Grid parity, also called socket parity, is a measurement that compares the cost of solar electricity with the cost of residential retail electricity. When grid parity is reached, it becomes more economical for you to install solar panels on your roof rather than purchase power from your utility company.

#### Revisiting the Levelized Cost of Electricity

In order to make an apples-to-apples comparison, it is essential to find a way to calculate the cost of solar in a simple, consistent and reliable way. This is where the concept of levelized cost of electricity comes in. As we discussed in a previous article, levelized cost is an "all-in" cost calculation at the point of connection to the grid, including both the initial installation costs and the ongoing expenses such as fuel (non-existent in the case of solar energy) and maintenance. Levelized cost is very useful when we need to compare the cost of different energy generation sources and when we need to determine if a particular location has reached grid parity.

Sunmetrix Interactive Grid Parity Map for Residential Solar in the U.S.

We built an interactive grid parity map for residential solar energy in the United States, that takes into account the latest state average cost of residential electricity for each state and compares that to the levelized cost of solar electricity in that state. You can switch the ITC on and off to see the impact and you can adjust the cost of solar panels to reflect falling prices. With the cost of solar PV systems falling rapidly, i.e. 50% over the last 5 years, and electricity prices rising, solar grid parity will be a reality for many more locations. (We also built grid parity maps for Canada and Australia).

So how do you determine if your home is in a location that is at grid parity? There are three main factors to consider: your Sunmetrix solar score, the lifetime cost of installing solar panels, and the utility rates in your area.

#### Sunmetrix Solar Score

The solar score is a number between 1 and 100 that indicates how much solar insolation is available in your area. This score directly affects your system's performance. Location is not the only factor that determines performance: it also depends on the type of solar panels (as we previously discussed in an article on solar panel efficiency), the orientation and tilt of your panels, and the degree of shading on your roof. In essence, the Sunmetrix solar score is your first step in getting good performance estimates for your location. For example, the solar score for Montgomery, the capital of Alabama, is 62, whereas the solar score for Annapolis, the capital of Maryland, is only 50. At first glance, Montgomery seems to be one step ahead of Annapolis on the path to grid parity, but there are other factors that can tip the balance.