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12V Autonomous Photovoltaic Systems

12v Autonomous Photovoltaics: Autonomous are those that are not connected to the PPC network. An autonomous system varies in size from 0.30kwh for DC lighting to 13kwh for the consumption of a small and medium permanent residence. The autonomous system is also known as or not interconnected (Off-Grid) photovoltaic systems.

Off-Grid systems (standalone) use a photovoltaic system to supply electricity to a consumer unit directly or via a battery, independent of other energy sources. These systems are suitable for small appliances and the equipment is not close to a source of electricity (eg lighting, water pumps, radio and signal equipment).

Photovoltaic (PV) Modules

The direct current generated by the solar panel or module (s) is used to charge the batteries via a solar charge regulator. Any DC devices connected to the battery must be fused. The DC lights are usually connected to the load regulator. Any AC devices powered by an inverter are connected directly to the batteries. NOTE: Inverters used in grid tie and standalone systems are different and should not be swapped.

Most autonomous photovoltaic systems need to be managed properly. Users need to know the limits of the system and the adjustment of power consumption depending on how sunny the charging status (SOC) of the battery is.

Configuration

The solar panels must be adjusted to match the DC system, which is determined by the battery. System voltages are usually 12V DC and 24V DC, larger systems will operate on 48V DC.

The operating voltage of a solar panel in a stand-alone system must be high enough to charge the batteries. For example, a 12V battery will require 14.4V to charge. The solar panel should be able to deliver this battery voltage after power losses and voltage drop across the cables and load regulator and in conditions where the solar cells are operating at high temperatures. A solar panel with a Voc of about 20V is required to reliably charge a 12V battery.

Charge Controllers

A load controller is designed to protect the battery and make sure it has a long service life without affecting system performance. The batteries should not be overloaded and the function of the load regulator is to ensure that the battery is not charged up.
• Charging controllers are designed to work as follows:
• Protecting the battery from excessive discharge, commonly referred to as low voltage (LVD), which disconnects the battery from the load when the battery reaches a certain discharge depth (DOD).
• Protecting the battery from overcharging by limiting the charging voltage - this is important with sealed batteries - is commonly referred to as high voltage disconnection (HVD).
• Prevent current from flowing back into the solar panel overnight, hence the so-called current.
NOTE: Controllers with MPP will ensure that solar panels operate at the optimum rating and can increase output by 10% or more.

Batteries

The power requirements of standalone systems are rarely in sync with the battery charge. Appliances and loads must be moved when there is sufficient sunlight, during cloudy skies and at night. Bad weather can last for several days and the daily charging and discharging of batteries takes its toll on them. Batteries that are able to handle continuous charging and discharging are known as deep cycle batteries. Batteries should have good charging performance, low charging currents and low self-discharge.

Ah Performance Battery

The Ah performance of the battery describes the relationship between the Ah being inserted into the battery and the Ah being taken out. Under ideal conditions a new deep cycle battery will be 90% efficient. Choosing the Most Suitable Battery The important features are:
• Capacity
• The life of the cycle
• price / performance
• size and space requirements
• Ah performance
• self-discharge rate
• Installation - vertical or horizontal
• environment - batteries should be placed near water supply or wildlife parks etc.

Cables and Accessories

12v Standalone Photovoltaic Cables must be UV resistant and suitable for outdoor applications. It is very important to keep the power losses and voltage drop in the cable to a minimum. It is recommended that this is less than 3% between the array and batteries and less than 5% between the battery and DC loads.
Stand alone or autonomous systems are not connected to the grid. Some stand alone systems known as PV-hybrid systems or island systems, may also have another source of power, wind turbine, bio-fuel or diesel generator, etc.

12V Autonomous Photovoltaic Systems - Video