☀️ On-Grid and Off-Grid Solar Systems
1. On-Grid Solar System
An On-Grid Solar System is connected to the electricity grid.
Working:
- Solar panels convert sunlight into DC electricity.
- The inverter converts DC into AC electricity.
- Electricity powers household appliances.
- Excess electricity can be exported to the grid if permitted.
- A standard On-Grid system usually shuts down during a power cut for safety.
Advantages: Lower electricity bills, no battery required in a typical system, and lower maintenance costs.
2. Off-Grid Solar System
An Off-Grid Solar System works independently of the electricity grid.
Working:
- Solar panels generate DC electricity.
- The charge controller regulates battery charging.
- The battery stores electrical energy.
- The inverter converts DC into AC electricity.
- Stored energy can power appliances at night or during a power cut.
Advantages: Independent power supply, battery backup, and suitability for remote areas.
3. Solar Calculator Formulas
A. Daily energy consumption
\[ E=\frac{P\times T}{1000} \]
- \(E\) = Energy consumption (kWh or units)
- \(P\) = Appliance power (watts)
- \(T\) = Usage time (hours)
B. Required solar panel capacity
\[ \text{Solar Capacity (kW)} =\frac{\text{Daily Energy (kWh)}}{\text{Sunlight Hours}\times\text{Efficiency Factor}} \]
Use approximately 0.75 as a preliminary efficiency factor.
Example:
Daily energy consumption = 6 kWh
Effective sunlight = 5 hours/day
\[ =\frac{6}{5\times0.75}=1.6\text{ kW} \]
Therefore, the estimated solar capacity is 1.6 kW. A practical system size must be selected after checking site conditions and actual loads.
C. Number of solar panels
\[ \text{Number of Panels} =\frac{\text{Required Capacity (W)}}{\text{Panel Rating (W)}} \]
Example: For a 2,000 W system using 500 W panels:
\[ =\frac{2000}{500}=\boxed{4\text{ panels}} \]
D. Battery capacity for an Off-Grid system
\[ \text{Battery Capacity (Wh)} =\frac{\text{Daily Energy (Wh)}\times\text{Backup Days}}{\text{Usable Battery Fraction}\times\text{Inverter Efficiency}} \]
Example: Daily backup energy = 2,000 Wh, backup = 1 day, usable battery fraction = 0.8, inverter efficiency = 0.9.
\[ =\frac{2000\times1}{0.8\times0.9} \approx2778\text{ Wh} \]
Estimated battery capacity = 2.78 kWh.
4. Main Differences
| Feature | On-Grid | Off-Grid |
|---|---|---|
| Grid connection | Required | Not required |
| Battery | Usually not required | Required |
| Power during outages | Usually unavailable | Available if battery has charge |
| Initial cost | Generally lower | Generally higher |
| Main use | Homes connected to the grid | Remote locations or independent power |
Conclusion: On-Grid systems help reduce electricity bills, while Off-Grid systems provide independent electricity using battery storage. Always consult a qualified solar installer for the final system design.
