Can I connect rooftop solar to my existing home inverter?

Most homes in Tricity already have a power-cut inverter: a box under the stairs with one or two tall tubular batteries, keeping the fans and lights on when the supply goes. So a common question when people consider solar is whether the panels can simply be connected to it. Sometimes they can, but the right answer depends on what you want solar to do: cut the bill, keep the backup, or both.

Why an ordinary solar system stops in a power cut

A standard rooftop system is on-grid. Its inverter converts the panels’ power and feeds it into your home and the grid. MNRE’s technical specification for rooftop systems requires islanding protection, which means the solar inverter must switch off when the grid fails, so it cannot send power down lines that a lineman may be working on. So in a power cut, an on-grid system makes nothing, however sunny it is.

Your existing home inverter works the other way. It charges its batteries from the grid and takes over the backed-up circuits when the grid fails. The two systems do different jobs, which is why the choice below matters.

Three ways to combine them

1. Keep both, side by side

Install an on-grid solar system, connected at your main supply, and keep the existing inverter and batteries exactly as they are.

• On a normal day, the solar system cuts your bill through net metering, and the home inverter keeps its batteries charged from the supply.
• In a power cut, the solar system stops, and the home inverter runs the backed-up circuits from its batteries, as it does today.
• The subsidy: a grid-connected home system with DCR panels qualifies for PM Surya Ghar, as long as the other conditions are met.

This is the cheapest way to get both a lower bill and backup, because nothing you own is wasted. Its limit is that the panels do not help during a cut, so long cuts on sunny days still drain the batteries.

2. Replace the home inverter with a hybrid inverter

A hybrid inverter does both jobs in one box. It feeds the grid when the supply is on, charges a battery from the panels, and keeps the backed-up circuits running from the panels and the battery when the supply fails.

• On a normal day, it works like an on-grid system and cuts your bill through net metering.
• In a power cut, the panels keep charging the battery and running the backed-up loads during the day.
• Your old batteries: some hybrid inverters can use an existing tubular bank, if its voltage matches the inverter and the batteries are in good health. Many work best with a lithium battery. A tubular bank that cycles every day also wears out faster than one that only covers occasional cuts.

This suits homes with long or frequent cuts. Our guide to on-grid or hybrid solar compares the two in more detail.

3. Add a solar charger to the home inverter

Some home inverters can take a solar charge controller, or come in a “solar” version, so that a few panels charge the batteries directly.

• What it does: cuts the grid power used to charge the batteries, and keeps them topped up in daytime cuts.
• What it does not do: it is not connected to the grid, so there is no net metering, and the saving is limited to what the batteries and backed-up circuits use. It does not qualify for the PM Surya Ghar subsidy, which is for grid-connected systems.

This can make sense for a small backup-only setup, but it does little for a large summer bill.

Which one to choose

Things to check before you decide

• The age and health of your batteries. A tubular bank near the end of its life is not worth building a new system around. Our guide to lithium or tubular batteries compares the two over ten years.
• What your backup needs to run. Lights, fans, a fridge and Wi-Fi need far less than an air conditioner. Our guide to how long a solar battery lasts in a power cut shows how to work it out.
• The wiring. Backed-up circuits are separate from the rest of the house. A proper design keeps them clear of the on-grid system’s connection.

How we approach it

At the survey we look at the existing inverter, the batteries and the backed-up circuits, and ask how long and how often your cuts last. The proposal then shows the option that fits, with the price of each part, and says plainly if your existing equipment can be kept. Our battery backup page covers hybrid systems.

Common questions

Can I connect solar panels directly to my home inverter?

Only if the inverter is made to take a solar charge controller, and then the panels only charge its batteries, with no net metering or subsidy. For a lower bill, install an on-grid system alongside the home inverter, or replace it with a hybrid inverter.

Will my on-grid solar system work during a power cut?

No. MNRE's specification requires islanding protection, so an on-grid inverter switches off when the grid fails. Your existing home inverter can still cover the backed-up circuits from its batteries, as it does now.

Can a hybrid solar inverter use my old tubular batteries?

Some can, if the battery voltage matches the inverter and the batteries are in good health. Daily solar cycling wears a tubular bank faster than occasional backup, so an ageing bank is usually better replaced when you switch to a hybrid system.

Do I get the PM Surya Ghar subsidy if I keep my home inverter?

Yes, if the solar system itself is grid-connected, uses DCR panels and meets the scheme's other conditions. Keeping a separate home inverter for backup does not affect it. A solar charger added to the home inverter does not qualify.