You can get a rough idea of what each PV panel will power by doing some simple sums. Assume 60% efficiency in the system, less than full sunlight, battery losses, inverter losses. Assume 12 hours of sunlight, obviously more in Summer, less in Winter. so say 60W panel gives 60 x 12 x 0.6 = 432 Watt hours of useful output per day. So you could run a 6 x 12W compact fluorescent bulbs for 6 hours, or 12 for 3 hours. Or you could run a 120W TV screen for 3.6 hours. Or run a 900W electric iron for 29 minutes.

You get the picture, you don’t get much energy …. A 120W panel gives you twice as much of course.

The cost of the solar set up is much greater than the cost of electricity in most cases.

The better savings are in improving your power conservation in the first place. Use LED lights, they give more light for less electricity used and last much longer and have cool options like dim-ability and colour change effects if you want. Avoid using electricity for heating cooking, that uses lots of electricity for little return, use solar heating, insulation and heat pumps instead of ‘heaters’.

If you want to go solar of course you should do all that as well to reduce your electricity use, but the savings are in the reductions.

I run an entire office with 10 staff all using computers on less than 8.4KW, so that is more than enough for a domestic house. [provided you use it wisely.]
References :

Home Power Magazine liked out idea so much 10 years ago that they ran an article on doing just what you are talking about. You should really subscribe, it is inexpensive and they are the only periodical that gets into the nuts and bolts of this. Then try to make it to one of the energy fairs listed in the back of the mag, we did 13 years ago, and now out cabin is completely powered by the wind and sun, both the AC and DC systems. If it were me, I’d start with 4 golf cart batteries and maybe a 120 watt panel. With this type setup, you don’t even need a charge controller. The charge controller is the part that always breaks down first in these systems. Our system today uses 2 50 watt panels for a total of 100 watts solar, 4 golf cart batteries, and no charge controller. Been that way for years with no problems. Just remember to put distilled water in the batteries each month.

The only thing you need between the panel and battery besides wire is a diode, which is an electrical check valve. This prevents the battery from back feeding the panel at night. Check out Richard Perez’s book on batteries, it should be in your library. He is the founding editor of Home Power by the way, and a really cool guy.

Even though we have regular AC power now, we still charge cell phones, run night lights, cabinet lighting, radios and phone answering machines on 12 volt, because we can. At night, I can even shut my inverter off and these important items keep running. Home Power will have lots of great articles with specs on parts, data and wiring diagrams. If you subscribe, you have access to the archives on their website and you can look for articles in the past that have info you need. Look for one called, Small System First, to read about out cabin. And be careful asking hacks like us online for advice, it is always amazing to me how many people are willing to offer advice on this subject, having never laid a hand on a panel or wind turbine. Take care Peter, Rudydoo
References :
Home Power Magazine, Homepower.com
Solar Energy International, Solarenergy.org
Midwest Renewable Energy Association MREA.ORG
American Wind Energy Association, AWEA.ORG
The Complete Battery Book, by Richard Perez, library
Superbrightleds.com

I know two people who run their houses off 12 systems, and 2 who have 12v lights and fans as backups for when the grid goes down……
References :

Also to be considered in the average supply of these whats when considered over a 24 hour period. A 60 watt panel may provide 60w in ideal conditions, and so will probably charge a laptop, or phone but probably not run a laptop.

Also if you want to run somting at night like a light bulb you will have to stor the power in batteries, maybe use an invertor to convert 12v flow to 240v all of these tings will loose power so a 60w panel may only just power a light bulb of say 12 watts after the powwer has been "messed about with" through the various efficiency losses of invesrion etc.

http://www.southwest-environmental.co.uk/projects/Sustainability%20Statement.html

If you want to save some power I would go for hot water solar, to heat water for baths / washing up, it is very low tech, and cheaper than PV (photo voltaic), you could probably make a crude system your self. Loads of energy is used in home to heat water, why not start there.

Regards

Will

http://www.environmental-consultants.info
References :