How a solar power plant works

The path of energy from the sun to your socket, step by step. Scroll down and try out how each part works.

Sun Panels Inverter Building Grid
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1 / 6 · Sun and panels

Sunlight sets electrons in motion

Light falls on the solar cells and sets electrons in the silicon in motion. This creates direct current (DC): no noise, no fuel and no moving parts.

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A photon of sunlight passes its energy to an electron in a silicon cell (the photovoltaic effect). The junction of two silicon layers pushes the freed electrons in one direction, creating direct current. A modern 620 W panel has more than a hundred half-cells connected in series, and a string of panels on the roof produces several hundred volts of DC.

DC

2 / 6 · Optimizers

Optimizers: every panel works on its own

Panels are connected in a string. Without optimizers, one shaded or weaker panel pulls down the whole string. An optimizer under each panel gets the most out of that panel, so shade only takes away what is actually shaded.

String output 2.48 kW2.11 kW1.00 kW

Example: 4 panels of 620 W on a sunny moment. The shaded panel delivers about 40% of its power. Without optimizers, panels in series work like the weakest link, so the whole string drops to the power of the shaded panel.

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The gain is largest with shade (a chimney, a tree, a neighbouring building) and on roofs with several orientations, where east- and west-facing panels work in different conditions. It also brings safety: when switched off, the roof voltage drops to a safe level (SafeDC). And monitoring: the app shows the output of every single panel.

620 W620 W250 W 620 W250 W250 W 620 W620 W250 W 620 W620 W250 W DC

3 / 6 · Inverter

The inverter makes power for your building

The inverter converts direct current from the panels into alternating current (AC), the same as in your wall socket.

On-grid: Works with the grid: it follows the grid voltage, frequency and phase and produces identical current. When the grid goes down, it switches itself off so that line workers stay safe.

Off-grid: Without the grid: the inverter creates its own grid for the building, and batteries store energy for the night and cloudy days. For cottages, farms and sites without a grid connection.

Hybrid: The best of both: it works with the grid, and the surplus charges a battery. When the grid goes down, the battery powers selected appliances.

We work with inverters from leading manufacturers: SolarEdge and Solis.

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An on-grid inverter synchronises with the grid (50 Hz) and must not run when the grid is down, because it would keep lines energised while crews are working on them. For three-phase buildings we choose a three-phase inverter; when consumption differs between phases, the choice of inverter makes a big difference (step 5).

DC AC

4 / 6 · Appliances

Your building uses it first

From the inverter, power goes to the AC switchboard and then to your appliances. The energy you produce is used on site first, and every such kilowatt-hour is one you do not buy from your supplier.

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That is why it pays off most when large consumers run during the day: water heater, washing machine, air conditioning, car charging. The AC switchboard holds the protection (fuses, surge protection) and is where the solar plant connects to the building's installation.

AC Lighting Fridge Heat pump Electric car

5 / 6 · Phases and export 0

Export 0: why phases matter

Until you have prosumer status, the plant must not send power into the grid (export 0). In Serbia this limit applies per phase, not in total. Consumption is never equal across phases, so a symmetric inverter has to drop down to the least loaded phase.

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A symmetric inverter delivers the same power on all three phases. With export 0 per phase, it must not deliver more to any phase than the consumption of the least loaded phase, so the total is 3 × the smallest phase. An asymmetric inverter follows each phase separately and delivers to each exactly what is consumed on it.

Adjust the consumption per phase
2.0 kW
0.5 kW
0.3 kW

Symmetric inverter 0.9 kW

Asymmetric inverter 2.8 kW

The asymmetric inverter uses 1.9 kW more at the same moment.

A simplified calculation for a sunny moment, when the plant can deliver full power. In this example the asymmetric inverter delivers at most half of its power to a single phase.

6 / 6 · Prosumer

Prosumer: the surplus goes to the grid

With prosumer status, surplus energy goes into the grid and is credited on your bill. We guide you through the whole process of obtaining the status, from paperwork to the new meter.

  1. Design and documentation

    We survey the building, design the plant and prepare the technical documentation.

  2. Application to the grid operator

    We apply to Elektrodistribucija Srbije for the grid connection of the plant.

  3. Installation

    We install the panels, the inverter and the equipment in the AC switchboard.

  4. Bidirectional meter

    The grid operator installs a meter that measures both imported and exported energy.

  5. Contract and status

    A contract is signed with the supplier and you become a prosumer.

What are solar panels made of and how do they work?

How much could you save?

Send us your electricity bill and we will propose a tailored solar plant, with a savings and payback estimate.

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