Solar panel regulator information
Solar regulators are used to control solar panel output
A typical stand-alone 12 volt solar power setup consists of 12 volt solar panels, a solar regulator and a 12 volt battery. The solar regulator is connected between the solar panel and the battery so the voltage can be regulated to prevent overcharging the battery. Repeatedly overcharging a battery will cause internal damage and shorten its life. Some of the better solar regulators can control the load to protect the battery from being run flat by the load. Compare this to a grid-tied system where the solar power is connected to the power grid through an inverter. Although the solar power from a small solar panel can be connected directly to a battery of reasonable capacity, a larger solar panel's output should be regulated to prevent overcharging the battery.
When a solar regulator is not required
A solar regulator is always required to properly recharge and maintain batteries but if you want to keep a battery topped up with a permanently attached trickle charge (float charge) then you can connect a small 12V solar panel directly to the terminals of a 12V battery. What size solar panel? A 200Ah battery can be trickle charged by a 5 watt solar panel with a charge current of about 250mA. Increase or decrease the solar power for larger or smaller batteries.
PWM solar regulators
Better designed solar regulators use PWM control to allow the current to the battery to gradually taper off as the battery nears full charge so as not to overheat and damage the cells. This also allows the battery to be more fully charged. PWM (pulse width modulation) has been a common circuit used in motor speed controllers and is now used in solar controllers and battery chargers. Instead of just switching the current flow to the battery as it nears full charge, the PWM controller begins to rapidly switch the electrical current on and off, creating pulses of current flow that decrease the average current. As the battery nears its fully charged state the 'on' periods become shorter and the 'off' periods longer until the battery is fully charged and the current is stopped completely.
MPPT solar controllers
Now we are talking about solar controllers and not solar regulators. MPPT (maximum power point tracking) is electronics designed get the maximum power out of the solar panels. It is a real cost saver for larger solar installations because it will deliver more power to the storage battery than a standard solar regulator. A normal solar regulator reduces the solar panels voltage from the nominal 18 volts to approximately 14.5V to conform to normal battery charging specifications, but when this done the unused power is wasted. What the MPPT controller does is track the maximum power point of the solar array and then use a DC/DC voltage converter that keeps the solar panel volts at the maximum power point while charging the battery at a lower voltage. This increases the current flow to the battery.
Solar regulator user notes
When should a solar regulator be used? There is no hard and fast rule, It depends on a few factors
The size of solar panel
Solar panels are essentially current generators, a large solar panel generates more amps than a small solar panel. A 100 watt solar panel and a 10 watt solar panel will both output the same voltage if they have the same number of solar cells making up the solar module but the 100 watt solar panel will deliver a current of about 5 amps while the 10 watt solar panel will deliver about half an amp.
The amp hour capacity of the battery being charged
The maximum charging current (amps) is often specified by battery manufacturers as C/5 where C refers to the Amp hour (Ah) capacity of the battery, so a 100Ah battery being charged at a C/5 rate corresponds to a 20A charging current. This is bulk charging current and must not be confused with continuous charging current of 5%Ah capacity mentioned before. This is the maximum charging current that can be applied if the charging source is to be disconnected once the battery is fully charged.
The type of battery
Ask your battery supplier about the recommended charging regime. Although most Lead acid batteries are fairly robust, some batteries using different compounds and chemicals need very specific charging sequences.