Off-Grid Solar Systems

An off-grid system carries the entire load itself. There is no import to fall back on, no export to be credited and no distribution company in the picture. Generation charges a battery bank, the battery runs the site, and if the design is short the site simply goes dark. That single fact governs every decision below.

Off-grid is the right configuration in a narrow set of situations: remote farms and field pump stations, workshops and telecom or monitoring sites beyond a usable line, and premises where a connection exists on paper but is unusable in practice. It is the wrong configuration almost everywhere else, and it is worth saying why before describing how it is built.

The subsidy position: there is none

Off-grid systems are not eligible for Central Financial Assistance under PM Surya Ghar. The scheme's eligibility conditions require a residential grid connection with a valid consumer account, and exclude off-grid installations explicitly.

That exclusion is not a technicality — it is the largest single cost difference between the two configurations. On a residential connection, ₹78,000 of a three-kilowatt on-grid system is paid by the Government of India. On the same equipment run off-grid, none of it is, and a battery bank has been added.

A grid-connected system that does not export — behind-the-meter or battery-hybrid — can be eligible, subject to state regulatory approval and verification of its reverse-power-relay protection. If you have a connection at all, that route is worth examining before committing to off-grid.

Where the process is genuinely simpler

Off-grid installations do not interconnect, so most of MPERC's RG-39(II) apparatus does not apply. There is no net-metering application, no technical feasibility study, no Letter of Approval, no bi-directional meter to be tested and installed by the DISCOM, and no commissioning inspection to wait on. The distribution-transformer capacity cap that constrains grid-tied rooftop is irrelevant, and so is the ceiling at your sanctioned load.

In practice this removes the two phases of a rooftop project that are paced by someone else, and those are the phases that account for most of the calendar time. An off-grid project is bounded almost entirely by procurement and installation.

What replaces that external process is internal rigour. Nothing external will catch an undersized array or a battery bank chosen on price. The design review is the only review there is.

How off-grid sizing actually works

Grid-tied sizing is forgiving because the grid absorbs error in both directions. Off- grid sizing is not, and it is built from the load upward rather than from the roof downward.

• The load audit comes first. Every appliance, its wattage, its hours, and — for motors and pumps — its starting surge, which can be several times running current and is what actually sizes the inverter.
• Autonomy is the number of days the system must run without meaningful sun. Central India's monsoon makes this the decisive parameter: a bank sized for a clear December is not a bank sized for four overcast days in July.
• Depth of discharge determines how much of the nameplate capacity you may actually use. Lithium ferro-phosphate tolerates deep daily cycling far better than lead-acid, at higher capital cost and much longer life; lead-acid remains defensible where cycling is occasional.
• Round-trip losses are real. Energy stored and retrieved is not energy generated, and a design that ignores charge/discharge and inverter efficiency will be short in the field.
• Seasonal generation varies more than annual averages suggest. Measured irradiance across Madhya Pradesh runs a narrow band statewide, but the monsoon months are what a battery bank has to survive.

Because there is no export, oversizing the array is not wasted in the way it is on a grid-tied system — surplus generation on a good day simply goes uncollected once the battery is full. Undersizing, by contrast, is felt immediately. Off-grid designs are therefore deliberately generous on the array and conservative on the battery.

Equipment

Modules, inverters and structures follow the same engineering standards used on grid-tied work, whether or not a subsidy is involved: IEC 61215 / IS 14286 qualification, temperature coefficient better than −0.4%/°C, minimum fill factor 75%, degradation under 0.5% per year, hot-dip galvanised or AA6063-T6 structures with SS 304 fasteners designed for the wind zone of the site at a factor of safety of 1.5 and a 25-year design life, and minimum ground clearance of 600 mm at the lowest point.

Off-grid adds components a grid-tied system does not have: a charge controller (MPPT rather than PWM on anything but the smallest installations), the battery bank and its enclosure, and protection and isolation appropriate to a DC bus that stays live whether or not anything else is running. Battery siting matters — ventilation, ambient temperature and access for replacement — because the bank is the one part of the system that will be changed within the life of the array.

Solar pumping

Agricultural pumping is the most common genuine off-grid application in Madhya Pradesh, and it is a special case in one useful respect: the load is daytime, and water in a tank is itself a form of storage. A direct-drive solar pump with adequate tank capacity can often avoid a battery bank entirely, which removes both the largest recurring cost and the component most likely to fail.

Where a battery is avoidable, avoid it. That is the single most valuable sentence on this page.

Before you choose off-grid, price the alternative

Ask what a grid extension would cost. Where a line can reach the site at reasonable expense, a grid-tied system with subsidy and net metering will usually beat an off-grid system of equal capability on both capital cost and lifetime cost — because the grid is doing, for free, the job the battery bank is being bought to do.

Off-grid earns its place where that comparison genuinely fails: where no line is coming, where the cost of bringing one is disproportionate, or where the existing supply is so unreliable that it cannot be planned around. In those situations it is not a compromise. It is the only design that works.