FPB 78-1 Cochise’s Solar Array: Even More Valuable Underway

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Cochise’s solar array is saving us substantial quantities of diesel on this passage.

We were aware this would occur of course, but doing the math and actually seeing the solar array work are two very different things.

The photo of one of our Maretron N2K view screens tells it all. The graph on the right is solar output by the hour. The left two items on the screen are the port and starboard alternator output. The data begins in the morning, and ends just after local noon.

It is easy to see the alternator output dropping as the solar array output builds.

We are averaging  11-13 kWh daily from the solar array on this trip. During the four hours midday when output is highest, this power is used first to run the vessel’s systems, with anything left over going to charge batteries. We estimate this saves about 1.75 gallons/6.7 liters per day. That doesn’t sound like much, but between Fiji and Panama this represents about 50 gallons/195 liters of fuel saved.

The solar array also gives us a backup system for powering the boat in case other gear is offline.

And there is enormous satisfaction in witnessing the process.


Posted by admin  (November 2, 2016)




12 Responses to “FPB 78-1 Cochise’s Solar Array: Even More Valuable Underway”

  1. Shannon (Shaz) Says:

    Very nice! Some time ago I was watching someone argue over payback time on the cost of the solar. They were missing the point. This is the point of the solar systems. That 100 gallons saved is increased range. That 100 gallons saved represents quiet time at anchor. That 100 gallons saved is fewer hours on the generator & reduced maintenance. That 100 gallons represents increased self sufficiency.
    Great Job!!!


  2. Carlos V. Sucre Says:

    Dear Steve. Once again you are setting standards for the powercruising world. What a wonderful thing to have an independent low maintenance power source.
    At 5$ gallon diesel that is aprox 10.000 $ savings for 20 of this 6000 NM trips. If is not considered impolite what is the aprox. cost of the solar power set up like the one in Cochise.
    We are enjoying your trip as much as you are (almost). Thanks for all your posts.

    steve dashew Reply:

    Howdy Carlos
    Re- pricing, check with Bob Williams at SALT Systems in Marathon, Florida. Bob supplies us our equipment and does complete systems.


  3. Passerby Says:

    I have to imagine there’s enormous satisfaction in all things ‘Cochise.’

    What strikes me about Cochise and its implementation of solar is the integration of solar into the overall use of the boat. Other boats I’ve seen treat this more as a tack-on item, a panel here or there and the batteries. Or as an experiment in ‘going green.’ What I like about Cochise is the relentlessly well-engineered way that solar is used to solve a manageable concern. A 100 gallons here, a hundred gallons there … pretty soon you’re talking an extra 1,000 miles of fun.


  4. PJ Says:

    Extrapolate the gains into the e780 series ……. a hands down winner.


  5. Markus Says:

    Dear Steve, 1 liter of diesel “produces” about 2.5-3.5 kWh of electrical energy using a generator or engine driven alternator.
    In order to substitute the daily 11-13 kWh from your solar array you would need about 4 liters per day.
    Those 4 liters/day are your savings. Best regards and a safe trip to Panama.


  6. Andy Says:

    Solar array saving barrels of fuel sounds like a super great thing, but something with the math does not add up. Sorry to spoil the party but 13 liters per day saved vs. 11-13 kWh solar power produced sounds like a pretty awful efficiency on alternator/charging system/engine loading part. You should be getting multiple kWh’s from one liter of diesel, say in the ballpark of 3-5 kWh. Can you double check the numbers, just to be sure!


  7. Corey Piatek Says:

    Out of curiosity, have you looked into a hybrid propulsion system? Being able to use some of this solar power to move the boat could be another level of self sufficiency. Combined with Lithium Batteries and possibly more solar panels or even a wind generator, short trips could be done with the engines off. Here is an example from STEYR: http://www.steyr-motors.com/marine-diesel-engines/marine/the-steyr-hds-hybrid-drive-system/

    steve dashew Reply:

    Hi Corey,
    We don’t think L-Ion batteries nor yacht hybrid propulsion systems are up to our needs service-wise…yet.

    Andy Reply:

    Regarding lithium batteries, check out for example: http://www.leclanche.com/markets-solutions/transportation/. 10k cycles , 100% DOD, DNV certified for commercial passenger service.


  8. admin Says:

    From Steve D:
    Electrodyne has told us for years the alternators we use require 10hp for every 4200 watts. That is 28.5 HP assuming 12kWh (we have some days at 20kWh). If there is no solar array then we have to allow for charging inefficiencies, which bring us to roughly 34 HP. At 19.5 HP/gallon of diesel this totals about 1.75 gallons/6.7 liters. Apologies for not checking my 0300-0600 on watch math. We have changed the numbers in the post.


  9. Andy Says:

    Electrodyne’s stated 10hp is around 7.5kW. That would mean efficiency of around 56%, so 44% or 3.3kW would be lost as heat. Does not sound too good to me, but could be the case. Car-type alternators are horrible when compared to modern permanent magnet generators, which routinely get to efficiencies starting with nine.