# Solar Panel Output Calculator

> Estimates the energy produced by a photovoltaic array from the panel rating, number of panels, average peak sun hours per day and a performance ratio (default 0.75 for system losses), and optionally the electricity cost saved.

- Calculator id: `solar-panel-output` · Category: Engineering & Automotive (`engineering`) · Tool name: `estimate_solar_panel_output`
- Canonical page: https://tttkmbb.com/engineering/solar-panel-output · This document: https://tttkmbb.com/engineering/solar-panel-output.md · JSON definition: https://tttkmbb.com/engineering/solar-panel-output.json

## Purpose

Estimates the energy produced by a photovoltaic array from the panel rating, number of panels, average peak sun hours per day and a performance ratio (default 0.75 for system losses), and optionally the electricity cost saved.

**Use when:** You want a first-order estimate of how many kWh a solar array will generate per day, month or year, or its yearly savings at a known tariff.

**Do not use when:** You need month-by-month production for a specific location, tilt and shading (use NREL PVWatts or a site survey), or battery sizing (use battery-runtime).

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `panel_watts` | number | W | required | Nameplate STC power of one panel in watts (typical residential panels 350–450 W). (> 0, max 5000) |
| `panel_count` | integer |  | optional, default 1 | Panels in the array. (min 1, max 100000) |
| `peak_sun_hours_per_day` | number | h/day | required | Daily solar irradiation in kWh/m² on the array plane, i.e. equivalent hours of 1000 W/m² sun. Typical annual averages: 3–4 northern Europe/Canada, 4–5 most of the USA, 5–6.5 desert southwest, Australia and southern Spain. (> 0, max 12) |
| `performance_ratio` | number |  | optional, default 0.75 | Fraction of nameplate output actually delivered after inverter, wiring, soiling, temperature and mismatch losses; 0.75–0.80 is typical for grid-tied systems. (min 0.4, max 1) |
| `price_per_kwh` | number | per kWh | optional | Optional tariff in your currency per kWh; enables the savings outputs. (min 0) |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `system_size_kw` | number | kWp | panel_watts × panel_count / 1000. |
| `daily_kwh` | number | kWh/day | system_size_kw × peak_sun_hours_per_day × performance_ratio. |
| `monthly_kwh` | number | kWh/month | yearly_kwh / 12. |
| `yearly_kwh` | number | kWh/year | daily_kwh × 365. |
| `specific_yield_kwh_per_kwp` | number | kWh/kWp/year | yearly_kwh / system_size_kw, a location-dependent figure of merit (≈ 800–1,800). |
| `daily_savings` | number |  | daily_kwh × price_per_kwh (only when price_per_kwh is given). |
| `monthly_savings` | number |  | monthly_kwh × price_per_kwh (only when price_per_kwh is given). |
| `yearly_savings` | number |  | yearly_kwh × price_per_kwh (only when price_per_kwh is given). |

## Formula

`daily_kwh = panel_watts × panel_count / 1000 × peak_sun_hours_per_day × performance_ratio; yearly_kwh = daily_kwh × 365; monthly_kwh = yearly_kwh / 12; savings = kWh × price_per_kwh`

Peak-sun-hour method. The performance ratio bundles all losses; NREL PVWatts defaults to 14 % system losses plus 96 % inverter efficiency and temperature derating, giving about 0.75–0.80 overall. Savings assume all energy offsets consumption at the given tariff (no export rate).

## Data Sources

- NREL – PVWatts Calculator documentation (system losses, performance) — https://pvwatts.nrel.gov/pvwatts.php (government, retrieved 2026-09-24)
- U.S. EIA – Solar explained — https://www.eia.gov/energyexplained/solar/ (government, retrieved 2026-09-24)
- Wikipedia – Photovoltaic system – performance — https://en.wikipedia.org/wiki/Photovoltaic_system#Performance (reference, retrieved 2026-09-24)

Data freshness: `static`. Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output.

## API

- `GET https://tttkmbb.com/api/v1/calculate/solar-panel-output?panel_watts=…&peak_sun_hours_per_day=…`
- `POST https://tttkmbb.com/api/v1/calculate/solar-panel-output` with JSON body `{"inputs": {…}}`
- Response: unified envelope (`success`, `request`, `result.values`, `result.units`, `sources`, `freshness`, `timestamp`, `next_actions`, `links`); see https://tttkmbb.com/docs/response-format.md
- Schema: https://tttkmbb.com/api/v1/calculators/solar-panel-output · OpenAPI operationId `estimate_solar_panel_output` in https://tttkmbb.com/openapi.json
- Authentication: none. Rate limit: fair use, see https://tttkmbb.com/docs/rate-limits.md.

## MCP

- Server: `https://tttkmbb.com/mcp` (Streamable HTTP, JSON-RPC 2.0, no auth)
- Tool:  `run_calculator` with `{"calculator_id": "solar-panel-output", "inputs": {…}}`

## Example

- 10 × 400 W, 4.5 sun hours, PR 0.75, 0.15/kWh: inputs `{"panel_watts":400,"panel_count":10,"peak_sun_hours_per_day":4.5,"performance_ratio":0.75,"price_per_kwh":0.15}` → `{"system_size_kw":4,"daily_kwh":13.5,"monthly_kwh":410.6,"yearly_kwh":4928,"specific_yield_kwh_per_kwp":1232,"daily_savings":2.03,"monthly_savings":61.59,"yearly_savings":739.13}`
- One 300 W panel, 5 sun hours, PR 0.8: inputs `{"panel_watts":300,"peak_sun_hours_per_day":5,"performance_ratio":0.8}` → `{"system_size_kw":0.3,"daily_kwh":1.2,"yearly_kwh":438}`

```
GET https://tttkmbb.com/api/v1/calculate/solar-panel-output?panel_watts=400&panel_count=10&peak_sun_hours_per_day=4.5&performance_ratio=0.75&price_per_kwh=0.15
```

## Limitations

You need month-by-month production for a specific location, tilt and shading (use NREL PVWatts or a site survey), or battery sizing (use battery-runtime). Peak-sun-hour method. The performance ratio bundles all losses; NREL PVWatts defaults to 14 % system losses plus 96 % inverter efficiency and temperature derating, giving about 0.75–0.80 overall. Savings assume all energy offsets consumption at the given tariff (no export rate). All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**What are peak sun hours?**

The daily irradiation in kWh/m² expressed as hours of full 1 kW/m² sun. A site with 5 kWh/m²/day has 5 peak sun hours even though the sun shines for 12; use annual-average values from NREL or PVGIS maps.

**Why not use the nameplate wattage directly?**

Panels rarely operate at the 25 °C, 1000 W/m² test conditions. Heat, dirt, wiring, inverter conversion and mismatch typically cut output by 20–25 %, which the performance ratio accounts for.

## Related

- [Electricity Cost Calculator](https://tttkmbb.com/everyday/electricity-cost.md) — Compare the array's output with your appliance consumption.
- [Battery Runtime Calculator](https://tttkmbb.com/engineering/battery-runtime.md) — How long a battery bank charged by the array lasts.
- [Battery Charge Time Calculator](https://tttkmbb.com/engineering/battery-charge-time.md) — Charging time of a battery from the daily solar energy.