Monitoring Batteryless PV Systems

Intermediate

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A monitoring system can help assess PV system performance in real time or over a duration of time, and provide on-site and remotely accessible information for system owners and installers, and the general public.
Batteryless PV monitoring systems provide Web portals for remote, online access to the system through a computer, smartphone, or tablet.
The Fronius Datamanager is a wireless data logger that comes preinstalled in new inverters, and can be retrofitted to older models.
Solectria’s SolrenView DAS Gateway can monitor up to 16 inverters and owners can opt to share data publicly.
While net-energy meters and PV production meters both look like the ubiquitous kWh meter, it’s their position in the system that defines what they are monitoring: A net meter is placed between the AC service entrance and the utility grid connection.
While net-energy meters and PV production meters both look like the ubiquitous kWh meter, it’s their position in the system that defines what they are monitoring: A PV production meter is positioned between the inverter and the AC service entrance connection.
PV system data can be displayed via a wireless tabletop unit, like the SMA America Sunny Beam.
A current transducer snaps closed around a wire to measure current via induction.
Data can be conveyed from the data logger to the display or network connection via dedicated cable, wirelessly (as shown), or over power lines.
Most monitoring systems display very similar data, albeit in different visual interfaces. The biggest difference is that MLPE systems, like this Enphase Enlighten display, allow monitoring of individual PV modules.
Schneider Electric’s Conext Monitor 20 can monitor data from up to three Conext RL inverters.
PV monitoring options offered by inverter manufacturers, such as Solectria’s SolrenView (above), offer similar features and customizable views.
The Enphase Envoy collects data via the power lines from Enphase microinverters; besides an AC power supply, no additional wiring is necessary.
The SolarEdge mobile app allows monitoring system performance from almost anywhere. Most portals also provide email alerts.
ABB’s Aurora Vision Web portal displays data from each microinverter. The eight inverters in this system appear as overlapping lines on the graph—each inverter’s production has been nearly identical for the week shown, indicating that the system is performing well.

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.

Monitoring Components

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.

Network connections are required to send data from the acquisition system to the Internet. The Internet connection can be made wirelessly via a cell or satellite modem, or using a hard-wired connection, such as cable, DSL, or fiber-optic lines. The monitoring system’s data logger or gateway is connected to the router (and on to the Internet).

Data display options include local displays or Web portals. Local monitoring on an inverter or remote tabletop or wall-mounted display usually includes array and grid voltage, current, cumulative energy, and power.

A Web portal is the viewing platform for the PV system data, displayed via a computer, smartphone, or tablet. Multiple portals may be available for one PV system, with one a publicly available version offering a few details, and another (password-protected) providing enough information for maintenance and troubleshooting. Web portals can be branded with logos, and customized with site-specific information such as amount of carbon dioxide offset or the dollar value of energy generated. Reports on historic system production (for days, months, or years) can be created and downloaded from a Web portal as well.

Communications for monitoring can be entirely wireless, or rely on hardwired network cables (like CAT5 or CAT5E Ethernet cables) to move data from the inverter to the data logger or gateway, and on to the Internet via a router. Data from individual inverters can be transmitted over power lines (power-line communications; PLCs); Bluetooth; hard-wired Ethernet cables; or wirelessly.

Power supplies, like AC wall cubes, may be needed for an external data logger/gateway, cellular modem and energy meters. Per the National Electrical Code, the inverter AC output circuit must be dedicated to the PV system and cannot provide this 120 VAC power source.

Monitoring Capabilities & Different System Types

The data hosted by Web portals varies slightly by system topology (i.e. MLPEs vs. string inverters) and by equipment manufacturer, but the data displayed by monitoring portals is very similar across different platforms. For a string inverter system, at minimum, the portal displays kilowatt-hours of production for each inverter on a daily, weekly, monthly, yearly, and lifetime basis. Inverter power, reported at 15-minute or hourly intervals; DC and AC voltage; and current are also commonly measured parameters. The portal will also indicate if there is a potential problem with an individual inverter, for example, if the data is not being transmitted, or the power or energy levels are outside normal thresholds.

For MLPE systems, data provided by a manufacturer’s portal is more in-depth, as the module-mounted electronics allow easy access to each PV module’s power (current and voltage) and energy data, plus historical system energy data (daily, weekly, monthly, yearly, and cumulative kilowatt-hours). Portals can indicate module-level failures or performance issues, and graphically represent a “bird’s eye view” physical layout.

Regardless of system type, reports on energy production history can be downloaded from the Web portal, and most portals can be configured to send emails if the system is offline or other errors occur. Web portal data is also available via smartphones and tablets. Most portals can report data collected from an optional revenue-grade energy meter as well as temperature and solar irradiance from an optional weather station. However, if a revenue-grade meter and/or weather station is a system requirement, double-check with the data system manufacturer to verify that the data can be captured and logged. If not, Web portals can access data from local public weather stations (see “Monitoring the Weather” sidebar).

String Inverter Systems

Fronius is one of the few residential inverter manufacturers that includes complete monitoring in the purchase price of the inverter. Fronius’s Galvo inverters (1.5 to 3.1 kW) have an integrated Datamanager 2 data logger to capture system information, which is relayed to its Web portal. The Datamanager uses WiFi to avoid cables and power supplies, although it can be connected to the router via network cable. The Datamanager includes a smartphone app for commissioning—just take a photo of the inverter’s barcode to set up online monitoring. Fronius IG-plus inverters can be retrofitted with the Datamanager 2 card, and the Fronius FE series can provide module-level monitoring with Tigo optimizers. The Fronius Personal Display unit can provide local monitoring of up to 15 inverters, and is available with or without data logging capabilities.

Kaco offers its watchDOG communication card; each can monitor three inverters. Installed inside the inverter, no external hardware is necessary except an Ethernet connection. The watchDOG transmits data to the Kaco Blueplanet Web portal, which is free for systems up to 10 kW (systems over 10 kW are charged $75 per year plus $1 per kW). Kaco’s M-series inverters have a preinstalled Energy Management Unit for use with Tigo MLPEs.

SMA America’s Webconnect Piggy-back card can collect and transmit data from up to four inverters to the free Sunny Portal website via a hardwired network connection. The card is installed inside the inverter, and uses a hardwired connection to the router—but could be connected by wireless adapter. SMA America also offers the Sunny Beam, a solar-powered tabletop display unit that communicates wirelessly via Bluetooth with up to 12 Sunny Boy HFUS inverters. Ninety days of data is stored in the Sunny Beam and can be transferred to a computer via a USB connection.

Solectria has an optional SolrenView DAS gateway for use with its PVI TL line of residential string inverters. One gateway can monitor up to 16 inverters. The hardwired gateway transmits data to the SolrenView Web portal via the household router. For systems under 10 kW, customized portal access is free for the life of system; owners can choose whether the portal is public or private.

Schneider Electric offers a similar data logger—the Conext Monitor 20 unit for up to three Conext RL residential inverters. Both Solectria and Schneider’s gateway devices require an external AC power source.

MLPE Systems

Systems with MLPEs capture module-level data via the module-mounted inverter or electronics, and transfer that data either wirelessly or using PLC. This level of data capture supplies deep details on the PV system’s functioning. An individual PV module’s power output (including DC or AC current and voltage) can be viewed as it changes throughout the day, and cumulative energy for a day, week, month, or year can be viewed and reported for each module or the whole system.

The method of data transfer varies by manufacturer. For example, Enphase, SMA America, and SolarEdge’s microinverter systems all gather data via PLC from the module-mounted electronics, while ABB/Power-One microinverters transmit data wirelessly to a gateway device.

The Enphase Envoy gateway collects microinverter performance data using PLC. A cable transmits data to the router, or an adapter that comes with the Envoy unit can enable a wireless option. The Envoy unit—which requires an AC power source—transmits data to the free Enlighten Web portal. Enphase recommends installing a dedicated circuit for the Envoy power supply outlet so that RF interference doesn’t disrupt data communication with the microinverters.

SolarEdge data is collected from MLPEs by the inverter (there is no separate gateway device to install as it is integrated into the inverter). The data is transmitted via cable or wireless to the router, and sent on to the free SolarEdge PV Monitoring Portal. Their portal can also be accessed from smartphones or tablets.

SMA America’s Sunny Boy 240-US microinverters require one SMA Multigate-US device for every 12 microinverters. The Multigate-US gathers inverter data via PLC, and is installed prior to the point of interconnection (for example, prior to the back-fed AC breaker), and feeds the microinverters’ AC output power collectively into the grid. It filters radio frequency from the power line to avoid data interference. The Multigate is hardwired (no built-in WiFi), but a wireless bridge could be installed to avoid a long cable run. PV system data is transmitted from the site router to the free Sunny Portal. There is a smartphone and tablet app available as well.

Up to 30 ABB (Power-One) MICRO inverters can be wirelessly monitored by one CDD gateway device, which requires an AC power source. The CDD gateway is required for commissioning the microinverters, and it wirelessly transmits data via a site router to the ABB Aurora Vision Web portal, provided free of charge and available on mobile devices as well. For both SMA America and ABB microinverters, the gateway device is a required system component and enables system monitoring, thus any installed system comes complete with a data monitoring package.

Third-Party Monitoring

Third-party monitoring providers, such as Deck Monitoring (now part of AlsoEnergy), Draker, eGauge, Locus Energy, and Solar-Log, offer options to monitor common inverters for systems small or large. For multiple systems monitoring, as an installer might need, choosing a third-party monitoring system means that different inverter brands can be monitored from the same Web portal, potentially saving time and making the installation and programming learning curve less steep. Hardware costs can range from hundreds to many thousands of dollars, depending on the PV system’s size and data granularity desired.  For smaller PV systems (less than 10 kW and up to 30 kW), third-party Web portal access may be free.

Deck Monitoring, Locus Energy, and Solar-Log all offer a residential revenue-grade energy meter with a cellular uplink, so no on-site Internet connection is necessary. The meter has inputs for direct communication with inverters and transmits data to the third-party’s hosted and customized Web portal.

eGauge and Solar-Log offer options for monitoring building energy consumption and PV production. The eGauge power meter can monitor up to 12 electrical circuits, and a building’s total electrical consumption, solar generation, and load consumption. With its built-in server, the data can be viewed by any browser. Data is updated as quickly as every second, and the device can record up to 30 years of data in its built-in memory.

Solar-Log’s 300 model can monitor multiple inverters up to 15 kW. Small appliances can be monitored individually with networked “smart-plug” devices, and two optional external electric meters can add metering capacity. A wireless model is available for connecting the Solar-Log to a WiFi network and the Solar-Log WEB portal provides basic monitoring free for systems 30 kW or less.

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