Solar Charge Controllers

Solar charge controllers (regulators) control how electricity produced by the solar panel(s) is used to charge the battery(ies). As with all things, there is a wide selection of the market which can be difficult to choose from. In some cases, however, it is possible to use a small solar panel without a charge controller to constantly top-up ('trickle' charge) a large capacity battery. If you wish to do this, please ensure that the short circuit current output of the panel (in Amps) is 2% or less of the capacity of the battery (in Ah).

Basic Pulse Width Modulation (PWM) Charge Controllers
Ten years ago, PWM solar chargers were cutting edge, whereas now this is the basic technology of choice. PWM works by slowly reducing the charge current to ensure that batteries don't detrimentally overheat or out-gas, resulting in a system that maximises the amount of solar energy available, improves battery life and maximises capacity.

Maximum Power Point Tracking (MPPT) Charge Controllers
MPPT is the latest development in the world of solar charge controllers. In short, they work by using advanced algorithms which constantly monitoring the point at which the solar panels will produce the maximum voltage and adjusting the charge current and voltage to maximise energy usage. Typical solar panels work at 15-17V, whereas typcial charging voltages for a 12V system may be 10-15V. This surplus energy is effectively wasted as PWM controllers cannot boost voltage to maintain charge current. MPPT controllers, however, use this surplus to create a 'voltage boost' when the solar panel output falls below the battery charge demand, resulting in a 10-15% greater use of available energy. This also allows us to use solar panels or arrays that have a significantly higher voltage rating (such as panels connected in series or high voltage 'grid tie' panels. MPPT controllers are, however, a lot more expensive.

Example of a MPPT charge controller: Victron Blue Solar MPPT 100/30 Controller.

Charge Controller Display Options

Solar charge controllers can be fitted with a number of different display options. As you would expect, the greater the amount of information that a charge controller displays, the higher the cost:

  • Standard LED Indicators
    All controllers, from the cheapest upwards, have a simple LED based status indicator, although more expensive models are fitted with multi-stage or mult-coloured LED's to show battery charge status as well as just an 'on/off' indication.

  • LCD System Information
    More advanced charge controllers have an LCD display fitted to them which can show a plethora of information about the status of a solar system. Nowadays, most LCD units display the amount of energy coming from the solar array, how this is being used to charge the battery(ies) as well as a fully diagnostic set of error messages. In some instances, it is also possible to fit a remote LCD display with your charge controller, sometimes allowing you to control the solar system through the remote display panel.

Dual Battery System Controllers
One of the latest product developments has been the ability to charge more than one battery system from a single charge controller. This has proven particularly useful on boats and motorhomes where there is both an engine starter battery plus an electricity storage battery bank. Typically, dual battery systems are set so that 10% of the charge is directed into the starter motor to maintain its health and efficiency, with the remaining 90% being sent to the main storage bank.

Controllers with Load Output Controls
All charge controllers have two basic connections: 1) solar panel(s) in, and 2) battery charge out. Some, however, have an additional output (often marked 'load') to which electrical devices can be fitted. The current of this load output is limited to the current rating of the controller, so inverters should still be connected directly to the battery, but using this load output offers added electronic protection of the system as well as the ability to monitor energy consumption through the LCD display and a single on/off switch.

Why does my solar charge controller show a low battery charge level, even though I'm sure that the batteries are charged?
Don't panic! This is a common issue and normally happens after the system has been disconnected and reconnected in the wrong order. Surprisingly, it is essential that the component parts of a solar system are connected in the exact order from the instruction manual.

Basically, many solar charge controllers use the battery voltage as their initial reference point. If connected in the wrong order, or at any point left with only the panel connected, they can pick up the panel voltage as the reference (typically 17V) and will show a low battery charge level.

To rectify the problem:

Disconnect everything in the following order:
1. detach the load
2. detach the panel
3. detach the batteries

Leave everything for a good 15-mins to reset.

If possible, ensure that the batteries are fully charged.

Reconnect the system in the following order:
1. cover the solar panel with an opaque cloth or turn it glass down, so that it cannot see any sunlight
2. attach the batteries
3. attach the panel
4. attach the load
5. uncover the solar panel so that it sees sunlight

If the above doesn't resolve the problem immediately, disconnect the system and then reconnect everything but the load. Leave for at least 24-hours (with the solar panel exposed to sunlight) then reconnect the load.

If you are still experiencing problems, please contact us directly: [email protected].

What is a blocking diode and do I need one?

Blocking diodes are typically placed between the battery and the solar panel output to prevent battery discharge at night. Where needed, solar panels are generally factory-fitted with a diode inside the junction box, although some, such as the Solara semi-flexible marine solar panels, are supplied with an external diode box.

The main exception to this is the DC-Solar range of solar panels. These PV modules are made of the highest quality monocrystalline cells which have a high electrical "back flow" resistance to night-time battery discharging. As a result, these solar panels do not contain a blocking diode. Most PV charge regulators do have night-time disconnect feature, however, and you may also fit an external diode onto the +ve terminal if you feel you would like to.