Understanding your footprint comparison
Why footprint and weight don't always track together
A chemistry can be relatively light but still take up meaningful floor space if its packaging is bulky, or heavy but compact if it's dense and well-packed. Check both the weight comparison and this footprint tool together, since either one alone can miss a real installation constraint, a combination the off-grid system weight and portability calculator treats as a single factor when space and weight both matter, such as in a van or trailer build.
Why flow batteries dominate the size comparison
A flow battery's energy lives in liquid electrolyte tanks rather than compact solid electrodes, which is the direct tradeoff for the near-unlimited cycle life and minimal self-discharge covered in the flow battery vs lithium comparison. Improving that volumetric density is an active area of NREL's energy storage research, but for now that footprint difference is usually the first thing that rules flow batteries out for residential installs regardless of the cost math.
Why the enclosure shape matters, not just the volume
Two batteries with identical total volume can have very different floor footprints depending on whether they're tall and narrow or short and wide, which is why this estimate factors in a representative enclosure height for each chemistry rather than just raw volume. Actual products vary, so treat this as a planning range rather than an exact figure, and remember that the clearance and spacing requirements around the finished installation are set separately by NFPA 855, Standard for the Installation of Stationary Energy Storage Systems.
What to check next
Once you've narrowed down chemistries by footprint, the energy density comparison covers the same tradeoff from the weight side, and the rack sizing calculator helps plan the actual physical layout for a multi-module system. The battery storage size calculator works the same problem from a target capacity down to how many physical units that actually means.