LELABSINES
Case study

Solar first, generator as backup:
the hybrid system in Chad

In the Abéché region, in eastern Chad, a town and its livestock rely on the water of a borehole: 100 m³ per day, without a single day off. The generator that does everything today costs a fortune in diesel trucked in by road. The NGO supporting the municipality is clear in its request: switch to solar, keep the generator, and make sure the switchover between the two depends on no one. Here is how this hybrid sizing is built in LE LAB, the solar pumping sizing application, with real screenshots and figures.

Abéché region · Chad Need: 100 m³/day, year-round 50 m borehole Existing reservoirs: 95 m³ Generator kept as backup NGO-led project
The project

The need, as the NGO expresses it

Water for a Sahelian town is not negotiable: residents, passing herds, small dry-season market gardening. The network relies on a water tower and tanks totalling 95 m³, filled until now on diesel. The association's goal is not to remove the generator: it is to make it fall silent. Solar as the main source, the generator as automatic backup, with no human intervention.

100 m³/daythe need of the town and its livestock, year-round, rainy season included
50 mthe water depth in the borehole, plus the tower and 200 m of pipe: 75 m of total head
95 m³the existing reservoirs, a little under one day's need
1 generatoralready on site and kept: the NGO's request is a genuine hybrid system, not a replacement

Chad is proven ground for solar pumping: documented installations have been running there for over ten years, including on larger supply systems than this one, often led by NGOs and international solidarity associations. In the Sahel, a kWh produced from diesel costs 3 to 4 times a solar kWh: every hour of sun used is an hour of generator run time saved.

Step 1

The input data in LE LAB

A few minutes of input. The solar reference city is Abéché, at the heart of the project region. Borehole at 50 m, delivery head of 15 m to the tower, 200 m of pipe: the total head is calculated automatically, 75 m. And one answer carries more weight than the others: electrical backup, yes. It is this answer that steers the study toward a hybrid solution.

Study summary in LE LAB: Abéché, 100 m³ per day year-round, depth 50 m, delivery head 15 m, 200 m of pipe, calculated TDH 75 m, electrical backup yes, water reserve 95 m³

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

Step 2

What LE LAB proposes: a 100% hybrid solution

The chosen solution is a LORENTZ PSk3-7 with the C-SJ12-15 end, and the tile announces it on its own: "100% hybrid". The solar array has 26 panels of 450 Wp in two strings of thirteen, for 11,700 Wp, with an average production of 114.6 m³ per day. The strings of thirteen are not a whim: the PSk3 controller operates at high voltage, between 400 and 850 V, and the array is adjusted by whole string. This generous array relative to the 5.5 kW motor has a benefit: the pump reaches full speed from the morning and holds it until late afternoon.

Solution proposed by LE LAB: LORENTZ PSk3-7 C-SJ12-15 pump shown as 100% hybrid, 11700 Wp solar array with 26 panels, average production 114.6 m³ per day

The solution at a glance: the "100% hybrid" label is carried by the pump itself.

What "hybrid" really means with a PSk3. The controller does not switch from one source to the other: it combines them. Priority goes to solar power, and when water demand requires it, generator power tops it up watt by watt, automatically; the SmartStart option starts the generator on its own, even in the middle of the night if the water setpoint calls for it. Compared with so-called "dual-supply" systems, which only switch, LORENTZ reports 60 to 70% savings. And the enclosure is built for the Sahel: IP66, operation up to 60°C ambient, active temperature management, remote monitoring through the LORENTZ app and platform, valuable for a remote site.
Step 3

Production, month by month: the Sahelian sun carries the year

Over sixteen years of the region's real solar data, all twelve months stay above the 100 m³ line. The low point is in August, at the heart of the rainy season: 106.6 m³ per day, still 6% above the need, for the worst August observed at 5.0 kWh/m²/day. The rainfall curve tells Abéché's climate: 0 mm in January, 181 mm in August. Solar alone already carries the year on a typical day; the generator now exists only for the bad days.

Estimated monthly production against the need of 100 m³ per day: all twelve months above the line, critical month August at 106.6 m³ per day, rainfall from 0 mm in January to 181 mm in August

The critical month is shown: August, 106.6 m³/day for 100 required. The blue line is monthly rainfall.

Daily output for a typical day in July: hour-by-hour flow rate, peak at 13.1 m³/h, plateau from 9 am to 3 pm, 100.7 m³ produced

The typical July day: a plateau around 13 m³/h from 9 am to 3 pm, 100.7 m³ produced. The generous array widens the plateau, and that is what makes the day.

Step 4

The 95 m³ reservoirs, and what is left to the generator

LE LAB simulates the water reserve day by day over sixteen years of real weather. With the existing 95 m³, 362 of 365 days are fully covered by solar alone. That leaves 3 days a year on average, at 74% of the need, an annual shortfall of 78 m³ out of 36,525, or 0.2%. The worst episode of the sixteen years: ten days of low sun in January 2009. That is exactly the generator's job.

Autonomy and water reserve block: 362 of 365 days covered with the 95 m³ reservoirs, 3 incomplete days a year delivering 74% of the need, missing volume 78 m³ out of 36,525 per year, benchmarks 160 m³ and 432 m³

The benchmarks show the price of all-solar: 432 m³ of reservoirs to cover every day of the sixteen years. No one pours that concrete when a generator is already there.

The hybrid system turns this trade-off into intelligence. Covering the last few days with storage alone would require quadrupling the reservoirs; covering them with the generator costs a few hours of diesel a year, triggered automatically by the controller. The generator that used to run all year becomes an insurance policy that starts three days a year. That is the exact answer to the NGO's request: solar first, the generator as backup, and no one to send on site to switch over.
Step 5

Manufacturer curves, at the real operating point

The pump's Q/H curves, plotted from official LORENTZ data, with the project's head highlighted: 13.1 m³/h at 75 m, and LE LAB honestly notes "at the pump's maximum". The C-SJ12-15 accepts up to 23 m³/h and 100 m: at this head, the system makes full use of its pump, and it is the controller that caps the power, not the sun.

Manufacturer curves for the PSk3-7 C-SJ12-15 pump: flow according to available power by head, operating point 13.1 m³/h at 75 m at the pump's maximum

Flow according to available power, by head. The yellow curve is the project's, at 75 m.

What this case shows

The tool frames, the trade decides

100% hybridthe PSk3 controller combines solar and generator watt by watt, priority to solar, automatic backup start
3 days/yearwhat is left to the generator once solar is in place: a few hours of diesel instead of a year of jerrycans
16 yearsproduction and the reservoirs are tested day by day over sixteen years of the Sahel's real solar data
Honestythe 13-panel strings imposed by the high voltage are explained, "at the pump's maximum" is shown, the ten grey days of January 2009 are named

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