University of Vermont

Snowy Day

Output Calculations and Report Writing

by Jack Lehrecke '12, CEF Summer Intern

Over the last two weeks I have spent my time finishing the fieldwork with the on-site surveys for the PV feasibility study. We have moved on from visiting the various locations to calculating the specifics of each possible installation and writing up formal summaries for each promising facility. Additionally, I have been extensively researching the various incentives offered by Vermont for solar installations and exploring the necessary requirements for each of our proposed installations to be applicable for the state programs. I have also been tracking the progress of the Equine Center installation as well as working on preparing an interview with the construction team.


When investigating each potential installation there are a number of factors that need to be considered including system sizing, product selection, cost estimates, projected paybacks, and overall building energy offset. System sizing simply refers to the overall number of modules required for the installation and the expected total output based on the orientation and tilt of each panel. These numbers are obtained by considering the total usable space on the roof of a given structure, which can be easily calculated using scaled satellite images. Once the size of the system is determined, the proper type of inverter needs to be selected to handle the projected output of the installation. The inverter is responsible for converting the DC energy generated by the panels into the AC power that is used in any given grid. 

After the necessary products have been selected, it is possible to estimate an overall cost for the installation given the materials used and the size of the project. Generally this cost is presented in two ways, total cost ($) and the cost of each Watt produced by the system ($/Watt). Larger projects will have a higher overhead but the price paid for each Watt decreases significantly as the size of the installation grows. The overall cost of the project is then projected over an extended period of time (20-30 years) accounting for each applicable state incentive and annual energy savings. This calculation ultimately confirms the amount of time required for the given project to pay for itself. Finally, the overall projected annual output of the proposed system is compared with the annual energy usage of the building to determine the resultant offset from the installation.

I have completed quite a few of these reports for all kinds of possible installations including sloped roofed buildings, flat rooftops and carport structures for parking lots. I have really become comfortable with the entire calculation procedure, which started out as a straightforward process of inputting numbers into a spreadsheet and has resulted in my understanding of every mathematical component of that spreadsheet. It is gratifying to learn these skills quickly through practice as well as utilizing information from my undergrad experience in a professional setting.