Renogy eclipse solar panels (newly released)

Boatycall wrote:

billtex wrote:

Boatycall wrote:

* Be careful installing them, install them inside a garage, not outdoors. 46Vdc can bite you, ask me how I know.

I thought you were a EE? ;)

What differentiates a high voltage from low voltage panel?
How do I know when panel shopping?

Also we are running 2 6V 250 AH AGM batteries.
Will the 100w be sufficient or should we be looking at a larger system?

We do not use a significant amount of power but do want to keep the batteries charged/maintained.

OK, so let me see if this helps--

Here is the specs on the Renogy panel being discussed:
Specifications
Maximum Power: 100W
Maximum System Voltage: 600V DC (UL)
Optimum Operating Voltage (Vmp): 17.7V
Open-Circuit Voltage (Voc): 21.2V
Optimum Operating Current (Imp): 5.70A
Short-Circuit Current (Isc): 6.10A

This is a 17.7v panel. This is a low-voltage panel. VMP means Voltage @ Maximum Power
It delivers 5.7amps of charging current. That's what IMP means -- Amperage @ Maximum Power
VOC doesn't really do anything for you other than bite you as you're installing them outside. Ask me how I know. VOC stands for Voltage Open Circuit - just two bare wires dangling on the roof, no load. My panels are 46v, wired in series/pairs for a VOC of 92v. Mine are considered high voltage panels.

So--
Multiply the two, Vmp * Imp = P, or Power, aka, 100 watts.

Now--
If you use a PWM controller, you will never get more than the 5.7amps of power the panel lists as it's IMP, or maximum amps. A PWM controller will never convert the wasted voltage into amperage. The panel will be a 17.7v panel charging a 12v battery. (The controller does however prevent overcharge.)

Now,
Lets say your batteries are low from running the furnace all night. For easy math, we'll say you're at 11.5v in the morning. Sun comes up.

If you spend a few more bucks for an MPPT controller, you could see as much 8.6amps of charge from that same panel--fully 33% more charge. 100watts divided by 11.5v = 8.6amps. It would be like buying a 133 watt panel. The MPPT controller converts the 17.7v down to the maximum possible usable amperage.

As the battery voltage rises, the current will come down to a theoretical maximum of 6.9amps @ 14.4v as the controller eventually then switches to trickle mode.

These numbers are all in a mathematically perfect world, not real world of course, but the gains of a PWM vs. MPPT would be proportional. Real world, I tend to see 75-80% of real usable watts out of my system on a nice sunny day vs. the published laboratory perfect world max ratings.

Using a MPPT controller allows you to get more from your solar panel(s) when in less than optimum conditions: dirty, not pointing perpendicular to the sun, less than full sunlight, etc. I think very few of us will have solar panels that aren't mounted flat on the roof. That's "less than optimum".

When the panel is in optimum conditions, you got a heck of a lot more from it with a MPPT controller.

I'm not an electrical engineer, just a guy who has designed, installed, and used solar power systems in remote areas for quite a while. And yes, I've been zapped too. Part of the business.