Power inverters or home UPS have been in use in India since quite some time. Thanks to frequent power cuts, home UPS or power inverter industry has done well in India. But with increasing interest in solar power and solar panels many people are thinking of using Solar Power to charge the batteries to save electricity drawn from the grid. Having heard of solar inverter, many people wonder if their existing inverter system is useful or not. In past, we at Bijli Bachao have got this question many times: what is the difference between solar inverter and regular inverter? With this article we would try to answer the question.
What is an inverter?
A power inverter or invert is a device that converts Direct Current (or DC) to Alternating Current (or AC) using transformers, switching and control circuits. And this is the basic function of any inverter: be it solar or regular inverter. A home UPS or home inverter take the DC power from the batteries and convert it to AC power used by appliances. A solar inverter also does the same if it is an “Off Grid” solar power system. In case of “Grid Connected” the DC power is from the solar panels and AC power is given to the grid. (To know more about “Off Grid” and “Grid Connected” solar power system, read our article: Solar electric, solar thermal, power generation, inverters, grid, off-grid: clearing the cobweb).
Working of a Home UPS/Inverter
A regular home UPS/inverter system has a system of inverter and batteries that is connected to the home power connection. When the power is coming from the grid, the UPS/inverter system charges the batteries using the power coming from the grid. When the power is off, the inverter takes the DC power from the batteries and converts it into AC used by appliances. There is an automated switch in the system that senses if the grid is not supplying power and switches the UPS into battery mode.
Working of a Off Grid Solar Powered system
An off grid solar powered system has an assembly of solar panels, charge controller, batteries and inverter as shown in the image below. The batteries are charged using solar panels and the inverter has the same function of converting DC to AC. It can also have an automated switch to sense if grid is not supplying power that can change the power source of the connected home from grid to batteries. Depending on the need the system can be designed to: 1) To completely rely on solar power 2) Charge the batteries from solar power when sun is available and from the grid when it is not.
An existing home UPS or Inverter system can be converted to be used with an off grid powered system by just adding a switch which can control the change source: solar or grid (based on availability).
Having said that, to answer the question posed in the title of this article: there is not much difference between a solar inverter used in off grid system and a regular inverter.
Working of a Grid Connected Solar Power System
A grid connected solar power system additionally supplies excess electricity to the grid. People go for this kind of system when they feel that they have enough space to install solar powered system and they can sell the extra electricity generated back to the electricity distribution company. The structure of a grid-connected system is shown below:
The purpose of the inverter in this kind of system is also to convert DC (generated from Solar Panel) to AC. But it additionally needs a MPPT (Maximum Power Point Tracking) feature to be built in it. Because the voltage generated by Solar Panel varies depending on the temperature and availability of sun (more on this on our article: Solar Glossary – photovoltaic, panels, modules, cells, voltage, watt and current), MPPT enables solar inverters t draw maximum power from the solar panels. The solar inverter used for grid-connected solution also includes an anti-islanding functionality to prevent risks to grid in case there is power failure in the grid.
The basic purpose of any inverter is to convert DC power to AC power be it solar inverter or regular inverter. Depending on the situation and setup one may need some additional features, which can be implemented in existing home UPS/inverters through simple modifications.