The Offshore Voyaging Reference Site

Replacing Diesel-Generated Electricity With Renewables, Part 1—Loads and Options

Originally I was going to continue from the last article by further analyzing Ed and Andy’s experiences with installing Watt & Sea hydrogenerators and removing their diesel generators.

But then I realized that it would be far more interesting to widen the mission to look at the overall practicality of replacing the generation of electricity from diesel fuel (main engine or separate generator) with renewables, particularly since there are so many claims being made out there that are based on pretengineering at best.

On the other hand, there’s no question that big advances have been made in renewables and batteries, which make replacing a diesel generator, or never installing one in the first place, far more practical than it was even a few years ago.

And we have Andy and Ed’s successes in getting rid of their generators after installing renewables to inspire us, too.

I plan to focus on boats that use more than 200 Ah at 12 volts (2.4 kWh) a day, (most live-aboard cruisers these days) since Eric has already done an excellent article on solar solutions for boats with lower needs.

Let’s dig in:


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More Articles From Online Book: Electrical Systems For Cruising Boats:

  1. Why Most New-To-Us Boat Electrical Systems Must Be Rebuilt
  2. One Simple Law That Makes Electrical Systems Easy to Understand
  3. How Batteries Charge (Multiple Charging Sources Too)
  4. 5 Safety Tips For Working on Boat DC Electrical Systems
  5. 7 Checks To Stop Our DC Electrical System From Burning Our Boat
  6. Cruising Boat Electrical System Design, Part 1—Loads and Conservation
  7. Cruising Boat Electrical System Design, Part 2—Thinking About Systems
  8. Cruising Boat Electrical System Design, Part 3—Specifying Optimal Battery Bank Size
  9. Balancing Battery Bank and Solar Array Size
  10. The Danger of Voltage Drops From High Current (Amp) Loads
  11. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 1
  12. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 2
  13. Battery Bank Separation and Cross-Charging Best Practices
  14. Choosing & Installing Battery Switches
  15. Cross-Bank Battery Charging—Splitters and Relays
  16. Cross-Bank Battery Charging—DC/DC Chargers
  17. 10 Tips To Install An Alternator
  18. Stupid Alternator Regulators Get Smarter…Finally
  19. WakeSpeed WS500—Best Alternator Regulator for Lead Acid¹ and Lithium Batteries
  20. Smart Chargers Are Not That Smart
  21. Replacing Diesel-Generated Electricity With Renewables, Part 1—Loads and Options
  22. Replacing Diesel-Generated Electricity With Renewables, Part 2—Case Studies
  23. Efficient Generator-Based Electrical Systems For Yachts
  24. Battery Bank Size and Generator Run Time, A Case Study
  25. A Simple Way to Decide Between Lithium or Lead-Acid Batteries for a Cruising Boat
  26. Eight Steps to Get Ready For Lithium Batteries
  27. Why Lithium Battery Load Dumps Matter
  28. 8 Tips To Prevent Lithium Battery Black Outs
  29. Building a Seamanlike Lithium Battery System
  30. Lithium Batteries Buyer’s Guide—BMS Requirements
  31. Lithium Batteries Buyer’s Guide—Balancing and Monitoring
  32. Lithium Batteries Buyer’s Guide—Current (Amps) Requirements and Optimal Voltage
  33. Lithium Battery Buyer’s Guide—Fusing
  34. Lithium Buyer’s Guide—Budget: High End System
  35. 11 Steps To Better Lead Acid Battery Life
  36. How Hard Can We Charge Our Lead-Acid Batteries?
  37. How Lead Acid Batteries Get Wrecked and What To Do About It
  38. Equalizing Batteries, The Reality
  39. Renewable Power
  40. Wind Generators
  41. Solar Power
  42. Watt & Sea Hydrogenerator Buyer’s Guide—Cost Performance
  43. Battery Monitors, Part 1—Which Type Is Right For You?
  44. Battery Monitors, Part 2—Recommended Unit
  45. Battery Monitors, Part 3—Calibration and Use
  46. Battery Containment—Part 1
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Jo Blach

It’s nice to get confirmation based on facts for my instinct. When I started to modernise my 40 year old boat, I got rid of both wind generators, mostly for aesthetic reasons but I also had doubts they’d be worth refurbishing. Now she looks more like a sailing boat again and less like a swamp-racer.

Arne Mogstad

I think maybe I’ve already written a little review on wind generation in the specific chapter, but anyway, I totally agree on wind being sort of outdated for most these days!

I use my boat in Northern Norway all year, and I’m rarely hooked up to shore power. In summer, even at this latitude (beyond the polar circle), I would say that solar wins, hands down! In winter, solar is useless here (actually it’s pretty much useless for about 8 months a year). This means wind is one of the few options on anchor that is truly self sufficient. During the winter we have a lot of wind! But personally, I would still recommend to put the money on a GOOD alternator and regulator combo instead, and just drop the wind generation.

For me, when living aboard on anchor in winter, the occasional running of the engine means having some hot water, plus a defroster on the cooling water gives some quick heat in the boat. That being said, the wind generator does sometimes significantly increase times between the need to run an engine. It is not useless (hence I have not removed it), but there are much better options for most people.

George L

I wouldn’t count wind generators out:

With the newer designs, the noise issue of wind generators has much improved.

Weight of a 350w unit (Superwind 350) is 11.5 kg for a super-sturdy unit and the weight of the support pipe that is welded to the arc (all alu) is about 1 kg. That doesn’t strike me as the end of the world even on top of the arc 2 m above deck, but our deck is bare when underway and the only contraptions above boom level are wind generators, wind instruments, radome and antennae. Cost is about 4K. In comparison a 2 ft radome is about 7 kg plus the weight of the bracket.

But clearly, it should be part of the mix and regardless what is done, good generation off the engine is indispensible.

Matt Marsh

We were recently docked beside a Niagara 35 that was decked out with all the liveaboard canvas and power generation you could ask for. Solar panels on top of the dodger, more solar panels on the bimini / dinghy davit arch, a full cockpit enclosure under the arch, a big wind turbine on a pole behind that….
The Niagara 35 is nominally just a hair behind our C&C 35 in most performance metrics, but viewed head-on, this one had easily double the drag area of our boat. Its owner had clearly given up most of his ability to sail to windward in order to fit all that stuff. In a region where two-thirds of all sailing is done close-hauled, his setup would have roughly doubled the amount of time he’d need to run the engine while underway.
In this case, it was a good tradeoff, since he rarely travelled far and simply preferred to do his job by laptop and cell modem in places without shorepower. But, on a boat that actually travels, all that solar and wind gear (and of course the big cockpit enclosure and the dinghy davits) may well have turned out to be a liability.

Michael Fournier

Well the solution would be to make most of that removable. The ideal setup for me would be to have anchored mode or ICW. Mode where you need power but not really moving much. And then passage mode when as much as possible is stowed below decks and the rig and decks are setup for sailing offshore. So take the canvas enclosure if it has flexible panels those panels can be removed and stowed in the v berth as no one really like sleeping in there off shore anyway. Disassembled the wind generator and stow that as well. Remove the dingy from the davits and stow in on the foredeck (or if a soft inflatable or folding floor deflate it and stow it deflated)

the way a cruising boat is setup inshore or at anchor does not have to be how it is setup when making a long offshore passage.

Colin Speedie

For me, a dyed-in-the-wool lover of wind vanes, It hurts to say that I think that there will be a definite spilt between suitable yachts for a vane or the W&S generator.
This would revolve around speed, with slower boats (i.e. less likely to surf) suiting the vane and faster boats (that can surf easily) suiting the W & S.
Slower ‘cruising’ type boats like our previous Ovni work brilliantly with a vane, but might not get the most out of a W & S.
I’d bet, though, that your J boat would be a challenge for any vane gear, due to her speed and the rapidly changing apparent wind that that tends to throw vanes off track.
Otherwise you have to change down a gear with a fast boat to keep the vane happy, and who likes putting the brakes on?
Looking forward to Part II as we’re facing the same conundrum!

Carl Johanson

Thanks for an interesting article and comments from you all so much more experienced than me. I sail mostly in Nordic coastal waters so no long passages (but I hope to sail further away when retired).
Most comments on wind turbines assume that they are permanently mounted on a pole in the stern or on an arc. But there is an alternative, is there not? I would not like to have a wind turbine on pole for reasons discussed above (and it would not go well with the teak and mahogany on my 54 year old yacht). But when at anchor or moored I do not mind hoisting my Ampair as high as possible in the fore triangle between mast and forestay. There, aloft, it is out of the way, catches the wind better 10 m above deck and can hardly be heard at all. All right, it takes me 15 minutes to bring it on deck, mount the turbine (propeller) on the alternator, hoist it, connect the cables and so on. And 15 minutes to lower it and stow it away. But anchoring or mooring a boat is not like parking a car anyway and I am not in a hurry. The Ampair can actually be used as a hydrogenerator too when sailing if connected to a line and rotor (like a Walker’s Taffrail Log) but I have never tried that. The Watt & Sea sure is a lot easier to use, probably more efficient and less prone to sharks bites.
It certainly would not suite everybody but couldn’t a hydrogenerator when sailing and a temporarily hoisted wind turbine when at anchor be a complement to solar panels, at least for some?

Matt Marsh

You would need a way to brake the spinning blades before lowering it. And if that brake failed, you’d have an interesting problem on your hands.
Also, the added drag of a wind turbine in the foretriangle will make most sloops & cutters yaw / slew around at anchor even more than they already do. To promote good behaviour in an anchored boat, we generally want less air drag forward and more air drag aft.
So,are jointed wind generators possible? Yes. Sensible? Maybe in a few cases, but they’d be a minority.

Alan Sexton

This is a very topical discussion for myself and a lot of other cruisers in the South Pacific coming to the end of the winter cruising season.
Passaging between New Zealand and the islands on a 14m yacht such as mine is around a 7-8 day passage depending upon destination typically one of Tonga, Fiji, Vanuatu or New Caledonia. We are running a weather gauntlet in both directions, particularly to avoid lows coming across the Tasman. So of course we look for a weather window to give us a good passage and this will typically involve motoring thru a high and any other time boat speed drops off. On my most recent passage to Vanuatu from NZ early June I clocked up ~75 engine hrs including 50 straight line motoring thru part of a high. There were probably only a couple of days where the engine was run purely for power generation.
At anchor this cruising season has seen a lot of overcast windy wet (just had 7 days continual rain here in New Caledonia) weather, which combined with low sun angles (its winter here) has meant solar generation, even for those with extensive arrays, has been way below expectations and hence required a lot more engine running. My 330W solar installation is normally more than adequate to cover loads at anchor, but not this year. Next time around for our cruising region (SE trade winds) I will certainly think about a wind generator. A small permanent generator would be preferable but I do not have the space for it. Have seen a lot of people running portable generators for battery charging, yes I know this has been discussed here previously.
I believe a hydro-generator makes sense for long passages eg trans-Atlantic, Coconut Milk run, Indian ocean, but for our sort of passage making not so much.

Stein Varjord

Hi John,
Your observations and calculations match mine.

You mention efficient fridge and freezer with huge amounts of insulation. I think most boats can save a lot of power by taking a good look at this. We have a brand new Isotherm, of their most efficient type. When I added just 19mm of soft foam on all sides but the door, its average consumption more than halved. A total fail of the original insulation! Other makes are not better. We want a freezer too, which puts way higher demands on insulation, so I’ll build that myself! (For space saving, it’s worth looking at vacuum bagged foam insulation.)

Wind power is in my mind only suitable when not moving, which indicates it’s a potentially good match with a Watt & Sea or similar. When one isn’t suitable, the other one is. However, as mentioned earlier by both you, me and many others, a wind generator needs wind, which is exactly what we try to avoid when anchoring. In my mind, the only way to make a wind generator significant is to have one with slightly bigger wing span than normal, a more powerful alternator, and then somehow hoist it to above the top of the mast. (Only when at rest, as mentioned.) That’s possible, of course, but I don’t know how to do that in a good way.

Since we have a cat, our solar situation is different from what’s possible on a mono. We can fit over 3 kiloWatt of semi flex solar with zero extra windage and no extra carrying structure, on cabin top and hard bimini. We’re doing fine with far less at the moment, have no diesel genset and never run the engines to charge, unless we want to move by them. We really don’t use much power. Thus, we don’t need a wind generator, unless we go to northern Norway or so in the winter, which we might some day.

Matt Marsh

Indeed…. Reducing energy consumption is usually easier and cheaper than generating more energy. John talks of 5 kWh/day being a heavy-demand boat, yet that is only 17% of what a couple living in a typical Canadian home on shore would use. Imagine the power generation we’d need on our boats if we hadn’t already optimized everything electric for efficiency!

Refrigeration is usually the biggest or second-biggest (after autopilot) component of a cruising boat’s power budget underway, and is almost always the dominant component at anchor. It’s the logical first point to attack if we are trying to replace diesel-generated electricity with renewables. Stock designs in production boats usually have just enough insulation to achieve acceptable chill-down times and compressor run times; any more would eat into usable fridge volume. A long-term cruiser needs better insulation. (Incidentally, while vacuum panels are great when brand-new, I’m inclined to prefer a modern aerogel like Aspen Spaceloft whose thermal performance isn’t lost if it gets a pinhole air leak.)

Matt Marsh

Aspen claims that Spaceloft Aerogel “repels liquid water but allows water vapour to pass through.” They claim to have wrapped 1700 km of subsea pipelines in the stuff and to achieve thermal conductivity of <15 mW/m-K at 25°C in that environment. (Compare to 25–40 mW/m-K for solid styrofoam or ~20 mW/m-K for double-layer polyisocyanurate with a foil-faced air gap.) Still three times worse than a perfect brand-new vacuum insulated panel, but also twice as good as a VIP with the slightest hint of a pinhole or seam leak.
I haven’t been able to get my hands on a sample personally yet, though.

Dick Stevenson

Hi Matt and all,
I was able to add some insulation on the outside, but things still needed improving so, as I had a big freezer, I added on the inside. A casual look at Aspen Aerogel seems to indicate there are handling safety issues and, perhaps, it should not be right close to food products.
Has anyone experience with this stuff?
My best, Dick Stevenson 

Matt Marsh

The only light blue rigid insulating foam that’s totally 100% waterproof on decade-plus timescales, that I know of, is DuPont Styrofoam XPS. Good stuff. We used to make floating docks out of it back in the days before welded plastic culvert-pipe floats were reliable.

Stein Varjord

Hi Matt,
The Aspen Spaceloft aerogel sounds very interesting. The only aerogels I’ve seen were early experimental stuff 35 years ago. I was at the national Institute of Technology, so I got to see much new stuff. The stuff I received was ridiculously light, almost floating in the air, but extremely fragile. I even tried to make an epoxy sandwich laminate with it, but it was too fragile for any treatment. I haven’t paid attention to it later. Cool that it has developed. I’ll look into it for our freezer.

I’ve no experience with vacuum insulated foam, but plenty with vacuuming foam and laminates. I’ve not planned the design yet, and might just go for normal foam, but my idea was:
– Build and glue up the insulation box, just foam.
– Make all surfaces smooth, no sharp corners.
– Cover all surfaces with some breather cloth.
– Make a flexible membrane for the whole thing, perhaps silicone.
– Connect a hose with a vacuum gauge and a connector valve.
– Mould a hard shell for the inside, perhaps also outside.
– Install the box in place and pull the vacuum.
– Monitor the gauge and pull more vacuum when needed. I don’t believe a vacuum will keep up unaided for decades, almost no matter how well the membrane is made.

I totally see that this isn’t a suitable plan for the average boater. I haven’t sorted out the always important details, but I think it could work for me. I do have a vacuum pump and probably also the other needed tools. I don’t know when I’ll start the process, not soon, but I’ll share what I learn from it.

Rene Blei

Thank you for this timely article. A few years ago i did buy a gasoline inverter genset. Our fridge is a domestic side by side and not well insulated and plug it directly into the genset, but had my concerns you mentioned. After reading one of the comments though I do feel better. Another reason we got it, is when there is a total black-out I can start it and run the two large submerceble pumps.
Was told the flexible solar panels dont have the long life like the rigid ones, but do like them. What is your experience ?
Hope you all came thru ” LEE” well, but at least the crew of fishing boat #51 can talk about after being hit by a 40ft rogue wave, while their boat sank shortly after being rescued.
Thanks again.

Eric Klem

Hi John,

I have to agree on wind generators, outside of very consistently windy areas like the anchoring in the trades or places where solar doesn’t work, I think their time has passed. When you consider typical apparent winds whether they be at anchor or underway, they are surprisingly low. At the times when the apparent winds are high, you are often beating to weather heeled over which really messes with blade efficiency due to the misalignment of the turbine axis to the airflow and you are also putting a lot of drag on the boat. I didn’t do my homework on our first boat and bought into the concept that either there will be wind and it will charge or you will be motoring and charging that way. In truth, most days really fell in between where we could sail but the wind generator output was very low so even for a boat that lacked refrigeration, we struggled to keep the charge up.

I think it is useful to look at the motivation for replacing generation with diesel. For some it is environmental (not always obvious what is better, some of these components have a lot of embodied emissions), noise, smell, maintenance, space, fuel range/availability, etc. This pushes you into different solutions and doesn’t always mean that the goal is to replace charging with diesel, it might just be adding no more engine hours but charging hard during those hours which I know you already advocate. Similarly, I think it matters how often one is likely to motor anyways, a lot of passages can go long periods of time without starting the engine. I have one solution that can work well for coastal cruisers but not long passagemaking that I am curious to see whether you will mention in part 2.

I get a little nervous equating average renewable energy output need in the same way as determining average diesel charging energy output need as you can control when you turn on the diesel but you can’t do the same with the renewables and there are periods of low charging output and high load. A giant battery bank can allow this as it essentially buffers everything for you, but it will be even bigger than the battery that I recommended which would get you through average periods of poor weather. Alternatively, you can use diesel to make up the difference but that gets away from the banish the diesel goal (completely banishing it is not my goal at least, a small amount of charging from it makes a lot of sense for the extreme cases). With typical northeast US weather and our sailing style, I have found that you need to multiply the amount of energy from diesel charging by 1.3 to 1.5 to get the actual average potential output to size the renewables but this amount will vary based on your weather and usage patterns and how adverse you are to using the diesel. On the other hand, excluding certain consistently windy passages, most boats do occasionally motor and if they have a good charging setup, it is amazing how much this can help and you are currently trying to model no diesel charging. In the modeling that I did, if you exclude the undersized battery bank example, the average solar potential was only 48-64% of the total energy needed for charging, the rest was from the alternator despite relatively little motoring.

Eric