# How many solar panels and batteries do I need

There are people interested in building a photovoltaic system but they do not know exactly how many panels to buy for their system and the batteries that will be needed. In this article we will analyze how many solar panels and batteries I need to store the energy coming from the panels .

## How many solar panels and batteries do I need

We are going to calculate how many panels and batteries we need for a photovoltaic project, starting from a certain energy demand or consumption.
We will express the demand in Watts hours per day (abbreviated Wh / day). Let’s solve this with an example: If we have an appliance that consumes 50 Watts, for 1 hour running it will consume 50 Watts hour (50 Wh is abbreviated); If every day it is turned on for 20 hours, then it will consume 1000 Watts hour day (result of multiplying 50 x 20 and 1000 Wh / day is abbreviated).

## Calculation of the power of PV panels

-Energy demand (DE): 1000 Wh / day  <- is an example, use your own consumption

-Solar radiation in the area (IS): 3 Kwh / m2 / day  <- use the annual average of the installation area

-Factor para compensar pérdidas (FP): 1.2 <- sugerido (1.2 significa 20% más)

Potencia total del arreglo de paneles  = FP x DE / IS = 1.2 x 1000 / 3 = 400 Wp

## Cálculo de la capacidad de las baterías

-Autonomía (AUT, tiempo sin brillo solar): 2 días <- sugerido

-Demanda energética (DE): 1000 Wh/día <- ejemplo

-Eficiencia de las baterías (Rend) : 80% <- asumiendo que son baterías de ciclo profundo

-Descarga máxima (Desc): 50% <- sugerido para no afectar demasiado la vida útil de las baterías

-Voltaje del sistema (V): 12 v <- se sugiere 12 v para sistemas no mayores de 1500 Wh/día

Potencia total del banco de baterías (PB) = (AUT x DE)/(Rend x Descarga) = (2 x 1000)/(0.8 x 0.5) = 5000 Wh

Capacidad total del banco de baterías   = PB/V = 5000 Wh / 12 v = 416 Ah

## Cálculo del controlador de carga*:

Potencia máxima de los paneles (Wp): 400 Wp <- obtenido al calcular la potencia de paneles

Voltaje del sistema (V): 12 v <- valor establecido en el cálculo anterior

Corriente en el controlador =  Wp / V = 400 W / 12 V = 33 A <- si no hay en el mercado,  se sugiere usar el valor comercial superior más cercano

* If a controller with charge and discharge functions is used, also consider the maximum current that will flow during discharge, for example, if a 600 watt device is connected through the controller, the current will be 600 W / 12 V = 50 A, the controller must be able to withstand at least that current in its discharge control circuit!