Electrical power is a very useful addition to a treehouse and will be almost essential if it is to be used as a place of work. The main advantage of a permanently installed circuit will be lighting, allowing the treehouse to be used during dark evenings and overnight. Please note that this article assumes a basic understanding of electrical principles and circuit design.
Sources of electricity
There are two sorts of electricity supply that can be used in a treehouse - low voltage DC (12/24V) and mains equivalent AC (110/240V). Low voltage is much safer than mains voltage. Both have dangers which should be understood completely before proceeding. It is certainly possible to build a treehouse with a safe mains electrical supply, just like a normal house, complete with safety devices that can detect unforeseen faults or damage in the circuitry.
Low voltage circuits
A normal battery operated torch/flashlight is a self-contained lighting circuit. It consists of a battery, wiring, a switch and a bulb. Scaling this up to illuminate a whole treehouse is quite straightforward. The battery can be something small, like a pack of AA batteries, up to car battery size. The cable size is determined by the expected current in the circuit under maximum load. Each lighting circuit will have a number of bulbs connected together in parallel and controlled by a switch. It is possible, though more expensive, to use mains style cables and switches for low voltage lighting. You can work out how long a battery will last by dividing its capacity in amp hours (Ah) by the current of your circuit in amps (A).
Whatever size of battery you use, it should be rechargeable. This will quickly save you money over normal batteries and allows you to use solar or wind power to keep the batteries full. It is useful to keep a backup for the main battery in case power fails unexpectedly.
Solar panels for car or caravan batteries are an economical way to keep your battery topped up by slowly trickle charging the battery during the day. They can be mounted on the roof of the treehouse, or on a pole which reaches into a sunnier spot above or near the tree and are almost maintenance free once fitted. Solar panels will keep working on cloudy days but will generate less power. The main disadvantage of solar charging is that most electricity demand (for lighting at least) will be during the darker months of the year, so the solar panel may not be able to keep up with the demand. A solution to this is to use a small wind generator. Depending on your location, this may be a good alternative, or addition, to solar power because wind usually increases at the same time as electrical demand. Wind generators can produce higher charging currents than solar panels for the same price, but even the smallest generators are more expensive than a good set of solar panels.
In addition to a solar panel or wind generator, you will need a regulating circuit between the power source and the battery. This maintains a constant charging voltage until the battery is full and then stops charging automatically. As the battery is used its voltage will gradually drop. The regulator detects this and restarts the charge process.
Solar systems are covered in more detail here.
Mains equivalent circuits
Mains voltages carry a risk of electrical shock, which can kill instantly. You should have mains voltage circuits installed and tested by a professional. Mains equivalent circuits can be supplied in a number of ways; as an extension from a normal house circuit, from a portable petrol generator or from a low voltage circuit via an inverter. The significant difference between a normal house circuit and a treehouse circuit is the risk of damage to the circuit by physical means or poor waterproofing. A residual current device (or ground fault interrupter) is essential for mains equivalent circuits used in a treehouse. This device is very sensitive to changes in the circuit and is designed to disconnect the power very quickly if a fault is detected. This could be as a result of a broken cable or a person touching a live part of the circuit. The speed of the device can help prevent a dangerous electrical shock.
Due to the numerous safety considerations with mains electricity, this article does not go into the detail of how to set up your own circuit. This job should be carried out by a qualified electrician.
Another consideration is that the installation of mains electricity can require a permit in some cases. This is partially for safety reasons and partially because the treehouse becomes closer to a habitable space, which means it needs to adhere to more strict building regulations. This technicality alone can make a low voltage system preferable.