The choice between off-grid, grid-tied, and hybrid solar is the most consequential system-level decision you will make. Get it right and your capital cost, operating cost, and reliability all improve. Get it wrong and you end up over-spending on batteries you don't need, or buying a system that shuts down every time the grid flickers.
The three architectures in plain English
Every solar installation falls into one of three categories, defined by how it relates to the public utility grid:
- Grid-tied (no battery): Solar inverter connects directly to the grid. Surplus power exports; deficits import. No storage, no backup. Lowest capital cost. Must shut down in a grid outage (anti-islanding safety requirement).
- Off-grid (fully autonomous): No grid connection at all. Battery stores solar surplus for night and cloudy days. Diesel or gas generator provides emergency backup. Highest capital cost. Viable only where grid connection is physically or economically impossible.
- Hybrid (grid-tied with battery): Solar inverter connects to both a battery and the grid. Battery stores solar surplus and provides backup during outages. Grid supplements when solar and battery are both low. Best of both worlds for most commercial sites with a grid connection.
Decision framework: four questions
You can determine the right architecture by answering four questions:
1. Is grid power available at the site?
If the site is remote — a mining camp, agricultural facility, island resort, telecoms tower — and extending the grid would cost more than $30,000–50,000/km, off-grid is typically the only economically sound option. If grid power is available, go to question 2.
2. Does the site need backup power during grid outages?
If the answer is yes — hospital, data centre, food cold chain, 24/7 manufacturing — you need a hybrid system with battery storage. A pure grid-tied system cannot support any load during an outage. If outages are rare and tolerable (e.g., a standard office building), a grid-tied system may be adequate. Go to question 3.
3. Are demand charges significant?
If your commercial electricity tariff includes demand charges above ~$10/kW/month, a battery (hybrid system) pays back through peak shaving independent of backup value. A hybrid system is often justified on demand savings alone, even if backup power is not a priority.
4. Is the grid connection weak or unreliable?
Sites in emerging markets, industrial zones with voltage fluctuations, or areas with scheduled load-shedding benefit from a hybrid system even without high demand charges. The battery absorbs grid quality issues and smooths power delivery to sensitive equipment.
Cost comparison
| Architecture | Typical CAPEX (100 kWp) | Key advantage | Key limitation |
|---|---|---|---|
| Grid-tied only | $55,000–75,000 | Lowest cost, fastest payback | No backup, no demand shaving |
| Hybrid (100 kWp + 200 kWh) | $120,000–160,000 | Backup + demand savings + flexibility | Higher upfront cost |
| Off-grid (100 kWp + 400 kWh + genset) | $200,000–280,000 | Full energy independence | Highest cost, genset O&M |
These figures are indicative for a tropical or temperate site with 4–5 peak sun hours. Costs vary significantly by location, roof type, grid connection distance, and battery chemistry.
Off-grid sizing: the autonomy calculation
Off-grid systems must be sized for the worst case, not the average case. The key metric is days of autonomy — how many consecutive low-irradiance days can the battery carry the site without the generator running.
- Determine daily energy consumption (kWh/day) from utility bills or sub-metering
- Identify your site's worst-case irradiance period (winter minimum in CIS markets; monsoon season in SEA)
- Size solar to cover average consumption during the worst month
- Size battery for 3–5 days of autonomy at average consumption, derated to 80% DoD
- Size generator to recharge the battery within 8 hours if solar is insufficient
For a 200 kWh/day facility requiring 3 days of autonomy: battery = 200 × 3 ÷ 0.80 = 750 kWh minimum. This is why off-grid systems are expensive — battery costs dominate.
Hybrid sizing: the simpler path
In a hybrid system, the grid handles worst-case nights and cloudy periods. You only need enough battery for the primary use cases:
- Backup priority: size for critical loads × backup duration (typically 4–8 hours)
- Demand shaving priority: see our peak shaving sizing guide
- Self-consumption priority: size for evening consumption after solar generation ends (typically 2–4 hours of average load)
A hybrid battery is typically 20–40% of the off-grid equivalent for the same site — dramatically lower cost.
Inverter selection by architecture
The inverter must match the architecture:
| Architecture | Inverter type | Sungrow recommendation |
|---|---|---|
| Grid-tied, < 50 kWp | String inverter | SG30CX to SG50CX |
| Grid-tied, 50–250 kWp | Multi-MPPT string | SG110CX-P2 to SG250HX |
| Hybrid, any size | Hybrid inverter + BESS | SH100CX to SH250CX-V21 + ST255CS-2H |
| Off-grid or weak grid | Off-grid / island-capable inverter | SH series with island mode enabled |
The Sungrow SH series hybrid inverters support seamless switching between grid-tied, islanded, and off-grid modes, making them suitable for sites that start grid-tied but may need to operate independently during extended outages.
Common mistakes to avoid
- Buying off-grid when weak-grid hybrid would work: even an unreliable grid dramatically reduces battery requirements. A 30% grid uptime is enough to size a hybrid system for 70% less battery.
- Grid-tied on a site with frequent outages: your solar generates zero power during the very grid events that matter most.
- Undersizing off-grid battery for autonomy: using annual average irradiance for sizing almost always produces a system that runs the generator daily in winter or monsoon season.
- Ignoring generator compatibility in hybrid: some hybrid inverters require specific generator configurations for seamless charge-from-generator. Confirm compatibility before specifying.