Solar photovoltaic technology works on DC power. So basically the power coming out of a solar PV panel is pure DC (Direct current) power. The DC power coming from a solar panel is unregulated power , and hence it can not be used directly for any useful application. We do need some kind of electronic circuit to control this unregulated dc power source into usable energy whether it is DC power or AC power.
Many a times people wonder whether they should prefer to use the DC power directly or choose the option of converting the DC power into AC power.
The answer is not a simple yes or no. Each of the options may be better depending on the type of system and application.
It is important to also bear in mind that the common electric supply in our houses, industries, offices, etc are working on AC (Alternating current). So most of the appliances, electrical devices, lights, fans, etc available in the market all operate on AC mode. DC-based appliances are not as commonly available as AC appliances.
Presented below are the different ways in which DC power from solar can be used in DC and how solar DC power can be used in AC.
A typical DC power system
To begin with we will definitely notice that in case of a DC power system it has the advantage of avoiding the DC to AC conversion losses. This also reduces the cost of any kind of inverter circuit or inversion technology.
But usually DC based systems can operate only on lower standard DC voltages such as 6v, 12v, 24v, 48v.
The DC systems are usually based on these voltages because of the availability of batteries in the market. Since batteries are only available in 6v or 12v voltages, hence, it is common to either choose a 6v system or a voltage system which is a multiple of 12v.
The AC power systems require an additional inverter circuit so as to convert the DC power into usable single or 3 phase AC power.
Solar AC power systems are primarily of 2 types:-
- Battery-based or hybrid solar power systems. These systems convert the solar power into AC but also have additionally a battery to act as a storage medium.
- On-grid and batteryless systems. Such systems directly convert in real time basis all the solar power into AC, but do not have any battery and hence can not store the solar power generated.
DC powered devices are not so common and hence usually require people to place special orders or otherwise look for very commonly available DC appliances only.
Devices such as LED lights, smaller fans, etc are commonly available in DC power.
However, many common appliances such as air-conditioners, refrigerators, etc suitable to operate on DC are not available in the market. Hence, for systems requiring the operation of such larger appliances, it is not feasible to opt for solar DC power systems. It is necessary to opt for a solar AC power system.
In case of DC power systems due to the lower voltage, the current rating increases very rapidly for higher power ratings. Eg. A 10000W solar system operating on a 12vdc bus, will have a current rating of 834 Amps !!!
It becomes very difficult and costly to manage such a high current rating. It also increases the cabling, switchgear and other costs so as to remove any other smaller benefits.
Also to be kept in mind is the fact that DC cables are costlier as compared to AC cables for the same size.
As a thumb rule, the DC power systems can be suitable for lower power ratings only or in applications whether the power load is by default operating in DC power such as LED lights, DC fans, telecom systems, cathodic protection systems, etc.
Whereas for larger power ratings, solar AC power systems are more appropriate, reliable and cost effective.
Considering the different points mentioned above and also commonly available solar inverter technologies, Presented here below are some different scenarios with a conclusion on which technology is better for that application.