Anyone who operates a solar system tries to consume as much of the electricity produced as possible themselves. After all, you can then save on the high end customer prices for electricity.
What does self-sufficiency mean - a definition?
In relation to a solar system, the term self-sufficiency refers to the degree of independence of a system operator from the electricity grid. If only self-produced solar power is consumed, this is referred to as complete self-sufficiency.
The higher the proportion of electricity consumed that is provided by the solar system, the higher the self-sufficiency of the system in question.
However, a typical photovoltaic system usually only has a degree of self-sufficiency of 30 to 40 percent. However, the degree of self-sufficiency can be further increased with the help of a solar storage system.
The less electricity is drawn from the grid, the higher the degree of self-sufficiency, also known as the "self-sufficiency rate". The degree of self-sufficiency is calculated from the proportion of self-generated solar power in the system owner's total electricity consumption.
Local and balanced self-sufficiency
In principle, a distinction can be made between local self-sufficiency and balance sheet self-sufficiency.
In the case of local self-sufficiency, electricity does not have to be drawn from the grid at any time, as the entire consumption is covered by the solar system or by corresponding solar storage systems.
In most cases, however, this local self-sufficiency does not exist. This is because in the summer months, more electricity is typically produced than is consumed. In winter, on the other hand, more electricity is often consumed than can be provided directly on site.
If these two values balance each other out, this is referred to as balance sheet self-sufficiency. In such a case, at least as much electricity is produced over the year as is consumed. However, electricity is still drawn from the grid in the meantime.
Why become self-sufficient?
In many cases, a high degree of self-sufficiency is an important criterion for evaluating a solar system.
Cost savings
For most private solar system owners, the focus is on the potential for cost reduction. This is because the state-guaranteed feed-in tariff for solar power is significantly lower than consumer prices for electricity. System operators therefore save with every kWh they produce themselves and do not have to purchase from the grid.
Environmental protection
Environmental protection can also be a reason for a high degree of self-sufficiency. After all, those who specifically reduce their own electricity consumption and adapt it to the production cycles of their solar system make a significant contribution to the energy transition and save large amounts of carbon dioxide.
Complete self-sufficiency
For consumers who are not connected to the electricity grid, solar self-sufficiency is an end in itself. However, even if there is access to the power grid, a high degree of self-sufficiency can have major advantages, at the latest when the next power outage occurs.
What is a good level of self-sufficiency?
Solar systems installed by private individuals often have a degree of self-sufficiency of between 30 and 40% without the option of storing electricity. This means that the majority of electricity is drawn from the grid despite the solar system.
With a solar storage system, this value can usually be increased to around 80%. This is because with appropriate storage capacities, surplus solar power can be stored and only used when consumption exceeds electricity production.
In most cases, private households do not achieve self-sufficiency levels that are significantly higher than 80%. One reason for this is that too little electricity is often produced in winter. On the other hand, it is usually not economically viable to cover the entire electricity consumption in the morning and evening hours with stored solar power, as the storage units would then have to be uneconomically large.
The following table shows an example of how self-sufficient your household should be with photovoltaics:
|
Power Consumption |
System Size |
Energy Storage |
Self-consumption |
Autonomy Level |
|---|---|---|---|---|
|
2000 kWh |
5 kWp |
Nein |
15% |
37% |
|
2000 kWh |
5 kWp |
8 kWp |
36% |
84% |
|
2000 kWh |
10 kWp |
Nein |
8% |
41% |
|
3000 kWh |
5 kWp |
Nein |
20% |
35% |
|
3000 kWh |
5 kWp |
8 kWp |
39% |
77% |
|
3000 kWh |
10 kWp |
Nein |
11% |
39% |
|
3000 kWh |
10 kWp |
10 kWp |
28% |
86% |
|
5000 kWh |
10 kWp |
Nein |
17% |
36% |
|
5000 kWh |
10 kWp |
10 kWp |
41% |
76% |
How can you increase the degree of self-sufficiency?
In order to increase the degree of self-sufficiency, several parameters can be optimized.
Reduce your electricity consumption
The simplest option is to reduce your own electricity consumption. This reduces electricity costs and increases independence. However, this is not a sustainable solution. You must bear in mind that a lower proportion of your own consumption means that you feed more electricity into the grid. With the EEG feed-in tariff currently below 9 cents per kilowatt hour, this leads to a lower return.
Plan electricity consumption intelligently
In addition, consumption patterns should also be analyzed over time. For example, as much electricity as possible should be consumed when the sun is shining. One simple way to optimize this is to use the washing machine's timer to do the laundry at midday, for example.
Good planning of the PV system
As a final optimization option, the self-sufficiency options should be considered when planning the solar system. In addition to the specific dimensions of the system, the storage options already mentioned must also be included in the planning.
Is 100% self-sufficiency possible with photovoltaics?
In principle, complete self-sufficiency with solar power is possible and is referred to as a stand-alone photovoltaic system. However, this is not economically attractive in most cases and is therefore usually only worthwhile for consumers such as mountain huts that cannot be connected to the electricity grid.
For average private users, on the other hand, the storage costs are too high to aim for complete self-sufficiency. After all, the electricity storage system used must be dimensioned in such a way that it can maintain the power supply over longer phases of low electricity production. Such phases exist in winter, for example.
In order to produce enough electricity for complete self-sufficiency in the cold season, very large available areas for the solar modules would be required in addition to powerful solar storage systems.
What is the difference between self-consumption and self-sufficiency?
Even though both self-consumption and self-sufficiency are related to the amount of solar power consumed by the user, these two terms refer to very different processes.
The degree of self-sufficiency is the amount of self-generated electricity that covers your needs without drawing electricity from the grid. The higher the proportion of electricity consumption covered by the solar system, the higher the degree of self-sufficiency. This can therefore also be increased by reducing electricity consumption.
Self-consumption, on the other hand, serves as an economic efficiency criterion for a solar energy system. It indicates the proportion of self-consumed electricity in the total solar production. This parameter is therefore particularly dependent on whether electricity production occurs at the same time as electricity consumption or whether there are corresponding storage options for the electricity.
How is the degree of photovoltaic self-sufficiency calculated?
It is relatively easy to calculate the degree of self-sufficiency. This is because it is the quotient of the self-consumed solar power and the electricity consumption.
The formulas for calculating self-sufficiency and self-consumption are as follows:
Self-sufficiency = 1 - purchased electricity / consumed electricity
Self-consumption = electricity consumed / electricity produced
An example: A household with an annual electricity consumption of 4,000 kWh has a solar system with an average electricity production of 2,5000 kWh. Of this, 1,500 kWh is fed into the electricity grid.
Self-consumption therefore amounts to 1,000 kWh.
The degree of self-sufficiency of the corresponding household is therefore 1,000 kWh / 4,000 kWh = 25%.
The degree of self-sufficiency calculated in this way represents an annual average value. Typically, the degree of self-sufficiency is higher in summer than in winter. After all, the sun shines longer in the summer months. This means that solar power can be used over a longer period of time even without storage options.
Calculating the degree of self-sufficiency of a PV system with storage
When using a storage system, the calculation is different and more complex.
The additional variables are as follows:
Capacity of the storage system in kWh
Maximum depth of discharge
Efficiency
A useful tool for calculating the self-sufficiency and self-consumption rate is the independence calculator from the Berlin University of Applied Sciences.
Conclusion
Self-sufficiency refers to the ability of a solar system to cover the electricity consumption of the system owner. The higher the degree of self-sufficiency, the less electricity has to be drawn from the grid.
Without appropriate measures, most private solar systems achieve a degree of self-sufficiency of 30 to 40%. With the help of electricity storage systems and consumption patterns adapted to electricity production, this can be increased to around 80% by private users.
Aiming for a higher degree of self-sufficiency is not economically viable in most cases. This is because the electricity storage units required for this would have to be extremely large, which would result in very high acquisition costs.
