SolarCharge Controller

Solar charge controller

The most basic solar charge controller simply:• Monitors the battery voltage • Opens the circuit• Stopping the charging, when the battery voltage rises to a

certain level. • Prevent the DC electricity flows back to solar panel at

night, when solar panels are not generating electricity, electricity can actually flow backwards from the batteries through the solar panels, draining the batteries

Older solar charge controllers used a mechanical relay to open or close the circuit, stopping or starting power going to the batteries.

Solar charge controller

There are 2 types of solar charge controller:• PWM solar charge controller• MPPT solar charge controller

PWM charge controllerSome modern solar charge controllers use Pulse Width Modulation (PWM) to slowly lower the amount of power applied to the batteries as the batteries get closer and closer to fully charged. This type of controller allows the batteries to be more fully charged with less stress on the battery, extending battery life. It can also keep batteries in a fully charged state (called “float”) indefinitely. PWM is more complex, but does not have any mechanical connections to break.

Problem on solar panel & batteryFor example:We have Kyocera KC130M solar panelBased on STD condition of sun intensity at 1,000 W/m2• Vmp = 17.6 V• Imp = 7.39 A• P max = 17.6 x 7.39 = 130 W

UNFORTUNATELY, what happens is not 130 W !For example the system is set 12 VAt a very bright afternoon (sun intensity = 1000 W/m2) the power arranged by a PWM solar charge controller = 12 V x 7.39 A = 88.8 WSo we lost over 41.2 W but we pay for 130W power

What happen if the battery is weak & it can produce 10.5 W only ?The power arranged by a PWM solar charge controller = 10.5 V x 7.39 A = 77.6 W So we lost over 52.4 W but we pay for 130W power

Problem on solar panel & battery

Also we cannot get a bright sunlight the whole day !• The sun intensity is always changing at all time in a day time• Not yet the peak sun hours (PSH) are different in different location• Since the sun is moving in a certain direction at a certain place

could be the solar panel is over shadowed by the shadow of the trees or a building it means the light intensity coming into the solar panel will be decreased too

The solar panel is testing at the STC condition to have Vmp = 17.6 V• But when the sun intensity is low (cloudy or raining) the solar

panel will produce lower volts than the Vmp stated at the STC condition At 800 W/m2 the Vmp become only 15.5 V

• Not yet if the temperature of the environment around the solar panel increases to for example 30°C The Vmp will drop too !

The usable voltage from solar cells depends on the semiconductor material. In silicon it amounts to approximately 0.5 V. Terminal voltage is only weakly dependent on light radiation, while the current intensity increases with higher luminosity. A 100 cm² silicon cell, for example, reaches a maximum current intensity of approximately 2 A when radiated by 1000 W/m². The output (product of electricity and voltage) of a solar cell is temperature dependent. Higher cell temperatures lead to lower output, and hence to lower efficiency. The level of efficiency indicates how much of the radiated quantity of light is converted into useable electrical energy

Solar cell voltage

Solar (sun) intensity

Sun intensity in different places will be different !

MPPT charge controllerThe most recent and best type of solar charge controller is called Maximum Power Point Tracking or MPPT. MPPT controllers are basically able to convert excess voltage into amperage. This has advantages in a couple of different areas.• Most solar power systems use 12 volt batteries (Some use other voltages and the

same advantages apply to these systems as well.) • Solar panels can deliver far more voltage than is required to charge the batteries.

In essence, converting the excess voltage into amps, the charge voltage can be kept at an optimal level while the time required to fully charge the batteries is reduced. This allows the solar power system to operate optimally at all times.

MPPT charge controller• Another area that is enhanced by an MPPT charge

controller is power loss. Lower voltage in the wires running from the solar panels to the charge controller results in higher energy loss in the wires than higher voltage.

• With a PWM charge controller used with 12v batteries, the voltage from the solar panel to the charge controller typically has to be 18v.

• Using an MPPT controller allows much higher voltages in the cables from the panels to the solar charge controller. The MPPT controller then converts the excess voltage into additional amps.

• By running higher voltage in the cables from the solar panels to the charge controller, power loss in the cable is reduced significantly.

To extract the maximum power out of the PV panels, the MPPT charge controller have to operate near peak power point of their volt-amp curve. This requires variable loading depending on the sun illumination and ambient temperature. MPPT charge controller for solar applications use maximum power point tracking algorithm that helps to extract maximum power from the panels (see: I-V characteristics of solar panels). Since sunlight intensity varies during the day, it may not be simple to size your system and find the required amount of the panels.

MPPT charge controller

MPPT stands for Maximum Power Point Tracking and it relates to the solar cell itself. Each solar cell has a point at which the current (I) and voltage (V) output from the cell result in the maximum power output of the cell. In the diagram below the curve is an example of the standard output expected from a solar cell, the Maximum Power Point is at the position marked on the diagram.The principle is that if the output from the cell can be regulated to the voltage and current levels needed to achieve a power output at this point, then the power generated by the solar cell will be used most efficiently.

As the cell temperature increases Voltage decreases. As the cell temperature increases Current increases.Since sunlight intensity & cell temperature are varied everyday Solar panel voltage & current will vary substantially it will greatly affected the system.

MPPT charge controller

I-V characteristic of solar panel

MPPT vs. PWM Charge Controllers –What’s the Difference?

Before solar panels became interesting for people that are on the grid, there were only 36-cell ones for charging 12 Volt batteries (and if you had a 24V battery you’d need two panels in series, to make 72 cells). With 36 cells the panel runs at about 18 Volt, and when it gets warm in summer, the Voltage will drop but still be enough to charge a 12 Volt battery (which really takes about 15 Volt).Charge controllers were developed for these 36-cell panels, to prevent overcharging and damage to the battery. These charge controller are essentially just switches that rapidly (many times per second) connect the panels to the batteries, and then disconnect them. By changing how long the panels are connected vs. disconnected the effective charge current changes, and that’s how the controller keeps the battery Voltage in check. These controllers are called Pulse Width Modulation controllers, or PWM controllers for short, because that’s how they do the charging.

MPPT vs. PWM Charge Controllers –What’s the Difference?

Then solar became interesting for people that are on the grid, and the standard there is for 60-cell panels. Almost all the panels you see on rooftops are 60-cell.

NOTE:BIPV = Building Integrated photovoltaic is solar panel for building purposes

These panels have an open Voltage of about 38 Volt, and run at about 30 Volt (though on a hot day in the sun they’ll run as low as 24 Volt). You can hook them up to a 12 Volt battery with a PWM controller, but since those controllers directly connect the panel to the battery (they’re just a switch) it forces the panel to run at 14 or 15 Volt, half of what it can do, and power output will be half as well. So by using a PWM controller with a 60-cell panel you will get about 100 –130 Watt out of a 260 Watt panel.

MPPT vs. PWM Charge Controllers –What’s the Difference?

To make 60-cell panels work with batteries a different type of charge controller was developed, called Maximum Power Point Tracking or MPPT charge controllers. Those run the panel at whatever Voltage it takes to make the most power and then convert that Voltage down to the battery Voltage.

So, with a 60-cell 260 Watt panel and an MPPT controller the panel could be running at 30 Volt – 8 Amp, while charging the battery at 14 Volt and 17 Amp.

To charge a 24 Volt battery takes at least 2 x 36 = 72 solar cells. That means you need two of the 60-cell panels in series (120 cells), and an MPPT charge controller.

Likewise, a 48 Volt battery bank needs 3 of the 60-cell panels in series to reach a Voltage that’s high enough to consistently charge the batteries.

MPPT vs. PWM Charge Controllers –What’s the Difference?

Now, MPPT type charge controllers have much more electronics inside and are much more complex than PWM type charge controllers. That means a 40 Amp MPPT controller is quite a bit more expensive than a 40 Amp PWM controller. But 60-cell panels are MUCH cheaper per Watt vs. 36-cell panels, and that more than makes up for the price difference in charge controllers

Sizing charge controller

Sizing MPPT charge controller