SolarYpsi is a group of volunteers in Ypsilanti, Michigan, who design and install photovoltaic projects around town (see “One Person, One Community”) and who have invented an inexpensive way to monitor electrical energy—including PV power and utility import and export power—for five Ypsilanti solar installations. The monitoring system also tracks daily, weekly, monthly, and annual energy (kWh) production and consumption.
SolarYpsi wanted a method to compare multiple solar installations uniformly. It made sense to simply figure out how to read the utility meters directly rather than relying on inverter- and fee-based monitoring systems. An added benefit of monitoring through the utility meters is that energy consumption problems could be spotted. For example, during the first week of monitoring at the Ypsi Food Co-op, it was noted that the power consumption did not drop as expected one night. It was discovered that the lights had been left on overnight, and actions were taken to educate employees on energy conservation.
One of the systems, the River Street Bakery, was awarded a $44,620 grant to make the bakery 100% solar-powered. The design process started by reviewing the electrical utility records for an entire year. Using this data and the information from the National Renewable Energy Laboratory’s solar radiation data (1.usa.gov/NRELmap), SolarYpsi calculated that the bakery would need a 6 kW PV array to turn their meager four hours of peak sun into enough electrical energy to run the bread-dough mixer, lights, and refrigerators. With a limited amount of roof space, 17.2% efficiency Sanyo HIT 200-watt modules were selected.
To help showcase SolarYpsi’s solar efforts to the public, a method was developed to directly read utility meters at installed PV systems with a laptop computer. With the help of an engineer at the utility, DTE Energy, SolarYpsi learned about “KYZ pulse output”—the means by which some digital utility meters are able to count energy use.
The local utility agreed to install these types of digital meters, which gave three data wires to use. The data wires are connected to a relay in the utility meters, and the other end is connected to the parallel port of a laptop. Every pulse detected in the wire means a specific amount of energy went through the meter. By counting these pulses with specially developed meter-reading software and sending the information to the software on SolarYpsi’s web server, real-time system information (array output, building consumption, and energy exported to the utility) can be tracked and recorded with the same accuracy the utility company uses for billing. The open-source software is available on the SolarYpsi website for free, along with information on how to use it (see solarypsi.org).