Distribution of photovoltaics in the site consumption

How is photovoltaic electricity distributed among consumers?

1. Electricity consumption is divided into two parts: that coming from the grid and that coming from the photovoltaic installation (PV).
2. To determine these two shares, Climkit relies by default on the input meter, which has two flows: the energy imported and the energy fed back from/to the grid, as well as on the consumption meters.
3. The PV share in the consumption is then calculated as follows: PV share = sum of consumptions - energy imported. The autonomy rate of the site is obtained by the formula: PV share / sum of consumptions.
4. Climkit distributes the PV share among consumers every 15 minutes by applying the site's autonomy rate to their individual consumption. The part not covered by PV is then supplied by the grid.
5. By basing the calculation on the input meter flows, it is guaranteed that the energy imported and the energy fed back are recorded in accordance with the billing and compensation of the distribution system operator (DSO), and that the energy imported is distributed fairly among consumers.
6. Photovoltaic production is therefore deduced using the following formula: Production = sum of consumptions - energy imported + energy fed back. The self-consumption rate of the site is obtained by the formula: PV share / production

Why is there energy fed back and energy imported from the grid in the same 15-minute period when production equals consumption?

1. If at the beginning of the period, consumption is higher than production, energy is imported from the grid. But if, at the end of the period, consumption decreases, the surplus production is fed back.
2. If the calculation were not based on the input meter, the site would show 100% autonomy during those 15 minutes. However, this would not reflect the reality recorded by the distribution system operator (DSO), which bills the energy imported at the beginning of the period and compensates for the energy fed back at the end of the period.

Why is there a small amount of production at night?

1. Since there are losses and metering discrepancies (for example, the input meter often measures a lower energy imported than the total of all consumption meters, even without production), these discrepancies are absorbed into the calculated deduced production.
2. If the energy imported is higher than the consumption, night production is observed. This means the input meter is less precise than the total of all consumption meters.
3. Conversely, if the energy imported is lower than the consumption, negative production is obtained, indicating that part of the consumption is not measured by a meter.
4. If these values remain minimal, they are normal losses in the installation that can be ignored, as they slightly decrease production without affecting the energy imported and therefore the grid share in consumption.

What to do in case of large discrepancies between energy imported and consumptions?

1. If the difference between energy imported without production and consumption is significant, it indicates that at least one consumption point is not measured, meaning at least one meter is missing.
2. While waiting for the installation of an additional consumption meter, a rule meter is created to deduce this “unmeasured” consumption. This rule meter can then be added to the site’s common areas meter or directly assigned to a billing point.
3. By deducing this unmeasured flow, the input meter, consumption meters, and production meter are all accounted for.

Why not create a rule meter and deduce the unmeasured flow in all cases?

1. This rule meter would absorb all small differences and thus sometimes record positive values and sometimes negative ones, which would influence the grid share in the consumers' consumption, and it would no longer exactly match the amount billed by the distribution system operator (DSO).
2. Furthermore, if the rule meter is assigned to the billing point of the common areas, it would increase or decrease the common areas' consumption, which would no longer match what is actually measured by the common areas' meter.
3. In conclusion, even if this would make the graphs more consistent (without night production), the unmeasured flow should only be deduced if it truly relates to an unmeasured consumer. In all other cases, the production flow is deduced, which absorbs discrepancies and losses while remaining aligned with the input meter as billed by the distribution system operator (DSO).

How does a battery work and what is its impact on self-consumption?

1. Installing a battery allows for storing surplus photovoltaic (PV) electricity produced on a site. When photovoltaic production exceeds instantaneous consumption, the surplus is stored in the battery.
2. Once the battery is fully charged, any additional surplus is injected into the electricity grid.
3. When consumption exceeds solar production, the battery discharges to supply the building's consumers. This mechanism significantly increases the self-consumption rate because the solar electricity produced during the day is also available at night.
4. When the battery is empty, the remaining electricity needed is automatically imported from the grid.

Why are there differences between data from the photovoltaic inverter, the distribution system operator (DSO), and the Climkit platform?

It is perfectly normal to notice discrepancies between the data displayed on the Climkit platform and those measured by the inverter, the battery, or the distribution system operator (DSO) meter.

Several reasons explain these differences:

1. Meter tolerance: Certified meters (e.g., MID) have an accuracy between 0.5% and 1%. Other meters, such as some "smart meters" integrated into the inverter, may be slightly less precise.
2. Metering type: Direct electricity meter (meter connected directly to the circuit) is more precise than indirect electricity meter with current transformers (CT). For better results, CTs adapted to the actual measured intensity should be used. In practice, DSOs often install oversized CTs, which can cause underestimation at low intensity.
3. Calculation methods: Self-consumption of electricity on a photovoltaic site is usually calculated from different measurements rather than read directly. Systems may deduce certain values from others, which induces differences: for example, an inverter might estimate building consumption from production and measurements at the input (energy imported and fed back), while another system might calculate production based on measured consumptions.
4. Measurement location and losses: The production indicated by the inverter corresponds to the electricity generated in direct current (DC), whereas Climkit measures what is actually injected as alternating current (AC) into the building's grid after conversion. The DC/AC conversion and cables result in a loss of 3% to 5%.
   In the case of using a MV/LV (medium voltage/low voltage) transformer, losses are approximately 5%.
5. Measurement frequency: Systems measure and transmit data at different intervals (every minute, every 5 or 15 minutes, at fixed or random times, etc.), which can generate small differences, especially if consumption varies rapidly. Additionally, rounding numbers can lead to slight discrepancies in the total for a period.
6. Presence of a battery: If the site includes a battery, the method of metering stored or returned energy varies between systems, especially at night when the battery discharges. Small amounts of energy may be injected or imported from the grid without always being accounted for by the battery monitoring system.

In summary, differences of a few percent (or a few kWh) between two metering systems are normal and do not mean there is an error or malfunction.

How to verify measurement accuracy?

Climkit regularly checks the consistency of its measurements. The simplest test is to examine data at night: without solar production, the sum of individual consumptions must correspond to the energy imported from the grid (main meter). This "night test" is a good indicator of system functionality.

For another system, you should contact the installer to verify the configuration and proper operation of the hardware.

Finally, to precisely compare two systems, it is recommended to export and compare the load profiles (in 15-minute steps) over several days. This data, available on the Climkit platform (Excel file), allows for a detailed analysis of any differences.