Stand Alone Solar Electric Installation

We have seen how solar panels can be used to supply our electrical needs and considered the basic precautions required to be observed in using them. We shall now consider the practical solar electric supply systems.

Solar electric systems are a boon to people living in remote areas where due to economic reasons utility companies (electricity distribution companies) do not supply power. Such a situation exists not only in under developed countries but even in industrially advanced countries. For a location to be suitable to derive the benefit of solar electricity the only requirement to be satisfied is adequate sunlight being available for reasonably long period of time. In such locations you could get electricity to run pumps, provide lights in the house(s), provide electricity to run radios and television sets, refrigerators. In under developed countries many villages use solar electricity to power community entertainment and communication equipments, provide village street lights and run pumps for their irrigation need. All this improvement in their quality of life is possible without depending on the utility or grid supply.

The Solar Electric System

Fig. 1 shows the basic ingredients of such an installation schematically. Roof mounted solar panel generates electric current when exposed to sunrays. This is a DC current. Solar panels can generate only DC current. This is used to charge batteries so that the energy generated can be stored for use when sun sets or when adequate sunlight is not available, as say in the early morning or late evening times. It also serves the purpose of supplying an almost constant voltage to other equipments.

The strength of the current generated by the panels, however, varies drastically depending upon the intensity of sunlight available; this unregulated current can damage the battery. So a charge controller is introduced between the panels and the battery. It avoids the battery being charged at a damagingly high rate; it also ensures that the battery does not get overcharged.

Most of the equipments we commonly use work on AC current, we shall refer to them as AC loads. So to provide AC current from a battery which can essentially give only DC current, an equipment called inverter is introduced. It accepts the DC current available from the battery and turns it into AC current of a level acceptable to the AC loads we use. Any DC loads may be supplied from the charge controller directly or from the battery, as necessary.

Solar Panels

Fig. 1 shows roof mounted solar panels. For roof mounted solar panels, you will have to ensure that the orientation of the roof and the tilt of the panel is appropriate. If this is not possible, you can put the panels on a rack, mounted on an appropriate frame out in the open, in garden or field as shown in Fig. 2. The type and size of the panel should be chosen to be able to provide adequate power as per your requirements. You may have to consult Metrological data to get information about the average intensity of light in your area as well as the average number of days in a year you may get sunlight.

Battery

One thing needs a special mention. Most of the people erroneously think that any battery, even a car battery could be used. Sorry, that is a wrong assumption! Only a Lead-Acid battery, the type used in car, but of the “Deep-Discharge type” is required. A car battery is required to supply a large current for a short time, for starting, and for the rest of the time it is getting charged when the car is running and it is hardly ever required to give any current.during the rest of the time. The battery used in the solar installation, on the other hand, is required to supply current in more or less a steady manner for a long period of time (may be for the whole night), when the solar panel is not supplying adequate current and is going to be discharged a lot before it receives charge again (in the daytime)– hence the name Deep Discharge Type. Sealed or vented type batteries can be used.

Lead Acid batteries, especially the vented type, give off a small amount of acid fumes in the surrounding air; these are very corrosive for materials around and very damaging for our respiratory system. The batteries therefore should always be installed in a well ventilated enclosure or room.

Other Components

The above description of the system covers all the basic items required in the solar electric installation; a few more minor components are necessary to be added from the point of view of safety. As required by the electricity regulations the AC loads must be supplied through appropriate individual circuit breakers to ensure safety and the entire load supplied by the inverter must be supplied through a mains circuit breaker. Common practice requires that the mains circuit breaker and the individual load circuit breakers are mounted in an enclosure at a convenient location for easy access. A DC disconnect switch also should be installed to cut off current from solar panel to the entire installation for safety.

As per the safety regulations, the entire installation requires to be provided with appropriate “earth” connection. This essentially means that in case a fault occurs in the electrical system, the fault current may be diverted safely to the electrical system through a connection made in ground so that the fatal accidents can be avoided.

This is, then, the Stand Alone Solar Electric Installation, in its basic form, that gives you independence from utility or grid supply.