Solar panels: efficiency and wiring...

neilfraser · Post by **neilfraser** » Fri Mar 14, 2008 3:24 pm

I see Maplins have their 13 Watt solar panel briefcase on special until the end of the week, which makes it £50.

Now 13 Watts doesn't sound like a lot, but if you adjust the angle and position it may be possible to increase it's effective rating by a factor of 5 if you believe what the manufacturers claim about this panel:

http://www.outdoorbits.com/alden-sunpow ... p-272.html

If so it would be worth a buy, especially as it includes a regulator.

We have a converted Bongo with Zig and leisure battery. Could I wire the regulator directly to the leisure battery terminals without upsetting the Zig charging mechanisms?

Any electrical experts out there?

mikeonb4c · Post by **mikeonb4c** » Fri Mar 14, 2008 3:52 pm

Dandywarhol has a panel on his roof and no doubt will be along shortly to advise, or you could try Search as its been discussed before. I'm interested in solar panels too - wait and see what Danady and other electrical gurus give as a view on the Maplins one

dandywarhol · Post by **dandywarhol** » Fri Mar 14, 2008 4:37 pm

Mine was a 12W panel until I recently sat on it when fitting the roofbox

To be honest Ithought it was too little to do much good - at less than an amp at source by the time it got to the front mounted leisure battery any gain was soon lost if an appliance was switched on.

francophile1947 · Post by **francophile1947** » Fri Mar 14, 2008 4:46 pm

The link leads to a 100W panel that never achieves it's maximum potential of 8.5A (max achieved 5.9A). It would therefore seem that a 13W panel is unlikely to achieve it's potential of just over 1A - fine for trickle charging the batteries, when no power is being used, but not much use for boosting the available power.

mikeonb4c · Post by **mikeonb4c** » Fri Mar 14, 2008 5:34 pm

Hmmm - disappointing. Wind generators anyone?

neilfraser · Post by **neilfraser** » Fri Mar 14, 2008 5:45 pm

My point was more along the lines of, if pointing at the sun directly throughout the day can increase the utilisation of the panel by a factor of 5, then this is going to be as useful as a 60W panel on the roof, is it not?

I would be using to supplement a 85 AHr leisure battery.

Just out of interest does anyone know how far you would have to drive to get the equivalent charge e.g. 8 Amps?

Neil

francophile1947 · Post by **francophile1947** » Fri Mar 14, 2008 6:02 pm

neilfraser wrote:My point was more along the lines of, if pointing at the sun directly throughout the day can increase the utilisation of the panel by a factor of 5, then this is going to be as useful as a 60W panel on the roof, is it not?

I would be using to supplement a 85 AHr leisure battery.

Just out of interest does anyone know how far you would have to drive to get the equivalent charge e.g. 8 Amps?

Neil

That's not the way I read it. They are saying that, by aiming it at the sun, you will get nearer it's maximum output. So a 13W panel may get near to 13W IF it is aimed at the sun all day - it cannot exceed it's maximum power output.

Peg leg Pete · Post by **Peg leg Pete** » Fri Mar 14, 2008 9:14 pm

mikeonb4c wrote:Hmmm - disappointing. Wind generators anyone?

Baked beans do that Mike

haydn callow · Post by **haydn callow** » Fri Mar 14, 2008 10:00 pm

The Bongo alternator is rated (I think) at 80 amps.So in theory in one hours running it should put a max of 80 amps into your batteries. However it is not that simple. Alternators output is not 100% and what they do put out reduces as the battery charges and fills up. Also a alternator produces it's max at about 10,000 revs. In a vehicle they turn at about 2 x engine revs so around 5/6,000 revs.
If your battry is discharged to around 12 volts (pretty flat) I would guess it would take a couple of hours running to fill it up
The reason I know a little about this is my life living on a narrowboat. I had 90amp and 70amp anternators working together to charge a 500 amp hour bank of battries. We fitted oversize crank pullyes to turn them at 10,000 revs and fitted remote ameters so we could monitor what was going on. Even with a management system fitted the output of the alternators dropped after about 20 min running. The most we could put into the batteries was about 130 amps at start up and this soon reduced to around 70 amps.
Solar panels we found were a bit of a waste of money. Wind generators were not much better.

missfixit70 · Post by **missfixit70** » Fri Mar 14, 2008 10:17 pm

What about an exercise bike with the right gearing connected to an alternator, add a couple of sugarladen kids ( connect up a supply for their playstation so they don't get bored) & voila, keeps the kids quiet & green energy

samuel · Post by **samuel** » Fri Mar 14, 2008 10:52 pm

So if:

wind power doesn't work?
solar power doesn't work?
All my recycing actually goes to landfill? (allegedly)
wave power might work!? Just hope the tides don't give up!
and we're runnig out of renewable energy resources?

Anyone for nuclear power? No. Just the French?

Excuse me while i just disappear for some Bongo Green Kryptonite!

lizard · Post by **lizard** » Sun Mar 16, 2008 7:43 pm

They can power up the Bongo with what they like, cost of fuel at the moment.

Nuke power sounds good at the moment

madmile · Post by **madmile** » Sun Mar 16, 2008 8:04 pm

Following from what Hayden said, you could max the output of your alternator by fitting a 'Sterling Battery to Battery Charger'. The self build motorcaravan club are always promoting these.
Never used one, and at £200 not likely to in a bongo, but they seem to work in a similar fashion to a voltage sensing relay, but fool the alternator into giving a max output for a longer period.

mikeonb4c · Post by **mikeonb4c** » Mon Mar 17, 2008 1:03 am

I love talking to narrowboat owners. On the subject of windpower they reminded me that i general canals weren't a good environment for wind generation as they were too often shielded from directional wind. Some of the places Bongo visit might be much more suitable I think. I'm tempted to look into it along with all the other futile experiments I can't resist trying out

andyfb78 · Post by **andyfb78** » Mon Mar 17, 2008 11:55 am

Just a bit of info on solar panels..... my thing....

The 'nameplate' rating of a solar panel is tkaen when the panel is tested at standard test conditions NOT real sunlight.

this is at 25deg C and 1000 W/sqm irradiance (light power), and perpendicular to the panel. it is very difficult to achieve this in reality as the sun is not likely to be at 1000 W/sqm and if it is, the temperature of the cells will be above 25 deg.
unfortunately, as temp increases efficiency falls.

the rating for the panel is likely to be VERY inaccurate for real conditions, and as yet there is no 'real' standard to allow analogy to the real world, they simply have to be tested......

you will therefore probably get significantly less power than the rated power in reality....

one thing this does mean though is that a particular cell is likely to produce similar levels of power here in less sun but lower temps, as it does in arizona at higher sun power but at detrimental higher temperatures.......

The angle of the panel makes a massive difference, the ideal angle for battery charging will vary, but assume due south, at an angle to the horizontal equivalent to the latitude (53degs ish for the UK). if the panel is immovable and to be used all year then increase this by 10 degs. Ie steeper, this trades some loss in summer for some gain in winter.

if it is movable then just under the latitude will give the best results. and if it can track the sun through the sky even better.

you will not get better than the rated power as this is at the perfect perpendicular angle, (ie all the light hits the panel).

Hope this makes sense...
Andy