Remote Home Solar Power
The pleasures and independence of remote living can be rewarding if one's lifestyle is suitable to the peace and quiet of the Toolies. However, some planning is required to allow one to live with most of the comforts of town. The biggest consideration for a remote home is the method of providing electricity.
Utility line extensions typically range between $15,000 and $40,000 per mile with significant up-keep costs attached to a monthly bill. A gasoline, propane or diesel generator running 24 hours per day can cost approximately $600 per month to keep fueled and operable. Running a generator this much almost requires one to be a mechanic capable of troubleshooting and repairing, if not overhauling, an engine.
Photovoltaic power, on the other hand, may initially cost between $10,000 and $25,000 for a comfortable system. After the initial investment, the daily operational cost is effectively free and the maintenance is that of adding water to the batteries three or four times a year.
When deciding to use solar power as the main source of electricity, one must be aware that the amount of watts consumed by lights and appliances in a 24 hour period must be replaced in a relatively short amount of time - called the Peak Charging Time - when the sun is at its highest during the day. During the Peak Charging Time in Arizona of 5 hours, each watt in the array of solar modules will generate 5-watt hours. Given that the solar array will produce a limited amounted of power each day, one's power consumption must be planned and as efficient as possible.
Intelligent alternatives must be found for such high wattage loads as those for electric space heating, air conditioning and water heating. For example, a well insulated (R-50+) building will eliminate the need for air conditioning; solar thermal water heating is excellent for hot water needs as well as radiant floor heating, and propane is an inexpensive heat source for cooking and clothes drying. Smaller wattage, efficient appliances such as compact fluorescent lights, televisions, stereos, computers, ceiling fans, microwave ovens etc., are very suitable for solar electricity. High efficiency refrigerators and freezers (500 to 1500 watt hours per day) that are now becoming available are also good choices.
Determining the power requirements is the first step in planning the power supply for a home. Calculating the total watt-hours per day to be consumed is the key factor when accurately sizing a solar electric system. This calculation will not only determine the wattage of the solar array, but will also determine the battery bank capacity, and the type and size of inverter and charge controller.
The solar array is a bank of panels, each producing a specific amount of watts per sunlight hour. Nominally tilted the same degree of the location's latitude and facing south, the modules will produce the most power when perpendicular to the sun. Stationary racks will require adjusting twice a year for maximum output, tracking racks that follow the sun across the sky can increase power output up to 35% on a daily basis. Solar modules are generally warranted for over ten years with a life expectancy of over thirty.
The deep cycle batteries used in a solar electric system are designed for a slow discharge and recharge unlike a vehicle battery that is designed for a quick discharge and quick recharge. A deep cycle battery can be discharged to 80% without damage, (however a regular discharge of this depth will significantly shorten its life). The battery bank must be capable of storing five days worth of the required daily watt-hours. This storage capacity allows for reserve power during cloudy days as well as supports a maximum daily discharge of only 20%, extending the life of the battery to its maximum of 12 years for a typical 370-amp hour battery.
The charge controller monitors the charge of the batteries and prevents the solar array from overcharging the batteries. The capacity and cost of the controller will depend on the present and future size of the array.
The inverter transforms the Direct Current (DC) from the batteries to Alternating Current (AC) at the 120 Volts so that standard electrical appliances can be used. With inverter efficiency of up to 95%, there is no longer any need to use 12V DC appliances or lights that tend to be more specialized and expensive.
There are many sizes and types of inverters to choose from. Sine wave inverters, which imitate the power curve of a utility generator, are becoming more popular for their quiet signal and ability to run motors more efficiently. Most inverters include a battery charger and can accept power from a back up generator when needed.
When planning a solar electric system, one must keep in mind that although the batteries, controller, and inverter should be chosen to allow for system growth, as one's power needs increase, more solar modules can always be added.
