Guide for Array and Battery Sizing in Stand-Alone Photovoltaic Systems
IEEE 1562 is a guide published by the Institute of Electrical and Electronics Engineers (IEEE) that provides recommendations for sizing both the PV array and the battery storage in stand-alone (off-grid) photovoltaic power systems. The guide addresses the interdependence of array and battery sizing, recognising that both must be co-optimised to ensure reliable power supply across seasonal solar resource variation.
Published by: Institute of Electrical and Electronics Engineers (IEEE)
Current edition: IEEE 1562-2007
Related standards: IEEE 1661 (lead-acid battery test in PV hybrid systems), IEEE 485 (lead-acid battery sizing)
Scope
IEEE 1562 applies to stand-alone PV systems using lead-acid batteries (vented or VRLA) as the primary energy storage medium. It covers residential, commercial, telecommunications, and remote monitoring applications where grid connection is unavailable or impractical. The guide provides a systematic design method rather than a prescriptive standard.
Sizing Methodology
Load Assessment
The design process begins with a thorough assessment of daily and seasonal electrical loads, expressed as watt-hours per day. Load profiles must account for seasonal variation where applicable (e.g., lighting loads higher in winter). A load uncertainty margin is typically added to ensure reliable supply under worst-case conditions.
Battery Sizing
Battery capacity is sized to provide the required number of days of autonomy — the period during which loads can be met without solar input. The days-of-autonomy figure depends on the criticality of the load and the local climate (more overcast regions require more autonomy). Maximum depth of discharge limits for lead-acid (typically 50–80%) are factored into the gross capacity calculation.
Array Sizing
The PV array is sized to replenish battery energy over the worst-case solar month (lowest insolation period of the year at the installation location). Array output must cover daily load plus battery charging losses, with the calculation based on peak sun hours at the site using standard insolation data.
System Optimisation
Array and battery sizing are iterated together to balance cost, reliability, and battery longevity. Over-sizing the array reduces battery depth of discharge and improves cycle life; under-sizing creates chronic undercharge which damages lead-acid batteries. The guide discusses the trade-offs and recommends iterative optimisation.
Disclaimer: This is not a definitive guide, just an indication and it is important that you always go back to the source for legislation.