Water Wheel Power Output Calculator

Water wheels turn the potential energy of falling water into useful rotation for milling, pumping, or driving a generator. This calculator gives a quick estimate of the mechanical power available from a site using three inputs: flow rate, effective (net) head, and wheel efficiency.

What this calculator does

• Converts flow rate from liters per second (L/s) to m³/s.
• Uses the standard hydropower relationship to estimate mechanical power at the wheel shaft.
• Optionally expresses results as W, kW, and kWh/day (assuming continuous operation).

Inputs explained (and how to choose them)

1) Flow rate (Q)

Flow rate is the volume of water reaching the wheel per second. Use an average sustained flow if you want realistic year-round expectations, not a short peak after rain. If you measured flow in m³/s, convert to L/s by multiplying by 1000.

2) Effective (net) head (H)

Head is the usable vertical drop of the water that actually contributes to turning the wheel. For water wheels this is often the height difference between the upstream water level at the intake and the downstream tailwater level near the wheel. If you have conveyance (flume/pipe/channel), the best practice is to use net head after subtracting losses (friction, bends, constrictions, entry/exit losses). If you don’t know losses, treat your head input as an approximate “effective head” and expect real output to be lower.

3) Wheel efficiency (η)

Efficiency captures how much of the water’s theoretical power becomes shaft power. It depends on wheel type, build quality, speed matching, and how well water is delivered to the buckets/paddles.

Formula used

The theoretical hydraulic power available from falling water is:

Where:

• P = mechanical power output (W)
• ρ = water density (assumed ~1000 kg/m³)
• g = gravitational acceleration (9.81 m/s²)
• Q = flow rate (m³/s). If you enter L/s, then Q(m³/s) = Q(L/s) / 1000.
• H = effective/net head (m)
• η = efficiency as a fraction (e.g., 70% = 0.70)

Interpreting the results

• Watts (W): instantaneous shaft power at the wheel (mechanical). This is not yet electrical output.
• Kilowatts (kW): watts divided by 1000; easier for comparing to appliance loads or generator ratings.
• kWh/day: energy over 24 hours at the computed power. This assumes the flow and head are steady and the wheel runs continuously. In real sites, seasonal flow changes and downtime can reduce daily energy significantly.

Worked example

Suppose a site can reliably deliver 50 L/s to an overshot wheel with about 3 m of effective head, and you estimate 65% efficiency.

• Convert flow: Q = 50 / 1000 = 0.05 m³/s
• Compute power: P = 1000 × 9.81 × 0.05 × 3 × 0.65 ≈ 956 W (≈ 0.96 kW)
• Daily energy (ideal continuous): 0.956 kW × 24 ≈ 23.0 kWh/day

If you add a generator, belt/gear drive, and electronics, the electrical output will typically be lower than the mechanical estimate due to additional conversion losses.

Assumptions & limitations

• Steady flow and head: the calculation assumes Q and H are constant. Real streams vary hourly and seasonally.
• Net head must be realistic: if you enter gross head (ignoring flume/pipe/channel losses), results will be optimistic.
• Water density is approximated: using 1000 kg/m³ is close for typical fresh water; temperature and sediment change it slightly.
• Mechanical estimate only: results represent power at the wheel. Generator efficiency, drive losses, and electrical conversion are not included unless you bake them into the efficiency input.
• Site effects not modeled: debris, ice, flood conditions, wheel immersion, poor water delivery, and speed/load mismatch can reduce performance.
• Practical constraints: permitting, water rights, environmental constraints, and safety considerations can limit feasible diversion and operating time.

Quick tips for better estimates

• Use conservative inputs (especially for dry-season flow).
• Measure head between upstream water surface at the intake and downstream tailwater near the wheel.
• If unsure, choose a modest efficiency (e.g., 50–70%) and refine after you know your wheel type and build quality.