# Setting up a Solar Power System

Before doing ANYTHING, think CONSERVATION! Every 1kw removed from your consumption will save approximately \$7,000- \$10,000 in equipment cost. Simple power saving measures, such as using LED bulbs and avoiding power hungry devices like photocopiers and water heaters, can save thousands of dollars. There are low power copiers on the market, while water heating and cooking can be done using gas.

Use the solar sizer spreadsheet as a guide to help ascertain the loads of your equipment.  Please note that the spreadsheet provides only an estimate and it is more accurate to get the loads from the EXACT equipment you will use. For example, not all laser printers are equal – a black and white Xerox can use as little as 300W whereas a power hungry HP could be as much as 1000W. Think carefully about these item procurement choices before ordering. A 1.5kW photocopier is an expensive doorstop.

### Steps to setting up Solar Power

Step 1 – calculate the daily WattHour usage of each device that needs power. This is done by multiplying the item wattage by the number of hours used each day. The wattage of an approved device/appliance can usually be found near the AC power cord.  Sometimes only the voltage (240) and amps (example 1.5) are given. In this case, simply multiply 240 x 1.5 and you have watts, 360 in this example. (P=E*I — This is the power formula from Ohm’s Law (Power = Voltage * Current))  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 Solar Sizer excel, this is factored into the equation.

Step 2 is to add up the WattHour results for all of your devices. This will give you the total daily WattHours required.

Step 3 is to assume that you want at least 1 or 2 days of operation before the batteries need to be recharged. So you multiply the total daily WattHours by 1 or 2. In practice, you will only have to be concerned about this in bad weather or very overcast conditions. A charge controller should be an integral part of any system so you can keep an eye on battery charge levels.

Step 4 is to find the total battery capacity required by multiplying the 1 or 2 day WattHour figure by 2. This way, if you run for 1 or 2 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 in emergencies.) Get more information about this in the Storage Batteries document.

Step 5 will calculate the size of the battery bank in AmpHours. We use AmpHours because this is how batteries are rated. 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 document has a chart for calculating wire sizes.) Example: 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.

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.

Alterntively, you can click on the following link to find the Average Daily Hours of Sunshine by scrolling to the bottom, putting in you location and utilizing the calculator to find your total solar hours  (This URl is best in Google Chrome).

Step 7 is to procure your calculated needs!