Since 2003 the bivy site at Steinbrückenhöhle (the stone bridge) has had a number of solar panels and a car battery, which are mainly used for charging lamps and drill battery packs, but also AA/AAA batteries and phones. Much bigger flexi solar panels arrived in 2007 and a second, larger, battery around the same time.
In 2018 two new PV panels were bought. These Jinko JKM270PP-60 (original site) beasts are 255W (peak), ~16% efficient and weigh 19kg each. They are glass-fronted, aluminium-framed, and measure 1650 x 992 x 40mm. These were installed at Steinbrückenhöhle top camp and the light-weight panels already there can be used at another camp. The rest of this text describes the situation in 2017 before these Jinkos were bought. Also new in 2018 is a new set of 12V sockets (car type). This page will be updated when they have been installed.
An MPPT controller charges the battery from the panels. It's a MakeSkyBlue S3 series. You can program the hours of operation (24hr), max charge voltage (14.2), float charge voltage (13.2), and battery load cutoff voltage (11.9V)
The system (in 2017) was two independent systems running in parallel.
The system can be made moderately weather proof, but in very windy or wet weather, it should be bought into the relative safety of the stone bridge.
The three big solar panels are bolted to the big wooden frame using spare non structural bolts on the frame (ie not on a joint). The panels have to be overlaped to fit. This whole frame is then lashed to the stone bridge using the 4 spits just above the animal hole. The cable with the connectors that fit these panels is then run through the small gap in the animal hole end wall and up to the back of the bivi. The solar panel cable is then connected to the solar input on the "bent plastic" charge regulator. The big battery is connected to the battery connectors of the "bent plastic" charge regulator
In 2014 the smaller panels were perched on the stone bridge above the big panels as no frame emerged from Tramgold! The solar panels are connected together 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). Then plug the two banna plugs on the end of the long cable into the end of the stick and insulate the two exposed ends of the sticks (we don't want them connecting!!). Now run the cable for this the same route as the big pannel cable. Connect the far end of this cable to the solar input on the project box charger and connect the small battery to the battery terminals of this box
Store the batteries full, this means that you should stop discharging the batteries a few days before they are to be put away to allow them to charge. Grease the battery terminals, and place the batteries where they will stay dry, do not cover with anything that may get soggy and short the battery (e.g. cardboard box).
In 2019, as we had long feared, inexperienced and under-supervised cavers in a hurry dropped a lead-acid battery several metres while putting it away. Fortunately no one was hurt. We now plan to try to run power cabling in a much longer run to the PV panels and the bivvy so that the batteries need to bemoved as little as possible.
Four 12V solar panels were 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. There is also a fifth panel that can be propped against a rock in good weather.
The charge discharge circuit contains a fuse some LEDs and a toggle switch. It has three modes:
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.