ILR vs Solar Direct-Drive Vaccine Fridges: Choosing for Off-Grid Sites

Q: What temperature must vaccine refrigerators hold?

Between +2 degrees Celsius and +8 degrees Celsius with no freezing, and WHO PQS type-testing allows no excursion below -0.5 degrees Celsius for any length of time and none below 0 degrees Celsius for longer than an hour, per the PQS type-testing protocol E003/RF03-VP.5.

Tony Miller
Aug 17
7 min read

Specify an ice-lined refrigerator only where the site has at least eight hours of reliable mains power a day. Below that, specify a solar direct-drive unit. Both must be WHO PQS prequalified and hold vaccines between +2 °C and +8 °C with no freezing.

What is the actual difference between an ILR and a solar direct-drive fridge?

An ice-lined refrigerator banks cold from the grid. A solar direct-drive refrigerator banks cold from the sun. Everything else in the comparison follows from which of those two inputs the site really has.

The ILR is a compression-cycle appliance designed for intermittent mains power. Water or ice packs line the vaccine compartment, freeze while power is available, then release cold slowly once it is not. WHO PQS records that ice-lined refrigerators hold vaccines below +8 °C on as little as eight hours of electricity per 24 hours, and stay within range for at least 20 hours after a power cut, per the WHO PQS E003 category.

A solar direct-drive unit runs the compressor straight off a photovoltaic array with no battery in the circuit. Instead of storing electricity it stores cold, freezing water or a phase-change material during daylight and coasting on that thermal mass overnight. WHO PQS separates these into two performance specifications, E003/RF05 for solar direct drive without battery storage and E003/RF06 for solar direct drive with an ancillary rechargeable battery, alongside E003/RF03 for the intermittent-mains ILR. Those codes matter in a tender, because "solar fridge" on a specification line can mean any of three quite different machines.

How much holdover time do you actually get?

Holdover is a defined test result, not a marketing number. WHO PQS defines it as the hours during which every point in the vaccine compartment stays between +2 °C and +8 °C after the power supply is disconnected, measured at the maximum ambient temperature of the zone the appliance is rated for, per the PQS independent type-testing protocol E003/RF03-VP.5.

Two details in that protocol, issued 2 December 2024, change how you read a datasheet:

Everything is now tested hot. All appliances must pass in the hot zone, a steady +43 °C ambient and a +43 °C / +25 °C day-night cycle, and must also demonstrate a minimum rated ambient temperature of +10 °C.
The manufacturer must declare the power it needs. Each appliance carries a stated minimum average daily duration of power, for example 8 to 20 hours per typical day, or less than 8 hours. Match that declared figure against your site, not a sales conversation.

Read holdover as a laboratory ceiling reached with a full load and a closed door, because every door opening during an outreach session spends part of it. If mains power really arrives for four hours on a good day, an ILR rated for eight will run warm however good its holdover figure looks.

What does WHO PQS prequalification actually guarantee?

It guarantees that one specific model, from one named manufacturer, passed type-testing at an independent ISO/IEC 17025 laboratory accredited by WHO. It does not guarantee that the unit in front of you is that model. The PQS E003 product listing carried 83 prequalified refrigerators and freezers when checked in August 2026, filterable by manufacturer, climate zone and freeze protection, and re-badged or re-packaged variants of an otherwise identical appliance are not listed, per the WHO PQS E003 prequalification guideline.

The specification detail most often skipped is freeze protection, and it deserves a clear view: for a rural health facility with staff turnover, specify Grade A and refuse Grade B or C. WHO PQS grades appliances A for user-independent freeze protection, where no action by the health worker is needed to keep vaccines above 0 °C, and B or C where the user must follow a manufacturer procedure such as using baskets. The tolerance is unforgiving: no excursion below -0.5 °C is permitted for any length of time, none below 0 °C for longer than an hour, and the appliance must return to +2 °C to +8 °C within two hours, per the same type-testing protocol. Freezing is the quiet failure mode. A fridge sitting at -1 °C looks fine on a dial thermometer and has already damaged freeze-sensitive vaccines.

Which should you choose for an off-grid site in eastern DRC?

Count the reliable mains hours at the actual facility across a full month, then apply three rules.

Eight or more reliable hours a day, with a working generator behind them: choose an ILR. It is cheaper to install, has no array to site or secure, and its holdover is designed for exactly that duty cycle.
Fewer than eight hours, or no grid: choose solar direct drive without battery storage (E003/RF05). Removing the battery removes the component that fails first and creates a disposal problem 200 km from anywhere.
Only accept an ancillary battery (E003/RF06) where the site genuinely needs it, such as a fixed load beyond the fridge sharing the array. Every battery is a resupply line committed to for the life of the unit.

In the Democratic Republic of the Congo, rule two covers most of the map. World Bank data puts access to electricity at 22.5% of the population in 2024, and the UNHCR operational data portal recorded 5,773,180 internally displaced people in the DRC as of 31 March 2026, concentrated in the eastern provinces where displacement outruns fixed infrastructure. Globally, Gavi estimates that one billion people are served by health facilities with no access to electricity, and has procured more than 62,500 grid and solar fridges through the Cold Chain Equipment Optimisation Platform, of which more than 46,000 were installed in Gavi-supported countries as of June 2021.

Running cost points the same way. WHO PQS estimates the 10-year life-cycle cost of solar direct-drive refrigerators to be equal to or lower than gas-powered systems where bottled gas is readily available, per the E003 category page. Where bottled gas is not readily available, which describes most of eastern DRC, the comparison is not close.

What does siting an off-grid unit really involve?

The fridge is the easy part. The site decides whether it works.

Array position. Shade-free through the whole year, not only on the day of the survey. A tree that clears the panel in August will not in December.
Roof and security. The mounting must carry the array in wind, and the array must be hard to remove. Panels are the most stealable asset on a health centre roof.
Room temperature. Appliances are rated to a hot zone of +43 °C, and a tin-roofed store at midday can beat that. Put the unit in the coolest room, with the ventilation clearance the manufacturer specifies, or improve the building.
Floor and access. Level, dry, lockable, and reachable by the vehicle that will eventually deliver a spare part.

That last point is where the structure and the cold chain meet. Cold-chain-capable modular and semi-permanent warehousing from SLS exists because a prequalified appliance dropped into an unsuitable building inherits the building's problems.

Who services it, and what happens when it fails?

Buy through the manufacturer's authorised chain, or your warranty is decorative. WHO PQS defines a reseller as a commercial entity licensed to act for the legal manufacturer and carrying product liability and warranty responsibilities no less onerous than the manufacturer's own, per the type-testing protocol. WHO also reserves the right to suspend or withdraw prequalified status where installation or maintenance service proves poor, or where field installations fail to meet performance requirements, per the PQS guideline. Prequalification covers the service chain, not only the box.

Write four things into the purchase order before you sign it: the spare-parts list with local availability, the temperature-monitoring device and its PQS conformity, commissioning and handover training, and a named party responsible for a site visit within a defined number of days. For cold-chain work in the DRC, that last item decides whether a fridge is still cold in year three, because a technician who cannot reach North Kivu in the rains is not a maintenance plan.

Frequently asked questions

Is a solar direct-drive fridge better than an ice-lined refrigerator?

Neither is better in general. An ice-lined refrigerator suits sites with at least eight hours of mains power per 24 hours, which is the duty cycle it is designed for, while a solar direct-drive unit suits sites below that threshold, per the WHO PQS E003 category.

What temperature must vaccine refrigerators hold?

Between +2 °C and +8 °C with no freezing, and WHO PQS type-testing allows no excursion below -0.5 °C for any length of time and none below 0 °C for longer than an hour, per the PQS type-testing protocol E003/RF03-VP.5.

How long does an ILR stay cold in a power cut?

WHO PQS records at least 20 hours for ice-lined refrigerators, measured with the door closed at the maximum ambient temperature the appliance is rated for, per the WHO PQS E003 category and its holdover test definition.

Do solar vaccine fridges need batteries?

No. Solar direct-drive units store cold rather than electricity, and WHO PQS lists them under E003/RF05 without battery storage, with a separate E003/RF06 specification for models using an ancillary rechargeable battery, per the PQS performance specifications.

How do I check a refrigerator is genuinely PQS prequalified?

Match the exact model and manufacturer against the WHO PQS E003 product listing, which held 83 products in August 2026, and remember that re-badged variants of an otherwise identical appliance are not prequalified, per the PQS guideline.