Once the facility’s carbon impact has been calculated, we can quantify its avoided emissions. Be careful: this does not mean mathematically subtracting these emissions from the project’s carbon footprint to display an artificially zero footprint. The battery will always have its own impact. The correct approach consists instead in comparing our project to a “reference scenario” (what would happen on the grid if this project did not exist?). It is through this comparison that we can demonstrate the overall environmental benefit of the project.

Indeed, the most common mistake when assessing the environmental impact of a storage project is to omit its use phase. A battery is a flexibility asset: its purpose is not to generate electricity, but to shift its use in time relative to when it was produced. It is through this role that GHG emissions can be avoided.

The idea is simple: how much CO2e has the project prevented from being released into the atmosphere through its operation? To calculate and highlight this, it is essential to understand the environment and the usage scenario of the installation. Let’s have a look at the following two examples, which are common setups for storage facilities:

Scenario 1: Integration with a solar photovoltaic plant: the hunt for curtailment
Let’s imagine that our project involves a battery integrated with a solar photovoltaic plant. During production peaks, the grid is sometimes unable to absorb all the electricity generated by the facility. National or even European demand may be lower than production. In such cases the plant’s electricity output must then be limited to avoid negative prices (where the producer has to pay to produce). The photovoltaic installation will then curtail (cap) its production, leading to a loss of renewable electricity.

When these situations occur on a facility coupled with a storage solution, the system will store this surplus electricity that would otherwise not have been produced. By feeding it back into the grid in the evening, when demand is higher, it injects 100% renewable electricity at a time when thermal power plants might have been fired up to meet demand. The environmental benefit here is direct: we maximize the production of renewable electricity that would otherwise have been wasted while limiting the activation of polluting thermal plants.

Scenario 2: A grid-connected battery (Stand-alone)

If the battery is simply connected to the national power grid for trading (buying/selling), the logic is different but equally valuable. And this is where the excellent news comes in: the economic optimum is (almost always) aligned with the environmental optimum. In the energy market, electricity is cheapest (or even negatively priced) when it is abundant, that is, when wind turbines and solar panels are producing. Conversely, it is expensive in the evening, during peak consumption hours, because the grid must turn on backup thermal (gas) plants to supply the electricity needed to meet demand.

By charging at low cost, the battery stores electricity that is very often produced by renewables and has a very low carbon intensity. By discharging at a higher price, it prevents the grid from starting up thermal plants that run on fossil gas. The emissions avoided by the project therefore correspond to the difference between the emissions of the avoided fossil source and the low emissions of the stored renewable energy.

By comparing the project’s avoided emissions to its net emissions, we can determine if the facility is virtuous from a carbon point of view. Indeed, if the emissions avoided by the project are greater than the emissions generated over its life cycle, then the project can be considered environmentally beneficial.

If we insist on precise modeling of the operating scenario, it is because each project is tied to its own specific industrial and economic context. The valuation of a project’s environmental footprint must therefore reflect its specific context.

Take the example of a company that couples its solar panels, its battery, and the charging stations (EVSE) for its electric vehicle fleet. The energy management system (EMS) algorithm will not just seek the financial optimum on the grid. It will have to respect an operational constraint: “The vehicles plugged into the charging stations must absolutely be recharged to 80% before 5:00 PM for the employees’ end of the day.” This constraint will force the battery to discharge at a specific time to power the cars, thereby altering its natural charging profile. In return, the system could use compatible vehicles (V2G – Vehicle-to-Grid) as additional storage capacity! This is exactly why the carbon footprint of every storage project is unique. There is no universal magic formula: the balance depends on geographic location, market prices, the storage technology used and its capacity, and above all, local usage constraints and the charge/discharge and integration scenario.