Solar PV and EV chargers in a housing community

Why surplus solar energy is worth so little

Under Poland’s net-billing system, energy exported to the grid is settled at the market price, which in the middle of a sunny day can be very low — and is sometimes even negative. Energy bought in the evening and at night, on the other hand, is paid for by the housing community at the full price, including distribution charges. The difference can be several-fold.

That is why every kilowatt-hour from the roof used on site is worth far more to the housing community than one sold to the grid. The higher the self-consumption, the faster the PV investment pays for itself.

Chargers as a load for surplus energy

The building’s common areas — lighting, lifts, garage ventilation — use little energy during the day. An electric car is the opposite: a large, flexible load that can take several dozen kWh in a few hours. Chargers connected behind the same meter as the PV installation use up the surplus before it reaches the grid.

• Higher self-consumption of rooftop energy during peak production hours.
• Lower energy bills for the common areas and a faster return on the PV installation.
• Cheaper charging for residents who charge their cars during the day.

Why a group of chargers rather than a single point

A single charger can only absorb surplus energy when a car happens to be plugged into it. A group of chargers with dynamic load balancing (DLB) spreads the available power across all cars charging at a given moment, so the energy from the roof is used much more fully. Shared infrastructure is also easy to expand with more points as the number of electric cars grows.

Example: how much a housing community can gain

A housing community has a 25 kWp rooftop installation, which in Poland produces approx. 25,000 kWh a year. Over the year, the chargers use 5,000 kWh of this energy — about one fifth of production — which would otherwise have been exported to the grid. If purchased energy costs the community approx. 1.00 zł/kWh and exported energy is settled at approx. 0.25 zł/kWh, every kWh used on site is worth approx. 0.75 zł. With 5,000 kWh, that is approx. 3,750 zł a year.

Illustrative calculation: the result depends on the PV installation’s capacity, energy prices, the tariff and how many cars charge during the day. We estimate the self-consumption potential individually for each building.

How to encourage daytime charging

The challenge is that PV produces energy during the day, while residents charge their cars mainly at night. During the day, however, the car park holds the cars of people working from home, retirees, second family cars and vehicles belonging to businesses renting commercial units. It is worth giving them a reason to charge at exactly that time:

• A two-zone tariff in the Domena Power system — a lower rate during PV production hours reflects the genuinely lower cost of that energy for the housing community.
• A dynamic tariff based on market prices (RCE, Poland’s market price of electricity), coming soon, will automatically lower the charging price when energy is cheapest.
• In-app view — residents see the price per kWh and the session cost, so they can choose the most favourable time themselves.

What to bear in mind when designing it

• The chargers should be supplied from the same installation and behind the same meter as the PV system — otherwise the surplus will not reach the cars.
• Every charger needs a MID-certified meter to bill residents accurately for the energy they use.
• The power assessment should take into account both PV production and the building’s peak evening load, when the PV system is not generating.
• Advanced load management can take into account current consumption and production on site — we confirm the scope of integration at the design stage.

Turnkey solar PV and chargers from Domena Power

Domena Power guides the housing community through the entire process — from checking how much rooftop energy can be used for charging to a system that bills residents automatically. One partner, one design and one point of responsibility:

• Power and self-consumption potential assessment — we analyse PV production, common-area consumption and the building’s evening peak.
• Collective installation assessment and design — 3,000 zł net (3,690 zł gross) for the first point and only 330 zł net (405.90 zł gross) for each additional one.
• Installation of chargers with MID meters and dynamic load management, ready for expansion with further points.
• A billing system with no commission on energy — 30 zł net (36.90 zł gross) per month for the first charger and 10 zł net (12.30 zł gross) for each additional one, with an M2M SIM card included.
• A two-zone tariff with cheaper charging during PV production hours, an app for residents and per-unit reports ready for issuing debit notes.

Want to find out how much your housing community could gain from solar PV and chargers? Book a free consultation — you can calculate the cost of the billing system right away in the calculator below.