WHAT SIZE SYSTEM DO I NEED?

There are a number of factors that will affect your choice of system size, including your roof (or other available) area, your budget and/or how much emergency energy and power you would like to be able to provide.  The list of systems (link to system list) shows the energy and power available from each system.  Note that ENERGY and POWER are different quantities.  Energy is measured in kilowatt-hours (kWh) and power is measured in watts (W).  Energy depends on how long a certain item is operated.  For example, a 20-watt compact fluorescent bulb can be operated for 50 hours on 1 kWh of energy, whereas a 1000-watt hair dryer can only be operated for 1 hour on 1 kWh of energy.

The power available from a PV system depends on the Power Rating of the Inverter.  Our systems use either Outback 3600 W inverters or Xantrex 5500 W inverters.  Note that this power is NOT the same as the power rating of the PV array.  The PV array POWER determines the amount of ENERGY that the system can deliver in a day.

So the system POWER is important, because it determines how many and what types of emergency loads can be run simultaneously without overloading the inverter.

The system ENERGY is important, because it determines how long a particular combination of loads can be operated each day without using up all the electricity produced during that day by the PV array.

In particular, older appliances generally use a lot more ENERGY than newer appliances, so it may make good economic sense to replace an old refrigerator with an Energy Star unit, rather than to install a larger PV system to run an inefficient refrigerator.  In many areas, either the State, federal government or utility may have incentive programs to encourage the purchase of more efficient appliances.

The following table lists common loads that might get priority under emergency conditions.  Add the watts to ensure that your inverter will not be overloaded and add the kWh to be sure your system will generate enough electricity to meet your needs.