«CSI Incentive Calculator User Guide 1. Guide Overview This User Guide provides background on the California Solar Initiative (CSI) Incentive ...»
Summer Months: These are the months that define the summer period. The proposed and reference optimal system output for these months is used to determine the “Summer kWh”.
Summer kWh: This is the estimated summer energy output of the proposed system.
at optimal tilt: This is the estimated summer energy output of the proposed system, optimized to maximize summer output.
facing south at optimal tilt: This is the estimated summer energy output of the proposed and reference location systems, both optimized to maximize summer output.
CEC-AC Rating: This is the product of the PV module PTC rating, module count and inverter efficiency. If the CEC-AC rating exceeds the rated capacity of the inverter by no
more than 125%, a warning is displayed on the results page. This warning is only informational and does not prevent the user from proposing the system in a CSI application.6 Design Correction: This is the ratio of the Summer Output of the Proposed System and the Summer Output of the Optimal System at the Proposed Location. It indicates how well optimized the proposed system is configured.
Geographic Correction: This is the ratio of the annual output of the summer optimal south facing system at the proposed location and the annual output of the summer optimal south facing system at the reference location. It indicates how well a PV system installed at the proposed location performs relative to the reference location. Note that this ratio is capped at 1.0.
Installation Correction: This is the ratio of PTCadj and PTC of the proposed system.
The PTC is the DC rating of the panels at PVUSA Test Conditions and is listed on the CEC eligible equipment website. The PTCadj rating is not reported on the CEC eligible equipment website and is not equivalent to the PVUSA Test Conditions. It is calculated depending on the mounting method, NOCT and power temperature coefficient for that specific module. See Appendix A of this User Guide for a detailed description of the modified PTC calculation. It accounts for the effects of mounting method on cell temperature and resulting power output. Note that this ratio is capped at 1.0.
Design Factor: This is the product of the Design Correction, Geographic Correction and Installation Correction. This Design Factor is used in the EPBB incentive calculation.
Incentive Rate: This is the current CSI EPBB incentive rate ($/W) and depends on the selected utility and customer type. It is obtained directly from the CSI Trigger Tracker located at www.csi-trigger.com.
Incentive: This is the total incentive for the proposed system.
Report Generated on: is a date and time stamp to document when the report run occurred.
PBI Incentive Calculator Outputs (Differences from EPBB Outputs Only) Capacity Factor: This is the estimated annual output of the proposed system divided by the product of 8760 annual hours and the proposed system’s CEC-AC rating.
Some inverters allow operation above their rated capacity, to a degree, for at least short periods limited by their operating temperature and amperage carrying capability. In addition, some PV systems will not achieve their CEC-AC rating in the field due to local weather conditions and system configuration. Allowing proposed oversized systems, up to 125% of inverter rated capacity, to calculate an EPBB incentive does not guarantee eligibility. The CSI Program Administrators reserve the right to seek justification for proposed oversized systems which may result in poor reliability due to mis-matched equipment.
Prevailing Capacity Factor: This is 18% for incentive steps 2 and 3 and 20% for incentive steps 4 through 10.
Design Factor: This is the ratio of the Capacity Factor and the Prevailing Capacity Factor. This Design Factor is not used to directly calculate the PBI incentive amount.
The Program Administrators use it to modify the CEC-AC rating of the system for incentive trigger tracking purposes.
Incentive Rate: This is the current CSI PBI incentive rate ($/kWh) and depends on the selected utility and customer type. It is obtained directly from the CSI Trigger Tracker located at www.csi-trigger.com.
Incentive: This is the estimated total incentive for the proposed system, and is calculated as the estimated annual output times the incentive rate times 5 years. The incentive paid will be based on the actual production of the installed system.
6. Multiple Arrays, Module or Inverter Types If a proposed system consists of PV arrays with different azimuths and tilts or if different PV module or inverter types will be installed as part of a PV system, a CSI calculator run must be done for each configuration and the resulting incentives totaled.
For example, a system with 30 PV panels type “A” with the same tilt and azimuth, and 2 inverters of type “Z” is proposed; only one calculator run has to be made for this type of system.
However, if a single system with 15 panels of type “A” and 15 panels of type “B”, with 1 inverter of type “Z” is proposed, the user must make one calculator run with 15 “A” panels and 1 “Z” inverter and a second calculator run with 15 “B” panels and 1 “Z” inverter. The incentives from the two runs must then be added together.
7. Shading Input Requirements Proposed systems meet the “Minimum Shading Criteria” if any surrounding object is no closer than a distance twice the height it extends above the PV modules (see illustration below). If this criterion is met and Minimal Shading is checked, no derating due to shading is applied.
For systems that do not meet the “Minimum Shading Criteria”, the user is required to input monthly shade impact results from a shading study conducted at the proposed system site. The study must use a shade analysis tool (and accompanying software) such as the Solar Pathfinder (http://www.solarpathfinder.com) or the Solmetric SunEye™ (http://www.solmetric.com. These inputs are used as monthly derate factors (100% = no shading, 0% = total shading) to adjust the PV Watts output for shading. The shade analysis tool must be specific to the location, azimuth and tilt of the system being measured and must correct for magnetic declination. Do not use a shade analysis tool that is only applicable to south facing systems if your system’s azimuth is different than 180º. Please reference the shade analysis tool documentation for more instructions on their use and interpretation.
The shading study must consist of shading measurements taken at of the system array’s major corners, and the average monthly derate factors input into the calculator. For rectangular areas, four shading measurements must be taken. For irregular areas, a shading measurement is taken at each corner as shown below.
It is not necessary to take measures at each panel corner, for example, in the case of staggered panels. Shade measurements should be made at the major corners of the array as shown below.
It is critical that the positions of the shade measurements are documented and communicated to the CSI field inspector so they may duplicate the measurement. The measurement locations must be accessible after the PV system has been installed for purposes of field verification by the CSI Program Administrators. It is the applicant’s responsibility to document the study.
8. EPBB Incentive & Design Factor Computation Details The EPBB incentive is calculated with the following formula.
EPBB Incentive = Incentive Rate x System Rating x Design Factor Where, EPBB Incentive – is the monetary incentive paid upfront.
Incentive Rate – is the maximum EPBB incentive rate ($/Watt) available at the time of application. The table below presents the EPBB incentive rate schedule.
System Rating – is the product of the PV module PTC rating, module count and inverter efficiency.
Design Factor – is a factor used to modify the maximum incentive rate based on the proposed system’s estimated performance relative to an optimal system at the proposed location, an optimal system at a reference location and a well ventilated module installation. This is the product of the Design Correction (Dcorr), Geographic Correction (Gcorr) and Installation Correction (Icorr). Dcorr is the ratio of the estimated summer kWh production for the proposed system at the proposed location and the estimated summer kWh production for a summer optimal system at the proposed location. Gcorr is the ratio of the estimated annual kWh production for a summer optimal system at the proposed location and the estimated annual kWh production for a summer optimal system at a reference location. Icorr is the ratio of PTCadj and PTC ratings of the proposed system. The PTCadj is calculated depending on the mounting method, NOCT and power temperature coefficient for that specific module.
The Design Factor (DF) calculation is
In addition, the calculator has these characteristics and features,
• The Summer Period is the defined as May1 through October 31. This encompasses the summer periods as defined by the three California investorowned electric utilities.
• All estimated kWh outputs are determined from NREL’s PV Watt v2 performance model.
• Gcorr is capped at 1.0 to prevent areas with higher performance than the reference location from obtaining incentives larger than the maximum incentive rate.
• All systems oriented between 180º and 270º are treated equally.
• The “optimal reference orientation tilt” is optimized for summer production corresponding to the different acceptable compass directions from 180º to 270º.
• Location-specific criteria which account for weather variation and varying degrees of solar insolation, based on local climate and geography.
• An “optimal reference latitude tilt” that relates to local latitude.
9. PBI Incentive Computation Details The PBI incentive is calculated with the following formula.
PBI Incentive = Incentive Rate x Est. Annual Output x Five Years
Where, PBI Incentive – is the total estimated monetary incentive paid monthly over a five year period. Note that this estimate is used by the Program Administrators to set-aside funds for future payments. It is not a guarantee of payment. Actual payments are based on the metered output of the PV system, which may vary significantly from the PBI Incentive estimate provided by the calculator.
Incentive Rate – is the PBI incentive rate ($/kWh) available at the time of application.
The table below presents the PBI incentive rate schedule.
Annual kWh: This is the estimated annual energy output of the proposed system. This value is not a guarantee of future system performance.
10. Calculator Interaction with PV Watts v2 The CSI EBPP calculator utilizes NREL’s PV Watts v2 to estimate the performance of proposed and optimal systems. PV Watts v2 calculates electrical energy produced by a grid-connected photovoltaic (PV) system. PV Watts v2 uses hourly Typical Meteorological Year (TMY) weather data and a PV performance model based on Sandia National Laboratories' PVFORM to estimate monthly and annual AC energy production (kWh). PV Watts v2 extends the capabilities of PV Watts v1 by incorporating NREL's 40 km resolution solar resource data to permit site-specific calculations.
PV Watts v2 calculates performance using hourly data for a nearby TMY2 site that is climatologically similar, and then the output is adjusted based on differences between the TMY2 site and the grid cell with respect to the solar resource (direct, diffuse horizontal, and global horizontal radiation) and daily maximum temperature.
PV Watts v2 has a number of default derate factors that it includes to account for various system losses. The CSI calculator assumes a fixed set of losses in the proposed and optimal systems totaling 16.3%, which is the default in PV Watts v2. These derate factors include –
Note that the CSI Incentive calculator adopts these factors as defaults except for “Inverter and Transformer”. The CSI calculator uses the proposed inverter efficiency specified by the user. A detailed discussion of appropriate derate factors can be found at http://www.nrel.gov/docs/fy05osti/37358.pdf.
NREL reports that PV Watts v2 results may vary due to weather patterns and other uncertainties associated with the weather data and the model used to model the PV performance. The variations may be as much as ±20% when compared to individual years. Compared to long-term performance over many years, the values in the table are accurate to within 10% to 12%. NREL also cautions that the energy production values in the table are valid only for crystalline silicon PV systems. In addition to these uncertainties, PV Watts v2 utilizes NREL’s 40 km resolution solar resource data to permit site-specific calculations. However, if the locations are within the same 40 km x 40 km geographical cell area, this may result in the same system production for different locations, even though it may appear that local weather patterns would dictate that they should be different.
Detailed information on PV Watts v2 and how it works may be found at – http://rredc.nrel.gov/solar/codes_algs/PVWATTS/moreabout.html - Overview of NREL’s PV Watts calculator.
http://rredc.nrel.gov/solar/codes_algs/PVWATTS/system.html - Discussion of PV Watts’ parameters.
http://rredc.nrel.gov/solar/codes_algs/PVWATTS/pvwatts2.pdf - Paper discussing how PV Watts v2 incorporates NREL's 40 km resolution solar resource data to permit sitespecific calculations.
http://rredc.nrel.gov/solar/codes_algs/PVWATTS/interp.html - Discussion of interpreting the results.
http://rredc.nrel.gov/solar/codes_algs/PVWATTS/revhist.html - Lists the revision history for PV Watts
11. Getting Help & Providing Comments Questions and comments regarding the CSI EPBB Design Factor Calculator or this User Guide should be emailed to CSI-EPBB@aesc-inc.com. Questions will be addressed on a first-come first-served basis.