Desalination Energy Cost Calculator

Desalination inputs and typical operating ranges

Water volume (m³/day)

How much product water you want the desalination plant to produce each day. Small pilot or industrial systems may be under 100 m³/day, while municipal plants may reach many thousands of cubic metres per day.

Salt concentration (ppm)

Total dissolved solids (TDS) expressed as parts per million (mg/L). As a rough guide, seawater is around 35,000 ppm, while brackish water often falls between 1,000 and 10,000 ppm. Actual seawater salinity varies by location, season, and intake conditions.

System efficiency (0–1)

A simplified factor showing how effectively the system turns input electricity into separation work, including the benefit of energy recovery hardware. A higher value means less electricity is needed per cubic metre. Modern reverse osmosis systems usually perform better than older equipment because pumps, membranes, and energy recovery devices are more efficient.

Electricity cost ($/kWh)

Your blended power price for the desalination project, including generation, delivery, and any demand charges averaged into $/kWh if that is how you budget. Many commercial rates are somewhere in the $0.08–$0.30/kWh range, though site-specific pricing can sit well outside that band.

Desalination energy model and formulas

Actual desalination energy use depends on feed salinity, temperature, recovery ratio, membrane performance, pressure losses, pretreatment, pumping, and, for thermal systems, heat integration. To keep this calculator practical, it uses a linear salinity scaling anchored to a typical seawater reverse-osmosis SEC, then adjusts that baseline by the efficiency factor you enter.

1) Specific energy consumption (kWh/m³)

The calculator begins with a reference SEC for seawater reverse osmosis and then scales it to match the salinity and efficiency assumptions in your case:

Where:

• SEC_ref is a reference specific electricity use for seawater RO, usually a few kWh/m³ for modern systems.
• S is the salt concentration (ppm) of the feed water you enter.
• S_ref is the reference salinity (ppm), typically about 35,000 ppm for seawater.
• η is the efficiency factor you enter (0–1). A larger value lowers the estimated SEC.

Interpretation: In this simplified model, higher salinity raises the estimated energy intensity, while better efficiency lowers it. If salinity doubles, the estimate doubles; if efficiency rises from 0.50 to 0.75, the SEC drops by one-third. That makes the tool useful for planning, but it also means the answer should be treated as directional rather than plant-guaranteed.

2) Total daily energy (kWh/day)

After SEC is estimated, the calculator multiplies it by the daily product-water volume so you can see the expected electrical load for the whole plant:

Energy (kWh/day) = SEC (kWh/m³) × Volume (m³/day)

This value matters when you are checking grid service, generator sizing, battery backup, or the amount of solar generation a desalination project would need to operate reliably.

3) Daily electricity cost ($/day)

The final step is to translate the energy demand into an operating cost using your unit electricity price:

Cost ($/day) = Energy (kWh/day) × Price ($/kWh)

If your tariff changes by time of day, or if a generator supplements grid power, the calculator still gives you a useful average-cost view. It is best interpreted as the energy portion of operating expense, not the entire cost of producing water.

Worked example: seawater reverse osmosis at 35,000 ppm

Scenario: You need 500 m³/day of product water from feed at 35,000 ppm. You assume η = 0.60 and electricity costs $0.12/kWh.

1. Salinity ratio: S/S_ref = 35,000/35,000 = 1.00
2. SEC estimate: SEC = SEC_ref × 1.00 × (1/η) = SEC_ref/0.60
3. Total energy: Energy = SEC × 500
4. Cost: Cost = Energy × 0.12

If SEC_ref were 3.5 kWh/m³, which is a reasonable planning reference for modern seawater reverse osmosis, then SEC would be about 5.83 kWh/m³. That gives roughly 2,917 kWh/day and about $350/day in electricity cost.

Note: The true answer can move up or down depending on recovery ratio, energy recovery device performance, intake lift, pretreatment demand, and how hard the feed water is to pressurize. Use the example as a directional screen before you compare vendor proposals.

Desalination limitations and assumptions (important)

• Linear salinity scaling: The model increases SEC in direct proportion to ppm. Real desalination behavior is not perfectly linear because osmotic pressure, recovery ratio, and pressure constraints all interact.
• Efficiency is a lumped factor: η rolls several effects into one input, including pump efficiency, membrane behavior, the energy recovery device, and fouling. Two plants with the same η can still have different real-world SEC values.
• Does not model recovery ratio: Higher recovery usually pushes brine concentration and operating pressure upward, which can materially change the energy requirement.
• Excludes intake and outfall hydraulics: Seawater intake lift, long pipelines, and brine discharge pumping can add a meaningful amount of kWh to the total.
• Excludes pretreatment and post-treatment: Filtration, chemical dosing, remineralization, and cleaning energy are not modeled separately.
• Electricity only: Thermal desalination systems such as MSF and MED are driven mainly by heat, and converting that to an electricity-equivalent number depends on the plant configuration.
• Not a guaranteed operating cost: Demand charges, time-of-use tariffs, minimum bills, and generator fuel use can all make the real cost differ from the simple blended $/kWh assumption.

If you need engineering-grade accuracy, use vendor performance curves, include feed temperature and recovery ratio, and break the plant into separate loads such as intake pumping, high-pressure pumping, pretreatment, and post-treatment. That kind of energy balance will always be more reliable than a first-pass calculator.

How to interpret the desalination results

• SEC (kWh/m³) is the cleanest way to compare desalination technologies or operating scenarios because it removes plant size from the picture.
• Total kWh/day tells you what the electrical system must actually deliver each day, which is useful for wiring, service capacity, generator planning, and storage sizing.
• $/day is the direct energy expense. To estimate a water production cost in $/m³, divide the daily dollar value by the daily cubic metres and then add the rest of your operating and capital costs.

For desalination planning, the biggest red flags are usually higher feed salinity, lower efficiency, and a power tariff that is much higher than expected. If one scenario looks expensive, compare it to a second scenario with lower salinity or improved energy recovery so you can see whether the cost gap is structural or just due to an assumption you can improve.

Scenario comparison for desalination planning

These illustrative desalination cases show how the calculator reacts when the feed water, efficiency, or throughput changes. They are not forecasts; they are a quick way to see which assumption is driving the result.