LELABSINES
Case study

Four panels for 470 animals:
solar watering on mountain pasture

In the Béarn Pyrenees, a pastoral association moves 470 animals up to its mountain pasture every summer. The captured spring flows at the bottom of the valley; the drinking troughs are 45 metres higher, on the plateau where the herd grazes. No power line, no track: everything that goes up must be light. Here is how this livestock watering system is sized in LE LAB, the solar pumping sizing application, from the herd to the pump curves, with real screenshots and figures.

Béarn Pyrenees, France Herd: 60 cattle, 400 sheep, 10 horses Pasture season: June to September Elevation gain 45 m · 300 m of pipe No grid, no accessible track
The project

The need, as the shepherd lives it

Every summer, the association's herd leaves the barns for the high-altitude grass. Water is not lacking at the spring, lower down; it is lacking where the animals graze. In dry summers, hauling water becomes a daily chore: go down, fill up, come back up. The goal fits in one sentence: let the spring fill the water trailer and the troughs on the plateau by itself, at the pace of the sun.

470 animals60 cattle, 400 sheep and 10 horses: the herd brought together by the pastoral association for the season
45 mthe elevation gain between the spring intake and the drinking troughs, with 300 m of pipe laid along the slope
10 m³the water trailer and troughs already in place: barely more than two days of herd needs
0 gridno power line, no track: equipment goes up on foot, and the system must stay simple and self-sufficient

A generator would mean hauling fuel up all summer. Fully solar pumping, without batteries, is built for situations like this: a few panels, a 3.5-inch pump, and no one left to send up there with jerrycans.

Step 1

The need calculated from the herd

No volume to guess: LE LAB asks for the herd, not cubic metres. 60 cattle, 10 horses, 400 small ruminants, on FAO figures per animal per day, and the application calculates: 4.7 m³ per day. Seasonality is declared in the same place: pumping runs from June to September, and the entire study is aligned with the pasture season.

Herd step in LE LAB: 60 cattle, 10 horses and donkeys, 400 small ruminants entered, pumping seasonality from June to September, need calculated at 4.7 m³ per day on FAO figures

The herd step: you enter head counts, the application calculates cubic metres, and the season is declared with one click.

Step 2

The site data

The solar reference city is Pau, at the foot of the Béarn valleys. The pump is immersed 3 m deep in the intake basin; a 45 m delivery head to the troughs, 300 m of pipe along the slope: the total head is calculated automatically, 51 m. No backup power possible up there, and the 10 m³ trailer is declared as the existing reserve.

Study summary in LE LAB: Pau, 4.7 m³ per day, pumping period from June to September, depth 3 m, delivery head 45 m, 300 m of pipe, calculated TDH 51 m, no electrical backup, water reserve 10 m³

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

Step 3

What LE LAB proposes: the smallest system in the series

A LORENTZ PS2-150 AHR-04S, a 3.5-inch helical rotor pump, powered by four 95 W panels in two strings of two, for 380 Wp at 24 V. The whole system, pump, controller and panels, can be carried up on foot. Production over the season: 5.1 to 5.4 m³ per day for 4.7 required. At the other end of our case study series, the hybrid system in Chad runs to 11,700 Wp, thirty times more: the same application sizes both.

Solution proposed by LE LAB: LORENTZ PS2-150 AHR-04S pump, 380 Wp solar array with 4 panels of 95 W, average production 4.5 m³ per day

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

Why a helical rotor? At 51 m of head for a small flow rate, this is the technology that excels: 0.6 m³/h at 51 m with only 380 Wp. The kit is completed with the dry-run probe, which protects the pump if the intake weakens, and the float switch that stops it once the trailer is full. The shepherd has nothing to operate.
Step 4

Production, aligned with the pasture season

Over sixteen years of the Pyrenean foothills' real solar data, all four pasture months stay above the need line: 5.3 m³ per day in June and July, 5.4 in August, 5.1 in September, the critical month shown. The winter months appear in red, and that is exactly right: the herd has come back down, the study is sized for the declared period, not for a January with no animals.

Estimated monthly production against the need of 4.7 m³ per day: the four months from June to September above the line, critical month September at 5.1 m³ per day, optimal angle 38 degrees

Sized for the pumping period: the reference month is September, the tightest of the season, not an irrelevant winter month.

Daily output for a typical day in July: hour-by-hour flow rate, plateau at 0.6 m³/h from 9 am to 3 pm, 5.0 m³ produced, need of 4.7 m³ covered with 5% margin

The typical July day: a plateau at 0.6 m³/h from 9 am to 3 pm, 5.0 m³ lifted to the troughs. While the herd grazes, the trailer fills.

Step 5

The 10 m³ trailer put to the test

LE LAB simulates the water reserve day by day, over the sixteen pasture seasons of sixteen years of real weather. With the 10 m³ trailer, 118 of the season's 122 days are fully covered. The 4 incomplete days of an average season still deliver 71% of the need, and the shortfall comes to just 6 m³ out of 573, or 1%. The worst episode shows the mountain's real risk: fifteen days of low sun from 6 to 20 June 2010, a gloomy start to the pasture season as Béarn can sometimes produce.

Autonomy and water reserve block: 118 of the season's 122 days covered with the 10 m³ trailer, 4 incomplete days delivering 71% of the need, missing volume 6 m³ out of 573 per season, benchmarks 14 m³ and 22 m³

The benchmarks quantify the next step: 14 m³ would bring incomplete days down to no more than one per season, 22 m³ would cover every day of the sixteen years. One more tank is enough, if the association aims for zero hauling.

The nuance of the trade. When it rains for fifteen days in June, the animals drink less, the streams run, and the shepherd knows it: the incomplete days in the calculation are also the days the mountain needs the pump the least. The tool shows the limit, the field puts it into perspective.
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: 0.6 m³/h at 51 m, at the pump's maximum, and LE LAB states it plainly. The AHR-04S accepts up to 0.8 m³/h and 60 m: the small rotor works at full capacity, and it is the 380 Wp array that was sized right at the edge.

Manufacturer curves for the PS2-150 AHR-04S pump: flow according to available power by head, operating point 0.6 m³/h at 51 m at the pump's maximum

Flow according to available power, by head. The yellow curve is the project's, at 51 m.

What this case shows

The tool frames, the trade decides

470 animalsthe need is calculated from the herd, FAO figures per animal per day: you enter head counts, not cubic metres
380 Wpthe smallest system in the series: four 95 W panels and a 3.5-inch pump that go up on foot
16 yearsproduction and the water trailer are tested day by day over sixteen pasture seasons of real weather
Honestythe 4 incomplete days are shown, the fifteen grey days of June 2010 are named, and the red off-season months are openly assumed

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