Why does the Energy chart show “Excess from Solar” providing more electricity than I use?
During sunny summer months, your solar system will often produce more electricity than
you consume. This excess electricity is typically carried over as a credit on your account
to make up the difference in future months when days are shorter and your solar system is
producing less.
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?
Most utilities include “fixed charges” on your bill, which are charges that
are the same no matter how much energy you use. Since your solar system can only be used
to offset energy related charges (charges on a per kilowatt-hour basis), your bill savings
will not exactly match your energy savings. Other times your solar system may offset
energy from higher tiers that is expensive. This energy may represent a small portion of
your total electricity consumption, but a large portion of your electric bill. In this
case your electric bill savings will be greater than your electricity savings.
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.
Derate Factors
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% |
| Inverter | 5% |
| Wiring losses, module mismatch and module soiling | 10% |
| Annual system degradation | 0.5% |
Environmental Savings
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.
System Size
The system size is calculated dynamically to offset 85% 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.
Tax Implications
WattPlan makes several assumptions about the tax impact of owning a solar system.
Residential customers can receive income tax credits and depending on financing, may be
able to take tax deductions due to loan interest payments. Commercial customers are
classified as taxable or tax exempt entities. WattPlan assumes tax exempt customers have
no tax benefits, as they do not pay any taxes. Taxable customers can have tax benefits or
costs related to investment tax credits, depreciation and change in expenses, etc.
WattPlan makes no guarantees about tax benefits, and users should check with their tax
advisor with regard to any tax treatments.