Thursday, March 3, 2016

Are Energy-Neutral Buildings a Good Idea ?

A Swiss farmer has covered a 200 square-meter-roof with photo-voltaic (PV) solar panels and claims to be self-sufficient because her yearly electricity production exceeds her consumption. She is right from a financial perspective, but this is not self-sufficiency: she produces excess power in the summer days and relies on the main grid to serve her needs at nights and in the winter. How could we be truly self-sufficient? Can we really live on renewables?

An answer to that question is attempted by energy-neutral building projects. For example, the Swiss energy provider Alpiq claims to be installing the world’s first energy self-sufficient apartment house. This building is not connected to the main grid and is thus truly self-sufficient. It produces electricity with PV panels, uses a battery for smoothing daily fluctuations, stores the excess electricity produced in the summer by means of an electrolyser into a hydrogen tank that feeds a hydrogen fuel cell in the winter. Is this the solution of the future for a sustainable electricity production?

These two examples both have drawbacks that generally make them economically non-viable. The former example, i.e. the Swiss farm that does only yearly balance, induces high operational costs into the main grid, which needs to provide backup and complementary energy sources for power balance, regulation and for handling outages. In other words, it uses the main grid as a free rider. The latter example, i.e. the energy-neutral building, does not push external costs to the collectivity, but is very expensive as it requires a large storage, much larger than what it needs in average, because it needs to be dimensioned with a large safety margin. Furthermore it cannot benefit from cheap energy produced in other parts of the country; for example, the wind blows and the sun shines often in the winter in the mountains, whereas wind and solar are abundant in the plain mainly in the summer. 

At EPFL, in the Commelec project, our vision is that distributed renewable energy sources should care about energy neutrality, but should also be connected  to the main grid and actively participate in its operation. In other words, we should combine aspects of the two examples mentioned above. We should envision buildings that produce their own energy and strive to be energy neutral, but are connected to the main grid and support it as needed. To achieve this goal, we need an efficient, simple, safe and secure intelligent infrastructure that is able to collectively drive all distributed energy sources. In some sense, what we need is a "grid operating system". We demonstrated a first version of such a system on the experimental microgrid developed in the EPFL DESL lab, with the support of the SNF Energy Turnaround NRP70 program. Stay tuned !

Wednesday, February 4, 2015

IP Multicast : the Revival ?

IP Multicast: a revival in smart grids?

Since its inception in the early 90's, IP multicast has been confined to local area networks and to TV distribution systems. With IP multicast, it is the routers that duplicate messages, not the sources or intermediate servers. This makes the job of the source much easier: with IP multicast, an IPTV server sends only one stream, even if there are 1'000'000 receivers. The magic is in that if there is in average 10 hops from source to destination, and if every router duplicates every packet of the stream 4 times (a modest piece of work for a router), then at the end there are 4 to the power 10 (ca. 1'000'000) duplicates reaching the destinations -- in reality this is never as simple as multicast trees are not balanced, but this gives the idea.

So if multicast is so powerful, why is it so little used ? Perhaps for several reasons. First, multicast needs a multicast routing protocol and there is overabundance of them, making it hard for an operator to choose the right one. Perhaps this problem will go away with software defined networking (SDN), which could replace multicast routing protocols in a much easier way. Second, multicast has a bad reputation when it comes to security: denial of service attacks are much more powerful if an attacker finds a way to use multicast (here, too, SDN will help). Also, widespread end-to-end security solutions such as DTLS do not support multicast.

Multicast IP is a natural solution for smart grids, where many simple sensors (such as Phasor Measurement Units, PMUs) stream measurement data every few milliseconds to multiple destinations. With multicast, you configure one single destination address in a PMU and then forget about it; if a new destination comes and listens to the data, no change in the PMU is needed. In contrast, without multicast, the PMU would need to start a new session for every additional destination.  In today's electrical substations, multicast is used at the MAC layer. In tomorrow's smart grids (which will be wide-area networks), this will not be sufficient and IP multicast will be needed. A good opportunity to solve the security problems posed by IP multicast ? Carl Gunter and Jianqing Zhang at University of Illinois have tackled the problem, see Jianqing's dissertation.