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Old 21-06-2010, 09:35   #1
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Current Strategies in Solar Power ?

I'm in the final stages of my GRAND PLAN of the boat's electrical system, specifically the solar panel system. I have been introduced to the Blue Sky MPPT controllers, specifically the Solar Boost 50, and it is affecting my plan. As I understand it, this system differs from the other systems I've been considering in that it can handle higher voltage output panels and improve the charging efficiencies by boosting current. It's pricey, but I think (always dangerous) I'll get the most bang for my buck and photon by exploring this path. Anyone out there with actual experience using this tack? Here is a link for further info: http://www.ecodirect.com/Solar-Boost...boost-50dl.htm
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Old 21-06-2010, 11:50   #2
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Hi, Roy.

I've not used one, but there've been a number of discussions here about them. Try using the custom Google search. There's a link in my signature line.
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Old 21-06-2010, 13:46   #3
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Roy:

You are going to need a controller no matter what you do. The MPPT controllers start at about $100 and are useful if you have about 150 watts or more of panels. Otherwise the controller doesn't improve the efficiency enough to pay for itself.

Higher voltage panels and controllers are mostly used on home systems. The high voltage- 40 or so, developed from wiring a couple of 17 volt panels in series or panels designed to produce high voltage, allows lighter gauge wire and saves a bit of money.

But unless you have a bunch of watts of panels, these probably don't pay for themselves.

In a typical boat solar system, you have 100-300 watts of panels. All are designed to produce about 17 volts open circuit and feed into a simple controller if less than 150 watts and into a MPPT controller if more. Even with 300 watts of panels (about 20 amps), you can get by with 10 gauge wire, but I would go for 8 gauge to limit voltage drop and efficiency loss.

David
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Old 21-06-2010, 20:29   #4
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Hi guys. Having a large multihull, I am looking at 2 or even three 200 watt panels over the sterncastle ( I have a center cockpit boat), to take advantage of the available real estate and absence of shadow. I have set up a substantial distributed wire system to deliver the juice to the controller near the 720 amp hour battery bank. The concept of the Blue Sky system was presented to me by a knowledgeable compadre in the biz, but I wanted to get some additional input. Thank you for contributing your information. I really want to have enough juice for the watermaker and a freezer to make unlimited gin and tonics in paradise. Oh, and vanilla ice cream.
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Old 21-06-2010, 20:46   #5
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Roy, an MPPT controller can give you about a 10% boost in actual power from the panels, by optimizing the voltage-vs-current at all times rather than simply dumping excess voltage. There's no magic there, it is simply transforming extra voltage into extra maperage, instead of dumping it.

You may also see another 10% gain in battery charging, as the MPPT controller keeps the voltage at the lowest effective level, minimizing bubbling and boiling in the electrolyte and providing pulsed DC to the battery, rather than "pure" DC, and batteries tend to charge faster and cooler when charged this way.

So if you are buying, say, 150W of solar panel(s)? Adding an MPPT controller effectively turns that into a 175W panel. (Very roughly!). Some of them also have some nice options, like turning on the anchor light or running lights when the solar panels are no longer providing power--which usually means it is near night time.

Expensive, yes, but they do provide a real gain in the amount of power that is actually available for use, instead of wasted.
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Old 22-06-2010, 10:27   #6
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So, if I purchase three 200 watt panels and use a 50 amp-rated MPPT controller, passing all the juice through conductors rated for 2% or less voltage drop, and I have a nice sunny day with no shadows on the panels, what do you reckon would be a potential day's charge? This is where my rationalization for all the expense would be.
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Old 22-06-2010, 10:47   #7
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Roy:

A good rule of thumb is that an X watt solar panel, mounted horizontally, on a sunny day will produce 1/3*x amphours of DC at 12 V. I have measured that with a battery monitor in practise so it includes all losses including battery charging losses.

The system you describe is a bit better in that you are using a MPPT controller and your wire losses are less than 2%.

So maybe you could get 120 amp hours out of your 300 watts of panels, more in the tropics in summer and less in Maine.

David
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Old 22-06-2010, 10:54   #8
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Go for it. After that, if you want any more power, just replace lights with leds.
Pretty soon you will have more power than you can use.

Have you got room for a washing machine???
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Old 22-06-2010, 10:56   #9
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Thanks, David. That sounds like a good investment, then. As with other investments, I will also try to diversify my alternative power generation resources, including running the engine, considering a wind generator, and possibly even towing a water generator. The use of a regular diesel generator is probably out of my options due to weight and available real estate inside the footprint of my boat. If anyone hears of a lightweight, affordable fusion reactor, please inform me ASAP. Also, I would dearly love a washing machine, but the size and weight are currently an issue. Hopefully, someone will come up with a new design, but I suppose that's another topic. Thanks folks for your input!
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Old 22-06-2010, 10:57   #10
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can only tell you what we have and how we like it or not -
we started with 2 130watt solar panels with a 2512 blue sky controller - our battery bank is 6 golf cart batteries and one starter - over the last 5 1/2 months in the bahamas they were ok and kept up with our usage and we did not have to start the engine to charge the batteries - we want to top off the batteries by the end of the day and not worry as much about conservation and we are adding a 12v watermaker -
we have room for one more panel but to add that we need to change out contollers and that we are not ready to do that yet -

we got all our stuff from e-systems and they seemed to have the best prices

just our thoughts on what works for us
chuck patty and svsoulmates
on the hook deltaville va
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Old 22-06-2010, 12:25   #11
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Roy, if you dig around the web there are sites from university studies and government labs (Sandia) that have charts showing panel output versus the average day in varying lattitudes over the course of the year. The ballpark I recall is that you'll get the equivalent to four hours of maximum rated output--if the panel is out all day. Don't remember if that's for a flat panel or one tilted to match your latitude for the best noontime results though.

You do also lose about 10% of the panel output for every 15 degrees that it is angled away from the sun, so if you're aboard and if you can rig a mount that allows you to tilt the panels every hour or two--you gain a lot.
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Old 22-06-2010, 16:00   #12
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Hello Roy.

Our choice for a solar panel controller was the Xantrex XW MPPT 60. It handles arrays up to 140 volts and will charge batteries from 12 volts to 60 volts.

We have 4 130 watt Kyocera panels connected in series with #10 wire. #6 wire connects the controller to the batteries through a 40 amp breaker.

The batteries (600 ah) have never been discharged enough to absorb a full day's output from the panels so the daily output is unknown. The maximum current that we have seen is 32 amps at 13.4 volts.

Because the panels are in series, the controller comes on very early in the morning and stays on until late in the evening. Very little light produces enough voltage to turn the controller on. The benefit of this has not been measured, but it can't hurt.

I did many calculations to determine the effect of shading on various series and parallel configurations. It turns out that in some cases parallel is better and in others series is better. All Kyocera panels have bypass diodes to protect the cells from overheating if they are shaded. These bypass diodes also reduce the effect of shading on series connected panels by bypassing the shaded sections.

So, my recommendation is to connect your 3 200 watt panels in series to a Xantrex XW controller with #10 wire. The maximum panel current will be 8 amps. The maximum voltage will be around 95 volts. Locate the controller close to the batteries. The maximum wire size the controller accepts is #6. The max current out of the controller will be about 45 amps.

An added benefit to this controller is that is electrically quiet. No noise on the radios.

As you might surmise, we are very happy with our setup.

A good source of information and equipment is Northern Arizona Wind & Sun.

Good Luck
Chuck
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Old 22-06-2010, 19:49   #13
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I love Cruisers Forum. Thanks, folks, for all of the great info. What a resource you are!
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Old 22-06-2010, 22:02   #14
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"The maximum voltage will be around 95 volts" (with 4 panels wired in series).

The National Electric Code would not allow 95 volts using typical boat DC wiring systems. I realize that boats aren't homes or commercial buildings, but the principle is sound.

It might be safe if it were wired like an AC system- all exposed wiring enclosed in conduit and all connections made in waterproof enclosures outdoors and all indoor connections protected from wandering fingers.

On a boat, this might not be too difficult to do. On my boat with 4 panels wired in parallel, the final connection was only exposed for a few feet. A plastic wire loom around this last few feet might not meet the letter of the NEC, but it would make it a safer system.

David
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Old 22-06-2010, 23:56   #15
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People are missing an important point here since this thread is all about "total efficiency" in solar charging.

You can do all the tweaking, adjusting and fine tuning, of solar regulators and adjusting the orientation of solar panels for optimum charging efficiency etc. but in the overall scheme of things it makes little difference if you have a super efficient charging set up while your AGM batteries are extremely inefficient in storing the generated power.

If you are really serious about having a truly efficient complete solar/electrical system on your boat really you need to be using a LiFePO4 battery bank and dumping your inefficient, antiquated lead batteries.

When you consider most lead acid batteries have a typical charging efficiency of 70% - 80% and LiFePO4 batteries are 95% - 99% charge efficient do the calculations yourself as to how much power your solar panels are producing which is just being wasted and not being transformed into useful, stored energy in your battery bank. In many boats it is more than likely one entire solar panel is doing little more than generating power which is completely wasted in the charging process in your lead batteries and none of this power is stored at all.

I would guess that many boat owners don't even consider this factor since they are preoccupied with trying to improve the efficiency of their charging system.

I can provide an actual efficiency comparison between using lead acid (SLA) batteries with Lithium Iron Phosphate (LFP) batteries in a standby power application running an inverter. The same efficiency considerations apply to running a load (in this case an inverter) with both battery types as they do in charging efficiency.
Sure the application might be a bit more complex and larger scale than in a boat (not too many boats I know have inverters rated at 200kVA and discharge their batteries in 10 minutes!) since the comparison is testing the performance of both battery types in a UPS but the concept is exactly the same as if it was on a boat. Think of the boating example as being a smaller version of what would be the result of these tests.
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File Type: pdf LFP vs SLA B -E.pdf (298.0 KB, 160 views)
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