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Old 26-11-2010, 19:58   #16
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Solar Panel Production

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Originally Posted by cfarrar View Post
For comparison sake, we've got a family of four, and we consume about 75-80 amp/hr a day. We do fine with a 420 amp/hr battery bank. Our 216 watts of solar is nearly enough... I wish we had 2x135 watt panels.
You're doing very well if you can get away with only using 80 Amp-hr/day (BTW, the correct term is Amp-hours or Ah, not Amps/hr). Our fridge/freezer uses ~60Ah/day just by itself. But since we're powering it from solar, the hotter the sun, the colder the beer!

Our family of 4 (2 teens) used ~130Ah/day including computers, radios, watermaker, stereo, pumps, fridge/freezer, lights, etc. Our son published an Energy Budget as part of his schooling, documenting both production & consumption. From this we found that if we divide the nominal wattage of our panels by 3, we got the approximate Amp-hrs/day that our panels will produce. This is for flat-mounted panels in the tropics (St. Martin). OK, crude & approximate, but derived from empirical readings so probably fairly accurate, at least for initial estimations. So I'd expect your 216W of panels to produce ~72Ah/day in the tropics. Higher latitudes will produce more in summer (longer day) & less in winter (more sun-angle reflections).

FWIW, we had a wind-charger when we cruised in the 80s but we didn't like the heightened tensions from the noise, which comes when the wind is howling & you're a bit on edge anyway. This time we're going pure solar (since 2001) with 480W (nominal) of photovoltaic panels into 660Ah of gel batteries. It works fine for us except that the panels can't keep up with the autopilot (100Ah/day) when we're on passage (~25 days/year). Day sails & sitting at anchor are just fine & we never have to run an engine just to charge batteries. At night, we drop down 45-75Ah, depending on what we're doing. Again, all this (& much more) is documented on our Solar Panels page. Hope it helps!
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Old 26-11-2010, 20:15   #17
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Jon,

Your numbers are spot on. We use fewer Ah b/c of much colder water, no watermaker, all-LEDs, no stereo, no TV, and younger kids, hence the 75-80 Ah. I still could use a few more watts. Thinking of upgrading to 2x135 watt panels.
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Old 26-11-2010, 21:34   #18
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LED lights

Yeah, we're just converting over to LEDs now. I've found a great source in China (http://LightingGreen.cn). They're a factory & seem to work more on Instant Messaging than just the website. I was talking to Jessie (skype://bylight-6), who was very helpful & speaks good English. They take PayPal & the prices were unbelievable. Like US$4.04 for G4 replacements using 12 SMD5050 Warm-White chips that produce ~130 lumens (more than a 10W G4 halogen)! Lots of other good stuff as well. They don't have stock so there's usually a 1 week delay while they make what you want, but shipping was by DHL & everything went smoothly.
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Old 26-11-2010, 21:46   #19
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my bet is with Questions on electrics is Nigel Calder, author of many boat books including the 12 volt bible.....
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Old 27-11-2010, 06:03   #20
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Yeah, we're just converting over to LEDs now. I've found a great source in China (http://LightingGreen.cn)...
how long have you been using these lights?
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Old 27-11-2010, 08:08   #21
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Not very long - about a month or so, I suppose. Long enough to find any infant mortality (none) but certainly nowhere near long enough for a life test.
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Old 27-11-2010, 11:10   #22
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Deciding on a green power strategy is a bit like herding cats. ;D

I've found there are 5 criteria that I need to weigh:
1) load on the system both underway and on the hook
2) converting the claims of green machines to real world/your location numbers
3) determining the storage bank for your requirements
4) deciding which system(s) give you the best return for your investment
5) determining that generally speaking one system won't do it all

(1) You first need to know what your power requirements are. A good DVM and a shunt can do most of the measurements for you. You also need to investigate alternative low power alternatives (more efficient fans, LED lighting, adjusting the freezer/fridge for less power draw, etc).

(2) While I have no doubt the numbers manufacturers provide are real, I don't think they're real world - or based on my location. I tend to divide solar by 4 because I'm not going to keep the solar panels perpendicular to the sun throughout the day, I may get 8 hours of daylight but not 8 hours of good charge light, panel performance is dependent on an unobstructed view of the sun (including keeping the panels clean), temperatures, and the losses incurred in getting the power from the panel to the controller to the batteries.

The same can be said for wind generators. While these green power providers can produce power 24/7, chances are the wind isn't consistent where you are, they are mechanical devices rotating at high speeds, and can be a real safety hazard. Their power curves (wind speed vs output power) look impressive but again, the wind isn't always at the speed you need.

(3) I think the general consensus is that you need a battery bank that has 4x the capacity of the maximum load you need per day. Deep discharges tend to reduce battery life. If you choose to never discharge lower than say 70% (realistic) and the maximum charge you generally get is 95% (generally unrealistic) then, in reality, you have 25% of the capacity of the battery system to work with. If it's a dark few days your batteries may not reach the magic number, and therefore your capacity will be less.

We all tend to have engines and alternators. Many folks dislike running the engine to charge batteries so having a large alternator can both reduce the charge time and provide a higher load on the diesel. Some folks go the way of gensets, either diesel or gas, but there are maintenance considerations as well as noise and pollution concerns.

OTOH, if you live in a cold climate, running the engine may help heat the boat, charge the batteries, and heat the hot water tank.

(4) There have been very successful and happy cruisers who sailed with only one system. The Pardy's use a small portable solar panel to do their limited charging. Some boats go with just the engine and sometimes a big alternator. Others have high power requirements and opt for solar, wind, or gensets. The decision on which to use is dependent on you - and there are no wrong answers or choices; only your decisions.

Everything costs - and you can either pay for it now or later. I think many of the members here tend to have a diesel and one other system. Proponents of a variety of systems have provided real world information on use, problems and features. I agree that there is no perfect solution and that by filling out a spreadsheet, the answer will not magically appear. I also think that mechanical systems are more prone to failure than those with no moving parts, but at a cost.

(5) A solution that works for you is based on your power requirements, your realization that reducing the load is far cheaper than buying more gear and adding to the complexity and as a result, reducing the reliability.

Living aboard a boat is unique and therefore presents unique problems. We all have minimum standards in order to be comfortable and safe. We all want to be able to enjoy this unique form of travel, lifestyle, and adventure.

Sometimes you can't get there from here, at least within your budget.
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Old 29-11-2010, 07:46   #23
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I went back and read all the posts I could find on Series vs Parralell wiring for my (4) panel arrangement and if I am reading correctly the big concern has to do with shading. If 1 of the 4 panels were to become partially shaded by the boom, seagull poop, rigging etc. the other panel it was in series with would do what? Be shut down? Have its cells overloaded/fried?

Im not dead set on series wiring but liked the idea of putting the 4 panels into two series banks then run to the Flexmax 60 controller as this would allow for smaller wire. If I have (4) 135 watt panels in parallel then the starboard bank will likely require some pretty big wire. The run roundtrip to the controller will be on the order of 35'. The round trip run to the controller of the port side panels will be shorter probably on the order of 10 feet.

Can someone elaborate on the risk of shading? FWIW I am hoping to use Kyocera KD135GX-LPU panels and an Outback Flexmax 60 controller (MPPT).
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Old 29-11-2010, 17:37   #24
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A PV cell generates about .5v when active. When shaded it becomes a rather leaky diode, & eats about .7v. So your net loss when shading a single cell is on the order of 1.2v. When talking about a single panel, this is usually enough to shut the panel down, as it probably won't have enough voltage left to drive a controller & charge your batteries. Certainly that will happen with 2 shaded cells.

That's for a SINGLE panel. Putting 2 panels in series means that you have LOTS of voltage for running your MPPT controller & charging your batteries. That shaded cell (or even several cells) might be eating .7v each, but 2 panels in series produce about 35v at max power, so you've got lots of voltage to spare. The shaded cells will still pass the current.

You'll get less current into your batteries with a shaded cell, of course, because the array voltage will decrease slightly. But the panel won't shut down as it would if they were all in parallel.

4 panels in series will be even better but remember that open circuit voltages will reach 85vdc, so you'll need good insulation. Also, make sure your controller can handle that much voltage. If it can't, perhaps parallel up 2 panels in series, although that gets into other weirdness.

I LOVE my 9-year old(!) MPPT controller, but it DOES produce a lot of RF in my radio. I have to turn off my panels (& my fridge & most small inverters) when I'm on the air.

BTW, do NOT cut the leads on the Kyocera panels. Yes, they require a special plug that's difficult to get & requires a special tool to install, but cutting those wires constitutes modification of the panels & voids your warrantee. That warrantee is worth a lot, as Kyocera just replaced my 4 8-year old panels in Malaysia for free, paying freight both ways! Story (& much more on PV systems) on our Solar Panels page.
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Old 30-11-2010, 08:56   #25
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Thanks Jon that make a lot of sense. I was planning to mount my panels on the sides of the boat along the railing that extends aft from about the cockpit area to the stern. They would be mounted on the outside of the railing on articulating mounts like wings. I was planning to put the panels on each side in series then run the wires to the controller so I would end up with 2 inputs to the controller (parallel) one from each side of the boat. From reading it sounds like the risk of shading is the shutting down of the panel that is shaded. If the 4 panels I use are all paralleled and one becomes shaded it takes that single panel out but if it is in series with another panel then it not only takes the one panel out but also reduces the output of the panel it is in series with? Am I understanding this correctly? Are there other risks to the panels by putting them in series? Can they be damaged by shading?

I did not intend to cut the special cables. Was going to buy the right lengths and connect as required. Thanks again.
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Old 30-11-2010, 19:20   #26
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PV panels, Parallel or Series

I'm probably not expressing myself well...

Shading a few cells will drop the voltage by ~1.2v/shaded cell. Your max power point for a hot panel is ~15.5v/panel, & your controller needs ~15v to put current into your (mostly charged) battery.

(Note that your KC135 panels are spec'd at 1000w/sq‑m of sunlight and 25°C, which is silly here in the tropics as panels subjected to 1KW/sq‑m get HOT. Kyocera also publishes specs for hot panels under 800W/sq‑m of sunlight, which are much more realistic values here in the tropics.)

So shading a single cell of a stand-alone panel will bring the voltage down enough to shut down that panel (but it won't affect the output of other panels in a parallel array).

If you series up 2 panels then your max power voltage for that array is ~31v. So dropping the voltage a couple of volts will reduce the power (current X voltage) that the array is producing, so your controller will reduce the output current into your batteries a bit. BUT that shaded panel will still be producing power into your battery. So putting your panels in series will lose less power if you're only shading a few cells. This is usually the better configuration.

If, OTOH, you end up shading a whole panel (or even a significant fraction of a panel) of a 2‑panel array then you could shut down BOTH panels. Each shaded cell will reduce the voltage by ~1.2v but if the voltage gets down to ~15v, your controller won't be able to put anything into your battery. So your margin, where you're still producing some current, is 31‑15=16v. If you lose 16v (by shading 16/1.2=13 cells) then you'll get nothing out of that 2‑panel series array.

If your controller can handle the open circuit voltage of 4 panels (~85v) & you decide to series up all 4 panels, then your max power voltage into your controller for hot panels would be ~62v. In this configuration you'd need to lose 62‑15=47v (by shading 47/1.2=39 cells) before the array stops producing current. That's only slightly more than 1 panel, & you've lost ALL your PV output. Happily, other factors usually help here...

Note from these figures that shading a single panel reduces the output of a series array by much more than that panel produces. This is silly, so most panel manufacturers put diodes across the outputs of their panels. This means that shading a whole panel only drops the voltage of a series array by 1 or 2 diodes (~1.4v) more than the voltage that the panel would produce. So shading an entire panel that has 2 diodes across its outputs only reduces the array voltage by ~17v. This is probably enough to shut down both panels of a 2‑panel series array, but means you'd have to shade 2 full panels plus ~11 cells before a whole 4‑panel series array would shut down.

This is a complicated subject & again, I'm not sure I'm expressing myself well here. If you're still confused, I'll try again & REALLY bolux things up

The upshot is: If you're going to be shading only a few cells now & then, wiring panels in series is probably the way to go. If whole panels will be shaded, or even large chunks of a panel, perhaps it's better to leave them in parallel. With your rail mounting on a mono, it's hard for me to say as I don't have the experience (Ocelot's a cat). But you can always change it later if you want.

BTW, Ocelot is #12 of the 13 cats that Wauquiez designed & built in the 90s.
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Old 01-12-2010, 09:53   #27
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Thanks John thats pretty much how I understood your earlier post. I am still inclined to set up my in series as I dont anticipate more than minimal shading. I will the two panels on the starboard side in series and the two on the port side in series. Then have these two arrays fed to the Outback Flexmax 60 controller. I will have to see how it goes and if I am having problems then I may go to a completely parallel setup but that will require larger wires.
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