If you want to take advantage of the sun's abundant energy to power an outdoor light, you have at least two options. You can hook the light up to a solar-powered battery system, or you can remove the light altogether and replace it with a stand-alone solar fixture. The first option costs more, but it's the way to go if you like your present fixture or want to convert an array of lights.
The Stand-Alone Option
Although it isn't really a conversion, replacing your electric light with a stand-alone solar light deserves some consideration. Solar light fixtures are inexpensive and easy to install. They draw energy from a photovoltaic panel, and although this is usually attached to the fixture, you can buy kits that include fixtures, panels and wire to connect them. These kits allow you to place the panel in a sunny location while keeping the fixture in a shady spot near the house or in the garden.
The main problems with standalone fixtures are that they aren't as bright as electric lights and that they gradually grow dimmer during the night as the charge on their batteries dies. However, during the early part of the night, when outdoor activity peaks, they provide enough light to illuminate a walkway or garden, and they do it for an affordable price that fits most budgets.
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Converting Your 120-Volt Fixture to Solar
If you like your outdoor light fixture, but you don't like paying for electricity, it's possible to convert it to solar without replacing it. To do this, you'll need a few system components besides the solar panels that will ultimately provide the power. It's also a good idea to replace the incandescent bulb in your fixture with an LED bulb. LEDs can produce the same amount of illumination as incandescents and use a fraction of the electricity.
When setting up the system, the best place to start is at the battery bank. After you size the battery, you'll know how much output you need from the solar panels.
- Battery Bank – You need at least one deep cell battery to power your lights, and it should be rated for at least 150 amp hours to allow the system to compensate for cloudy days and to power the inverter. The more charge the battery can hold, the longer it will power your lights, but keep in mind that a bigger battery needs a bigger solar array to keep it charged.
- Solar Panels – Virtually any solar panel with an output of 5 watts or more will charge the battery, but larger panels charge the battery more quickly, and that's important. If you have a 150 Ah battery and get about eight hours of sunlight a day, the panel output should be at least 120 watts to ensure the battery charges fully during the day. You can use a single 120-watt panel or any combination of identical smaller panels wired in series. For example, you can use two 60-watt panels or four 30-watt ones.
- Charge Controller – A charge controller isn't a requirement, but it's strongly recommended. When you connect it between the panels and the battery, it prevents the battery from overcharging.
- Inverter – The purpose of the inverter is to convert 12-volt DC power to 120-volt AC. You can wire your existing light directly to the inverter. A 600-watt inverter should provide more than enough power for your light without quickly draining the battery.
Setting Up the System
The battery needs to be protected from the elements, so it should be in an enclosure, such as a shed. The panels, on the other hand, should be located in a place that maximizes the amount of sun they receive.
After you install the panels, connect them to the charge controller, which should be close to the battery, using low-voltage wire. Next, connect the charge controller to the battery using battery cables. Finally, connect the inverter – which should also be located close to the battery – with battery cables.
When these components are placed and connected, you have power, and all that's left to do is to connect the light to the inverter. Since most inverters have receptacles, the easiest way to do this is to disconnect the light fixture from the electric panel, run a length of 12- or 14-gauge outdoor cable from the light to the inverter, connect one end to the light, install a plug on the on the other end and plug it into the inverter. After a full day of sunshine, your light should continue to shine brightly at night.
Don't Forget the Switch
You probably don't want the light to come on during the day, so you need a switch. If you want to be able to operate the light manually, install a conventional wall switch in a convenient location. Run 12- or 14-gauge outdoor cable from the light to the switch and run a second length of outdoor cable from the switch to the inverter. Don't forget to install a plug on the wire that runs between the switch and the inverter.
If you want the lights to come on automatically, plug a timer or light sensor into the inverter and plug the lights into that. If you opt for a light sensor and you can't locate the inverter in a place where there is light during the day, you can run a length of outdoor cable from the inverter to a safe outdoor location. Install a female receptacle on one end of the cable and a male plug on the other end. Plug the cable into the inverter and plug the sensor into the female end of the cable.