Solar PV output
The key idea
The PV array's DC rating is a reference-condition power. Actual AC output also depends on irradiance, cell temperature, losses and the inverter limit.
Follow the energy through the equipment
Sunlight reaches the modules. The modules produce DC electricity. An inverter converts that electricity to AC. Losses occur along the path, and the inverter has an AC power ceiling.
PV reference conditions include irradiance of 1,000 W/m² and a cell temperature of 25°C. The temperature is the cell temperature, not the surrounding air temperature. The simplified power relationship used here follows the form documented by the Sandia PV Performance Modeling Collaborative.
Find the clipping point
Start with a 20 kW DC array and a 15 kW AC inverter. Reduce cell temperature and inspect the noon output. Then increase the DC array rating without changing the inverter limit.
- Array rating
- 20 kW DC
- AC energy
- 119.1 kWh
- Clipped energy
- 1.6 kWh
- DC output
- Delivered AC
- AC ceiling
Read the exact values
| Time / step | DC output | Delivered AC | AC ceiling |
|---|---|---|---|
| 00:00 | 0.00 | 0.00 | 15.00 |
| 01:00 | 0.00 | 0.00 | 15.00 |
| 02:00 | 0.00 | 0.00 | 15.00 |
| 03:00 | 0.00 | 0.00 | 15.00 |
| 04:00 | 0.00 | 0.00 | 15.00 |
| 05:00 | 0.00 | 0.00 | 15.00 |
| 06:00 | 0.00 | 0.00 | 15.00 |
| 07:00 | 4.29 | 4.11 | 15.00 |
| 08:00 | 8.28 | 7.95 | 15.00 |
| 09:00 | 11.71 | 11.24 | 15.00 |
| 10:00 | 14.34 | 13.77 | 15.00 |
| 11:00 | 16.00 | 15.00 | 15.00 |
| 12:00 | 16.56 | 15.00 | 15.00 |
| 13:00 | 16.00 | 15.00 | 15.00 |
| 14:00 | 14.34 | 13.77 | 15.00 |
| 15:00 | 11.71 | 11.24 | 15.00 |
| 16:00 | 8.28 | 7.95 | 15.00 |
| 17:00 | 4.29 | 4.11 | 15.00 |
| 18:00 | 0.00 | 0.00 | 15.00 |
| 19:00 | 0.00 | 0.00 | 15.00 |
| 20:00 | 0.00 | 0.00 | 15.00 |
| 21:00 | 0.00 | 0.00 | 15.00 |
| 22:00 | 0.00 | 0.00 | 15.00 |
| 23:00 | 0.00 | 0.00 | 15.00 |
Model note · Constructed irradiance day. Fixed cell temperature, −0.4%/°C power coefficient and 96% inverter efficiency are teaching assumptions. Shading, wiring, spectral effects and low-light nonlinearities are omitted.
When potential AC output exceeds the inverter ceiling, the delivered curve becomes flat. The difference is clipped energy. Increasing DC capacity can still increase morning and afternoon output even when noon output is limited. This does not prove that a higher DC-to-AC ratio is the least-cost choice; compare annual energy, costs and operating constraints.
Keep different losses separate
Inverter conversion loss occurs even below the power limit. Clipping occurs only when the available converted power exceeds that limit. Shading, soiling and wiring losses are separate effects. Combining them without clear boundaries makes it difficult to explain an output difference.
The temperature slider uses a fixed cell temperature for the full teaching day. A production model estimates temperature over time from its declared thermal model and weather inputs.
The math, if you want itOptional — the page reads completely without it
The DC output scales the array rating by irradiance and derates it with cell temperature, using the linear form on the PVWatts page cited above:
DC power from the array
Pdc = Prated · G1000 · [ 1 + γ ( Tcell − 25 ) ]
bounded below by zero, with γ = −0.004 per °C as an assumed teaching value, not a specification for every module. At G = 1,000 W/m², a 20 kW array gives 20 kW DC at 25 °C and 18 kW DC at 50 °C.
AC power, after the inverter
Pac = min( η · Pdc , Pinv )
With η = 0.96 and a 15 kW inverter, the 25 °C reference point clips 19.2 − 15 = 4.2 kW. Hourly clipped powers integrate to the clipped energy in the readout.
The linear model omits low-light nonlinearities, changing cell temperature, orientation, shading and other system losses. It explains the boundaries; it does not reproduce a full yield model.
See it in Phasor
Set PV and inverter sizes against the project's resource series. Save the design and inspect simulated output and unused energy before selecting a larger array.
Continue the design path
Next, see how battery power and energy constrain the use of surplus solar. Then connect the components through the hybrid plant energy balance.