Frequently Asked Questions
Why does the Energy chart show “Excess from Solar” providing more electricity than I use?
What is included in the upfront cost of my solar system?
The upfront system cost represents what you can expect to pay initially to get your system up and running. Depending on how you finance your system, the upfront cost can be a portion or all of the net system cost. The net system cost is the complete cost of your system after incentives. Solar panels, balance of system components (wiring, mounting hardware, inverter, etc.), and labor for installation are all taken into account in the upfront cost.
Why don’t my energy savings match my bill savings?
What is Net Energy Metering Service?
How is my electric bill reduced by having a solar panels system?
Bill Savings Calculation
To calculate utility bill savings, WattPlan calculates a before-solar and an after-solar bill, and compares the bill details. The after-solar bill is calculated by modifying the before solar load profile based on the estimated output of the proposed solar system.
Customer Energy Usage
When consumption data is not available, WattPlan generates an hourly consumption profile from the user provided average monthly bill. WattPlan uses statistical average profiles published by utilities to synthesize an hourly consumption profile for the user based on their electric rate plane and average monthly bill amount. This assumption will be reasonably accurate for the majority of users, but those with unique profiles, such as users with time - of - use rates, may experience notable differences.
The solar system derate factors used in WattPlan are as follows:
|Component||Default Derate Factor|
|Standard Test Conditions rating to PVUSA Test Conditions rating||10%|
|Wiring losses, module mismatch and module soiling||10%|
|Annual system degradation||0.5%|
Environmental impact figures for CO2 are computed using EPA regional emission rates derived from the fuel mix used to generate electricity within the region. These savings are then displayed as equivalent measures(trees planted or miles not driven) using EPA approved conversion factors.
Operation and Maintenance
In the course of this analysis, WattPlan assumes an annual maintenance cost of $10/kWdc, and a one-time inverter replacement cost of $400/kWdc, halfway through the life of the system. These costs can be seen in the cash flow details and lifetime cost breakdown.
PV Module Temperature
The solar production simulation process uses a module’s rating under PVUSA Testing Conditions(PTC). Because ambient temperature, and not cell temperature, is specified by PTC, a cell reference temperature of 45°C is assumed in the calculation of temperature derate.
Solar Data Source
To calculate solar system production, WattPlan uses SolarAnywhere® Typical GHI Year satellite data where GHI stands for Global Horizontal Irradiance. More info can be found at solaranywhere.com.
The system size is calculated dynamically to offset 80% of the user's annual electricity use. Depending on the user’s electric rate plan, the annual bill savings may be greater than, or less than, the percentage of electricity that is offset.
WattPlan makes several assumptions about the tax impact of owning a solar panels system. WattPlan makes no guarantees about tax benefits, and users should check with their tax advisor with regard to any tax treatments.