You asked
Islanded, behind-the-meter, off-grid — are those the same?
Three different facts people collapse into one word
Behind-the-meter is a commercial boundary, islanded is the absence of a synchronous grid tie, and off-grid is the absence of any utility connection — a plant can be two of three, or all three, and the protection design only changes when islanded is true.
Islanded, behind-the-meter, off-grid — are those the same?
Behind-the-meter is a commercial boundary, islanded is the absence of a synchronous grid tie, and off-grid is the absence of any utility connection — a plant can be two of three, or all three, and the protection design only changes when islanded is true.
A boundary is not a physics fact
Where the meter sits and who pays the tariff is a commercial and contractual boundary, not a statement about how frequency is controlled.
You asked: “Islanded, behind-the-meter, off-grid — are those the same?” Behind-the-meter means the generators sit electrically inside the customer's service boundary. Power does not cross a utility transmission tariff to reach the load. That fact changes billing and often interconnection paperwork. It does not, by itself, say whether the machines are synchronized to a regional grid.
Behind-the-meter
Inside the customer's electrical boundary
Utility-side
Delivers through a utility tariff
Commercial boundary and synchronous tie are independent axes.
Islanded means no synchronous tie
An islanded plant has no live synchronous connection to the regional grid; the machines on site are the grid for their load.
Islanded operation means there is no infinite bus to absorb frequency error, contribute fault current, or supply inertia. Frequency is the real-time balance of mechanical power in versus electrical power out on the machines that are online. Protective relaying, black start, and load steps all change when this is true.
Frequency
Held only by machines on site
Fault current
Only what the generators still produce — and it decays
Inertia
Only rotating mass on the island
Voltage support
Excitation and plant reactive resources only
No external bus to lean on.
Off-grid is physical isolation
Off-grid means no physical utility connection at all; it is neither required for islanded operation nor implied by behind-the-meter.
A plant can be behind-the-meter and still synchronized to the utility. A plant can be islanded while a utility line still exists for other purposes or for a future tie. Off-grid is the stronger claim: no physical path to the utility. Collapsing all three words into one slogan is how protection philosophy gets copied from the wrong book.
- Behind-the-meter
- Islanded
- Off-grid
Behind-the-meter
does not imply
Islanded
Islanded
does not imply
Off-grid
Behind-the-meter
does not imply
Off-grid
Independent facts. Check each on the one-line and the contract.
Where the picture breaks
Relays that never pick up on island faults, or frequency collapses on load steps that a grid-tied plant would ignore.
In the field
Electrical one-line, interconnection agreement, and plant mode descriptions in the controls narrative. One-line revision that shows presence or absence of a utility tie; protection study basis statement. Copying grid-connected protection settings onto an islanded plant because the slide said behind-the-meter.