Solar-pumped potable — making the maths work at 1.8 bar.
Operating pressure is the single variable that makes or breaks an off-grid water supply. Conventional UF runs at 4-6 bar; RO at 10-60 bar. Both demand a power profile that small solar arrays can't sustain reliably. Drop to 1.8 bar and the whole power budget collapses to something a station, eco-resort or remote community can actually fund and operate. Here's the maths.
Why pressure governs everything else
For a membrane plant of any kind, the dominant electrical load is pumping. The pump pulls feed water through the membrane against the trans-membrane pressure differential. Higher pressure means more energy per litre — it's directly proportional. Specific energy (kWh/m³) maps closely to operating pressure in this class of system, with secondary contributions from controls, instrumentation, ancillary motors and (for some configurations) heating or chemistry dosing.
The practical implication for off-grid is binary. Pumps that need 4-6 bar continuously demand multi-kilowatt motors and either a substantial battery bank to ride out solar production troughs or a generator backup. Pumps that need 1.8 bar can be specified at a fraction of that draw and run on the kind of solar array a remote homestead, eco-resort or rural healthcare facility already has installed.
kWh/m³ specific energy for a Purus + RO polishing combination — versus 3-5 kWh/m³ for standalone RO. Tested in deployed customer systems and consistent with the published technical comparison.
A worked example — regional homestead, 2 kL/day
Take a representative scenario: a regional Australian homestead serving five people plus livestock-water demand, drawing about 2 kL/day from a roof-fed rainwater tank. ADWG-grade output required because the property runs short-stay accommodation through summer. Off-grid solar with a modest battery bank.
Daily energy budget — UF + UV vs Purus
| Component | Conventional UF + UV | Purus 50.2 (+ optional carbon polish) |
|---|---|---|
| Operating pressure | 4-6 bar | 1.8 bar |
| Specific energy (kWh/m³) | 0.8-1.5 (UF only) plus UV continuous | 0.8-1.5 combined |
| UV continuous draw | ~30-50 W continuous | N/A |
| Daily energy demand (2 kL/day) | ~3.6-4.8 kWh/day | ~1.6-3 kWh/day |
| Indicative solar array size | 1.5-2 kW dedicated to water | 600-900 W dedicated |
| Battery buffer required | Substantial (UV needs night-time draw) | Modest (no continuous load) |
| Backup generator | Recommended | Often optional |
All figures indicative. Actual sizing depends on raw water quality, tank insolation and load schedule.
The architectural difference
The key technical move is what happens in the absence of disinfection-by-exposure. Conventional UF + UV systems rely on continuous UV irradiation to inactivate microbiological contamination. UV doesn't remove anything — it damages DNA so contaminants can't reproduce — but it does require continuous power whenever water is flowing, and it degrades silently over time as the lamp ages.
The Purus dynamic membrane physically excludes pathogens at 10 nm pore size. Bacteria, protozoa, most viruses — all stopped on the gel layer rather than passed through and irradiated. Bonus: the membrane runs in cycles, with backwash on TMP triggers (typically 1-5 short cycles per day at this scale). When the system isn't being drawn from, the pump isn't running. UV would still need a recirculation loop or warm-up cycle.
Where this matters most
The off-grid power budget collapse opens up customer segments that effectively can't run conventional treatment economically. We see strong fit across:
- Remote pastoral stations — homestead supply plus food-prep and short-stay accommodation
- Eco-resorts and lodges — sustainability-positioned operators where chlorine taste and bottled-water dependency are brand contradictions
- Rural community supplies — small village or indigenous community potable systems where the operator-burden of a UV+chemistry program is unsustainable
- Regional schools and healthcare facilities — off-grid sites where ADWG compliance is regulated and reliable diesel backup is increasingly hard to justify
- Construction and industrial camps — temporary deployments where the goal is to minimise dependency on fuel deliveries
One implementation note
The system needs to be specified as a complete power-and-water package, not as treatment hardware bolted onto an existing solar setup. The pump motor, solar array sizing and battery buffer should all be sized together — getting the operating pressure right is necessary but not sufficient. We typically work alongside the property's existing solar installer or a regional electrical contractor to land a specification that doesn't undersize either side.
If you're planning a remote install or a solar retrofit on an existing rural water supply, send us a brief on the daily volume, current architecture, and solar/battery specs. We'll come back with an integrated treatment + power-budget recommendation inside five business days.