So this is the minimalist system for photovoltaic for a solar cell system. It will have no solar panel with older solar cells. These are silicon solar cells, they are about 25-30 watts maximum power that it can produce in full radiation from the sun. There is our charge controller that controls how much charge the battery should receive in order not to overcharge or undercharge, and of course, the lead acid battery that we use for the storage of all the energy. Of course, remember, this is a 12-volt battery, this is let say a 50 watts solar cell module, so we are going to produce substantial amount of current. The battery itself, the amount of current that it will deliver will be related to the resistance of the load. What do you put in there the DC load that you are putting? What is the DC equipment, like a DC motor? It can deliver very large amount of current. Remember, what produces heat is the current going through a resistor, and it's going to be proportional to the square of the current. So we have to be very careful with the amount of current that we allow. So when you have specified the charge controller, the charge controller will be specified for certain amount of current that you will not like to exceed. If you exceed that current, you are endangering the charge controller, or the battery, or wherever is around. Another thing that you have to be concerned is that the batteries, most of the inexpensive batteries, this is a completely sealed battery, but most of the batteries have outlets where you can put the electrolyte. The electrolyte usually contain either an acid or a very strong alkaline substance that can burn, so you don't want it through a splash on your hands or in something that is delegate and can be burned or can be damaged by acidity. Another thing that you have to be concerned is the voltage. Of course, this is a 12-volt battery, your skin will protect you from voltages below, let's say 50 volts, but if you exceed 50 volts, you are playing with danger. So you can put two of these batteries in series, maybe up to four of these batteries in series that will give you 48 volts, but don't exceed 50 volts please because it can be very dangerous. So right here, we have some of the other equipment. We mentioned out there the charge controller that controls how much current goes through there battery. We have here another charge controller. The charge controllers as we will discuss eventually come in three different flavors. This is the most expensive of them all, it's called an MPPT, a Maximum Power Point Tracking Charge Controller. So what this controller does is that it sends the voltage of the battery and sends the voltage produced by the solar panel. The open-circuit voltage of the solar panel is much larger than the voltage of the battery. The difference in voltage is converted into current, and that current is fed into the battery. So actually, it's far more efficient of course. As we mentioned before, you pay for what you get, and this is perhaps more expensive than the other by a factor of five. But they are different, and the charge controllers depends on the current. The larger the current, the bulkier they are and these are all to be mounted on a rag or in the wall. Of course, batteries produce DC current, direct current. Very few devices, very few of the features in your home are energized by DC current. They are all energized by AC current, the one that you obtain from the outlet, that is 110 volts, 60 hertz frequency. So in order to change the DC current from the battery into AC current, we have to use a device. This device is called an inverter, and this particular inverter, it's 1,500 Watts. Watts is the unit of power. So if it is 1,500 watts, imagine that the battery, it's 10-volts instead of 12, more or less. So if you divide 1,500 by 10, you're going to get 100. So it can handle a 150 amps. You can see. Look, can you see the size of the connections in there? All these are very massive connections that can handle the amount of current. Remember, the amount of current is the one that produces the fires if you don't handle it properly. So they are trying to make it as safe as possible by overbuilding devices like this. So this is an inverter, and these are the outlets. It's just a common outlets that you utilize. So you can actually put your refrigerator in here or your whatever is the device, your video recorder or your tv, or whatever, and then of course, there's a switch in there for turning on and off. So the solar panel that goes on the roof, and the charge controllers, and the batteries that are somewhere in your home, and the inverter that is somewhere in your home form the bulk of stand alone system.
