The Residential Solar Calculator is a web application that helps users make estimate their return on investment for installing residential solar panels.
Our application seeks to address two major issues:
1. Generating a reasonable estimate of power generation capacity and revenue for a solar installation
2. Overcoming the fixed cost burden associated with panel installation
The basic calculation of energy generated per month is dependent on some user provided data:
- Postal code
- Surface width and height in feet
- Surface incline
- Surface orientation (some cardinal direction)
- Daily energy usage: GreenButton aggregated at the daily level.
These inputs determine an approximate fixed plate panel configuration. Along with NREL daily solar radiation maps and LBL provided solar PV efficiency charts, we can estimate rough energy production.
Revenue estimation requires a few extra inputs:
- Average daily energy cost: $/kwH figures from GreenButton data
- Yearly energy price inflation rate: Roughly 3%, as quoted by the Bureau of Labor Statistics in November, 2013
- Installation cost: The cost of installing each panel, estimated from California Solar Initiative. Typically around $6/W.
- Federal Tax Credit: 30% of the cost for qualified property.
The results of the calculations include two interactive line charts:
- Projected Power Generation: Months on the X axis over several years, and kw/h on the Y axis. Two lines, showing projected power generation and consumption will be plotted.
- Cost of the installation slider: Changing this value will result in an update in the “power generation” line, as well as the “return on investment” chart. The maximum cost of installation will be that of using the maximum given surface dimensions.
- Return on Investment: Years on the X axis, and revenue in USD will be on the Y axis. This plot will display two lines representing the estimated cumulative revenue of the solar panel installation with and without financing.
- Size of loan slider: Loan principal, defaults to total cost of installation
- Term of loan slider: Loan repayment schedule, in years.
- Loan interest rate text entry: Interest rate percent, defaults to 2.5%.
The user will also be shown a list of possibly applicable energy incentives for their state and nearby municipalities. Each entry in this list will be a link to the DSIRE site for more information.
Armed with this information, users will have better, more transparent insight into gains from a residential solar installation. Seeing cumulative returns laid out in a simple way encourages individuals to take the next step towards “realizing returns now”, instead of perceiving an installation as being "too expensive".
- Andrew Wan, Tom Beckford