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Details of the Solar Energy System used in this small, energy efficient, earth sheltered home.

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Design Tools : System Sizing Estimator
(Note: These design tools require javascript to be turned on in your browser)
System sizing estimator Quick Start guide
Let's get started. I'll figure it out as I go. I want to start clicking buttons!
Just give me the basics. Just give me the short explanation so I can get started.
Give me the complete explanation You better explain it to me fairly completely. I want to get it right.
Brief Instructions for the System Sizing Estimator
Use this estimator to get a pretty good idea of how many Solar Panels you will need to generate electricity and how many Storage Batteries you will need to store that electricity. The estimator lets you make simple choices and then calculates the WattHour usage based on typical configurations. After you see how the estimator works, you can figure your own system size much more accurately by determining the wattage needed for each of your appliances and then manually calculating the required WattHours. This procedure is explained under the details of the Estimator's Calculations below.
Select closest Size and Use factor for each Item
Just click the 'Calculate' button below to see the pre-selected default settings which approximate the typical usage for a small household of 2 persons. Or, select the choices that apply to you from the drop down lists then click the 'Calculate' button below.
System Sizing Estimator
Select size in cubic feet. With an icemaker, select the next larger size.
How many persons are using it? 2 persons is average use (35% run time).
Select a screen size. If it's LCD, select the next smaller size.
How many hours per day is the TV on?
Select a MicroWave Oven based on Power rating (Wattage).
How many minutes per day is the MicroWave used?
Add wattage of lights in all rooms. (four 60 watt bulbs =240 watts)
How many hours per day are the lights on?
LCD displays use less wattage than CRT types. Printers and/or sound systems will increase wattage.
How many hours per day is the computer used?
This section allows you to add power usage from 25 to 1500 watts for extra items or items not included above.
How many hours per day is the device used?
* Number of Solar Panels (80-100 watt)  =
* Number of Batteries (12v @ 105 AH)  =
Refrigerator watts = WattHours =
Television watts    = WattHours =
MicroWave watts = WattHours =
House lights watts = WattHours =
Computer system = WattHours =
Misc items watts  = WattHours =
 Summary of WattHours required
Total daily WattHours required     =
WattHours required for 3 days     =
Battery capacity (50% discharge) =
 Battery Bank size in AmpHours
12 Volt 24 Volt 48 Volt
* NOTE: The number of Solar Panels required is based on a typical 90 watt panel. The batteries are assumed to be standard 12 volt @ 105 amphours.
Detailed Instructions for the System Sizing Estimator.
Step 1 is to calculate the daily WattHour usage of each item. This is done by multiplying the item wattage by the number of hours used each day. The wattage of a UL listed/approved appliance can usually be found near the AC power cord. Sometimes only the voltage (120) and amps (example 1.5) are given. No problem. Simply multiply 120 x 1.5 and you have watts, 180 in this example. P=E*I This is the power formula from Ohm's Law.
SPECIAL NOTE: In the case of refrigerators, freezers, and similar appliances, keep in mind that although they are on 24 hours per day, they actually cycle on and off and really only run about 1/3 of the time. The more times you open the door, the longer they run. In the Estimator, this is figured into the equation.
Step 2 is to add up the WattHour results for all of your appliances. This will give you the total daily WattHours required.
Step 3 is to assume that you want at least 3 days of operation before the batteries need to be recharged. So you multiply the total daily WattHours by 3. In practice, you will only have to be concerned about this in bad weather or winter. See Meters and Monitors for more about keeping an eye on things.
Step 4 is to find the total battery capacity required by multiplying the 3 day WattHour figure by 2. This way, if you run for 3 days without recharging, you will only discharge the batteries to about 50% capacity. You can greatly increase performance and battery life by not going below 50% charge. (except of course for emergencies) Get more information about this in the Storage Batteries tutorial.
SPECIAL NOTE: You can combine step 3 & 4 by simply multiplying the total daily WattHours (from step 2) by 6.
Step 5 will calculate the size of the battery bank in AmpHours. We use AmpHours because this is how batteries are rated. (Kind of how much fuel they can hold). This is figured by dividing the total battery capacity required (from step 4) by your system battery voltage, usually 12, 24, or 48 volts. Simply stated, the higher battery voltage you use, the smaller (and therefore cheaper) size copper wire can be used to connect the solar panels to the batteries. (The Wires and Cables tutorial has a chart for calculating wire sizes.) Here is an example of this calculation: The default values in the Estimator give you a total battery capacity of 21120/12 volts = 1760 AmpHours. Then divide the 1760 AmpHours by the 105 AmpHour rating of a typical 12 volt battery (1760/105 = about 17). In this example you would need about 17 batteries rated at 12 volts & 105 AmpHours each. More information is available in the Watts & Power tutorial.
Step 6 is to determine the number of solar panels you'll need. For this step you will divide your total daily WattHours by your solar panel wattage times the hours of sunshine. Example: 3520/(90*5)=8. The Estimator uses the value of 450. This assumed a 90 watt solar panel times 5 hours average daily sunshine for mid latitudes in the US. So, using the Estimator's default selections as an example, you get 3520 daily WattHours divided by 450 = 8 solar panels rounded up to the next panel. See Solar Radiation to find the number of average daily hours of sunshine for your area.
DISCLAIMER : Alway make sure that all of your equipment is properly fused and grounded for safety. Also, be sure to read and follow the advice and instructions that come with your equipment. Additionally, our Design Tools, while reasonably accurate, are not meant as a substitute for the recommendations of a licensed electrician. We provide these Design Tools as a guide only and to assist in the explanation of the information presented. We do not warrant their accuracy where equipment is improperly installed or operated under extreme or unusual conditions.
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