Solar Set Up Advice

[twodzusfittings]

I have purchased a 15Volt, 7 amp solar panel with controller. I have the mounting design all thought out. No issues there. Question to the forum is : Can the solar panel through the controller to the battery be a constant when the outboard motor is running and chargeing via the alternator? Would it be advisable to have an on/off switch on the solar panel wiring after the controller and before the battery, seperating the two sources of incoming power?

 

[Stu Jackson]

Nope, not a problem. No need to shut it off.

 

[gpdno]

No that's what the controller is for, to regulate the power going from the solar cells to the battery.

 

[Bill Roosa]

As the voltage comes up due to the engine alternator being on the solar controller will think it is just a really well charged battery and turn the solar down to trickle charge.
Solar panels can operate with a dead short across the leads and with the leads open with no problem so there is nothing to concern yourself about except:
a 15 volt panel will not be producing much over 13 volts once it gets into full sun and gets hot. Most panels are 36 cell (count yours) to produce 18 volts max and 14.4 in full sun when hot.
when the day is cloudy you will be just dragging the panels along for the ride as they will not have enough voltage to do much charging.
They will certainly help keep the bats charged though but I'm thinking you will not be getting nearly as much as you think ( or the manufacturer touts)

 

[Maine Sail]

I have purchased a 15Volt, 7 amp solar panel with controller. I have the mounting design all thought out. No issues there. Question to the forum is : Can the solar panel through the controller to the battery be a constant when the outboard motor is running and chargeing via the alternator? Would it be advisable to have an on/off switch on the solar panel wiring after the controller and before the battery, seperating the two sources of incoming power?

Are you sure it is not a 7 WATT panel. A 7 AMP panel is quite large and will be in the range of 120 - 130 watts. Panels this size are usually 18+ volts. Big differnce in mounting a 7W panel vs. a 7A panel as a 7A panel woulf be roughly 55" long X 25 wide"... There is no issue running both especially when the batteries are below 80% state of charge/absorption voltage.

 

[Bill Roosa]

hey MS the panel that I built from cells had each cell outputting 8 amps and 4 watts (but only 0.5 volts) so 7 amps is pretty possible for a small wattage panel just depends on how big each cell is to get the watts at a specific voltage.

 

[twodzusfittings]

My mistake. it is a solar charging kit which provides up to 15 Watts of power with a 7 Amp solar charge controller.

 

[shanker]

That's better. I've been googling that type of cell...

Shanker,

 

[twodzusfittings]

Hooked it up yesterday. Have it located like a spoiler off the stern rail. Ran the cable through the same waterproof plug as the outboard motor. wire tied it to the rail. Currently, just to see if it will work for me, I have the cable along the port side of the interior, tucked up inside the capping above the carpet and then down to a one of the two batteries. If it works for me my aim is to bring it through under the floor boards and up through the same hole as the cables for the motor.

In less than 6 hours it brought up the levels considerably. I think this might be a winner.

I used a piece of azek board 1x12x38. I used two magma grill mounting brackets to hold the board horizontally off the stern rail, like an automobile spoiler. The solar panel is mounted to the azek board.

For those not familair with azek board, it is very light but strong plastic board, used as primarily exterior house facias etc. Cuts like wood, comes in lumber dimensions. I use it alot around the house to replace rotting areas. It comes in white, which is paintable. I will post pictures next week.

 

[Maine Sail]

In less than 6 hours it brought up the levels considerably. I think this might be a winner.

Robert,

Try not to confuse voltage rise with a capacity increase. In order to get current flowing into a battery you need to increase the voltage. A voltage increase while charging is not representative of state of charge until you can hit and hold an absorption voltage for a while. If you are at absorption voltage (roughly 14.4V) you can safely guess that you're at close to 80% state of charge or higher. This is with healty batteries. Batteries suffering from sulfation will come up to 14.4V well before they are actually at 80% SOC and this is then misleading. If you have an inexpensive shunting controller then the last 20% of charge will take a loooooong, loooong time regardless of sun.

A 15W panel will pump out about 0.9A for 3 - 4.5 hours per day, roughly. This is also with no shading. So if we figure 0.9 X 4 hours this = 3.6Ah per day of charging.

With a 100Ah battery at 50% state of charge 50 Ah's, plus about 15% charge inefficiency, would need to be replaced or 50Ah X 1.15 = 57.5Ah.

57.5Ah / 3.6Ah per day = 16 days to get a single 100Ah battery from half full to full, in perfect conditions with a 15W panel.

A 200 Ah bank would take approx 32 days to reach full, from half full...... These are averages and you may do slightly better and you very well can do considerably worse. A 15W panel is really in the "maintenance" realm of maintaining a charge not necessarily charging/replacing it quickly or in a timely fashion.

It your OB motor can get the bank back to 80% state of charge regularly then base these figures on 20% of the capacity.

A 100Ah battery at 80% SOC - 20 Ah X 1.15 = 23 Ah / 3.6 =6.4 days to go from 80% to 100% in perfect conditions.

 

[twodzusfittings]

Thanks MS. I like the calculations. So clear. Any day on the boat is a perfect condition!

 

[twodzusfittings]

Finally a picture of the set up!