What a Higher HTA Connection Threshold Means for PV + BESS

Under the current rules, a production installation above 17 MW cannot be connected to the Enedis HTA (medium-voltage) network. Between 12 and 17 MW, an HTA connection is only possible by derogation, when the study shows it can be made on a direct feeder from the source substation. Anything larger has to go to the HTB transmission network, with the longer lead times and higher costs that come with it.

The announced reform raises that ceiling to 25 MVA. On paper it is a technical threshold. For PV + BESS developers it changes which projects are worth structuring, and how.

On a hybrid site, solar and storage share one connection point. The connection capacity caps how much the site can inject at any moment, whether the energy comes from the panels or from the battery.

Many projects are therefore designed backwards from the HTA limit: the solar plant is sized to stay under the threshold, and storage has to fit into whatever headroom is left. The limit, not the site or the market, ends up setting the configuration.

• Larger hybrid sites can stay on HTA. Projects that would have been pushed to a transmission connection, or cut down to avoid one, can be kept whole on the distribution network.
• More room for storage power. Additional connection capacity can be used by the battery to discharge at peak prices, instead of being fully occupied by midday solar output.
• A different PV-to-connection ratio. When storage can shift energy out of the midday peak, oversizing the solar plant relative to the connection becomes a design choice rather than a curtailment loss.

A higher regulatory ceiling does not create network capacity. Many source substations are already saturated, connection queues are long, and the cost of the connection itself still weighs on the business case. Enedis is also developing connection offers with modulated power for storage, which trade firm access for faster, cheaper connection. Each of these options has a value that depends on how the battery will actually trade.

The useful question becomes the value created per MVA of connection. Solar capacity, battery power and battery duration should be sized together against the connection limit, alongside when the site injects, how often prices turn negative in the hours it produces, and which markets the battery can access.

That is a dispatch question as much as an engineering one. In ValuationPro, the connection limit is a constraint in the dispatch model, so configurations on either side of the threshold can be compared on the same basis: revenue, curtailment and IRR.

Projects that were sized to the old limit are worth revisiting once the new threshold is published. The best configuration may no longer be the one the rules forced.

Lucas Durupt