Going Solar Chapter 17 : Know how to monitor your Solar PV power output

To know if your solar PV system working as planned, it is important to know how to access the performance status of your system. It is like having a dashboard meter in your automobile that tell you the fuel level, speed and distance traveled, which will tell you the miles per gallon efficiency of your automobile.

There is two main parameters that can be measured to understand the status of your solar PV systems. The Energy Generation Parameters and the System’s Health Parameter.

Energy Generation Parameters

Energy Generation is the main reasons we install a solar PV system. With this parameter you can calculate how much energy it is generated and correlate with how much it had save you from paying the bills to the power utility.

Another reason for energy generation parameters taken into consideration is to compare the efficiency of the system over time. Over time, some new obstacles can cause partial shading, which not limited to stained solar PV panels, covered with dust or leaves etc. It also provide an early indicator to check your maintainance schedule before the system fail to recover your return of investment. Other issues like degraded connectors, faulty cells etc will degrade the systems performance significantly.

Volts and Amps

The simplest method to know what the panels are producing is simply hook the wires up to a voltmeter and amp meter. By directly connecting a volt meter across the solar panel output will tells whats the volt of the open circuit (Voc) of the panels during solar power generation. Placing Amp meter in series with the solar panel and the load will tell whats the current is flowing across.  This crude and simple method can be use in the initial experimentation and placement of the panels. Both is useful when to decide on input limit of subsequent devices like charge controller or  inverters.


The voltage and ampere that measured from the panels can varies allot depending on the attached load. A better option to measure voltage and ampere to represent the output of the panel is to measure after it goes through a charge controller,  preferably with a MPPT charge controller that is connected to a battery. The voltage and amperage that goes into the charging of the battery will be defined as your power generated from the panels.

By manually calculating, you can derive the wattage being produced from the panel by simply  using “Watt = Volt x Amp”. However it will be hard to calculate the total energy produced by the panels.

Watt and Watthours

Watt is the power generated or used by a device at any time. To make sense how much power it had generated in order for easy understanding is by using a power meter. A power meter will have important component such as Voltage, Amperage and Duration used. It tells you the energy transferred in a easy to understand kilowatt per hour (kWh), which is a unit that can be easily seen on utility bills.


A good example will be a Kill-a-Watt power meter that can be bought from electronic stores, it will tell you how many kilo watt hours of energy been transferred. With internal power calculation algorithm, it can log the actual voltage and current transferred, converted into wattage used, then plot it over a duration to get the parameter for energy used – kWh. In some some power meter you can preset the cost per kWh, which will be calculated into total cost of energy transferred. This estimated total power cost will be equivalent to the cost you saved (which you not paying that amount to the power grid utility). Applicable to both grid tie and off grid system.

Alternatively you can know your grid-tied solar PV system is working well if you find the utility power meter rotates backward (indicating the power is been injected back to the grid) , or finding that your total electricity bill reduced. It will be easy if you had a dual direction meter that tells you how many kWh been sell to the grid and how many kWh you have been consumed from the grid.

However these method is general estimation on your system. To know how well each panel perform, you might need a advance inverters that can log the detailed information and send to a computer or a portable device. Some MPPT controller and Microinverters allows a wired or bluetooth data connection.

Solar Monitoring Software

The type of solar monitoring software installed will depend on your solar panel system and the type of inverters it uses. Good quality inverters from SunPower, Solar Edge, Enphase and Locus solar panels each include monitoring systems that can help you to track all the system’s energy production.


From the solar monitoring software, you will know how each string is performing. It will show  in a graphical representation on when is the time of the day or days of the year where the performance of the panels is the highest. It will also allow you to detect faulty panels or potential panels with partial shading issues. For advance users, they can use these information to fine tune their solar PV system to be more efficient, or potential to scale up their solar power production.

System’s Health Parameters

System health is also important, as it will tell you potential issues that can arise from your system and detect it early for early correction before catastrophic events occurs. This includes information such as temperature and battery health.

It correlated strongly with the lifespan of your system. If your system works at extreme of condition, it will have lower life expectancy than a system works in optimum condition.


Temperature is one of the important parameters to be monitored as it affects your solar power generation.

  • In Solar Panels : The higher the temperature of your solar PV panels, it will reduce the power generated from the panels by causing a drop in the voltage due to thermal coefficient.
  • In Inverters : The high temperature from your inverters may be a warning that there is poor cooling of the inverters, or there is potential of overloading of the inverters due to unexpected increase load.
  • In battery : When the battery is being charge , there is heat dissipated from the battery due to chemical reaction and current flow. Cool battery works better than cold battery, but overheating battery may shorten the life span of the battery, and reduce the charging efficiency.

Battery Health

Battery health is also important parameter to be monitored. In a off grid system, the battery will store all the energy need for operation when the night falls. Thing that can tell a battery health are:

  • Battery voltage : Usually after a full charge, the battery should remains its voltage at a recommended value of full charge, e.g 12.6V for a lead acid battery. If your battery still reads less than 12V after a full day charging, it indicates the battery had lost it charging capacity, which in lead acid battery, sulfaction or lack of battery water will be the primary culprit.
  • State of Charge: The parameter that will tell you how much charge is there in the battery. Like a fuel gauge, the higher the bar, the more fully the charge. If you noted there is slow degrade of the state of charge over the days, it may tell you that either your battery cannot hold a charge, or the load usage had exceed the power generated by the solar panel, causing a negative net in a off-grid system.
  • Charge Discharge cycles : Some battery such as Lithium Ion battery have a more advance battery management system that can tells how many cycles had gone through. It will not tell you how many cycles left, but it gives a good rough idea on how near it will be closing to the next battery change.

NEXT CHAPTER >> Know Your Solar PV lifespan and maintenance