Power Requirements and Solar Power

Power Requirements and Solar Power

  1. Calculate your power requirements by determining each device power needs and adding them to find the total.

Ptotal = P1 + P2 + …

  1. Use the formula, Voltage x Current = Power , V x I = P, where: V = voltage (volts)

I   = current (amps)

P = power (watts)


a. Laptop power requirements: Looking at the voltage, current requirements on the laptop power adapter, I get: 19.5 V DC, 3.34 A

Using V x I = P:   19.5V x 3.34A = 65.13W ~ 65W

b.WiFi Internet Modem:

12 V DC, 3 A

12V x 3A = 36 W

Total Power = 65W + 36W = 101W

Solar Panel Power System

Above shows a diagram of our solar power system, with a solar panel, solar panel charge controller, and 12V Marine battery.

A marine battery is used instead of a car battery because, car batteries are made to put out maximum current for a short period to start the car and marine batteries put out a consistent current for longer periods, which is what we need.

Most solar panels do not come with the solar panel controller but some do. The separate solar panel controllers provide more functionality like a LCD read out with voltage charging information.

Solar panels cost about $100 for 100W, 12V.

Solar panel charge controller cost about $13.

Marine 12V battery cost about $100 and up.

You should also get a DC car outlet, so you can plug useful devices into it like,

an DC to AC 112V converter so you can plug in your computer like you do in a

regular home outlet, and to plug in your internet, wifi Modem.

You can run devices directly off the solar panel charge controller and solar panel, with out a battery but the voltage will vary depending on how much sunlight you are getting so

it is best to use a battery to store the power and get a consistent voltage.

The battery will take hours to charge up completely.

Battery Specifications

Batteries are specified by voltage and Current per Hour (Ah) or Power per Hour (Wh)

Our marine battery specs. Are listed as 12V – 35AH

Using V x I = P (VIP): 12V x 34AH = 420W/h or 420W per hour.

This means we can run devices that consume a total of 100W for about 4 hours, since we only need about 100W of power, that is if the battery is fully charged. If it’s connected to a solar panel, which continuously charges the battery, we may be able to use the battery power longer.

So for our example, we need 101W of power for my internet modem and laptop, so the 12V, 100W battery will give us a little less than an hour of power. Since we have to use a DC to AC adapter to plug my devices into, we will lose some power in the adapter.

If you need more power, then you can add additional batteries in parallel, to keep the voltage to 12V. That is, connect the positive terminal of one battery to the positive terminal of the other and the negative terminal of one to the negative terminal of the other.

Use thick wires, like house wiring, to make the connections because the batteries can produce a lot of current, which can heat up and melt smaller wires.