Best Solar Panels For The Buck

[prroots]

Originally Posted by hellosailor

"As mentioned, they are nominal 18 Volt panels ...The open circuit voltage of my panel is 33."

I smell smoke. As Jared says, that's a nominal ~24V panel, NOT a 12V panel at all.

Nope, it's a nominal 18 Volt panel with 54 cells in series.
Pete

[hellosailor]

Pete, I'm confused here. Panels designed for mobile systems (as opposed to higher-power off-grid cabins, etc.) are normally either a nominal "12" or "24" volt panel. With the "12" volt panels typically putting out some 17-21 volt under open circuit, etc. but still being nominal 12-volt panels if they are designed for 12-volt systems. Which would be a standard marine system in the US.

So just what kind of panel do you have anyway?

[prroots]

Originally Posted by hellosailor

Pete, I'm confused here. Panels designed for mobile systems (as opposed to higher-power off-grid cabins, etc.) are normally either a nominal "12" or "24" volt panel. With the "12" volt panels typically putting out some 17-21 volt under open circuit, etc. but still being nominal 12-volt panels if they are designed for 12-volt systems. Which would be a standard marine system in the US.

So just what kind of panel do you have anyway?

I can't tell you why it's nominal 18 Volts, just that it is. Just remember that a nominal 12 Volt panel typically has 36 cells and a nominal 24 Volt panel typically has 72 cells. Ours is half way between which makes it a nominal 18 Volts. With the advent of MPPT controllers the exact number of cells has less significance than in the old days.
Pete

[s/v Jedi]

Originally Posted by prroots

I can't tell you why it's nominal 18 Volts, just that it is. Just remember that a nominal 12 Volt panel typically has 36 cells and a nominal 24 Volt panel typically has 72 cells. Ours is half way between which makes it a nominal 18 Volts. With the advent of MPPT controllers the exact number of cells has less significance than in the old days.
Pete

Exactly. The whole 12/24/48V thing is gonna disappear and MPPT controllers will be the standard, as will be series connection. For new buyers a non-MPPT controller makes no sense.

ciao!
Nick.

[prroots]

My testing of parallel vs series has been frustrated by cloudy days. Here are the results from today. You can tell which is which from the array voltage. Notice the voltage shifts with shading. I can't make sense of it, can you?
Pete

[hellosailor]

A couple of the leading chipmakers have released MPPT core chips and complete application notes, so anyone can easily produce a well-engineered MPPT controller from a recipe now. Very different from the all-custom-roll-your-own of five years ago.

Nevertheless...anything you can build or buy can and will fail at some point. If you've got nominal 12-volt panels and your MPPT controller fails, you can ship it out for repairs and run the panels "raw" and still function.

Got a special panel array at some voltage that will blow the batteries out? TFB, you're up the creek without a paddle unless you've got a spare controller to swap in. So running oddball panels will still entail mixed benefits and risks even if MPPT controllers start turning up on the electronics rack at 7-11's.

If the whole system depends on the MPPT controller...I'd at least throw in a cheap PWM regulator to carry onboard as a spare.

[prroots]

This graph shows array Voltage for the same period as above. Showing it by itself makes it easier to observe
Pete

[s/v Jedi]

Originally Posted by hellosailor

Nevertheless...anything you can build or buy can and will fail at some point. If you've got nominal 12-volt panels and your MPPT controller fails, you can ship it out for repairs and run the panels "raw" and still function.

You can do that with 18V nominal panels too. It only becomes a problem when your batteries are full, at which time you don't need the charge anymore.

(the empty or half charged battery is a very low resistance creating a large current which makes the array voltage drop to that of the battery)

ciao!
Nick.

[prroots]

Originally Posted by s/v Jedi

You can do that with 18V nominal panels too. It only becomes a problem when your batteries are full, at which time you don't need the charge anymore.

(the empty or half charged battery is a very low resistance creating a large current which makes the array voltage drop to that of the battery)

ciao!
Nick.

Thanks for making that point. I was about to as well, but wasn't totally confident. It's nice to have someone keep the rest of us on the straight and narrow
Pete

[s/v Jedi]

Originally Posted by prroots

Thanks for making that point. I was about to as well, but wasn't totally confident. It's nice to have someone keep the rest of us on the straight and narrow
Pete

Now it's better to add that the current must stay under the value that the battery can accept or voltage will go up too. I don't see a boat with that many panels or so few batteries but you never know what happens

For regular lead acid batteries, the current in A must stay under 20% of the bank capacity in Ah. So an 800Ah bank will accept up to 160A. If you put an 18V supply that can deliver 200A on that, things will get rough but the cells will be equalized allright

ciao!
Nick.

[s/v Jedi]

Originally Posted by prroots

My testing of parallel vs series has been frustrated by cloudy days. Here are the results from today. You can tell which is which from the array voltage. Notice the voltage shifts with shading. I can't make sense of it, can you?
Pete

I think you will need to test like Mark did: at least a week in one configuration followed by the same period in the other configuration. You need stable weather too so that the average sunlight received is the same over both test periods.

or....

you make a test setup in a controlled environment: dark shed or cellar with panels and artificial light source. Emulate shading with cloths on the panels etc.

ciao!
Nick.

[prroots]

Originally Posted by s/v Jedi

I think you will need to test like Mark did: at least a week in one configuration followed by the same period in the other configuration. You need stable weather too so that the average sunlight received is the same over both test periods.

or....

you make a test setup in a controlled environment: dark shed or cellar with panels and artificial light source. Emulate shading with cloths on the panels etc.

ciao!
Nick.

I think I can eliminate the second option. We are not only subject to the variations in the weather (ie, cloud cover), but also the boat orientation caused by shifts in wind and current while on the hook/mooring which drastically affects the shading. I was really hoping for a really nice cloudless day and then switch back and forth numerous times between parallel and series. This would give me an average watt output difference as opposed to a daily Ah collection difference.
Pete

[prroots]

Originally Posted by s/v Jedi

Now it's better to add that the current must stay under the value that the battery can accept or voltage will go up too. I don't see a boat with that many panels or so few batteries but you never know what happens

For regular lead acid batteries, the current in A must stay under 20% of the bank capacity in Ah. So an 800Ah bank will accept up to 160A. If you put an 18V supply that can deliver 200A on that, things will get rough but the cells will be equalized allright

ciao!
Nick.

Thanks. We have 416 Ah and the short circuit current of my two panels in parallel is 17.2A (ie 2 X 8.6A). Therefore, I should have no trouble provided I stay in bulk phase and disconnect when I reach the absorption voltage.
Pete

[GeoPowers]

Originally Posted by Cotemar

Should be able top get the SunPower E19 240 watt panel in the $600 range.
They are not cheap, but if you need small and light these are the way to go.

There are a lot of boats out their using the SunPower panels now.
These guys are going around the world with them panels

Hi Cotemar,

I know you and some other folks got some SunPower panels, but I don't think they sell to boats anymore.

I called two local "premier dealers", and was told that they only sell the panels as part of a complete install package to residential or commercial folks. One even recommended I buy the Sanyo HIT 225W panel. I then called SunPower directly, and the agent I talked to said the same thing. When I asked him if he realized that his panels were on PlanetSolar's RTW solar boat, all he said was "yeah"......

SO, being a stubborn guy when he's getting told an answer he doesn't like, I "liked" them on facebook and posted the following:
"Hi, I am very interested in SunPower solar panels for an installation on a sailboat. However, when I called two authorized dealers I was informed that they could not sell panels unless installed as part of a residential system. Is this correct, or is there another way to procure these panels? The high efficiency rating of your panels is perfect for the limited space typical of a marine environment, which is probably why PlanetSolar has your panels on their around-the-world boat! How can I buy some of your panels?"

....and got no response. I hate having to work to spend my money, so I'm going to go with the Sanyo model. The SunPower would have been a perfect sizing and wattage, but the Sanyo allows me to better add more panels later based on available "real estate".

Unless you can PM me with how to get two 240W E19's... I could even make a pair of 320W's work..

I do have to chuckle and note the irony that the company that makes the solar panels on PlanetSolar's RTW boat won't supply to boats....!

Frank

[Cotemar]

GeoPowers,

We have 6 boats now that I have worked with that have the SunPower panels.
I was told all the same things you were. I stopped asking installers and called a few distributors and they said sure they will sell them to me. They drop shipped a pallet of four of them in my driveway for two boats.

You just have to call around in your area. I also worked with a few boats in Australia and they also purchased the SunPower panels with no problems.