By Vivian Pleul, Special to Solar Power World
Malfunctions in a solar power plant are more than just annoying: They cost hard cash — especially if they go unnoticed for a long time. Modern monitoring equipment helps to prevent drops in yields and offers a range of useful additional functions, which make operating a solar power plant even more cost-effective.
Michael Schneider, a PV installer, was recently called to a plant that was offline because of a technical fault after operating three years. The customer didn’t notice the breakdown until two months later and had to call Schneider to repair the PV plant so that the plant could generate power fault-free again. Due to the fault, the customer lost out on payments during the prime summer months.
To prevent this from happening again, the customer followed Schneider’s advice and installed a monitoring system so that they are immediately notified about any malfunctions within their PV plant. The system is also set up so that Schneider, as the plant installation supervisor, is also informed about any malfunctions. “In this way, I can offer my customers comprehensive service, so that when problems arise, I can immediately analyze them and carry out any necessary repairs or other measures,” Schneider says.
Ensuring PV Yields And Avoiding CO2 Emissions
Today, many plant operators use a monitoring system for more than just detecting disturbances. They use monitoring devices (so-called data loggers) to calculate the current solar power yield, the total yield for a particular day, month or year, as well as the total yield for the plant’s entire operating time. The reporting programs show how high the yields are in the currency for the country (euro, pounds, dollars etc.) and how much CO2 emissions have been avoided with solar energy in comparison to conventionally produced electricity.
There are various ways of viewing an analysis of yield values. A few data loggers have an on-board display that depicts all the key indicators in the form of simple graphics and tables. For more convenience, some data loggers make it possible to connect the monitoring device to the Internet through a modem or an optional wireless card, and to view the analysis in large-screen format at home. Data can also be incorporated on a website homepage or on the website of the installer, meaning that the information can be accessed around the clock from anywhere in the world.
Applications for mobile devices such as iPhones are even available now. In addition to the yield in kilowatt-hours and currency, savings in terms of CO2 and prevailing efficiency level of the inverter, the online view can also show the inverter temperature characteristics. These are fundamental to the efficiency rating of the plant. The characteristics curves of individual inverters can also be read out from plants with several inverters.
Feed-in Power Management Regulations Become Relevant In More countries
In Germany, the regulations for feed-in power management are rather complex. PV plants are divided into various size classes, each with its own set of regulations. However, feed-in management is also becoming relevant in other countries as the amount of PV power installed continues to increase. For example, standardized communication between grid operators and decentralized generating plants will be regulated by law in the future in some countries, according to IEC Norm 61850. The norm specifies a general transmission protocol for electrical switching systems.
This fall, Solar Data Systems is starting a pilot project for standardized communication according to IEC 61850 and IEC 60870. It will then be possible for the monitoring system to communicate directly with the grid operator’s control center. This standardized communication between PV power generator and the respective grid company will then become more attractive for the international PV market.
From Shade To Rodent Damage, Faults Have Numerous Causes
The underlying causes of faults can be many and varied, ranging from shade caused by a fallen tree to rodent damage to cables — and even the complete failure of an inverter.
How does a data logger function? Where does this information come from, and how does the device know that there is a fault in the system? A data logger is connected to the inverter by a data interface, from which it receives up-to-the-minute data such as the amount of electricity fed in, inverter error messages or the temperature of the inverter. The data logger compares the outputs between the inverters or individual strings.
A separate irradiation sensor can also determine deviations between the potential and actual output. If those values differ over an extended period the data logger reports a fault and sends an e-mail or text message (SMS) to the operator or to the solar power support specialist.
Effectively Managing And Using Self-Produced Power
Data loggers can do much more than just saving, evaluating and processing data, however. With an additional power meter that transmits power consumption to the data logger, some devices are able to manage and optimize the consumption of self-produced power. This is not only worthwhile for environmental reasons, but it also increases the returns in some countries and makes it possible to install larger plants. The current power production and consumption are subsequently displayed in a clear graphic. With just a quick glance at this graphic, it can be determined if enough power is being generated to start additional electrical appliances.
In addition to recording the amount of power generated and consumed, this monitoring system offers the possibility to turn on electrical appliances automatically. Appliances can be switched on or off depending on the amount of energy being produced. For example, water heaters can be turned on when power is being produced and remain active throughout the day. If power production increases further, then additional appliances can be automatically turned on (for example air conditioners). It can be determined if appliances are turned on for a minimum period of operation or if they are turned off again once a certain power production threshold is reached. It is also possible to configure the latest time by which the appliance is to be turned on even if there is not sufficient production.
New Remote Control Technology Offers Additional Functionality
Since the beginning of 2012, new regulations for feed-in power management in Germany have been in force. With the help of feed-in management technology, utility companies now have access to privately generated PV energy. They are able to establish how much energy is allowed to be delivered from decentralized power generation sources to the grid.
To enforce these regulations, special control technology is usually employed. It’s especially important for grid stability to be able to adjust the reactive power. Of course, the inverter must support the possibility to control the reactive power. Many utility companies also require a feedback of the actual power and reactive power of all the connected PV plants, and there are monitoring systems available to do this while helping utility companies stabilize the grid.
Portioning The Amount Of PV energy
Monitors designed for feed-in power management can also be configured so that a certain percentage of power is fed into the grid, while the rest is available for industrial or household self-consumption. The option is particularly attractive in regions outside of Germany, where only a certain amount of PV power is allowed to be fed into the grid. This new control technology ensures that only part of the generated power is fed into the grid and that the rest is available only for self-consumption.
An example from Germany shows how controlling PV energy works.
If the amount of DC power from a PV plant should be limited to 70%, it is possible with the a data logger to use the rest of the power for self-consumption. The 70% throttle only applies to the ‘feeding point.’ As a consequence, it’s possible to generate more AC power at the inverter when it is warranted that the surplus power in used for residential or commercial self-consumption. A plant with 10 kWp then has to be limited to a maximum of 7 kWp with the 70% throttle. If a 600-watt appliance, such as a stove, is turned on, the inverter can convert 7.6 kWp to AC power. At the feed-in point, then only 7 kWp is delivered.
For this practical form of utilizing self-produced power, the only requirement in addition to an appropriate monitoring system is a digital power meter.
Vivian Pleul is the director of marketing for Solar Data Systems.
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