Decentralised renewables such as solar panels on people’s roofs can actively support the grid, rather than being a nuisance for it. This is the main conclusion from an EU research project called “MetaPV”, whose final results were presented at a conference in Brussels on 24 March.
“MetaPV is the world’s first project to show on a large scale and in historically grown distribution networks how photovoltaics can support the grid actively,” says Geert Palmers, CEO of 3E, the technology and software consultancy that coordinated the project, in its final report.
“We show that intelligent control of photovoltaic inverters can increase the capacity of a network for hosting distributed generation by 50%. This is possible at less than 10% of costs of the classical grid reinforcement.” (See Box at the end for a definition of solar inverters.)
This is therefore an alternative way for grids to absorb a greater share of renewables. It does not replace the need to build out the grid, but can offer some breathing space that allows a more strategic, less reactive – and hence more cost-effective – approach to the latter.
“We wanted to show DSOs [distribution system operators] that there are other options than expanding grid infrastructure to deal with more decentralized renewables,” said Joris Lowette, Limburg Investment Company (LRM), on 24 March.
One point to watch out for is that the costs of sophisticated features for communication (with the DSO) do not eat up the savings from the substituted grid reinforcement, the final report cautions. The economics of voltage control also depend on whether it is central (coordinated across an area) or local, and whether it is complemented by either storage or active curtailment (gradually limiting power output as the grid’s maximum capacity is neared).
“We wanted to show DSOs that there are other options than expanding grid infrastructure to deal with more decentralized renewables”
What makes the project so interesting is that it demonstrated active grid support from PV inverters in real-life trials, not simply in the lab. It did this at two sites in Limburg, Belgium: a residential area with controllable inverters of 428kW peak power on low voltage (400V) and commercial-scale installations with 2.4MW on medium voltage (10kV).
These sites were chosen because they have some of Europe’s highest PV penetration rates: 8% of electricity demand, like in Germany and Italy (vs. 3.3% for Europe overall). It is therefore here that PV most tests the grid – remember that the majority of renewables are plugged into the low-voltage distribution, not high-voltage transmission, grid and bottlenecks are local.
The European Commission will delve into the debate over the role of DSOs and “prosumers” (citizens that produce as well as consume energy) in the future energy system as part of a forthcoming package of policy papers centered on a re-design of the European electricity market. One aspect of this could be to get capabilities like that demonstrated by MetaPV deployed more broadly.
The MetaPV project received funding from the EU’s Seventh Framework Programme (FP7) for research and ran from October 2009 to March 2014. Apart from 3E, the project partners were the Austrian Institute of Technology, Infrax (Flemish DSO), the Limburg Investment Company (LRM), SMA Solar Technology (solar inverter manufacturer) and the University of Ljubljana.
What are solar inverters?
Solar inverters are the technology that connects solar panels to the grid; they convert variable DC to useable AC power. More “intelligent control” of them means that they can adapt their active and reactive power exchange with the grid to influence the grid voltage around the connection point. (For the studied distribution networks, the voltage limit on distribution feeders was the most prominent constraint for PV).