Desalination Energy Calculator

Modern SWRO plants with energy recovery devices (ERDs) typically consume between 3 and 5 kWh per cubic metre of product water. Older plants without ERDs can consume 8–15 kWh/m³. The exact figure depends on feedwater salinity, recovery rate, pump efficiency, and membrane fouling conditions.

An ERD captures the high-pressure energy from the brine reject stream and transfers it back to the incoming feedwater, drastically reducing the net power needed from the high-pressure pump. Pressure exchanger ERDs can recover up to 95% of brine energy, cutting total plant energy consumption by 50–60% compared to systems without ERDs.

Recovery rate is the percentage of feedwater that becomes usable product water. Higher recovery means less water is wasted as brine, but it also increases the osmotic pressure the pump must overcome — raising energy demand per cubic metre. For SWRO, 40–50% is typical; brackish water systems can achieve 70–85%.

Higher TDS means higher osmotic pressure, which requires more energy to overcome during the reverse osmosis process. Seawater at ~35,000 mg/L TDS requires significantly more energy than brackish water at 1,000–5,000 mg/L TDS. This is why brackish water desalination can be 5–10 times more energy efficient than seawater desalination.

Yes — solar PV is increasingly used to power RO desalination plants, especially in remote or off-grid locations with high solar irradiance. The main challenge is intermittency; plants typically pair solar with battery storage or grid backup. Solar-powered desalination is most cost-effective where grid electricity prices are high and solar resources are abundant.

Energy costs for SWRO desalination typically range from $0.20 to $0.60 per m³ depending on electricity price and plant efficiency. When capital costs, labour, chemicals, and maintenance are included, the total cost of water from large SWRO plants is generally $0.50–$2.00/m³, though smaller or remote plants can be significantly higher.

The utilisation factor (also called capacity factor) is the percentage of time a plant operates at full rated capacity over a year. Most plants don't run at 100% due to maintenance, seasonal demand variation, or downtime. A typical utilisation factor is 80–90%. It directly affects your annual energy consumption and total operating costs.

The theoretical minimum SEC is based on the osmotic pressure of the feedwater and the recovery rate. In practice, SEC accounts for high-pressure pump efficiency, energy recovered from the brine stream, and auxiliary loads (pre-treatment, post-treatment, instrumentation). The formula used here estimates SEC from osmotic pressure (driven by TDS), pump efficiency, and ERD recovery efficiency.