How far can a solar panel be positioned from the light it powers?

August 17, 2010 7:35 PM

Can I position a solar panel a distance from the lights it powers and still have an effective power source?

I'm interested in using solar lights to illuminate the trees in my backyard. I want to position the solar panel that will power them in a sunny area of my backyard, about twenty feet from the trees. Is that possible, or do solar powered devices need to be closer to their panels?

Bonus question: If it is possible, how far can solar power be effectively conveyed? 100 feet? A thousand? A mile?

posted by arnicae to home & garden (10 answers total)

Solar power is just electricity, and it can be conveyed exactly as far, and as effectively, as any other electricity.
posted by Tomorrowful at 7:42 PM on August 17, 2010 [2 favorites]

Ah, my guess is that you'll have a simple DC (direct current) power. DC power does drop by distance, which is why we have AC (alternating current) power for our power infrastructure. High voltage direct current can go pretty far, and is replacing AC now, but a simple solar panel will probably not be generating that high of a voltage!

The DC power that you'd be making with a solar panel, probably twelve volts, not transformed in any way or run into an inverter, might make a mile or two.
posted by adipocere at 7:52 PM on August 17, 2010 [1 favorite]

Electrical power depletes over distance; this is why there are transformers to ramp up the energy over power lines.
posted by dfriedman at 7:53 PM on August 17, 2010

Given that it's lights you want to power, you'll have a battery or power supply unit along the line anyway. So I wouldn't think twenty feet would be a problem.
posted by Ahab at 8:01 PM on August 17, 2010

Electrical power depletes over distance; this is why there are transformers to ramp up the energy over power lines.

That's misleading, dfriedman. Electrical current encounters the small inherent resistance of the wire and loses some voltage. Via Ohm's Law, you can deliver the same power over the line by increasing the voltage with a corresponding drop in current. With the drop in current, you've incurred less voltage losses.

This is why, for long haul transmission of large amounts of power, the grid uses insanely high voltage (110000 Volts, 230000 Volts, etc.) and then transforms it further and further down as it gets into your town, your neighborhood, your house. It's not "boosting" or "ramping up" the voltage to compensate for the losses. It's use HV for long haul to minimize losses, then transforming it down before it gets to your house so you don't blow the sockets out of the walls.

My advice for the OP's original question would be to look for panel/light combos that produce/consume at higher voltage. Failing that, just use really fat wire, meaning 12/0 wire not lamp cord. Wire gauge solves everything :)
posted by intermod at 8:17 PM on August 17, 2010 [3 favorites]

Are you going to have a battery and a converter in your system? You need a battery to collect the electricity to use at night in the lights. You need a converter to converter solar electricity (which is DC) into use-able electricity (which is AC). Many light fixtures out there will not work with DC power, though a basic incandescent bulb will work on DC.

As to the effective distance question - The concept you are looking for is commonly called Voltage Drop, which as noted above is the loss of volts over distance.

Electricians frequently have calculate voltage drop when sizing wire for certain jobs. You can find lots of voltage drop calculators on-line if you want to play with one.
posted by Flood at 8:50 PM on August 17, 2010

According to this article from Sail Magazine, you should be okay if you're using a marine-style solar setup, as long as you use a thick enough cable.

The maximum nominal output of my panels is 4 x 85 = 340 watts, which is 14 amps at 24 volts (340/24 = 14). The cable run from my panels is approximately 30 feet. With solar-panel circuits it is important to keep voltage drop to a minimum, which requires relatively large cables—in this case at least 10 AWG.

However, you seem to be talking about a complete solar lighting system, e.g. this Smart Solar Set. That particular set has a 32 ft. cable between the panel and the lights. Most solar light sets meant for landscaping use have a at least a 15 ft. cable.
posted by ob1quixote at 9:47 PM on August 17, 2010

"How far can a solar panel be positioned from the light it powers?"
Depends on voltage and watts.

"Can I position a solar panel a distance from the lights it powers and still have an effective power source?"
Yes

"Is that possible, or do solar powered devices need to be closer to their panels?"
It is possible, it needs big enough wire and that depends on voltage and watts.

"Bonus question:If it is possible, how far can solar power be effectively conveyed? 100 feet? A thousand? A mile? "
It is possible, it needs big enough wire and that depends on voltage and watts.

1 amp at 12 volts could go 500+ feet with #6, 84 feet with #14
8 amps at 12 volts could go 16 feet with #12, 168 feet with #2

You need watts and voltage of array, distance to batteries and a photovoltaic wire loss table. Make sure you add (if not in the table) 125% for edge of sky, cold temp days (US nec).

One of my customers had a 75 watt 12v array far enough away that they started a fire in the the pine needle duff on the ground, yes from the glowing bit of wire (in the middle even). 75 watts doesn't seem like enough but it was, 3 times.

There are many details (fuses) but for some backyard lights, you will be fine.

All that said, yes get big enough wire after you do the calculation after you know array size and distance. Also IANYE.
posted by blink_left at 11:09 PM on August 17, 2010

If you are running a DC system, the thickness of the cable between the solar panels and the lights will determine how much the voltage drops (and therefore how much power gets to your lights). Generally, a thicker cable will have a smaller voltage drop.

Here is a voltage drop calculator which will help you select a cable of sufficient thickness to prevent voltage drop.
posted by girlgenius at 11:27 PM on August 17, 2010

DC power does drop by distance, which is why we have AC

If you are running a DC system, the thickness of the cable between the solar panels and the lights will determine how much the voltage drops

This is not a DC vs AC issue. Power loss [in watts] over a resistance R [your cable] is determined by the current I [which depends on the load you're powering], the relationship is I^2 * R, [i.e. if you double the current, you quadruple the power loss]. This is true of both AC & DC.

AC is used for transmission because it is simple to transform to a higher voltage [and thus lower current for the same power] and back again.

How far can a solar panel be positioned from the light it powers?

This depends entirely on the current you're drawing [determined by the wattage of your lighting], and the resistance of your wiring [less is better, i.e. thicker wires]. If your load is modest, you should be fine.
posted by HiroProtagonist at 7:35 PM on August 18, 2010