Wallbox Charging Management with PV Surplus and Load Balancing

Intelligent control of the wallbox — charges primarily from PV surplus, respects the grid connection load limit and distributes across multiple vehicles.

How does wallbox charging management with PV surplus work?

A simple 11 or 22 kW wallbox charges at full power as soon as a vehicle is plugged in, regardless of whether solar electricity is currently available or whether the grid connection can handle the load. Charging management instead controls charging power based on three variables. First, PV surplus charging: an energy manager measures at the grid connection point how much solar electricity is not being consumed in the building and releases exactly this power to the wallbox. Second, dynamic load distribution: with several charging points, the available connection capacity is continuously shared between the vehicles so that the load limit of the grid connection is never exceeded. Third, tariff optimisation: the remaining demand is charged during off-peak periods or at favourable spot prices. Communication runs via Modbus or the OCPP protocol (Open Charge Point Protocol), which also enables billing per user.

Which properties benefit from charging management?

The prerequisites are a wallbox with a Modbus or OCPP interface and either a PV system or a dynamic electricity tariff. Typical properties range from a detached house with an electric car, through underground car parks in multi-family buildings, to company car parks, hotels and shopping centres. For companies with several charging points, load distribution is usually the decisive argument: it avoids a costly upgrade of the grid connection or transformer. Company fleets charge 20,000 to 200,000 kWh/a depending on size; a single electric car 2,500 to 5,000 kWh/a.

What does wallbox charging management actually deliver?

Charging costs fall by 30 to 60 %. PV surplus charging raises the self-consumption rate of the PV system from around 35 to 60 to 80 %; every kWh charged this way saves the difference between the purchase price (standard €0.22/kWh) and the feed-in tariff (€0.07/kWh). Off-peak charging additionally saves the difference between peak and off-peak tariffs. A detached house with 4,500 kWh/a of charging, PV and a battery saves around €430/a and avoids roughly 520 kg CO2. Costs are €800 to €2,500 per charging point; an OCPP back end for several wallboxes costs €150 to €500/a. Payback is 3 to 7 years, considerably faster if a connection upgrade is avoided.

Energy carrier

Strom (Netzbezug Hochtarif) → Strom (PV-Überschuss + Niedertarif)

Savings potential

30-60 % der Ladekosten

Worked example

A detached house has a 5 kWp PV system, a 5 kWh battery and an electric car that charges 4,500 kWh per year. So far, the wallbox has charged at full power at the moment of plugging in, usually in the evening at the peak tariff. With charging management, 50 % of the charged energy is covered by PV surplus (share 0.50) and a further 30 % is shifted to the off-peak tariff (share 0.30). Per PV kilowatt-hour, the difference between the purchase price of €0.22/kWh and the feed-in tariff of €0.07/kWh is saved, i.e. €0.15/kWh; per off-peak kilowatt-hour, the difference between the peak tariff of €0.25 and the off-peak tariff of €0.18/kWh, i.e. €0.07/kWh. The calculation is: 4,500 × [(0.5 × 0.15) + (0.3 × 0.07)] = 4,500 × 0.096 = €432/a. This gives around €430/a in electricity cost savings and roughly 520 kg CO2/a less, because solar electricity replaces grid purchases.

Investment & payback

Wallbox mit Lastmanagement: 800-2.500 € pro Punkt; OCPP-Backend für Mehrwallbox: 150-500 €/a · Service life: 10 a · Payback: 3-7 a

Applicability

Requirements

Typical buildings

Frequently asked questions

What is PV surplus charging with a wallbox?

PV surplus charging means the wallbox only charges with the power the PV system is currently generating beyond the building's consumption. An energy manager measures the surplus at the grid connection point and adjusts the charging power in real time. Solar electricity thus flows into the car instead of into the grid for €0.07/kWh. The self-consumption rate of the PV system rises from around 35 to 60 to 80 % as a result.

How much does a wallbox with charging management save?

Charging management reduces charging costs by 30 to 60 %. For a detached house with 4,500 kWh/a of charging, 5 kWp PV and a battery, that comes to around €430/a. For company fleets with 20,000 to 200,000 kWh/a of charging, the benefit scales accordingly. On top of that, there is often the avoided upgrade of the grid connection, which quickly reaches five-figure sums with several charging points.

Do you need load management with several wallboxes?

From two to three charging points, load management is practically indispensable. Three 11 kW wallboxes require 33 kW simultaneously, which overloads many grid connections. Dynamic load management continuously distributes the available power between the vehicles and keeps within the connection limit. This avoids upgrading the connection or transformer and is the prerequisite for equipping company car parks or underground garages with charging points step by step.

How much does a wallbox with load management cost?

A wallbox with load management functionality costs €800 to €2,500 per charging point. For several wallboxes, an OCPP back end at €150 to €500/a is added, which handles load distribution, user management and billing. With a payback of 3 to 7 years and a service life of 10 years, the investment pays off, particularly if it removes the need for a connection upgrade.

Which standards apply to wallboxes and charging management in Austria?

In Austria, IEC 61851 applies to charging infrastructure as the basic standard for conductive charging, together with ÖVE/ÖNORM E 8001-4-722 for the electrical installation of charging points. For communication between wallbox and back end, OCPP 1.6 and 2.0.1 have become established as the open standard. Wallboxes must be registered with the grid operator; above certain power levels, load management functionality is a prerequisite for approval.

Related measures

Standards & sources

Metering points in the EDM Toolbox

Wallboxen liefern via OCPP/Modbus alle relevanten Daten: Ladeleistung, kWh pro Session, RFID-User. Integration in EDM Toolbox erlaubt: (1) Kosten-/CO2-Zuordnung pro Fahrer, (2) PV-Eigenverbrauch-Optimierung, (3) Lastspitzen-Vermeidung im Hausanschluss.

All measures