Solar System Planning and Sizing Examples

Examples for Planning and Sizing

Initial Planning Questions

a. 12 Volts, 24 Volts, or 48 Volts for your batteries?
Battery voltage is difficult to change after your system is built, so choose carefully at the start. 12 volts is simplest and most standard, used in vehicles, RV, and boats. If you want a small simple power system, 12 volts will probably be easiest. You can use 12 volt DC directly in very small systems, adding 120 volt AC with an inverter. 24 volts battery systems have some technical advantage. System size, If you think you will have more than 1000 watts of solar modules, consider 24 volts. A technical advantage is that 24 volt wires can run longer distances. If you must place solar modules over 100 feet from the house for adequate sun exposure, or if your wind generator or hydropower is over 300 feet away, choose 24 volts. Most of your power will be changed to 120 volt AC power. Voltage converters are available to run 12 volt DC equipment from 24 volt batteries.

48 volts has great advantage if longer wire run is unavoidable to reach the only good solar location, up to 400 feet from the house, or hydro turbine 1,000 feet from the house. Presently there is limited selection of 48 volt charge controls and inverters, but these are the best quality, well suited for larger power systems. Voltage converters are available to run 12 volt DC equipment from 48 volt batteries. Charge controls by Outback Power Products and Blue Sky Energy can charge a 12 or 24 volt battery from a 48 volt solar array. With these, power systems of any battery voltage can reach longer distances to place solar modules in the best sun location.

b. Separate Components or a Power Center?
A prefabricated power center is the other choice to decide on at the outset. This costs a little more than separate hardware and components of equal quality, but can save as much in cost of design and installation. You get a clean, safe electric system with just 3 components in the power room: inverter/standby charger, a power center with charge control , and the batteries. A power center may be the only way to pass your local building code inspection. Consider your long term goals. Separate components are suitable for smaller systems, and may allow budgeting for an additional solar module. But where you will be adding on, increasing the power of your system over the years, a power center approach is safer, neater, makes expansion easy, and passes building and electrical codes.
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Finding the right size and cost for your power system

The exact sizing of solar is not terribly risky, since solar modules can be added any time, and since a backup generator can supplement charging if there is a shortfall. There is some flexibility because the power you receive varies with the sunshine of each year and with seasonal changes in weather. Your own flexibility in energy usage, plus use of a backup generator allows you to adapt to temporary shortages, while the automatic charge control manages any overproduction. We caution against the temptation to start with generator, batteries and inverter, but postpone solar modules until later. If you can, start with enough solar modules required to do the job, since this is where most of your power originates. If budget requires, perhaps start with half or a third of the panels, and add the rest in subsequent years. This will help avoid battery problems and save many generator hours. Solar charging is what made home power systems practical! Solar power is modular. When the family grows or the cabin becomes a full time home, you add more solar modules. If you need to upgrade a charge control or AC inverter.

With this flexibility, several methods of estimation can give a close idea of what equipment you need. System Examples of power systems from smallest to largest are described and priced at the end of this page. Choose from these balanced and expandable designs for the best way to a good starting point.
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Usage Calculation:

how many watt hours you will need, then find the number of solar modules to produce that much power in your climate. The method is best learned from one of the books we sell, which contain worksheets and instructions.

Visit Independently Powered Homes in your area:

Notice what works for folks with life-style, family size, home, and climate like yours. The amount of electricity needed depends on the number of people in the house, their hobbies, business activities and conservation habits. Ask about their use of special energy saving appliances.
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