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  • Rob Rallo

Did you know there were industry standards for sizing off-grid solar systems?

Updated: Apr 14, 2020

Nowadays there seems to be a standard for almost everything, and the same holds true for solar. There are actually several industry standards for solar, that vary from components (e.g. solar modules) to system design (e.g. stand-alone solar, hybrid design). I'd like to focus on a couple: IEEE 1561 "Guide for Optimizing the Performance and Life of Lead-Acid Batteries in Remote Hybrid Power Systems" and IEEE 1562 "Guide for Array and Battery Sizing in Stand-Alone Photovoltaic (PV) Systems". I have been involved in writing and developing both standards.

IEEE 1561 is focused on optimizing hybrid systems, where you have at least one renewable energy source (e.g. solar, wind, microhydro, etc.) and at least one on-demand energy source (e.g. generator, fuel cell, Thermal Electric Generator [TEG], etc.) The standard has been written to maximize the energy from the renewable source, while extending the life of the battery, and optimizing the fossil fuel source. The battery can be one of the these most expensive components in an off-grid system, by using a 1-3 day battery autonomy and minimizing the daily depth of discharge the battery life can be extended. Further the on-demand energy source can insure the battery is properly charged. The renewable energy source then reduces the amount of fossil fuel that needs to be consumed by the on-demand energy source, minimizing maintenance and extending refueling requirements. Hybrid systems are a great option in areas with poor sunlight conditions or variable loads. Solar System Services has a simulation tool that can help to optimize your off-grid hybrid system.

IEEE 1562 is focused on properly sizing stand-alone off-grid solar systems. When the sun is your only source of energy, properly predicting the system performance is critical to the availability and reliability of the system. The standard recommends a minimum of 5 days of battery autonomy and an Array to Load Ratio (ALR) of 1.1. The array to load ratio, is the ratio of energy produced daily from the solar array verses the amount of energy consumed daily by the load. Several commercially available programs are available for running simulations, or a worksheet is included in the standard for doing manual calculations.

Contact Solar System Services for help in sizing your off-grid system.

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