What a widely repeated number gets wrong
A widely repeated claim says smallholder farmers, people who farm small plots mainly to feed their own families, spend up to 50% of their income on diesel fuel for water pumps, and that switching to a solar powered pump removes that cost entirely. None of the 5 sources read for this article support a figure anywhere near 50%. The real figures are smaller, more specific, and come from named villages rather than a global average.
What diesel really costs 2 groups of farmers in India
In the Little Rann of Kutch, a salt producing region of Gujarat, India, farmers who pump brine, the concentrated salt water used to make salt, spent about 40% of their annual income on diesel fuel before a program helped them buy solar pumps instead. In Chakhaji village in Bihar, India, vegetable farmers who owned no pump of their own paid a diesel pump owner for irrigation water, at 120 to 150 rupees an hour, and that water cost about 20% of the revenue they earned per acre each season. These 2 figures measure 2 different activities in 2 different states, and neither is a national or global number.
What happened after farmers in Gujarat switched
The Gujarat program is run by SEWA, a group that organizes self employed women in India. Its own reporting, once the program had grown past 1,100 pumps, found that farmers who switched from diesel to solar earned 94% more income, about 35,000 rupees more a season, rising to about 71,000 rupees once the loan on the pump was repaid.
These figures come from a 2020 field case study of a solar pump program run by the same organization that promotes it, not an independent evaluation.
Show the numbers
| While repaying the loan | 35,000 |
| After the loan is repaid | 71,000 |
What independent studies actually found
2 studies built to separate cause from coincidence, rather than to show off a program, found a less certain picture. A study of 815 households in Kenya compared farmers who adopted a solar pump made by a company called SunCulture with similar farmers who had not. Solar adopters irrigated their land 20 percentage points more often, but the study found no change in farm income or revenue large enough to rule out chance. Total household spending fell instead, which researchers attribute to families buying less food as their diets became more varied. A field trial in Ghana grew cabbage, then onions, using a solar pump and a diesel pump on the same plot in the same season. The diesel pump earned a higher gross farm profit margin, the share of farm revenue left after costs, 71% against 49% for the solar pump, in that first year.
A field trial grew cabbage, then onions, with a solar pump and a diesel pump on the same plot in the same season. Profit margin is the share of farm revenue left after costs.
Show the numbers
| Diesel pump | 71 |
| Solar pump | 49 |
The solar pump used in the Ghana trial cost 1,100 dollars to buy against 138 dollars for the diesel pump, but is built to last 20 years against 7 years for the diesel pump. Under the trial financial model, a solar pump only earns back more money than a diesel pump would have after 9 to 14 years. A solar pump does remove the diesel bill a farmer pays, but neither independent study found that it reliably or quickly raises income.