Calculate/size photovoltaic stand-alone (autonomous) set

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Result of the dimension calculation

Warning: Results are approximate, it is recommended to doublecheck with sales representative and validate your installation before buying materials.

Photovoltaic panel

Here we are looking for the power (peak, expressed in W) from solar panels to be mounted to fulfill your needs according to your geographical location. The formula is as follow :

Pp = Dn / (Yb X Yi X Rd)

  • Pp (Wp) : Peak power (goal)
  • Dn (Wh/d) : Daily needs = 120
  • Yb : electrical yield of batteries 0.85
  • Yi : electrical yield for the remaining installation (charge controller, ...) = 0.87
  • Rd : average daily radiation of the worst month in the plane of the panel (kWh/m²/d)

In your case, result is :

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Pp = 120 / (0.85 * 0.87 * 5) = 32 W

Photovoltaic panels produce electricity from sunlight (solar radiation).

According entered data, 32W of solar panel are required to fulfill your daily needs of 120Wh/d.

See, understand the procedure, the calculation

One possibility could be to have 1 panel(s) monocristalin of 50W each (?). Which extend the unit capacity to 50W


We are looking here for the nominal capacity expressed in ampere per hour (Ah, given in C10)

Cap = (Dn x Aut) / (DD x U)

In your case, result is :

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Cap = (120 x 2) / (0.3 x 12) = 67 Ah

Batteries are used to store electric energy produced by the panels. You will need a battery plant of 67 Ah at 12 V.

See, understand the procedure, the calculation

A wiring hypothesis would be to have 1> AGM 12V 80Ah (90Ah en C20) type batteries, which increases the plant capacity up to 80Ah

Charge controller

The charge controller stands between batteries and panels, its role is to handle batteries charge depending on what the panels can provide.

A wiring hypothesis would be to have a MPTT 75/10 type charge controller(?) on which would be connected 1 panel

A type MPTT 75/10 charge controller, with a 12V battery plant, allows :

  • 145W max panel power :
    • With a total of 1 50W panel(s), we reach 50W (?)
  • 75V max PV voltage of open circuit :
    • With 1 serialized panel(s) of 22V of (Vdoc) voltage, we reach 22V (?)
  • 10A max PV short-circuit current :
    • With 1 parallel panel(s) having 3A intensity (Isc) and a 38% security margin, we reach 4A (?)

Note: serialization multiplies voltage (V) and paralleling multiplies the intensity (I)

All these characteristics are available in the product's technical sheet. You can customize your charge controller characteristics in Export mode.

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Cable diagram

A wiring diagram was established according to panel/charge controller/battery hypothesis :


The converter goal is to transform batteries DC current (here 12V) in AC current usable for standard devices. You need a converter able to deliver the 9W max electric power you need.

An hypothesis would be to choose a 12/180 type converter that goes up to 175W max power with possible peaks at 350W.

Battery controler

It is recommended to have a bettery controleur in order to check battery plant charge state.However, considering the small size of your system, a voltmeter would be more appropriate. With a correspondence table you can approximately determine the charge percentage .

The wiring

Wire section choice ( calculate) is important in order to avoid electricity lossess :

Another and more complete wire section calculator is avalaible at sigma-tec.


Which brings to a total budget between 359 and 508€. Cost of panels support, wire, wire terminal and protection elements (fuse, battery cut-off, ...) is not included.

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Summary (HTML/BBCode)

Your consumption :

This is the most important step for sizing. If you don't know this value go to daily needs calculator

W ?

Geographical location

  • Map
  • Manual

Click on the map to set your position and deduce solar resource :

Latitude : Longitude :

Solar irradiation data is collected on PVGIS .


Sizing of photovoltaic panels


I use a solar tracker on the 2 axes

You can detail the technical specifications of your panel :

  • W
  • V
  • A

Battery plant sizing

This software is preset for lead batteries (AGM/Gel/OPvS/OPzV)

V (?)

You can detail the technical characteristics of your battery :

  • Ah
  • V

Charge controller

You can detail the technical characteristics of your charge controller :

  • W
  • V
  • A


Considering solar flexible copper wiring.