As practice shows, autonomous power supply of a private house or a small industrial enterprise using mini-stations on solar panels is a profitable investment.
Owners of household solar systems pay for energy resources at “green” tariffs, but in fact they use electricity for free.
According to statistics, solar panels with a capacity of 20-30 kW pay off after 5-7 years of active operation. In order to integrate innovative eco-technologies into the current power supply scheme of a private house, in addition to the photo panels themselves, you will additionally need to purchase auxiliary equipment: storage capacities (batteries), inverters, fuses, as well as a solar battery charge controller – a voltage regulator.
What functions do regulators for solar systems perform?
The battery discharge charge controller is a compact electronic device with a built-in microprocessor, which automatically distributes the electricity received from the photocells.
The primary task of smart electronics is to maintain a stable voltage. In addition, the switching device reliably protects stationary storage batteries from overcharging and over discharging.
Other primary tasks for solar charge controllers include:
- protection of the system against overvoltage and circuit breakdown;
- selection of the optimal current value for a specific type of battery;
- battery condition monitoring (shutdown when 100% charge is reached or the set limit is exceeded).
The solar battery controller programmatically regulates the operation of the batteries connected to the system and ensures the optimal consumption of the generated electric current.
This increases the efficiency of the power plant as a whole, and also doubles the service life of the equipment and optimizes the battery charge level. Installation of an automatic regulator will save on maintenance of solar systems in the future.
How the battery charge controller works
Without an intelligent power distribution system, the generated current will flow to the battery terminals constantly, which will inevitably lead to an increase in voltage.
Each battery has its own limit values - this parameter depends on the type of battery design and the ambient temperature.
When the voltage exceeds the recommended level, an overcharge will occur, which will lead to a sharp increase in the temperature of the electrolyte.
The battery will begin to boil and vigorously throw distilled water vapors into the air. If nothing is done, then the battery life will be halved. In practice, there are cases when the accumulating tanks after a while completely dry up. To avoid this, manufacturers of modular photo panels offer two alternatives:
- measure voltage manually and independently control the process of generation and accumulation of electric current;
- install a controller for solar panels – in this case, the switching device automatically adapts the solar system to the needs of the consumer.
At night, the battery controller is in “sleep” mode. After the sun’s rays hit the photocells, the generated direct current will pass through the switching device.
When the voltage rises above 10 V, the electric current will be redirected to the Schottky diode, and then only flow into the battery.
If the voltage exceeds 14 V, the amplifier will automatically turn on, which will open the MOSFET – an insulated gate transistor. At this point, the batteries will not be charged.
After the capacitor is completely discharged, the MIS transistor will close and the battery will be automatically charged. The recharging process itself lasts until the voltage rises again to the maximum level.
What controller parameters should be taken into account
The solar panel controller can be supplied with voltage simultaneously from several solar systems, which are connected in different ways.
For the Battery Charge Controller to function properly, it is imperative to take the total input voltage and current ratings into account.
It is also desirable to provide a margin of technical characteristics at the level of 20-25%. What is it for? Firstly, manufacturers often overestimate the actual operating parameters of photovoltaic cells on solar panels. Secondly, the sun’s radiation is unstable – with abnormal activity, solar energy indicators can easily exceed the permissible design limit.
The formula for approximate calculations is 1.2P ≤ I × U, where:
- P is the total power of the photo panels;
- I is the current at the output of the switching device;
- U is the output voltage under load.
It is undesirable to use controllers for solar panels as universal power supplies – it is not recommended to connect electronic appliances to them for household use, since by default these modules are designed exclusively for “direct contact” with batteries.
Where should the regulator be installed
The device is mounted directly between the storage battery and the active solar system.
When using household appliances (washing machine, TV, etc.), it is imperative to add 1-2 inverters to the wiring diagram, which are necessary to convert direct current (12 V) into alternating current at 220V. The inverter is connected to the system immediately after the battery.
Additionally, you will need to install a fuse to reliably protect the equipment from overloads and short circuits. If several photo panels are used at once, it is recommended to mount automatic fuses between each working unit of the system, starting from the solar battery.
What are the different types of controller modules
Before choosing a charge controller, it will not be superfluous to understand the main technical characteristics of the devices.
The main difference between the popular models of solar charge regulators is the method of bypassing the limiting voltage limit. Functional characteristics are also distinguished, on which the practicality and usability of “smart” electronics directly depends. Consider the popular and demanded types of controllers for modern solar systems.
1) On / Off controllers
The most primitive and unreliable way of distributing energy resources. Its main drawback is that the storage capacity is charged up to 70–90% of the actual nominal capacity.
The primary purpose of On / Off models is to prevent overheating and overcharging of the battery. The solar controller will block recharging when the over voltage limit is reached. This usually happens at 14.4V.
On such solar controllers, an orderly outdated function is used to automatically turn off the recharging mode when the maximum values of the generated electric current are reached, which does not allow charging the battery to 100%.
Because of this, there is a constant shortage of energy resources, which negatively affects the battery life. Therefore, it is impractical to use such solar controllers when installing expensive solar systems.
2) PWM controllers (PWM)
PWM control blocks do their job much better than On / Off devices. PWM controllers prevent excessive overheating of the battery in critical situations, increase the ability to accept electrical charge and control the very process of energy exchange within the system. The PWM controller additionally performs a number of other useful functions:
- equipped with a special sensor for measuring the electrolyte temperature;
- calculates temperature compensation at various charging voltages;
- supports work with different types of storage tanks for the home (GEL, AGM, liquid acid).
As long as the voltage is below 14.4 V, the battery is directly connected to the solar panel, which makes the recharging process very fast.
When the values exceed the maximum allowable value, the solar controller will automatically lower the voltage to 13.7 V – in this case, the recharging process will not be interrupted and the battery will be charged to 100%. The operating temperature of the device ranges from -25 ℃ to 55 ℃.
3) MRPT controller
This type of regulator constantly monitors the current and voltage in the system, the principle of operation is based on the detection of the “maximum power” point.
What does this give in practice? It is advantageous to use an MPPT controller, since it allows you to get rid of excess voltage from the photocells.
These regulator models use pulse-width conversions in each separate cycle of the battery recharging process, which allows to increase the efficiency of solar panels.
On average, the savings are about 10-30%. It is important to remember that the output current from the battery will always be higher than the input current from the photocells.
MRPT technology ensures battery charging even in cloudy weather and insufficient solar radiation intensity. It is more expedient to use such controllers in solar systems with a power of 1000 W and higher. The MPPT controller supports work with non-standard voltages (28 V or other values).
The efficiency is kept at the level of 96–98%, which means that almost all solar resources will be converted into direct electric current. The MPRT controller is considered the best and most reliable option for household solar systems.
4) Hybrid charge controllers
This is the best option if a combined power supply scheme is used as a power plant for a private house, which consists of a solar plant and a wind generator. Hybrid devices can operate using MPPT or PWM technology, but the current-voltage characteristics will differ.
Wind turbines generate electricity unevenly, which leads to an inconsistent load on the batteries – they operate in the so-called “stress mode”. When a critical load occurs, the hybrid solar controller discharges excess energy using special heating elements that are connected to the system separately.
How to connect the regulator block yourself
The charge controller circuit for connecting to a solar plant is quite simple: you need to connect all the working elements together without breaking the polarity.
Some owners of solar systems adhere to a mixed connection method, when the batteries are connected to each other in parallel, and are connected to the regulator unit in series.
The number of batteries for connection to the system is not limited. But for large accumulating “arrays”, you will additionally need to install a powerful block-inverter that can cope with the increased load.
Do-it-yourselfers can make a battery charge controller with their own hands – for this they usually use transistors that can withstand an electric current of up to 50 A, a car relay-regulator, diodes and a 120 kΩ resistor.
The efficiency of self-made models of controllers for a solar battery will be “lame” in comparison with factory devices, but for low-power and experimental solar systems, this option is quite appropriate.