Allocation of photovoltaic 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 (PV) installation.
2. To determine these two shares, Climkit relies by default on the input meter, which includes two flows: energy imported from and energy fed back (electricity) to the grid, as well as on the consumption meters.
3. The share of photovoltaics in the consumption is then calculated as follows: photovoltaic share = sum of consumptions - imported energy. 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 the PV is then provided by the grid.
5. By basing the calculation on the flows of the input meter, we ensure that imported energy and energy fed back (electricity) are recorded in accordance with the billing and remunerations of the DSO, and that the imported energy is distributed fairly among consumers.
6. Photovoltaic production is therefore deduced using the following formula: Production = sum of consumptions - imported energy + energy fed back (electricity). The self-consumption rate of the site is obtained by the formula: PV share / production

Why is there energy fed back (electricity) and imported energy from the grid in the same 15-minute period even though 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 (electricity).
2. If we did not base it on the input meter, we would have 100% site autonomy during these 15 minutes. However, this would not reflect the reality recorded by the DSO, which bills for imported energy at the beginning of the period and remunerates the energy fed back (electricity) 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 imported energy lower than that of all consumption meters combined, even without production), these discrepancies are absorbed into the calculated deduced production.
2. If the imported energy is higher than the consumption, production is observed at night. This means the input meter is less precise than the set of consumption meters.
3. Conversely, if the imported energy 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, these are normal losses in the installation that can be ignored, as they slightly decrease production without affecting the imported energy and thus the grid share in the consumption.

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

1. If the difference between imported energy 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 meter or directly assigned to a billing point.
3. By deducing this unmeasured flow, we take into account the input meter, the consumption meters, and the production meter.

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, sometimes negative, which would influence the grid share in the consumers' consumption, and it would no longer exactly correspond to the quantity billed by the DSO.
2. Furthermore, if the rule meter is assigned to the billing point of the common areas, it would increase or decrease the consumption of the common areas, which would no longer correspond to what is actually measured by the common meter.
3. In conclusion, even if it would make the graphs more consistent (without nocturnal production), the unmeasured flow should only be deduced if it is truly an unmeasured consumer. In all other cases, we deduce the production flow, which absorbs discrepancies and losses while remaining aligned with the input meter as recorded 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 photovoltaic (PV) electricity produced in excess 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 higher than 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 additional electricity is automatically imported from the grid.

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

It is completely normal to notice 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 precise.
2. Metering type: Direct metering (meter connected directly to the circuit) is more precise than indirect metering with current transformers (CTs). 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 generally calculated from different measurements, rather than read directly. Systems may deduce certain values from others, which induces differences: for example, an inverter may estimate building consumption from production and measurement at the input (imported energy and energy fed back (electricity)), 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 what is actually injected as alternating current (AC) into the building grid, after conversion. The DC/AC transformation and the cables lead to a loss of 3 to 5%.
   In the case of using a MV/LV (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. 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 by system, especially at night when the battery discharges. Small amounts of energy may be injected into 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 the accuracy of the measurements?

Climkit regularly monitors the consistency of its measurements. The simplest test consists of examining 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 operation.

For another system, it is advisable to contact the installer to check 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.