These types of photovoltaic installations are designed for cases where the cost of maintenance and installation of power lines is not profitable. For example, this would be the case of mountain shelter.
What Applications Do Autonomous Photovoltaic Installations Have?
The main applications of isolated systems are:
- Electrification of homes and buildings, mainly for lighting and low power appliances.
- Street lighting.
- Agricultural and livestock applications.
- Pumping and water treatment.
- Telephone antennas isolated from the network.
- Signaling and communications.
These installations are used mainly in those places where there is no access to the electricity grid and it is cheaper to install a photovoltaic system than to lay a line between the network and the point of consumption. The electricity generated is used for self-consumption.
What Advantages and Disadvantages Do Autonomous Solar Installations Have?
Isolated photovoltaic solar installations have the advantage that they do not depend on external elements to supply energy and the direct cost of the kilowatt hour of energy is zero.
On the other hand, it has certain drawbacks. The main disadvantage of this type of renewable energy source is the dependence on the variation of the received solar radiation. The solar radiation that the photovoltaic panel will receive depends on the solar schedule, the inclination of the Sun at different times of the day and at different times of the year and the weather. Solar radiation hours can be calculated. What can not be calculated is the amount of hours and cloudy days that are going to have exactly (statistically it can be obtained).
Unlike the photovoltaic solar installations connected to the network, it is necessary to provide an energy accumulation system to be able to use it in those hours that the photovoltaic panels do not generate electricity because they do not receive radiation. Installations connected to the network do not have this drawback since the surplus of energy can be supplied to the power grid generated and supplied with it when necessary.
What Elements Make Up a Photovoltaic Solar Installation Isolated from the Power Grid?
In addition to the common elements of photovoltaic solar installations there are a number of elements that are completely necessary for the operation of this type of installations:
- The accumulators of electrical energy.
- The charge regulators.
- DC inverters to alternating current.
What Are Energy Accumulators?
The electric energy accumulators, which are responsible for storing the energy generated by the photovoltaic panels at times of low consumption so that they can be used at times of energy demand. Generally these are batteries, although there are some installations where solar energy is mixed with hydropower and the energy generated in the solar panels is used to drive a pump and raise water at a certain height. Water at a certain height has potential energy that can be converted back into electrical energy by operating the turbines.
What Are Charge Regulators?
Charge regulators are responsible for both the charging process and the discharge of the accumulators (in this case the batteries), are always within the correct operating conditions.
What Are Load Inverters?
The inverters are responsible for converting the energy in the form of direct current that is obtained in the solar panel to alternating current. Because the photovoltaic solar panels generate electricity in direct current and that the majority of electrical appliances that we are going to use require that the current input be in alternating current we will need to convert the generated direct current into alternating current.
The basic configuration of the isolated installations of the electricity grid is composed of the photovoltaic generator, a charge controller and a battery. The battery is the element responsible for accumulating the energy delivered by the panels during the hours of greatest radiation for use during the hours of low or no heat stroke. The charge regulator controls the battery charge preventing excessive overcharges or discharges that decrease its life. With this configuration, consumption occurs in direct current.
Another basic configuration is solar pumping, consisting of panels, small equipment and the pump, in which water is pumped when there is sunshine, not needing batteries.
The most used configuration in homes is the one composed of the photovoltaic generator, charge controller, batteries and inverter, the latter to convert the accumulated energy in the batteries into alternating current, which is used for most applications.
For the calculation of this type of facilities, the design criteria are different. In installations connected to the network, an attempt is made to maximize annual production, facing south and with the most favorable inclination. On the other hand, for isolated installations, the criterion must be to produce the maximum in the most unfavorable month, December, and thus the rest of the year will have at least the energy calculated for the worst month, always covering the needs.