DSO


Today's environmental challenges and climate policy have led to an increased interest in distributed generation (DG). The level of grid connected DG units in low voltage distribution grids is still fairly modest, but the share is expected to increase in the years to come. Particularly, the number of PV systems is expected to rise. Another trend, perhaps even greater, is the growing share of power demanding appliances in private households, such as electric vehicles, instant water heaters and induction ovens. Both phenomena can lead to high-current peaks, which further affect the quality of supply and future grid investments.

Voltage quality is usually a dimensioning factor for grid reinforcement if the customer is located more than 300m from the transformer.  Closer to the transformer, capacity is the dimensioning factor. Demand response in private households can help DSOs ensure a satisfactory voltage quality and prevent overloading of the line components.  Through smart shifting of consumption, one can adjust to fluctuating production and demand. The peaks can be shaved without affecting the prosumer’s comfort.

Case 1 shows that DR proves a profitable alternative to conventional grid reinforcement, if its costs are below

€ 8.000-10.000

The reference impedance for 230V distribution grids, recommended by the IEC, corresponds to about 0,1Ω or a short circuit current Isc of 1173A. This means that all customers connected to the 230V grid, shall have an impedance in the connection point equal to, or lower than, 0,2Ω. The short circuit current shall be equal or higher than 1173A. The Norwegian DSO has about 180 000 customers. 75 000 of these are connected to a 230V grid with an impedance higher than the reference impedance (it should be noted that everything new being built is 400V grids, with an impedance that satisfies the recommendations provided by IEC. The problem is hence a 230V grid problem).

Simulations show that the overall cost of lifting all 75 000 customers to the level of the reference impedance would be 8 bn NOK (€ 860,720,000). The further away from the reference impedance the grid is, the more expensive it is to rehabilitate the grid (the cost relation is hence not linear). In Table 2, the customers are divided into two groups based on the level of the reference impedance. A rough estimate of what it costs to rehabilitate both groups are shown.

Table 2: The Rehabilitation Costs Associated with Lifting all Customer Installations to the Reference Impedance

Zref

(expressed as current I)

Number of customers

Costs/customer

(NOK/€)

Total Costs

(bn. NOK/€)

Isc< 500A

23 000

136 812 (43478*)

€ 14,719.60 (€ 4,677.80*)

3,1 (1*)

€ 333,529,000

(€107,590,000*)

500A<Isc<1173A

52 000

80 000- 93 333

€ 8,607.20 – € 10,041.70

4,2 – 4,9

€ 451,878,000

€ 527,191,000

* The grid is reinforced to 500A only

It is assumed that peak shaving can help customers belonging to the second group only, where 500A<Isc<1173A. For the first group, there is no getting away of grid reinforcement. It is possible to imagine that grid is rehabilitated such that Isc= 500A, and the peak shaving can "take it from there". However, the current potential is 52 000 customers, and the possible saving per customer is 80 000 – 93 333 NOK (€ 8,607.20 – 10,041.70).

In other words, if peak shaving is cheaper than 8,607.20 – € 10,041.70 €/customer, the Norwegian DSO could consider buying it.