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Calculate Power Needs

We need to calculate how many WATT hours we will need. Then find the number of solar modules (Panels) needed to produce that much power based on our location.

Start by finding how many watts each appliance needs. Be sure you use watt figures from special energy-efficient appliances recommended for solar electric homes, like compact fluorescent bulbs and solar-electric designed refrigerators. Do not add appliances that should be propane fueled.

Then multiply listed watts of each appliance by the number of hours per day, on average, that appliance runs. This gives watt-hours per day for that light or appliance. Do this for each appliance. The total for all appliances is your total watt-hours needed each day.

So lets us my ICOM 746 Pro Radio that uses from 5 to 100 watts. Lets use 100 Watts.

100 x (How many hours I need to use this in a day) = Watt hour per day

100 x 8 = 800 watt hours per day.

Take into consideration the type of batteries you will use to run the radio. If I have a Deep Cycle Marine Battery I can use the battery for powering the radio while I am charging the batteries with the solar panels.

On a fully sunny day, each solar module produces the equivalent of six hours of its maximum charging ability. Divide your total watt-hours needed each day by six. Theoretically, this calculation tells you how many rated watts of solar modules you need to produce your day's power from a day's sunshine.

So we said 800 watt hours per day. We will divide 800 by 6 = 133.3. (So we need solar panels that will produce at least 133.3 watts per day).

Now for the trickey part. We need to add 50% more solar watts to allow for solar panel derating (actual working watts is less than theoretical maximum rating) and for power loss in wiring, batteries and inverter. This gives the watts of solar we need to install if every day is fully sunny.

133.3 + 50% = 200 Solar Watts.

OR (Being in Hawaii I could probaly go with 10% since it is sunny quite a lot.)

133.3 + 10% = 146 Solar Watts.

Sun Hours per day in Honolulu, HI.   Honolulu is in ZONE 1.
HIGH: 6.71
LOW: 5.59
6 Hours of full sun each day on average.
Just go here and it will do the calcuations for you.

A good website.

 So at Costco's they have the solar back up below. I believe that I would need 3 of these to run my radio for 8 hours a day.

Sunforce 60 Watt Solar Back Up Power Kit  with 1.8 Watt Solar Battery Maintainer

7 amp Battery Charge Controller, 200W Inverter


Determine your solar needs  |   Estimating your solar needs  |   How to Determine How Many Solar Panels Your Home Needs | Home Power |

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