On Grid Solar System Diagram: How the Power Flows
An on grid solar system diagram shows power moving in one continuous path: solar panels produce DC, a DC isolator allows safe disconnection, a grid-tied inverter converts DC to AC and synchronises it with the grid, an AC isolator and distribution board deliver it to your home's circuits, and a bi-directional net meter records whatever flows out to the grid or in from it. There is no battery anywhere in that chain, which is the defining feature of the design and the reason the whole thing shuts down when the grid does. This page walks the diagram component by component and shows how the current path changes in three different conditions.
The components, in order
# | Component | Function | Current type |
|---|---|---|---|
1 | Solar panel array | Converts sunlight to electricity | DC |
2 | DC isolator / disconnect | Safe isolation of the array for maintenance | DC |
3 | DC surge protection device | Diverts lightning-induced transients to earth | DC |
4 | Grid-tied inverter | DC to AC conversion, MPPT, grid synchronisation, anti-islanding | DC in, AC out |
5 | AC isolator | Safe isolation of the inverter output | AC |
6 | AC distribution board with MCB / RCD | Circuit protection and distribution | AC |
7 | Household loads | Consume solar first, in real time | AC |
8 | Bi-directional net meter | Records import and export separately | AC |
9 | Utility grid | Absorbs surplus, supplies deficit | AC |
10 | Earthing system | Reference for surge protection and fault clearance | n/a |
Two components on that list are the ones most commonly missing from cheap installations: the DC surge protection device and a properly tested earthing system. They protect a 25-year asset from a class of event that takes seconds, and they are the easiest line items to quietly delete from a quote.
How an on grid solar system works: three states
Reading the diagram is easier when you see how the current path changes rather than treating it as one static picture.
State 1: daytime, generating more than you use
Panels produce, the inverter converts, your loads consume what they need, and the surplus flows past the net meter into the grid. The export register increments. You are running entirely on solar and banking the excess.
State 2: night, or generating less than you use
Panels produce little or nothing. The inverter has nothing to convert. Your loads draw from the grid through the same meter, and the import register increments. Your bill reflects the difference between the two registers.
State 3: grid failure
The inverter loses its voltage and frequency reference, detects the condition, and disconnects within milliseconds. Panels may be in full sun, producing nothing. Nothing flows in either direction.
State | Panel output | Inverter | Net meter | Your supply |
|---|---|---|---|---|
Daytime surplus | High | Converting | Export increasing | Solar |
Daytime deficit | Moderate | Converting | Import increasing slowly | Solar plus grid |
Night | Nil | Idle | Import increasing | Grid |
Grid failure | Available but unused | Disconnected | Static | None |
The fourth row is the one worth sitting with. It is not a fault condition and no diagram from any manufacturer will label it as one. It is required behaviour under anti-islanding rules, so that a lineman working on what should be a dead conductor is not fed by a thousand rooftops. The full reasoning and the alternatives are in the on grid vs off grid solar comparison.
Where the wiring commonly goes wrong
Six issues account for most of what goes wrong between the diagram and the roof.
Problem | What it looks like | Consequence |
|---|---|---|
Undersized DC cable | Thin cable on a long roof-to-inverter run | Voltage drop, lost generation, heat |
No DC surge protection | SPD absent from the DC side | One nearby strike takes the inverter |
Poor or untested earthing | Earth pit present but never measured | Surge protection cannot function |
Strings mixed across orientations on one MPPT | East and west panels on a single channel | Whole array pulled to the weaker string |
Inverter mounted in direct sun | No shade or ventilation | Derating in summer, shortened life |
Net meter position wrong | Meter not capturing the full solar path | Export not credited correctly |
The earthing point deserves emphasis because it silently defeats other protection. A surge device works by diverting energy to earth, so an earth path with high resistance leaves the "protected" side still carrying dangerous voltage. Earth resistance should be measured and recorded at commissioning, not assumed.
What the diagram does not show
Diagrams flatten a few things that decide whether the system performs.
- Shading is dynamic. A line drawing shows an unobstructed array. The water tank shadow at 4pm in December is not on it.
- Cable length has a cost. Every metre between array and inverter costs voltage. Two identical diagrams can perform differently.
- Roof orientation is not neutral. South-facing at the correct tilt is the reference case; east or west costs output that no diagram indicates.
- The meter is the DISCOM's, not yours. Its installation timeline is outside your installer's control and is usually the longest step.
- Protection devices are optional in practice. They appear in every published diagram and not in every quotation.
Who needs to understand this diagram
Fit | Why you need it |
|---|---|
Buying a system | To check the quotation includes the DC isolator, SPD and earthing that the diagram shows |
Comparing quotes | Two quotes at different prices often differ in exactly these components |
Troubleshooting output | Knowing the three states tells you whether low output is a fault or normal night-time behaviour |
Deciding on hybrid | State 3 is the whole argument, seen clearly |
Studying or specifying | The component sequence is the same at any system size |
Frequently asked questions
What does an on grid solar system diagram show?
It shows the path of power from the solar array through a DC isolator and surge protection device to the grid-tied inverter, then out through an AC isolator and distribution board to your household loads, with surplus passing through a bi-directional net meter to the grid. Crucially, it contains no battery, which is what distinguishes on-grid from off-grid and hybrid layouts.
How does an on grid solar system work?
Panels generate DC, the inverter converts it to AC synchronised with the grid, and that power serves your home first in real time. Surplus is exported through a bi-directional meter and credited against your bill, while any shortfall is drawn from the grid. There is no storage, so the grid performs the function a battery would.
Why is there no battery in an on grid solar system diagram?
Because the grid itself performs the storage function through net metering. Removing the battery removes the largest cost and the main maintenance item, which is why on-grid is the cheapest configuration. The trade-off is that the system cannot operate when the grid is unavailable.
What is the DC isolator for?
It allows the solar array to be safely disconnected from the inverter for maintenance or emergency. Solar panels cannot be switched off, since they produce voltage whenever light falls on them, so a disconnection point on the DC side is a safety requirement rather than an optional extra.
Do I need a surge protection device on the solar side?
Yes, on any rooftop array. Panels sit at the highest point of the building and their cabling presents a path for lightning-induced transients into the inverter. A DC surge protection device diverts that energy to earth, and it only works if earth resistance has actually been measured and is low.
Where does the net meter sit in the diagram?
Between your distribution board and the utility grid, so that it records everything crossing that boundary in both directions. It replaces your existing unidirectional meter and is installed by the DISCOM, not by your solar installer, which is why its timing is usually the longest step in commissioning.
What happens in the diagram when the grid fails?
The inverter detects the loss of grid voltage and frequency reference and disconnects within milliseconds under anti-islanding requirements. Panels may still be in full sunlight but nothing flows, in either direction. The state resumes automatically after a reconnection delay once the grid returns.
Is the wiring different for a 3kW and a 10kW on grid system?
The component sequence is identical. What changes is cable sizing, the number of strings and MPPT channels, the protection device ratings, and whether the connection is single phase or three phase. A 10kW residential system is usually three phase, which changes the meter and the distribution board arrangement but not the logic of the diagram.
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