As a voyager who has had a generator for the past 20 years, it suddenly struck me that for most usage profiles, the decision, generator or not, is an amazingly simple one.
Do You Need A Generator?
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How about DC Generators?
I have not crunched any numbers but converting down from AC back to DC is fraught with losses in efficiency. Why not just use DC ? For ac loads an appropriately sized inverter should do the trick. Although I personally would try to avoid having 220v AC anywhere on my boat.
Food for thought…
Rgds
Patrick
Hi Patrick,
A very good point that we have discussed at some length in the comments to other posts. The bottom line seems to be that while DC generators are undoubtable more efficient than making AC and then converting to DC, the problem is reliability. AC generators are made in large volume for commercial purposes and are extremely reliable. DC generators are made in small volume, mainly for yacht use and we have had a large number of reports of problems with these units.
I see your point regarding the production volumes. On the other hand it baffles me a bit to hear of lots of problems with them, what sort of problems ? . I have never actually used/maintained one so I have no first hand experience with DC generators but … DC generation is not an exotic science …. your are still looking at an alternator and a some regulation circuitry. Or am I completely off base here ?
Regards
Patrick
Hi Patrick,
You are right, the technology is not complex. However, never underestimate the combination of low production volume, no proper prototype testing and no proper quality control to produce products with very high fail rates. Come to think of it, much of the yacht gear market is living proof of that! That’s why Phyllis and I use commercial gear whenever we can fit it in, even when it is substantially more expensive than the yacht equivalent.
For example, our Northern Lights generator—designed and built for commercial use, on and off the water—has run reliably for 22 years with only one failure—an oil pressure sensor. Contrast that with the yacht DC generators that, from what I’m hearing, have a hard time running for more that 20 months without problems. Alternator alinement, overheating, regulator problems, burned bearings, and on it goes.
I understand that existing “yachts DC generators” are in fact home hobbyist equipment sold to yachtsmen, and are much lower quality than typical “yacht AC generators”, because the yachts DC generator market is not big enough to justify specialized fabrications (better than home-hobbyist and not as good as professional equipment..).
Being a electrical engineer by training, I think it is pretty easy, and not very expensive, to assemble yacht-AC-generator type diesel-engines and alternators to build very decent yacht DC generators, but that is my opinion and you won’t find them today on the market.
Technically speaking, it looks very easy to assemble a small genset diesel engine with a marine-grade DC alternator+regulator and associated paraphernalia.
The diesel engine could be the same as Fisher-Panda’s gensets (Farymann brand, made in Germany, looks like all Fisher-Panda engine paraphernalia are stock farymann parts….). The alternator should be a 2500 rpm, 4KW heavy-duty or marine type, directly coupled to the engine.
As an added bonus, diesel-engine regulator might be coupled with alternator-regulator and perhaps batteries management system to slow-down the engine when operating at limited power.
This solution seems technically obvious and should not be very expensive. Point is that today’s market for this kind of equipment seems too limited to allow the development of commercial/industrial offerings in that field, but I guess many good mechanics can assemble that using standard components.
The DC generator situation basically boils down to there being a lot of options that are light duty, low production volume, and aimed at markets where gear failure is more easily tolerated.
If you’re on a tight budget and want a DC generator for battery charging only, you could do far worse than to mount a 150 amp truck/bus alternator to one of the small industrial diesel engines that are normally used for refrigerated trucks, mini excavators, etc. Assuming you make sufficiently beefy mounts and brackets, such a setup is quite reliable and can be easily repaired in the field with common parts.
If you want an off-the-shelf unit, and you want it to be long-lived and reliable, then a conventional AC generator (the kind with big heavy coils and no fancy electronics) is probably the way to go.
And for something entirely different: An engine driven variable speed AC generator that is not a DC alternator plus an inverter.
http://www.marine-surveyor.com/newsletters/9711.html
It looks very much like a DC alternator plus a regulator, an inverter and a switch in the same box.
The main point is that you don’t need an intermediate battery when using this system, because the power regulation logic of the inverter seems to regulate directly the alternator’s excitation circuit. Plus you may hope that a regulator plus an inverter in the same box are more efficient than a regulator and an inverter in 2 separate boxes (?…).
Last, this system can generate up to 3.5kw (30A. * 115V) from a 150hp engine (about 110KW), that is at most 3.2% of the engine output. I think it is not a good idea to keep that engine running at idle just to use the microwave or the curling iron with this device. Corresponding diesel-fuel costs and diesel-engine amortization/repairs costs might well be prohibitive…
Hi Laurent,
No idea whether this is a useful system or not.
Looks like a DC alternator plus an inverter/controller to me as well, even though they imply otherwise.
It does come in sizes up to 18 kVAwhich would have an input power requirement of 34.2 hp. Certainly enough to load the typical propulsion engine in a 40′ sailboat. Of course, would you have the capacity to use or store that much output?
For a boat with an autopilot but no freezer or air conditioner, I usually lean towards specifying no generator. Instead, I’ll often call for a larger battery bank and larger main alternator than might ordinarily be expected. The autopilot can then run from the batteries alone for at least a day, ideally more, along with all other on-passage loads. And the bigger the battery bank, the greater the charging current it can accept.
With perhaps 300 Ah (@ 12V) more battery and 50 amps more main alternator than would be typical, you can come closer to properly loading the main engine when running it for charging purposes. A big alternator drawing 5 hp from a 30 hp engine is a big enough load to get the engine into a comfortable (although admittedly not optimal) region of its fuel map. The extra batteries take up a fair bit less space than the generator would.
If you want air conditioning or a big freezer, you need a generator. (But I do think it’s easier, and an awful lot cheaper, to simply decrease clothing and/or increase latitude if you find the weather too hot.)
I think that the charging profile of new battery technology could change the analysis. While I am not rushing out to buy lithium ion batteries for my offshore boat today, hopefully the EV industry will be pushing the limits and the reliability factors for us in the near future (very near?). Almost all new battery technology is focused on aggressive (fast) charing profiles which will ultimately eliminate the need for a generator and allow sailors to use main engine charing more efficiently.
Simplicity is what we try to stick to… so we won’t have to worry about the complicated systems required to support something equivalent to a floating apartment.
My husband, Bill, and I have been circumnavigating since 2011 for 6 to 9 months each year. Our ocean crossings have been long (the longest from Victoria, B.C. to Hiva Oa, in the Marquesas Islands, which took 40 days). The Indian Ocean crossing was the next longest at 21 days… and many in between.
We do not have a refrigerator let alone a freezer. We use a wind vane. We use LED lights. We do not have a watermaker. We catch fish and eat them when they are fresh. And we appreciate the fresh meat when we get it. Otherwise our food is delicious though not refrigerator dependent.
We do have a 85 watt solar panel to supply enough amps to run our lights and electronics. I can’t imagine having to deal with a complicated, noisy, bulky, generator on our sailing vessel.
I guess in answer to your question “Do you need a generator?” we say a resounding “NO”. 🙂
I concur with John’s determination that a freezer of any reasonable size means a generator. I also think that for many cruising boats, a dc genset is a much more sensible solution than an ac genset. I have lived with a dc genset for 8 yrs now and paid attention to the field and feel that they are every bit as difficult as has been implied above. Mine is basically a Kubota tractor engine attached to a 150 amp alternator and, with a good deal of effort, have made it work for me. The problem is usually not the engine or alternator, it is the “marinization”: the emergency fuel shut offs, the temp sensors, etc. I have slowly stripped mine of much of its marinization and made it more a manual operation. I still believe that dc generation is a more sensible approach, and just wish someone built one you largely did not have to think and worry over.
Dick Stevenson, s/v Alchemy
This is what I did to solve this DC Generator puzzle
http://www.cruisersforum.com/forums/f14/dc-generator-the-smart-way-to-go-65703.html
Great resource , Morgans Cloud.
Regards
And then there is “Do you want a genset?” We are increasingly wimps. We cruised in very warm climes for decades, and gradually we lost our youthful tolerance for heat and sweat soaked sheets, etc, etc. So in addition to wanting to freeze a lot of food, I would add, do you want to provide a reasonably cool sleeping environment in the lower latitudes.
When we equipped our boat we included a genset. Driven by a Farymann, it has failed us three times based on bad water pump design, bad exhaust system design and a bad starter motor. But absent those incidents (more frustrating than anything else) we have almost as many hours on the genset as we do on the main propulsion. That was until we installed solar panels. Now the genset only gets used when we simply cannot sleep because of heat and, more so, humidity — and when the solar panels have been cloud impaired for a few days. The reduced usage is now to the point we run the genset for a few minutes each Tuesday to keep it fit.
As to DC gensets. We looked at this long and hard. It came down to not wanting an inverter large enough to run the air conditioning. And we didn’t want the associated cycling stress on the batteries. The payback point on a DC genset + inverter + batteries was unattractive compared to AC + charger/inverter + batteries. This wouldn’t matter to folks not planning to own a boat for very long, but we set the minimum period to 15 years in our assessment.
In retrospect, we goofed, but got the same answer (serendipity). The load that has been the system determinate has been the water heater. And just as we won’t use the main engine for charging at anchor, we won’t use it for hot water either.
Oh the tribulations of life afloat.
Hi John,
In general, I agree with your assessment. However, I think that it is really important to look at your loads before going to a genset option. The most obvious one to me is refrigeration although Chris brings up good points with AC (I have no experience with AC on a boat). At steady state, your refrigeration load is determined by the insulation, how often you open the door and what the coefficient of performance is for the system. Your major transient state will be getting the system cooled down and that will largely depend on how much you put in and how much you want to change the temperature. This transient issue can be important in some cases such as where you are bringing groceries straight from a supermarket to your boat on the hook and not an issue in others such as where you pre-freeze your food or are plugged into shore power when loading.
The variation in refrigeration loads that I have seen on the different boats that I have been on are absolutely staggering. Many modern production boats have absolutely terrible insulation which isn’t overly difficult to improve and some have good insulation. Also, it is really hard to find any data on the coefficient of performance of the different systems available, I took a quick look through all of the systems available on West Marine’s website and I didn’t see any real efficiency numbers which makes it really hard to understand the trade-offs of different systems. Not having actually specifically metered it, I would guess that I have seen loads of similar sized units in similar climates range from 30Ah/day to 150Ah/day. If you can get on the lower end of this range, a very reasonably sized solar array should be able to take care of the loads in a climate where solar works well and the ambient temperature is reasonable.
From a cost perspective, ripping out your existing icebox and building a new one which has much better insulation is definitely going to be less expensive than a generator and likely less work too.
You could also look at loads for other systems like your autopilot but I think that it would be much more difficult to change these. I think that the conclusions in the post will apply to most people but I also think that there is a large group of people who get a generator when they could save time and money by reducing their refrigeration load.
Eric
Hi Eric,
I think you are absolutely right, there is a lot more that can be done to make yacht refrigeration systems much more efficient. At one point Glacier Bay were doing a lot of work in that area. We have one of their original holding plate systems that, when we bought it, some 20 years ago, reduced run times in independent testing by, if memory serves, some 30% compared to existing systems of the day. And that by just making some quite basic improvements, most notably to the surface area of the refrigerant heat transfer in the holding plate by the simple change of using multiple small tubes after the expansion valve, instead of one large one.
And that was 20 years ago. I’m sure much more can be done today, although you would know much better than I where to look for those gains.
And as you say, the insulation on many, perhaps most, yacht freezers is woefully inadequate.
If Edison won the “current battle”, we’d be in a DC world. I’m converting my house and heating is easy, it’s the electric and as Matt stated, it comes down to freezing, air conditioning and the stove. Had DC won, engineers would have had these systems more efferent and fossil fuel dependence would look very different. In a house, the systems are way too AC dependent and they don’t need to be. AC is a raw material consumption pig, from fuel to copper. Tom Wagner of Passport yachts, tells me, on the 545 he has water making and refrigeration running off solar and wind entirely. He’s using keel coolers on the refrigeration. Real or selling a boat ? not sure. I just use my genset for refrigeration. I’d rather use it as a mooring.
The trouble with DC used to be that there was no easy way to convert voltages. For long distance transmission, you need hundreds of kilovolts (to keep current, and thus I2R losses, low). But there’s no easy way to make multi-kilovolt stuff cheap enough, safely, for the general public. Generating AC, and converting between AC voltages to build a cross-country grid, is a simple matter of winding copper around iron yokes. Edison’s DC system could never have scaled beyond single small cities.
It is now easy to convert between DC voltages at high currents. (Basically, you switch it to square-wave AC at tens of kilohertz, convert the voltage, then rectify back to DC.) The power electronics to do this are now being mass produced at low cost, and high power DC systems are becoming more popular. If you want a 300 V, 10 kW DC main bus driving a mix of 5VDC, 12VDC, 24VDC and 120VAC hardware, you can assemble it from off-the-shelf parts.
There’s no simple answer, though. Every application has its own requirements and nobody has, or will, ever come up with a one-size-fits-all solution.
Hi All,
Thanks for all there great comments and and amplifications on my original post.
Apologies for being out of the loop. I have been on a plane all day and am beat. Back tomorrow.
A few brief comments:
– I think wind/solar can cover a well balanced boat with an electronic pilot. If you get the protracted combination of little wind and cloud you may need to run the main engine but if the panels are good and systems thought through this can be very rare (or probably extremely rare for those who motor as much as, well, most people.
– Big solar arrays can be unseamanlike, sure, but often don’t have to be. I have velcroed panels into a collapsible Bimini. They are cheap solbian copy new generation flexible panels and are going well. If a blow is really coming, they can be down and the Bimini folded quick smart. They fit under a mattress. Easy. There are some passages where you might not want such a contraption up at all, but for those in the tropics a Bimini is a given and it’s just the obvious use of the space. I think we’ll see a lot more of this solution with a lot less genset action at anchor (our Bimini is not so big and we are seeing 25amps for hours).
– my current genset (largely idle since solar added) is a little nanni 2 pot with a large (300) amp alternator retrofitted on. I don’t see where the scary complexity is. The engine is easy, the alternator off a shelf, and it charges efficiently and fast.
– The answer to the aircon load seems easy to me – don’t fit aircon. It’s complex, bad for the environment and – it’s often observed – cossets people into never leaving their boats. Hatches, sleeping on deck or even just a small dc fan are sufficient.
Cheers
Marv, Largely agree and sounds well thought out. A moderate sized freezer may push the limits some in warm water & air. Did you design the Nanni/alternator setup yourself?
Dick Stevenson, s/v Alchemy
No, I inherited it. The main issue is just a beefy enough bracket and that’s the only part of the setup I would change (cracked a weld in the original bracket but that was easily fixed). But basically the issues are as per any main engine alternator. Note it’s set up to use the same size serpentine belt as the main engine, a small but helpful detail.
We have a large freezer but tend to use it intermittently (not when staying near civilisation – we fill it before a long passage). If it’s cloudy the panels don’t keep up with it running. If it’s a solid windward passage a Windgen can cover it all, but it needs a decent wind.
Hi Eric.
I just has to reply to the line in your post “ripping out your icebox….”. I did this, and replaced everything from internal box, through insulation, to condenser and plate. It was a nightmare! I believe that the result is worth it – and my boat is too small anyway for a generator – but it wasn´t easy. I cursed the original builders many times during the process, and also the suppliers of the new refrigeration equipment – the mechanical thermostat didn´t work and I discovered this only after everything was reinstalled.
Yours in sorrow,
😉
Bill
Hi Bill,
I did went through the same process on my first offshore boat. It was brutal!
Our Fischer Panda DC genset has caused some problems from water ingress. Twice I have rebuilt the head with seized valves. This was down to the water lock installation which should have been 600 mm below the exhaust outlet. Difficult to do sometimes!!! FPs installation manually had one paragraph on water lock installation! After being sued in the USA they now have 16 pages.
Also the devices are almost too small and quiet so there are 50 hour checks that need to be carried out. If you are not a diesel engineer these will just not get done!
We have a 2.5Kva Victron inverter to power our air con and microwave, usually just from the batteries.
A 12 volt diesel genset is quieter and more efficient because it runs at a variable speed to deliver only the load that is needed. It uses less fuel and requires less maintenance than an AC genset, which must run at a constant speed, no matter what the load, just to supply AC at 50 cycles/sec.
Large inverters are up to 95% efficient in converting to AC, so together with an efficient DC generator, the DC option is a better and more compact all-round solution for both DC and AC. Another major advantage is a DC genset can charge batteries at a very high current, up to 120 A from Mastervolt, 280 A from Fischer Panda. With AGMs this is a very good option.
The other great advantage of this “DC Option” is that you can go for a smaller DC genny than you would need if you went the AC route. With a Mastervolt or Victron “Power Assist” inverter it takes extra AC power from the batteries when needed for start up of air con etc.
Hi Matt,
I certainly agree that a DC generator is more efficient than an AC on most smaller voyaging boats. However, to clarify, not all AC generators are fixed RPM.
Your problems seem to highlight the issues, once again: DC more efficient, AC more reliable. Of course there is no fundamental engineering reason why that should be so, so hopefully it will change when more people embrace DC and more are built.
I spent a week reinsulating the ice box on my 1984 Catalina 36. There was only 1 inch insulation which I increased to between 4 and 6 inches whilst retaining the ice box in situ. Yes I lost some internal volume but it is still pretty big. I bought an air cooled Isotherm unit based on the Danfoss BD50 compressor which is mounted in the cockpit lazarette. The unit only switches on typically for about 5 mins or less per hour and draws about 5 amps when on. There is a small freezer compartment. I live at the moment in Channel Islands Harbor in Southern California. I think the freezer issue is all about doing a really good job on the insulation, particularly for higher latitudes. Wonderful site John. Thank you and your colleagues for providing it.
Hi Duncan,
You are absolutely right that insulation is the key. But just to clarify, the premise of my post above is that you need a generator is you wish to freeze significant amounts of food. I’s not talking about the very small amount you can keep frozen in the freezer part of small evaporator type systems.
For example, our freezer is a separate box from the refrigerator and holds enough meat for a crew of two for three months.
Hey John, I did get your point but I was just surprised at how much difference my insulation job made and thought it worth sharing. I did note in the specs of the isotherm unit that it could work as a freezer with 2 cubic feet capacity. What freezer size do you think crosses the threshold for a generator requirement, assuming good insulation. I plan on upgrading to a bigger off shore cutter next year and freezer capability will be a requirement, hence my interest.
Hi Duncan,
Well, a lot of variables here, but I would guess that a 2 cubic foot freezer might be just viable without a generator.
Yep there are a lot of unknowns here. Thanks for your response.
we have for ,2014, 2015 sailed from Norway to Scotland,Hebrides, Orkney, Norway, Danmark,Germany, and never needed shorepower.
we have 570 watt solar, 2 Kw inverter, 190L cooler, 22 L Frezzer, and al my toys, even give power to other boats so they can charge there batts.
wife has here hair blower, we have coffemaker(220V)
So no need og gen. or windmill.
And sailing around we did not have sunshine every day 🙂
We also use autoP as soon as we can.
Now for next season we have change out the heavy 15hk outboard with a 3.5hk el outboard, (11 kg) and we have power to charger it every day if we like.
Hi Geir Ove,
Thanks for the real world experience, always the best.
A note to others. Make sure you understand Geo Ove’s usage profile and how it relates to your own before you apply it. For example, the kind of cruising he’s doing includes quite a lot of motoring (even if just leaving and entering harbour) that will charge the batteries. Also probably for a high percentage of the cruise the boat will be at anchor or in port with no autopilot and navigation drain, but the solar still charging.
So what works here might not work for a long passage where the autopilot will be working for weeks at a time and motoring maybe rare. In this profile I have yet to see a boat that can run an autopilot, and a freezer off solar, at least unless the array is so big that it impedes the safe sailing of the boat.
The bottom line is that when designing a system we need to do actual calculation of the electrical requirements based on our own usage profile.
Hi Geir/John/Duncan – interesting comments.
Recently we had to remove and replace our old generator and I spent some weeks studying AAC valuable resources including of course this article by John. We were also keen to remove the 100Kgs of weight from our stern, and reduce our diesel consumption for South Pacific cruises as we have limited tankage. We have chosen to do this by up-rating our alternator from 50 amps to a single 130 amp unit (thanks John for that steer). We are then adding four 120 watt flexible solar panels giving us 480 watts of solar energy, currently being installed on our Bimini top. Testing to date shows we will get up to 30 amps of charge into our batteries per hour on a typical summer day. Since we aren’t permanent cruisers and do not have a major freezer requirement we believe, like Geir this will be sufficient for us.
One thing we considered in our decision, is the incredible advance in solar technologies. They are on an exponential trajectory similar to micro-processors (actually doubling in capacity / area roughly every 22 months). Most of us, schooled in linear thinking don’t quite appreciate the impact of exponential growth, but even coming from a tech-industry background, I was startled by what is happening in solar tech. Essentially, we should expect that within 10 years most of us will use solar as our primary source of energy in our yachts, and well within 20 years in our homes, industries and vehicles. I have read comments that this is a major factor behind the recent falls in oil prices as the Gulf Nations try to sell off their oil while it still has value! Let me illustrate:
In 5 years from now, the same panel area we use today will provide around 3 kilowatts of solar power per hour. Within 10 years close to 20 kilowatts. Hey, on this trajectory, when will we see hybrid electric/diesel/battery power plants become the primary propulsion units?
For completeness – our lightweight panels will be zipped onto the Bimini under velcro storm flaps, with the whole structure folding away (the canvass rolls up) and the panels safely stowed below on the approach of bad weather – should take about 5 minutes. I appreciate there is still a risk of an extreme and unexpected event at night carrying away our Bimini before we can stow it but this is an acceptable risk for us, given it can all be replaced relatively easily. After all we will still have our new grunty alternator as a back-up power plant in emergencies – we may lose some home comforts for a while but that’s probably a good thing!
Rob
Hi Rob,
Great analysis. Sounds like a good system to me. I particularly like the thinking you have put into snugging the boat down for heavy weather.
On solar. I hope you are right, but some recent reading I have been doing seems to indicate that advances in solar efficiency will slow down now and are no where near exponential. I believe we are already as 22% efficiency on the very best panels. This means that even if we can achieve say 50% efficiency that would be less than a gain of 2.27 times from today.
Said gain will certainly make all solar boats, even with autopilots and big freezers, possible, but I’m pretty sure that the idea that solar will solve the world’s energy/carbon problems may be more marketing hype on the part of solar boosters rather than fact. The other issue is viable large scale storage of solar power, which is a very hard nut to crack.
Anyone who is interested should read this interview with Bill Gates, who has spent a bundle and hired the very best people to really understand this stuff: http://www.theatlantic.com/magazine/archive/2015/11/we-need-an-energy-miracle/407881/
Hi John,
Thanks for the link – didn’t Bill Gates also refer in the mid 90’s to the internet as a passing fad? I sense despite his cautious tone, he is still excited about solar and that is the most encouraging take-out for me, because investment is a really important factor in breakthrough innovation – but not the most important interestingly.
From a sustainability viewpoint, I sincerely hope you are wrong that future solar gains are more hype. Forgive my optimism John as a long time tech marketer, but I remember in the 90’s engineers briefing me that we were approaching the limits of semi-conductor gains due to heat and diminishing returns from silicon. I remember radio engineers telling me in the late 90’s we would soon reach the limits of mobile capacity/subscriber numbers due to finite bandwidth availability.
I do think you’re absolutely right that energy storage will be a (probably the) major market hurdle/cost, as we boat owners know very well. But the original technology (from the Greek word technos) was basket weaving, so we have come some way.
I confidently look forward to pottering around in a solar powered displacement launch in my dotage!
Hi Rob,
Good point on the lousy track record of technology nay sayers.
Having said that, I guess the thing that I can’t get past on solar is that there is no way to collect more energy than the sun provides per square meter. So even if we achieved 100%, which no machine ever has, we would only be collecting a little more than four times what we do today.
That leads me to wonder whether solar energy systems based on concentrating sunlight and then running turbines to generate the energy, rather than photo voltaic may not be a place to look for the exponential gains. Of course that still leaves us with the storage problem.
The other issue with photo voltaic (and large scale batteries) that the boosters like to ignore is the huge environmental damage that the production and eventual disposal of both technologies carries with it.
In summary, this stuff is really complex and I don’t think the problem will yield to a single simple solution.
And that leads me to my favourite rant: we need to start paying the real cost of hydrocarbon based energy (like the Norwegians do) in the form of realistic carbon taxes. Once we do that, all of these better technologies will bloom—price always wins.
The efficiency of silicon-based photovoltaics is currently around 15% (cheap polycrystalline cells) to 22% (good monocrystalline cells). Silicon is never going to get much above 25%.
But it doesn’t have to.
Capital costs for medium- to large-scale solar PV are already pushing the $2/watt mark and will fall by half within three more years. Residential rooftop PV is now under $3.50/watt. A Saudi utility (ACWA-Power) recently issued a solar PV contract at a record low price, 5.8 US cents/kWh for 20 years.
Even after accounting for the capacity factor (usually in the 0.3 range, and never over 0.5, for solar PV) these installations are now well ahead of nuclear in capital cost, and nearly competitive with coal and natural gas in operating cost. There have been massive improvements in the efficiency of the manufacturing process in the last few years.
As for large-scale storage: pumped reservoirs are a perfected technology, and batteries are becoming cheaper and longer-lived. As long as solar is part of a mixed-source grid, though, storage isn’t too big a problem; you just shut down the most polluting sources and then close some hydro dams when supply outstrips demand, and keep the peaking plants in reserve for when the sun isn’t shining and all the hydro dams are open.
The hardest part is coming up with business structures that encourage solar PV to go on industrial rooftops and other dead space, rather than taking over good agricultural land.
It is true that solar power is changing quickly but not necessarily in ways that really benefit cruisers. While we are all cost conscious, the most important thing to me on a sailboat is panel efficiency as you can only fit so much panel area on a boat. Our single 140W panel is just adequate for our usage but it would be a total change for us if we could get 300 W out of the same size panel. The most we can ever hope for is about a 4X improvement before we start violating the laws of physics. I am certainly not complaining about the cost reduction, when I installed the first set of panels on my parents house, the panels alone were over $6/watt, but the cost reduction will benefit areas where space is not the issue more quickly.
Concentration of solar is certainly an interesting idea. Solar thermal systems are very appealing from an engineering standpoint (I designed a steam expander for one) but they have some serious scaling concerns if you want to produce power in smaller amounts. The large scale tower type solar thermal plants with mirror arrays on heliostats require something like a 1/2 square mile of area to be feasible. Below that you have dish and trough type collectors which produce heat well but require a different form of energy conversion to shaft power. On the smaller end of the scale, the limitation is your conversion from heat energy to rotational motion as steam turbines don’t make sense below 100kW or so. The most popular dish systems actually use a stirling engine and are in the 25kW range. All of this is great for grid based systems but it doesn’t apply to boats right now (you can concentrate a bit onto a PV panel but this is pretty limited).
In land based applications, there are interesting questions about timing of production. There are people who specialize in modeling these scenarios and I have heard many different numbers for when they become necessary, probably based on the existing infrastructure. Sources like nuclear are not very good at ramping quickly so you either need storage that can ramp quickly or something like gas turbines. Pumped storage is a very appealing concept and has some precedent but there is also a lot of interest in compressed air storage through companies like SustainX and General Compression.
Eric
John, this winter I’ll be installing our battery bank, and my calculations on usage vs. storage back that up. We have four 135 W panels and a 400 W wind generator, but the limiting factor for “autopilot and frozen food (and a bit of radar, AIS and VHF) while underway is the size of the battery bank. The solar and wind merely slow the inevitable draw-down unless the bank is large enough to stay in the 70-100% “band” for the better part of a week.
Hey Geir, thankyou for that information. I am in the process of planning out an electrical power system to allow me to throw away my yellow shore power cord. How big (what type) of autopilot do you have? How big is your boat. Thankyou and good luck.
We have a prop shaft generator on our Boreal 44 and it is a great addition to our power supply. Also have 200 watts of solar and a super wind wind generator. Crossing the Atlantic we had 100% full batteries the entire time.
The prop shaft generator makes about 5 amp hours at 5 knots boat speed and somewhere near 20 amps at 8 knots. A little better than the super wind generator does with wind between 15 kts and 25 kts. With the sun out 20 kts of wind on the beam and sailing at 7.5 kts we are making about 40 amp hours of power. We can run everything on board while under way including the Spectra 150 water maker, auto pilot, fridge and electronics and we still are filling the batteries.
This season we plan on adding two more solar panels to bring that up to 400 watts. We have found that when at anchorage and it’s cloudy and not much wind we loose power. Hoping that the extra 10 amp hours will help out a lot. By the way we do not have a big freezer ours is just big enough to make 12 ice cubes for evening drinks.
Cheers
Hi Steve,
Interesting, and similar approach to what we are trying to achieve. We have solar, and have been considering supplementing this with a Super Wind generator for trade wind conditions in the South Pacific Islands – how have you found it? I am particularly interested in cockpit noise, lighter wind performance (say under 12 knots) and reliability. I did a delivery voyage earlier in the year from NZ to Tonga in company with a few other yachts. On arrival one of these yachts had lost all the blades from its Super Wind overnight – so I am keen to get another perspective please.
Hi Rob,
We have no complaints about our super wind. She is quiet beyond what we ever dreamed a wind generator could be. She does not put out much power at 12 knots, maybe 3 to 4 amps but really begins to put out power at 15 kts true. I can’t for the life of me figure out what happened to that super wind that lost all its blades. Maybe they had a one of those great sea birds that call home in those waters fly into it. We have come close to that happening more than once. Even though the blades are very strong on a super wind I don’t think they would fare well in a collision. We also have had excellent service from our super wind rep in the USA. I lost a part overboard while putting the machine away for the summer in Panama. I emailed them and they sent the part to us and for free.
I highly encourage the super wind purchase.
Cheers
Steve and Tracy
Managed to put my reply in the wrong spot – see below.
Thanks for your prompt reply Steve – nice to hear your ownership experience has been good. The quietness is what attracted me to your wind generator in the first place – last season we were in a small anchorage with another yacht (strangely the one that lost their rotor blades) and even though their unit was spinning quite fast in about 12-15 knots of wind, we couldn’t hear it. A pleasant change.
The Super Wind seems to make the perfect partner for solar here in NZ. If the sun’s not shining in the sub-tropics, the wind is usually blowing, but even more so in the South Pacific Islands where the sun shines and trade winds blow together.
Sounds like I may need a set of spare blades though – I hadn’t considered bird strike! I sincerely hope it wasn’t an albatross, as they were our close companions for the first week out of NZ, and take your breath away with their command of wind and waves.
cheers, Rob
Hi Rob,
In addition to Steve’s excellent comments, colin has a piece on the superwind here:https://www.morganscloud.com/2010/05/03/quietening-boat-wind-generator/
Hi Gill,
I think the spare blade idea is a good one but no doubt expensive.
Did you notice I did not mention the type of bird that may of hit the wind blades. They are beautiful birds we always look forward to seeing in your part of the oceans. Maybe we will see you this coming season as we will be there and in NZ by November.
Cheers
Steve and Tracy
Not trusting the voltage in many marina we visit, I usually prefer to run the diesel generator when needed. The noise outside is low, but more so inside.
In order to keep the fridge cold, I was thinking of using an aircooled Honda 2200watt gasoline genset on the upper deck where it can be placed in a good size alloy chest to keep the noise level very low and plug in the fridge directly.
I don´t see a problem, ………..but a little knowledge can be dangerous.
Comments?
Hi Rene,
Hum, I guess the question that jumps out at me is why don’t you trust marina voltage? I would start there before adding another gas device, particularly since you have a diesel generator. The other option would be to look at ways to quieten down said generator.
Thanks John, my dis-trust re ; shore power originates from my motorhome days, when the voltage very often was much lower than it should be and have experienced it in some marinas too.
I can live with diesel generators, but it is more a resonance problem than decibels.
Our ¨home slip¨ has a brand new electrical system, so no problem there.
When at anchor I thought of trying out my quiet Honda with little or no resonance. Always like to try out things.
Thanks again.
Another reason to have a diesel generator, and the primary use for ours, is to run a watermaker. I am always pleasantly surprised to see that our wind and solar always keeps up with our autopilot and on-passage electrical needs for days on end. On passage we run the generator every 4 or 5 days to make water which tops up any deficit in the batteries. At anchor the balance is different and our electrical consumption is greater and wind generator makes a smaller contribution, then we would run the generator every two or three days, depending on how much sun or wind we get.
Our genny is a small single cylinder one so little chance of ‘under-loading’ it.
I would love to equalise our batteries more often but sadly we are never hooked up to shorepower. I draw comfort from the fact that it wouldn’t take too many nights docking fees to buy a new house bank.
Hi John, I am not sure if this is the right place for this question but i guess it has something to do with energy consumption. What is the best boat fan (AC or DC) that you would recommend? i lived in the tropics and do not have a generator on board. I have lots of Hella 12 volt fans on the boat to cool things down. I find them at worse inefficient (you have to be quite close to them to feel the breeze), noisy and often rattles as the blades touches the fan guards. It can be quite annoying in the rising heat. I looked into AC fans as they have the volume to make them really efficient (like an AC genset). But they draw about 4-5 amps per fan over an inverter, which is a lot if you run 2 fans all day… is there a better solution to a more efficient fan (wind and amps wise). thanks,
Hi Rob,
Sorry, we have Hella fans too, and I agree with your criticisms, but I have never found anything better. One thought, they have two models and the larger ones are a great deal better, although far from perfect, than the smaller. I can suggest one solution: come and join us here in Atlantic Canada in the summer: fans rarely required!
Friends who’ve spent 10 years in the Caribbean strongly endorse Caframo fans for the same reasons, and of course, there’s always the option of setting up wind scoops.
Hi John
Please excuse the question:
Your blue Glacier freezer compressor in the picture, which you rightly say makes your generator necessary:
Judging by the fat wiring going into it, it’s powered by a 12V DC machine? So it runs 24/7/365 duty cycled by a thermostat, yes?
Hi Oliver,
No, it’s a holding plate system and a very efficient one with heavily insulated boxes, so we only need to run it once a day in a hot climate and less than that when it’s cold. We leave it turned off and only turn it on when the generator or main engine are running. It then runs until the plates are refrozen, a process that’s is controlled by a thermostat.
Typical run time is less than an hour a day and the motor takes about 60 amps at 12 volts.
Hi John, I’d love to know more about your total food refrigeration system on your boat. Sounds super efficient. I don’t have any experience with keel cooled stuff or the different parts associated with a system. Thx!
Nigel Calder Integrel Demonstration
https://www.youtube.com/watch?v=p6jMN2HTlmc
Hi Doug,
Yes, interesting and innovative. I watched the video a couple of months ago. The thing that worries me is how complicated and highly loaded the whole thing is. It’s also all proprietary, which is often a problem too. And finally it’s totally dependant on the main engine, so does not provide backup like a separate generator.
If enough people are interested I will do an analysis.
I came here to this page wondering if anyone had commented on this new system. 🙂 It seems intriguing but I doubt I understood half of what was going on in the demo video! Very curious to here informed opinions on whether such a system might be a good fit for cruising, especially on a new build.
Hi Scott,
Seems like I need to do a piece on this machine. I will try and fit it in.
Thanks John, I look forward to any analysis you can share on the topic!