Short answer: yes, a solar deep freezer can be connected to the grid, but the cabinet itself never touches the grid. It is a DC appliance, and the label says so: 12 V and 24 V input, 77 W, 6.5 A at 12 V. The grid connection happens upstream, through a battery charger, an AC to DC supply, or a hybrid inverter. Get that box right and the cabinet neither knows nor cares where the electricity came from.
The question keeps coming up because the same words mean three different things. A shop owner may be asking whether the freezer keeps running when the sun is gone, whether surplus power can be sold back, or whether the battery can be dropped from the budget. Each has a different answer and a different price, and mixing them up is how people end up with an inverter that trips every time the compressor starts.
Start with the nameplate, not with the inverter
Every cabinet we build carries a plate with the model, the power source, the rated input, the current, the refrigerant charge and a printed circuit diagram. Read it before designing anything, because the plate describes the shape of the problem.
Nameplate of a 258 L DC cabinet: model BD/BC-258, rated input 77 W, power source 12 V and 24 V, rated current 6.5 A and 3.3 A, R134a 165 g, climate class T, CE mark, and the internal circuit diagram on the right half of the plate.
Three lines on that plate matter more than the rest. Power source 12 V and 24 V means the cabinet expects a battery bus, not a wall socket, so any grid connection has to produce that bus voltage. Rated current 6.5 A at 12 V is the running figure; the compressor start is several times higher for about a second, and every supply in the chain has to survive that second. Electric heat protection class III means the cabinet is safe because it runs on extra low voltage, which is why the supply, and not the cabinet, has to carry the earthing and the isolation.
Three ways to put a DC freezer on the grid
| Topology | What you add | How it behaves | Where it fits | What to watch |
|---|---|---|---|---|
| Grid as a charger | An AC to DC power supply or an inverter charger feeding the battery; cabinet unchanged | The battery stays in the middle. Grid tops it up at night, the array tops it up by day, and the cabinet always sees a stable DC bus | Retrofit into an existing solar freezer, and shops with a grid that exists but cannot be trusted | Buy a charger with proper three stage charging. A fixed 13.8 V supply will cook a lead acid battery |
| Hybrid inverter | One unit with PV input, battery terminals, grid input and an output | The inverter picks the source automatically: solar first, battery second, grid last. Transfer is fast enough that the compressor does not notice | New installations where the freezer is one load among several, and where a generator may be added later | Confirm the output is the cabinet voltage, not 230 V. Many hybrids output mains only, which forces another converter into the chain |
| Grid tie, no battery | A grid tie inverter on the array, plus a mains voltage cabinet or a DC supply | Surplus goes to the meter and is credited. The cabinet runs from the grid at night, and stops when the grid fails because of anti islanding protection | Cold storage with a stable grid and a tariff that pays for export | This is not a backup system. A freezer full of product on a grid tie system spoils in the first long outage |
For most enquiries we get from Africa, South Asia and the Pacific, the first topology wins. It keeps the cabinet the customer already owns, it keeps the battery that already works, and the only new component is a charger sized on the cabinet current. The second is what we recommend for a new shop build, because one box replaces three and the transfer logic has been tested by the manufacturer rather than assembled on site.
Side panel of a 110 mm cabinet: fused power inlet, controller and digital display on one plate. On a grid connected job this is where the DC feed terminates, and where an installer can measure the bus voltage without opening the refrigeration compartment.
The wiring checks that decide whether it works
The failures we see in the field are almost never mysterious. They are the same six mistakes, usually in the same order.
- Confirm the input voltage, and whether the controller detects 12 or 24 V by itself. A cabinet set to 24 V on a 12 V bus will not start, and it looks exactly like a dead compressor.
- Size the supply on surge, not on average. 77 W running is a small load. The same compressor starting is several times that for a second, so an undersized supply trips, the cabinet restarts, and the food warms while it hunts.
- Fuse at the battery, not at the cabinet. A short in the run between them is the one that starts a fire, and a fuse at the far end will not see it.
- Use 4 mm² or larger for runs over 4 m at 12 V. At 6.5 A, a 10 m loop of 2.5 mm² drops 0.46 V, which is 3.8 percent of the supply, and it shows up as a low voltage cut-out at dusk.
- Earth the supply enclosure, and keep AC and DC in separate conduit. Class III protection covers the cabinet, not the box that feeds it.
- Test the transfer before you leave. Pull the AC feed with the cabinet running and watch the compressor: it should continue on battery without a stall, and the controller should show the bus voltage recovering within a few seconds.
What the grid gives you, and what it does not
What it gives you is a floor under the battery. A week of rain stops being a spoilage event, and the battery bank can be sized for one night instead of three. Where net metering exists, the surplus the freezer does not use is credited instead of wasted, and in a shop with a daytime cooling load that credit is real money.
What it does not give you is an AC freezer. The cabinet still runs on 12 or 24 V, so the converter stays in the chain and its losses stay in the budget, a few percent typically. It also does not remove the battery if you want the freezer to survive an outage, and it does not remove the permit, the meter or the inspection. In some markets the connection fee is larger than the array, and that is the point at which we tell a customer to stay off grid.
Cabinets waiting for packing beside the panels that will run them. On a grid connected job the same array feeds the battery bus, and the grid covers only what array and battery cannot.
Sizing the array and the battery when the grid is in the picture
The grid changes the battery, not the array. The array still has to replace the daily consumption with a margin; the battery only has to carry the night, because the grid covers the rest. Using 12 V, four peak sun hours a day, a 30 percent recharge margin for the array and 50 percent depth of discharge for the battery, the numbers come out like this.
| Daily consumption | Night share at 12 V | Battery at 50 percent depth | Array at 4 peak sun hours | Role of the grid |
|---|---|---|---|---|
| 1.2 kWh, a 258 L cabinet at rating | 50 Ah | 100 Ah | about 390 W | Charger only, on consecutive poor days |
| 1.8 kWh, hot room with daily openings | 75 Ah | 150 Ah | about 585 W | Charger on poor days, and the evening peak |
| 2.4 kWh, two cabinets or heavy traffic | 100 Ah | 200 Ah | about 780 W | Charger most nights, and the only source in a long outage |
That table is planning arithmetic, not a quotation. The real array depends on latitude, tilt, shading and how much of the load runs in daylight, and the real battery depends on chemistry: a lithium pack can be taken deeper, a lead acid pack should not be. Send us the consumption figure you expect and we will run the same arithmetic on your numbers.
When we advise against the connection
- The site has no meter and the nearest line is a kilometre away. The connection cost buys a much larger array and battery, and the array sends no monthly bill.
- The grid fails every day. A connection is worth its cost only if it is present when you need it. Where the supply is a four hour window, treat it as a charger and size the battery for that.
- The permit takes longer than the season. A cold storage business that opens before the inspection is signed does not need the inspection to be signed first.
What we build, and what we can tell you about your site
110 mm cabinets on the assembly floor with the lids open for foam and liner inspection, before the refrigeration circuit is charged.
- 65 mm single door, 12/24 V, the counter cabinet that is often the first unit on a hybrid inverter.
- 85 mm single door, 208 L class, the volume most households and small retailers actually need.
- 110 mm double door, 358 L class, the cabinet we recommend when ambient is high and the grid is unreliable.
- 110 mm double door, 408 L class, for volume storage with the cabinet running near full.
About the manufacturer
JUKA is Zhejiang Juka Solar Technology Co., Ltd., a solar refrigeration factory in Hangzhou, Zhejiang. Sheet metal, foaming, refrigeration assembly and final testing all happen in our own plant, under an ISO 9001 quality system and an ISO 14001 environmental system. The chest freezer and upright cooler ranges carry CE certificates E24031861 and E24031881, and the company holds 2 invention patents and 17 utility model patents. OEM, CKD and SKD orders are supported.
Contact us for purchase and negotiation
Send us the volume you need, the ambient you work in and how the cabinet will be powered, and we will tell you which cabinet and which supply fits, instead of selling you the bigger one.