Short definition
The self-consumption ratio describes the proportion of generated energy that is used within the energy system under consideration rather than exported to the public grid. In the PV system considered here, the metric refers to the generated PV energy and is calculated for a defined period.
Self-consumption ratio at a glance
- The self-consumption ratio compares the self-consumed PV energy with total PV generation.
- Self-consumed PV energy can include energy consumed directly and PV energy temporarily stored in a BESS for subsequent on-site use.
- A high ratio does not automatically mean that a site covers a large proportion of its total consumption itself.
How is the self-consumption ratio calculated?
The ratio is normally calculated for a day, month or entire year:
In a simple system with PV as the only generator, clearly attributable grid export and no BESS energy charged from or subsequently discharged into the grid, the self-consumed PV energy can be calculated using the following simplified difference:
If a PV system generates 100 MWh within one year and exports 30 MWh to the public grid, this simplified calculation gives a self-consumed PV energy value of 70 MWh. The ratio is therefore:
The 70 MWh may be consumed directly by loads or partially stored in a BESS. Whether storage losses and energy remaining in the BESS at the end of the evaluation period are counted as self-consumption depends on the defined calculation method.
Typical applications of the self-consumption ratio
The self-consumption ratio is primarily used to assess and monitor PV systems in commercial, industrial and other similar applications. Typical uses include:
- Operators can determine what proportion of PV generation is consumed on site or stored for subsequent use.
- Planners can compare different PV and BESS system sizes.
- Continuous monitoring can identify changes over time and shifts in load or generation profiles.
- The metric supports the evaluation of self-consumption optimization measures, such as load shifting or the use of a BESS.
Difference between self-consumption ratio and self-sufficiency ratio
The two metrics use different reference values and therefore answer different questions:
| Metric | Reference value | Meaning |
|---|---|---|
| Self-consumption ratio | PV generation | What proportion of the generated PV energy is used on site? |
| Self-sufficiency ratio | Total energy consumption | What proportion of total consumption is supplied by PV and, where applicable, a BESS? |
A small PV system may use almost all of its generation on site and therefore achieve a high self-consumption ratio. If the site’s total consumption is significantly higher, its self-sufficiency ratio will nevertheless remain low.
Benefits, limitations and required measurements
The self-consumption ratio provides a concise assessment of the local use of PV energy. For a meaningful economic and technical evaluation, it should be considered together with the ratio, total PV generation, site consumption and the energy flows over time.
A reliable calculation requires time-consistent values for PV generation and clearly attributable grid export. More complex systems additionally require measurements of grid import and the charging and discharging flows of the BESS. The calculation method must define whether storage and conversion losses or changes in the state of charge over the accounting period are treated as self-consumption.
If a BESS is also charged from the grid or exports energy to the public grid, the simplified difference calculation may produce incorrect allocations. The same applies to systems with additional generators, multiple grid connection points, different measurement intervals or meter failures. The evaluation period, system boundary, measurement concept and calculation method should therefore always be specified with the metric.
How can EcoPhi support the evaluation?
EcoPhi can combine measurements of PV generation, site consumption, grid export, grid import and BESS energy flows. These values can be used to visualize and evaluate the self-consumption ratio and energy flows over defined periods.
The specific evaluation depends on the available measurements and device interfaces. Inverter data alone are often insufficient. A suitable meter at the grid connection point is normally required to record grid import and export correctly.
Self-consumption ratio summarized
The ratio indicates what proportion of the generated PV energy is consumed directly or stored for subsequent use on site. For systems with a BESS, additional generators or complex energy flows, the calculation method must be clearly defined and adapted to the measurement concept.
Frequently asked questions about the self-consumption ratio
Is a high self-consumption ratio always economically beneficial?
Not necessarily. The economic assessment depends on factors including electricity purchase prices, feed-in remuneration, investment in a BESS and the resulting energy losses.
Does charging a BESS count as self-consumption?
PV energy stored in a BESS and subsequently used on site can be allocated to self-consumption. The calculation method must define how storage losses and energy remaining in the BESS at the end of the evaluation period are treated.
Can the ratio exceed 100%?
No. A value above 100% indicates incorrect measurements, inconsistent evaluation periods, unsuitable system boundaries or an incorrect allocation of energy flows.
Which meters are required?
In a simple PV system, reliable measurements of PV generation and grid export are required as a minimum. Systems with additional generators or complex BESS energy flows require further measurements of grid import, site consumption and BESS charging and discharging energy.