Heat and Panels

basewindow · January 2013

Hi a quick question in relation to heat and panels:

I have 2x 120w (12v) panels in para to a PWM CC into a 12v bank.

On a cold/cool winter (15 deg C) day in full sun I get about 12amps in (Each panel produces max 6.58amp) so I guess that is about right.

I noticed the other day, now full summer here (40 deg C) that I was only getting about 7.8amps in full sun.

Can heat effects the panels to this degree? Or am I going to have to get up and check components and connections?

2nd Question and totally different topic:

What is the difference between 'Grid Tie' panels and 'Off Grid' type panels and why the price diff?

Cheers,

Cam.

Cariboocoot · January 2013

Re: Heat and Panels

Heat actually has little effect on panel current, but big effect on panel Voltage. It can also have quite an effect on connections, sorry to say.

Most likely, though, you are seeing a decreased current output because more current isn't needed; longer daylight hours of Summer adding up to more charge time and more Float time so less battery discharge. The only way to truly test the panel output question is to run them into a dead short before the controller and measuring the Isc. Otherwise all you're really looking at is varying current output on different days due to varying charge needs.

"Grid tie" panels is not an official term, but one that applies to any panel whose Vmp is not "ideal" for battery based system (used with PWM controller). An "off grid" panel would have a Vmp around 17 to 18 for a "12 Volt" panel and 34 to 36 for a "24 Volt" panel. The "grid tie" panels are cheaper because of volume production, I'd say (although I'm not in the industry); a lot more GT installs than OG installs means more "GT panels". The reason why the GT panels have odd Vmp, by the way, is that they are designed to make up series strings to power inverters whose input Voltage is 250 to 500. Often the Vmp is 30, and twelve of those make a nice 360 Volt string at about 3kW of power (give or take).

icarus · January 2013

Re: Heat and Panels

Welcome to the forum. I had to chuckle,, winter temps 15C! We are lucky to see -15C for a high in winter. -30 is more normal, -40 quite common, and -50 not unheard of.

Tony

basewindow · January 2013

Re: Heat and Panels

Thanks for that, it might be the case as you suggest, that the current just isnt needed due to the amount of sun hours we have at the moment. I'll monitor and see how things go. I'm only pulling about10% out of my batteries (200Ah) and they are into float my 12.

And so in Theory when/if I need to replace my CC and I get a quality MPPT, I could use "Grid Tie" panels in a serparate string with my existing panels?

Cariboocoot · January 2013

Re: Heat and Panels

basewindow wrote: »

Thanks for that, it might be the case as you suggest, that the current just isnt needed due to the amount of sun hours we have at the moment. I'll monitor and see how things go. I'm only pulling about10% out of my batteries (200Ah) and they are into float my 12.

And so in Theory when/if I need to replace my CC and I get a quality MPPT, I could use "Grid Tie" panels in a serparate string with my existing panels?

With the existing panels on the same controller, possibly not. Whenever you put panels together you want to keep specs close. For parallel connections it's Vmp that is most important. For series connections it's Imp that makes the difference.

So your existing string could be 18, 36, 54, or 72 (multiples of a 18 Vmp) but the 30 Vmp panels in series give you choices of 30, 60, 90. As you can see, there's no combination there that matches closely.

Sometimes people will make "new" strings out of one "old" and one "new" panel, but then the Imp is limited to the lower value of the two (or more) panels. So if you take an 18 Vmp panel with a Imp of 8 (18 * 8 = 145 Watts) and put it in series with a 30 Vmp with an Imp of 8 (30 * 8 = 240 Watts) it works, making a string with Vmp 48 and Imp 8. But if you try the same thing with a 35 Vmp * 5 Imp (175 Watts) and the 30 Vmp * 8 Imp (240 Watts) panel the higher Wattage panel will be limited to 5 Amps, effectively reducing its power to (30 * 5) 150 Watts.

basewindow · January 2013

Re: Heat and Panels

Got it, I think. You can combine current of different amounts but you dont want to mix voltage ie a sting of panels with Vmp of 18 producing x amps and a different string of Vmp 30 producing z amps. Or paralleling a panel with Vmp of 18 and another with Vmp 30. In that case it reverts to the lower Vmp and Imp of the two panels and you effectively lose the value of the higher panel?

westbranch · January 2013

Re: Heat and Panels

you can also go for the GT panels with a new MPPT CC and still use the old setup in parallel to the new one...as long as you stay at 12v.

Cariboocoot · January 2013

Re: Heat and Panels

basewindow wrote: »

Got it, I think. You can combine current of different amounts but you dont want to mix voltage ie a sting of panels with Vmp of 18 producing x amps and a different string of Vmp 30 producing z amps. Or paralleling a panel with Vmp of 18 and another with Vmp 30. In that case it reverts to the lower Vmp and Imp of the two panels and you effectively lose the value of the higher panel?

Close. If you parallel two panels or strings of panels with different Vmps the higher Voltage is pulled down (but current is not effected) and the lower Voltage is pulled up (where it may exceed Vmp and the current from those panels will fall off as a result).

To make it easier; the closer the Voltages and currents of the panels the better the chances of success no matter what configuration is used.

basewindow · January 2013

Re: Heat and Panels

Okay thanks all.

That said it's probably easier and cheaper just to get some more of the same spec panels as I already have!

Cheers.

Heat and Panels

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