We have a solar array (2 120-watt panels ) and we plan to add a wind generator. The array by itself has met all our electrical needs keeping our 700 AH battery bank fully charged. But admittedly we don't have any really heavy draws, just the refrigerator, lights, fans and electronics. With the wind generator I was assuming that we could handle a watermaker (Spectra 150 running an hour or two a day) as well. But, there seems to be a consensus on this thread that you need a genset tor un a watermaker so what am I missing?
No, you don't need a genset to run an RO watermaker, provided it is a relatively small unit. When setting up a watermaker, there will be a few things you will want to do that the watermaker manufacturer may or may not tell you.
First, you want the watermaker output to have a dedicated water tank. This is for a couple reasons. First, if the RO membrane fails, you aren't mixing salt water with the potable water in the other tanks. Second, it gives you a source of chlorine free water to backflush the RO membrane. Chlorine will destroy an RO membrane.
Second, you want to have some way to transfer water from this tank to the regular water tanks on your boat, but have a check valve so that water only goes from this tank—see above for why.
Third, you want to size the watermaker so that you don't necessarily have to run it every day...but more like every third or fourth day. This reduces the amount of water used to backflush the RO membrane percentage wise, but keeps the watermaker operating regularly enough that pickling the membrane isn't necessary.
Fourth, remember, you don't want to run an RO watermaker in the harbor. Bacteria and petroleum wastes are fairly common in the harbor and both will damage the RO membrane. An RO watermaker should only be run in clean seawater—harbors and populated areas rarely qualify for this.