designing an off-grid solar system. Unfortunately, this is the one calculation where a majority of sizing mistakes occur. Performance and longevity depend on many factors including ambient temperature, overall capacity, and charge/discharge cycles. Ideally, a system should have enough battery capacity to ride through most any weather event without ever fully discharging the batteries.
4. Available Footprint. To properly size a solar system requires a healthy balance between the size of the solar array and battery capacity. In many cases, a larger solar array can reduce the size of the required battery bank. However, if array space is constrained, best practices mandate increasing the number of batteries.
5. System Autonomy. Simply put, the more mission-critical your load, the more you want to provide for extra capacity to ensure worst-case weather events don’t impact performance. It is far less costly to oversize a system by a little than to continuously visit a failing undersized one.

Even the best designed solar systems can fail out in the field if not installed correctly.

To properly install a solar system, one must follow these three guidelines.

1. Avoid Shade! Shade will crash a solar system more than any other factor. Even if a fraction of the solar array is shaded, it can significantly diminish the total output of a system.
2. Place the solar array away from trees, fences, structures, and buildings. As the seasons change, so do the direction and angle of the sun. It is important to be far enough away from trees, fences, and structures, and buildings to ensure that they don’t shade any part of the solar array.
3. Face South. For most solar installations in the continental Northern Hemisphere, the best direction to face the solar array is due South for maximum sun exposure. This will yield the greatest output.

Finally, when configuring a solar system, there are a few additional things to consider.

1. Type of Enclosure. For outdoor applications, one of the causes of failures in solar systems are problems created by a faulty or poorly specified enclosure. It is important that the enclosure is built to Type 4X standard to protect the electronics from moisture, and Type 3R standard for the battery compartment. Otherwise, water can damage the electronics and improper ventilation can negatively affect battery life.
2. Angle of the Solar Array. In general, for off-grid, battery-based solar applications, the recommended solar array angle for the US is the degree of latitude plus 15 degrees to achieve maximum exposure to the sun. For example, if the location is at 30 degrees latitude, the array angle would be 30 + 15 = 45 degrees. It is important to research your location to determine the optimal pitch.
3. Know NREL. The National Renewable Energy Laboratory (NREL) has an informative website, nrel.gov, that provides useful information and resources about solar.

In all, solar is a tremendous primary power source for remote applications. When sized and installed properly, your systems will give you years of reliable performance. Best of all you are helping the environment by utilizing a renewable and cost-effective energy resource.

Todd Bermont is a Vice President of Sales for Solarcraft (www.solarcraft.net). He can be reached via phone at (877) 340-1224 or via email at tbermont@solarcraft.net.