Frequently Asked Questions

California Distributed Generation Statistics (California DG Stats) currently includes data for all solar photovoltaic (PV) systems interconnected through the California Investor Owned Utilities (IOUs) net energy metering (NEM) tariffs. California IOUs include Pacific Gas & Electric (PG&E), Southern California Edison (SCE) and San Diego Gas & Electric (SDG&E). Publicly owned utility (POU) interconnection solar PV NEM data is not available. However, POUs annually report their cumulative incentivized capacity to the California Energy Commission per Senate Bill 1. These values are only added into the “CA Leads the Nation” numbers on the homepage and updated annually. See See here for more information about POU solar PV data.

California DG Stats does not currently include any other interconnection data from other technologies such as wind, fuel cells, biomass, etc. However, non-solar PV projects which received an incentive from the Self-Generation Incentive Program (SGIP) can be downloaded here.

California DG Stats also makes available various incentive program data sets. For a full list of data available for download visit the Data Downloads.

California DG Stats currently updates solar PV NEM interconnection data in monthly intervals, though there is often a six week delay. For example, data through the month of May will likely not be posted until mid-July. Most incentive program data is updated on a weekly basis, typically Thursdays.

Net energy metering, or "NEM," is a special billing arrangement that provides credit to customers with distributed generation systems (such as solar PV) for the electricity their system generates. Under NEM, the customer's electric meter keeps track of how much electricity is consumed by the customer and how much excess electricity is generated by the system then sent back into the electric utility grid. Over a 12-month period, the customer has to pay only for the net amount of electricity used from the utility over-and-above the amount of electricity generated by their solar system (in addition to monthly customer transmission, distribution, and meter service charges they incur).

Please note that net energy metering policies may change. Please visit PG&E, SCE or SDG&E’s respective websites for more information.

Unless otherwise noted, the most recent “Currently Interconnected Data Set” is the basis for all charts and graphs on California DG Stats. Per CPUC Decision (D.)14-11-001 starting in mid-2015, PG&E, SCE and SDG&E started collecting standardized fields such as ownership type, customer sector, etc. For a list of CPUC required fields and allowable values please see Appendix A of the CPUC decision.

Please direct questions about California DG Stats and data to csisupport@energy-solution.com.

The Interconnection Applications Data Set contains all solar PV NEM IOU interconnection applications including those that are pending or decommissioned. Additionally, when a project is modified (such as adding capacity) a new interconnection application must be submitted to the IOUs, so some projects have multiple interconnection applications. The Currently Interconnected Data Set contains all interconnected (excluding pending and decommissioned) projects with one row per interconnection address/project site. When an application in the Interconnection Applications Data Set has a “Superseding ID” or a “Preceding ID,” it will be combined and summed with another application then represented as one project “row” in the Currently Interconnected Data Set.

To make the Interconnection Applications Data Set, hundreds of data integrity tests are applied to the raw data from the IOU interconnection departments to remove any applications with data errors, such as a data field outside acceptable ranges. The applications removed due to errors are reviewed (and fixed) regularly by the IOU interconnection departments. California DG Stats does make these excluded applications available for public download. User should, however, process this data carefully.

Unless noted otherwise, capacity is reported in California DG Stats as "CEC-AC" megawatts. The CEC-AC rating for a given system is the product of the PTC rating of the PV modules multiplied by the inverter efficiency. PTC refers to PVUSA Test Conditions, which were developed to test and compare PV systems as part of the PVUSA (Photovoltaics for Utility Scale Applications) project. PTC are 1,000 watts per square meter solar irradiance, 20 degrees C air temperature, and wind speed of 1 meter per second at 10 meters above ground level.

The PTC does not account for “real world losses”. Actual solar systems will produce lower outputs due to soiling, shading, module mismatch, wire losses, inverter and transformer losses, shortfalls in actual nameplate ratings, panel degradation over time, and high-temperature losses for arrays mounted close to or integrated within a roofline. These loss factors can vary by season, geographic location, mounting technique, azimuth, and array tilt.

Per CPUC decision (D.)14-11-001, starting in 2015 PG&E, SCE and SDG&E began collecting cost data as part of the interconnection application process. For host customer owned systems, the “Total System Cost” is reported. For 3rd party owned systems the “Investment Tax Credit (ITC) Cost Basis”, a figure commonly reported in tax filings, is reported. These numbers are self-reported by the applicant of the interconnection application. Users of this information should note that no additional cost verification has been performed on this data.

The Find a Solar Installer tool provides a list of recently completed (starting August 2015) solar PV projects in a given area (zip code, city or county) and displays the "Cost/Watt" (in AC capacity) for each project. This tool is meant to be helpful for potential solar customers so they can compare solar PV costs in their region. As mentioned in the previous FAQ, per CPUC decision (D.)14-11-001, this cost data is self-reported by the NEM applicants. No additional cost verification has been performed on the data. To remove erroneous data, the top and bottom 1% of applications are removed from the underlying data set due to their respective high and low cost per watt values. However, users should be aware that data errors likely remain and that there are many factors impacting the overall cost of a solar PV system.

Two factors that significantly determine the production of a solar PV system are the tilt and azimuth of the solar array. Per CPUC decision (D.)14-11-001, the IOUs started collecting this data for all solar PV NEM applications in 2015. The tilt of a solar array is its angle relative to the ground whereas the azimuth of a solar array is its compass direction relative to true north (as distinguished from magnetic north). A tracking system allows a solar array to change its tilt, azimuth, or both to optimize production.

A tilt of zero degrees would represent a panel lying flat on the ground, whereas a tilt of 90 degrees would represent a vertical solar array. Typically, to optimize solar production, a solar array’s tilt should be close to the location’s latitude. For example, a fixed solar array in Los Angeles (with a latitude of 34.05 degrees north) would have its optimal tilt around 34 degrees. An azimuth of 180 degrees indicates an array pointed true south whereas an azimuth of 270 degrees indicates an array pointed to the west, etc. While many factors affect how a project’s tilt and azimuth are selected, theoretically an array with its tilt close to its latitude facing true south would optimize solar production.

In the Currently Interconnected Data Set and the Interconnection Application Data Set, "Tilt" and "Azimuth" are listed for every application for which data are available. If there are multiple arrays for a given project and they have the same tilt or azimuth, the system’s tilt and/or azimuth will be listed. However, if there are multiple arrays with multiple tilts and/or azimuths the word "Multiple" will be listed.

For the "Tracking Type" column, if the project is a single- or dual-axis tracking system, it will be indicated as such. If it includes a mixture of tracking and fixed array systems, "Mixed" will be listed.

In the Currently Interconnected Data Set there is a column titled "Matched CSI Application Number" that indicates which NEM interconnection applications have received a CSI incentive. To date, roughly 90% of completed or in-payment CSI applications have been matched with a NEM interconnection application. For more information about this matching process see the Currently Interconnected Data Set "Read Me" document.

Other incentive programs such as the Emerging Renewable Program, the Self-Generation Incentive Program, the New Solar Homes Partnership, etc. have not been matched with corresponding interconnection applications.

As of December 31st, 2015 there were 281 MWs from 310 customer sited solar PV projects in IOU territories interconnected under a tariff other than NEM (such as non-exporting projects). Currently, these applications are not in the Currently Interconnected Data Set or accounted for in any charts, graphs or figures (such as home page totals) throughout California DG Stats. For more information see the 2016 CSI Annual Program Assessment.

Where indicated, some cost values on the California DG Stats site can be displayed on either a real or nominal basis. Real values are calculated using a Consumer Price Index (CPI) for California, found on the California Department of Finance site. The default setting is to display cost-per-watt (CPW) data on a real basis, i.e. adjusted for inflation (the exact calculation is described below). However, you can also view CPW data on a nominal basis, i.e. not adjusted for inflation.

Months with No Data
The spreadsheet specified above provides exact California CPI data for every other month and interpolates between the surrounding months for each month without data. For example, data in the spreadsheet is provided for February and April, but not for March. The CPI for March = [(February + April) / 2].

Normalization
In all cases, dollars are normalized to the current month, so that ${today} = [(CPI{currentMonth} / CPI{Month}) * ${Month}]. For example, assuming the current month is April 2017 the listed CPI is '261.851'. Current dollars are multiplied by CPI{currentMonth} / CPI{Month} , which in this case is (261.851 / 261.851 = 1). In other words, for today's dollars, $1 = $1. The listed CPI in August 2015 is 251.253. To find the value of an August 2015 dollar in today's dollars, one would take CPI{currentMonth} / CPI{Month} = (261.851 / 251.253) = 1.04218. In other words, one August 2015 dollar = $1.04218 in April 2017.

Treatment of Quarters and Years
For the purposes of calculation on this site, quarterly values are based on the average CPI for 3 months in each quarter and annual values are based on the average CPI for 12 months in each year.