Three Ways to Size a Solar System
There are three basic ways to size a solar system for your house. Rooftop solar systems come in many shapes and sizes. In this article, you will learn the three ways to size a solar system for your house.
First, budget.
Many people will decide on how much solar to install on their house by the amount of money they have saved or are willing to spend. The average cost of solar for a house in the U.S. is about $3.00/watt. If you have set aside $10,000 for your solar system, you can afford a 3.3kW system (about 9 modules). This is the simplest way to decide how much solar to buy.
The second (and most common) way to size your system is based on your historical consumption.
The first step is to determine out how much electricity you consume annually. This information is available online from most electrical utilities. Here in California, the three main utilities are PG&E, SDG&E, and SCE. These companies allow you to download your historical consumption data as an Excel or .CSV file. The figure you need is measured in kilowatt-hours (kWh). Download the data and sum up the amount of kWh you consumed over a consecutive 12-month period. Next, decide how much of your annual consumption you want to offset with solar (100% is a good option). Next, determine how many solar modules are required to produce the amount of electricity (kWh) you wish to offset. PV Watts (https://pvwatts.nrel.gov/) is a free online tool you can use to calculate this: PV Watts was developed by the U.S. Department of Energy for prospective customers like you! See our guidance for using PV Watts, [here].
The last way to size your solar system is based on your available roof space.
As a homeowner, this method can be difficult since it requires taking actual measurements from the roof or using specialized design software. Keep in mind that many state and local jurisdictions have limitations (they call them "setbacks") on where the modules can be installed. Most systems sized this way are done by a solar provider since they typically have the software to produce a quick and accurate array layout.
Not all homes are a good fit for solar. Keep in mind solar works best when the modules face south, followed by west, then east (assuming you live in Northern Hemisphere!) Solar works very poorly when it's installed in the shade or on northern facing roofs. Your solar production will be limited if you do not have a shade-free, unobstructed roof surface that faces south, west or east.