The landing page for the Present Value of PhotoVoltaics tool includes an illustration of houses with solar panels on their roofs.

A software tool developed by NIST, called Present Value of PhotoVoltaics, analyzes the economic and environmental impacts of rooftop solar technology.


B. Hayes/NIST

Whether it’s to live more sustainably, save money or both, many people are thinking about adding solar panels to their homes. Homeowners consider many factors, including which type of solar panel is best for them, when deciding whether the investment is worth it.

Now, an online software tool from the National Institute of Standards and Technology (NIST) can help answer homeowner questions. The software is called [PV]2 — Present Value of PhotoVoltaics — and it analyzes the economic and environmental impacts of rooftop solar technology. The tool helps homeowners and even installers when evaluating rooftop solar photovoltaic systems.

Photovoltaics are semiconductor materials that convert sunlight into electricity. It consists of individual cells that form solar panels. But how do homeowners know if the technology is right for them?

To help answer this question, [PV]2 uses a method called life-cycle cost analysis, which assesses the total cost of a structure, project or product over time. It considers various costs and can determine the most effective options for the long term.

The idea for the device came from NIST economist Joshua Kneifel when he was thinking about installing solar panels on his own home a few years ago. “Solar installers provide some basic information on costs and savings based on simple and sometimes vague assumptions. I want to know if installing solar is a better investment than just invest the money, and there was no tool available at the time to do that,” Kneifel said.

He ran his own calculations using an Excel spreadsheet but realized the format was untranslatable for the average person. “I realized what was missing was a tool for a homeowner or solar installer to use to get a fundamentals-based, independent economic analysis of an actual quote to install solar for a specific home. I wanted to provide all the necessary details, account for all the potential complexities, while simplifying the experience for the user in a digestible way,” said Kneifel .

When users access [PV]2 on the web, they first encounter a landing page that introduces them to an online tool. The page has links to a user guide that provides a quick tutorial on how the tool works.

The tool does most of the calculations and analysis, so users only need to have two pieces of information: an actual solar quote – a cost estimate from a solar installer – and an electric bill. . If a user does not have these items, they can enter an example quote and electricity bill from the landing page to get a rough estimate.

Once they hit the start button, users must go through six steps, such as entering their address or ZIP code, the price of electricity found on their bill, information about the solar panel system, and any monetary incentives for which they are eligible. Users do not need to know all of this information; some steps contain default information based on the latest research and data. Information entered by users is not stored on a server or in the web application, Kneifel said, which protects the privacy of a user’s personal data.

“Once a user completes these steps, they hit the finish button and get a breakdown of the costs, electricity and carbon footprint associated with the photovoltaic system. Graphs are also included, and the everything can be downloaded in a spreadsheet or PDF,” Kneifel said.

[PV]2 uses the Economic Evaluation Engine (E3), an application programming interface (API) developed in conjunction with [PV]2 by experts in the Applied Economics Office of NIST.

“The new concept is to provide a generic API that can be used as the ‘back-end’ calculation engine for many ‘front-end’ applications, such as a web application,” said said Kneifel. “This simplifies and speeds up the future development of new tools and reduces the time and cost to maintain existing tools. The solar evaluation tool is a perfect use case to validate and demonstrate the capabilities of the generic economic API and how it can be used with other tools that assess long-term projects that require a life cycle perspective. For example, any project related to building or facility focusing on energy efficiency, sustainability or sustainability can use E3 for economic analysis.

The web application went through beta testing before being made available to the general public and received feedback from beta testers, such as solar installers, homeowners who have recently installed solar panels, homeowners who are considering but have not yet installed solar panels, and other tool developers. [PV]2 It can also be useful for solar installers who need to provide a transparent, independent economic assessment of solar panels. “The hope is that the layman can use this web application to do the same analysis I did to feel comfortable with my solar investment,” Kneifel said.

This is the initial version of the tool and the new features are considered; users are welcome to joshua. kneifel [at] (giving feedback) to further develop the tool.

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