Can a watermaker run on solar alone?
Yes — but the system decides it, not the sunshine. 6 of the 30 rated systems make 100 litres inside 500 Wh, which is comfortable on a modest array. 11 land between 500 and 1,000 Wh — most of a 400 W panel's entire clear day. The other 13 are not realistic on solar alone.
The number that decides this is your surplus, not your array. A 400 W panel yields roughly 1,600 Wh on a clear day, and the fridge takes a large and non-negotiable share of it before the watermaker sees anything. For many cruising boats the honest water budget is 500 to 1,500 Wh a day — which is why the tiers above are measured against that rather than against a panel's rating.
The systems in the comfortable tier are almost all energy-recovery designs, which use the pressure in the outgoing brine to help drive the incoming seawater instead of dumping it overboard. That one difference is worth a factor of three or four in watt-hours per litre, and it is the whole reason solar-only watermaking works at all.
Two practical caveats. Solar output collapses under cloud, so size the tank rather than the array for a bad week. And run the watermaker in the middle of the day, out of the panels, rather than in the evening out of the bank.
The 6 systems that make 100 litres for under 500 Wh a day.
| System | Power | Output L/hr | Draw W | Wh per litre | Price |
|---|---|---|---|---|---|
| Zen 30 Schenker | 12/24V DC | 30 | 110 | 3.7 | $6,300 |
| Zen 100 Schenker | 12/24/48V DC or AC | 100 | 400 | 4.0 | $9,600 |
| Ventura 150 Deluxe Spectra | 12/24V DC | 24 | 108 | 4.5 | $6,000 |
| Ventura 150 Connect Spectra | 12/24V DC | 24 | 108 | 4.5 | $7,400 |
| Newport 400C Spectra | 12/24/48V DC | 64 | 288 | 4.5 | $14,500 |
| Zen 50 Schenker | 12/24V DC | 50 | 240 | 4.8 | $7,800 |
Where this is worked through
Other quick answers
Where these numbers come from. Every figure on this page is computed at build time from the comparison table — rated output and rated draw as the manufacturer publishes them, with watt-hours per litre derived as one divided by the other. Nothing is typed in by hand, so nothing here can drift from the table. Where a figure is an assumption rather than a specification it is labelled as one. Methodology · the table.