Common Solar Power related questions and answers

• Author: DigitalMind
• Filed under: Solar Power and Off-Grid Living
• Date: Sep 14,2008

I spend a lot of time monitoring the search terms that send people to Techie NATION, and I’ve found that lots of them are related to power consumption and knowing how many solar panels or batteries you need for a specific product.  Although i’ve talked about these things before, I will try and address these very simple questions one more time.  For anyone that is confused about a certain subject, you’re welcome to send me an email or ask questions in the comments section and you will get replies.

1 - How do I calculate my daily power consumption ?

To know this, you simply figure out how many Watts each electrical item takes.  (Look at the label of the power supply, or on the item itself, it will at the very least say how many volts it takes and how many amps it takes.)  You multiply the volts by the amps and the answer will be the amount of WATTS that that appliance takes PER HOUR of run time. Then you multiply that by the amount of hours it will be running per day and you have your total daily watts for that item per day.  You continue to do that with all other electrical products you plan on running on solar and add up all the WATTS and that will give you your daily power consumption.

Certain items are harder to calculate power consumption.  A fridge is a good example because it takes LOTS of current to get the compressor started and to get the fridge to a certain temperature, and then it takes very little power to maintain it.  I’ve always called the fridge manufacturers and ask them for the power consumption specifications.  They’ll usually tell you the average Kilo-watt hours it takes per year.  You simply divide that by 365 (days) and it’ll give you the average daily power it uses in Kilowatts. (Multiply by 1000 to get it in watts)   I’ve always been surprised that most manufacturers customer service departments ACTUALLY do have this information on hand.  If there is no way of contacting the manufacturer, it’s sometimes easier to purchase a kill-a-watt meter that will measure the power consumption of ANY electrical device you want.

2 - How many solar panels do I need  ?

The most important part of figuring out how many solar panels you need for your solar power system is to figure out your DAILY POWER CONSUMPTION. (Explained in the question above this one)  This is very important, and you shouldn’t go any further until you know more or less how many watts of power you use per day.  When you do know how much power you need per day, it’s easy to figure out how many solar panels you need.

Another thing you need to know is the average amount of sunlight you have per day in your area.  (It’s best to not be optimistic on this)   Where i’m at in Canada, I calculate 4 hours of peak sun on average per day.  (Winter has little sun, but the summer has LOTS of sun, averages out to about 4 hours per day)

Now you simply divide the TOTAL WATTS you use per day by the average hours of sunlight you get per day, and that will tell you how many watts you need to generate per hour.

Solar Panels are rated in Watts.  The number it gives (lets say a 100 watt solar panel) is the amount of power it generates per peak hour of sunlight.  So a 100 Watt Solar panel will generate 100 watts in 1 hour, and 400 watts in 4 hours.  So if you figured out in the previous step that you need to generate 400 Watts of power per hour, you would need either 1 400 Watt panel, or 4 100 Watt Panels, or 8 50 Watt panels. (etc, etc, etc …)  It’s always best to get a little more panels than you think you need.

You can read my other post about deciding how many solar panels you need and how to calculate your power consumption by clicking here.

3 - How many batteries do I need for my solar powered system ?

The simple answer is that you want double the battery power than what you’ll be using every day.  To keep the batteries alive, you want to drain them the least amount possible.  50% is the MAX that you should drain them.  So if you use 1000 Watts per day, you need a battery bank that’s capable of holding 2000 Watts so that you don’t discharge them more than 50%.

Batteries are usually labeled with their Voltage and AMP HOUR capacity (AH).  Once again multiply the volts by the amps and you’ll get the amount of WATTS that this battery holds.

For more information about batteries for your renewable energy system, click here.

4 - How much power does a 60 Watt light bulb take ?

you wouldn’t believe how often I see questions like this. I almost wish I was making this up.  It takes 60 WATTS ! (Per hour of run-time)   Watts is a universal way of calculating power consumption because it takes into account the voltage it works at and the current that it draws.  Volts * amps = Watts.

As crazy as this sounds, a 100 watt bulb takes 100 watts, and a 75 watt bulb takes 75 Watts.  Spooky eh ? 

5 - How many solar panels to power my house ?

Read questions 1 and 2

6 - Can you help me set-up my system ?

Yes, simply send me an email to digitalmind (AT) techienation (DOT) com.  I give lots of free tech support and help by email and chat.  I’m open to travelling to certain places and helping with solar setups in exchange for simply being taken care of while i’m down there.  (A place to sleep and food to eat, i’m not picky ) I am located in Montreal, Quebec, Canada.

If you’ve made it this far, you’d probably be interested in reading about my small $600 solar power installation by clicking here.  OR, read about SolarSuno’s recent installation in Spain (with a little tech support help from TechieNATION) by clicking here !.

If you’re looking for LOTS of information on solar power and wind power systems, you might consider buying these sets of e-books that are filled with tips and tricks for solar and wind power.

If you have any more questions, please contact me at the address above or leave a comment here. Thanks for reading and visiting TechieNATION !