Short answer: a solar refrigerator uses the same four-part vapour-compression loop as a grid refrigerator - compressor, condenser, expansion device, evaporator. What makes it solar is everything around that loop: a DC compressor that runs on 12 V or 24 V, a controller that accepts a swinging panel voltage, and a cabinet whose insulation and thermostat are set for an intermittent power supply.
The loop itself has not changed in a century. What changed is where the electricity comes from, and that single change pushes the whole design: the compressor becomes a DC brushless unit, the condenser has to shed heat with a small fan instead of a big one, and the door seal stops being a detail and becomes the part that decides whether the battery lasts the night.
The loop, in four steps
- Compressor. It draws low-pressure refrigerant vapour from the evaporator and squeezes it into a high-pressure, high-temperature gas. On a solar cabinet this is a DC brushless compressor, driven by an inverter board in the compressor compartment rather than by a mains motor.
- Condenser. The hot gas passes through the coil on the back or the side of the cabinet and gives its heat to the room. The refrigerant condenses into a high-pressure liquid. This is the part of the system that a hot room fights against, which is why condenser airflow matters more than the compressor brand.
- Expansion device. A capillary tube or a valve drops the pressure. The liquid flashes into a cold low-pressure mixture and the cycle turns around.
- Evaporator. The cold mixture absorbs heat from the food compartment and boils back into a gas, and the compressor pulls it in again. On most of our cabinets the evaporator is bonded to or wrapped around the liner, and a small fan moves the cold air across the shelves.
Back of a DC refrigerator: condenser coil across the full width, fan behind it, terminal box at the bottom. Airflow past this coil decides how hard the compressor has to work.
Why a solar refrigerator uses a DC compressor instead of an inverter
The obvious alternative - a normal AC refrigerator plus a solar inverter - loses energy at every step. The panel makes DC, the inverter turns it into AC, the refrigerator turns it back into DC for its own motor, and each conversion costs a few percent. A DC cabinet deletes both conversions: the panel or the battery feeds the compressor driver directly, and the driver modulates compressor speed to match the load.
That is why a 90 litre DC refrigerator can hold temperature on roughly 200 W of panel in good sun, while the same cabinet behind an inverter needs a noticeably larger array and a bigger battery for the same duty. The saving is not in the refrigerant; it is in the number of times the electricity changes shape before it reaches the motor.
DC compressor in the open: the dome is the compressor, the copper lines are suction and discharge, and the small plate carries the model and the refrigerant charge.
Where the heat actually goes
Every watt the compressor consumes ends up in the room as heat, plus every watt that leaks in through the walls. A refrigerator is therefore a machine for moving heat from a box you care about to a room you do not, and the whole energy budget is decided by three numbers: the temperature difference between the box and the room, the surface area of the box, and the insulation between them.
In practice the third number is the one you can buy. Foam thickness and foam density do more for daily consumption than a more expensive compressor, because they cut the heat that has to be removed in the first place. That is the reason our chest freezers moved from 65 mm to 110 mm walls, and the reason a household refrigerator with a well foamed cabinet can hold -18 °C on a modest array.
Compressor and DC driver on the inspection bench. The black box on the right is the driver that turns battery voltage into the three phases the brushless motor needs.
Read the nameplate before you read the brochure
A DC refrigerator has to declare its whole electrical identity on the label, because it has no socket to hide behind. The plate on the back of our BCD-198 is a good example of what to look for:
| Nameplate line | Reading on a BCD-198 | Why it decides your system |
|---|---|---|
| Rated power input | 83 W | The compressor load your panel and battery have to carry, not the volume of the box |
| Power source | 12 V / 24 V DC | Two battery banks, one cabinet; the driver accepts either without a jumper |
| Foaming current | 6.9 A at 12 V / 3.45 A at 24 V | The start-up and pull-down current, which is what sizes the cable and the fuse |
| Refrigerant | R134a, 140 g | A small charge, so a leak is a service job rather than a scrapped cabinet |
| Climate class | N / ST | The ambient range the cabinet is rated for; ST is the one to look for in a hot room |
| Total storage volume | 198 L | Declared volume, useful when comparing cabinets at the same wall thickness |
The nameplate and circuit diagram on the back of a DC refrigerator. 83 W input, 12/24 V supply, 6.9 A foaming current at 12 V: these are the numbers a solar system is built around.
What the cooling system buys you, and what it costs you
- Low running energy. A DC compressor at part speed moves the same heat for less input than an AC compressor cycling on and off, because it avoids the start-up surge and runs at the pressure the load actually needs.
- Independence from the grid. With a panel and a battery the cabinet keeps working through an outage, and in off-grid sites it is the only option that does not burn fuel.
- Fewer parts to fail. There is no inverter, no mains transformer and no separate charge controller in the cabinet: the driver board does the whole job, which removes a box and a set of connections.
- The cost of all this is that the cabinet is tied to a DC supply. Buy the wrong panel voltage window or a battery that cannot deliver the start current, and a perfectly good refrigerator will not pull down. The cooling system is not fragile; the supply around it is what gets chosen badly.
Five faults we see on solar refrigerators, and their real cause
| Symptom | What is usually wrong | What to check first |
|---|---|---|
| Box runs but never reaches temperature | Panel or battery cannot carry the pull-down, so the compressor never gets ahead of the heat load | Measure voltage at the compressor driver, not at the battery; long thin DC cable drops more than people expect |
| Compressor starts, then stops after a few seconds | Supply voltage collapses on start-up, or the battery is below the driver cut-off | Check battery state of charge and cable cross-section against the foaming current on the nameplate |
| Cabinet runs constantly in a hot room | Condenser cannot shed heat because the back is against a wall, or the coil is matted with dust | Leave clearance behind the cabinet and clean the coil; a blocked condenser can double the run time |
| Ice on the back wall, warm shelves | Door seal leaking humid air, or the thermostat probe has drifted | Paper test around the gasket, then compare box temperature against the set point |
| Works in the morning, fails in the afternoon | Panel overheating or partial shade, not a refrigeration fault | Check for shading after noon and feel the panel back sheet; hot panels lose output |
Maintenance that actually matters
Three jobs cover most of it. Clean the condenser coil every few months, because dust on the coil is the same as a smaller condenser. Keep the door gasket clean and check it with a sheet of paper: if the paper slides out easily when the door is closed, cold air is leaving and humid air is coming in. And leave the cabinet room to breathe, since a refrigerator pushed against a wall is fighting its own heat.
Refrigerant does not need topping up. These are sealed systems with a factory charge of around 140 g, so if the charge is low there is a leak, and the answer is to find the leak rather than to add gas.
The models this system goes into
- Single door solar home refrigerator BC-90RV - 90 litres, 12/24 V, the size that suits an RV or a small household.
- Double door top freezer BCD-98 - 98 litres with a separate freezer compartment on the same loop.
- Single door BC-50 - 50 litres, the smallest cabinet in the range and the easiest to run from one panel.
- Double door top freezer BCD-142 - 142 litres for a family, still on a single DC loop.
- BCD-270 with panel and battery - 270 litres, supplied as a complete kit when the customer has no DC infrastructure at all.
A solar refrigerator is only half a system: the cabinet holds the cold, the array on the ground refills the battery that keeps the compressor turning after sunset.
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
Tell us the ambient temperature you work in, the volume you need and how the cabinet will be powered, and we will size the compressor, the insulation and the panel around that instead of around a catalogue page.