LELABAPP
Case study

A well, no basin: direct solar
irrigation in Senegal

In Pout, in the Thiès region, a community of growers is preparing a first solar installation on a 5-hectare pilot plot. The project calls for direct pumping from a 30 m well, with no buffer basin, for a demand of 30 m³ per day.

Pout, Thiès region · Senegal 5 ha pilot field 30 m well Target: 30 m³/day Direct supply, no reservoir
The project

The need, as the client expresses it

The first client of a collective venture: if the pilot plot convinces, the other growers will follow. The brief fits in three lines: pump from the 30 m well, water directly without going through a basin, and target 30 m³ per day. No backup, no storage: the field drinks at the pace of the sun.

30 m³/daythe target requested, year-round: enough to drip-irrigate a little under one hectare at the height of the dry season
30 mthe well depth, pump set at around 25 m; the water level and well yield will be measured on site
0 reservoirthe client's deliberate choice: direct irrigation, with no buffer basin
5 hathe pilot plot's field, to be equipped in stages

The figure to face head-on: 30 m³ per day will not irrigate 5 hectares of market gardening in the dry season. It will irrigate a fraction of it, and that is precisely the spirit of a pilot plot: prove the principle on the first block, then expand the solar array once the community commits.

Step 1

The input data in LE LAB

A few minutes of input. The solar reference city is Dakar, around fifty kilometres from Pout. The pump is set at around 25 m in the 30 m well, the delivery head to the irrigation network is low and the field-head pipe is taken at 100 m. The total head is calculated automatically: 38 m. And to the water reserve question, the client's answer is respected: none.

Study summary in LE LAB: Dakar, 30 m³ per day year-round, depth 25 m, delivery head 2 m, 100 m of pipe, calculated TDH 38 m, no electrical backup, no water reserve

The summary before calculation: nine answers are enough, the total dynamic head is calculated for you.

Step 2

What LE LAB proposes

A LORENTZ PS2-1800 with the HRE-32 end, a helical rotor, powered by 3 panels of 450 Wp, for 1,350 Wp in a single string. Average production: 35.4 m³ per day, from 29.8 in August to 41.1 at the height of the dry season. LE LAB is multi-brand: the study scans the catalogue and selects the pump whose curves fit the project's operating point, here a LORENTZ; the alternative offered just behind it is a GRUNDFOS SQF 5A-7, which calls for 1,545 Wp of solar array for 33.7 m³ per day.

Solution proposed by LE LAB: LORENTZ PS2-1800 HRE-32 pump, 1350 Wp solar array with 3 panels of 450 Wp, average production 35.4 m³ per day

The solution at a glance: pump, solar array and average production.

Why this pump here? HRE-32 denotes a helical rotor pump end, built for moderate flows under high head. At the project's point, 38 m, it reaches 5.5 m³/h, and it needs 1,350 Wp of solar array where the GRUNDFOS SQF 5A-7 alternative calls for 1,545 Wp to deliver 33.7 m³ per day. The dry-run probe is part of the proposed installation: the pump stops itself if the level drops too far, and restarts once the well has caught its breath.
Step 3

Production, month by month: a red bar that falls in a good spot

Monthly production is read against the need, over sixteen years of the region's PVGIS solar history. Eleven months stay above the 30 m³ line. The only one that misses the target is August: 29.8 m³ per day, within 1%. The rainfall curve puts this dip in context: August is the heart of the rainy season, 191 mm of rain, the moment when the irrigation need is at its lowest. Effective rainfall and the plot's actual need remain to be assessed on site. Market gardening in Pout, meanwhile, peaks in the dry season, when production runs between 34 and 41 m³.

Estimated monthly production against the need of 30 m³ per day: only August falls under the line at 29.8 m³ per day, at the peak of 191 mm rainfall

The critical month is shown in red, not hidden: August, 29.8 m³/day for 30 required, under 191 mm of rain. The blue line is monthly rainfall.

Step 4

The typical day: watering at the rhythm of the sun

With no basin, daily output becomes the grower's working tool: it dictates when the water flows. The typical August day shows a plateau from 11 am to 2 pm around 4.5 m³/h, with a peak at 4.6 m³/h: watering rotations are scheduled around this window, and drip irrigation does the rest. In August, the tightest month, the day produces 30.3 m³: the need is covered with a 1% margin, right at the edge.

Daily output for a typical day in August: hour-by-hour flow rate, peak at 4.6 m³/h, 30.3 m³ produced, need of 30 m³ covered with 1% margin

The typical August day, hour by hour: the midday plateau is the irrigation window.

Step 5

No reservoir: coverage, quantified

The choice of direct supply is respected, and its price is shown. Without a water reserve, the installation covers the need in full 309 days out of 365. On the other 56 days, the pump still delivers 71% of the need on average, and four days a year fall below 20%. The chart shows where these days concentrate: July, August, September, the rainy season, precisely when the irrigation need drops.

Need coverage block with no water reserve: 309 of 365 days fully covered, the other 56 days deliver 71% of the need, incomplete days concentrated from July to September

A benchmark is given too: 33% more panels would raise coverage to around 346 days out of 365. And if a basin enters the project one day, LE LAB simulates it on demand.

Fully solar pumping owns its rule. Water is stored, not electricity: no batteries to buy or replace. In direct irrigation, the crop itself absorbs the swings: a grey day delivers 71% of the water, and the soil and mulching buffer the rest. It is a trade-off market gardening tolerates far better than a village water tower.
Step 6

Manufacturer curves, at the real operating point

The pump's Q/H curves, plotted from official LORENTZ data, with the project's head highlighted: 5.5 m³/h at full power on the 38 m curve. The pump accepts up to 5.8 m³/h and 50 m of head: at 38 m the project sits at the pump's maximum, and the application says so in plain words.

Manufacturer curves for the LORENTZ PS2-1800 HRE-32 pump: flow according to available power by head, operating point 5.5 m³/h at 38 m

Flow according to available power, by head. The yellow curve is the project's, at 38 m.

What this case shows

The tool frames, the trade decides

309/365 daysgoing without a reservoir is not a gamble: it is simulated day by day and quantified before signing
71%what the pump still delivers on grey days, concentrated in the rainy season, when the irrigation need drops
16 yearsproduction and coverage are tested day by day over sixteen years of the region's PVGIS solar history
HonestyAugust's red bar is shown, the fraction of the field actually irrigable is stated, and the well's yield still needs to be measured before the offer

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