That's the way to go if you're using a cheaper PWM controller, you need to keep the panel voltage as close to the charging voltage as you can. An MPPT controller negates that need and lets you go with higher voltages and converts it down to the charging voltage. The MPPT will have a listing for Max PV Input which is the MAX voltage you can put into the controller before you let out the magic orange smoke. Your panels have a VoC rating on the sticker that you use to calculate it. Here's an example of how that all works:
OK, so you got yourself 4 new Generikk brand 100w solar panels. On the label it shows a VoC of 22v, a Vmp of 20v and an ISC of 5a. VoC is the maximum voltage the panel puts out at test conditions and is used to make sure you don't fry your controller. Vmp is the voltage the panels should produce in test conditions and the Isc is the maximum amps the unit can put out. Your label shows that you can draw 20v *5a for 100w of power.
When you connect panels in parallel you add the AMPS but don't change the VOLTS. In series it's the other way around so you add VOLTS but keep the same AMPS. 4 panels in parallel would be 20v @ 20a, or 400w. The same panels in series would be 80v @ 5a = 400w. Same net output, different wire sizes there.
So you take these 4 panels and you throw them all together on a PWM controller. The way a PWM controller works is by just shluffing off any extra voltage over what's needed for charging. Lets say (for napkin math ease) that your system needs 15v to charge the batteries and run the controller itself. Well, if you're feeding 20v in but it is only using 15v, then 5v is getting wasted, meaning you're only going to see 15v * 5a = 75w out of each panel at best. With inefficiencies and imperfect weather if you were using a single panel you'd only be getting 80w maybe out of it anyways so no big loss there. Because it just wastes the extra voltage if you connect them in series you'll have 80v going in (which will probably fry your controller) and still 15v coming out. PWM controllers are limited to whatever amperage the panels put out so your 5a of current is still 5a. You'll connect 4 panels and still get 75w. That sucks!!
So you spring for one of those fancy pants MPPT controllers and it lists a Max PV Input of 100v and is rated for 40a. The 40a is the maximum amperage the SCC can shove into the batteries, not the panel amperage. So now you take those 4 Generikk panels and you put them in series to get 88v on the VOC (Well within range) and 5a, which turns into the 80v (Imp number) and 5a. Since it's a single string you don't even need the fuses on there, it's just 1 set of wires. That's 400w going in. Because an MPPT controller is basically a DC-DC converter it's going to use black magic and vegetable sacrifices to convert that 80v into 15v and since Watts = Volts * Amps, 400w / 15v = 26.6a are now going into your batteries. That can take your tiny batteries from dead to full in about 4 hours. MUCH better!!
Now lets say that you bought yourself 2 more of the Generikk panels and want to add them to your system. Well, if you put 6 of them in series that would be 22v * 6 = 132v which is WAY over what your controller can handle. This is where you get into multiple strings and connect you panels up in a 3s2p configuration. 3 panels in series gets you 66v (well under the limit) and another set of 3 in series paralleled to that for 10a total current coming in. Now you're getting 600w of power.
And then the addiction really takes hold and you find yourself having thousands of posts on some internet forum and your family is planning an intervention.
Does that help make sense?
