How to make photovoltaic solarpanels to suit our boatdesign

Actually I'm a wee bit older than 15, so you must be referring to the photovoltaic doormat on my boat.

All these futuristic ideas of solar shingles, sails and rolls of photovoltaic roof material ignore the need for interconnections that handle the generated power.
If there would exist an electricity generating plastic foil to cover your roof, sold as 10 meter rolls of 1 meter wide, is would only generate 0.5 volt unless you cut it up in small pieces and series connect it. But then your roof would certainly leak....

There is also the problem that on a small roof, the conductive strips may be much narrower than on a large one, unless someone is prepared to spend days with a soldering iron adding larger conductors.

 

clip connectors CDK
and frankly I'd love to be 15 again
ah if I had only known then what I know now

 

I said " refer CDK reply !!! His ( meaning solar panel) is ...

 

did you say refer
stuffs legal here in good old Colorado

 

heat vs output

Something to remember if you like the idea of reflecting devices to increase the output of PV cells -

Reflecting light means that you're also reflecting heat (infra-red part of the spectrum) and the cell voltage goes down although the current stays the same.
So output (voltage x current) will drop as the temperature of the cells rises.

If they get very hot they will lose voltage to the point that they won't charge anymore.

This is why a nominal '12 volt' panel has an open-circuit (ie. not connected to a load) voltage of 18 volts or thereabouts. A '12-volt' panel needs an extra couple of volts to make charging happen (your 12 volt car has an alternator output above 14 volts), and another couple of volts to deal with heat rise.
So reflectors are probably okay in a cool climate, but not when it's hot.

 

Hi Sand groper,

Do you feel it gets too hot just above the sea water on a boat? Do you have some curves for us to see the relation of temperature versus output? Monocrystaline and polycristaline cells. One could always cool the panel down with some cold seawater. The glas is normally hardend and can absord temperature fluctuations. Also, normally at the sea, there is some wind. If the panel is not used, one could fold the reflector over the panel as a protection.

 

Fully agree with you and also during lightning , I think the thunderstorm would have a ball with all those roofs.

 

Curves for output vs temp are out there in googleland (panel power is rated at 20º or so and has a derating expressed as volt drop per degree rise) but the thing is - PV likes to be cool, just like cables like to be short, thick, and cool.
Here's a link to an experiment using a concentrator that has a power/temp curve - http://www.mantaro.com/downloads/Using_a_Solar_Concentrator_with_Photovoltaic_Cells.pdf
Attached (hopefully) is an IV curve. The shoulder is where the maximum power lurks (because amps x volts = power), and the curves for different temperatures tell the power story too.
Splashing seawater onto a hot panel may not crack the face, but it may cause a chemical or physical change as a result of the minerals in the sea, leading to less output.
I'm guessing here however - mr google might know.
It would be better to cool the back of the panel (maybe with, or combined into, a desal system ? -http://www.seapanel.com/) if cooling must be done. Air cooling by windchute might do it.
Maybe aluminium fins a la heatsinks perhaps.
For all the fiddling about you'd be better off to just add more PV in my opinion.
Trackers are good for water pumping because they get the pump going early which simply adding fixed PV won't necessarily do, but for other applications fixed arrays are cheaper per Wh produced. So following the same logic suggests that simple is good, but a boat doesn't have acres of bimini to play with, or PV sails, or PV decks, (or a magic pixie system that uses the earth's magnetic field as a power source).
Err, back to the cooling story - apparently a factory in Malaysia thought that their array would benefit from misting from the nearby waterfall and built the array to suit. Cool panels, self-cleaning, all good. Except that the received light intensity was diminished by the mist, and output suffered.

 

Sand groper has a point here.
Leakage current in silicon junctions depends on the operating temperature. That goes for diodes, transistors, thyristors and also for solar cells, which are in fact large area silicon diodes. They have the disadvantage that because the substrate must be cheap, it is contaminated and because it is heavily doped to do what it was designed for, the leakage current is considerable at room temperate already.

The leakage current at rising temperature gradually reduces the cell's output until a point is reached where the voltage of a panel drops below that of the battery and charging stops. Both mc and pc cells suffer from this, but for mc cells the horizontal part of the graph is longer and the curve steeper so they behave more like a constant current source.

This is the main reason why there always is a diode in the charging circuit. Without it, solar panels during twilight draw current instead of generating it.

The temperature dependency is the reason why solar panels must be mounted above a surface with enough clearance to allow air circulation and keep the cell temperature as low as possible. It is also the reason why fixed installations should not be pointed south but sse of se. The morning light is cooler so the panels perform better.

If cells are mounted on a surface directly in hot areas, full output at midday cannot be expected unless there is a provision to cool the array location from under the surface.

 

Using plastic light guides to boost output.

My LCD TV sets are all in good working order so I cannot provide proof and it is just an idea I present here.

Behind the LCD is a plastic layer with remarkable properties. At the bottom of the screen is a thin gas discharge tube in a metalized cavity with a slit where a plastic layer starts which extends over the screen area. The plastic layer effectively transports the light uniformly to the whole screen area.

Many years ago a client gave me a few colorful pieces of plastic bar that lit up at both ends very brightly when light reached the length of the bar. It seemed like the light was amplified because the longer the bar, the brighter. They have been on my desk for years, but I never found a useful application for them.

That same material is now used in every LCD screen, but it could also be used for a solar panel where the cells are placed in a row at the bottom of the panel.
There would be no heat problems because the plastic transmits only visible light.

 

You have to be careful with those extra volts tho. I found out the hard way. Had an old Ford Ranger with mechanical regulator set up for the average driver under average conditions. while taking it on the road for a summer tour of the west I burned out the radio, horn, both headlights same time, and two batteries in a 6 month period before a sharp auto electrician spotted the overcharging problem and set the regulator down a volt. Under very sunny conditions an overcharge could slowly cook some of your more sensative electronics.

CDK that is kind of the logic behind a "freeze roof" in heavy snow areas. by mounting the metal roof an inch above a regular roof the roof freezes and snow won't stick to it and avalanches off. something I wish I had done as I have icicles from roof to ground right now.

 

"This is the main reason why there always is a diode in the charging circuit. Without it, solar panels during twilight draw current instead of generating it."

Yes how true CDK. I neglected to mention the reverse-current thing.
PV cells can indeed be little radiators if they're powered-up at night or in low-light conditions by a battery. And they won't be PV cells for long.

Concentrators that are water-cooled may be fine for land but too much messing around at sea, though CDK's 'wonder-plastic' might see him wildly rich perhaps .....

Exploiting hot conditions with a thermocouple connected to the heat on one side and the cool deep sea on the other may seem promising, but they don't produce much power.
It seems that there's no free or cheap lunch, which is a good thing as energy degrades environments whether that energy is PC or not - if we ever perfect a very cheap energy source then the natural world had better start running (or increase it's present speed!).

 

PV technology

And obviously mono-crystalline panels are more efficient than poly- crystalline which are more efficient than thin-flim / amorphous etc.

Boats have limited space, so mono panels are suited.

Also, little PV boosters like car dashtop battery boosters don't need regulators because the input is so small compared to the battery's energy content and loss rate, but anything else requires a regulator, and MPPT regulators (that turn any 'extra' volts in to 'extra' amps, and therefore 'extra' power electronically) are the best but cost more of course.

 

How true Sand Groper,

The only free energy is usually energy we don't want or need. Riding the lava flows in Hawaii would be a real cheap source of locomotion

Much of this is under the heading of Rube Goldberg Contraptions like sterling engines or those little solar motion vanes we sometimes see in the windows of gift shops. Energy which can be used to power nothing but itself.

But that's what makes us thinkers and inventers I guess. People thought Alexander Graham Bell was nuts for inventing the telephone cuz there was nobody to call until he invented a second one.

 

wasting energy

I've done about 20 grid-connected domestic PV installations and some customers get it, but others have old, empty, unventilated beer fridges, swimming pool pumps, giant TV's, halogen down-lights, etc etc.
SUV's, heaps of airconditioning, fertile human females - where will it all end ?