Autonomous solar power plants

Autonomous solar power plants do not need to be connected to the electricity grid for their operation. The main task of autonomous solar power plants is the accumulation of produced energy in batteries in order to ensure energy supply during the night and due to unfavorable weather conditions. In addition to battery accumulators, a regulator for controlled battery charging and discharging is indispensable, and by adding an inverter (DC / AC), autonomous solar power plants can satisfy all types of typical network consumers who need alternating voltage. Such systems are suitable for providing the required quantities of electricity where there is no public distribution network and where the cost of connection to the network is too high.

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The advantages of autonomous solar power plants are:

• easy installation of the system,

• longevity,

• possibility to upgrade the system,

• cheap maintenance,

• complete energy independence,

• Autonomous systems protect the environment and there are no electricity bills.

Possibilities of application of autonomous solar power plants are:

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• insulated / isolated areas (cottages, coastal cottage settlements, farms, shooting box etc.),

• telecommunication systems (transmitters, repeaters, base stations),

• street lighting, bus stops, parking lots,

• water wells,

• various signalization,

• mobile units, caravans, campers and boats,

• systems for automatic data collection and monitoring (measuring and control stations for meteorological, climatic, seismological, hydrological, ecological and similar purposes).

Considering the purpose, three basic versions of autonomous solar systems are most often used today:

• to supply individual consumers

• to supply more direct current consumers

• to supply more AC power.

Selection of autonomous solar power plant components

The autonomous system consists of the following components:

• solar panels,

• substructure (panel supports),

• charging regulator,

• DA / AC converter (inverter),

• rechargeable battery.

When procuring an autonomous system, off-grid, it is necessary to know either the average or maximum monthly electricity consumption that would be replaced by this system (given in kWh), or a list of electrical devices is required, which means their power and average operating time in during the day. Therefore, such data are necessary to optimize the autonomous solar system.

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Another important thing for off-grid systems is the autonomy of stored energy. It must be known that the batteries for solar panels when charged do not have an efficiency of 100%, ie how much energy is given to them to accumulate so much, but ranges between 95-85%. Then, when they are charged and not consumed, the accumulated energy decreases. And most importantly, it is recommended to discharge the batteries up to a maximum of 50% of their rated capacity, because discharging them to the nominal limit value significantly reduces the number of charging and discharging cycles, ie their total service life. units should correspond to an electricity value of 12 kWh. In addition, it must be known that consumers of higher power (eg over 1.5 kW) can lead to rapid discharge and unwanted consequences in the batteries. This is very important for cloudy days when the insolation of the Sun is low.

 

The battery bank itself can be organized-connected in series (the voltages on the batteries are added) or in parallel (their amperage is added). Therefore, if you want two 12V DC batteries to be connected in series, you will get a 24V DC system, but with the same current (amperage). If it is a 240Ah battery, then the accumulated energy of such a circuit is 24V * 240Ah = 5.76 kWh and 2.88 kWh should be used.

 

Third, the battery unit is charged and discharged under the control of a special electronic device, controller or charge controller. Here it is very important to match the power of the controller with the power of the installed solar panels and the power of the battery unit!

 

Then, what is common to off-grid and grid-tie (grid-connected) systems are the basic elements: solar panels and inverters. For this system, it is desirable that the panels be monocrystalline and polycrystalline when it comes to higher power. Amorphous can also be used for small needs, such as boats, caravans, etc. Why such a proposal? Due to the reliability and durability characteristics of the panels themselves. Monocrystalline and polycrystalline panels have far more stable current and voltage characteristics than amorphous ones, and in order to be placed in inaccessible places (for example on roofs), it is better to take them. By the way, amorphous ones are cheaper, but they are also less efficient,

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Inverters are different for off-grid and grid-tie networks. Then, they differ from each other in AC rated power and DC voltage. In autonomous systems, there are inverters that also have charge controllers. That is why it is very important to know the approximate power of consumers and the time of their exploitation. In addition, there are DC-DC inverters, which have applications for example in video surveillance, lighting and the like.