Solar resource and weather
The key idea
Solar output depends on the resource at the site and when it occurs. A weather profile must have the right quantities, units and time basis before it is paired with demand.
Irradiance is a rate
Irradiance, in W/m², describes solar power arriving at a surface. Irradiation, in kWh/m² over a stated period, describes the accumulated solar energy. The relationship is the same as the relationship between kW and kWh in a demand profile.
The surface matters. Global horizontal irradiance describes a horizontal plane; the irradiance arriving on a tilted module plane can differ. A plant model needs a declared method to convert the weather input into the resource seen by the array.
Check the clock as well as the total
Move the timestamp offset below. The daily resource total stays the same, but its peak moves. In a hybrid plant that change can alter how much solar directly supplies the load, how much passes through storage and when the generator starts.
- Daily irradiation
- 6.84 kWh/m²
- Peak irradiance
- 900 W/m²
- Time offset
- 0 h
- Aligned clear reference
- Selected resource
Read the exact values
| Time / step | Aligned clear reference | Selected resource |
|---|---|---|
| 00:00 | 0.00 | 0.00 |
| 01:00 | 0.00 | 0.00 |
| 02:00 | 0.00 | 0.00 |
| 03:00 | 0.00 | 0.00 |
| 04:00 | 0.00 | 0.00 |
| 05:00 | 0.00 | 0.00 |
| 06:00 | 0.00 | 0.00 |
| 07:00 | 232.9 | 232.9 |
| 08:00 | 450.0 | 450.0 |
| 09:00 | 636.4 | 636.4 |
| 10:00 | 779.4 | 779.4 |
| 11:00 | 869.3 | 869.3 |
| 12:00 | 900.0 | 900.0 |
| 13:00 | 869.3 | 869.3 |
| 14:00 | 779.4 | 779.4 |
| 15:00 | 636.4 | 636.4 |
| 16:00 | 450.0 | 450.0 |
| 17:00 | 232.9 | 232.9 |
| 18:00 | 0.00 | 0.00 |
| 19:00 | 0.00 | 0.00 |
| 20:00 | 0.00 | 0.00 |
| 21:00 | 0.00 | 0.00 |
| 22:00 | 0.00 | 0.00 |
| 23:00 | 0.00 | 0.00 |
Model note · Analytic teaching curves, not NASA POWER data, a weather forecast or a measured day. Values are hourly mean irradiance; the shift moves timestamps without changing daily irradiation.
The clear curve is an analytic teaching shape. The reduced-resource choices scale that shape. They are not observations, forecasts or typical meteorological years.
Identify the weather evidence
For a design, record location, provider, year or period, units, sample interval and time standard. State whether the series comes from a measurement, a model, a climatology or a constructed scenario. Keep missing-data treatment visible.
NASA POWER provides hourly data in UTC and local solar time. Local solar time is not automatically the site's civil time zone. Read the time standard in the supplied data and align it with demand before simulation. NASA POWER hourly API documentation.
An annual total can hide a poor week. A representative or climatological year is useful for one question; several actual weather years help explore variability. Neither is a guarantee that the next year will match the simulation.
The math, if you want itOptional — the page reads completely without it
Irradiance G is a rate in W/m². Summing hourly means over the day gives the irradiation H, in kWh/m²:
irradiation from hourly irradiance
H = Σ Gi · Δt1000
A six-hour period at a constant 500 W/m² gives 3 kWh/m². The teaching curve is a half sine that peaks at 900 W/m² at noon and is zero outside 06:00–18:00:
the clear-sky teaching shape
G(h) = 900 · sin( π · h − 612 ) for 6 ≤ h ≤ 18
This is a declared example, not a location-specific solar-position calculation. The timestamp control rotates the 24 samples, so H is unchanged while the peak hour moves.
See it in Phasor
Set the site location, inspect weather availability, then fetch or import the resource series. Check its period and provenance before attaching it to a saved design version.
Continue the design path
Use the resource to understand solar PV output. Return to load profiles and diversity to check that demand and resource use compatible clocks.