Distribution of photovoltaic in site consumption

How is photovoltaic electricity distributed among consumers?

1. Electricity consumption is divided into two parts: that sourced from the grid and that sourced from the photovoltaic (PV) installation.
2. To determine these two shares, Climkit, by default, bases its calculations on the input meter, which includes two flows: offtake from and feed-in to the grid, as well as consumption meters.
3. The PV share in consumption is then calculated as follows: PV share = sum of consumptions - offtake. 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 offtake and feed-in are accounted for according to DSO billing and remunerations, and that the offtake is distributed equitably among consumers.
6. The photovoltaic production is thus determined using the following formula: Production = sum of consumptions - offtake + feed-in. The site's self-consumption rate is obtained by the formula: PV share / production.

Why is there feed-in and offtake 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, electricity is drawn from the grid. But if, at the end of the period, consumption decreases, the surplus production is fed back into the grid.
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 accounted for by the DSO, which bills for offtake at the beginning of the period and remunerates feed-in at the end of the period.

Why is there some production at night?

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

What should be done in case of large discrepancies between offtake and consumptions?

1. If the difference between the offtake without production and the consumption is significant, it indicates that at least one consumption point is not being measured, meaning at least one meter is missing.
2. Pending the installation of an additional consumption meter, a rule meter is created to account for this "unmeasured" consumption. This rule meter can then be added to the site's common area meter or directly assigned to a billing point.
3. By deducting this unmeasured flow, the input meter, consumption meters, and production meter are correctly accounted for.

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

1. This rule meter would absorb all minor differences and thus sometimes record positive and sometimes negative values, which would influence the grid's share in consumer consumption, causing it to no longer exactly match the quantity billed by the DSO.
2. Furthermore, if the rule meter is assigned to the common area billing point, it would artificially 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 it would make the charts more uniform (eliminating nocturnal production), the unmeasured flow should only be deducted if it genuinely corresponds to an unmeasured consumer. In all other cases, the production flow is deducted, 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. The installation of a battery allows for the storage of 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 further surplus is fed into the electrical grid.
3. When consumption exceeds solar production, the battery discharges to supply 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 drawn from the grid.

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

It is completely normal to observe discrepancies between the data displayed on the Climkit platform, 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 accurate.
2. Metering Type: Direct metering (meter connected directly to the circuit) is more accurate than indirect metering using current transformers (CT). For best results, CTs adapted to the actual measured current should be used. In practice, DSOs often install oversized CTs, which can cause underestimation at low currents.
3. Calculation Methods: Self-consumption of electricity on a photovoltaic site is generally calculated from different measurements, not measured directly. Systems may deduce certain values from others, leading to differences: for example, an inverter might estimate building consumption from production and input measurements (offtake and feed-in), while another system might calculate production based on measured consumptions.
4. Measurement Location and Losses: The production indicated by the inverter corresponds to electricity generated as direct current (DC), whereas Climkit measures what is actually injected as alternating current (AC) into the building's grid after conversion. The DC/AC transformation and wiring result in a 3% to 5% loss.
   When using an MV/LV transformer (medium/low voltage), 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 slight differences, especially if consumption fluctuates rapidly. Furthermore, rounding figures can lead to minor deviations in the total for a period.
6. Battery Presence: If the site includes a battery, the method for metering stored or released energy varies between systems, particularly at night when the battery discharges. Small amounts of energy may be fed in or drawn from the grid without always being recorded 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 involves examining the data at night: with no solar production, the sum of individual consumptions must match the energy imported from the grid (main meter). This "night test" is a good indicator of system functionality.

For other systems, you should contact the installer to verify the configuration and proper functioning 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.