Solar Pump for Dam: Sizing, Costs and Floating Options

Start with the water you need at the destination, rather than the number of panels beside the dam. Ask each supplier to state daily and monthly water delivery, the assumptions behind that estimate, and how much comes from solar alone versus backup power, as recommended by the NSW Farmers solar-pumping quote checklist.

Our guide to integrating solar energy with farm dams covers the broader energy system. Here, the decision is narrower: which pump arrangement will deliver your required water, through your pipework, when the dam is low? The following calculations are worked examples, not a pump specification for an unmeasured property.

Size a solar pump for dam water demand first

Flow rate is the volume of water delivered per unit of time, commonly measured in litres per minute. Record the busiest day’s requirements, the destination and when water must arrive; NSW guidance recommends designing livestock supply around the highest carrying capacity and realistic consumption per animal, rather than an average quiet day (Local Land Services water-system guidance).

In an illustrative system, transferring 12,000 litres over six effective pumping hours requires an average 2,000 litres/hour, or about 33.3 litres/minute. The six-hour assumption must be checked against the supplier’s seasonal delivery model, not treated as guaranteed sunshine (NSW Farmers delivery checks).

A header tank is an intermediate storage that receives pumped water before supplying downstream outlets. Separate the pump-to-tank calculation from the tank-to-trough calculation: livestock can draw water faster than the pump refills storage, so pipe and valve capacity must also meet peak drinking demand (Local Land Services design guidance).

Local Land Services uses roughly four hours as a rule of thumb for concentrated stock drinking demand, not as a universal solar-pumping window. In the same 12,000-litre example, four-hour delivery to troughs would require 3,000 litres/hour from storage (NSW livestock supply guidance).

Calculate pumping head and check the pipework

Pump duty is the flow rate and total head the pump must supply. Head is pressure expressed as the equivalent height of a water column, measured in metres; the NSW pump-selection guide identifies duty as the basis of selection, rather than choosing a pump from its power rating alone.

Static lift is the vertical height difference between the source water surface and the delivery point. Friction loss is the pressure consumed as water passes through pipework and fittings; ask the designer to assess elevation, required outlet pressure and these losses at the intended flow, because longer and narrower pipes can restrict delivery (NSW guidance on distance, elevation and friction).

Use the lowest operating dam level in the design brief, not just today’s full-water level. Ask the supplier to show the selected duty on a pump curve, which is the manufacturer’s graph relating flow, head and operating conditions; this is the selection method described in the NSW pump guide.

Do not specify a suction height from a theoretical limit. NSW explains that atmospheric pressure could support about 10 metres of water at sea level, but actual pump suction lift must be lower to allow for friction, pump design and wear (NSW suction-performance guidance).

Compare floating, submerged and bank-mounted options

An intake is the point where water enters the pumping system. Ask the supplier to distinguish a floating intake, which supports the water entry point on a float, from a floating pump, which carries pumping equipment; neither description tells you where the solar panels must sit. Require a drawing showing each component before comparing quotes.

A submersible pump is a pump-and-motor assembly designed to operate underwater. A surface pump is installed outside the water and draws through an intake pipe; the choice involves suction limits, water quality, cooling, access and protection, not just whether the equipment floats (NSW pump types and installation considerations).

Arrangement to compare	Questions for the supplier
Bank-mounted pump with intake pipe	What suction limit applies at low water? How will priming and maintenance be handled?
Submersible pump supported in the dam	What cooling, orientation, screening and retrieval arrangements does this model require?
Floating intake connected to a separate pump	How will the intake stay clear of sediment and remain accessible as levels change?
Floating pump assembly	How will the complete assembly be secured, retrieved and protected from movement and debris?

Ask for the intake and service-access details in writing, including who checks the strainer and how equipment is recovered safely. Keep this separate from the farm’s livestock access and dam-protection plan, so a convenient equipment position does not become an unplanned cattle access point.

Plan usable storage and a backup water supply

Usable storage is the volume available to supply demand before the system reaches its minimum operating level. Establish this separately from the tank’s advertised capacity, then agree how long the property must cope with poor solar conditions, equipment failure or delayed repairs; NSW guidance specifically recommends reserve tanks to prevent stock running out of water (Local Land Services backup-storage advice).

Local Land Services suggests about five days’ tank supply for solar-only pumping and about three days for mains-powered pumping. These are planning references, not guarantees or substitutes for a property-specific outage assessment (NSW reserve-water guidance).

At an illustrative demand of 12,000 litres/day, five days of reserve equals 60,000 litres of usable water. Allow separately for water below the outlet or other unavailable volume when selecting nominal tank capacity (NSW storage planning guidance).

Ask for separate options for water storage, backup power and batteries, with the same required water service in each proposal. The NSW Farmers checklist asks whether battery storage is cost-effective, whether pumping can continue if the solar equipment fails, and who has the parts and expertise to restore supply (solar-system operational checks).

Compare solar pump costs on an installed basis

Request an installed price against a written water-delivery requirement, not an isolated pump price. The NSW Farmers checklist separates the pump, motor, controls, solar array, cabling, footings, fencing, freight, installation and commissioning, making it useful for identifying omissions even though its historical prices and policy references should not be treated as current (NSW Farmers quote comparison checklist).

Add project-specific questions about pipe supply, trenching, tanks, intake support and safe maintenance access. Have each supplier mark inclusions, exclusions, GST, ongoing monitoring charges and who performs each task; request current written pricing rather than importing another property’s total into your budget.

Compare running costs over the same period and include maintenance and replacement assumptions, not just avoided diesel or electricity purchases. The checklist also asks suppliers to explain output assumptions, future component replacement and the local repair arrangements behind their payback estimate (NSW Farmers whole-system cost checks).

Check the dam layout before commissioning

Commissioning is the process of checking and recording that an installed system performs as specified. Ask for measured water delivery, control checks and a handover record, rather than accepting panel output as proof that the water requirement has been met; the NSW checklist expressly asks suppliers to quantify water delivery and include commissioning (supplier proposal requirements).

Big Ditch founder Lindsey Hughson’s published Herons Creek project account records Overflow Dam No.4 behind Dam No.2 on the NSW Mid North Coast, completed on 19 March 2020. That is a verified multi-storage construction outcome, not a documented solar-pump installation; for a property with several storages, identify the actual source and destination on the supplier’s plan.

1. Record peak daily demand and the periods when outlets need water.
2. Mark the source dam, minimum water level, tank location and pipe route.
3. Ask the supplier to confirm flow, head and seasonal delivery assumptions.
4. Obtain itemised options for intake arrangements, usable storage and backup supply.
5. Agree commissioning measurements, control tests and the written handover record.
6. Confirm maintenance access, spare-parts support and the response to a water-supply failure.

Before seeking a final equipment quote, contact Big Ditch about the dam layout and site access. Keep the irrigation designer’s pump selection and the electrical installer’s responsibilities explicit in the proposal, alongside any dam works being considered.

Frequently asked questions

Will a solar pump work on cloudy days?

Do not assume its normal daily delivery will continue through cloudy weather. Ask for the supplier’s seasonal water-delivery estimate, the assumptions behind it and the contribution expected from backup power; the NSW Farmers checklist requires these distinctions (solar-pumping proposal checks). Set the reserve-water requirement against your property’s demand and repair access, and make the response to a prolonged shortfall part of the purchase decision.

Do floating pumps need floating solar panels?

Do not treat a floating-pump quote as a quote for floating panels. Ask the supplier to show the pump, intake, panel location, controller and connecting services separately on a layout drawing. Compare the proposed arrangement against access, water-level movement and the specified pump duty, rather than the product label; those operating conditions and maintenance requirements belong in pump selection (NSW pump-selection guidance).

Can I reuse the existing delivery pipe?

Reuse it only after its suitability has been checked for the proposed flow and pressure. Record its length, diameter, route, condition and fittings, then ask the designer to assess losses and pressure rating; NSW guidance explains why undersized or unsuitable pipe can restrict delivery or fail (farm pipe-selection advice). Request a comparison between retaining the existing pipe and replacing it before assuming a larger pump is the answer.

Planning a solar pump for dam water delivery? Book a site inspection with Big Ditch before fixing the intake position and pipe route.