Sizing, Payback Examples and Checklists
On-grid vs hybrid vs off-grid solar for Indian homes: which one fits?
How on-grid, hybrid and off-grid home solar systems differ in India, what happens in a power cut, which qualify for PM Surya Ghar subsidy, and how to choose.
Choose on-grid if your grid supply is reasonably reliable and your goal is a lower bill: it is the cheapest per kW, qualifies for PM Surya Ghar subsidy when it uses DCR modules, and uses net metering instead of batteries. Choose hybrid if you also need backup during frequent power cuts and are willing to pay for a battery. Choose off-grid only where there is no reliable connection at all, such as a remote farmhouse, because it gets no net metering and its batteries dominate the cost. A point many buyers miss: a plain on-grid system switches off during a grid outage, by design, so it does not give backup on its own. This guide explains how each works, what it costs relative to the others, and the questions that decide the choice.
How each system works
| On-grid | Hybrid | Off-grid | |
|---|---|---|---|
| Grid connection | Yes, via net meter | Yes, via net meter | No |
| Battery | None | Yes | Yes (essential) |
| Works in a power cut | No (anti-islanding shutdown) | Yes, for the loads on the backup circuit | Yes |
| Exports surplus | Yes | Yes, after charging the battery (settings dependent) | No |
| PM Surya Ghar CFA | Yes, with DCR modules and scheme conditions | CFA is on solar capacity; battery at own cost | Not under the residential grid-connected component |
| Relative cost per kW (illustrative) | Lowest | Higher | Higher, depends on battery bank |
On-grid
Panels feed a grid-tie inverter that synchronises with the DISCOM supply. Your home uses solar first; any shortfall comes from the grid, and any surplus goes to the grid through the net meter. If the grid fails, the inverter must stop exporting within a fraction of a second so that linemen working on the line are not put at risk. That safety function, called anti-islanding, is required by the connectivity standards, and it is why on-grid systems do not power your house during a cut.
Hybrid
A hybrid inverter manages panels, a battery and the grid. During normal supply it can power the house, charge the battery and export surplus. During an outage it isolates your backup circuit from the grid and runs those loads from the battery and panels. Hybrid systems can be grid-connected and net metered like on-grid systems, subject to your DISCOM's approval of the inverter.
Off-grid
Panels charge a battery bank through a charge controller, and an inverter supplies the house. There is no grid connection to fall back on or sell to. The battery must be sized for night use and cloudy days, so the system is usually larger and more expensive per unit used.
What about my existing home inverter?
Many Indian homes already have a backup inverter with a lead-acid battery, charged from the grid. You can:
- Keep it alongside a new on-grid solar system. The solar system lowers the bill; the old inverter gives backup as before. This is often the cheapest way to get both.
- Replace it with a solar PCU or hybrid inverter that charges the battery from the panels. Check compatibility, and whether your DISCOM will net meter that inverter.
Do not connect solar panels to an inverter not designed for them.
Worked comparison (illustrative)
A household uses 330 units a month and suffers about two hours of cuts most evenings.
| Option | Illustrative price | CFA | Net cost | Backup |
|---|---|---|---|---|
| 3 kW on-grid + keep existing home inverter | ₹1,80,000 | ₹78,000 | ₹1,02,000 | Existing battery, ~2 hours for fans and lights |
| 3 kW hybrid with 5 kWh lithium battery | ₹3,00,000 | ₹78,000 (if scheme conditions are met for the solar part) | ₹2,22,000 | Fans, lights, fridge, TV for several hours |
| 3 kW off-grid with lead-acid bank | ₹2,40,000 | None | ₹2,40,000 | Full house within battery limits; no net metering |
For this household the first option gives the bill saving at the lowest cost, while the existing inverter handles the evening cuts. The hybrid makes sense if the cuts are long or the household wants to run a fridge or work-from-home equipment through them.
Questions that decide the choice
- How often and how long are your power cuts? Note them for a month.
- Which loads must run in a cut? Fans, lights, router, fridge, a pump? Add up their watts and the hours needed.
- Do you already have a backup inverter? If yes, on-grid plus the existing inverter is often enough.
- Is your connection reliable enough to export? Very weak grids can cause on-grid inverters to trip frequently.
- What does your DISCOM accept for net metering? Ask whether hybrid inverters are allowed and what tests are needed.
Sizing the battery (brief)
Battery capacity is in kWh. Usable energy = rated kWh × usable depth of discharge. Backup hours ≈ usable kWh ÷ load in kW. Example: a 5 kWh lithium battery at 90% usable gives 4.5 kWh; running 400 W of fans, lights and a fridge, that is about 11 hours (illustrative, ignoring inverter losses). Details in home batteries: lithium vs lead-acid.
Mistakes to avoid
- Expecting backup from on-grid alone. It shuts down in a cut.
- Oversizing an off-grid battery bank to run air conditioners, which is very costly.
- Using a hybrid inverter your DISCOM has not approved, delaying the net meter.
- Assuming a battery speeds payback. It usually slows it.
Back to the pillar guide: how many kW of solar you need. Related: payback worked examples, solar panel and inverter types.
Frequently asked questions
Can I add a battery to an on-grid system later?
Usually by replacing or supplementing the inverter with a hybrid or adding an AC-coupled battery system. Plan for it in the original design if you think you will want it.
Does off-grid solar get any subsidy?
Not from PM Surya Ghar: MNRE's guidelines say off-grid installations are not eligible for the residential CFA, while grid-connected hybrid or behind-the-meter systems can be, subject to your SERC's approval. Some state or off-grid programmes may exist; check your state renewable energy agency.
Will a hybrid system run my AC in a power cut?
Only if the inverter and battery are sized for it, which is expensive. Most backup circuits cover fans, lights and small appliances.
Is a solar PCU the same as a hybrid inverter?
Terms are used loosely. Ask whether it can export to the grid under net metering and whether your DISCOM accepts it.
Official sources
- Ministry of New and Renewable Energy — scheme scope and technical specifications
- Central Electricity Authority — connectivity standards for distributed generation
- PM Surya Ghar national portal — eligible system types
