Sunpower 320 Solar Panels – Real World Output Data

Wind Horse Solar 2 246

We have finally had a proper day of solar energy testing: free of the dock, booms out so no shading, minimal overcast. The results are surprising.

We were worried that we’d not care for the appearance of this array. However, it does not bother us on or off the boat, and we’ve just had a couple of days with the new look. Within a week they will disappear from our consciousness.

Wind Horse Solar 2 106

The transition from deployed to storage mode (shown above) takes less than three minutes. Once we add a few Wichard snap hooks to the tie downs, this process will go even faster.

Wind Horse Solar 2 102

The final tilting and swiveling mechanism is very simple, and robust. Main support is a schedule 80 one inch (25mm) 316L stainless steel pipe (3/16″ /4.5mm wall). ┬áThe masts are two inch (52mm) aluminum tube with 3/8″/10mm thick wall. There are no bearings.

Wind Horse Solar 2 221

Paralleling the pivot pipe are a pair of two by one inch aluminum rectangular tubes. The solar panels themselves are electrically isolated from the framework using G10 (epoxy) blocks.

Wind Horse Solar 2 104

Anchored here in front of Beaufort with minimal swinging room, and traffic, we decided to store the panels so they didn’t overhang. It was the end of the day, the sun was low, and we were pleasantly surprised to find an output of 10 amps/25 volts from one of the two arrays in this orientation. That is a little under half power output, which we think is wonderful at the end of the day.

The Outback 80 MPPT charge controller through which these four Sunpower 320 Watt panels feed the batteries, reports on maximum and minimum voltage/amps in and out plus the day’s power generation. Yesterday the maximum amperage we saw was 43 at 26.5 volts. The theoretical max is 50 amps. However, this is with panels at right angles to the sun, standard temperature (25C), with no allowance for wiring or conversion losses. Chuck Meier of SALT in Marathon, Florida, who supplied our panels, did a few calculations for losses from temperature, conversion, etc, and came up with 44 amps. So, we are right on target here.

Output varies with the changing sun angle and cloud cover, or lack thereof. The real question is total power generated for the daylight period. The Outback 80 reported yesterday at 7.5kW. Today we did not deploy the panels until 1030, and by 1500 it was overcast with a thunderstorm blocking the sun. The reported accumulation was 5.4kW.

Our daily power burn is between 7500 and 11,000 watts per day, depending on how much time we spend on the computers and whether or not guests are aboard. If we can average half of our daily power burn with the solar panels it would be great. We could easily cut our burn to 5/6000 watts if needed, which means the solar system is capable of sustaining us if required.

We have not yet totaled up the costs, but the old rule of installation doubling the acquisition cost will probably hold true. We think this makes sense compared to a backup genset.

It will be interesting seeing how this works out over the summer.


Posted by Steve Dashew  (June 23, 2012)

12 Responses to “Sunpower 320 Solar Panels – Real World Output Data”

  1. Mike Gehl Says:

    Steve, not to be pedantic, but you wanted to do, (and did) was to measure *energy*, not power; power is the instantaneous output while energy is what you gathered for the day.

    Thus you really meant kWh, not kW – you could generate a trillion watts for a picosecond, and only end up with 1 watt-second.

    Plus, we can all relate to kWh – that’s what we see on our household utility bills!


  2. Gene LeBeau Says:


    Any issues with windage in the storage position?

  3. Steve Dashew Says:

    At anchor there is less shearing,so they are working as a riding sail, better when vertical. There will be some drag, but we don’t think it will be significant.

  4. Cole Says:

    I was hoping to meet you this weekend in cape lookout for the pot luck on the beach. Your boats are amazing.
    Cole aboard the Hooligan

  5. Steve Dashew Says:

    Hi Cole:
    Sorry we missed the pot luck. Our grand kids and their parents were with us just for the weekend and they wanted to be off on their own. But come by any time you see us. We’ll be out again at the Cape later this week.

  6. Really? Says:

    Your installer electrically isolated the modules from the ship?!?! That’s a pretty serious violation of NEC and a total bonehead maneuver. We have this thing called a Ground Fault. We normally worry about it burning down buildings, but in your case, it could be a heart stopper. It takes very little electricity (voltage and amperage) to stop the heart. Where would a fault come from? It would come from the fact that your modules are moveable and wire fails. The modules should have been bonded to your system to detect faults. But you used yahoos instead of pros.

    Don’t even touch the module without check the voltage between the frames and the ship.

  7. Steve Dashew Says:

    You jump to conclusions too quickly. These are positive ground panels and have to be isolated from a negative ground hull, and panels are 60 volts, in parallel rather than the higher voltage of many terrestrial systems. There is no choice of which we are aware. If you have a suggestion, we would love to h ear it. What we are doing is installing a ground fault warning system. Regarding our installers, I think they would be considered pro’s in the industry, fully up to date on the correct procedures for this and much more complex issues. We are continuing to research the issue.

  8. Andy Says:

    I think you are both right, partly. NEC does require panel grounding, but as stated it is not really that relevant to boat environment, though I see no problem doing it either. The panels basically have three electrically separated poles: frame, which is usually grounded to earth, positive pole and negative pole. Both positive and negative are arbitary, insulated from frame and thus floating, and they have to be – if they were not, it would be impossible to wire panels in series. So I guess it would do no harm whatsoever to mount the panels grounded to the hull, frame is aluminium so no corrosion issues doing that either.

  9. Lofty Says:

    Looking at the pictures, the panels are grounded to the boat through the aluminum frame of the panels to the stainless steel tubing down to the aluminum hull of the boat. If the negative leg of the battery would be connected to the frame of the boat there shouldn’t be a problem. The boat represents the ground (-), just like the frame of a car, any area of it is a ground. This is the proper application for grounding. The accumulated static charge from the glass of the solar panel to the frame of the solar panel will be very minimal for these 4 solar panels and positive grounding would be recommended to recover the loss of this energy. The fuses, ground faulting equipment and the breakers are all fail safes for the entire electrical system and the boat.

    I’ve stuck my tongue on a lot of 9V batteries, but I believe this installation should be perfectly fine.

    Here is a good explanation on positive grounding from Morningstar:

  10. Tom Beaty Says:

    Hey Steve,
    We said HI (actually we said we were big fans) to you guys this morning as we past in our dinghy to get our first up-close view of Windhorse. We got a chance to make a good close-up lap of her and were kind of excited to see her. We are sitting on The Town Docks and have had an unobstructed view of Windhorse all day. In fact, at the time I am writing this, you are hauling your dink back onboard. What a cool thing to gaze upon. It’s like having a celebrity in our midst. The panels look neat. I hope they work out. As we told your story to our friends last night, we told them that if the day comes when we win the lottery or come into enough money, the first call would be to our lawyer and the second would be to you to commission new boat for us to enjoy.
    m/v Skinny Dippin’
    Cary, NC

  11. Steve Dashew Says:

    Enjoyed meeting you at the Moorehead City Marina.

  12. Daryl Lippincott Says:

    We will be heading North from in the next week or two. Hope to see you and Wind Horse if you are still in the area.

    The NEC is not controlling or even the “go to” document for boats. You showed nice restraint.