Now that you have all the equipment (Lesson 2), it’s time to build the system. If you have no or little experience with electric circuits, you should learn about safety first. Especially if you’re using this guide to set up an educational solar system, make sure your students take safety concerns seriously and never let them handle batteries/solar panels by themselves before they have enough experience. In the following, we go over some safety considerations and then we outline the steps we took for setting up the array.
Garrett working on a 135 W solar battery charger. Follow these instructions and build one yourself!
The beauty of solar panels and batteries is that there are no moving parts and that it is completely silent. So there is no noticeable difference between On and Off unless you have a little light bulb or an amp-meter installed. At the same time, this makes the whole system a silent hazard and you should therefore be very careful at any point in time.
Don’t be fooled by low voltages. 12 V is as dangerous as 10,000 V: it is the current that affects how hazardous a shock is. Shocks of above 0.1 Amps can be lethal already (note, the panels that we use in our system each produce ~1.5 Amps at full output). Electric shocks can also cause burns and muscle contractions that can lead to a fall. You can imagine that Installing solar panels on roofs is therefore extra dangerous.
If you're interested in seeing what electric burns look like, please Google them. I didn't want to put any of those graphic pictures on our website because this is an instruction guide and not a horror webpage.
Also the battery is something to be very careful with. A battery like ours holds almost half a kWh of energy, which is enough to let your tumble dryer run for an hour or so. Now imagine what that battery is capable of destroying when that energy is released in a couple seconds… For example, this kid who’s building his own electric motorcycle had an accident: his wrench fell on his charged battery pack and brought the positive pole in contact with his grounded EV frame. The metal started glowing red-hot and then a flash appeared that blinded him for a while. To the right is a picture of what was leftover of his wrench.
What happens to a wrench when it short-circuits a battery... From: Experimental EV
'Hot' wires and grounding
‘Hot’ wires are wires that connect the positive pole of the battery or panel with the load. They are sometimes referred to as ‘active’ or ‘live’ and present serious shock hazards. The neutral wire completes the circuit as it is attached to the other terminal of the load and the negative pole of the battery. The neutral wire is usually grounded; this side of the circuit will then present no shock hazard. For this reason it is important to know what wires are hot and neutral and we would therefore suggest to label them properly.
To ground an object, you can connect it to a large conducting frame (this is what is done in cars) with a conducting wire or simply stick the other end of the wire into the ground.
The right tools and equipment: use insulated tools, wear protective gloves, shoes with rubber soles and safety glasses;
Do not attach current generating components (battery/PV panels) until you have completely built the rest of the circuitry;
Double-check all your cables and connections for damage before you connect the panels and batteries;
Label ‘hot’ and ‘neutral’ wires;
Follow installation guides that come with your charge controller and panels;
Use correct size fuses;
Ground your batteries and panels;
Avoid touching both hot and neutral connections and exposed wires at all times.
Find a board you can use to mount your components onto;
Determine layout and draw it on the board. Try to keep the wiring distance to a minimum but don’t strain the wires.
Mount the components but do not yet connect them;
Consult the charge controller’s guide on the order of connecting components and where to install fuses, grounding connections, etc.
Some MPPTs have special settings optimized for certain battery types. Make sure to read about this in the manual. Our charge controller (Morningstar Sunsaver MPPT) presents this order:
Load wiring (with a fusebox on the positive load terminal, DO NOT INSERT A FUSE AT THIS TIME);
Battery wiring (ground the negative terminal and connect a fusebox to the positive battery terminal. Again, DO NOT INSERT A FUSE AT THIS TIME);
Solar wiring: cover up the panels with a dark blanket, especially if you’re working outside. This will reduce the chance of shocks and injuries.
Double check the wiring and confirm correct polarity at each connection. Make sure all screws of the charge controller terminals are tightened.
Now, install fuses (20 Amps in our case), first insert the load fuse, then the battery fuse.
Confirm Power-up: a power-up light sequence of the LEDs on the MPPT should begin.
All done! Remember that other people might not be aware of the shock hazards from touching connections: so either cover hot wires and connections up with some insulating material or make a nice transparent plastic cover so that people can see, but not touch!
I hope you liked this installation guide and that it helped you make the right decisions on your array. Please let us know what you think can be elaborated some more and post any questions you have in the Facebook Plug-in below.