Help needed with Solar

[GulfportBarb]

We are replacing our old flexible solar panels with these new ones: Renogy Solar Panel 100W 12V Lightweight Semi Flexible Black Division Monocrystalline Bendable Mono Off-Grid Charger for RV Boat Van Car Uneven Surfaces, LTWT-Flex.
We have 4 100 watt panels and a Victron MMPT 100/30 charge controller. The max amps for the 4 panels is less than 30 amps, so this size should be OK whatever we do.
We don't know whether we should connect in parallel or in series. Our AGM battery bank is 2 Group D (245 amp hrs each) 12v batteries. If we connect in series, then we will have 48v running into the charge controller. Will it convert the volts to 12 volts or do we need another controller? Or would it be easier to run the panels in parallel? If so, what connectors should we use? 4 in 1? Thanks for the help, trying to figure all this out is not easy!

[deltaten]

Call Renogy and talk to tech folks. Thier panels, they'd know best practices. I ordered panels and controller set up from them. Had some confusion on my part. Called and tech sorted it out pleasantly and efficiently. Near ten yrs on and still operating full-tilt ��

[Franz.Capitan]

the controller Victron MMPT 100/30 -

100 means maximum volts from the solar panel: 100V
30 means maximum amps to the Batteries 30A - you have to check this. With 4 panels 100W and 12v batteries the maximum curent is 33amps!
33A x 12V = 400W

[dougweibel]

Originally Posted by Franz.Capitan

the controller Victron MMPT 100/30 -

100 means maximum volts from the solar panel: 100V
30 means maximum amps to the Batteries 30A - you have to check this. With 4 panels 100W and 12v batteries the maximum curent is 33amps!
33A x 12V = 400W

You will probably be OK on amps capacity as when you are charging your battery voltage will be above 12 volts and it will be rare that you get a full 400 watts out of the panels, so exceeding 30 amps would be an unusual occurrence. Some controllers will be very unhappy if supplied with too much power such that their ampere output would exceed their stated max. Most, including Victron AFAIK, will be OK as long as the power mismatch is not excessive and will just limit the power out to not exceed the ampere limit. Check the manual for your controller.

Also, while controllers are happy to convert voltage down to the battery voltage most controllers have a minimum solar voltage which is higher than the battery voltage. If your panels truly will only produce 12 volts then you probably need to wire them in series, at least as pairs. Again, check your controller manual.

[Madehn]

If possible use two controllers and divide the panels into two banks. Preferably port and starboard so as to get the most out of panels if one side is shaded. Personally I would wire each bank in series so that you have two banks supplying 24+ volts to the charge controllers. By doing this you can run smaller wire which is easier to install. If you. Used two 20 amp controllers that can handle 24-28 volt input then you will make the most of your charging potential and not stress the components. Costs a little more in that you have the have some extra breakers and a second controller. I wish I had gone that route on my boat. ( I have two 80 amp Outbacks charge controllers and everything in the 1.4kw array runs at 12-17 volts. ). If running in parallel make sure that the charge controllers can handle your input voltage.

[noelex 77]

As others have said, the 30A limit applies to the output, not the input current, but this controller is (just) large enough for your 400w.

Connecting the panels in parallel is generally preferred over series connection on a shadow prone boat, although using multiple controllers is better again. The only consideration is the relatively high start up voltage of the Victron controllers. This rarely seems to cause any practical problems, but when contemplating connecting "12v" panels in parallel or to a single controller, consider the Voc of the panel. If this is very low then a series-parallel configuration is sometimes better.

The Renology panels you are planning to use have a very high Voc (23.5v) for a "12v" panel so if using a single controller, parallel connection will produce the most solar yield.

Do not connect all four panels in series with this controller. The combined Voc of 94v is too close to the 100v limit of the controller. If you exceed 100v even briefly the controller may be permanently damaged. Solar panels can sometimes produce more voltage than their Voc STC specifications so most manufacturers recommend at least a 10-15% buffer between the solar panel and controller voltage specifications.

[sailingharry]

I am upgrading to a pair of 400W bifacial panels, and am having the same conundrum.

In theory, 30A is nearly perfect for 400W. In my case, the bifacial aspect means I'm probably looking at closer to 440W. Still, the amount of time that I'll be leaving power on the table is very small. In your case, with 4 panels, the odds of having ALL FOUR at full power is very low. And being flexible, the output degradation over time means you will be losing even less.

One important point. Unlike many other types of devices, there is no "100% load risk." The land solar folks install controllers to support their normal load, and build their panels to support that load in mid-winter. That means they are "over paneled" as they call it in the summer.

Another point -- the footprint and heat sink for the 30A is the same as the 50A, so the 30A is well cooled.

Me? I'm about 90% convinced I'm going to spring the extra for 50A, even if I never get a single extra amp from it... LOL

[svtickles]

I have 2x 245w Panasonic panels installed in parallel which routinely hit the current limit of the 100/30 Victron MPPT (at 30 Amps). Every amps counts so I wouldn't recommend under sizing the mppt. As others mentioned, if you can afford it put each side of the installation on a separate mppt. Shade on a single panel can cause the entire set to reduce output.