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Old 21-08-2012, 07:39   #181
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re: Best Solar Panels For The Buck

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Don, another point about the Solarworld panels from AltE: "Allow several weeks for delivery." Like many others I'm hardly ever in one spot for two weeks at a time lately, so fast and reliable delivery is important to me. I've never had a problem with Amazon, other than worrying they will take over the world someday.

Not an issue for me, they are close and the location is a plus. These are just details for someone when ordering and doesn't change the $1.06/watt price tag. But who knows what will change by the time I get around to it as this wil be an off season project for me.
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Old 22-08-2012, 14:24   #182
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re: Best Solar Panels For The Buck

DM is no small producer of panels. About a month ago I purchased a pair 145W panels from Amazon for $320. That represents a cost of $1.10/watt! Amazon just received another batch so I last night ordered another pair.

Here in Massachusetts the sun is quite iffy. The pair now on my boat is set for 12vdc (panels in parallel not series) and the best I was able to see for current was 12 amperes around noon. Early mornings 8-9AM I saw anywhere from 3-5 amperes depending on the clouds.

I am hoping to see the current doubled by adding another pair. If so that should solve my 12vdc charging problems using a PWM controller. I have to develop an acceptable (to me) power plan. Currently I have both 12 & 24vdc battery storage for power. I might just go later with 24vdc IF THESE PANELS can be placed in series. As I type, I cannot think of a reason they could not be. However series panels will be more susceptible to shadows.

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Old 22-08-2012, 15:05   #183
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re: Best Solar Panels For The Buck

"DM is no small producer of panels."
I suspect they are no producer of panels at all, but rather some guy with a connection at Hyundai is bring in containers of Korean or Chinese panels as a "white label" product.
To be a producer, they'd need a plant. Not a residential address in Florida.

Doesn't mean anything about the product--other than your warranty is from "some guy". Could be some guy in his parent's garage, you know, like Bill Gates or Steve Jobs.
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Old 22-08-2012, 18:13   #184
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re: Best Solar Panels For The Buck

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"DM is no small producer of panels."
I suspect they are no producer of panels at all, but rather some guy with a connection at Hyundai is bring in containers of Korean or Chinese panels as a "white label" product.
To be a producer, they'd need a plant. Not a residential address in Florida.

Doesn't mean anything about the product--other than your warranty is from "some guy". Could be some guy in his parent's garage, you know, like Bill Gates or Steve Jobs.
Yeah--- I quickly scanned their web site this afternoon--- saw many buildings with "glass panels" and went on. One thing is for sure, the panels seem to arrive in batches, sold by Amazon. Another thing for sure is the delivered cost/watt is $1.10. Hard to beat. So for $640 I have 580 watts of panels. That is MUCHO better than Harbor Freight's three panel set with a total of 45 watts at whatever the market will bear but advertised around $180 in their flier.

If anybody want to take the chance, they appear to be a good chance to take.

Foggy

EDIT: WHO KNOWS--- maybe Obama has a deal with Solindra to use Amazon to help retrieve a small part of the $500 million he wasted chasing the sun.

Purloined from a Solar Panel web site dated 12 July 12

"There is no way of knowing how many we sold so far, how many members have bought so far for sure. But we do know that 200 of the 704 are already gone in less then two hours.

We aren't kidding, if you wanted any of these....DO IT NOW!
"
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Old 22-08-2012, 18:20   #185
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re: Best Solar Panels For The Buck

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... I have to develop an acceptable (to me) power plan. Currently I have both 12 & 24vdc battery storage for power. I might just go later with 24vdc IF THESE PANELS can be placed in series. As I type, I cannot think of a reason they could not be. However series panels will be more susceptible to shadows. Foggy
Foggy, a MPPT controller can take input from panels in series (typically ~34v) & use that to charge a "12v" battery (typically at 14v). Such a configuration is actually LESS susceptible to shadows. With solar panels, each shaded cell will drop the panel's output by about 1.1v. The 0.4v that the cell produces goes away & the cell becomes a simple diode, eating ~0.7v. With panels in parallel, you only have to shade a single cell (if the panel is hot - maybe 2 if it's cold) before the panel is shut down completely. But with series panels, you have to shade multiple cells before the voltage drops down to where the charger can't charge a 12v battery.

Working out how many amp-hours you use in a day is tedious but not difficult. Find out the current usage of each item on your boat (measure it, don't depend on advertising specs) & write down how long each one is on. A spreadsheet will help enormously. Multiply the 2 numbers together & add up the products & you'll have your answer. Our son did this as a school project & published his results (~130Ah/day for our family of 4).

He also integrated the input from our panels & came up with an interesting number. If you take the nominal wattage of your panels & divide that number by 3, that is about how many amp-hours you'll get into your batteries on a sunny day in the tropics with horizontally mounted panels (aimed panels will get more, higher latitudes will get less).

We've put a lot more info on our Solar Panel page if you're interested.
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Old 22-08-2012, 18:32   #186
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re: Best Solar Panels For The Buck

HOLY SMOKY ANDY!!!!!!!!!!!!!!!

I saw that Amazon had the panels in stock either yesterday or the day before. I ordered mine last night.

THEY ARE SOLD OUT!!!

Amazon.com: DM 145w Polycrystalline Solar Panel (2 Pack): Patio, Lawn & Garden

Foggy
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Old 22-08-2012, 18:49   #187
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re: Best Solar Panels For The Buck

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Foggy, a MPPT controller can take input from panels in series (typically ~34v) & use that to charge a "12v" battery (typically at 14v). Such a configuration is actually LESS susceptible to shadows. With solar panels, each shaded cell will drop the panel's output by about 1.1v. The 0.4v that the cell produces goes away & the cell becomes a simple diode, eating ~0.7v. With panels in parallel, you only have to shade a single cell (if the panel is hot - maybe 2 if it's cold) before the panel is shut down completely. But with series panels, you have to shade multiple cells before the voltage drops down to where the charger can't charge a 12v battery.

Working out how many amp-hours you use in a day is tedious but not difficult. Find out the current usage of each item on your boat (measure it, don't depend on advertising specs) & write down how long each one is on. A spreadsheet will help enormously. Multiply the 2 numbers together & add up the products & you'll have your answer. Our son did this as a school project & published his results (~130Ah/day for our family of 4).

He also integrated the input from our panels & came up with an interesting number. If you take the nominal wattage of your panels & divide that number by 3, that is about how many amp-hours you'll get into your batteries on a sunny day in the tropics with horizontally mounted panels (aimed panels will get more, higher latitudes will get less).

We've put a lot more info on our Solar Panel page if you're interested.
Thanks Jon--

I completely forgot about the by pass diodes! I am pretty much on top of my energy consumption both by monitoring my fridge's duty cycle which is the main load on my 12vdc batteries and the 24vdc system by monitoring the recharge time. I measure the recharge time by noticing how long it takes for the 24vdc inverter/charger to unload my generator. And of course this load depends almost entirely on how Wifey uses our 120watt 32" TV.

Now if we had better sun conditions here and another "if" I had the panels cleaned every day and properly aimed I would get much closer to the advertised output specifications. Of course, my panels are almost flat although not. They are mounted on my rear deck's hardtop which has curvature. One panel could have a better angle to the sun while the other panel would have a poorer angle. Yes, things in the real world are real, not perfect.

So I just doubled up on the panels. I have until next year to really get my act together. I am leaning towards going strictly 24vdc and leave the 12 stuff just for running the boat along with its electronics.

And of course your right on the mark suggesting a decent MPPT controller. That also will be on next year's task list of things to do. I muddle over designing and building one during the winter if I can get my projects caught up. Too many projects currently ongoing.

I think a continuous current flyback circuit concept controlled with a microcontroller might be the best approach. But the cheapest way out is simply to just purchase one. Great forum!

Foggy
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Old 22-08-2012, 19:19   #188
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re: Best Solar Panels For The Buck

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Thanks Jon--



And of course your right on the mark suggesting a decent MPPT controller. That also will be on next year's task list of things to do. I muddle over designing and building one during the winter if I can get my projects caught up. Too many projects currently ongoing.

I think a continuous current flyback circuit concept controlled with a microcontroller might be the best approach. But the cheapest way out is simply to just purchase one. Great forum!

Foggy
Foggy,
I think it is true that you will get more output from your panels with a MPPT charge controller especially on a sailboat where shading cannot be completely avoided, but in real life application most people report an 8% gain vs the advertised 20 to 30% gain. Lets look at the cost difference for a Morningstar Tristar 45 WPM vs MPPT: $167 vs $467. For the $300 difference, unless perhaps you have 3200 W of panels, I think it is more cost effective to just buy another 290 W of panels.
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Old 22-08-2012, 19:20   #189
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re: Best Solar Panels For The Buck

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...If ... I would get much closer to the advertised output specifications... Foggy
Advertised specs are usually at 1kw/sq-m of sunlight & 25C module temperature, which is ridiculous. Any panel under that much sunlight (mid-day in the tropics might get to 1kw/sq-m) will be MUCH hotter than 25C. Heat affects performance pretty drastically, which is why panels should never be mounted to a deck. Kyocera publish specs for their panels (which will be very similar to other panels, I'd think) at 800W/sq-m & 20C ambient, with coefficients to get to 47C (~120F) which is much closer to reality.
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Old 22-08-2012, 19:57   #190
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re: Best Solar Panels For The Buck

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HOLY SMOKY ANDY!!!!!!!!!!!!!!!

I saw that Amazon had the panels in stock either yesterday or the day before. I ordered mine last night.

THEY ARE SOLD OUT!!!

Amazon.com: DM 145w Polycrystalline Solar Panel (2 Pack): Patio, Lawn & Garden

Foggy
You can go to there site and buy them as well. I think they are maybe $20 more after shipping but still a good deal.

DM 145w solar panel, solar module 145w, 12V Solar Panel
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Old 22-08-2012, 20:13   #191
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re: Best Solar Panels For The Buck

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Foggy,
I think it is true that you will get more output from your panels with a MPPT charge controller especially on a sailboat where shading cannot be completely avoided, but in real life application most people report an 8% gain vs the advertised 20 to 30% gain. Lets look at the cost difference for a Morningstar Tristar 45 WPM vs MPPT: $167 vs $467. For the $300 difference, unless perhaps you have 3200 W of panels, I think it is more cost effective to just buy another 290 W of panels.
Azul-- I agree, that is why I purchased another set and not a MPPT at this point. But consider Vmp = 18.7 for a panel and consider 14 vdc into a battery along with about 1.5vdc drop across the PWM switch and reverse protection diode, the loss as I see it is about 18.7 - 14-1.5 = 3.2 volts. Current Imp for a panel is 7.75 amps so with this sloppy calculation uncaptured power is 3.2*7.75 = 24.8 or about 25 watts.

Now that calculation was for one panel; I have or will have 4 panels upon the arrival of my last order. Theoretically, that would be 100 watts not captured. Now sure, I agree I will never, ever see teh panel's Pmp of 145 watts under any condition although I should see at least half that.

Jon's above post provides better predicted data under many conditions. Bottom line for my installation is if it is good enough, maybe nothing is needed. If after making a bunch of data point measurements maybe a MPPT controller is worth consideration. Time will expose many of today's unknowns.

Foggy
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Old 22-08-2012, 20:19   #192
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re: Best Solar Panels For The Buck

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You can go to there site and buy them as well. I think they are maybe $20 more after shipping but still a good deal.

DM 145w solar panel, solar module 145w, 12V Solar Panel
Unfortunately, Amazon.com does all of their inventory for them. So if you order a panel directly from them all it does is take more time. The good news is their next shipment (from China I guess) will have MC4 pigtails or cables for the same price according to the tech guy I talked to. Expect 10 to 14 days before that happens.
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Old 22-08-2012, 20:28   #193
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re: Best Solar Panels For The Buck

Azul-- My last order had the MC4 connectors on about 3' pigtales. I just got them a few weeks ago.
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Old 23-08-2012, 03:12   #194
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re: Best Solar Panels For The Buck

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Azul-- I agree, that is why I purchased another set and not a MPPT at this point. But consider Vmp = 18.7 for a panel and consider 14 vdc into a battery along with about 1.5vdc drop across the PWM switch and reverse protection diode, the loss as I see it is about 18.7 - 14-1.5 = 3.2 volts. Current Imp for a panel is 7.75 amps so with this sloppy calculation uncaptured power is 3.2*7.75 = 24.8 or about 25 watts.
The Vmp is published for a cell temperature of 25C. In practice the cell temperature will be about 40C. The negative temperature coefficient of Vmp means that Vmp drops by about 1.5v under real world operating conditions.
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Old 23-08-2012, 08:32   #195
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Re: Best Solar Panels For The Buck

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The Vmp is published for a cell temperature of 25C. In practice the cell temperature will be about 40C. The negative temperature coefficient of Vmp means that Vmp drops by about 1.5v under real world operating conditions.

No debate on that Noelex! I tried to avoid doing a complex analysis, just wanted to show that an MPPT might provide reasonable performance improvement because of having four panels. 10% of a small number results in a smaller number not worth the bother/cost although 10% of a larger number is still smaller than the original it could be a worthwhile number.

From my post " Now sure, I agree I will never, ever see teh panel's Pmp of 145 watts under any condition although I should see at least half that. "

Add a qualified "maybe" to that.

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