HPP-Design — Documentation

HPP-Design is an online tool for the preliminary design of hydropower turbines. Enter the two parameters that define a site — net head and flow rate — and the tool returns the feasible turbine types, their valid configurations, and a complete engineering data sheet for the one you select: main dimensions, efficiency curve, cavitation limit, runner weight, hydraulic thrust, generator configuration and a cost estimate.

It is built for engineers, consultants and hydropower developers who need reliable preliminary data for feasibility studies, optimization of existing plants, or the early engineering of a new project — without installing software and without a full detailed-design package.

This page explains the engineering method behind the tool, the inputs it needs, the four turbine families it covers, the results it produces, and how the free and professional tiers work.

1. The engineering method: specific speed

A turbine is not uniquely defined by head and flow alone. Two sites with the same net head H and discharge Q can be served by different machines, because a third quantity is free to the designer: the rotational speed n. Head, flow and speed together define the specific speed of the machine.

The specific speed is the parameter that groups turbines into families of geometrically similar machines — machines of very different size and power that share the same hydraulic behaviour and process a given head and discharge at the highest achievable efficiency. Once the specific speed is fixed, the most efficient turbine type and its main dimensions follow from over a century of hydropower practice and from similarity theory.

HPP-Design works with two common forms of this parameter:

• n_q — the engineering specific speed, nq = n · √Q / H^(3/4) (n in rpm, Q in m³/s, H in m).
• k — the dimensionless specific speed, k = ω · √Q / (g·H)^(3/4), where ω = 2πn/60 is the angular velocity in rad/s and g the gravitational acceleration.

The reference standard is IEC 60193:2019 (EN IEC 60193), which defines the speed factor n_QE = n · Q^(1/2) / E^(3/4), with n in revolutions per second and E = g·H the specific hydraulic energy in J/kg. The dimensionless k above is the same quantity expressed with the angular velocity: k = 2π · n_QE.

Each value of specific speed corresponds to a well-defined turbine type — with some overlap regions (Pelton/Francis and Francis/Kaplan) where more than one type is technically valid and experience decides. This is why, in practice, the designer studies several candidate rotational speeds, computes the resulting specific speed for each, and compares the solutions on efficiency, cavitation behaviour and main dimensions before committing. HPP-Design automates exactly this comparison.

Note on manufacturers. A given specific speed fixes the type and the main dimensions, not the final machine. Every manufacturer then develops its own geometry, which differentiates turbines on operation, reliability, cost and efficiency. HPP-Design produces the preliminary, manufacturer-independent design.

2. Inputs

To size a turbine HPP-Design needs:

• Net head — H [m]. The head available at the machine after hydraulic losses.
• Maximum discharge — Q [m³/s]. The design flow rate.
• Grid frequency — f [Hz]. 50 Hz across most of the world, 60 Hz in others. The frequency constrains the synchronous speeds available to the generator.

From these, and by scanning the admissible rotational speeds n, the tool determines which turbine types are feasible and enumerates their valid configurations.

Supported units. Results are returned in SI units. Discharge can also be entered in GPM, head in PSI. Power is shown in kW, and switches to MW above 5000 kW.

3. The sizing workflow

Step 1 — Enter the site. Create a new sizing and enter net head H and maximum discharge Q (and grid frequency where relevant).

Step 2 — Choose the turbine. The tool displays the feasible turbine types for that site and, for each, the valid configurations (number of units, layout, etc.). One option is marked as the suggested configuration, highlighted in green. If you are not yet sure, start from the suggested one. A head–flow chart shows where your site falls inside the application ranges.

Step 3 — Read the data sheet. On the sizing-detail page the tool shows the full output for the selected machine — main dimensions, efficiency curve, cavitation limit, runner weight, hydraulic thrust and generator configuration — and lets you refine secondary options (e.g. layout, regulation strategy, generator type). You can download the complete specification as a PDF data sheet.

"No configurations available" — what it means

A hydropower plant usually contains more than one turbine. If a single machine cannot take the whole flow, the discharge must be split across several units. For example, a plant with 150 m of head and 150 m³/s is typically divided into four or five turbines, both to fit the machines inside their valid range and to increase reliability. When the tool reports no configuration, the site parameters are outside the valid envelope of that type — adjust H/Q, or split the discharge across more units.

4. Turbine families

HPP-Design covers the four turbine families that span the practical range of small and medium hydropower. Their application ranges overlap: for a given head and flow, two or even three types can be valid, and the right choice depends on the factors in section 5.

4.1 Pelton — impulse turbine, high head

A Pelton turbine extracts energy from one or more high-velocity jets striking the buckets of the runner. It suits high heads and comparatively low flows. The discharge is shared among the jets, so configurations are described by the number of jets (1J … 6J) and by the shaft orientation: horizontal axis (typically up to 3 jets) and vertical axis (up to 6 jets). During selection the tool shows the preliminary power and the suggested configuration, and a simplified layout drawing is produced for the standard jet/axis combinations.

4.2 Francis — reaction turbine, medium head

A Francis turbine is a reaction machine for the medium-head, medium-flow range — the most widely used turbine type worldwide. It can be arranged with a vertical or horizontal axis. As with all reaction machines, the cavitation limit (the suction head Hs) is a design output to watch. During selection the tool reports the resulting turbine type, since Francis sits in the Pelton/Francis and Francis/Kaplan overlap regions.

4.3 Kaplan — propeller turbine, low to moderate head

A Kaplan is a propeller turbine in which both the runner blades and the wicket gates are adjustable, giving a wide, flat efficiency curve. It is used for low to moderate heads and medium to high flows.

• Range: H from 2 to 50 m, Q from 1 to 100 m³/s per machine. Multiple units increase the total plant discharge.
• Two numbers on the icon. The first is the number of available configurations without a gearbox; the second, when present, the number with a gearbox.
• "Enable gearbox" switch. A gearbox lets the turbine and generator run at different speeds, matching each to its optimum. It is offered only below a certain nominal power, where a low turbine speed would otherwise be required; above that power a multi-pole generator is more effective and cheaper.
• Regulation strategy (set on the detail page), from highest cost/efficiency to lowest:
  1. Full Kaplan — both blades and gates adjustable; best part-load efficiency.
  2. Semi-Kaplan rotor — adjustable blades, fixed gates.
  3. Semi-Kaplan stator — adjustable gates, fixed blades.
  4. Propeller — neither adjustable; a fixed-blade propeller turbine for nearly constant flow, the cheapest option, with the steepest drop in part-load efficiency.
• Generator. For small powers only asynchronous generators are available; for large powers only synchronous. In between you can choose: synchronous allows reactive-power control and is slightly more efficient but more expensive; asynchronous is cheaper.

4.4 Archimedean Screw Generator (ASG) — positive-displacement, low head

An ASG is a positive-displacement machine: a screw rotor turning in a semicircular trough, where the weight of the water trapped in the buckets produces the torque. It is robust, cheap to build, tolerant of debris and floating objects, and well suited to low heads and medium flows.

• Range: H from 1 to 5 m, Q from 0.5 to 7 m³/s per screw. Screws are commonly installed side by side to raise the plant discharge up to about 30 m³/s.
• Multiple solutions. The required flow can be met with different numbers of screws. More screws cost more and take more space, but each is smaller, easier to transport and maintain, and gives better part-load efficiency. The suggested configuration minimises the number of screws, hence width and total cost.
• Single-screw discharge limit. Set by construction and transport constraints; the lower the head, the lower the discharge per screw because of aspect-ratio limits.
• Regulation. Being positive-displacement, an ASG needs no adjustable blades or gates — it self-adapts to falling flow through partial filling of the buckets. A variable-speed option (inverter) keeps the intake level constant and raises part-load efficiency; fixed-speed is the simpler alternative.
• Efficiency. Hydraulic efficiency exceeds 80%, since water velocity in the screw is an order of magnitude lower than in reaction turbines, keeping friction and discharge losses small.

ASG vs Kaplan (overlap 2–5 m). Both are valid between roughly 2 and 5 m of head. The Kaplan is slightly more efficient and more compact; the ASG is usually cheaper (lower CAPEX and OPEX), easier to inspect, and lets debris pass without an automatic trash rack. HPP-Design lets you compare the two side by side.

5. Choosing among feasible options

Where ranges overlap, nominal efficiency alone is not enough. A sound preliminary choice weighs:

• Nominal efficiency at the design point.
• Average annual efficiency — how well the part-load efficiency curve matches the variation of flow (and head) over the year.
• Cost of the turbine and electromechanical equipment.
• Operation and maintenance cost.
• Trash-rack / water-screen requirements relative to the debris the river carries.
• Plant layout for the site, and the civil costs that follow from it.

HPP-Design surfaces the data behind these factors — efficiency curves, dimensions, configuration options — so the trade-off is made on numbers rather than habit. The suggested configuration is a sound default (for Kaplan, the most efficient solution; for the ASG, the one minimising the number of units), but the final choice is the engineer's.

6. Outputs

For the selected machine HPP-Design returns a complete preliminary data sheet, including:

• Main hydraulic and geometric dimensions of the runner and machine.
• Efficiency curve, linked to the output power and to the chosen regulation strategy.
• Cavitation limit — the suction head Hs — for reaction turbines.
• Runner weight.
• Hydraulic thrust, for horizontal and vertical layouts.
• Generator configuration (type, poles, speed).
• Preliminary cost estimate.

All results can be exported as a PDF specification from the sizing-detail page. The on-screen detail page and the PDF are generated from the same source, so they never diverge.

7. Energy calculator

The Energy Calculator estimates the annual energy production of the plant directly online, reversing the usual workflow: instead of deriving turbine data from a measured flow-duration curve, you start from the turbine's design data (Q and H) and apply a flow-duration curve to estimate production.

How it works and its current simplifications:

• One input model: a flow-duration curve. You edit a curve of (% of time, discharge) points — the same in Single (one machine) and Compare (several side by side on one site flow). Two presets (Torrential, Basin) seed the curve, and every point is editable.
• Presets scale to the turbine. A preset is a normalized shape, scaled to absolute discharge by Qref — the Qmax of the selected turbine (in Compare, of the chosen reference turbine). Discharge is shown in the sizing's own unit (l/s or m³/s).
• Turbine efficiency is included, varying with flow along the part-load curve; the generator + transformer efficiency is applied from the machine's design point.
• Constant head. Energy is computed at a constant net head: in Single the turbine's own head; in Compare the reference turbine's head is applied to all (one site = one head, isolating the machine choice). To keep that honest, Compare is blocked when the turbines' heads differ by more than 10%. Head varying with flow is a future extension.

The result is a fast, transparent first estimate of energy yield, intended for screening rather than final energy accounting.

8. Free and Professional sizings

A sizing is Professional when the preliminary power of the turbine is above its type's threshold: 10 kW for Pelton, Francis and Kaplan, and 5 kW for the Archimedean screw. At or below that threshold the sizing is Free, with no limit on the number of sizings.

• Free. Unlimited sizings with preliminary power ≤ 10 kW (≤ 5 kW for the Archimedean screw). No credit required.
• Professional. Each sizing above its threshold consumes one credit. Credits unlock the full data sheet and PDF for plants of any size.

Credits. Professional credits are sold in bundles and never expire:

One credit = one Professional sizing. There is no subscription and no expiry; buy credits when you need them and use them whenever you like.

9. Your account

Your account has no expiry and your credits never expire — once bought, they stay in your balance until you use them.

To keep accounts tidy, an account left inactive for 24 months is frozen, and after a further 12 months of inactivity (36 months total) it may be closed. Freezing keeps your data and is reversible — just log back in. The current terms are defined in the Terms of Service.

10. Support

Need a specific turbine parameter, a configuration outside the standard ranges, or help interpreting a result? Contact us at info@hpp-design.com and we will review your data and assist with the correct sizing.

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HPP-Design is operated by 54 Holding Srl. This documentation describes the preliminary-design behaviour of the tool; it is engineering guidance, not a substitute for detailed design or a manufacturer's quotation.