A eutectic plate is a sealed, rigid panel filled with a eutectic solution, usually water mixed with salts or other solutes, and mounted to the ceiling or walls of a delivery vehicle or a display cabinet. The plate is frozen solid overnight, then carried through a working shift without any power running on board. As the sealed solution melts, it draws heat out of the air around it and holds close to a fixed temperature until the last of the charge has thawed.
The format is built for the last mile: small refrigerated vans doing multi-drop rounds, and static chilled display units in shops, where a quiet, engine-free cold source matters more than raw cooling power. A cabinet on a shop floor with a plate hidden behind its panels stays silent for customers and staff, at the cost of needing a recharge cycle rather than continuous power the way a plugged-in compressor gets.
The eutectic point and a flat melt
A eutectic mixture is formulated so it freezes and melts at one specific temperature, its eutectic point, rather than over a range the way plain water or a loose mix of ice and salt does. That gives the plate a flat melt: it absorbs heat steadily while changing from solid to liquid, and the temperature it presents to the air around it barely moves until the solid fraction is gone. A gel pack conditioned in a home freezer behaves less predictably; a plate built around a eutectic solution is engineered to sit at one number for as long as any of its charge remains frozen.
The solution itself is chosen for the job. A different mix of salts and water shifts the eutectic point up or down, so a plate built for a cabinet holding a few degrees above freezing uses a different formulation from one built to sit closer to 0°C. The plate itself is sealed for the life of the unit; the solution inside does not wear out or lose capacity the way a rechargeable battery does, so the same panel goes through years of nightly freeze-and-thaw cycles without needing to be replaced.
Charging overnight, discharging through the round
Plates are charged by connecting them to a compressor plant at the depot, or by loading them into a blast freezer, and typically need somewhere around eight to ten hours to freeze solid. Once charged, they go into the vehicle or cabinet at the start of the shift and are left alone. There is nothing to switch on and nothing to refuel; the cold comes from the plate itself, releasing steadily as it thaws over the hours the round takes.
Quiet running for the last mile
This is the case for choosing plates over a powered unit. No diesel transport refrigeration unit runs or idles during stops, which matters on early-morning or residential rounds where engine noise is restricted or simply unwelcome outside someone's front door. There is nothing mechanical on board beyond the plates themselves, so there is less to maintain and no fuel burned on the route.
The thermal mass of a plate also buffers a multi-drop round better than a blown-air unit does. Every door opening lets warm air in and a powered unit has to work to recover; a plate simply keeps releasing cold at close to its fixed point, unaffected by how many times the doors have opened that morning. Route planners size a eutectic round around this ceiling: the plate's charge, not the driver's hours, sets how long the vehicle can stay out before it has to head back.
The one-shift limit
A plate is sized for one working day. It cannot be recharged on the road, so a round that runs long, or a vehicle rerouted onto a second shift, risks drifting out of band well before it gets back to the depot. Deep-frozen loads at the coldest end are also a poor fit: a plate cold enough to hold that band needs a larger charge and a longer freeze than most eutectic fleets are built around, which is why most eutectic vehicles run a chilled band rather than a deep-frozen one.
There is also no way to add capacity mid-shift. A powered unit running low can sometimes take on fuel or a fresh battery at a stop; a eutectic plate that has fully melted has nothing left to give until it goes back to the depot for a fresh freeze.
Set beside a powered fleet
Eutectic plates belong to local and regional delivery: bakeries, dairies, chilled grocery rounds and catering supply, where the vehicle returns to its own depot every night. That is a different job from refrigerated road transport, where an active mechanical unit holds a fixed band across days on the road rather than a single shift. The overnight charge itself usually comes from a depot's cold room or cold store, which is where the plates spend the hours between one round and the next.