Help Desk

Components

• What is Voltage?

  This is the electrical potential of the circuit.

• What is Current?

  Current is the flow of electrons and can be seen as the kinetic energy of the circuit. Current is the element that actually flows through the circuit.

• What is Resistance?

  Resistance is the opposition to the flow of current and it can be compared to friction like the tires of a car when driving on the road.

• What are Transistors?

  Transistors make up the solar cells and are capable of converting the light from the sun into electrical energy.

• What is a Kilowatt hour?

  1x kilowatt hour or kWh is equal to 1 x unit of electricity. (New average is between £0.28p and £0.36p /kWh).

• What is a Module?

  A module is simply another name for a solar panel. Several modules make up an array.

• What is an Array?

  The array is the group or string of panels within a system.

• What are Strings in a solar system?

  Strings is the name given to the linking of panels. You could have an array made up of 10 panels and this would be on 2 strings of 5 panels (If this was 20 panels it would be 4 strings of 5 panels).

• What is the outer frame?

  The frame helps in holding all of the layers of the solar panel together; it also helps in preventing damage that might take place during transportation of panels. It is a key component to securing the panels on the mounting system of a roof or ground mount system. (On roof mounted systems are more reasonable than ground mounted systems).

• What are Solar Cells?

  The solar cells are made up of transistors. These transistors are capable of converting the light energy given by the sun into electrical energy. The transistors are made up of a silicon material and this is where the actual conversion of energy takes place.

• What are Encapsulates?

  Encapsulates are the second line of defence for the solar panel. They hold the solar cells in place and help in keeping the panel together.

• What is a solar panel Junction Box?

  This is the output for the entire solar panel. It usually consists of two wires; one end of the wire is connected to the solar cells internally, the other end of the wire as the output.

• What is a unit cost?

  This is how much you currently pay, or will be paying for 1kWh of electricity. This can range from £0.28p to £0.36p /kWh. We will need to know this information so we can work out how much a system may save you on your bills.

• What are Inverters and optimisation?

  There are two main types of inverter for residential or on grid systems: String inverters and micro inverters there is also another option called DC optimizers designed for a string inverter system like SolarEdge.

• What are String Inverters?

  String inverters are quite large units that usually mount on a  wall or a cupboard at ground level. They are often near the rest of the components (MPPT, Switches and Isolators) and usually in a garage or storage area. They are designed to be enclosed and not on external wall. (Although some are weather rated for external mounting like the Tesla Powerwall.)

  They receive DC power from the series strings from the array and deliver AC power to the electrical circuit  of the property. Most residential PV systems with string inverters have one or two inverters depending on the array size and the layout. String inverters for an on grid system are commonly referred to as a ‘grid tie’ inverters to distinguish them from standalone and  sometimes known as ‘battery inverters’.

  String inverters get input from modules as strings (a group of panels) not as individual modules. The inverter monitors and optimises the output of the entire string. This is because the inverter can’t distinguish or separate one panel or module from the other.

• What are Micro-inverters?

  Micro-inverters are small units that mount onto the back side of each module or onto the panel / array railing system below the modules. Typically each module has its own micro-inverter although some micro-inverters can feed from two modules. Micro-inverters convert DC power to AC power from the individual module so the wiring that connects the modules and runs back to the property consumer unit already carries AC electricity.

  Micro-inverters offer module level monitoring and MPPT optimisation. If a module is shaded, a micro-inverter can adjust its production without affecting the other modules. There are other benefits to module level monitoring, it also gives you the flexibility to design the array with smaller groups of modules on different roof slopes.

  You could even use different sizes of panels and different models of modules. Individual module monitoring also helps with troubleshooting problems. However it can be expensive to service micro-inverters. This is because it does require the panel to be removed from the railing. This could require a scaffold or access equipment. It often means a new micro-inverter and/or panel.

• What do inverters do?

  Inverters do more than convert power from DC to AC they also monitor the modules performance or the performance of the string (A group of panels wired together) and automatically make adjustments to optimise power output. Solar electricity production is constantly fluctuating throughout any given day due to multiple changes in the Solar irradiance, (this is how much sun is hitting the modules) air temperature, shading, and other factors.

  Inverters are always monitoring the changing conditions and respond by shifting the balance of voltage and amperage to get the highest possible output from the modules. This is known as Maximum Power Point Tracking (MPPT for short). Most Callidus systems with batteries will have their own MPPT device.

  Inverters are also the tools with which PV system owners and technicians can monitor the output and other performance factors of their modules or model strings helping with maintenance troubleshooting and service. Cerbo is a great example of this. Callidus have been able to remotely connect and change simple settings, rectifying a fault code in minutes and saving our customer valuable time and electricity.

• What are DC optimisers?

  You can check on the performance of your array using a data monitoring system that you can access on your computer or smartphone through the manufacturer’s online software. As you might guess, string inverters can tell you what’s happening only with each string in your array while micro-inverters and DC optimises report on every module in the array. If a module is significantly under performing for no apparent reason you will instantly be aware that something is wrong with it. This is the same for a micro-inverter or if an optimiser has gone offline.

• What are Charger inverters?

  Charger inverters are needed for all off grid solar systems, because the module of strings from solar panels put out much higher voltage than the batteries can handle. The largest battery banks are rated at 48 volts, while a typical UK home is working off 240 V. The charger inverter regulates the amount and rate of charging that the batteries require at all times. Callidus will make sure the optimum settings are configured to your specific set up and array. It’s a truly bespoke system.

  Charger inverters come in many different types, with different ranges, cost and capability. Callidus would highly recommend that if you opt for an off-grid system you have an MPPT charger inverter, which can accept an input voltage from the array that’s higher than its output voltage that goes to the batteries.

• What is the difference between micro-inverters and optimisers?

  The key difference between micro-inverters and DC optimisers is DC optimisers do not convert DC power to AC power at the module.  They are always used on systems with a string inverter for the power conversion, they do however allow for individual module monitoring and MPPT optimisation.

  For any residential solar installation adding optimisers will increase the initial cost, but this needs to be looked at over a longer term as the optimisers will give your panels, better efficiency meaning your using less electricity from the grid.

• What does MPPT mean?

  Maximum Power Point Tracking (MPPT) capability on a charger inverter is similar to the MPPT with micro-inverters and DC optimisers. In this case the charger inverter constantly monitors the voltage and current of the module strings and adjust the levels as needed to maintain the Maximum Power Point (MPP).

• How does an MPPT work?

  We don’t live in a perfect world and there are constant adjustments required to keep the system performing. The MPPT Inverter Charger is always managing poor sun conditions, extreme temperature conditions and low battery conditions. MPPT inverter chargers really earn their keep in low light or cloudy weather, when the modules are partially shaded or during any extremes in solar irradiance or temperature. Callidus therefore recommend the MPPT in any solar system.