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 has two flows: withdrawal from and feedback to the grid, as well as the consumption meters.
3. The share of photovoltaic in the consumption is then calculated as follows: share of PV = sum of consumptions - withdrawal. The site's autonomy rate is obtained by the formula: share of PV / 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 supplied by the grid.
5. By basing on the flows of the introduction meter, it ensures that the withdrawal and feedback are accounted for in accordance with the billing and reimbursements of the DSO, and that the withdrawal is equitably distributed among consumers.
6. The photovoltaic production is therefore deduced using the following formula: Production = sum of consumptions - withdrawal + feedback. The site's self-consumption rate is obtained by the formula: share of PV / production

Why is there both feedback and withdrawal from the grid in the same 15-minute period when production equals consumption?

1. If at the beginning of the period, consumption exceeds production, we withdraw from the grid. But if, at the end of the period, consumption decreases, the surplus production is fed back.
2. If we didn't base calculations on the introduction meter, we would have 100% site autonomy during those 15 minutes. However, this wouldn't reflect the reality accounted by the DSO, which bills for withdrawal at the beginning of the period and reimburses feedback at the end of the period.

Why is there some production at night?

1. Given that there are losses and counting discrepancies (for example, the introduction meter often records a withdrawal lower than that of all consumption meters, even without production), these discrepancies are absorbed in the calculation of the production deducted.
2. If the withdrawal exceeds consumption, production is observed at night. This means that the introduction meter is less precise than the overall consumption meters.
3. Conversely, if the withdrawal is less than consumption, a negative production is obtained, indicating that part of consumption is not measured by a meter.
4. If these values remain minimal, they account for normal losses in the installation that can be ignored, as they slightly decrease production without affecting the withdrawal and thus the grid's share in consumption.

What to do in case of significant discrepancies between withdrawal and consumption?

1. If the difference between withdrawal 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 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 account for the introduction meter, the consumption meters, and the production meter.

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

1. This rule meter would absorb all minor differences, sometimes recording positive values, sometimes negative values, which would influence the grid's share in consumers' consumption and would no longer match the amount billed by the DSO.
2. Furthermore, if the rule meter is assigned to the commons billing point, it would increase or decrease the commons' consumption, which would no longer match what is actually measured by the commons meter.
3. In conclusion, even though this would make the graphs more uniform (without nighttime production), the unmeasured flow should only be deducted if it is truly 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 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 excess photovoltaic (PV) electricity produced on-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 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, additional electricity is automatically withdrawn 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 network manager'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, like some "smart meters" integrated into the inverter, may be slightly less accurate.
2. Type of measurement: Direct measurement (meter connected directly to the circuit) is more accurate than indirect measurement with current transformers (CT). For better results, appropriately sized CTs for the actual measured current should be used. In practice, DSOs often install oversized CTs, which can lead to underestimation at low current.
3. Calculation methods: The self-consumption of electricity on a photovoltaic site is generally calculated from different measurements, rather than measured directly. Systems may deduce certain values from others, leading to differences: for example, an inverter may estimate the building's consumption based on production and the measurement at the introduction (withdrawal and feedback), while another system may calculate production based on measured consumptions.
4. Location of measurement and losses: The production indicated by the inverter corresponds to the electricity generated in direct current (DC), whereas Climkit measures that which is actually injected in alternating current (AC) into the building's grid after conversion. The DC/AC transformation and the cables incur a loss of 3 to 5%.
   In the case of using a transformer HV/LV (high/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 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 for measuring stored or returned energy varies depending on the systems, especially at night when the battery discharges. Small amounts of energy can be injected 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 measuring systems are normal and do not mean that there is an error or malfunction.

How to check the accuracy of measurements?

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 should match the energy imported from the grid (main meter). This "night test" is a good indicator of the system's functioning.

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

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