Glossary · DC and AC electrics
Allowed connection power
The power stated in the grid connection contract; the total power of the PV inverters may not exceed it.
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Definition
Allowed power is the value in the contract between the consumer and the distribution system operator (DSO). The Distribution System Code (cl. 4.1.35, 4.12.1) ties generation to it: the total rated power of the PV inverters may not exceed the allowed connection power.
Note that inverter (AC) power is compared, not panel power. So 12 kWp of panels on a 10 kW inverter with 10 kW allowed is an acceptable combination, and the DC/AC of 1.2 does not matter here. Conversely, two 6 kW inverters with the same 10 kW allowed exceed the limit, however many panels they carry.
The second condition is the number of phases. A three-phase inverter cannot be connected to a single-phase supply. If the allowed power is not enough, it is increased through the DSO; this is a separate procedure, and it is worth starting before buying the equipment.
Where to find the number. The allowed power is written in the contract with the DSO or in the connection specification. It is often this limit, not roof area, that sets the largest size of a home PV plant. So plan in this order: first find the allowed power and the number of phases, then choose the inverter, and only then the panels and strings. That way you will not have to replace the inverter after the DSO refuses the connection. The DC/AC ratio can still be above one: the limit concerns inverters, not panels.
How Solispec applies it
The Solispec constructor has "allowed power under the contract" and "number of connection phases" fields. The engine sums all inverters in the project and compares the total with the allowed power: an excess is an error citing the Distribution System Code, suggesting less power or a higher allowance via the DSO. A three-phase inverter on a single-phase connection is also an error. While the field is empty, the engine reminds you to fill it in.
Related terms
- DC/AC ratio (inverter loading)The ratio of the panels’ peak power to the inverter’s rated power; no norm sets it, it is an engineering choice.
- MPPT and the inverter voltage windowThe inverter’s maximum power point tracker; its voltage range sets the minimum and maximum number of panels in a string.
- PV stringA chain of panels connected in series: voltages add up, the current is shared; frost and the inverter MPPT window limit its length.
- PV earthing and equipotential bondingConnecting PV frames, rails and structures to the building’s earthing; under PUE:2026 the earthing must be common with the building.
- PUE:2026 for solar plants: what changedNorms explained
Solispec’s calculation is preliminary: for a design it has to be checked by an engineer. The values and clauses follow the current editions of the norms on the date of the page.