[groar]

I thought about a little off-the-grid system to supply a laptop. I search the Internet and found the following rules :

• the solar panel must supply every day at least 1.5 times the medium daily consumption
• the battery must permit to supply power during several consecutive days without solar power, generally 3 days is chosen.
• the battery must never be discharged more than 50% to last longer.

As a laptop consumes 20W (mine is currently using 22W with LCD on but background light at 50%, when LCD is off then it's 17W) :

• the solar panel must supply 20 * 24 * 1.5 = 720Wh/day.
  As I live in an area where solar panels supply 5.5 times their nominal value per day they must be 720 / 5.5 = 130W
• the battery will have to supply 720 * 3 = 2160 Wh without solar power.
• the battery capacity will be 2160 / 50% = 4320 Wh.
  As they are 12V, this is 4320 / 12 = 360 Ah.
  Such capacity doesn't exist so it can be obtained with 3 x 120 Ah batteries.

So you have to buy :

• 1 solar panel : 120W (130W doesn't exist). 2 x 60W is also OK.
• 3 batteries : 12V & 120Ah.
• 1 charge controller (plugged between solar panel(s) and batteries)
• 1 inverter (plugged between batteries and laptop)

Several weeks of research on French web sites and the lowest cost corresponded to more than 80 years of electricity for the laptop... the problem is that all that material will not last 80 years :

• the batteries will have to be changed every 5-10 years, and maintained yearly !!!
• the inverter will have to be changed every 10-15 years
• the solar panels will have to be changed every 30-40 years...

As at this time my son was just born and we were then spending a lot of money for him, I couldn't afford to spend 1500€ in such a project and it disappeared (not my son, the project

Denis.