How to Choose a Solar Inverter for Your Home

What the inverter does

Solar panels produce direct current (DC). Your home runs on alternating current (AC). The inverter converts one to the other, and it does several other jobs at the same time. It finds the best operating point of the panels through a function called maximum power point tracking (MPPT), it matches the voltage and frequency of the grid, and it shuts down safely if the grid fails or a fault appears.

The inverter works every sunny hour, converts large amounts of power and sits in a warm place, so it is the component most likely to need attention over a system's life. Panels are passive and typically last 25 years or more. An inverter has electronics, capacitors and fans, so it ages faster. Choose it as carefully as you choose panels.

This guide is general information for homeowners and small businesses. Specifications differ between brands and models, so always rely on the manufacturer's datasheet and your installer's written proposal for decisions.

The three main inverter types

Rooftop systems in India mostly use one of three types. An on-grid (grid-tied) inverter feeds the grid and works only when the grid is live. A hybrid inverter can do that and also manage a battery, so it can supply backup during outages. An off-grid inverter runs without any grid and needs a battery bank. Our guide on on-grid, off-grid and hybrid solar explains the trade-offs between systems.

Separately, inverters differ in how they connect to panels. A string inverter takes the output of a series of panels. A microinverter is a small unit under each panel. Power optimisers sit at each panel but still feed a central inverter. The right one depends on shade, roof layout and budget.

Sizing the inverter

An inverter is normally chosen close to the total panel capacity. A 3 kW array typically pairs with a 3 kW inverter. Some designers use a slightly smaller inverter, for example 10 to 20 percent below the panel rating, because panels rarely produce their full rated power for long. This is called a DC to AC ratio above one. It can lower cost with only a small clipping loss, but it should be an informed decision, explained to you in writing.

An inverter that is too small clips the extra output. If the inverter cannot take the full output, it cuts off the surplus and you lose energy. One far larger than needed adds cost without benefit. Also check the input voltage window and the number of MPPT channels. A roof with panels facing two directions usually needs two MPPT inputs so that each direction is tracked on its own.

For single-phase homes up to around 5 kW a single-phase inverter is common. For larger loads or three-phase connections, a three-phase inverter is often used. Your sanctioned load and the DISCOM's rules limit what you can connect, so ask the installer to confirm the allowed capacity for your connection.

• Ask for the DC to AC ratio and why it was chosen.
• Check how many MPPT inputs the inverter has and how the strings are divided.
• Confirm single-phase or three-phase compatibility with your connection.
• Compare the inverter's maximum input voltage with the string voltage on a cold winter morning.

Efficiency, what the numbers mean

Datasheets list a peak efficiency, often 97 to 98 percent for good string inverters, and sometimes a weighted efficiency that reflects real operating conditions. These figures are measured in test conditions. A difference of one percentage point between two good models is small compared with factors like shade, dust, cable losses and correct sizing, so do not choose on peak efficiency alone.

More useful in daily life are the temperature behaviour and the operating range. In Uttar Pradesh summers, rooftop temperatures are high. Inverters reduce output when they overheat, a behaviour called derating. A unit installed in direct afternoon sun or a closed cupboard may derate often. Look at the rated operating temperature and plan a shaded, ventilated location.

Grid approvals and safety features

A grid-connected inverter must follow the technical standards set for the grid, including anti-islanding protection, which stops it feeding power into a line that utility staff believe is dead. Ask the installer to confirm that the model complies with the applicable Indian standards and can be accepted by your DISCOM for net metering. Models that are not accepted can delay your connection.

Check that the system includes proper protection on both sides of the inverter: DC isolators, surge protection devices, AC breakers and earthing. These belong to the installation and are as important as the inverter. Our guide on earthing and lightning protection describes what to look for.

If you are buying under a subsidy scheme, check the current programme rules on approved equipment and listing, because requirements for panels and inverters can change. The official PM Surya Ghar portal is the place to confirm this.

String inverters, microinverters and optimisers

For an unshaded flat roof, a string inverter is usually the best value. It is a single box, easy to monitor and to replace, and costs less per kilowatt than panel-level electronics. Its weakness is that panels in one string share the same current, so shade on one panel can pull down the others on that string.

Microinverters convert at each panel, so shade, dirt or a failure on one panel affects only that panel. They also remove high DC voltage from the roof, which some owners like for safety reasons. The trade-offs are higher cost, more electronics on a hot roof, and more units that could fail. Optimisers are a middle path, giving panel-level tracking with a central inverter.

If your roof has little shade and one main direction, you do not need panel-level electronics. If you have chimneys, tanks, trees or several roof faces, ask the installer to compare a design with and without them, and to show the expected gain in units, so the extra cost can be judged against the benefit.

Warranty and local service

Inverter warranties commonly run from five to ten years, and some brands offer paid extensions. Read what is covered: parts, labour, transport and replacement. A long warranty from a brand with no technician near you is hard to use in practice. Ask where the nearest service centre is, how fast they respond and whether the installer will handle claims for you.

Keep the invoice, the serial number and the commissioning report. If the inverter fails after the installer's workmanship warranty ends, you will need these documents. Also note the cost of an out-of-warranty replacement, since most inverters need replacing once during a 25-year panel life. Plan for it as a future cost.

Monitoring and display

Choose an inverter that shows daily and total generation on a display or an app. The simplest way to catch a problem early is to notice a drop in output on a sunny day. Check whether monitoring needs Wi-Fi, a data logger or a subscription, and whether it keeps working if your internet is unreliable.

Ask whether you will have access to fault codes, and whether the app is available in Hindi or at least easy to read. Check the monitor once a week for the first few months, so you learn what a normal day looks like for your home.

• Note your system's typical generation on a clear day, in units per kW.
• Compare with the same day in other months, remembering that seasons change output.
• If output falls well below normal on a clear day, clean the panels and then call the installer.

Questions to ask before you buy

Before you accept a quotation, ask for the inverter's brand, model number and datasheet, and check that what is installed matches what was quoted. Some sellers substitute a lower model after payment, so put the exact model in the contract. Our article on common mistakes when buying rooftop solar covers more such traps.

To get help comparing proposals, use the quotation form on our home page. We will visit, check your roof and bills and explain the inverter choice in plain language.

• What are the exact brand and model, and can I see the datasheet?
• What are the warranty length, claim process and nearest service centre?
• Is it approved for net metering with my DISCOM?
• What are the MPPT inputs, DC to AC ratio and operating temperature range?
• How can I monitor generation, and does it work without strong internet?