- Filed under: Solar Power and Off-Grid Living
- Date: Apr 11,2008
I’ve already written a few articles about solar power, this one is going to be ONLY about figuring out how many solar panels you need to buy to meet your electrical needs.
If you’re currently living with “regular” power, and are wanting to switch it all over to solar, you’re in for a pretty large investment. (Well over $10000) However, if you just need some power for a weekend cottage, an RV, a garage, etc ; solar power may be a great option !
The first step is figuring out how many WATTS of power you use every day. Basically, Watts = Volts * Amps. I do all my calculations in WATTS. If you don’t know what a WATT is, just think of it as a unit of power. That’s all you REALLY need to know to understand this article.
Most household appliances run on either 120 volts AC (The Americas), or 220 VOLTS. (Most other places) You should atleast know what you’re running before going any further. If you don’t, i’m sorry, I can’t help you. Maybe you can send me an email telling me where you live …
Make yourself a chart listing everything you NEED to run on solar electricity, how many hours per day you want to run it, and how many AMPS it takes. (Look on the unit, under it or behind it, there should be a sticker that says INPUT 120 volts XXXX amps or something along those lines) Multiply the volts by the amps and you will get how many WATTS that thing takes per hour of run time. Add that to your chart for each item.
Here is a small chart of the approx. watts per hour certain things take (List from EVSOLAR) :
|Blender||300||Refrigerator (20 cf.)||150|
|CB radio||5||Satellite dish||30|
|CD player||35||Sewing machine||100-500|
|Ceiling fan||10-75||Table fan||1-25|
|Coffee maker||800-1200||TV: 25″ color||150|
|Computer||80-150||TV: 19″ color||70|
|Dishwasher||1200-1500||TV: 12″ B&W||20|
|Dryer (elec.)||4000||Vacuum cleaner||200-1200|
|Elec. blanket||200||Waffle iron||1200|
|Elec. clock||3||Washing machine||500|
|Evap. cooler||300-1000||½” Drill||900|
|Frying pan||1200||71/4″ Circ. saw||750|
|Garage door opener||350||Lights:|
|Garbage disposal||450||100W Incandescent||100|
|Hair dryer||900-1500||60W Incandescent||60|
|Laptop||20-50||25W Comp. flourescent||28|
|Microwave||600-1500||15W Comp. flourescent||18|
|Printer: laser||300-475||42W Halogen||42|
|Printer: ink jet||60-75|
Running a standard fridge on solar power is tricky. I wouldn’t recommend it. You have to get a fancy 12 volt fridge, or a propane fridge. Otherwise you’re looking into a LARGE investment to get the proper inverters to support the start up load and enough solar panels to keep up. That’s not what this article is about though.
So now you should have a chart with all the electrical things you want to run, how many hours per day you will run it, and how many watts per hour it takes while running. Multiply the WATTS by the HOURS for each item, and then add up all your readings. This will tell you how many watts per day you will be using.
At this point in time, you need to decide how often you will be using this amount of power. If it’s for a weekend cottage, you don’t need to recharge the batteries in one day, you have all week to charge the batteries to last a weekend. If you’re using it for an off-grid house however, you need to replenish your battery bank on a daily basis. For this article, we will pretend you need to replenish the battery bank every day.
Lets say you NEED 1500 watts of power per day to run all of your electrical needs, EVERY DAY. This means you need your solar panels to add atleast 1500 watts of power into your batteries. (off grid solar systems ALWAYS runs on batteries. Panels charge a bank of batteries, batteries powers inverter, and inverter supplies regular 120 volt electricity) I like to not be too optimistic when sizing systems, so I pretend there’s only 4 hours of useable sun per day. So we need to create 1500 watts total in a day, and we have 4 hours to get it in. 1500 watts divided by 4 hours means we need to make 375 WATTS of power per hour.
Solar Panels are rated in this format as well. (Watts per HOUR). If you research solar panels, and one is advertised as being 100 Watts, it means it creates 100 watts of power per hour of sunlight. We’ve decided above that we need 375 Watts of panels in order to meet our minimum power requirements. In this case, I would buy 4 100 WATT panels to make 400watts per hour of sunlight. (Times 4 hours means 1600 Watts into the batteries every day, enough for all your power needs and to make up for Inverter losses)
THAT’S how I calculate how many solar panels are needed for your solar array.
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 power.
Stay tuned at TechieNATION.com for my future article about figuring out how many batteries you need for your solar installation!