EngiMetric Arena / Design Challenge
How many solar panels does a 9.6 kWh/day load need?
Competency Design and sizing primary Quantitative reasoning supporting
What you should take away: Convert daily energy demand into an array rating and a whole-panel count using peak sun hours and a system derate.
The situation
What is happening
An off-grid equipment room uses 9.6 kWh per day. The site has 4.5 peak sun hours, the system derating is 15 % and the selected panels are rated 450 W. How many panels are required?
Given
| Quantity | Value | Unit | Note |
|---|---|---|---|
| Daily energy demand | 9.6 | kWh/day | Equipment-room load. |
| Peak sun hours | 4.5 | h/day | Site-specific design value. |
| System derating | 15 | % | Soiling, heat, wiring and inverter losses. |
| Panel rating | 450 | W | Nameplate at standard test conditions. |
Assumptions this challenge makes
- Peak sun hours are the design value for the site, not an annual average.
- The derating is applied to the array output, not to the load.
- Panels are whole units and are not mixed within the array.
Your call
Your answer
Hints
- Convert the daily energy to watt-hours. Then divide by the peak sun hours to get the array watts before losses.
- Apply the derating by dividing by (1 - 0.15), not by multiplying by 0.85 after sizing.
- Divide the required array watts by 450 W and round up to a whole panel.
Your answer Engine result
Where that comes from
Each limit, checked
Why
- The daily load is 9 600 Wh. At 4.5 peak sun hours the array would need 9 600 / 4.5 = 2 133 W before losses.
- The 15 % derating means only 85 % of nameplate is usable, so the array rating is 2 133 / 0.85 = 2 510 W.
- At 450 W per panel, that is 5.58 panels. Panels are whole units, so the design needs 6 panels (2 700 W).
- The installed array produces about 10.33 kWh/day at the stated conditions, a small margin over the 9.6 kWh load.
- The margin is not a guarantee: a cloudy day, higher temperature or soiling can reduce output below the design value. Battery autonomy is a separate decision.
What this challenge does not establish
- Peak sun hours are a single design value; seasonal variation and weather are not modelled.
- The derating is a single allowance. Actual losses depend on the inverter, wiring, temperature and soiling.
- The calculation sizes the array only; it does not size the battery, inverter or charge controller.
- Panel orientation, tilt and shading are not assessed.