- Determine the appliances within your solar power system. Go to each unit, note how many watts it consumes, and then form an estimate of that appliance's daily usage. Every appliance should have this information on a plate (usually with the UL logo) on it. Light bulbs depend on the wattage of the individual bulb. Wattage is an hourly consumption figure, making this easy to calculate For example, let's take a laundry room, which on a typical usage day has two 60 watt light bulbs for three hours (360 watts) and two uses of the washing machine (2,300 watts) for a total of 2,660 watts.
- Convert the wattage figure to amps. You will also need to know the voltage, which for our example will be the typical American outlet voltage of 110 volts. The formula is amps = watts/volts. In this case, that is amps = 2,660/110, or 24.1 amps.
- Use the amps determined in Step 2 to describe the needs of the solar system's battery. To prolong their lifespan, batteries should never be drawn below half of their capacity, so that means the battery should be 150 percent of the amps from Step 2. In this example, that is about 36.2 amps. If any rounding off needs to be done, round up to increase the margin of power available. So, the system needs a 110 volt battery with at least a 36.2 amp capacity. Let the available batteries guide your choice, but always go up on the amps.
- Determine the total power output that the solar panels need to achieve. Your panels need to be selected on the basis of meeting the entire 2,660 watt demand determined in Step 1 during the standard 6 hours of full daylight they will receive. That requires a minimum of 443.3 watts. Let the available panels guide your choice, but as with the amps, always go up on the wattage output when a rounding-off is needed.
- Measure the space proposed for your solar panels. This is a physical limit on the placement and arrangement of your solar power system, and may influence your choice of panels. A good space-saving solution is to use solar shingles.
- Using the figures determined so far, and go shopping for your battery or batteries, and solar panels. Note your proposed choices. Remember the dimensions of the space the panels will go into, and sketch an arrangement for them to make sure their placement will work.
- Use the information collected in Steps 1 through 6, shop for and choose a fuse box, charge controller for the battery and inverters. The inverter may be necessary if there are any AC appliances on the system. Light bulbs can be run on DC current, but the washing machine will need an inverter to convert to AC current.
- Consider adding other solar-powered items to your system. For example, this system could swap the light bulbs for solar tubes to provide light, eliminating that electrical demand. Also, the home's gas water heater could be replaced with a solar water heater. While outside this system, that would cut the gas bill substantially.