1. October 2025
Multiple solar installations installed out on long feeders, as you typically see in rural settings, have become one of a DSO’s biggest headaches. This is because of two factors:
- The ‘simultaneity factor’ is extremely high i.e. all the solar arrays behave in the same way at the same time.
- The solar arrays need to produce a voltage higher than that of the network to be able to feed their electricity in.
This leads to large spikes in voltage during sunny periods, and this is a problem for DSOs as they are required to maintain a stable voltage level of 230v +/- 10%. The consequence of these higher voltages can be damage to more sensitive electronic devices and/or financial penalties for the DSOs for not complying with regulatory requirements. In turn, this leads to DSOs being particularly cautious about allowing solar systems to be connected to their networks, which then in turn leads to a slowing down of the instruction of low carbon electricity production.
So, the question is: How can DSO allow more solar installations without at the same time allowing voltage level violations?
If you talk to any DSO who has parts of their network with significant portions of roof top solar installations, then you’ll hear them talk about voltage issues. What are these issues, what are they caused by, and what can a DSO do about it?
What is the problem?
For solar systems to be able to feed-in to the grid they need to raise their voltage level higher than that on the cable they are feeding into. Using the age-old analogue of the water pipes and pressure you could image if you wanted to feed-in water back into the water pipes in the road the pump in your house would need to generate a pressure greater than the incoming water pressure for the water to flow ‘backwards’. This increased voltage doesn’t need to be much; it just needs to be higher than the incoming voltage. The problem is based on two factors, the first is that the DSOs must conform to EN50160 which says that voltages need to be maintained within +/-10% of 230v. The second factor is the cumulative effect of separate solar installations i.e. as one system raises the voltage the next needs to raise it further to also be able to feed-in. Another compounding factor is that the solar generation is greatest at the same time and to the same degree for all the systems on a feeder.
What can a DSO do about it?
The first step is to identify the issue, where is it happening and to what extent. This can be done through modelling and simulation packages so long as the DSO has all the relevant data (the emphasis being on ‘ALL’ – these models are only accurate if the whole system is accurately represented). If not all the required data is present then the DSO needs to have some working assumptions to fill the gaps, these assumptions can be refined through taking measurements at certain points in the network and using these measurements to refine the assumptions and thereby get closer to reality.
Once the issue has been clearly identified i.e. where is it happening and to what extent, the DSO has the choice of either a ‘hardware fix’ or a ‘smart fix’. A hardware fix is one where the DSO installs a piece of hardware within the network specially designed to adjust voltage levels such as a transformer with a variable tap changer or a voltage regulator. These have a fixed CAPEX cost which will be reflecting in the network fees. A smart fix on the other hand is one where DSO either sets up a mechanism by which it can communicate with the solar systems and activate some form of curtailment i.e. ask the systems to stop or at least reduce their output. This would have to have some form of compensation as the customer would normally expect to earn money through the sale of the energy generated. Another solution is to try and activate loads (which have the opposite effect on voltage i.e. they reduce the voltage along a feeder). The key thing here is the location of the loads i.e. it doesn’t help if the solar feed-in is high within a particular residential area and the load is increased at an office complex on the other side of town. The load increase needs to happen downstream of the same secondary substation where the voltage increase is being experienced, and ideally on the same feeder. To enable this a high level of information granularity is required i.e. I need to know which assets are installed where and have some level of information about their availability and capacity i.e. an EV charger doesn’t help me very much if the car isn’t plugged in or if the car is fully charged. As you can see this really is an information and coordination problem.
This is where flexibility market platforms can help. In essence, they help match up the requirements for flexibility with the capacity for flexibility. In our example they can help connection up requirement of dropping the voltage with the capacity of EV chargers. Flexibility platforms aren’t the main topic of this article – you can find out more here.
How can DSOs allow more solar systems to be connected without endangering voltage levels?
Another part of ‘the problem’ is that DSOs tend to use models and simulations to work out whether they can allow the connection of additional solar systems. The issue being that these models and simulations tend to be setup with overly conservative assumptions and/or have low quality data feeding into them. At SMIGHT we can help with both issues by feeding these models with real measurements which allows the models to more closely represent reality and thereby usually allow for more solar systems to be connected.
