Distribution of photovoltaics 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 the introduction meter, which includes two flows: the extraction and the feedback to/from the grid, as well as the consumption meters.
3. The share of photovoltaic in consumption is then calculated as follows: PV share = total consumption - extraction. The site's autonomy rate is obtained by the formula: PV share / total consumption.
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 the PV is then supplied by the grid.
5. Basing this on the flows of the introduction meter ensures that the extraction and feedback are accounted for according to the invoicing and reimbursements of the distribution system operator (DSO), and that the extraction is fairly distributed among consumers.
6. The photovoltaic production is thus deduced with the following formula: Production = total consumption - extraction + feedback. The site's self-consumption rate is obtained by the formula: PV share / production.

Why is there feedback and extraction from the grid within the same 15-minute period when production equals consumption?

1. If at the beginning of the period, consumption is higher than production, extraction from the grid occurs. But if, at the end of the period, consumption decreases, the surplus production is fed back.
2. If we did not base this on the introduction meter, we would show 100% site autonomy during those 15 minutes. However, this would not reflect the reality accounted for by the DSO, which bills for extraction at the start of the period and reimburses the feedback at the end of the period.

Why is there some production at night?

1. Given that there are losses and measurement discrepancies (for example, the introduction meter often measures extraction lower than that of all consumption meters, even without production), these discrepancies are absorbed in the calculation of the deducted production.
2. If extraction exceeds consumption, night production is observed. This means the introduction meter is less accurate than the totality of the consumption meters.
3. Conversely, if extraction is lower than consumption, a negative production is obtained, indicating that part of the consumption is not metered by a counter.
4. If these values remain minimal, they are normal losses in the installation that can be ignored, as they slightly reduce production without affecting extraction and thus the share of the grid in consumption.

What to do in case of large discrepancies between extraction and consumption?

1. If the difference between extraction 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 an additional consumption meter to be installed, a rule-based meter is created to deduct this "unmeasured" consumption. This rule meter can then be added to the common meter of the site or directly assigned to a billing point.
3. By deducting this unmeasured flow, we consider the introduction meter, consumption meters, and production meter.

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

1. This rule meter would absorb all small differences and could thus sometimes account for positive values and sometimes negative ones, which would influence the share of the grid in consumer consumption, and it would no longer precisely match the amount billed by the DSO.
2. Moreover, if the rule meter is assigned to the common billing point, it would increase or decrease the consumption of the commons, which would no longer correspond to what is actually measured by the common meter.
3. In conclusion, although it would make the graphs more homogeneous (without nocturnal production), the unmeasured flow should only be deducted if it is genuinely an unmeasured consumer. In all other cases, we deduct the production flow, which absorbs discrepancies and losses while remaining aligned with the introduction 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 additional surplus is injected into the electrical grid.
3. When consumption becomes greater than solar production, the battery discharges to supply the consumers in the building. This mechanism significantly increases the self-consumption rate, as the solar electricity produced during the day is also available at night.
4. When the battery is empty, the additional electricity is automatically extracted from the grid.

Why are there differences between the photovoltaic inverter data, 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 grid operator's (DSO) meter.

Several reasons explain these differences:

1. Meter tolerance: Certified meters (e.g. MID) have an accuracy between 0.5 to 1%. Other meters, like some "smart meters" integrated into the inverter, may be slightly less accurate.
2. Type of metering: Direct metering (meter connected directly to the circuit) is more accurate than indirect metering with current transformers (CTs). For better results, appropriate CTs for the actual measured intensity should be used. In practice, DSOs often install oversized CTs, which can cause underestimation at low intensity.
3. Calculation methods: The self-consumption of electricity on a photovoltaic site is generally calculated from various measurements, not directly recorded. Systems may deduce certain values from others, leading to differences: for example, an inverter may estimate the building's consumption from production and the measurement at the introduction (extraction and feedback), while another system may 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 the electricity actually injected in alternating current (AC) on the building's grid, after conversion. The DC/AC transformation and cables lead to a loss of 3 to 5%.
   In the case of using a MT/BT transformer (medium/low voltage), losses are around 5%.
5. Measuring frequency: Systems measure and transmit data at different intervals (every minute, every 5 or 15 minutes, at set times or randomly etc.), which can generate small differences, especially if consumption varies rapidly. Additionally, rounding of figures 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 accounting for stored or released energy varies by systems, especially at night when the battery discharges. Small amounts of energy may be injected or extracted 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 that there is 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 should match the energy imported from the grid (main meter). This "night test" is a good indicator of the system's operation.

For another system, it is advisable to consult the installer to verify the configuration and proper functioning of the hardware.

Finally, to accurately compare two systems, it is recommended to export and compare the load curves (in 15-minute intervals) over several days. These data, available on the Climkit platform (Excel file), allow for detailed analysis of any differences.