Batteries, Batteries, Batteries, Hmmmm.....

[Captron]

Efficiency of solar panels

Just a comment on the relative efficiency of solar panels ... typically solar panel efficiency is measured in terms of watts output per square foot of surface area but there are other considerations. If you measured output per pound of panel for example, the flexible panels are more efficient than rigid panels. Also you need to consider windage. The flexible panels offer a much smaller wind profile than rigid panels.

It just depends on how you use the boat and the panel. Racers that stow the panel on board when racing for example might prefer the lighter weight flexible panel. Cruisers that don't care about weight and windage might prefer bigger rigid panels.

Just throwing a little gas on the fire.

 

[jkm]

Don't we just love a little fire?

Ron are you saying that while at anchor it makes little or difference on which type, rigid or flex, one has?

John

 

[Mike.Gritten]

We've been doing some checking on solar panels and how they might benefit our cruising plans. We've come to the conclusion that the thin film, flexible type are what we're going to install on Papillon. While not producing the same number of amps under "ideal" conditions, they have the ability to produce a larger percentage of their rated power over a much wider range of conditions. They are not as finicky (real word?!) as the rigid panels as far as shade goes either.

 

[jkm]

Mike

Since you've done the research.

Why can't one lay out the panel and simply plug it into, say a socket like a cigarette socket?

You'd need some sort of a controller component to prevent discharge.

Wouldn't this trickle charge the batteries?

Also what flexible units are you looking at???

John

 

[Mike.Gritten]

John,

you're right. You can get a small, flexible panel and lay it out, plug it into a cigarette lighter socket and trickle charge your battery just like many automotive products you can buy. It's just that we don't want to trickle charge our battery bank, we want to re-charge it, and that's where the charge controller comes in. With the right panel(s) attached, it will feed your batteries at a rate far exceeding a trickle charge. We have not actually picked out the brand of hardware we will purchase, but have decided on the type of equipment we want to buy. We will be watching the internet and the local chandlers for deals on flexible panels around the 50W size and will then purchase several of them to install above our bimini and anywhere else we can put 'em where they'll be out of the way. I open to where these might come from so any suggestions would be welcome!

 

[Captron]

Efficiency

Don't we just love a little fire?

Ron are you saying that while at anchor it makes little or difference on which type, rigid or flex, one has?

John

Nope,

Just suggesting that there may be other considerations than efficiency based on square footage of surface area.

One issue with efficency measures is that they measure maximum output under ideal conditions ... meaning perfect solar angle, no shadows, cool ambient temperatures, etc.

Mono-crystaline panels are considered to be most efficient but if the solar angle isn't perpendicular to the crystal structure, polycrystaline and amorphous (flexible) cells deliver more power.

Also if rigging shades even a small amount of some panels, the whole panel shuts down. Some polycrystaline and flexible panels continue to deliver power in proportion to the unshaded area even though most of the panel may be shaded. Most monocrystaline panels shut down.

I think weight and windage are important too.

FWIW, on my catamaran (in a past life) weight and windage were very important for permanently mounted solar power so we chose the biggest flexible panels available and mounted them on the bimini where rigging shadows always hit part of the panels.

On Kismet we went for a Kyocera 120 watt unit mounted on top of the stern davits. Once in a while we get rigging shadows but the polycrystaline Kyocera doesn't mind minor shadows.

I'd have to go back and check the numbers but the single Kyocera weighs maybe 2 or 3 times as much as 4 of the flexible panels. That plus the 4 flex panels laced to the bimini presented almost zero additional frontal area compared to a 2 inch thick rigid panel.

The net result is about the same ... maybe half of our daily cruising electrical consumption was met by solar panels.

Of course, cruising is mostly anchoring. Racers or part time racers may have other considerations such as removing the the panel(s) when racing or only putting the panel out when docked or moored.

Consider the whole picture not just the panel efficiency numbers.

 

[jkm]

What a concise lesson, Ron.

No doubt, that for the weekend cruiser that I am, the flexible panel would suit me best. I can drape it over my sunshade, facing south, since at anchor we're almost always facing west.

Trickle charge! What do I need is the question.

My intent is to run my refrigeration. I've upgraded to larger batteries and the question will be how much can I generate with a 50 watter via trickle charge in a given day, on average.

Mike, what will a controller do that increases the charge?

John

 

[NateHanson]

You need a controller for panels that are more than about 15 watts for a typical ~200 Ah bank. Larger panels could potentially overcharge the battery bank without a controller.

Also, controllers take the output voltage of the panel (anywhere from 12 to 18 volts), and do DC-to-DC inversion to transform the panel voltage to the optimal charging voltage for your batteries. (Something like 14 volts).

 

[jkm]

ah ha

That makes it very clear. Nate are we going to see pictures of your set up??

John

 

[NateHanson]

It could happen. We had a lovely sail Saturday evening to Bartletts Island (wife and kids first trip on this boat), and of course - forgot the camera.

One of these days I'm sure I'll bring it though.

 

[jkm]

Hobnobbing with the Rockefellers?

 

[NateHanson]

Bless those fithy rich bastards. It sure is nice that they've kept that island undeveloped, and open to 4-year-old sailor/explorer/princesses.

 

[jreddington]

Not the big panels being discussed here, but came across this relatively cheap solution for trickle charging the batteries.

It appears VW, Audi, and some other European manufacturers put small solar panels in the windshields of their cars when they ship them here. The panels plug into the cigarette lighter socket. This keeps a trickle charge on the batteries during shipment or long waits in yards. Works well on European cars since they have lighter sockets that are always hot. Japanese and U.S. convention is that the socket turns off and on with the ignition so the panel can't juice the batteries with the key out on these cars. The units do have diodes to prevent battery discharge when the sun is down.

These panels show up by the dozens on E-bay. Not sure if someone at the dealerships are collecting these and making a few bucks on the side or some owners find them in the trunk. Just search on solar panel and VW, Audi, etc. Runs in the low $20s with shipping.

They have suction cups so if you can attach them to the bottom of a clear hatch within reach of an outlet, just leave the battery selector on and the breaker to the outlet on. I usually select just one of the two batteries and alternate (battery 1 when I leave on a odd day of the month, battery 2 on even days). My companionway hatch is smoked so I have a small square of plexiglass I use to cover the panel, then leave it out secured on the cabin top. Seems to be holding up well, even in the weather.

Hard to tell if it really makes a difference since the only time I've had trouble starting after being away for a couple weeks was with a pretty old battery. Then just switched the selector to its buddy, fired up, and took the bad battery home with me to replace.

 

[Captron]

Trickle charge

I have a small solar panel (5Watt) that was designed to plug into a cigarette lighter. I use it on a camper I have in storage. Works great. Keeps the battery up for months.

It cost less than $12 at Harbor Freight Tools on sale. I'll buy another one to keep the truck battery up when we go cruising.

 

[Captron]

Homeless in Largo

I couldn't resist passing this along.

Largo, Fl (between St Pete & Clearwater west of Tampa) police arrested a homeless man living in a wooded area of Largo because he had broken into a commercial battery distributor's shop repeatedly over the last several months.

Apparently each time he broke in, he stole a single 'truck battery'.

When police captured the suspect, they also recovered six batteries. Apparently he was stealing the batteries to power the TV in his tent. Unfortunately all the batteries were dead. Probably a capital crime in Largo.

I guess after food, shelter and clothing, comes TV. Good thing they didn't sell gensets. They'd have never caught him.