Boston Grid Headroom

Feeder headroom. National Grid publishes, for each three-phase feeder in its Massachusetts territory, the summer rating, the 2025 peak, the peak plus load already in its connection queue, and forecasts to 2030 and 2035 (MVA). Headroom here is the summer rating less the peak plus queued load. It is a distribution-level signal: a large campus needs a transmission connection, which these figures do not describe.

Ranking. DC sites within 3 km of each other form a cluster. Clusters are ranked by the total headroom of National Grid feeders within 5 km. Where the nearest feeder is more than 2 km away, usually because the cluster is in Eversource territory, the card marks the feeder figures as an estimate.

Substations. Each National Grid distribution substation with feeders in the heat map is ranked by the summed headroom of its own feeders. It is located from National Grid's substation layer by ID, then by name; where neither matches, it is placed where most of its feeders start and marked approximate.

Grid. High-voltage substations (69 kV and above) and lines (115 kV and above) come from OpenStreetMap, which is volunteer-mapped and incomplete. National Grid's own substation layer gives locations but no capacity.

Land use. Each DC site is checked against the MassGIS standardised parcel layer (assessor use code and lot size) and the 2016 land cover and use layer. Owner and valuation fields are never requested. Massachusetts zoning is set town by town and is not published as one statewide layer, so the assessor class is the closest statewide signal.

Flood. Each DC site is checked against FEMA's National Flood Hazard Layer (the Esri Living Atlas copy, since FEMA's own service was unreachable). The card shows the flood zone and, inside the special flood hazard area, the base flood elevation: the level of the 1%-annual-chance flood, in feet above the NAVD88 datum. NOAA sea-level-rise layers were tested and left out because they could not be read reliably at a point.

Candidate sites. Every commercial and industrial parcel of an acre or more in Massachusetts (41,000 of them, from MassGIS assessor data) is scored against the grid. Size bands are ranked differently because they connect differently: a 1–5 MW site can take one feeder, so it is ranked on the best single feeder within 1 km; 5–20 MW needs several feeders and a substation nearby; 20 MW and above is ranked on total headroom within 5 km with a high-voltage substation within 5 km. No more than three parcels per feeder are listed, so one strong feeder does not fill the table. Assessor owner names are never fetched.

Demand forecast. ISO New England's yearly CELT report gives a 90/10 peak forecast per load zone, ten years ahead, for summer and winter. Boston is the NEMA zone. The figures are zone-wide peaks, not what any one substation can deliver. ISO-NE publishes no map of the zone, so the outline on the map is our approximation from Suffolk, Essex, Middlesex and Norfolk counties.

Interconnection queue. ISO New England's public queue lists generation, storage and transmission requests, not data center loads, which connect through the utilities. The page shows active Massachusetts requests and, per county, the active generation and storage MW; offshore wind has no county. Most queued projects never connect, so this indicates competition for grid capacity, not what will be built.

What is missing. Transmission limits (held by ISO New England as critical infrastructure information), data center loads in the ISO-NE queue (large loads connect through the utilities), and Eversource headroom for Boston proper. These are tracked as requests.