conflicting information about solar install?

[centerline]

I have read 2 different ways for sizing the wire for the run from the panels to the controller and then to the batteries....
one way says the that the distance from the panels to the controller is one leg that gets sized for that run, and then, the run from the controller to the batteries is another run and gets sized depending on that distance... the reasoning is that the controller breaks/separates/modifies the flow of current.... and this allows the use of lighter wire than what would normally be needed if the controller was not in the system, or was right at the batteries....

the other way says to measure the total run from the panel connection to the batteries and size the wire according to this total distance.... and install the controller wherever one wants to in this run because it doesnt matter...

which is correct?

 

[rgranger]

how much can you save sizing the wire down from the controller... ??? It is such short run anyway.

When in doubt, I go one size up on wire.

 

[Stu Jackson]

The former. For example, of your panel to controller is sized for 21V if you're going series, the controller to the bank will be much less, right?

 

[LeoLambert310]

I just installed 2 65w panels with controllers and a fuse bus unit. What I used was 10/2 gauge from the panels to the controllers and fuse bus unit then 6 gauge to the main bus, both pos and neg.

 

[centerline]

how much can you save sizing the wire down from the controller... ??? It is such short run anyway.

When in doubt, I go one size up on wire.

Im not sure where others mount the controller, but mine will go inside near the nav station, so I wouldnt consider it a short run.... it will take 15 ft of wire to reach the nav station, and another 10 to reach the batts from the nav station...
so for (2) 140w panels, being able to count it as 2 seperate runs, it would make the difference of needing 5 gauge wire or being able to use 7 gauge wire.

and it isnt all about the cost, but a combination of cost and ease of working with it and connecting it... these sizes offer less than a 3% drop so I have no doubt that it is acceptable, so I would forgo "going one size bigger"....

BUT, if I need to size the wire to the 25ft total run, then 5ga it will have to be... unless my math is off somewhere

 

[centerline]

The former. For example, of your panel to controller is sized for 21V if you're going series, the controller to the bank will be much less, right?

I have 2 12v 140w kyocera panels...with a bluesky 2512iX-HV controller....
I have never connected 2 panels in a system before, so is series better than parallel, and can I do it with the equipment I currently have?.... my thinking was to connect them parallel....

 

[sesmith]

I'm assuming you would be connecting the panels in parallel, not series. You can use smaller wire and shading will be less of an issue when one panel gets some shade. Are they 12v or 24v panels. Using the max output current of each panel, and the voltage, you can calculate the size needed for each, separately, for the run from the panels to controller. (it will be much smaller than 5 ga). Then calculate controller to battery bank using either max current and voltage possible from controller (if you ever think of adding on) or max output of panels, if you don't. Fuse for the size wire you are using. This is my take on it...someone with more knowledge may chime in.

 

[walt]

For an MPPT controller.. If you size the wire for the run from the panel to the controller for 3% voltage loss, the current from the panel will remain the same but the voltage that "arrives" at the controller is 3% down. P = V*I so you also just lost 3% of the power the panel generated and that the MPPT controller could have taken advantage of. There is a 1 to 1 correlation between power loss and voltage loss for MPPT for the run between the panel and the controller.

If you have a PWM controller, when the controller is doing full charging (like in bulk), it simply forces the panel voltage to be the same as the battery voltage. If you have a voltage loss in the wire between the controller and the panel, it does not matter at all, the actual panel voltage will just be 3% higher than what is at the controller but the current from the panel will be the same. Since power in this case is current * battery voltage, the drop in the run between the panel the controller just doesnt matter. Remember that is ONLY with a PWM controller.

For the run between the controller and the battery and for MPPT, if you size the wire for 3% voltage loss, you also get about a 3% power loss (a little more complicated because this also affects the MPPT conversion efficiency). This power loss will add to power loss in the wire between the panel to the controller so if you sized both of those runs for 3%, you now will have a 6% total power loss from what the panel generated.

The run between the controller and the battery has another issue and that is the controller is determining when to cut back charging for going into the float phase by attempting to measure the battery voltage. If you have a 3% voltage loss in the wire between the controller and the battery, the controller will "think" the battery is 3% higher voltage that it actually is and will cut back the charging algorithm too early.

So you have some trad-offs to consider. The 3% sizing between the controller and the panel is probably reasonable (if you cant tolerate a 3% power loss, you might be running with too small of margins in the first place). However, my .02 is that 3% between the controller and the battery is too much.. I think 1% would be better. This also is easier if the controller is near the battery. And.. the controller is also trying to "know" the battery temp with a temp sensor usually located on the controller itself (part of the controller assembly) so another good reason to try and mount the controller near the battery.

 

[Stu Jackson]

Walt's wire sizing makes sense. Just recognize that when you review either the sizing tables or the nice graph on West Marine's website/advisors, that it could well be that if you fall between two wire sizes, it's a no-brainer to just use the bigger or next size up. This is called "The Use of the Available" and is not rocket science. For example, they don't make #3 AWG wire, do they?

 

[centerline]

You can use smaller wire and shading will be less of an issue when one panel gets some shade.

ive never heard of the practice of using smaller wire so shading will be less of an issue.... how does that theory work?

you can calculate the wire size needed for each, separately, for the run from the panels to controller. (it will be much smaller than 5 ga). someone with more knowledge may chime in.

I know that if I run seperate wires from each panel to the controller, I could use smaller wire, but that is defeating the purpose of both cost and ease of installation.... there is only one set of connections at the controller to connect the load to, so if there is something im missing about how it should properly be installed, I need it explained/spelled out to me so that i can understand the reasoning behind it...

I have been involved in installing single panels in 3 different applications... 2 boats and one RV, but I have never wired 2 panels in a single circuit...

 

[Stu Jackson]

I have never connected 2 panels in a system before, so is series better than parallel, and can I do it with the equipment I currently have?.... my thinking was to connect them parallel....

cl, this is Solar Basics 101, suprised if you haven't come across it yet. Parallel: better if you have shading issues (and who on a sailboat doesn't, right? ) Series: higher voltage.

Here's a looong thread on the issue: http://www.cruisersforum.com/forums/f14/solar-panels-series-or-parallel-68096.html

 

[Stu Jackson]

I have never connected 2 panels in a system before, so is series better than parallel, and can I do it with the equipment I currently have?.... my thinking was to connect them parallel....

cl, this is Solar Basics 101, suprised if you haven't come across it yet. Parallel: better if you have shading issues (and who on a sailboat doesn't, right? ) Series: higher voltage.

Here's a looong thread on the issue: http://www.cruisersforum.com/forums/f14/solar-panels-series-or-parallel-68096.html

 

[capta]

The former. For example, of your panel to controller is sized for 21V if you're going series, the controller to the bank will be much less, right?

If you reduce the voltage from 21 to 12, won't the amperage go up?
When I installed our solar, I sized the wire for the max amps possible as solar can push high amps for a lengthy period, whereas the windgen is all over the place and rarely achieves max amps. I maintained the size from the controller to the batteries as it was only 2 feet and I had the wire. 25 amps of 12 volts is a significant amount of heat if the wire isn't sufficient, IMO.

 

[centerline]

For an MPPT controller.. If you size the wire for the run from the panel to the controller for 3% voltage loss, the current from the panel will remain the same but the voltage that "arrives" at the controller is 3% down. P = V*I so you also just lost 3% of the power the panel generated and that the MPPT controller could have taken advantage of. There is a 1 to 1 correlation between power loss and voltage loss for MPPT for the run between the panel and the controller.

If you have a PWM controller, when the controller is doing full charging (like in bulk), it simply forces the panel voltage to be the same as the battery voltage. If you have a voltage loss in the wire between the controller and the panel, it does not matter at all, the actual panel voltage will just be 3% higher than what is at the controller but the current from the panel will be the same. Since power in this case is current * battery voltage, the drop in the run between the panel the controller just doesnt matter. Remember that is ONLY with a PWM controller.

For the run between the controller and the battery and for MPPT, if you size the wire for 3% voltage loss, you also get about a 3% power loss (a little more complicated because this also affects the MPPT conversion efficiency). This power loss will add to power loss in the wire between the panel to the controller so if you sized both of those runs for 3%, you now will have a 6% total power loss from what the panel generated.

The run between the controller and the battery has another issue and that is the controller is determining when to cut back charging for going into the float phase by attempting to measure the battery voltage. If you have a 3% voltage loss in the wire between the controller and the battery, the controller will "think" the battery is 3% higher voltage that it actually is and will cut back the charging algorithm too early.

So you have some trad-offs to consider. The 3% sizing between the controller and the panel is probably reasonable (if you cant tolerate a 3% power loss, you might be running with too small of margins in the first place). However, my .02 is that 3% between the controller and the battery is too much.. I think 1% would be better. This also is easier if the controller is near the battery. And.. the controller is also trying to "know" the battery temp with a temp sensor usually located on the controller itself (part of the controller assembly) so another good reason to try and mount the controller near the battery.

Walt, Thank you.... this all makes sense to me now.
so even though it could be connected either way, sizing the wire to the entire run is by far the most efficient....
Stu mentioned about when falling between, or at the "edge" of the chart when sizing the wire, to use the next bigger wire. this has always been my practice, but for my preliminary estimates the 5ga wire is at the front edge of the chart, so it will be able to handle another 5-6 amps before thinking of jumping up a size....and I dont ever expect to come near the max output anyway because the panels will be slightly tipped away from one another on the bimini top....

the chart I was using did not run as low as a 1% loss, but only down to "less than 3%".... I know there are many charts available and will do some more research on it, but with the conflicting information ive read, and without knowing what the best way to figure the wire size with the controller in there, there was some confusion as to what I really wanted to do...

and I fully agree that for a few dollars more using heavier wire, amortized over several years, a 1% loss of power in that same period is much better than a 3% loss....

the controller will be mounted closer to the batts, and I can get it as close as 3ft if necessary, but I have a temp sensor for the bank so that the controller can be as efficient as possible...
and, no, I dont need all the power that the panels can theoretically produce (yet), but due to my location and the gloomy foggy days of winter, and because the solid mounted panels wont track the sun across the sky, I firmly believe in the 50% rule when sizing the panels.... but with more power, Rochelle is hoping for a refrigeration system of some type... we will have to wait and see

 

[centerline]

cl, this is Solar Basics 101, suprised if you haven't come across it yet. Parallel: better if you have shading issues (and who on a sailboat doesn't, right? ) Series: higher voltage.

Here's a looong thread on the issue: http://www.cruisersforum.com/forums/f14/solar-panels-series-or-parallel-68096.html

I remember reading about series or parallel, but at the time it didnt interest me, but now it does... and cant remember where I read it.... and along with the cronic shading issues on the boat, I also admittedly have memory issues. I have read that memory loss can be caused by working too hard. this is just another thing I need to do some research on.... maybe somewhere with white sand, neked girls and powerful and fruity rum drinks

and as I was typing this, fedex has arrived with the 2 panels. the controller got here thursday, so as soon as I can get the wire I get to start in on the latest boat project....

 

[Sumner]

.....I know that if I run seperate wires from each panel to the controller, I could use smaller wire, but that is defeating the purpose of both cost and ease of installation.... there is only one set of connections at the controller to connect the load to, so if there is something im missing about how it should properly be installed, I need it explained/spelled out to me so that i can understand the reasoning behind it.....

You can run separate wires...
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aaBs2IaOCzUmbxAGSqV0j7ImzVrO402fMrqC5t9lIipWHBjPm5dJWasERFAVZ0lwJr4arRbm5hjvFwPMAKzRB+aq7CCWuBBBIIOYOoPAqLVXcOl3QajjCarD8KvHbAlroy3268JF+9cu250NxuGneoOe389IGo3yaN5o72jvyWpWbGtuPv6LFUMgRn5+8l5qOuRwPjPPy9Eab/ANltjxXVTBgj1PmffFYoB1PzsJ5hXGNwe+Ji6qKlOLfOT9e9GoGnwI9i+ffxWKpRdwPzz7l7ZTLuEccwOZ5KbhwxvYa6o6czLWjITui+pzIRaqb38v39AfJe6NYNsWB19bEfus+Kw7iZcACdLDScr298ViGHcMs4AsQc7xY3y0HBZrTHVqXMCBp4LwCR77uaOB1Btx0k+81kGDMA2MgGxExlcO+ig+0qpGRPnGp+sKfQ2jUEdbzvzi6hVKDuDuEgSLZwQI8ckb4z/jyVgt6WLDs2s00g2vNive80xAI1Nw75i+pVTRqZe+9WVEzrf3PqtMsu6MpHcQRpxyXh2FbeGCM7Qe/K8fsVmaLZfJfHUge/35qZDahv2S2bAi8GxPA6qywmEcwboBAykiMriSY4hRnM5m06n2OEqRQpxe6YX9VLbhx+Igng3LxMRkpuGbeeKj0m+/kpdFylHQfsqP3tf9DP6nLpC5r9lR+9r/oZ/UV0pYrQiIgIiIC+EL6iCBtDY2HriK1ClV/WxrvmFp3S37OMM6g9+EoCnWb1mhpMPjNm6TugnQ8YXQF8IQfmRnl32UHaWDnrD0yXS/tQ6LfBqHGUm/dVD96B+B5/HH5Xa/xfqWjxIutystX3YPLXS3LgpQ2i4Hdp2HLwg2uTYZ3ss+Mwknn7y/ZVooub8pBy0/fzVXtlxIeLuqgHgCZuZyaIHd3LHTZeRUB7yRN8r2J5SvPwHO7LXO06oLsr3gLz8Bw7bHN/UwjykKVXqpV0cBA0yI0kAROc6ZZrC1sWGWemdua+/wCncbDLu01zUzDYJ5bZu8BrAA88s0EUTnkZ95c17+IdYdEdq/z8PIK2pbJAu54tkG9Y5cctFnpYOm24ZPN1/QABVm2KTD0N8w1hJMRug8RplCsqOFcwDegfwm5g8xZWO8YibcBAFuQWHEC3j9YCqWvNMend79lfbpuISpqvHKFIp9yjzJ81noi59+/8qiaxSKajtCtuj+yn4qs2izXtHRrRm4+7mAs0dC+y7ZxbSfiHCPiENb+lkyfFxI/lW9LBgcM2lTbTYIawBrRyAgLOsNCIiAiIgIiICIiDDjMKyqx1Oo0OY8FrmkSCCIIIXCel3Rp+Brbt3UXT8J5vIF91x/MB5i/GO+KDtnZVLFUnUard5p8wdHNOhHFWUfnGoxYKjeQPeJORiD4raOlPQ/EYJxJBfRnq1GiRHB4HZPpzWtlq1GWKpXeBDHPZ+l7gM5yGfvuWBznus9z3CZu8n0PNZXtXhoV9S3GfDtGe63vgny3iVIc4nMk95J/x3LHQCk0aJcd1oJJ0AknkALlBjk5e8khbRsroHja1zT+G061Du/8AW7vRbfsr7L6Lb16z3n8rOo3xJlx8IU5LjlIZlzVrQ6I42u3ep4WoQLy6GSP4fiFs+C7fszo9hsP/ALVBjT+aJd4uMn1VoFOS4/NWP2VWof71CpTjVzCG/wD1G6fNQxEWMr9QEKFidjYep28PRf8AqptPzCcjH5qc3370WWmOK/QruimBP/p4fwpMHyCyUOjeDYd5mEw7TxFJgPnCcjHGej/R7EYsj4TDua1HSGDj1ov3CV2Hoz0dp4OnuMu49t5F3H6NGg+quWiF9WQRERRERAREQEREBERAREQeXNmy1ra3QPBVyXGl8Nx/FSO547vZ9Fs6IOa4r7JaZPUxTwP4qbXHzaWrBS+yFv4sY7wpgfN5XUUV2jSNn/Zjg6fbNWr+pwaPJgHzW1bO2TRoCKNJlMfwtAJ7zmfFTUUAIiICIiAiIgIiICIiAiIgIiICIiAiIgIiICIiAiIgIiICIiAiIgIiICIiAiIgIiICIiAiIgIiICIiAiIgIiICIiAiIgIiICIiAiIgIiICIiAiIgIiICIiD//Z

... to a 2 post terminal block near the controller and then one wire from there to the controller. The panel you have puts out a max of just under 8 amps at full power (which it will hardly ever be producing on a boat). Using this wiring calculator...

http://boatstuff.awardspace.com/awgcalc.html

.... and using a 2% acceptable loss and the one-way option I come up with 8 gauge from each panel to the terminal posts (15 ft.) and then 14 gauge for 16 amps from the post to the controller. If it is an MPPT controller and can increase the amps at Walt was talking about then theoretically you would have 22 amps going to the the batteries from the controller and would use a 6 gauge to maintain 2% max. loss.

Saying that I'd feel fine with the 8 gauge from the controller to the battery for a max of 3% loss considering that the controller isn't 100% efficient and neither are the panels for most of the day if not all of the day as they are most likely never pointed directly at the sun. With the above wire sizes and considering the inefficiencies of the panels most of the time I'll bet you would be running around 1% loss or maybe even less most of the time for all of the runs.

I run separate wires from....

....the panels on the Mac down to a terminal block at the stern and then a larger wire forward to the controller and ...

... do the same with the six 80 watt panels on the Endeavour with a junction box up by the panels. The individual panels are fused in the box since if one shorted the power from the others could travel through it and the wire too it.

Sumner
========================================================
1300 miles to The Bahamas and Back in the Mac...
Endeavour 37 Mods...
MacGregor 26-S Mods...http://purplesagetradingpost.com/sumner/endeavour-main/endeavour-index.html
Mac Trips to Utah, Idaho, Canada, Florida, Bahamas

 

[capta]

and cant remember where I read it.... and along with the cronic shading issues on the boat, I also admittedly have memory issues. I have read that memory loss can be caused by working too hard. this is just another thing I need to do some research on.... maybe somewhere with white sand, neked girls and powerful and fruity rum drinks

Sounds like the onset of "old timer's disease'. You might want to see if your doctor could suggest a medication for it. Mine hasn't been able to help at all, but he's just a young thing so he has no idea. Gettin old sucks, but it beats the alternative, especially when you're anchored in a lovely tropical bay, somewhere south of civilization.

 

[capta]

Are you saying that is an array on a 26 foot boat, not the International Space Station?
Seems as if you have more surface area there than you do sail area. It must be a blast to dock that boat in a bit of a breeze.
Not to say it isn't beautiful work though.

 

[walt]

Sumner, your solar panel and experience are also interesting from the mechanical aspect of solar panels. In your Bahama trip blog, you mentioned issues with rounding up in higher winds and eventually a rudder failure. I have the same boat (Mac 26S) and dont experience the round up issue and I think your issues were due to all that solar panel area back there. Both lift and induced drag equations have a coefficient that increases for angle of attack. When your sails cause the boat to heel, it increases the angle of attack of all that panel area so you get both lift and drag vectors generated and the strength of these vectors go up with the square of the wind speed - ie, increase rapidly with wind speed. In higher winds, this creates a large force vector at the back of the boat that the rudder must deal with (and was not designed for). The rudder does this compensation by its own lift and this has its own induced drag penalty but at some point, the extra lift required to compensate for the panel force vector causes the rudder to stall - you get a round up. The more the heel of the sailboat, the higher the angle of attack of the solar panel "foil" and the higher of all those force vectors the panel creates. .

If you dont beleive a solar panel acts like a foil, get a small one and hold it out the window of a car and then rotate it (like the sailboat does to the panel when it heels). The solar panel will generate lift, parasitic drag and induced drag.

The very end of a sailboat is almost the best place for a solar panel (only better place is at the top of the mast), but the back of the sailboat is also the best place to create a force vector that the rudder must counter. That extra force the rudder must compensate for creates rudder drag. If the sailboat never heeled over, this would not be much of an issue.. but they do heel..

For the small sailboat, this is one of the reasons I like a nominal size panel.

 

[centerline]

Sounds like the onset of "old timer's disease'. You might want to see if your doctor could suggest a medication for it. Mine hasn't been able to help at all, but he's just a young thing so he has no idea. Gettin old sucks, but it beats the alternative, especially when you're anchored in a lovely tropical bay, somewhere south of civilization.

I truly believe its because I run so hard during the week.... I can only hold so much information at once (my hard drive is an old one with very limited space).... and the information is constantly changing and revolving thru.... I have seen the doctor and he said its probably stress (but the ticker and bp is still ok), and that I should find a way to slow down ... now, if only I could get him to write a prescription for the white sandy beaches and the neked girls I could probably make the slow down happen... and there would probably be much less I would ever need to remember...or even want to remember...