Maximizing An 80 Watt Panel?

Maine Sail · May 2011

Hi All,

I have a customer with a Shell/Siemens 80 Watt panel on his sailboat. It is currently using a Flex Charge PV7 controller. He is limited in panel size and would like to get more out of his current system. I would like a controller that can be set for 14.6-14.8 absorption voltage for his T-105's and he wants to get more amperage input to the batts on a daily basis.

Which controller would you recommend? I am heavily considering the Morningstar MPPT or the standard Morningstar units but want one that can do the absorption voltages I want and that offers more voltage than just 14.4V absorption for wets.

Will he see more amps if going to MPPT over the Flex Charge PV7 or is MPPT only beneficial on larger arrays?

Is any upgrade from the Flex Charge PV7 to another controller worth while and worth the money?

I do not want a unit that does on/off charging and would prefer a full three stage charging controller.

Any input greatly appreciated!

Cariboocoot · May 2011

Re: Maximizing An 80 Watt Panel?

Welcome to the forum.

You've got a problem, alright. As you suspect MPPT controllers really only have an advantage with larger or high Voltage arrays. About the smallest one you can get is the Morningstar 15 Amp unit. Therein lies the problem: 80 Watts of panel just isn't much power. It's bound to have an output like this:

80 Watts @ 77% efficiency = 61.6 Watts / 14.2 Volts charging = 4.3 Amps. That is way below the recommended 10% of Amp hours for those Trojans (22.5 Amps). If this is the only charge source, it is a recipe for early battery death.

If you had 200+ Watts of panel you could use an MPPT controller.

Most good PWM controllers do have 3 stage settings. But frankly the real problem is that there just isn't enough panel, and no controller is going to make up for power that isn't there.

Morningstar controllers: http://www.solar-electric.com/mochco.html

Maine Sail · May 2011

Re: Maximizing An 80 Watt Panel?

It is not the only charge source. He has a 125A alternator and external regulator. The solar is really only for topping up the batteries during the week when the boat is on the mooring unoccupied. I would like to push the voltage however to match Trojan's recommendation.

Which of the Morningstar controllers would you recommend that I can adjust the voltage of or is the PV7 about as good as it gets for an 80 watt panel?

Cariboocoot · May 2011

Re: Maximizing An 80 Watt Panel?

At 80 Watts there really is no point in spending the big money required for fully programmable set points. The Sunsaver units have a flooded battery setting of 14.4 Volts, but that isn't much improvement over what you have now and doesn't approach Trojan's 14.8 V recommendation.

As is, that panel is just a trickle charger.

bmet · May 2011

Re: Maximizing An 80 Watt Panel?

At higher ambient temperatures, it's only 14.1 volts.

Cariboocoot wrote: »

At 80 Watts there really is no point in spending the big money required for fully programmable set points. The Sunsaver units have a flooded battery setting of 14.4 Volts, but that isn't much improvement over what you have now and doesn't approach Trojan's 14.8 V recommendation.

As is, that panel is just a trickle charger.

dak664 · May 2011

Re: Maximizing An 80 Watt Panel?

Maine Sail wrote: »

Hi All,

I have a customer with a Shell/Siemens 80 Watt panel on his sailboat. It is currently using a Flex Charge PV7 controller. He is limited in panel size and would like to get more out of his current system. I would like a controller that can be set for 14.6-14.8 absorption voltage for his T-105's and he wants to get more amperage input to the batts on a daily basis.

He loses daily output when (if) absorption takes less power than the panel can put out. How about an intervening LiFePO4 battery that can always take peak panel output, and run the absorption charger off that? Size the battery for 500 watt-hours and run it to near empty every night. Charge with cheap buck converter that maximizes current, it's probably almost as good as MPPT in that application.

mike95490 · May 2011

Re: Maximizing An 80 Watt Panel?

dak664 wrote: »

He loses daily output when (if) absorption takes less power than the panel can put out. How about an intervening LiFePO4 battery that can always take peak panel output, and run the absorption charger off that? Size the battery for 500 watt-hours and run it to near empty every night. Charge with cheap buck converter that maximizes current, it's probably almost as good as MPPT in that application.

80W is not going to go far, recharging both the LiFePO4 and it's losses, and then the PB and it's losses too.

For these big honking batteries, hook the panel up with a anti-backfeed diode, and enjoy whatever you get. But it cant even keep up with daily losses, just offset them some, for the hour while the sun angle is good.

dwh · May 2011

Re: Maximizing An 80 Watt Panel?

The Morningstar MPPT has a connection for either a remote meter (RM-1) or a serial communications adapter. Using the Morningstar MSView software and the serial adapter, you can program the unit for the voltage set points you want.

Not cheap, and you're only going to get a few extra amp*hours per day - but you can punch the battery voltage up to where it needs to be, and that alone might make switching to MPPT more in the realm of "worth it".

Of course, if money is no object, then certainly go for it.

Maximizing An 80 Watt Panel?

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