We are at anchor, it is quiet, just three other cruising yachts in this bay, and the sun is shining for a change. With the sun now dropping towards our neighbors in the Southern hemisphere, or the earth tilting if you prefer being accurate, the sun’s angle to our flat solar panels is less than optimal. But is it worth adjusting the solar array angle?
At 0730 sun time (daylight savings time still being in place here), with the four panels flat we were seeing 10 amps at 25 volts output. With the stern facing southeast, angling the panels on a common axis, and bringing them almost vertical, kicks up output to 33 amps. The stern then swings to the southwest, and the panels are no longer aimed directly at the sun.
As a test we aimed the starboard array directly at the sun. This partially blocks the port array, so that its inboard (shaded) panel is shorted out and therefore not contributing. We are surprised to find that the three correctly angled panels produced more power–30 amps–than the four panels on a common horizontal axis.
If we were tied to a dock, held in place with a stern anchor, or steady trade winds, it would be easy to optimize angles and thereby improve average output during the day. But for us, with the boat moving at anchor, the answer is still flat panels, on the assumption that we do not want to bother with constant changes. However, if we needed to, we now know that with a little extra work, say a stern anchor, we could substantially increase daily energy capture.
This leaves the question of a tracking system, of which there are now commercially available systems. You could generate the same power from three panels as we do from four, if your array kept the sun at optimal angles. However, adding a fourth panel is a much simpler and less expensive method of matching the tracking power output.
We continue to be impressed by the function of these four panels, which have essentially eliminated the need to run the genset in the short-hop, long-stay cruising mode we are presently enjoying. And there is something very satisfying about the ability to generate all this power without burning diesel.
Yesterday, for example, we did three loads of wash, the big computer with its external drives was operating for eight hours, three meals were cooked electrically, and we consumed just 3% of our battery capacity beyond what we received from the solar panels (clothes were dried on the life lines rather than running the dryer).
It is 0700 the next day (sun time) as we edit this post, and we have taken five minutes to put the panels back to vertical; those 30 amps are again flowing at this early hour.We are going to work on making the panel rigging system more amenable to quick angular adjustments.
Two days later, we are on a mooring in Southwest Harbor, swinging back and forth with the tidal current.Panels are flat. In Maine, at the end of August, on a sunny day with 20% cloud cover, those four panels produce 7.4kWh.
Posted by Steve Dashew (August 27, 2012)
August 27th, 2012 at 6:11 pm
Steve,
Thanks for the real world information on your panels. One question and it may be real simple. Do you isolate the panels from the electrical system when another source is charging the batteries?
Thanks.
Mike
August 27th, 2012 at 8:50 pm
The panels feed the batteries through an Outback 80 MPPT controller. If another source is present, say the engines are running or shorepower, and the output of the panels is not needed, then the controller isolates them. Their is provision to divert the excess power that is then available, perhaps to a large hot water heater.
August 28th, 2012 at 1:54 pm
Thanks for the info. Mike
September 6th, 2012 at 6:05 am
What type of cells are in these panels Steve…monocrystalline ?..or ?…30 Amps seems quite high….
I found with my MPPT controller that if the absorption times on the alternator reg and the MPPT are not set the same, the charge light on the engine panel comes on when the alternator reg thinks its done, but the MPPT wants to keep going….the alt reg is reducing the field current to the alt to try to float the batteries but it can’t ‘cos the MPPT is still driving the voltage to 14.6…ergo, no field current needed, the light comes on… I don’t think it’s really an issue …do you see this ??
BTW I don’t move my panels (I can’t !)…but Between about 1100 and 1500 in Fiji, my 520Ah bank is usually fully charged.
Thanks for all your input over the years
September 6th, 2012 at 6:14 am
Each of the four panels is rated at 320 watts, under perfect conditions, so theoretically as much as 50 amps at 24VDC. However, the most we have seen is 44 amps so far. Panels are made by Sunpower.
September 10th, 2012 at 7:34 pm
Steve, I am also very impressed with a solar array I just added to Turnagain (our Oceanis 50). I have an arch with davits on the stern and put two 235 watt pannels on in June connected with an Outback 60. I have not had to plug in yet. We run our 12 volt fridge and separate freezer plus inverter for microwave and tv/DVD. As well as computer and iDevice charging. We spent 7 weeks aboard with little motoring every 3 or 4 days here in the pacific north west. This winter I plan on looking into designing a system to tilt the panels fore and aft (left and right will be too complicated) as well as putting a third panel up. Do you take your panels down if you are going to be in a big blow?
September 10th, 2012 at 8:25 pm
The lowest resistance configuration for our four panels is horizontal. The masts onto which these arrays sit, the mast bracing, and the panel frameworks are designed for substantial loading. And it is possible to remove and dismantle the arrays, lifting them off with the boat’s own booms (which were used to position the panels int he first place). However, unless we were leaving the boat in an area of extreme cyclone danger, we would not go through the hassle of pulling the arrays apart.