Monitoring allows you to obtain real-time data about your system anywhere you can access the Internet and/or email. In the past, Web-based PV system monitoring was an expensive add-on (to an already-expensive system) and thus often left out. The days of checking out the inverter’s screen on the garage wall to see how much renewable energy a PV system is generating are quickly falling behind us. Modern grid-tied PV systems, whether installed with module level power electronics (MLPEs), or string inverters, now come with affordable (and in some cases, free) options for gathering and viewing the system data on a computer, smartphone, or tablet, either in a local network or via an Internet Web portal.
Monitoring systems can alert owners to a problem when it occurs, instead of waiting to be surprised with an unusually high electricity bill. Many monitoring systems can send email alerts to the system owner and installer when production isn’t meeting projections, or when inverters or other equipment are offline or showing other errors.
Monitoring can also show household electricity use and PV system production, which can help homeowners manage consumption habits. Monitoring can be fun and engaging, and provide great publicity and educational opportunities for an otherwise static system.
Data loggers and/or communications gateways capture data and may be able to relay the data to the Internet. Inverters are connected to integrated or external data logging or gateway communications devices. Data loggers can record data to memory and often display it (see “Data Display Options”). A communications gateway sends data to a Web portal but may not record it locally. Data is transmitted in intervals—most commonly every 15 minutes—but varying from one minute (for “real-time” display) to daily. A gateway may transmit data wirelessly or be hard-wired to a router.
Net energy meters measure the AC energy exported to the grid from the PV system, and energy used from the grid, to show net consumption or production. Because the meter is positioned between the loads and the grid, a net energy meter does not measure PV production alone.
PV production meters are positioned between the inverter and the loads to measure only the PV system’s AC energy production. Note that some utilities or third parties (especially residential leasing financiers) may require installation of a revenue-grade PV production meter. (A revenue-grade meter conforms to American National Standards Institute [ANSI] Standard C12.20 and provides readings with ± 0.25% accuracy.)
Current transducers (CTs) clamp over wires to measure current, and report to a meter or data logger that records the values. They can be very small and installed on individual circuits in a house to measure the energy draw for specific loads. Larger CTs can measure a PV system’s production or the building’s total electricity consumption.