What Size Pipe Do I Need for My Solar Pump?

The short answer: match your pipe diameter to your pump outlet diameter. If the pump has a 2-inch outlet, use 2-inch pipe. For runs over 100 meters, consider going one size up to reduce friction losses. Never use a pipe smaller than the pump outlet — it’s the most common and most costly installation mistake.

When buyers send me installation photos, undersized pipe is the problem I spot most often — usually chosen from what the local shop had in stock, not what the pump needs. Let me give you the full picture so you don’t leave performance in the ground.

Why pipe size matters

Your pump is rated for a certain flow at a certain head. But the pipe between the pump and your tank adds friction — effectively increasing the head the pump must overcome. The smaller the pipe, the more friction.

Example: A pump rated for 10 m³/h at 80m head, connected with a 1.5” pipe over 50 meters:

• Friction loss in 1.5” pipe at 10 m³/h: ~12m per 100m of pipe
• 50m of pipe → ~6m additional head
• Effective head: 80 + 6 = 86m
• At 86m head, the pump delivers only ~8 m³/h (20% less than rated)

The same pump with a 2” pipe:

• Friction loss in 2” pipe at 10 m³/h: ~3m per 100m
• 50m of pipe → ~1.5m additional head
• Effective head: 80 + 1.5 = 81.5m
• At 81.5m head, the pump delivers ~9.5 m³/h (only 5% less)

Lesson: the right pipe diameter preserves your pump’s rated performance.

Why flow velocity matters

Flow velocity is the hidden factor behind most pipe sizing mistakes. Velocity = flow rate ÷ pipe cross-section, and friction grows roughly with the square of velocity — double the speed, quadruple the friction.

For water in plastic pipes, keep the velocity between 1 and 2 m/s:

• Below 1 m/s: fine, just slightly larger pipe than needed.
• 1-2 m/s: the sweet spot — low friction, quiet operation.
• Above 2 m/s: friction climbs fast, water hammer gets violent when the pump stops, and flow can erode fittings over years.

That’s why the quick table below lists a maximum flow per pipe size — those numbers are effectively the 2 m/s limit for each diameter.

Quick pipe sizing rule

Go one size up if:

• Horizontal run > 100 meters
• You want to future-proof for a larger pump later
• The pipe has many bends (> 5 elbows)

Pipe material comparison

Our recommendation: use HDPE pipe for most solar pump installations. It’s the industry standard for agricultural water systems worldwide.

Pressure rating: the PN number on the pipe

Every plastic pipe is stamped with a PN rating — the maximum working pressure in bar (1 bar ≈ 10m of head). It matters because a pump’s shut-off pressure (at zero flow, when a valve is closed) is higher than its working head. A pump rated for 80m working head produces roughly 8 bar at shut-off — so PN10 is the minimum, and PN16 gives real margin. Fittings, valves, and the tank inlet are often the weakest points — check their ratings too.

Vertical vs horizontal friction

• Vertical pipe: friction adds ~10-15% to the total head. This is already included in the “well depth × 1.15” rule.
• Horizontal pipe: every 10 meters adds ~1 meter of equivalent head. This is the often-overlooked factor.
• Combined: TDH = (well depth + drawdown + delivery height) × 1.15 + horizontal pipe ÷ 10

See our head calculation guide for the full formula.

Worked example: a 40m well with a long run

Let’s put it together — 40m well, 200m of horizontal pipe to the tank, 6 elbows:

• Vertical: 40 × 1.15 = 46m
• Horizontal: 200 ÷ 10 = 20m
• Fittings: 6 × 1m ≈ 6m
• Total ≈ 72m TDH

A pump rated for max head 80m would run at 90% of its capability — the edge of the curve, low flow, high stress. You’d want one rated 90m+ (the 60-80% rule from my pump curve guide). Note the horizontal friction was almost half the well depth — that’s why long runs deserve a pipe size up.

Fittings and bends: the hidden friction

Fittings add friction too, and they’re usually forgotten in the calculation:

So 10 elbows on a 100m run add the same friction as 10 extra meters of pipe. Use 45° or sweeping bends, keep the fitting count low, and leave ball valves fully open when running.

Common pipe mistakes

Need help choosing pipe size? Message me on WhatsApp with your pump model and pipe run length. Or use the sizing tool — it factors in horizontal pipe distance automatically.