Solar Power

Summary

Since 2003 the bivy site at the stone bridge has had a number of solar panels and a car battery, which are mainly used for charging homemade battery packs, drill and AA/AAA batteries. This document is unfortunately written from memory, so someone with some electronics knowledge and a multimeter should set things up, so they can spot the errors and omissions in this document.

Setup of solar panels

Four 12V solar panels are mounted on an aluminium frame, which has been put on some flat limestone, slightly downhill and to the right from the stone bridge. The solar panels are waterproof, but are liable to be being blown over and damaged, hence large rocks must be used to keep it in place. The panels should be orientated pointing into the sun, without any shadows on them. Looking at the panels you can see the individual ~0.6V photo-arrays, each one not getting sunlight reduces the voltage output of the panel.

Setup of charge-discharge circuit

The next part is to connect the lead-acid charge-discharge circuit, which is found mounted in a Tupperware box with wires coming out. The solar panels are then connected to the circuit to it in parallel to give ~12V input (i.e. connect all the red and all the black solar panel banana plugs together, to make a long red stick and a separate long black stick). The car battery should also be connected to the circuit, and so should the power distribution box (The one that looks like it has been properly made and designed). The charge discharge circuit contains a fuse some LEDs and a toggle switch. It has three modes:
  • Battery charged: The battery no longer receives current from the solar panels
  • Battery partial charged: The battery will receive and supply current
  • Battery discharged: The battery no longer supplies current
    • It is left to the user to work out the interface, to work out the mode from the LEDs etc. The circuit will automatically enter the charged and discharged state at set voltages, which are adjustable by two potentiometers. Do not adjust these unless you know what you are doing, they should remain at sensible values. To get back into the partially charged state from the discharged, it is necessary to push the toggle switch.

    Setup of the power distribution circuit

    The input power from the charge-discharge circuit, goes into the connectors marked solar panels, the battery connectors are now redundant. This box is also fused, and has a number of cigarette socket outputs, a four way cigarette socket adaptor, will increase this number. Note that battery power is not unlimited, so any chargers at the stone bridge do not mean that you should not carry your batteries down the hill to be charged when you are able.

    Waterproofing

    All the circuits should be covered with plastic sheeting (There should be a cut open inglesport bag for that purpose). The sheeting is held down by medium sized rocks all around its perimeter.

    24V drill battery charging

    To charge 24V drill batteries, the four solar panels should be connected together with two pairs of serially connected solar panels connected together in parallel. Crocodile clips can then be used to connect to the battery terminals. Note that the battery will not stop charging, and may damage the battery if left to over charge.

    Putting the battery away

    Store the battery full, this means that you should stop discharging the battery a few days before it is to be put away to allow it to charge. Grease the battery terminals, and place the battery where it will stay dry, do not cover with anything that may get soggy and short the battery (e.g. cardboard box).

    Thanks

    On behalf on anyone using the system, thanks go to Earl Merson who provided most of the equipment, and more importantly carried a car battery up the hill. More thanks go to whoever carries it down again should it ever become knackered.