Datalogger Modem or Gateway

Datalogger Modem or Gateway

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Monitoring Battery-

Several inverter manufacturers now provide wireless meters to allow system monitoring from any room in your house.

While infrequent, PV system equipment failures or faulty installation work can have a significant financial impact when they go unnoticed. This is especially true of large installations, or systems that receive performance-based incentive payments tied to the kilowatt-hours a system generates. These potential issues are being met by a wave of inverter-based and third-party system monitoring solutions that, with a few components and a computer or handheld mobile device with Internet access, allow PV owners, installers, and integrators to verify system performance on-site—or from the other side of the globe.

There are two basic approaches for monitoring the performance of your PV system with a computer—local and Web-based. Local monitoring can be as simple as checking the data your inverter collects and displays daily, or using a local storage device, such as a datalogger or computer, to store information collected by the inverter. Web-based monitoring relies on either independent or inverter-based communications, and a "gateway." Besides aggregating the data and serving as a node on your local network, this can provide the connection to an outside network (like your Internet service provider) to send the data to the Web for display.

Battery-based systems, both off- and on-grid, can be monitored with more sophisticated equipment than a standard battery amp-hour meter. Regular monitoring of battery state of charge can make the difference between a battery bank lasting ten years—or less than a year, if the batteries are overdischarged or not fully recharged on a regular basis.

Most battery-based inverter manufacturers offer local monitoring solutions, using software either designed by the manufacturer or by a third-party developer. Several third-party solutions allow battery-based systems to be monitored over the Web, including Chuck Wright Consulting, Draker Solar, Fat Spaniel Technologies, RightHand Engineering, and Watt Plot. Software that interfaces with inverter-direct communication, as well as stand-alone, inverter-independent datalogging equipment, is available.

Local Monitoring Options

Meters & Wireless Displays. The simplest method for local PV monitoring relies on the built-in meter that accompanies most batteryless grid-tie inverters. Here, you can view basic performance data that typically includes AC power, voltage, and current, as well as DC array voltage, daily energy production, and cumulative energy production since the inverter was commissioned. Some inverters have transmitters that broadcast data to a small wireless receiver that you can place in a convenient location in your home for easy viewing.

The Fronius datalogger can record information from up to ten inverters. Fronius also offers free Web-based data hosting via their new SolarWeb site.

The Fronius datalogger can record information from up to ten inverters. Fronius also offers free Web-based data hosting via their new SolarWeb site.

the data. The amount of data that can be stored is a function of the datalogger's memory capacity, the number of different types of data being collected, and the rate of collection.

Many dataloggers have the flexibility to accept information from additional environmental sensors, such as temperature probes, irradiance sensors, and anemometers. You can essentially build your own weather station and synchronize the collected environmental data with your PV system data. When viewed together, environmental and PV performance data can shed a lot of light on how things like temperature and cloud cover affect the voltage, current, and KWH output of your PV system. Some dataloggers can also be used to monitor electrical loads or even individual series strings within a PV array.

SMA's WebBox provides a link the between the PV plant and the Internet.

Depending on the inverter design, performance data may be available for only a fixed amount of time, and some of the information may disappear with the sun when the system stops producing energy for the day. In this case, reviewing the details of your system's performance after sunset becomes an impossible task. Your utility KWH meter will always be tracking the amount of energy your PV system generates, but for users who enjoy or require access to both ongoing and cumulative system data, basic inverter-based collection may not be sufficient.

Computers & Dataloggers. If you want to collect and store data over longer periods of time, or want the ability to export system data to a spreadsheet program for further analysis, the next step in local monitoring is to incorporate an interface between the inverter and a data storage medium. A common method is to connect the inverter directly to a computer via a standard RS232 or RS485 serial connection. The computer monitors and logs the system data, which is generally the same information that's tracked by the inverter's integrated meter. Software, either developed by the inverter manufacturer or a third-party developer, runs on the computer, stores the data, and presents it in a simple graphical format. One potential drawback to this method is that the computer must be running the monitoring software for data to be collected. Another minor inconvenience is that many newer computers do not have the older-style serial ports. To make the connection to a USB port, you'll need to pick up an adapter.

Some inverter manufacturers offer add-on datalogging devices that interface between the inverter and a computer. These dataloggers usually have the ability to monitor multiple inverters, allowing you to track individual inverter operation, as well as the functioning of the entire PV system. The datalogger collects and stores data independently, and enables you to connect a computer at a convenient time to download

Data can be accessed for free through the SunnyPortal site.

Web-Based Monitoring

Web-based monitoring is a great way for both individuals and businesses to promote the benefits of their PV systems to a larger audience. In addition, it allows system installers easy, remote access to performance data if troubleshooting is required. An increasing number of installers are including Web-based monitoring during system installation for just this reason.

The two most common approaches for "pushing" PV system data to the Web use equipment and services provided by the inverter manufacturer or use a third-party data service provider. Some system integrators offer Web-based monitoring options as well.

Inverter-to-Web. Most batteryless grid-tie inverter manufacturers have developed equipment for displaying PV system data on the Internet. With a moderate investment in additional communications hardware, you can access system data from any Internet-connected computer or handheld mobile device. Some manufacturers also offer free data hosting services.

Inverter direct-to-Web connectivity requires an inverter with communications capability and, ideally, a high-speed Internet connection—although most manufacturers can facilitate communications with a dial-up service. The inverter is connected to the Internet through a gateway, and the data is sent to a server either hosted by the manufacturer or a third party, where it is compiled and placed in graphical format for display. Some manufacturers offer additional services such as monitoring environmental conditions or sending notifications when abnormal or fault conditions occur.

Manufacturers that currently offer inverter-to-Web solutions include Fronius, GridPoint, Kaco, Power-One, PV Powered, SatCon, Solectria, SMA, and Xantrex. The level of sophistication varies from manufacturer to manufacturer, so make sure to ask your installer what options are available, or do your own research on the manufacturers' Web sites.

If your PV incentive program does not require independent, third-party energy production tracking, perhaps the simplest and least expensive approach for pushing system data to the Web is to choose an inverter manufacturer that also offers free data hosting. Several manufacturers, including Fronius, Kaco, PV Powered, and SMA, currently offer this service, and in the next few years it will likely become a standard feature industry wide.

Kaco Solar has developed a Web-based monitoring solution that offers PV system fault notifications via e-mail, as well as data hosting services.

California's Production-Based Incentive Programs

The majority of PV incentive programs in the United States are capacity based, with an up-front financial incentive provided based on the size (in rated KW) of the installed PV array. Although this approach can be attractive to home and business owners because it lowers the initial expense of investing in PV, it does not necessarily encourage optimal system installation, maintenance, or performance.

In 2007, California implemented a new production-based incentive (PBI) program that ties financial incentives to the number of kilowatt-hours a system generates, rather than a one-time up-front rebate. Not surprisingly, the PBI program requires an independent third-party monitoring system (see list below for approved monitoring systems). PV systems that are larger than 10 KW and receive incentives from California's Emerging Renewables Program also require the installation of an approved production-monitoring solution. For updates on California Solar Initiative-approved monitoring and reporting services, visit: erprebate/monitors+rsp.html.

CSS Technologies •

Draker Solar Design •

Energy Recommerce •

Fat Spaniel Technologies •

Glu Networks •

Meteocontrol •

PowerNab •

Pyramid Solar •

Thompson Technology Industries •

Kaco Solar has partnered with Meteocontrol and Integrated Metering Systems to develop the PBI Log, which has been designed to meet the performance-based metering requirements of the California Solar Initiative.

GridPoint manufactures an integrated, battery-based line of products that provide backup energy during grid failures. Advanced Web-based monitoring is included.

Third-Party Solutions. Third-party datalogging services with Web hosting are another popular approach to Web-based monitoring. These services typically involve a monthly or annual service fee that is included in the base price. Once the initial service time has expired, a periodic service fee will be applied.

There are two main data collection methods: use a computer to log system information and upload it to the Internet, or use a gateway to continuously transfer data to a remote server via the Internet. Most third-party systems also give you the capability to monitor multiple pieces of system performance data, independent of the inverter, that is compiled into a single stream of information to be used by the host's servers. If the connection between your site and the host's servers is lost, the on-site hardware will store information and send it to the remote servers once the connection is re-established.

Some third-party monitoring systems obtain data directly from the inverter's internal protocol, which reduces the need (and expense) of additional hardware. For systems that do not communicate directly with the inverter, additional hardware to capture the data is required. One common method is to use an

Third-Party Web-Based Monitoring Systems

Vendor Web Site Data Collection Equipment Method*

Chuck Wright Consulting

Dedicated datalogger connects to external transducer, meter, or inverter

Inverter-direct or independent

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