Being “climate neutral” means only releasing as much greenhouse gas as can be recaptured or absorbed. Many nations have set themselves this goal, however the path to doing so is lengthy and exacting on all involved. Germany, for instance, has declared its intention to be climate neutral by 2045. To do this in the time available requires pressing ahead consistently with the expansion of renewable energies, amongst other measures, which itself brings new challenges.

The expansion of electricity generation from wind and solar power necessitates a diverse range of action. This includes upgrading the power grid and constructing energy storage facilities, both of which to the required extent are more likely in the medium term. One approach that can be immediately pursued is intelligent management, also referred to as feed-in management, of decentralised energy producers and consumers. Feed-in management allows decentralised electricity producers to feed in their electricity and energy suppliers to ensure the necessary stability of the power grid.
Figure 1 shows how grid operators ensure the balance of the power grid (voltage and frequency). The approach involves balancing supply (production of electricity) and demand (consumption of electricity).

Schema

Figure 1: Grid stability – grid operators must balance the power grid (voltage and frequency). Supply (production of electricity) and demand (consumption of electricity) must be kept balanced.

 

The challenges of decentralised energy generation

Feed-in management is therefore about intelligently controlling energy flows. Due to the fluctuating availability of wind and solar energy and because consumption doesn’t remain static, generating plants must be controllable and effective power feed restrictable. This is the only way to ensure grid stability with the increasing number of decentralised generating plants.
Feed-in management has been established in Germany since 2012 and has assumed this role for many photovoltaic plants. The major objective then was to integrate decentralised electricity producers into the power grid without having to expand it right away.

Some 9 years on, new rules are needed for the controllability of photovoltaic plants. This is because it’s now about suitably equipping the increasing number of generating plants to cope with future requirements. Grid stability in this respect is tested in particular by new technologies such as e-mobility and heat pumps, i.e. continually increasing energy requirements, alongside sluggish grid expansion and lacking storage capacity.

Feed-in management in medium-voltage grid

Solar-Log GmbH was amongst the first manufacturers in 2012 to bring to market a solution for feed-in management for photovoltaic plants. The Solar-Log energy management system allows photovoltaic plants of any size to meet the corresponding requirements.
A new regulation came in 2019, known as VDE-AR-N 4110 (VDE 4110). Faced with the rapidly increasing prevalence of photovoltaic plants amongst other factors, new connection rules became necessary in the medium-voltage grid intended to safeguard stability within the infrastructure. In many other countries too with increasing use of renewable energies, the same or similar regulations are now coming into effect.
The new rules in Germany concern all photovoltaic plants that are grid-connected via a grid operator’s medium-voltage infrastructure.

Grid

Figure 2: The graphic shows which plants belong to the medium-voltage grid.

The VDE-4110 regulation also became necessary in light of the projected further development of the European domestic energy market. The new requirements have been set out in the European Domestic Electricity Market Directive and the Domestic Electricity Market Regulation. The goal is to ensure a frictionless electricity market in the EU that is also capable of functioning cross-border. The objective also includes to generate further competition and to establish a transparent wholesale market. (Source: Zentrale und dezentrale Elemente im Energiesystem, Nationale Akademie der Wissenschaften Leopoldina, acatech – Deutsche Akademie der Technikwissenschaften, Union der deutschen Akademien der Wissenschaften, 2020 (Central and decentral elements in the energy system, German National Academy of Sciences Leopoldina, acatech – German National Academy of Science and Engineering, Union of German Academies of Sciences and Humanities, 2020)
This makes the new VDE regulation a constituent part of European requirements,which will also affect, now or in future, many other countries in the EU.

Solution for connecting photovoltaic plant to medium-voltage grid

First of all, the question arises: what exactly do the new regulations require of the plant owner or operator? Examining the German market shows just how complex the requirements are (see Figure 3). Various characteristic curves for instance, such as Q(U) for stabilising voltage, are implicated. Moreover, it must be possible to retrieve different measurement values such as P, Q, U and I. Only when these and other requirements are satisfied can the photovoltaic plant feed into the German electricity grid.

Voltage

Voltage

Figure 3: Requirements for active power and reactive power control for grid operators governing connected photovoltaic plants with intention to feed in photovoltaic power.

Roland Löhr is Technical Manager for utility and other projects at Solar-Log GmbH, a world-leading photovoltaic monitoring, smart energy and feed-in management manufacturer. He and his team are responsible, amongst other things, for the implementation of the VDE-4110 standard at Solar-Log. In a short interview, he describes the nature of the challenges faced, past and present, and the benefits to the photovoltaics industry of the standard.

What solutions does the Solar-Log system offer for implementing such complex requirements?

One standard, many different demands. That could be the title of the VDE-AR-4110 standard. Not only the new rules, but also requirements on the speed and accuracy with which rules must be implemented have been tightened. That presented one of the biggest challenges for us. Since we were quite ahead of the game at the time – when it came to introducing feed-in management, we welcomed this new project at Solar-Log despite the many hurdles.

It was therefore necessary to expand the capabilities of the Solar-Log system in the area of active and reactive power and also, for the respective grid operators, to fulfil the requirements around plant regulation in the medium-voltage range.
Nearly every grid operator places different requirements on photovoltaic plants feeding into “their” grid. This is why we now offer a full range of regulation options. The positive side effect of this diversity is that the Solar-Log system is now also prepared and ready for photovoltaic plants, e.g. in Switzerland and Austria.

One of the most in-demand solutions of grid operators is shown in Figure 5. In order to satisfy the requirements and regulations, a data logger (Solar-Log Base 2000), DIN rail power pack, Modbus TCP and direct marketing licences and a utility meter are needed. This makes it possible to implement the respective requirements with all components such as inverter, data logger, telecontrol technology and direct marketer.

Components

Figure 4: Various components are needed in order to satisfy the requirements of grid operators. An EZA controller with telecontrol technology and direct marketing and Q(U) or Q(P) characteristic curve are used in this example.

Can you explain again in more detail how you implement a newly added requirement?

With pleasure. Relatively new for the connection rule VDE-4110 is the Q (P/Pn) regulation or Q(U) with voltage deadband. In the example given (Figure 6 a), we have four different levels for this regulation, whereas there are also grid operators requiring up to seven levels. In this case, we can, of course, adjust these on the data logger, too.
Figure 6 b further below shows where these values must be met, i.e. where they can be measured and how high they may correspondingly be. These points are, for instance, at the substation or at the generating plants. It is furthermore clearly regulated what needs to be fulfilled in the case of failure of telecontrol technology or measurement systems. In this example, operation would then continue, in fact with the last valid value received. All of these settings can then be made in the Solar-Log system.

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Figure 5: Questionnaire on which requirements the grid operator places on the respective PV system.

We’ve just seen the questionnaire that customers need to complete. Does Solar-Log offer customers additional help and support around implementing the VDE regulation?

Yes. We are aware of the multitude of requirements and bureaucracy plant operators have to contend with and understand that they can’t be experts in every area. This is why we offer an all-round service, if needed, or project support. Four steps are involved:

1. We inform the customer of possible solutions around implementing the required regulation.
2. We plan and coordinate the solution with the customer and grid operator. The necessary components are subsequently ordered.
3. When installing components and setting them up, we are there to support the customer.
4. And finally, we work to ensure seamless commissioning and take care of the subsequent reporting.

How does the plant operator benefit and how does the solar industry progress in all of this?

Essentially it’s about ensuring grid stability and thus allowing as many renewable energy and photovoltaic plants as possible to feed into the grid. The proportion of renewable plants should increase in future, and the VDE regulation effectively creates the basis for this. In the long term, this will probably not be enough, however, work is ongoing on grid expansion. The photovoltaics industry and individual plant operators thus benefit from the regulation – even if at this stage it means further outlay.

Can you give us another practical example?

We had an industrial firm not long ago that wanted to feed in power from a photovoltaic plant that had been installed. This plant again shows that often custom solutions are sought after when it comes to feeding in power in the medium-voltage grid.
For implementing the Q(U) characteristic curve, measurement is required at the grid connection point in the substation. For this, Solar-Log requires the measurement values of a compatible grid analyser. Retrofitting such an appliance, however, would have been extremely difficult, since the company’s entire power supply would need to have been shut off.

It was possible to find another way, however, together with the grid operator. The grid operator already had a corresponding measurement and agreed to supply to Solar-Log the necessary measurement values via the Modbus TCP PM interface. This allowed the customer to save a lot of time and money for the additional installation.

We were able to complete the configuration and commissioning tests together with the installer and network operator, again in quick time. This ultimately meant timely feed-in for the photovoltaic plant and no additional outlay for the customer.