Please compare these two panels for me

sunnyside

Please compare these two panels for me, one is half the price of the other. Is one better?

http://www.grapesolar.com/index.php/products/modulesandkits/gs-s-100-ts/

http://www.ebay.com/itm/100W-Watts-100-Watt-Solar-Panel-Off-Grid-12-Volt-12V-RV-Boat-USA-Solar-Cells-/300907458483?pt=LH_DefaultDomain_0&hash=item460f7b6fb3

Mods, I hope this is ok I need to understand more about the ratings

waynefromnscanada

Re: Please compare these two panels for me

Welcome to the forum.
There's not a lot of difference in their specs.
one has a max power output voltage rating of 18.9V and a Max power amperage rating of 5.29 A
The other, a slightly lower MPP voltage of 17.7, but a slightly higher current of 5.7 Amps.
Is one better than the other? Depends on your situation I suppose. They weigh basically the same, which should indicate relatively equal material in the frames etc.
If you have long wire runs, you might be better off to use the one with slightly higher voltage to offset cable losses, On the other hand, if that's not a problem, the second one might give slightly higher charge current, as long as there's very little loss in the connecting wires.
Even so, there's very little difference.

sunnyside

Re: Please compare these two panels for me

Going to be installed on top of a Sprinter van, four in total. Does one look better for wind loads?

BB.

Re: Please compare these two panels for me

The EBay panel is rated for 50 lbs/sqft wind load and the Grape for >30lb/sqft wind loads. And the EBay panel is rated for even ~112 lb/sqft snow loading...

So, all things being equal (and assuming that all vendors meet their specs), the EBay should be a stronger unit. Given that both units are about identical thickness and weight--Not sure that the lbs/sqft difference is real or not...

-Bill "guy who already had an array 100% replaced--so I did not pick well" B.

niel

Re: Please compare these two panels for me

now i find that interesting as that grape pv seems to be of the sunpower design. i didn't think sunpower would ever do that, but i'm sure the cells in it are probably 2nds. these have had grounding issues and require a + ground when grounded, but for an rv or such i don't think that would be a problem. the grape has a higher efficiency if space is an issue. my choice would most likely be the ebay one as it eliminates the higher costs associated with the higher efficiencies and takes away any doubts with the grounding issues.

sunnyside

Re: Please compare these two panels for me

niel wrote: »

now i find that interesting as that grape pv seems to be of the sunpower design. i didn't think sunpower would ever do that

Neil could you expand a little on the Sunpower design.

The Grape solar cells are supposed to be made in Germany and assembled in Oregon
The Ebay cells are supposed to be made in the USA and the panels assembled in Taiwan
I would prefer the Grape solar panels only because of their smaller foot print but the GS panel is 277.00 compared to 140.00 fro the Ebay panel
I just hate a bad purchase decision, thats why I have reached out to the great folks on this forum, thanks for the comments

BB.

Re: Please compare these two panels for me

True "Sunpower" solar cells use a different contact arrangement to gather power from the solar cell. The usual cell has those metal grids to collect power from the front surface of the cell. Those metal contacts/traces block sun from the cell and cause some loss of power (less efficient cell).

Sunpower modifies the contact arrangement so that they can be more efficient. The downside is that the solar cells can become "charged" like a capacitor. And, over time (weeks/months) can loose upwards of 10-30% (don't remember exact numbers) of their output.

The way around that is to "positive ground" the solar array--This prevents the cells from building up the charge (and the process is reversible--A negative grounded array switched to positive ground will dissipate the excess charges over a few hours/days).

This is not a real problem for Grid Tied systems. With minor changes (or a jumper change) they can have a positive or negative grounded array.

For off grid systems, we normally negative ground the battery bank/power systems. Why negative--As far as I can tell, there is no good reason. Just convention with the American automotive market.

For telecom (and some electrified rail systems), we do positive ground because it prevents underground pipes, metal tanks, etc. from being corroded if there is an electrical short somewhere. However, positive ground with standard off grid solar power systems can be a mess (or worse) as they are usually designed for negative ground systems (communications grounds, and such are negative referenced).

I don't know anything about the Grape panels and their Negative/Positive ground requirements.

-Bill