Utility Bill Calculation Details

Overview

SolarNexus partners with Genability to provide its utility bill calculations. Genability maintains the most comprehensive and accurate database of electric utilities and rate information in the world. SolarNexus collects your customer's electric consumption and passes it to Genability, who projects the future bill amounts based on that consumption.

Current and Post Project Tariffs

The electric tariff for many customers will be changed AFTER installing solar, but not necessarily. For example, in some parts of the country you MUST switch to a solar specific rate tariff (or rate schedule). That may not be necessary for your market.

SolarNexus Projects Usage by Hour

Unless you provide actual hourly usage for your customer using Green Button Data (see below), SolarNexus does its best to take whatever usage data you've provided, and build an hourly usage profile for the customer over 8760 hours in the upcoming year. This is necessary to model how an irregular production of solar energy will affect the customer's future bills. SolarNexus applies usage profiles modeled by the US Department of Energy for building types in each zip code. That ensures that weather affects are taken into consideration.

Bill Calculations based on Green Button Interval Data

The customer consumption you provide is always moved to the target date range of the calculation. So if you provide 2015 Green Button data and start your savings analysis on 1/1/2016, the usage will be adjusted for 1) day of the week, 2) daylight savings time, and 3) leap years. This can cause some small shifts of the monthly kWh distributions from the actual monthly totals from the Green Button file (for example, a month may have a small number fewer or more kWh than the same month's total from the year before). The annual sum of the individual monthly totals will be the same for both the Green Button interval data and the projections for future bills, however.

What if we upload more than one year of Green Button intervals? When an interval file containing more than 12 months of data is uploaded, SolarNexus only uses the most recent 12 months of data as the usage for the savings analysis.

What if we upload fewer than 12 months of Green Button intervals? When you provide only one month's usage for example, we match that month's usage to the usage in our typical profile for that month to determine a multiplication factor. That factor is then applied to the remaining 11 months to complete the 12 month profile.

Supply Rates / Deregulated Markets

In deregulated markets (like Texas), customers pay a utility to provide electric service to their home, but may buy the actual electricity from another energy provider. This of course complicates things. In SolarNexus, we know the amount that the utilities charge to their customers for the "transmission and distribution" so we have those rates in the system. When you pick a utility and tariff from our lists, we show you an box to input your specific customer's "energy rate" - this is the amount that they pay the energy provider per kWh and should be available from the customer's bill. In SolarNexus, we add the energy rate you input to the known transmission and distribution rates for the utility and use that in the analysis.

Using Manual Rate Input | Rates Outside the US

The SolarNexus manual rate input feature assumes a simple NET metering / avoided cost calculation.
You can If you use the manual input, you need to input a sum of the utility's transmission/distribution/other charges and the energy provider's rate to get a blended rate.

Utility Bill Projections

When you run an Analysis on a solution, SolarNexus is projecting future utility bills with the solution you've defined, versus the future utility bills without the solution. SolarNexus is actually doing its best to project future usage onto the actual upcoming year's calendar, on an hourly basis. This means:

1. You may see some small variances in individual monthly use numbers for a variety of reasons. SolarNexus is doing its best to distribute given amounts into hourly usage profiles. For example, one future month may have 5 weekends versus same month past year having four weekends. This will cause variations in monthly usage and bills, but as a year, the numbers average out. Also remember if you input billing periods, BILLING PERIODS DO NOT MATCH CALENDAR MONTHS. So there will be a shift from what you see in numbers you input to what you see in results.
2. Future bill projections WILL NOT MATCH HISTORIC BILLS! Past bills may have been calculated using a rate before a recent rate increase. Also, future bills may include an assumed annual rate increase.

Bill Analysis Outputs

SolarNexus outputs a detailed table for use in documents, such as proposals. The variable that outputs the table is called "yr_1_summary_elec." In order to fit the bill amounts into the table, SolarNexus rounds the monthly bill values. SolarNexus also rounds the totals

In the table, every "bottom line" number (i.e. "Electric Use With Solar" and "Utility Bill Savings"), both monthly and annual, is always calculated by subtracting the two whole numbers above it in the table. Thus, you won't see any obvious discrepancies due to rounding. The annual totals are still the actual annual amounts (rounded to nearest dollar).

Since this means the annual totals may not equal the sum of the given (rounded) monthly values, in any row, added the footnote: "annual totals may not equal sum of monthly values due to rounding".