No problem Francisco.
Typically, my computer and monitor will draw around 11 amps at 12 volts dc nominal, from my 600 watt Samlex pure sine wave inverter. This is at night when, of course, there is no sunshine so its all from the batteries.
11 amps X 12 volts = 132 watts
So for each hour that it is on, being used, thats .132 kWh's. If I am on the computer for 8 hours that would be,
8 hours X .132 kW's = 1. kWh (By the way, a power company might only charge about $0.12 for that.)
Now to figure out what it would take to create an off grid dedicated PV system just for that (and maybe a small desk lamp), I would look at the 11 amps and multiply that by 8 which is 88 amp hours. To size a battery bank I would at least multiply that 88 amp hours by a factor of 5 so that, what is used from the batteries is only the top 20 percent of battery capacity. Doing this helps the batteries to live an over all longer life and it is easier for the PV array to recharge them the next sunny day.
5 X 88 = 440 amphour battery bank at the 20 hour rate.
Remember, this example is at 12 vdc nominal.
Your location would have about 5 to 6 hours of equivalent full rated power from a single PV module.
http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/ This is based on an average over one year with the PV module mounted at an angle equal to the latitude, facing solar south. What this means is, if it where a single 100 watt PV module, in a whole days time it might make as much as .5 kWh's. There are a lot of factors to take into account for your exact site like; trees, buildings, smog, and of course, the weather.
Now to figure out what I would need for a PV array.
I would take that 1. kWh and divide that by 5 hours of equivalent full rated charge, 1000 / 5 = 200
So at the very least I would need a 200 watt PV array. I would probably increase that though. Maybe even double it to a 400 watt PV array. Doing that could make a big difference in keeping the battery bank in the top 20 percent of full charge on those cloudy days and such.
From this example I would know that if I wanted a dedicated PV system for my computer I would need at least a; 400 watt PV array, 440 amphour battery bank, 200 watt pure sine wave inverter and of course, PV array mounting, charge controller, wire, conduit, breakers, fuses, disconnects, etc., etc..
There is quite a bit of stuff to safely conduct all this power and you will need to know the correct size and type wire, breakers and, such for each particular use such as PV array to charge controller or batteries to inverter.
Me personally, I keep a fire extinguisher near my stuff. You just never know when or why but something can happen. I have learned that, when dealing with electricity its not so much a matter of probabilities as it is possibilities. It may not happen but it can happen and thats enough for me. One can reduce the probabilities of an electrical fire greatly if one follows the NEC. (National Electrical Code)
http://www.nfpa.org/index.aspMy only advice to you Francisco is, if you plan on designing and installing your PV system yourself, take your time now and learn all you can about safely conducting electricity. If you are not, or don't have a friend, that is an electrician familiar with the NEC, make one or learn the Code.
Some more places to learn are;
http://photovoltaics.sandia.gov/ (Look accross the top of the page at the above site and go to "publications" then scroll down to "codes" and go to "John Wiles code corner." These articles were written and published in Home Power magazine.)
and then there is,
http://www.dsireusa.org/index.cfm?EE=0&RE=1