Máximo de decimales: 2; Al más cercano; empates alejándose de cero
Panels
18panels
Size before rounding to panels
6.98kW
Generation per year
11,300kWh
System cost after incentives
$20,160.00
Savings per year
$1,808.06
Simple payback
11.2years
Simple payback ignores panel degradation (about 0.5% a year in the PVWatts manual), price changes and financing, and assumes every kWh offsets a kWh bought at the full price.
Covering 30 kWh a day takes 6.98 kW, which rounds up to 18 panels of 400 W (7.2 kW). They make about 11,300 kWh a year, worth $1,808.06 at $0.16 per kWh, so the $20,160.00 system pays for itself in about 11.2 years.
System size is the daily energy to cover divided by the peak sun hours and by one minus the system losses. Dividing that by the panel rating and rounding up gives the panel count, and yearly generation is the rounded size × sun hours × (1 − losses) × 365. Cost is the size in watts times the installed price per watt, less incentives, and simple payback is that cost divided by the yearly saving.
With the defaults, 30 kWh a day at 5 peak sun hours and 14% losses needs 6.98 kW, which rounds up to 18 panels of 400 W (7.2 kW). They make about 11,300 kWh a year. At 2.80 a watt the system costs 20,160 and saves 1,808 a year at 0.16 per kWh, a payback of 11.2 years.
The 14% default is the PVWatts figure for soiling, shading, wiring and similar losses. PVWatts models the inverter and cell heating separately, so including a 96%-efficient inverter raises the loss to about 17.4%.
Fuente de comprobación: Python decimal: 15 ÷ (4.5 × 0.86) = 3.88 kW → 10 panels; 4,000 W × 3 × 0.7 = 8,400; 5,650.2 kWh × 0.2 = 1,130.04 a year
Preguntas
How many solar panels do I need?
Divide your daily use by the peak sun hours and by one minus the losses to get the system size, then divide by the panel rating and round up. 30 kWh a day with 5 sun hours and 14% losses needs 30 ÷ (5 × 0.86) = 6.98 kW, which is 18 panels of 400 W (7.2 kW). Monthly kWh from your bill divided by 30 gives the daily figure.
What are peak sun hours?
The day's solar energy on the panels written as hours of full sun at 1,000 W/m²: 5 kWh/m² a day is 5 peak sun hours. Panel ratings refer to 1,000 W/m² and a 25 °C cell, so a 1 kW array makes about 1 kWh per peak sun hour before losses. PVWatts, now run by the US National Laboratory of the Rockies (formerly NREL), gives yearly averages for any location.
What system losses should I use for solar panels?
PVWatts uses 14% by default: soiling 2%, shading 3%, mismatch 2%, wiring 2%, connections 0.5%, light-induced degradation 1.5%, nameplate rating 1% and availability 3%, combined by multiplying rather than adding. It models the inverter (96% efficient by default) and cell heating separately, so 1 − 0.86 × 0.96 ≈ 17.4% here covers the inverter as well.
How long do solar panels take to pay for themselves?
Divide the installed cost after incentives by the yearly saving. The default 7.2 kW system at 2.80 a watt costs 20,160 and saves 1,808 a year at 0.16 per kWh, so it pays back in 11.2 years. The PVWatts manual puts long-term panel degradation at about 0.5% a year, and power exported for less than the retail price also stretches the payback.
Is there still a federal tax credit for home solar?
Not for new systems. The IRS says the 30% Residential Clean Energy Credit covered property installed from 2022 through 31 December 2025 and is not available for property placed in service after that date. State, utility and local rebates may still apply; enter them as a percentage in the incentives box to update the cost and payback.
¿Qué precisión tiene «Solar panel calculator»?
La precisión depende de tus datos y de los supuestos del método. El cálculo decimal usa 50 cifras significativas, pero las estimaciones, los métodos numéricos y los datos de origen pueden ser menos precisos; el redondeo mostrado no elimina esos límites. Ejemplos resueltos comprobados con fuentes independientes: 4. Por ejemplo, «30 kWh a day, 5 sun hours, 400 W panels» se comprueba con Python decimal: 30 ÷ (5 × 0.86) = 6.977 kW → 17.44 → 18 panels = 7.2 kW; 7.2 × 5 × 0.86 × 365 = 11,300.4 kWh; 20,160 ÷ 1,808.06.
¿De dónde procede el método?
Dobos, PVWatts Version 5 Manual (NREL, 2014) — system losses default 14%, inverter efficiency 96%; PVWatts calculator, National Laboratory of the Rockies (location-specific sun hours); IRS — Residential Clean Energy Credit.
Solo para planificar. Prestamistas, autoridades fiscales y mercados aplican sus propios redondeos, comisiones y reglas; confirma las cifras con ellos antes de comprometerte.
Verificado con las referencias
Esta calculadora incluye 4 ejemplos resueltos con respuestas de fuentes independientes. Forman parte del conjunto de pruebas y también puedes ejecutarlos aquí.