Energy Recovery Watermakers — Running a Watermaker on Solar and Batteries
- Adam Morris
- 2 hours ago
- 8 min read
After ditching power generation from marine diesel generators a few years back, all new equipment that goes on Connie has to fit into our (mostly solar-generated) power budget. It was long past time to re-add watermaking to Connie's list of skills.
There's a big allure to the Energy Recovery—or "ER"—watermakers, namely the promise to use a fraction of the power per gallon/liter. "Save 75-80% energy per liter/gallon!" is prominently featured on every ER manufacturer's marketing materials.
Long story short, we decided to test out a Schenker Smart 60, and found that the claims can be true, but strangely not under the advertised circumstances.
Was it worth it? For Connie's generator-less setup, yes, I believe so. For those not looking to ditch the generator? Very questionable. There's the premium cost to consider and added points of failure.
Today let's dig into the truth to those 75-80% power reduction claims, review some comparisons, and discuss who I think an energy recovery watermaker (and it's hefty budget) makes sense for.
Jump to...
Energy Recovery vs Conventional Comparison
Instead of wasting the pressure in the salty reject stream (brine), an energy-recovery device (ERD) captures that pressure and uses it to help pressurize the next slug of seawater going into the membrane—which means your electrical pump doesn’t have to do all the work.
A conventional watermaker uses a beefy high-pressure pump to push all the incoming seawater through the membrane. The brine leaves the membrane still at very high pressure and is then thrown away across a valve—along with that sweet sweet energy. In an ER system, the brine’s pressure is handed back to the incoming seawater through a pressure-exchange or intensifier mechanism.
In the past, there were very few energy recovery options—Spectra being the original followed by Schenker out of Italy. Now we have options from the likes of ElectroMaax, Osmosea, Aqua-Base, Parker, Eco-sistems, and Blue Gold.
Depending on where you live, availability of these newer brands may be scarce, however. Parts and support may be even scarcer.
Comparison Table of Energy Recovery vs Conventional Watermakers
There are many watermaker manufacturers targeting the recreational marine industry, but let's focus on common ones that I've actually seen installed on boats in the wild (and not just in booths at boat shows).
We'll compare a couple of energy recovery (ER) watermakers with a few conventional units. Note that there are watermakers with rated outputs all across the range for both ER and conventional. However, as we'll discuss, most conventional watermakers that people own are going to have a much higher total rated output than an ER, as you'll see in my examples below.
Pay special attention to the "W/L" or Watts per Liter in the table below:
A few notes on this table:
Prices are from United States distributors as publicly available at the time of writing and may vary drastically by country.
There are a number of conventional AC watermakers that I have personally seen at boat shows that are in the $10,000-15,000 range for the same 40gph output. I have not included these, as I have never seen one in the wild.
Price comparison gets very muddy when you start adding options, especially automatic features. The Rainman, for instance, goes from $5,000 to $10,000 in a hurry.
We can see that based on just the advertised specs, the gains in W/L are impressive, but 75-80% power reduction seems like some pure marketing nonsense.
When we put it to the test, though, our Schenker ER unit can actually live up to the marketing claims, albeit when it's set to half capacity.
Our One-Year Test of the Schenker Smart 60—Sipping Power
The headline efficiency of 75% energy savings vs traditional did show up for us, but only running it on single-pump mode. The Schenker Smart 60 actually has two pumps, allowing you to run only one at a time to run at half power usage. Pretty neat, actually.
With one pump, the Smart 60 was producing 40-42 liters per hour (10.5-11GPH) at only 110W. That's a seriously impressive 2.75 W/L. However, in dual pump mode, the watermaker hits (or slightly beats) the advertised 60 L/h at ~240 W, but efficiency falls back toward ~4 W/L.
The power usage for one pump is so low that it barely requires any consideration in our power budget. If we're starting the watermaker as we leave the boat, the solar more than keeps up, and we usually come back to fresh water and full batteries.
Quick note: almost all of our testing was done in ideal watermaking conditions thus far—clear, warm Caribbean waters. The conditions can have a significant impact on water production, so we'll have to provide updates as we do further testing.
To Generator or Not to Generator
As I mentioned earlier, most of the conventional watermakers that I see in the wild are going to have a much higher rated output than energy recovery. That's because folks are going to want to optimize for different things. If you're using a conventional watermaker, the goal is to produce water as quickly as possible to minimize generator runtime. The energy reduction is much less important since you're producing so much power anyway.
Cruisers tend to run all of their high load appliances at the same time while the generator is running, so energy reduction can have an impact if you're already reaching limits in your generator output. But, most folks can comfortably run a watermaker, an air conditioner or two, and the water heater, as well as still get some battery charging in there.
However, if you're one of the many that is on the mission to get rid of the generator entirely or only run it sparingly, this equation changes completely.
So, Who is an Energy Recovery Watermaker for?
The Case that a Generator is Becoming Irrelevant.
If you're at the stage that your generator is ready to be retired or you've outgrown your current generator—or maybe you just don't want to hear an engine ruining your most peaceful anchor moments—you've already got significant investments to make.
Today's marine generator can easily start at $15,000 before even discussing the installation. In our case, to even remove the old generator, we had to dismantle part of a stateroom ceiling, hire a crane, pull the propulsion engine, and then have a crew help us get the generator out. That's a lot of budget that can be put into other systems. And, on a catamaran, that's some decent weight savings.
I have discussed this at length in other articles, but, just as a refresher, today's marine tech gives us high output alternators, smart regulators, and many more solar options than before—plus cheap lithium battery options to store all of that energy. If you're looking to squeeze in more solar, I also suggest my article on the new CIGS panel consturction and its advantages.
The upsides, of course, are not having a whole entire extra engine to maintain and your peace and quiet at anchor. However, the tradeoff is that we're on a much more strict power budget, and power efficient marine systems are more expensive and often more complicated.
More Complexity Means More Maintenance and More Failures
The process that ER systems employ means that there’s a bunch of new parts that are going to be taking abuse. When I listen to the signature “heartbeat” from an ER watermaker, I hear a combination of innovation and components taking abuse.
I'm impressed with ElectroMaax's take on this problem. Their goals are to make wear parts more serviceable, and upgrade various parts to titanium for a longer service life.
The video below, while a bit dry, is a great explanation of what ElextroMaax focused on tweaking, It's also a good explanation of additional maintenance to be expected and what failure points look like.
This Clark Pump based design, for instance, still requires piston maintenance, seals to be changed, and various other wear parts that need to be monitored. And incorrect maintenance or operation can cause catastrophic failures.
Automation Features Add Even More Complexity
For our install, I added Schenker’s touch panel and all the optional sensors that go with it—automatic salinity divert, flow, and pressure. That's roughly $2,000 worth of add-ons .
This makes the unit very set-it-and-forget-it. If we're producing less water per hour than a conventional, we're running the unit for longer and more often. But, a goal of this whole generator-less setup is more nature sounds, less mechanical noise.
In actual usage, we wanted to be able to just hit a button on our way off the boat to our next adventure mission, and arrive back stocked up with freshly made water.
With the added salinity sensor and diverter relay, the unit knows when the water salinity level is safe, and automatically diverts it to the tank, without any user input. With an extra button push at startup, the unit also auto-flushes itself with fresh water after the run—extremely important if you don't want to severely reduce the lifespan of your expensive components.
This is all managed from the remote panel, which is very helpful for anyone whose watermaker is tucked away in an engine compartment or any hard-to-get-to space.
All this culminates into a great experience so far running the watermaker. We hit two buttons before hopping off the boat and come back to fresh water. If cruising is about spending a lot of money to make everything in life harder, these conveniences won't aid in that quest.
Schenker-specific Install Learnings
These may all be specific to the Schenker install, but I suspect similar issues to exist across the industry. Watermaker companies are generally small manufacturers. If you're expecting a Victron level of polished documentation, Schenker's manuals and labeling is going to be quite lacking.
The documentation in my box didn’t include the optional wiring diagrams for the touch panel, flow sensor, and pressure transducer. They exist; they just weren’t there.
The English translation in the manual is serviceable but occasionally asks for a second pass. Coupled with the organization, you might end up doing something like ordering 3/4" hose after seeing the spec for 3/4" thru-hulls, when pages later you'll see that a 5/8" hose is actually the spec.
Also, the feed pumps are more sensitive to getting enough water flow than the manual will lead you to believe. My seawater inlet is within the specified distance from the pump group. However, in full power (both pumps) mode, I still had cavitation problems from the pump's not getting enough water.
I figured that my run was a bit too complicated, and that was confirmed by Rich from Cruise RO Water and Power, a US importer for Schenker Watermakers. Ninety degree bends are an issue for the run.
I also wish that the Schenker came with NMEA 2000 integration. There is an expensive optional box that can be added for MFD integration, however, I see no reason why N2k can't be built into the remote panel and then easily connected to the N2k network. This would allow me to get all of the data into SignalK and provide easy remote monitoring when we're away from the boat.
Wrapping Up
Given the added complexity, points of failure, extra maintenance, and increased cost of ER Watermakers, I think they really only make sense if you're on a generator-less or generator-minimizing mission like we are. In fact, it's kind of a must-have if you're heading into this journey.
I do think that the automation features (on any watermaker) change the way we handle watermaking. It's squarely in the quality-of-life improvement category, albeit at a hefty price tag.
If you've got questions or have an energy recovery watermaker nightmare to share, drop a line in the comments to help folks who are also making this investment!
