What a widely quoted number gets wrong
A solar cold room is a unit about the size of a shipping container that runs on rooftop solar panels and keeps produce cold so it does not spoil before it is sold. A company called ColdHubs builds and runs many of these in Nigerian markets, and a claim keeps circulating that a shared solar cold room cuts vegetable spoilage from 40% down to 2%. Neither number could be verified in the 5 sources read for this article. The number that did survive comes from an actual trial with a comparison group, not a marketing claim, and it is smaller.
The trial behind the real number
The International Food Policy Research Institute installed 7 solar cold rooms in 7 horticulture markets in northeast Nigeria between December 2020 and January 2021, then compared what happened there with 7 similar markets that got no cold room. Each cold room holds up to 3 tons of produce at 4 degrees centigrade, runs on 5.6 kilowatts of solar panels, and cost about 40,000 dollars to build. A trader could rent space for 1 crate of 20 kilograms for 100 Nigerian naira a day, about 28 US cents. Researchers tracked 1,050 market agents across both sets of markets before and after the cold rooms went in.
Before any cold room existed, market agents in these markets lost 9.4% of their gross revenue to spoilage on average, and produce stayed fresh for 4.5 days in the open air. Produce that traders actually placed inside a cold room lost 11.2 percentage points less of its sales value to spoilage than produce sold in the open, and it stayed fresh 7 to 11 days longer.
The trial compared 7 Nigerian markets that got a solar cold room with 7 markets that did not, over the 2020 to 2021 season.
Show the numbers
| Less lost to spoilage, stored produce | 11.2 |
| Less lost to spoilage, all produce sold | 4.7 |
| More price margin earned per sale | 15 |
Traders who used a cold room also earned 15 to 20% more for what they sold, and their price margin, the gap between what they paid and what they charged, rose 15 percentage points. Sales volumes and revenue rose by as much as 69%. A cold room owner cleared about 1,653 dollars a month in extra gross profit, and about 8,000 dollars in net profit a year after running costs, so paying back the 40,000 dollar build cost took about 10 years even at a 7% interest rate. Traders who did not use a cold room in the same markets saw no measurable harm from its presence.
The bigger loss numbers describe a different stage
The 40% figure the industry repeats is close to a real number, just not the one a cold room measures. Nigeria loses about 40% of all the food it produces nationally, and separate figures put tomato losses at 45 to 60% of the harvest, onion losses at 50%, and chilli losses at 20 to 30%. All 3 figures describe loss between the farm and the first sale, before produce reaches a market stall, so a cold room there cannot fix a loss that already happened on the farm or the road.
These figures measure loss from the farm to the first sale, before produce reaches a market stall, a different measurement from the trial figures in the other chart.
Show the numbers
| Tomato | 45 to 60% |
| Onion | 50% |
| Chilli | 20 to 30% |
How far the idea has reached
By 2024, ColdHubs was running 58 solar cold rooms and 7 separate ice points across 28 Nigerian states, serving 11,100 farmers, retailers and wholesalers, up from 54 cold rooms in 22 states in 2022, growth the company reports about itself. A separate solar cold storage company, SokoFresh in Kenya, works in a market where a joint report by the International Renewable Energy Agency and the Food and Agriculture Organization of the United Nations records post harvest loss that can reach 40%.