Solar panel Amps

[Pedro_The_Swift]

Is there any advantage in going to a 200w panel over a 130 if they both put out over 5A?(infact the 130 puts out nearly 6)
Its going on the van roof so size is no problem,, but one weighs 10kgs more,,

[JDNSW]

The 200w panel puts out more power than the 130 - this is the difference. I do not follow your comment about both putting out 5A - why is this a magic number? Whether the extra power from a larger panel is worth the cost, space and weight depends on what you are using it for. Or are you asking about whether to make up the same total power from larger or smaller panel? More information needed!

John

[seano87]

Is there any advantage in going to a 200w panel over a 130 if they both put out over 5A?(infact the 130 puts out nearly 6)
Its going on the van roof so size is no problem,, but one weighs 10kgs more,,

For them to both to put out 5A or so, the 200w will be putting out a higher voltage. 5A x 40volts = 200w. 5A x 26volts = 130w.

Sent from my Galaxy Nexus using Tapatalk 2

[Utemad]

If you mean you only need 5 amps then I guess it depends on if you need reserve capacity or not.

However I have two 59w panels linked so nearly 120w. Together they will easily reach and sit on 8 amps. So the 130w panel should do more than that.

This formula will give you an idea of max output in a perfect system (which you will never achieve due to heat losses etc).
Amps=watts/volts

[Blknight.aus]

depending on who made your panel....... the reported output watts (and amps) may not be the same, confused?

ok in theory all you need to out put 5a@12v is a 60W panel 5amps x12v=60W But depending on how "honest" the seller is about what the panel can put out you can get a lot of variance.

the nominal charging voltage for a generic 12v system is 13.8V so to me to put 5a into a 12v system you really need a 70w panel But thats only really good in ideal conditions add 10% to that and now you're looking at an 80W panel to put 5A into a 12v system.

then youve got the losses through the regulators.

the big advantage to a 200w panel over a 130w panel is simply that it puts out another 6A @12v however depending on the construction of the panel you may loose all of the output if just a small portion of the panel is covered.

[Pedro_The_Swift]

Mornin! :D


soooo,, its OK to put 38V thru my batteries?

late edit,,
well no its not.
my controller has a max open circuit voltage of 26V

heres a (maybe dumb) question, do 2 panels double the voltage input to the controller?

[Vern]

need a voltage regulator, like the Morningstar range.

Oh and as for your doubling the voltage, if you wire them in series then yes.

[Pedro_The_Swift]

Vern
I would be using the standard solar connectors, so just one set of cables to deal with inside,,
what does that make it?
though with voltage reg it makes no difference,,:D

[Blknight.aus]

Mornin! :D


soooo,, its OK to put 38V thru my batteries?

late edit,,
well no its not.
my controller has a max open circuit voltage of 26V

heres a (maybe dumb) question, do 2 panels double the voltage input to the controller?

depends on how you wire them.

theres a handfull of numbers you need to know.

1. full short amps. this is how much the panel will try to pump out if you just short the output, all your wiring needs to be able to handle this if you dont have fusing or circuit breakers at the panel. its aslo the maximum amps that can be pushed through the panel if you have a string of panels
2. rated voltage, this is the nominal voltage the panel works best at
3. rated watts, in theory the best out put the panel can achieve
4. rated amps, in theory the designed amps out of the panel at the nominal voltage (2,3+4 should more or less follow ohms law)
5. open circuit voltage of the panel, what it puts out with no load on it
6. maximum voltage of the panel, if you hook a string of them up in series this is the maximum voltage the insulation can handle

typically, a panels open circuit voltage will be its nominal voltage +~50%

very very roughly when it comes to wiring them up think of them as batteries and the usual rules of parallel and series apply.

If your battery is flat enough (and can handle the amps) you can hook a panel set rated a lot higher than the battery voltage as the load of the battery taking charge will pull the voltage from the panel down and the amps will increase. This gets hairy as the battery charges up and the process reverses (volts go up amps go down) as eventually you'll boil the batteries.

This is what your charge regulator takes care of.

No you shouldnt put a panel onto a regulator if the panels open circuit voltage is higher than the regulators max input voltage.

My personal preference is to run multiple panels with multiple small regulators, The advantage of this is that you always get something out of the system and you can piecemeal the system up to the required out put. It costs more in the long term, less in the short term (if you build in stages) but is cheaper to repair and upgrade. one other advantage is that it lets you run mismatched gear.

[weeds]

i like to keep it basic

i assume you have a regulator, what is this rated at? either way you need a regulator either in each solar panel or one in the van

by the biggest solar panel you can afford, or two smaller panels to create redundancy

mount them on top of your van and forget

dont get wound up in how many amps you need over a day, the outputs/inputs etc.......its better than your existing setup (no solar panels) and its the best you could affort at the time. if its doesn't keep up for the duration of your stay at least your beer will be colder for longer than if you didn't have solar panels

have you considered the 2 panels folded up and tranported in a carry bag, this allows the van to be in the shade, just face the panel to the north at 30-40 degrees off the deck, sit back and enjoy your beers.

if you van is under cover when parked at home you can than put your solar panels on the roof which will trickle/float charge your batteries, this in theory will extend the life of your batteries........keeping you beer colder for longer

[Pedro_The_Swift]

My god Weeds,, thats the longest post you've ever made:eek:

[weeds]

My god Weeds,, thats the longest post you've ever made:eek:

and it took hours of typing.........

[rovercare]

1. full short amps. this is how much the panel will try to pump out if you just short the output, all your wiring needs to be able to handle this if you dont have fusing or circuit breakers at the panel. its aslo the maximum amps that can be pushed through the panel if you have a string of panels
.


You don't use overcurrent protection on the panels, they are current limiting and with any protection it would either be to big to operate or too small and operate in good conditions

eg. ISC of 5A, maximum current ouput of the panel, so when it shorts out, it has 5A current flow in ideal conditions, so what overcurrent protection do you plan on fitting? 4A so it blows all the time or 6A where its completely useless as its impossible to achieve that current draw?........just wondering?:p



Pedro, just buy what ever is cheap and fits within the voltage regs limits

[Blknight.aus]

read again
your wiring must be able to handle these amps IF you dont have fuses or circuit breakers,

Ergo IF your wiring can deal with what the panel can pump out THEN you dont need fuses/CB.

however

I generally use the nominal flat battery voltage to work out the amp rating of a fuse for a solar panel for a 12V system I use 10V just because its easy and most fuses have a fairly generous margin unless you're fitting exotic fuses (auto fuses are about as slow as you can easily buy) and then for a cricuit breaker I use the nominal amps at the correct charging voltage for the battery (so perfect world a 10a breaker on a 138W panel to charge 12V batteries)


on an 80W panel I fit a 10A fuse and on a permamant fixture intended to be left unattended an 8A self resetting circuit breaker.

some panels have a blocking diode built in and others have the regulator as part of the panel. If you're using the blocking diode you dont need the fuse as the diode will burn out doing the same job and the jobbies with an inbuild regulator deal with the problem via the regulator.

[Utemad]

have you considered the 2 panels folded up and tranported in a carry bag, this allows the van to be in the shade, just face the panel to the north at 30-40 degrees off the deck, sit back and enjoy your beers.

For the fold up panel thing, I just have two normal 59w panels and screwed two hinges to them. This folds the glass fronts onto each other.
Then I double sided taped a Morning Star regulator to the back of one and added long twin cable with the usual small andersen connector on it. Even then I had to make an extension lead.
You will get lots more power back into your batteries if you can move your panels around to avoid shade and follow the sun.

Only down side is they are bulky to pack like this.

[mike123]

Just make sure you're comparing apples to apples. In my experience the larger panels are generally 24vDC and the smaller 12vDC. Once you get to around 130W panels and above then some are still 12vDC but most are generally 24vDC.

As for a regulator I'm using a Plantronics 40amp and that works fine.

Mike

[rovercare]

read again
your wiring must be able to handle these amps IF you dont have fuses or circuit breakers,

Ergo IF your wiring can deal with what the panel can pump out THEN you dont need fuses/CB.

however

I generally use the nominal flat battery voltage to work out the amp rating of a fuse for a solar panel for a 12V system I use 10V just because its easy and most fuses have a fairly generous margin unless you're fitting exotic fuses (auto fuses are about as slow as you can easily buy) and then for a cricuit breaker I use the nominal amps at the correct charging voltage for the battery (so perfect world a 10a breaker on a 138W panel to charge 12V batteries)


on an 80W panel I fit a 10A fuse and on a permamant fixture intended to be left unattended an 8A self resetting circuit breaker.

some panels have a blocking diode built in and others have the regulator as part of the panel. If you're using the blocking diode you dont need the fuse as the diode will burn out doing the same job and the jobbies with an inbuild regulator deal with the problem via the regulator.

No need too, the panel has an ISC rating which it won't exceed, current limiting, no need for any protection on the feed from the panel to the regulator, it will either be a nuisance or never work...ever. after the reg on the other hand is different as it will be fed ffrom the battery, capable of lots of amerageres;)

[Blknight.aus]

after having seen the wires from an array merrily melting away I'll fit fuses..

If it only burns your vehicle down once a year, its a bad year.

[rovercare]

after having seen the wires from an array merrily melting away I'll fit fuses..

If it only burns your vehicle down once a year, its a bad year.

Correct, they will melt away merrily, but aside from trying to take it to an extreme^^^^, the facts remain, you either fuse it below its rated ISC and it will blow/trip the overcurrent protection or fuse it over the ISC rating and if there is a fault it will continue to merrily melt away;)

So, either your fitting overcurrent protection on the array side, that will nuisance trip or wont function at all

[TerryO]

Large panels, like a 200 watt one aren't often fitted to vans because it is hard to mount them so they won't flex and sooner or later break. I have two x 135 watt Kyocera's and they can churn out when the sun is overhead around 12 to 13 amps according to the Morning Star regulator.

5 amps per hour isn't much if you like to use an average amount of power daily. Good quality panels work well, as do some eBay specials, but the only way to find out if the eBay specials are any good is to buy them and then hope for the best. Whereas the quality panel is pretty much assured of doing what it's makers claim.

cheers,
Terry

[Wahroonga Farm]

My two cents worth ... appropriate or not ....

Don't forget the most critical aspect of all solar panels, their design MPP, or Maximum Power Point.

This is specified for all good panels and is the voltage at which the panel achieves the maximum power transfer (to the load).

ie P (watts) = E (volts) x I (amps)

For many 12v panels this is 18v. So a 120watt panel could theoretically output 120 watts at 18 volts and a current of 120/18 = 6.6 amps.

Panels with higher MPP voltages are often selected, when an MPPT (maximum power point tracking) regulator is used. The higher MPP panel raises the volts but lowers the current for the same power (or energy) transfer. e.g a 32 volt 120watt panel would output only 3.75A, reducing energy loss in the solar panel cabling.

For 18 volt panels a simple PWM regulator will do a fair job; but do get one with a sufficient panel VOC (Volts Open Circuit) rating and also ensure that it has a few bells and whistles.

I like a regulator to display at least the following:

Panel and load volts plus amps (power from panel and power to load is also handy), total A/H (since last reset or time etc) generated by the panel and total A/H consumed by the load.
Panel temperature has a considerable effect on panel efficiency.

High temperature (typical in Sunny Oz) considerably de-rates both the panel output (watts) and the panel MPP (volts).

Whilst this is an unfortunate fact of life, it DOES mean that the simple PWM regulator is relatively effective, as the panel volts (18v could easily be 15.6 volts at 50 degrees C) which now more closely matches the battery charge volts of say 14 volts; more or less negating the need for a more expensive MPPT regulator. In cooler climes, early and late in the day etc, a MPPT regulator will likely show a greater efficiency benefit.

Have a look at this simple graphhttps://www.aulro.com/afvb/images/imported/2012/11/63.jpg which demonstrates the effect of temperature on a silicon panel MPP.

Any way that should be enough to ensure my (renewed) membership does not evaporate in 12 months time through lack of posting. :angel: