DC Network: The Control Paradox

A case study from our flagship installation

The Trap Almost Everyone Falls Into

Imagine this scenario:

You're on vacation. 500 kilometers from home. Your phone shows a notification: Firmware update available for your inverter. Security patch. Should be installed promptly.

You open the VPN, connect to your home network, navigate to your inverter's web interface, or via the service portal or... flash the firmware and: The inverter shuts down. The 230 V supply to the house goes off. And with it... your router. Your switch. Your internet connection.

You've just locked yourself out.

The Control Paradox

A control system must not depend on what it controls.

Sounds obvious. But it isn't - at least not in typical home installations.

Most households with photovoltaics and storage have an architecture that looks like this:

Power Grid ──┬── Inverter ── 230V AC ──┬── Router
             │                         ├── Switch
             │                         └── Access Points
             │
             └── Battery Storage

Everything depends on the inverter's 230 V AC output. If the inverter fails, restarts, or is shut down, everything goes dark. Including the infrastructure you'd need to diagnose the problem.

Halfway There: Where Many Installations Stand

To be fair: Many modern PV installations already use DC for parts of the infrastructure. In Victron systems, for example, the GX device (Cerbo GX, Venus GX) runs directly on battery storage. Locally, it's independent of the 230 V grid.

That's a good start. During a brief inverter restart, monitoring stays intact. Locally.

But:

The communication path from the GX device to the outside world typically looks like this:

GX Device (DC) ── Ethernet ── Switch (AC) ── Router (AC) ── Internet

The switch runs on 230 V mains. So does the router. When the inverter fails, the GX device is still active - but it can no longer communicate outward. You can't access it. Notifications don't arrive.

That's the gap we've closed.

The Solution: Direct to the Battery

In our flagship installation, we resolved the control paradox:

Battery Storage (48V)
        │
        ├── Inverter ── 230V AC ── House
        │
        └── DC Network Infrastructure
                    │
                    ├── Switch (DC Input)
                    │       │
                    │       └── PoE (48V)
                    │             │
                    │             ├── Access Points
                    │             ├── IP Cameras
                    │             └── VoIP Phones
                    │
                    └── Router/Firewall (DC)
                            │
                            ├── Fiber Uplink
                            └── LTE Backup

The entire network infrastructure is independent of the inverter.

The switch draws its power directly from the battery storage. So does the router. When the inverter restarts, the network notices... nothing.

Why 48 Volts Fits Perfectly

The voltage level choice isn't a compromise - it's a fortunate coincidence of industrial history.

Battery Storage:

• LiFePO4 systems typically operate with 16 cells in series
• Nominal voltage: 48 V (16 × 3.2 V)
• Range: ~42 V (empty) to ~58 V (full)

PoE (Power over Ethernet):

• IEEE 802.3af/at/bt operates at 48 V
• Tolerance range: 44-57 V
• Perfect overlap with the battery range

Ubiquiti Equipment:

• Many UniFi switches have DC inputs
• Specified for ~54 V DC
• Direct connection to battery storage possible

This means: No DC/DC converters needed. Battery voltage can be fed directly into the switch. Fewer components, fewer losses, fewer failure points.

The Chain of Independence

Let's walk through the critical components:

Switch

The central switch is the heart of the system. It distributes network and power to all end devices.

• Input: Direct from battery storage (48 V nominal)
• Output: PoE to all end devices

As long as the battery supplies voltage, the switch runs. The inverter can do whatever it wants.

Access Points

All WLAN access points are powered via PoE. No separate power supplies, no 230 V dependency.

• If the switch runs, the APs run
• If the APs run, there's WiFi
• If there's WiFi, you can control your smart home

Router/Firewall

The router is the connection to the outside world. It must function under all circumstances.

• Primary: Fiber uplink (the ONT is also DC-powered)
• Backup: LTE modem (integrated or external, DC-powered)
• Power supply: Direct from battery storage

Even if the fiber uplink fails (excavator cuts cable, provider outage), the LTE connection remains. And both are independent of the house grid.

The Uncanny Valley Experience (Part 2)

In our article about SELV-DALI, we described the strange feeling when the lights stay on during a power outage.

With the DC network, there's a second level:

You shut down the system. The inverter powers down. The 230 V grid is dead.

• The refrigerator is off
• The coffee maker shows nothing
• The TV is dark

But:

• WiFi works
• Internet works
• Your smart home app shows all sensors
• You can turn the inverter back on

It's as if the house has two separate nervous systems. You can shut one off (230 V AC). The other (48 V DC) just keeps running.

Practical Scenarios

Scenario 1: Remote Firmware Update

You're not home. A critical update needs to be installed.

1. VPN connection via LTE or landline
2. Access the Victron portal
3. Start update, inverter restarts
4. 230 V grid briefly interrupted
5. Network stays online
6. Inverter comes back
7. Full control throughout the entire process

Scenario 2: Grid Outage

The power grid fails. The inverter switches to island mode.

• The switchover takes a few milliseconds
• Sensitive devices might notice this interruption
• The DC network notices... nothing
• You can monitor grid status remotely

Scenario 3: Inverter Failure

The worst case: The inverter fails completely.

• 230 V house supply: dead
• Critical loads: dead
• But: Network, cameras, communication: working
• You can diagnose the situation
• You can organize help
• You're not blind

Scenario 4: Malicious Attacker

An attacker wants to disable your security cameras.

• He cuts off your house from the public grid
• He even tampers with your inverter
• The 230 V supply is completely dead

Result: The cameras keep running. They're powered via PoE from the switch, which connects directly to the battery. The attacker would need to physically enter your home to disable surveillance - and would be filmed doing so.

System Limitations

Honesty matters: The DC network isn't perpetual motion.

Dependency on Battery Storage:
When the battery is empty, the DC network also goes down. However:

• A typical storage system keeps the network running for days
• The network consumes only a few watts
• Long before the battery is empty, you've recognized the problem

Voltage Fluctuations:
Battery voltage fluctuates with charge state (42-58 V). The devices used must handle this:

• Ubiquiti switches: specified for this range
• Router: must be selected accordingly

Cost:
DC-capable network hardware isn't always the cheapest option. But:

• The additional cost is manageable
• A traditional UPS for the same functionality would be more expensive
• The solution is more elegant and requires less maintenance

Summary

The control paradox is a trap that's often overlooked in the enthusiasm for smart homes and photovoltaics. You build a highly integrated system - and in doing so create a critical dependency that can become fatal at the decisive moment.

The solution is conceptually simple:

1. Identify the control infrastructure - routers, switches, access points, management interfaces
2. Power it directly from storage - not through the inverter
3. Ensure redundant uplinks - landline and LTE, both DC-powered

The result is a system that never locks you out. Whatever happens - as long as the battery has charge, you have access.

And yes, here too there's that strange feeling: You turn off the "power supply" and the internet keeps working. After a while, it feels right. Everything else feels like a design flaw.

This article is part of our case study series about the WHIP flagship installation. More articles: SELV-DALI: Light Without the Grid

Technical Specifications:

• Battery storage: 48 V nominal (LiFePO4, 48-58 V range)
• Network switch: DC input, PoE output
• Router: DC power supply
• Uplinks: Fiber + LTE, both grid-independent