A Closer Look at Components
Although several types of solar panels are on the market, the performance of all depends primarily upon two factors: Intensity of sunlight and cell temperature. Panel output current is directly related to the amount of sun striking the panel. Even faint shading will reduce the sun's intensity. Output voltage is affected by panel (cell) temperature, and this becomes a problem in hot climates. Either of these conditions will reduce a panel's output power and thus increase battery charging times. 

There are two main types of charge control approaches. A series controller is basically a voltage controlled switch. It monitors the batteries and opens a relay to disconnect the array when the fully charged voltage is reached. A more advanced PWM (pulse width modulation) controller pulses array current into the batteries in order to hold the fully charged voltage. This allows for more complete charging to occur.  A diversion controller diverts excess power to an auxiliary load (such as a heating element) when the batteries reach a full charge. The excess power is deliberately burned off. This is a necessary control method when either wind or hydro energy is used as a charging source.

A battery is an electro-chemical storage device, accumulating power for later use. Storage also allows heavy loads which require more power than is generated instantaneously by the array to be run. Battery capacity is rated in units called amp-hrs, which is the amount of current the battery can supply over a 20 hour period. The best balance of performance vs. cost is found in deep cycle lead acid batteries. Lead acid batteries are composed of lead plates and an electrolyte solution of sulfuric acid (25%) and distilled water (75%). 

Temperature has a significant affect on lead acid battery capacity. Batteries should ideally be kept at room temperature. It's important that lead-acids be maintained at or near a full state of charge if exposed to freezing temperatures. At a low state of charge, the electrolyte is a higher percentage of water, making its freezing point higher. Note: Only deep cycle batteries should be used in a renewable energy application. They are made to survive continual deep discharge/recharge cycles.

Inverters are available with either sine wave or less expensive modified sine wave AC wave form output. A sine wave inverter produces a high quality wave form which closely resembles utility power. Since AC appliances are designed to be powered by a sine wave, no degradation in performance will occur. A modified sine wave is of lesser quality but still compatible with most AC appliances.  Modified sine wave power will, however, generate radio frequency interference (RFI). This RFI will be may manifest as background noise on the telephone, make AM radio unlistenable, and create vague “stripes” on TV and computer monitors. The effect of RFI can be reduced or eliminated through proper shielding and wiring practices. 

In addition, some electric devices are incompatible with the modified wave form, and may be damaged as a result. Laser printers and less expensive cordless tool chargers may fail. Microwave ovens may take longer to cook when battery voltage is low. Ceiling fans may emit an annoying buzz under slow speeds. 

Despite these peculiarities, modified sine wave inverters are attractive due to their lower cost. A competent designer/installer can suggest ways to make these obstacles invisible to the homeowner.