The One-Mile Rule establishes that if an electricity generation facility uses the same kind of generation (e.g. wind, solar, natural gas) and has the same ownership as another facility within one mile, then those generators are considered the same facility. If their aggregate generation exceeds 80 MW then it is too big to be a Qualifying Facility (QF) under the Public Utilities Regulatory Act (PURPA) of 1978 which governs small power producers and co-generation facilities.
Some Minnesota utilities have misread or misapplied this rule to groups of solar installations with the same ownership on the same site. In doing so, they have attempted to deny net-metering contracts to one or more of those installations. MnSEIA has been presented with situations where the utility misinterprets the One-Mile Rule to read that the combined solar installations cannot exceed 40 kW. This misreads both the purpose of the One-Mile Rule and its appropriate context, which is on the transmission side of substations.
For a more detailed legal analysis, please see the MnSEIA Legal Memo on the subject. Feel free to show that memo to a utility that seeks to misapply the One-Mile Rule to net-metered solar installations.