Outdoor Lantern Solar Solution needed

BillG · 02-15-19, 11:04 PM

Pool Man, there are a couple of things to consider regarding sizing of the battery and the panel.

1) How many days do you want the light to operate in the absence of sunlight?
2) How fast do you want the battery to recharge to full capacity?

I think that the first one is the most important, and that determines the battery size. Lets say that you want to turn on the lights at sunset, and leave them on for 12 hours. And you want them to be able to run for 10 days with no good sunlight.

7watts x 12 hours/day x 10 days = 840 Watt hours. Because you don't want to ruin your battery, size it for double that, and don't let it discharge below 50% capacity. So for this example, you might want two 24 series deep cycle batteries, which have about 1000 Watt hours of capacity each.

You will want a charge controller that prevents overcharging and over discharging, the two enemies that destroy batteries. The charge controllers that give the best utilization of your solar panel are called MPPT, or "Maximum Power Point Tracking."

In some cases, you can find a charge controller which also controls the lights. Morningstar makes one, although I don't think it uses MPPT for charge control, rather, the less efficient PWM.

The size of the panel depends on how fast you want to fully charge the battery after being fully discharged. Some also depends on how efficiently the charge controller uses the panel capacity to deliver the charge to the battery.

Figure that the panel can only deliver its full output for 2-3 hours per day on a good day - when the sun is shining directly at it. Before and after that, it is shining at an angle and the capacity is reduced. You will probably want it to deliver in a day, about double what the light bulb draws (84 watts hours in the above example.) If you had an efficient MPPT charge controller, you might want at least 100 Watts of panel. With a less efficient charge controller, you will need a bigger panel, maybe double that.

For what it is worth...

02-15-19, 11:04 PM	#17
BillG Lurking Renovator Join Date: Jul 2016 Location: Minneapolis Posts: 16 Thanks: 2 Thanked 3 Times in 2 Posts	Pool Man, there are a couple of things to consider regarding sizing of the battery and the panel. 1) How many days do you want the light to operate in the absence of sunlight? 2) How fast do you want the battery to recharge to full capacity? I think that the first one is the most important, and that determines the battery size. Lets say that you want to turn on the lights at sunset, and leave them on for 12 hours. And you want them to be able to run for 10 days with no good sunlight. 7watts x 12 hours/day x 10 days = 840 Watt hours. Because you don't want to ruin your battery, size it for double that, and don't let it discharge below 50% capacity. So for this example, you might want two 24 series deep cycle batteries, which have about 1000 Watt hours of capacity each. You will want a charge controller that prevents overcharging and over discharging, the two enemies that destroy batteries. The charge controllers that give the best utilization of your solar panel are called MPPT, or "Maximum Power Point Tracking." In some cases, you can find a charge controller which also controls the lights. Morningstar makes one, although I don't think it uses MPPT for charge control, rather, the less efficient PWM. The size of the panel depends on how fast you want to fully charge the battery after being fully discharged. Some also depends on how efficiently the charge controller uses the panel capacity to deliver the charge to the battery. Figure that the panel can only deliver its full output for 2-3 hours per day on a good day - when the sun is shining directly at it. Before and after that, it is shining at an angle and the capacity is reduced. You will probably want it to deliver in a day, about double what the light bulb draws (84 watts hours in the above example.) If you had an efficient MPPT charge controller, you might want at least 100 Watts of panel. With a less efficient charge controller, you will need a bigger panel, maybe double that. For what it is worth...