Photovoltaic Cost/Benefit Calculator

Welcome to the Northern California Rooftop Photovoltaic Cost/Benefit Calculator. Unlike most other similar calculators on the internet, this runs against an accurate model of your utility rate structure, including correct modeling of Time-Of-Use (TOU) rates as well as an accurate model of solar insolation in your area. Electric load (your use) is estimated from one of two sources. The first is the dynamic residential load averages available on the PG&E website, the second is a 24-hour model that you can configure with your own particular load curve.

Please fill in all the questions, the click the submit button. The analysis will take several secdons, and you will be presented with statistics on cost, generated power, etc.

Your Utility and Rates

Residential rate information is available for the three major Investor Owned Utilities (IOUs) in California.

Three rate types are available. A simple, fixed residential rate, like the PG&E residential rate, a basic TOU rate, like the E6 rate from PG&E, and an experiment TOU rate specifically for households with electric vehicles, like the PG&E's E9 rate.

Your baseline area determines how much electrity you are allocated before your rates increases to higher "tiers." This determined geographically. You can find you baseline area on your bill.

Rate Type
Baseline Area All Electric household?

Your PV System

Please enter the size of your PV system, it's size in kW normalized based on 1kW/m2 insolation. Also provide it's tilt and orientation. PV arrays are typically tilted at an angle equal to one's latitude. The orientation is typically southward (180°), but some may turn their panels slightly westward to obtain later-afternoon generation (which correlates well with TOU peak pricing) at the expense of maximizing overall generation.

Tilt and Orientation do not work right now. —dgj

Physical Characteristics
Size kWp
Tilt ° (typical good value is equal to your latitude)
Orientation ° (0° is north)

Please enter basic information on the system cost. These costs vary by the type of system and the particulars of the installation, so no effort is made here to estimate them for you. As a quick and dirty guess, $10.00/kW p (installed) is not an unreasonable figure for the Bay Area.

Inverter pricing is included here separately, because inverters tend to fail and need to be replaced during the lifetime of the system. We can model thost costs.

Total Installed Cost $
Expected System Lifetime years
Inverter Cost $
Inverter Lifetime years

Interest Rate

This model uses two interest rates. The first is your guess at the general discount rate for society; what you could get if you invested in something else rather than a PV system that gave a “typical” return.

The second rate reflects your guess as to what the price of electricity will be in the future. If you believe that it will go up at the same rates as everything else in the world, use the same rate as the nominal rate. If you think electricity is going to get more expensive faster then, entier a higher rate.

Interest Rates
Nominal Interest Rate %
Energy Cost Growth Rate %

Your Location

This site uses solar insolation data collected by the California Irrigation Management Information System. CIMIS has various radiometers scattered throughout California. Please choose the site closest to your home, or that you think best approximates the sun you get at home. The list below is of all sites that had hourly data for all of 2006.


Your Electric Use

Your load can be specified one of two ways. First, you can use the actual average hourly PGE residential values from 2006 for the entire year, or you can specify your own 24-hour load profile that will be repeated for the year.

Choose load data source for analysis:

Actual 2006 PG&E E1 Dynamic Load

You will use average residential data from PG&E for the year 2006. This is an hourly estimate for every day of the year and shows variation of weekdays vs weekends, holidays, weather particular to 2006, etc.

Scaling Factor for load

Residential Load Graph

Use the sliders and buttons below to create an estimate of your daily residential load. There is a slider for each hour of the day. The number at the top represents the number of kWh consumed in that hour.

time 12 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11
am pm
Electric Vehicle
Adjust incrementally:

Okay, that's all we need. Go ahead and click...