Share of photovoltaic in site consumption

How is photovoltaic electricity distributed among consumers?

1. Electricity consumption is divided into two parts: that from the grid and that from the photovoltaic (PV) installation.
2. To determine these two shares, Climkit defaults to using the input meter, which involves two flows: grid import (soutirage) and grid export (refoulement), as well as consumption meters.
3. The PV share in consumption is then calculated as follows: PV share = sum of consumptions - grid import. The site's autonomy rate 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 share 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 grid import and export are accounted for in accordance with the Distribution System Operator's (DSO) billing and compensation, and that the grid import is distributed fairly among consumers.
6. The photovoltaic production is therefore deduced using the following formula: Production = sum of consumptions - grid import + grid export. The site's self-consumption rate is obtained by the formula: PV share / production.

Why is there grid export and grid import within the same 15-minute period when production equals consumption?

1. If consumption exceeds production at the beginning of the period, electricity is imported from the grid. However, if consumption decreases at the end of the period, the production surplus is exported.
2. If we did not rely on the input meter, the site would have 100% autonomy during these 15 minutes. However, this would not reflect the reality accounted for by the DSO, which bills for grid import at the beginning of the period and credits for grid export at the end of the period.

Why is there some production at night?

1. Since there are losses and metering discrepancies (for example, the input meter often measures less grid import than the sum of all consumption meters, even without production), these discrepancies are absorbed in the inferred production calculation.
2. If grid import exceeds consumption, some production is observed at night. This means that the input meter is less accurate than the sum of all consumption meters.
3. Conversely, if grid import is less than consumption, a negative production value is obtained, indicating that a portion of consumption is not measured by a meter.
4. If these values remain minimal, they represent normal losses in the installation and can be ignored, as they slightly reduce production without affecting the grid import and thus the grid's share in consumption.

What to do in case of large discrepancies between grid import and consumptions?

1. If the difference between grid import without production and consumption is significant, it indicates that at least one consumption point is unmeasured, meaning at least one meter is missing.
2. Pending the installation of an additional consumption meter, a rule meter is created to deduct this "unmeasured" consumption. This rule meter can then be added to the site's common meter or directly assigned to a billing point.
3. By deducting this unmeasured flow, the input meter, consumption meters, and production meter are taken into account.

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

1. This rule meter would absorb all small differences and thus sometimes register positive and sometimes negative values, which would influence the grid's share in consumer consumption, making it no longer correspond exactly to the amount billed by the DSO.
2. Furthermore, if the rule meter is assigned to the common area billing point, it would increase or decrease the common area consumption, which would no longer correspond to what is actually measured by the common area meter.
3. In conclusion, even if this would make the graphs more consistent (without nighttime production), the unmeasured flow should only be deducted if it genuinely corresponds 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 accounted for by the DSO.

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

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

Why are there differences between the data from the photovoltaic inverter, the DSO, and the Climkit platform?

It is entirely normal to observe discrepancies between the data displayed on the Climkit platform, those measured by the inverter, the battery, or the Distribution System Operator’s (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 accurate.
2. Metering Type: Direct metering (meter connected directly to the circuit) is more accurate than indirect metering with current transformers (CTs). For optimal results, CTs adapted to the actual measured current should be used. In practice, DSOs often install oversized CTs, which can lead to underestimation at low currents.
3. Calculation Methods: Self-consumption of electricity on a PV site is generally calculated from different measurements, rather than being directly recorded. Systems may infer certain values from others, leading to differences: for example, an inverter might estimate building consumption from production and input measurement (grid import and export), while another system might calculate production based on measured consumptions.
4. Measurement Location and Losses: The production indicated by the inverter corresponds to DC electricity generated, whereas Climkit measures the AC electricity actually injected into the building's grid after conversion. The DC/AC transformation and the cables cause a loss of 3% to 5%.
   When using an MT/BT (Medium/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. Furthermore, rounding figures can cause slight deviations across the total for a period.
6. Battery Presence: If the site includes a battery, the method for metering stored or delivered energy varies between systems, particularly at night when the battery discharges. Small amounts of energy may be injected into or withdrawn 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 indicate an error or malfunction.

How to verify the accuracy of the measurements?

Climkit regularly checks the consistency of its measurements. The simplest test is to examine the 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 function.

For other systems, you should contact the installer to check the configuration and proper functioning of the equipment.

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 detailed analysis of any differences.