Anyone who operates a solar system tries to consume as much electricity as possible themselves. After all, you can save money on electricity prices for high-end customers.
What does it mean to be self-sufficient – definition?
In the context of solar energy systems, the term “self-sufficiency” refers to the degree to which the system operator is independent of the grid. If only self-produced solar energy is consumed, this is called full self-sufficiency.
The higher the proportion of electricity consumption provided by a solar system, the more self-sufficient the system is.
However, typical photovoltaic systems usually have a self-sufficiency rate of only 30% to 40%. However, the degree of self-sufficiency can be increased further with the help of a solar energy 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 self-sufficiency rate is calculated based on the proportion of total electricity consumption that is generated by the system owner itself.
Locally 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 taken from the grid at all times, as the entire consumption is covered by the solar system or the corresponding solar storage system.
However, in most cases, this local self-sufficiency does not exist. This is because in the summer, more electricity is usually produced than consumed. On the other hand, in the winter, more electricity is often consumed than is directly provided on site.
If these two values balance each other, it is called balance sheet self-sufficiency. In this case, at least as much electricity is generated throughout the year as is consumed. However, at the same time, electricity is still taken from the grid.
Why be 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 solar feed-in tariff is significantly lower than the electricity price for consumers. Therefore, system operators can save every kWh of electricity they produce themselves instead of buying it from the grid.
Environmental friendly
Environmental protection is also a reason to be highly self-sufficient. After all, those who exclusively reduce their own electricity consumption and adapt it to the production cycle of solar systems make a significant contribution to the energy transition and save a lot of CO2.
Completely self-sufficient
For consumers not connected to the grid, solar self-sufficiency is an end in itself. However, even with access to the grid, a high degree of self-sufficiency can bring significant advantages, at the latest during the next power outage.
What is a good level of self-sufficiency?
Privately installed solar systems typically have a 30% to 40% self-sufficiency rate, without the need to store electricity. This means that despite the solar system, most of the electricity comes from the grid.
With solar energy storage systems, this value can typically be increased to around 80%. This is because, with appropriate storage capacity, surplus solar energy can be stored and used only when consumption exceeds generation.
In most cases, the level of self-sufficiency of private households cannot be significantly higher than 80%. One reason for this is that electricity generation is often too low in winter. On the other hand, it is usually not economically feasible to cover the entire electricity consumption in the morning and evening with stored solar energy, as the storage units would have to be very large and uneconomical.
The table below shows an example of how your home could become PV self-sufficient:
| Energy consumption | System Dimensions | Energy Storage System | Self-consumption | Level of autonomy |
|---|---|---|---|---|
| 2000 kWh | 5 kWh | No | 15% | 37% |
| 2000 kWh | 5 kWh | 8 kWh | 36% | 84% |
| 2000 kWh | 10 kWh | No | 8% | 41% |
| 3000 kWh | 5 kWh | No | 20% | 35% |
| 3000 kWh | 5 kWh | 8 kWh | 39% | 77% |
| 3000 kWh | 10 kWh | No | 11% | 39% |
| 3000 kWh | 10 kWh | 10 kWh | 28% | 86% |
| 5000 kWh | 10 kWh | No | 17% | 36% |
| 5000 kWh | 10 kWh | 10 kWh | 41% | 76% |
How to improve self-sufficiency?
To increase the degree of self-sufficiency, several parameters can be optimized.
Reduce electricity usage
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 have to remember that a lower proportion of your own consumption means that you provide more electricity to the grid. Since the EEG feed-in tariff is currently below 9 cents per kWh, this leads to lower returns.
Intelligent power planning
In addition, consumption patterns should also be analyzed over time. For example, when the sun is shining, electricity should be consumed as much as possible. For example, a simple way to optimize this is to use a timer on your washing machine to do your laundry at noon.
Good PV system planning
As a final optimization option, the option of self-sufficiency should be considered when planning a solar system. In addition to the specific size of the system, the storage options already mentioned must also be included in the planning.
Can photovoltaic power generation achieve 100% self-sufficiency?
In principle, it is possible to be completely self-sufficient in solar energy, known as a stand-alone photovoltaic system. However, in most cases this is not economically attractive and is therefore usually only of value to consumers such as mountain huts that cannot be connected to the grid.
On the other hand, storage costs are too high for ordinary private users to achieve complete self-sufficiency. After all, the electricity storage systems used must be sized to maintain the power supply during longer periods of low electricity production. Such periods exist, for example, in winter.
In order to generate enough electricity during the cold season to achieve complete self-sufficiency, a very large available area is required to install the solar modules in addition to a powerful solar storage system.
What is the difference between self-consumption and self-sufficiency?
Although both self-consumption and self-sufficiency are related to the amount of solar energy consumed by the user, the two terms refer to very different processes.
The degree of self-sufficiency refers to the amount of self-generated electricity that can be used to meet your needs without taking electricity from the grid. The higher the proportion of electricity consumption covered by the solar system, the higher the degree of self-sufficiency. Therefore, this can also be increased by reducing electricity consumption.
Self-consumption, on the other hand, is a criterion for the economic efficiency of a solar system. It indicates the share of self-consumption in the total solar power generation. Therefore, this parameter depends in particular on whether electricity production occurs simultaneously with electricity consumption or whether there are corresponding electricity storage options.
How to calculate photovoltaic self-sufficiency?
The self-sufficiency rate is relatively easy to calculate because it is the quotient of self-consumed solar energy and electricity consumption.
The calculation formulas for self-sufficiency and self-consumption are as follows:
Self-sufficiency rate = 1-power purchase/power consumption
Self-use electricity = power consumption / power generation
Example: A household with an annual electricity consumption of 4,000 kWh has a solar system that produces an average of 25,000 kWh of electricity, of which 1,500 kWh is fed into the grid.
The self-consumption is therefore 1,000 kWh.
Therefore, the corresponding household self-sufficiency rate is 1,000 kWh/4,000 kWh=25%.
The self-sufficiency rate calculated in this way represents an annual average. Usually, the self-sufficiency rate is higher in the summer than in the winter. After all, the sun shines longer in the summer. This means that solar energy can be used for longer periods of time, even without storage options.
Calculating the self-sufficiency of a photovoltaic power generation system
When using a storage system, the calculations are different and more complex.
The additional variables are as follows:
A useful tool for calculating self-sufficiency and self-consumption rates is the stand-alone calculator from the University of Berlin’s School
of Applied Sciences.
in conclusion
Self-sufficiency refers to the ability of a solar system to meet the system owner’s electricity consumption. The higher the level of self-sufficiency, the less electricity is drawn from the grid.
Without appropriate measures, most private solar systems can only achieve a level of self-sufficiency of 30% to 40%. With the help of power storage systems and consumption patterns adapted to power production, private users can increase this to around 80%.
Pursuing a higher degree of self-sufficiency is not economically feasible in most cases. This is because the required electricity storage units would have to be very large, which would result in very high acquisition costs.
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