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GEESYS Technologies SWITCHING AND PROTECTION PHOTOVOLTAICS INSTALLATIONS. Introduction Range Applications. Bharathiraja.K. INTRODUCTION. Solar thermal energy

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GEESYS Technologies







  • Solar thermal energy

  • A technology for harnessing the solar energy for thermal energy. Water is heated by solar energy and is commonly used for domestic solar hot water and heating

  • Solar photovoltaics energy

  • Sunlight is directly converted into electricity. The main applications of PV are

    • Grid tied systems Refers to solar electric systems that are capable of generating electricity to the grid (or utility company). i.e. Solar farms, solar roofs.

    • On-grid systems A system connected to the utility grid which utilises the grid for backup electricity

    • Off-grid or stand alone systems A system not connected to a utility grid that utilises batteries to store electricity, it is used in areas that are not connected to the electricity grid.

SOLAR PHOTOVOLTAICS. Grid-tied Systems. Components

  • Solar panels

  • A solar panel is composed of solar cells made up of semiconducting material which absorbs sunlight to produce electricity. Common rates of voltage and current for a single panel are 24Vdc and 8 Amps

  • Combiner boxes

  • Since the voltage for a single panel is too low, several panels are connected in series to provide an output voltage within the inverter’s working rates (500-750Vdc). A group of panels grouped in series is called array. Depending on the power of the inverter and the number of arrays we will have now to group several boxes in parallel in order to get higher currents.

  • A combiner box is composed of: Switch-Disconnector, protection against short circuits and, optionally, surge arresters

  • Inverter

  • A device that converts direct current (DC) produced by solar modules to alternating current (AC) that is used by most appliances

  • Metering and AC protection switchboard

  • Protection and measurement of the electrical energy both used and injected into the grind.

  • Transformer

  • A device that transfers the electrical energy before being injected into the grind

SOLAR PHOTOVOLTAICS. Combiner boxes. Components

Short-circuit protection

Protection against short-circuits upstream the fuse-holders

10x38 1000Vdc fuse-holders where arrays are directly connected

900Vdc ultra-quick gR fuse-links specially indicated for solar applications.

AC fuse-link breaking risk eliminated.


Safe disconnection by means of a 900Vdc Switch.Disconnector

Inverter isolation provided in OFF position

Over-voltage protection

Protection against over-voltages caused by lighting

Class II Surge Arresters

Other features

IP65 enclosure

Significant reduction in wiring and connection time

IP20 components

Protection against indirect contacts by means of a methacrylate cover.

SOLAR PHOTOVOLTAICS. Combiner boxes. Components

Monitoring system

Remote monitoring of the principal parameters of a solar plant in addition to the standard Protection against short-circuits upstream the fuse-holders


1) DC switch

2) Surge Arrester

3) Fuse protection of the Positive pole

4) Monitoring Kit & Fuse protection of the Negative pole

- (VMU-M): Data logger

- (VMU-P): Environment measurement (cells temperature, air temperature, wind speed)

- (VMU-S): String control and fuse protection

- (VMU-O): Digital inputs and output for alarms or inputs disabling

Other features

IP65 enclosure

Significant reduction in wiring and connection time

IP20 components

Protection against indirect contacts by means of a methacrylate cover

SOLAR PHOTOVOLTAICS. Combiner boxes. Types

Power splitting

Division in areas is recommended in order to keep producing in the rest of the installation and not having a complete loss of production

Level 1 combiner boxes

Located under the panels structures, combine the arrays coming from the solar panels. Output can go directly to the inverter or, depending on the installation, several of these boxes are re-combined in another combiner box in order to get higher currents

Level 2 combiner boxes

They are often situated beside the inverter and re-combine the arrays coming form the other primary boxes.

The pattern is the same as in the primary boxes but adapting the components to the rated currents. The resulting output comes up directly into the inverter

SOLAR PHOTOVOLTAICS. Combiner boxes. Selection

  • Features

    • Minimum number of arrays to be combined: 2 / Maximum: 36

    • Max. Rated Voltage: 900Vdc

    • Max. Rated Current: 500Amps (Even higher depending on voltage)

    • 10x38 Fuse-links 2…20Amps 900Vdc gR

    • NH0 Fuse-links 32…160Amps 900Vdc gR

    • Surge arresters. Class II.

    • Knockouts and cable glands under request

    • IP66 Polyester or IP65 metal enclosures

Selection details

1) Open circuit voltage (Voc)

2) Short-circuit current (Isc)

3) Arrays number

4) Type of protection (Positive&Negative poles, Negative pole)

5) Surge arresters (if included)

SOLAR PHOTOVOLTAICS. Grid connected systems.

Places where a switch-disconnector can be placed in a PV installation

* In the sub-combiner boxes afterwards the solar panel series up

* Just before the inverter (This is required by inspectors)

Why is necessary a Switch-Disconnector in a String-Box?

- Base holder is not a safe disconnection method in normal conditions

- Our switch is able to interrupt short-circuit conditions

- Having a switch in the combiner box the customer can interrupt on the spot in case he detects a problem. If you only have a switch before the inverter you have to run to the inverter cabinet and disconnect

-Having a switch in the combiner box which is close to the solar panels, you are confident in case that you need to carry out maintenance labours that the circuit is open and operator can work safely

- At the time of closing the circuit for the first time it is not a good idea to do it by closing the fuse holders, it is better to close the fuse holders without load and close the circuit with the switch. In case of wrong connection of the arrays it is much safer for the operator to provoke it when operating the switch than the fuse holder with the fingers.

SOLAR PHOTOVOLTAICS. Grid connected systems.

Fuse Selection

Fuses must be properly dimensioned or they won’t work properly

i.e. For an Isc of 10Amps a fuse is commonly overdimensionated a 25% percent. That’s 16Amps (not 30Amps as they say). This needs to be checked depending on the Isc of the panels

In a combiner box, a fuse does not melt due to the Isc of the own panel array, it melts due to the reverse currents of the other arrays. Suppose that you have a short-circuit above the upstream the fuse between a positive/negative of the same array, you have here a non-voltage point and the other arrays will tend to supply current to that point. The current will be added and will try to pass through the fuse which is going to melt (7x10Amps = 700Amps). This is represented in the below diagram

SOLAR PHOTOVOLTAICS. Grid connected systems.

  • Switch-Disconnector versus MCCB’s

  • When a switch is required in the installation, an MCCB can be used as a switch but it is much more expensive because it incorporates thermal and magnetic protections and require a maintenance when short-circuits

  • A switch is required before the inverter to protect only the positive pole, but there is no point in protecting the line with a fuse or MCCB thermal/magnetic protection right before the inverter to protect the positive pole.

  • When you have a short circuit immediately upstream the MCCB/Switch+Fuse, it won’t be able to interrupt because it does not detect it.

  • When you have the a short-circuit immediately downstream the MCCB/Switch+Fuse, it won’t be able to interrupt because:

  • -Fuse option: Isc generated < I melting of the fuse

    • MCCB option: Isc generated < I minimum release

  • In any case if we use a fuse/MCCB very adjusted in current the protection could release very often, causing frequent stops and if the protection is overdimensionated it would never work

  • Conclusion:An MCCB is not necessary to protect the installations because the string box fuses will do it. MCCB are expensive and require a maintenance in case of short-circuits. When the customer wants to protect the positive pole, a combination of fuse+switch is more effective and less expensive than a MCCB.

  • SOLAR PV Grid-tied Systems. Switch-Disconnector


    Since a fuse-holders it is not a safe disconnection method for PV installations, DC load break switches are required . They are capable of withstand making and breaking of circuits even in short-circuit conditions.

    Also provides isolation to the inverter´s input and maintenance labours can be done safely.

    Each switch has four breaking contacts and bridging-links must be used to connect in series two of them.

    The size of the switch must be selected depending on the voltage and the short-circuit current that the switch must withstand. Five sizes are available

    Size 00: 800Vdc 12,5Amps

    Size 0: 900Vdc 40Amps

    Size 1: 900Vdc 175Amps

    Size 2: 900Vdc 200Amps

    Size 3: 900Vdc 500Amps

    Size 4: 900Vdc 650Amps

    A switch must be selected according to the voltage and current of the following table


    Handle (Direct or panel handle)

    Bridging links

    Terminal protection

    DIN rail mounting kit (Size 0)

    Auxiliary contact

    SOLAR PHOTOVOLTAICS. Switch-Disconnector. Accessories

    Handle (Required)

    Direct or external door handle (includes metallic shaft that can be cut to the required depth enclosure)

    Door handle satisfies IP65/NEMA-4 rating.

    It is made of polyamide which confers a great heat/ultraviolet-resistant.

    The replacement of our handle does not imply the replacement of the switch. It is very easy to replace

    Bridging-links (Required)

    Series up the poles is a requirement to withstand the full current/voltage stated by the switch.

    Example: A single pole of a 250A switch withstands 175A/225Vdc, in order to work at 900Vdc we have to series up the poles and increase the number of breaking of the DC circuit. 4P…900Vdc / 3P…675Vdc

    Solar applications in the US involve only breaking positive connections because in installations where the negative pole is grounded it is not necessary to break both negative and positive poles, it is enough with breaking the positive one. In Europe these type of installation are not allowed and both positive and negative poles must be switched. As per the sketches we are showing that we get the same result by putting in series 2 positive + 2 negative, 3 positive + 1 negative or in your case 4 positive breaking. The important thing is the total number of breaking that there are (adding positive + negative breaking) At the stage of designing the string box if you want to enter in the switch from the top and exit from the bottom you will use the first diagram, if you want in&out from the same side you will use diagram number 2

    SOLAR PHOTOVOLTAICS. Switch-Disconnector. Accessories

    Over-voltage protection (Optional)

    Protection against over-voltages caused by lighting

    Class II Surge Arresters

    Terminal Cover (Optional)

    Fiberglass made

    Available for all sizes

    USA connection set up

    Negative pole is directly grounded before entering the inverter

    Europe connection set up

    SOLAR PHOTOVOLTAICS. Grid-tied Systems. S-W application


    A Switch-Disconnector in DC and another in AC is used to break and isolate an inverter from source and load


    AC Disconnect switch


    DC Disconnect switch





    SOLAR PHOTOVOLTAICS. Off-grid Systems.

    • Off-grid or stand-alone Systems

    • It is an energy system that is not connected to the grid. They are intended to cover small supplies in the same place where is generated and public utility are of difficult access. In order to provide continuous power, these systems must be connected to storage units that can store excess power produced during daylight hours for use in at night.

    • Some examples of application are: Residential, solar street lighting, solar pumps.

    • A residential off-grid system is composed of:

      • Solar panels

      • Regulator

      • Batteries

      • Inverters

  • The rated voltages (12-48Vdc) are not very high,

  • the products that we have for this application are

    • Two poles Switch-Disconnectors intended to isolate the regulator for maintenance operations

    • Fuse-bases with DC fuse-links

    • An enclosed mounting combination

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