A school is considering installing solar panels on its flat roof. The specifications and daily energy requirements are shown in the table below:
| Item | Value |
|---|---|
| Area of one solar panel | 2.0 m22.0 \text{ m}^22.0 m2 |
| Area of roof available | 120 m2120 \text{ m}^2120 m2 |
| Maximum daily energy output of one panel | 15 kWh15 \text{ kWh}15 kWh |
| Daily energy needed by the school | 840 kWh840 \text{ kWh}840 kWh |
Using calculations based on the data, explain whether the maximum energy generated by the solar panels on the available roof area is sufficient to meet the school's daily energy needs. State one practical reason why the school might still need to rely on the main electricity grid.