To make twice as much water you may need to either install a set of batteries to run at night, or install twice as much RO hardware to run during the day. Whichever's cheaper.
I made a comment with regards to this a while ago [1]. I'll repeat it here as I think it is relevant:
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I’ve heard on the grapevine that facilities are now being designed which work at under 100% capacity in order to soak up excess/cheap power.
I believe this is coming about because: 1) the high cost of power and presence of sporadically cheap power makes it economically viable, and 2) designing equipment with lower duty cycles can actually provide substantial cost savings. Ie a facility which only runs 50% of the time is much cheaper to build & run than once which runs 100% of the time.
It'd be a boon for renewables if energy consuming plant costs were less dominated by investment in equipment.
Imagine doing shift planning at such a site though. Eight days from now, there's a 60% chance of wind in excess of 5m/s between 22.00 and 06.00. But labour costs would be 130% higher than 06.00 to 14.00 on that day. On that morning shift there's a 50% chance of clear skies ...
If only there was some form of programmable electronic computation device that could be used to solve such complex sets of constraints modelled as equations :)
I think the savings in planning for low duty cycle probably result from reduced redundancy i.e. installing one pressure pump instead of two. Which naturally means when there is a low chance of excess energy is a good time to work on maintaining the systems rather than just taking one off line and working on the other.
This means that you just staff it at a consistent level and plan the work around the energy levels.
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I’ve heard on the grapevine that facilities are now being designed which work at under 100% capacity in order to soak up excess/cheap power.
I believe this is coming about because: 1) the high cost of power and presence of sporadically cheap power makes it economically viable, and 2) designing equipment with lower duty cycles can actually provide substantial cost savings. Ie a facility which only runs 50% of the time is much cheaper to build & run than once which runs 100% of the time.
Sorry I cannot cite sources right now.
[1]: https://news.ycombinator.com/item?id=18929542