You’ll need a charge controller with all but the smallest of solar panels. A charge controller goes between the solar panels and the batteries. It’s job is to limit, or control, the power your panels put into your batteries. This keeps you from destroying expensive batteries by overcharging. There are two types charge controllers.
PWM Solar Charge Controller
Power Width Modulation (PWM) controllers are relatively inexpensive, but may not be the best choice for a Frugal Boater. They work by literally switching your panels on and off very rapidly. That works fine as long as your panel voltage is fairly close to your battery voltage. If you’re a weekend boater who just wants a small panel to keep your battery topped up while you’re away, a PWM solar charge controller might do the job. Using a PWM controller will limit the size panels you can use because they don’t have the capability to change the voltage, only turn it on and off.
MPPT Solar Charge Controller
Multi Power Point Tracking (MPPT) charge controllers are a big step up in performance and price. This one is from Midnite Solar. These controllers actually adjust voltage/current in an attempt to wring the most power out of your panels. They also have the capability to step the panel voltage down to whatever your batteries need. An MPPT controller takes the 60 volts coming in from our panels and steps it down to our battery charging voltage (around 13.5). When the voltage comes down the amps go up, so very little power is lost in the controller.
Beware of cheap “MPPT” found on Ebay and the like. Some are actually PWM controllers with “MPPT” printed on them. Since the charge controller is the heart of your system, and could prove dangerous to you and your batteries, it’s best to stick with a quality unit from a reputable manufacturer.
Optimizers
A standard system with one MPPT controller is striving to optimize all panels. That means that during partial shading some of your panels are 
running higher and some lower than optimum. None of your panels are really performing their best because the controller is working with an average. MPPT optimizers on each panel can be useful in environments like our sailboats where partial shading is unavoidable. Obviously no two systems and shade scenarios are identical, but tests with optimizers show that during partial shading power output can be increased by 15-25%. If your out of space on your sailboat these can wring a bit more solar power out of your system.
Multiple solar charge controllers
Alternatively, you could use a series of smaller, networked MPPT controllers, one for each solar panel. This example is from Victron. This does the same thing as optimizers and as prices continue to drop on these controllers it may be more cost effective. Be sure that your controllers are meant to work this way, so that they can coordinate battery charging between them.
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