Building a Smart Grid based on direct current
One small step for man, one giant leap for mankind
In my first post about direct current I wrote about the war on currents. Today I will highlight a Dutch pilot project to build a smart grid based on direct current. The DC-network will be realized in a new greenhouse near Schiphol Airport in the municipality of Haarlemmermeer. It was granted a subsidy by the Ministry of Economic Affairs, Agriculture and Innovation in December 2011, and will be operational in 2014. The DC-net will be self-sufficient and has a backup to the underlying alternating current distribution system (hereinafter AC distribution). The electrical output of the DC-net is between 300 and 1500 watts.
The DC-network consists of a ring around the sustainable horticulture area PrimAviera near Schiphol (Haarlemmermeer). The energy will be generated by both solar panels and combined heat and power plants (hereinafter CHP), which will be connected to the DC network. The energy generated will be used for lighting and ventilation of the greenhouses, which will be connected to the ring. Also charging points for electric vehicles will be connected to the DC network.
What makes this project unique?
Networks are needed to transport electricity from the place where electricity is generated to the place where it is used. A major task for operators of electricity networks based on alternating current is to ensure stability of the AC-grid. Imbalance in supply and demand of energy disturbs the stability of the AC-grid and can lead to a widespread blackout. Maintaining stability is relatively easy with centralized energy production, but becomes more difficult with decentralized energy generation. With The Netherlands slowly following the lead of other countries towards more sustainable energy and decentralized generation of electricity ensuring stability of the AC-grid becomes more difficult.
In a DC network ordination between supply and demand of electricity also exists. However, this balance question does not have to be accurate with millisecond as in the AC-world and can be planned well. Because storage of local DC is also possible (batteries typically use direct current), maintaining the energy balance is more easy, particularly as the management is done by electronics.
Thanks to the technical characteristics of DC, the DC network manager can determine that the locally generated energy is used before energy generated elsewhere is transported to the user. If there is an excess in energy generated locally it may be stored locally, or the excess can be transported to other local consumers. If there is more energy generated than needed in the DC grid the excess can be supplied back to the AC grid.
In essence, the DC network doesn’t need a AC-network as an underlying network. So in case of a blackout the DC smart grid in Haarlemmermeer will prove to be a beacon of light.
The phenomenon of DC will lead to different forms of energy planning and open up new markets. Now let’s talk about innovation! That’s one small step for man, one giant leap for mankind.
This contribution was written in close collaboration with Bob Zijderveld, independent Consultant DC, Conventions and member of the board at Stichting Gelijkspanning. Any mistakes or technical errors and omissions are solely the responsibility of the author. For more technical background please contact Stichting Gelijkspanning or Direct Current.