adding more solar panel & battery?
That charge controller is notoriously cheap and burns up easily. If you are going add solar panels, also buy another charge controller to go with them. They can both be connected to the same battery bank. I don’t believe the kit comes with batteries, so you would buy whatever size 12V battery bank your power requirements call for.
The size of the inverter depends entirely on what you are going to power with it, not the size of the panel array. As long as you are not powering anything that is over the 300W rating, you don’t need a new one. Just be sure to check the details of the inverter, is it 300W continuous, or can it handle up to a 300W surge? Also, it’s a modified sine wave inverter instead of a pure sine wave inverter, so don’t plug any sensitive electronics into it. They may not work, or you may get a buzz or hum from it.
what type of solar panel should i use?
You can build an efficient solar panel on your own for less than $200. You could be saving up to $800.
So why not make your own? It’s not as hard as it may look.
How do I find the maximum wattage for a solar panel?
Best way is to read the specs.
Are you measuring the amperage across the resistor? That’s why you’re getting zero. You need to hook the meter in series with the resistor. (Panel to meter, meter to resistor, resistor to panel.)
Keep reducing the resistance until the voltage drops below about 5 volts. That’s when you’re trying to draw more than the maximum amps.
Be careful. Unless this is a tiny panel, you’re going to be creating an extreme amount of heat in that resistor. Your resistor probably won’t be able to handle it, and you’ll have a scalding hot component even if it can.
1 ohm at 7 volts is 7 amps. (V=IR)
7 amps at 7 volts is 49 watts. (P=IV).
You can start putting 1 ohm resistors in parallel, effectively lowering the resistance of the load until the voltage drops, but don’t be surprised if one of them fractures from the heat.