To deal with the peaks and troughs in the existing low-voltage electricity grid, two principles are possible: Solution 1. Increasing the voltage in the low-voltage grid from 400 V /230 V (AC) to 660V / 400 V (AC), which can increase the transmission capacity over the cables to the connections (e.g. factories / remote residential houses) almost 3 times, This solution has been used in industry for many years and is the solution for special location with very long house connections (farms), However, this would require a step-down transformer 400 V /230 V (AC) at the connection for domestic use. Solution 2. Equip the transformer (10,000 volts / 400 V /230 V) in grid stations in residential areas with automatic (smart = intelligent) voltage regulation to cope with the many and rapid load fluctuations of solar panels (and wind energy). The need for timely solutions becomes clear, using the following examples:

From TW dated 18 September 2018.

Dutch solar power capacity is growing stormily: 60% more in 2017. This year, growth is expected to be even stronger. Solar power now accounts for 2.2% of total electricity production. Grid operators need to give all this decentralised generation a place on the power grid. Private individuals with solar panels can help by registering their solar panels in the PIR register. With this information, the grid operator can provide the required grid capacity.

Last month, however, grid operator Stedin reported that private individuals are massively failing to register. Based on a spot check with aerial photos, Stedin (Utrecht and South Holland) estimates that a quarter of private individuals with solar panels do not register their system, something that has been punishable by a fine of €150 to €20,000 in Flanders for a year now. The advantage for the private individual of concealing solar panels is, in the first instance, that even after 2020, when the current generous net-metering scheme is to be scrapped, he can de facto continue to net-metering by leaving his classic reversing Ferraris meter hanging in the meter box. In doing so, the phantom power producer hopes that the smart meter will not yet be compulsory by then.

What this can lead to becomes clear in streets with many solar panels: switching off inverters and thus faltering power production. When many solar panels simultaneously add power to the grid, the grid voltage increases. That voltage is 230 V on average and may increase or decrease by 10%. To prevent overloading, the law stipulates that the inverter switches off at 253 V. Many inverters are adjusted slightly more stringently for safety. Thus, solar panels are switched off precisely when there is a lot of sun and the owner loses income.

The foreland of ghost power generation is in the Groningen town of Loppersum. There, thanks to the depreciation scheme, homeowners have received €4,000 from NAM since 2015 to make their houses more energy efficient. Solar panels are a favourite among them. Entire streets were filled with solar panels at such a rapid pace that Enexis Netbeheer could not keep up. Consequence: the grid voltage shot up on sunny days and inverters switched off.

Massive grid reinforcement by extra cables in the ground is costly and time-consuming. A cheaper and smarter way to maintain voltage quality with all those solar panels is in transformer houses where the voltage of the medium-voltage grid (usually 10 kV) is reduced to around 240 V via a fixed ratio, explains Han Slootweg, professor of Smart Guide at TU/e and director of asset management at Enexis Netbeheer. Normally, the grid voltage from the transformer house to the end of the capillaries drops from around 240 V to around 220 V. However, if many solar panels are connected, the voltage does not drop from the transformer house, but rises. As a result, at the end of the low-voltage cable, the voltage exceeds 250 V and the solar panels automatically switch off. To avoid this, the voltage at the transformer house can be lowered in summer by adjusting the transformer's transfer ratio and then reset in winter, if necessary. However, this is a physical operation that requires technicians to go out and interrupt the electricity supply.

This can be done smarter, thought Enexis Netbeheer. That is why the first smart transformer in quake-prone areas of the Netherlands has been in Loppersum since last year. Until now, the technology used has only been applied to large high-voltage transformers. If the grid voltage changes, the transformer's turnover ratio is automatically adjusted (usually stepwise). At €20,000, the mains transformer with smart voltage control costs twice as much as an ordinary mains transformer. Prof Han Slootweg expects, that the smart transformer will be used on an increasing scale in the Netherlands.

The smart transformer is a solution if the grid runs up against the voltage limit, says Slootweg. But if the low-voltage grid reaches current limit, for instance when we start driving electric vehicles en masse, more cable still needs to go into the ground. This also applies to connecting large solar parks to the electric grid. The Netherlands now has 176 MWp of generating capacity in solar parks, with another 13 times the current capacity under development. Many of these parks are coming up in Groningen and Drenthe a.g. due to low land prices. Several grid operators, including Enexis Netbeheer already informed entrepreneurs, that these will sometimes have to wait several years for a feed-in connection.

Dutch firm Alfen in Almere supplies energy storage systems that can be placed at grid stations to balance supply and demand of electrical energy.

A further solution is to equip existing grid transformers with LS-LS voltage regulators:

'Smart' transformer in quake area from Dagblad "Het Noorden" 23 June 2017

The LS-LS regulator is located at Hogestraat 4. You should know it's there: the 'smart' transformer. Enexis' only one in the whole of the Netherlands. Because Loppersum is a unique area. With lots of solar panels.

An outgrowth of NAM's 'value increase scheme'. For 1,000 euros or more of quake damage, a homeowner can get up to 4,000 euros of subsidy to make the house energy efficient. For example, with solar panels. A large number do so and this has implications for the cable network. After all, the power no longer runs only from source to home, but also the other way round.

The excess energy generated by the solar panels goes back onto the grid, generating more voltage fluctuations and that needs to be absorbed. On a trial basis, a collaboration between Enexis and other grid operators such as Enduris, Liander and Rendo, this is being done in Loppersum with a self-regulating 'smart' transformer. Unique in the Netherlands.

Experiment

pThat's going well,'' says Jan Flonk, Enexis project manager. ''We are still experimenting, but it will soon be in the standard package, giving us a choice. We are not placing it everywhere, because it is two to three times more expensive than a normal one.''

There are 12 transformer stations in the municipality of Loppersum. The fact that experiments are taking place there in particular is no coincidence. Flonk: ,,In the centre of the earthquake area, many private homes with solar panels have been added. In the process, whole rows of rented houses are being reinforced and made more sustainable. Also with solar energy. The situation there is quite unique.''

Tension stable

Although Loppersum also has many local energy cooperatives managing small solar parks, that is not the reason for using the self-regulating transformer: ''As a rule, these are located on a roof of business sheds or farmers' barns and there is usually already a heavy connection there.''

A transformer is needed to convert the 10 kilovolt (10,000 volts) supplied by a high-voltage substation to the 230 volts used in homes. That voltage is not stable during transport, fluctuating. Partly due to the resistance of the cable and variation in load or production.

This is not a problem, as there is a margin of plus and minus 10 per cent. Below 207 volts, some devices no longer work; above 253 volts, they can break down and the solar inverter shuts down.

Flonk: ,,You can cope with the increasing voltage fluctuations with thicker cables. But it is quite expensive to replace them everywhere. With the self-regulating transformer, it also works.''

Low voltage

Enexis is also experimenting with so-called LS-LS regulators. LS stands for low voltage. These are in Garnwerd and soon also in Kropswolde. Also areas with relatively many solar panels. These are connected to an electricity cable lying in the street and they too keep the mains voltage within the legal margins.

The trials mark the advancing development of renewable energy. ''It's really a recent thing,'' Flonk explains. ''In the province of Groningen, between 800 and 900 megawatts of solar panels on private roofs were added last year. Plans for this year include between 1,000 and 1,500 megawatts. Whether that will all go ahead is the question, but these figures do say something.''

Report

Developments sometimes even go beyond the grid operator. Satellite photos showed that there were 20 per cent more rooftops with solar panels in the province of Groningen than Enexis was aware of. ''That can cause a problem. Because you don't have an exact picture of the situation. If you want to manage the network properly, you have to calculate with the right figures.''

The appeal to people is also to report to the PIR (production installation register), when installing panels. Just as Enexis should facilitate development, so citizens should be aware of the impact on the grid.

''If a neighbourhood or street section takes solar panels together, the grid may have to be adapted and that takes time. We have to apply for permits if we need to lay a thicker cable in the ground, for instance. That takes three months. During that period, the surplus power cannot be fed into the grid and you don't earn anything back. That doesn't make anyone happy