Off Grid Inverter

What is an off grid inverter

An off grid inverter, also called a standalone inverter or island inverter, is a solar inverter that creates its own AC voltage and frequency from a DC battery bank. There is no electrical connection to the utility grid. The inverter is the grid for whatever is connected to it.

It sits at the centre of a closed system. PV modules feed a charge controller, which charges the battery. The inverter pulls DC from the battery and produces 230 V, 50 Hz AC for household and three-phase 400 V, 50 Hz for industrial sites. When the sun is out and the battery is full, surplus PV is either dumped or curtailed by the charge controller. There is nowhere for it to go.

Off grid inverters used to be the only practical option for solar in unelectrified India. They are now a niche segment, since rural electrification under Saubhagya and the rapid rollout of net-metered rooftop solar have pushed most installations toward grid-tie systems. The niche remains real: telecom backhaul sites, border outposts, mountain villages without reliable supply, mid-stream irrigation, and ecology-sensitive resorts that cannot tolerate diesel.

Off grid inverter explained simply

Picture a small island with no power line coming in from the mainland. You have solar panels on the roof and a battery in the shed. The off grid inverter is the device that takes battery DC and turns it into the wall-socket AC that runs your lights, fan, fridge and laptop.

When the sun is up, panels charge the battery and run the loads at the same time. When the sun sets, the battery alone runs the loads until morning. If you draw too much at once, the inverter beeps and shuts down. If the battery drops below its safe floor, the inverter shuts down to protect the cells.

There is no grid to bail you out. Sizing has to be honest. Most off grid failures in the field are not equipment failures, they are sizing mistakes.

Why off grid inverters matter

Energy access. Roughly 18 million people in India still live with daily outages exceeding 6 hours, even after Saubhagya. Off grid solar plus inverter is the only viable answer in many of those locations.

Economic alternative to diesel. A 5 kVA diesel genset costs ₹2 to ₹3 lakh upfront, burns ₹15 to ₹25 of fuel per kWh, and needs monthly servicing. A 5 kVA off grid solar plant costs ₹3.5 to ₹5 lakh once and delivers power at near zero marginal cost.

Telecom and critical infrastructure. Indian telecom towers run on hybrid solar plus battery plus backup diesel. The off grid inverter is the heart of that stack.

Resilience for institutions. Schools, primary health centres and water pump stations in low-supply areas operate reliably on off grid solar even when the grid is out for days at a stretch.

How an off grid inverter works

A typical off grid system has four functional blocks.

1. PV array. Strings sized to charge the battery within solar window hours.
2. Charge controller. MPPT or PWM. Limits charge current, applies bulk, absorption and float stages, and protects the battery from overvoltage.
3. Battery bank. Sized to support load through one or two cloudy days. Lithium iron phosphate is the modern default. Tubular lead acid still appears in cost-sensitive rural projects.
4. Inverter. Pulls battery DC, runs it through a high-frequency or low-frequency inverter stage, and outputs AC.

Internal sequence of events:

1. DC input from the battery enters a DC bus, usually 24, 48 or 96 V for smaller systems, 200 to 600 V for larger ones.
2. An H-bridge of IGBT or MOSFET switches chops the DC at 10 to 20 kHz.
3. An LCL filter smooths the chopped output into a sine wave.
4. A control loop regulates output voltage to 230 V and frequency to 50 Hz, even as the load fluctuates.
5. Protection circuits monitor battery voltage, output current and inverter temperature. Cutoffs kick in at low SOC, overload and overtemperature.

Many integrated off grid inverters also include an AC input. When a diesel genset or weak grid is available, the inverter can either charge the battery from that source or pass it through to loads. This crossover is what distinguishes a true hybrid inverter from a pure off grid unit.

Technical deep dive

Sizing the inverter

The inverter VA rating must cover continuous load plus surge. Inductive loads like fridges, water pumps and air conditioners pull 3 to 7 times their nameplate current at startup, for 200 to 500 ms.

For a household with a 1.5 kW continuous load and a 1 ton AC compressor that starts twice an hour, the surge is roughly 4.5 kW. A 5 kVA inverter with 10 kVA surge rating is the right pick.

Sizing the battery

Battery capacity in usable kWh equals daily AC consumption divided by inverter efficiency divided by DoD.

See Off-Grid Solar Battery Bank Sizing, India Complete Guide for a full worked methodology.

Add a multiplier of 1.5 to 2 for autonomy through cloudy days, sized against energy storage capacity rather than nameplate rating. The same site sized for one day of autonomy needs roughly 12 to 16 kWh nominal LFP.

Sizing the PV array

PV must replace daily consumption plus battery losses within the solar window. For 6 kWh of daily AC consumption at 88 percent battery round-trip and 95 percent MPPT efficiency in 4.5 peak sun hours: PV = 6 / 0.88 / 0.95 / 4.5 = 1.6 kWp minimum.

In practice add 25 to 50 percent overhead for monsoon, dust and morning load before battery is recharged.

Topology choices

Real-world applications

Rural households. Single-phase 1 to 5 kVA inverters with 3 to 10 kWh of battery serve lighting, fans, mobile charging, fridge and television in unelectrified or weak-grid villages.

Solar water pumping. Three-phase off grid inverters drive submersible pumps for irrigation and drinking water under MNRE PM-KUSUM Component B. Many use direct PV-to-pump operation without battery, with frequency control standing in for charge regulation.

Telecom towers. Hybrid configurations with off grid inverter, lithium battery and diesel backup. Diesel runtime is cut by 70 to 90 percent compared to pure diesel sites.

Eco-resorts and remote tourism. Off grid inverters in 5 to 50 kVA range, often three-phase. Used where grid extension cost exceeds ₹5 lakh per kilometre or where the site is in a protected zone, which usually calls for a dedicated site survey and land feasibility study before design begins.

Defence and border outposts. 5 to 100 kVA off grid systems, often with hardened enclosures and dust filtration. Used by ITBP, BSF and Army at high altitude and remote posts.

Mobile and emergency. Compact 1 to 3 kVA off grid inverters for disaster response, mobile health units and field offices.

Advantages of an off grid inverter

Independence from the utility. The system works whether the grid is dead, brown or absent. There is no DISCOM bill and no curtailment by the discom.

No anti-islanding constraint. The inverter is free to run during grid outages, because there is no grid to feed back into.

Predictable energy cost. Once paid off, the marginal cost of energy is the battery wear cost, typically ₹2 to ₹4 per kWh on LFP and ₹4 to ₹7 per kWh on lead acid.

Lower civil and electrical work in remote sites compared to extending a grid line.

Better fit for critical loads. With proper sizing, an off grid system meets a defined load with a defined autonomy. No surprises from the grid.

Limitations

Higher upfront cost. The battery alone often costs more than the rest of the system. A 5 kVA off grid system with 10 kWh LFP is 60 to 100 percent more expensive than a comparable on grid system.

Sizing is unforgiving. Underestimate load by 20 percent and you will be running short by month two. Overestimate and you have paid for capacity that will never be used.

Maintenance is more involved. Battery temperature, electrolyte level for lead acid, ventilation and dust on PV all need active management.

Energy is wasted when batteries are full. Without grid export or large dump loads, surplus PV is curtailed in afternoon hours during low-load months.

Not subsidy-eligible under most rooftop schemes. PM Surya Ghar and most state subsidies target grid-connected systems.

Common problems

Premature battery failure. Almost always traceable to undersized PV, over-cycling or chronic operation at low SOC. Lead acid batteries that cycle daily below 30 percent SOC die within 18 months.

Inverter overload trips. Air conditioners and pumps with start surges higher than the inverter can support cause repeated trips. Fix by sizing the inverter VA at surge, not at nameplate.

No-load drain. The inverter itself consumes 20 to 80 W in standby. Over 24 hours that is 0.5 to 2 kWh, a significant fraction of a small system. Search mode helps if loads are pure resistive or pure inductive, but causes flicker on mixed loads.

Lightning damage. Off grid sites are often rural and exposed. SPDs on DC, AC and battery DC are essential. Earthing must be tested every monsoon.

User abuse. Adding loads that were not in the original sizing brief is the most common reason for off grid systems failing within two years. Train the user explicitly on what can and cannot be added.

Best practices for off grid inverters

Match charge controller to battery chemistry. LFP needs a current-limited bulk and a near-zero float. Lead acid needs proper absorption time. A controller in lead acid mode will undercharge or overcharge LFP.

Ventilate the battery room. Heat kills batteries. Keep ambient under 30 degrees Celsius wherever possible. For lead acid, vent hydrogen with a passive vent at the ceiling.

Use a low-voltage disconnect. The inverter should cut load at 20 percent SOC for LFP and 50 percent SOC for lead acid. Many failures occur because users override the cutoff.

Document the load list at the time of installation. Use a printed sticker on the inverter naming the maximum simultaneous load. Train the user with examples of what can run together and what cannot.

Use pure sine wave for almost all loads. Modified sine wave kills CFLs, BLDC motors and many LED drivers.

Plan for capacity expansion. Lithium-only systems are easier to expand than mixed chemistry, but each step still requires a balancing exercise and a charge controller resize.

Comparison: off grid vs on grid vs hybrid

For a fuller decision framework across all three architectures, see On-Grid vs Hybrid vs Off-Grid Inverters, The 2026 Decision Guide.

Indian market context

The MNRE supports off grid solar through several streams. PM-KUSUM Component A funds standalone solar pumps. The remote village electrification program under DDUGJY funds off grid micro-grids. State agencies like CREDA in Chhattisgarh and APEPDCL in Andhra deploy off grid systems for schools and health centres.

Telecom operators including Reliance Jio, Bharti Airtel and Tata Communications have moved roughly 50,000 towers to solar-plus-battery operation, cutting diesel usage by 70 to 90 percent.

Off grid inverters for subsidised projects must hold BIS certification under IS 16221 and follow MNRE technical specifications for capacity, surge and battery interface. Listed manufacturers tend to include Su-kam, Luminous, Microtek, Sofar, Victron, Schneider and a growing list of Indian OEMs.

PM Surya Ghar does not fund off grid systems. The scheme is grid-tied by design.

Standards and certifications

Common mistakes

Sizing the inverter to nameplate load instead of surge load. The fridge starts and the inverter trips.

Using lead acid batteries for daily cycling without proper charge controller settings. Premature death within 18 months.

Mixing battery sizes or chemistries. The weakest cell dictates pack life.

Ignoring no-load consumption. A 60 W standby drain on a 3 kWh battery is 50 percent of usable capacity gone before the first load.

Skipping a low-voltage disconnect. Users will keep drawing power past 20 percent SOC, and the battery will reward them with a six-month lifespan.

Putting the inverter and battery in an unventilated cupboard. Heat above 40 degrees Celsius slashes both inverter MTBF and battery cycles.

Sizing PV too small for the daily load plus losses. The battery never fully recharges, and capacity quietly fades.

Forgetting to plan for expansion. An off grid site that runs a fridge today often wants an AC tomorrow.

Key takeaways

An off grid inverter is the right choice when there is no grid, or when the grid is so poor that it is functionally absent. Costs are higher than on grid because batteries do most of the heavy lifting. Sizing must be honest, both at peak surge and across cloudy-day autonomy. Lithium iron phosphate has replaced lead acid as the default chemistry for serious off grid work. Maintenance is simpler than it used to be, but still more involved than a grid-tie installation.

Further reading

For how Off Grid Inverter plays out in real projects, these guides go deeper:

• On-Grid vs Hybrid vs Off-Grid: Decision Guide
• Solar Inverter for Power-Cut Backup, UP, Bihar, MH
• Off-Grid Solar Battery Bank Sizing for India
• WhatsApp Monitoring for Solar Inverters

Sources

• IEC 62109-1, -2, Safety of power converters for use in photovoltaic power systems, International Electrotechnical Commission.
• IEC 62619:2017, Safety requirements for secondary lithium cells and batteries for use in industrial applications.
• IS 16221, Indian Standard for PV inverter safety.
• IS 13314 and IS 14257, Indian Standards for solar lanterns and small standalone PV.
• MNRE Specifications for Off-grid and Decentralised Solar Applications.
• IEC 62257 series, Recommendations for renewable energy and hybrid systems for rural electrification.
• PM-KUSUM scheme guidelines (Components A, B, C), MNRE, Government of India.
• IRENA Off-grid Renewable Energy Solutions: Global and Regional Status and Trends, International Renewable Energy Agency.
• NREL Technical Report TP-7A40-72399, Cost-Optimized Approaches for Off-Grid Systems.