Solar Power Technology

Learn more about microinverters and
view the block diagram.

An inverter takes DC current and converts it to AC current. There are two types of inverters used for solar power generation and depending on the design, a solar power system will use only one type:

A micro inverter is a small inverter that is built inside of the solar panel itself, converting the DC current generated by the solar panel into AC current. With solar panels that use microinverters, the solar string is effectively generating AC current.

Each micro inverter includes a microcontroller running a control loop that manages the complete DC to AC conversion process, while maximizing the solar panel's output power to produce the optimum AC power for the grid. The conversion process can vary depending on temperature, time of day, and cloud cover. The output of the microinverters are fed to the Combiner Box.

If the solar cells do not contain their own microinverters then a single string inverter is used. A string inverter combines the DC current of a string of solar panels without microinverters in parallel. In solar power, a string is a row of solar panels tied together in parallel. The output of a string inverter is the combined output of all the solar cells, converted into usable AC current. The output of a string inverter is fed to the AC Disconnect Box.

» Learn More About Solar Power Inverters

Disconnect boxes separate generated power from systems and circuits downstream from the box. These are important safety devices that are used during normal maintenance procedures as well as emergencies.

It’s important to note that as long as there is still enough light to see the solar arrays, then the solar arrays are still generating current, and so there is still a danger of a serious or even fatal electric shock. Disconnect boxes safely disconnect power generated by the solar arrays from downstream circuits.

There are two types of disconnect boxes:

For strings without microinverters generating DC current, DC Disconnect Boxes disconnect the DC current generated from a string of solar cells so that it does not reach the String Inverter. Each string has its own DC disconnect box, so to disconnect all power to the String Inverter all DC Disconnect Boxes for each string must be turned off. They are similar to the AC disconnect box.

Depending on the configuration of the system, the AC output of either the String Inverter or the Combiner Box is fed to the AC Disconnect Box. This allows the solar array power to be easily disconnected during emergencies or just general maintenance. All the AC disconnect does is prevent AC current from reaching the AC grid. The AC disconnect is simple, just a big red knife switch with the top labelled ON and the bottom labelled OFF. Just grab ahold and pull. The output of the AC Disconnect Box is fed to the house mains.

» View components for Solar Power Disconnect Boxes

The combiner box combines multiple solar panels power inputs into one power output. Imagine a typical AC circuit breaker box found in every home that takes one AC power input and splits it into multiple AC outputs each with its own circuit breaker. A combiner box is the exact opposite of that - as a matter of fact, many combiner boxes are simply modified AC circuit breaker panels.

The combiner box is housed inside a rugged, locked, weather-proof enclosure. The strings are connected in parallel in order to combine the power of each string. Combiners are high voltage devices and can handle thousands of volts. External connectors allow connections to the box without needing to open the box itself. A ground bolt provides additional system safety by allowing the box to be safely attached to system ground, while a ground fault relay monitors the ground connection and provides an alert in the event of a ground fault.

Each string in a combiner box has its own fuse or circuit breaker. While circuit breakers may be accessible from outside the box enclosure, fuses are always kept safely inside the locked box. In order to meet code requirements in most countries, a Combiner Box cannot be opened using standard tools but requires a special device to open the lid. To further insure safety, many combiner boxes have a second, inner transparent lid. This allows visual inspection of the fuses without exposing the operator to the dangerous voltages inside.

» View components for Solar Power Combiner Boxes

Solar power systems use cables and connectors that are resistant to exposure to rain, heat, cold, ozone, salt, abrasion, UV, and sunlight. They are usually IP67 or IP68 rated (mated).

Connectors are keyed for an error-free installation. Today’s solar power systems have standardized on weatherproof MC (Multi-Contact®) connectors. These connectors have very low contact resistance and form a strong solid connection that is resistant to the elements. In general there are two types of connectors used for solar power systems. These connectors must meet local codes including UL (USA), CSA (Canada), TÜV (Germany), and/or GOST-R (Russia).

Today’s solar connectors provide a solid connection with a locking sleeve that requires a special unlocking tool to open. New solar panel installations are encouraged to use these types of connectors and many international standards now require these connectors, including National Electrical Code 2008 690.33(C).

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