Power supply with solar panels: DIY system assembly

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The article examines the practical application of solar panels, describes in detail the nodes necessary for an uninterrupted power supply, self-connecting and setting up solar panels.

Solar power supply

Power supply system equipment: range, characteristics

In the previous article, we looked at the types of solar panels. But in solar power generation systems, these elements are only primary converters. To create a full-fledged home power plant, we need the following set of equipment:

  • battery charge controller
  • storage battery (joint stock bank)
  • voltage inverter

Battery charge controllers are of two types: PWM controllers (PWM controllers) and OTMM controllers (MPPT controllers).

The PWM controller is a simpler and cheaper device that controls the battery charge. The efficiency of a PWM controller is usually higher than that of an OTMM controller due to the fact that at the initial stage of charging it connects the battery almost directly to the solar battery without converting the generated voltage. OTMM controllers are recommended to be used with modules with non-standard output voltage of 28 V and higher.

PWM controller

The use of OTMM-controllers will be economically justified in generation systems with a rated power of more than 400 W. Another reason for using such a controller is designing a solar station for year-round power generation. On cloudy winter days, when charging batteries, the OTMM controller will show its best side.

Battery in the solar power supply system plays the role of a buffer that accumulates electrical energy.

Solar battery

Unlike all other solar station equipment, the battery is a consumable item. Therefore, the longer it works without replacement, the shorter the payback period of the components you purchased will be. In order for the battery to serve for a long time, you need to responsibly approach its choice. The main parameters of the battery that are of interest to the potential owner are:

  • voltage (Volt, V) – there are 12, 24 and 48 V solar batteries on sale. For small home stations with a capacity of 200-300 W, 12 V batteries are quite suitable;
  • electrical capacity (Ampere? hour, A? h) – characterizes the amount of electricity that can be accumulated. Accordingly, the greater this parameter, the more the electrical system can work in autonomous mode (in cloudy weather or at night);
  • self-discharge level (% of rated capacity) – the lower this parameter, the better the battery.

Voltage inverter designed to convert the constant voltage of the battery into the alternating voltage of the 220 V mains supplying the household load.

Solar power supply

There is a wide range of inverters on the market with a variety of functions. Among the most important parameters are the following:

  • inverter power;
  • primary circuit voltage (voltage of the connected battery);
  • the presence of built-in protections (against overload, against battery polarity reversal, against short circuit in the load, against excessive battery discharge);
  • sinusoidal output voltage (in principle, if the connected load contains motors, for example, washing machines, refrigerators, circulating pumps, fans, etc.).

It should also be noted that an excessive number of functions only leads to an increase in the cost of the device and complication of its configuration and operation..

Connection diagram for solar station equipment

The assembly of a solar power plant circuit is quite simple. Below is the sequence of connections illustrated by photographs. To assemble a simple system, a solar panel with polycrystalline cells, a charge controller and a battery are used. We start the assembly by connecting the cable to the solar panel.

Solar power supply

This step is not required for the batteries that come with the cable. We connect the battery to the output terminals of the controller. Further, the wires coming from the panel must be connected to the input terminals of the charge controller.

All connections are made according to the principle “+” to “+”, and “-” to “-“. We supply power from the battery to the input terminals of the inverter. After turning on the charge controller and inverter, we see that the electricity generated by the solar panel starts charging the battery.

Solar power supply

In order to determine the polarity of the terminals of the solar battery, it is enough to measure the voltage at the terminals with a multimeter. If there is a minus sign next to the voltage readings, then the position of the black probe corresponds to the positive terminal (check the correct connection of the probes before measuring). If there is no minus sign, then the position of the black probe corresponds to the negative terminal of the battery.

Solar power supply

Installation of solar panels and auxiliary electrical equipment

Installation of the solar station electrical equipment is carried out with a copper wire. The cross-section of copper wire for one panel should be chosen at least 2.5 mm2. This is due to the fact that the normal current density in a copper conductor is 5 amperes per 1 mm2. That is, with a section of 2.5 mm2 the allowable current will be 12.5 A.

At the same time, the short-circuit current of the RZMP-130-T panel with a power of 145 W is only 8.5 A. When combining several panels with parallel connection, the cross-section of the common output cable should be selected based on the maximum total current of all panels according to the above concept (5 A per 1 mm2).

There are a variety of solar cables on sale. Their distinctive feature is that the outer insulation of the cable has undergone a special treatment and has an increased resistance to ultraviolet radiation. It is not necessary to buy such cables. Solar panels can be connected with a cable with ordinary PVC insulation, but lay it in a corrugated sleeve, which is designed for laying external wiring. This option will cost 30-40% less.

The battery charge controller and inverter should be placed in a dry room with room temperature, such as a closet or hallway. It is impractical to place this equipment outdoors, since the electronic components of the equipment should not be exposed to significant fluctuations in temperature and humidity. The battery itself can be placed together with the electronics.

Solar power supply

If you decide to use acidic or alkaline batteries, you should place them in a well-ventilated non-residential area, as they release electrolyte vapors that are harmful to health. In addition, there should be no sources of spark and fire hazard in the room with batteries, since oxygen and hydrogen released in poorly ventilated rooms can form an explosive mixture..

The solar panel can be installed in two ways:

  • Fixed installation involves the stationary placement of panels on the roof of the house or on a bracket attached to a wall or foundation. In this case, the panels should be directed to the south, the horizontal inclination of the panels should be an angle equal to the latitude of the area plus 15 °. The latitude of your location can be determined, for example, by the readings of a GPS navigator or in the Google Maps service;
  • movable installation of the panels is made on a traverse, which is able to rotate azimuthally (in the direction of the sun along the horizon) and zenith, tilting the panels so that the sun’s rays fall on them perpendicularly. Such an installation system allows to increase the efficiency of the used solar panels, but requires additional tangible financial costs for the construction of the traverse, drive motors and the system for their control..

Solar power supply

Ways to improve the efficiency of autonomous power supply

To improve the efficiency of a solar power plant, you can go in two ways: increase the amount of generated electricity on the one hand and reduce its consumption on the other. The ways to increase the generated electricity can be as follows:

  • installation of solar panels on a movable traverse or on a zenith tilt control mechanism (half-measure, but also quite effective, mainly for monocrystalline panels);
  • use of high-quality batteries with a low self-discharge percentage and a long service life without a significant decrease in capacity;
  • regular maintenance of the system: cleaning the panels from dust and snow, maintenance of detachable and terminal connections in order to reduce contact resistance and, as a result, power losses.

On the load side, the energy efficiency can be increased as follows:

  • allocation of a low-voltage supply circuit directly from the battery, for example, for connecting LED lighting. This will avoid double conversion of energy in the inverter;
  • turning off the inverter when the load is disconnected at its output, since the inverter, which is idle, still consumes a small amount of energy;
  • installation together with lighting of motion sensors with a timer to exclude the annoying consumption of electricity due to the fact that they simply forgot to turn off the lamp in the hallway.
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