Who the Grid Is Built For

Prologue · 1822 – 1920

Power on the waterfront

Boston's first energy plants stood on land made from the harbor, where coal arrived by ship.

The lens shows the 1867 fire-insurance atlas over today's aerial photo. Move it with your cursor. Drag the map to explore; use the slider to change the atlas year.

This is the North End gas works, the city's first energy plant. Its gasholder stood here from 1828 until the works moved to Commercial Point.

Sites and method from Genna Kane, "Making Power, Making Land" (Leventhal Map & Education Center, 2025).

Prologue · L Street, South Boston

L Street Station, 1898. Built on filled flats by the Boston Electric Light Company, bought by Edison, and run for six decades.

Prologue · Sargent's Wharf

Sargent's Wharf, 1895: ferry slips and a coal shed. Next door, a cold-storage warehouse would soon build a power plant of its own.

Prologue · Lincoln Wharf

Lincoln Wharf, 1898. The atlas records the ground itself: dock, piles, solid fill. The power station that rose here in 1901 ran until 1972.

Chapter 1 · 1886 – 1900 · The first customer: lighting

The grid begins with lamps

On 20 February 1886 the Edison Electric Illuminating Company lit its first customer, the Bijou Theatre: 800 lamps from one engine. Demand came in the evening, when the lights went on.

The state counted the new system the only way it knew how. Until about 1910 the regulator reported electric companies in lamps, not kilowatts.

Chapter 2 · 1889 – 1901 · The first big customer: streetcars

A customer big enough to build its own plant

The streetcar system needed more power than any lighting company could sell it. So it built its own stations. This is the Central Power Station on Harrison Avenue, the largest in the city.

Look at the label on the 1902 atlas: Boston Elevated Railway Company (Lessee), printed over West End St. Railway Co. The biggest plant in Boston was rented.

Chapter 2 · Quincy Market Cold Storage, 1906

Boston was unusual. In 1910 its Edison company sold only 4.5% of its output to street railways. In Hyde Park the figure was 83%. Here, the traction company was its own utility.

Even a warehouse could do it. The Quincy Market Cold Storage company built a power house of its own at Sargent's Wharf. Remember this site.

Chapter 3 · 1910 – 1940 · Motors, then appliances

The grid learns to grow demand

Between 1910 and 1920, motors overtook lamps. The appliance era began on a grid that industry had already rebuilt around all-day load.

The rates were not written to reward size. They were written to reward buying a machine. A household that lit its rooms paid a flat 10½ cents a kilowatt-hour, and the schedule said plainly: no free wiring. The same household, having bought a range, a water heater or a refrigerator, dropped to 2 cents on everything above ten kilowatt-hours a month — a fifth of the price, on one condition, which was not how much it used but what it used the electricity for.

This is the thing worth holding on to. A volume discount rewards consumption you already have. An end-use rate manufactures consumption you do not: it pays for itself only once you own the appliance, so the appliance is what the price is really selling.

And the Commonwealth had already built the bookkeeping for it. The Department’s own Uniform System of Accounts, prescribed in 1922, requires every electric company to keep an account for canvassers, solicitors and demonstrators, one for “newspaper advertisements, booklets, posters, dodgers”, and one — E665, “Wiring and Appliances” — for the cost of wiring customers’ homes and appliances “furnished without charge to the consumer for the purpose of securing new business.” There are matching accounts for selling appliances and for renting them out.

Massachusetts wrote the ledger lines for demand creation before it ever had to rule on it. Load-building was not a deviation from the regulated utility here. It was a chart-of-accounts category.

Chapter 4 · 1950s – 1990s · Air conditioning

The day the grid is sized for moves to July

For most of the twentieth century, New England's biggest hour of demand came on a winter evening. Around 1990, a July afternoon overtook it — and stayed ahead.

The chart shows every year we could verify. The crossing was narrow: in 1993 the two seasons were 36 megawatts apart, two tenths of one percent. Boston got there earlier. By 1986 the city's summer peak was already 12% above its winter peak.

It arrived unevenly, and the unevenness is the point. In 1960 6.2% of homes in Boston’s suburban ring had air conditioning against 3.9% in the city. By 1980 the metropolitan figure was 42.7% and the city’s 30.5%. The ring was ahead at every census — and the ring is where the wires had the most room. Massachusetts also never ducted itself: central air reached 0.5% of homes in 1960 and 5.1% by 1980, so the cooling load arrived as window units, plugged in one at a time, on circuits nobody re-sized to receive them. Each pair compares places in the same census; the 1960 figures count occupied units and the 1980 figures year-round units, so read the ring-against-city gap rather than the climb between them.

Chapter 5 · 1960s – 2014 · Gas heat

The second network under the street

Heating went to gas. Under Boston runs a second grid: 1,513 miles of cast-iron main and 580 miles of bare steel — more leak-prone pipe than every other Massachusetts gas company combined.

The map shows reported gas leaks per square kilometer by census tract. Switch to see where pipe is being replaced.

The wires today · 1 of 3

How electricity reaches Boston

No power plant remains inside the city. Electricity arrives on high-voltage transmission lines — … of them at 345,000 volts, … at 115,000 — and steps down at … substations across Suffolk and Middlesex counties.

Thick lines are 345 kV, thin lines 115 kV. Dots are substations. Hover either.

The wires today · 2 of 3

The neighborhood wires

From each substation, feeders run beneath and along the streets at 13,800 volts — … circuits on this map — or on the older 4,000-volt network that still serves parts of the city, … circuits. A transformer on a pole or a pad drops each feeder to the 120 and 240 volts at your meter.

Everything in the rest of this story — the data center, the charger, the solar roof, the heat pump — plugs into one of these lines.

This is Eversource's own map of its distribution feeders. Hover any line for its circuit number, substation and voltage.

The wires today · 3 of 3

The one number the utility publishes about each line

For every feeder, Eversource publishes how much new solar it could accept — its hosting capacity. … of … feeders have room for a megawatt or more; … have less than a tenth of that.

It publishes nothing about how much new load — chargers, heat pumps, computers — each feeder can take. That is the number the rest of this story keeps asking for.

Switch between voltage, room for solar, and the feeders that serve the downtown secondary network — the densest part of the grid, where the data centers sit. Then press Room for load. Same lines, same map, and the fourth one is blank: that figure is published for none of the … circuits.

Chapter 6 · 1997 – 2010s · Data centers, first wave

Generation leaves the city. A flat load arrives.

In 1998 Boston Edison sold its power plants — 1,987 megawatts, Mystic and New Boston among them. Since then the big Boston-area plants have closed one by one. The last of Mystic shut in 2024.

The new customer ran flat, all day, every day. Massachusetts has … listed colocation buildings; … of them sit inside this map, and two are carrier hotels shared by more than one operator — 1 Summer Street, where Markley and DataBank both sit, and 70 Inner Belt Road in Somerville, shared by CoreSite and FirstLight.

They did not scatter. … of the facilities on this map draw from feeders supplied by one substation: Mystic — which carries the name of the generating station that closed in 2024. The plant left; its substation stayed; the new load plugged into it.

Blue lines are the feeders that serve the downtown network. Gold rings mark buildings with more than one operator. Hover a data center for its operators, feeder and supply substation.

The data centres · 1 of 2 · Who they are

Twenty-seven facilities, twenty-five buildings

Massachusetts has … listed colocation buildings in the Boston market, holding … separately operated facilities. … of the buildings are inside this map. They are not hyperscale campuses; they are floors and suites inside older commercial buildings, run by carriers and colocation landlords.

The map is 2023 aerial photography. Click any dot — or any building below — to fly in over its roof and read its operators, size, tier, certifications and feeder.

The data centres · 2 of 2 · What they will not tell you

The load is the one number nobody publishes

Of the … buildings, … publish how much power they draw. Inside this map, exactly … does.

… publish a floor area, and most advertise their tier rating, their fibre carriers and their audit certifications in detail. Electricity — the thing that decides whether the feeder outside can carry them — is absent.

The four facilities in eastern Massachusetts that do publish a figure add up to … megawatts, and every one of them is outside Boston: Needham, Bedford, Northborough, Medford. (A fifth, the university consortium in Holyoke, publishes 10 MW and is across the state.) The downtown carrier hotel that anchors New England's fibre publishes its tenant count and its carrier count, and no megawatts at all.

Chapter 7 · 2010s · Solar

Loads that run backward

Now the customer's equipment feeds the grid, or is paid to hold back. Boston has 4,466 solar installations, and a household battery enrolled in ConnectedSolutions is paid $275 per kilowatt each summer to discharge when the grid asks.

Massachusetts records every installation by ZIP code, not by address. The largest concentration is ZIP …, with … systems.

Each circle is a ZIP code, sized by its number of installations. Hover for the split between houses, multifamily buildings and commercial roofs.

Chapter 7 · 2010s – 2020s · EV charging

Chargers arrive on the curb

By April 2023 Boston had … public charging stations with … Level-2 and … fast ports — … of them opened in 2021 alone. The city's own program adds … sites: … ports installed, … planned, … of the sites at the curb, and … curbside segments scored for the next round.

Blue dots are public chargers, sized by ports. Dark dots are the city's own sites. The tint is a ten-minute walk from an existing charger. Toggle the scored candidate segments.

Chapter 7 · The connection

Every charger plugs into a feeder

Each dot is a charger, coloured by the feeder it sits on. … of the … public chargers are on feeders that also serve the downtown network; the rest spread across the territories of … substations. … sit on feeders with almost no published room for solar — which says nothing about room for a charger, because that number is not published.

Each charger is matched to its nearest feeder from the map geometry — our computation, not the utility's. Hover a charger for its feeder and substation.

Chapter 8 · 2020s · Heat pumps

Heat moves onto the wires

Heat pumps put winter heating on the electric grid. ISO New England expects the winter peak to overtake summer again around 2036.

The transformers sized for July in chapter 4 will be the wrong size. Massachusetts publishes no map of where the wires have room for new load; the utility's public map shows where solar can connect, not where heat can.

Behind the chart, the feeders are coloured by their published room for solar. Toggle the forecast between ISO New England's central and high cases.

Chapter 9 · 2026 · Compute, now

The next customer is small, and it's on your wall

The data-center boom is going around New England. ISO New England's 2026 forecast counts about 110 megawatts of large new loads across all six states in the 2030s — and only one data center, a 200-megawatt project in the Boston zone, which it discounts by 70% as "speculative."

What comes instead is small: compute in homes, on the feeders with room. The first such home was connected in 2026. Nobody publishes how much power one node draws.

The map shows household energy burden — the share of income spent on energy — by census tract. The ghost marker is the 1906 cold-storage power house from chapter 2: a private load big enough to want its own plant.