Solar Powered RF Network

We built a large RF network for a local nursery in Massachusetts that covered both indoor greenhouses and 250 acres outdoors. Many of the outdoor access points didn't have AC power available, so we powered them with solar panels.

How it works

The 120 Watt solar panels are wired to a charge controller, which charges a 12 volt, 100 amp hour marine battery. A power converter steps the power up to 48 volts, which is then connected to the access point. The access point supports Power Over Ethernet (POE), and we supply DC power over the same pins a POE adapter would.

The system also uses a timer to shut the system off at night. This is done to preserve battery life, and as additional security. All of the components are protected by lightning protectors, and we installed lightning rods with two large ground spikes on each pole.

Details

We switched to a Blue Sky MPPT controller because we weren't getting sufficient power from our first simple shunt controller. MPPT controllers vary the voltage output to compensate for the battery's state of charge. Keep in mind that this is installed in New England, which isn't the best part of the country for a solar application. The Blue Sky controller also had a temperature sensor, which greatly helps charging during the cold months.

The batteries are connected to the system with a molex connector, so that we can do annual maintenance on the battery by connecting it to a desulfating charger.

This system uses Intermec access points, which have dual 802.11 b/g radios installed. One radio is connected to an omnidirectional antenna, which provided the RF coverage. The second radio is connected to a parabolic antenna, which provides a wireless hop to another access point, and provides the link to the network.

This system has been operating for two years now and had proved to be very reliable. In fact, we believe that the access points that are solar powered are more reliable than those powered by AC, due to the cleaner power supplied to the unit.