Power System Transformation for Dummies
Power system transformation
understanding the challenges
Large vRES projects often are installed at (electrically) remote locations.
What is the point?
Quite some large vRES projects are located at sites far from the load centres. Extreme examples are PV plants in deserts or offshore wind farms. But onshore wind farms too are erected regularly in unpopulated, windy areas. Remote projects are connected to the transmission networks via dedicated, often radial lines.
There are many criteria for site selection of a power plant. Always, there have been generation facilities close to mines, harbours or hydro resources and often this implied significant distance to load centres. But, if possible power plants are erected close to or even within load centres.

Why is this important?
New generation far from the existing infrastructure requires planning and construction of new, dedicated lines. There are various factors making this a complex exercise:
  • The longer an AC line is, the more effort is required to manage voltage and reactive power under varying loading conditions. This management implies extra assets and effort and, hence, increases the operational complexity for the transmission system operator.
  • Because of the radial character of vRES connections there is little or no redundancy in case the connection is interrupted. The connection is not n-1 secure (read n minus one). From a generators point of view, this lack of a fall-back option may be perfectly acceptable. However, in case of very large generation capacities, this interferes with planning criteria of the transmission system. Deeper network extensions and reinforcements may be necessary.
  • Utilisation of transmission assets solely for renewables generation, in general, is lower than in case of a dispatchable plant. Network charging schemes have to reflect this in order to allow investments and financing.
  • In various countries, public acceptance for new transmission infrastructure is very limited. This causes delays and represents a severe obstacle for vRES expansion.
Where is this relevant? - Country characteristics
Obviously, countries with favourable vRES resources at remote sites may particularly experience this challenge. The reach of the existing infrastructure is an important factor. But more important is the policy framework. This is decisive for investors decisions regarding size and location of their projects.
The same issue appears, at a lower scale, with vRES generation connected to distribution networks in rural areas.

When is this relevant? - Stage of development
Very large, remote projects will not be the first to be implemented in a country just starting vRES development. But if the policy framework is favourable and infrastructure development is following specific connection applications individually, the issue becomes relevant with the first project.

How to approach - Addressing the challenges

The right to connect is a precondition for any successful vRES policy. Of course, costs and benefits of network extension have to be evaluated. But without network development, there will be little vRES development.
Beyond this obvious consideration, there are various detail questions like:
- How are costs for dedicated transmission assets shared?
- What are sound planning horizons and permitting periods?
- What are the right technology choices (e.g. AC or HVDC transmission)?
Voltage (and reactive power) management of long AC lines requires dedicated attention. This is of particular importance because lines may be intentionally underrated. As a consequence, temporarily they will be highly loaded.
More issues related to operation of networks with high shares of vRES are described in the next section 'vRES plants are dispersed.
Fluctuate vRES output is fluctuating.
vRES forecasts are never perfect.
Distributed vRES plants are dispersed.
vRES generate using power electronics.
small vRES plants run without professional operator.
vRES generate at zero marginal costs.