Bringing PV parks and agriculture to cohabitation

Posté le 27 octobre 2011 @ 18:18 par Manfred

The last summer I was involved as project manager in the construction of a 10 MWp ground-mounted PV power plant in the south of France and had thus the chance to deal with the interesting topic of the cohabitation of such project with agriculture.

One of the most common critics toward renewable energies and solar energy in particular is that they are land-extensive. As with biofuels, when the land used to be a farming area, the competition between producing energy and producing food is a perfectly arguable indictment. The French government issued last year a circular to state that no more ground-mounted PV park projects would be allowed on farming lands .. unless they could argue that no farming capacity was lost due to the project.

I had myself being exposed to the importance of keeping the agricultural value of the land during my work among the department of agricultural engineering of the University of Kassel and with the GTZ/GTI in Peru. One good reading I can recommend on the subject is a report from the company Quattrolibri [1], which sums up the standard solutions : pasture, crops that do not require huge mechanized equipments (at the biggest, narrow trucks capable of fitting between the lines of modules), integration of the PV modules to greenhouses and apiculture (bee-keeping).

There are options to choose from, but they are better included from the stage of project design, as not all engineering solutions - the structures, in particular - are as easy to make cohabit with a farming activity. In addition, even if the chosen engineering solutions were perfect, the mere construction works themselves will create disturbances during the works and/or at their end : rubbish managed and soil compacting due to the heavy construction vehicles.

But have all agricultural activities the same value ? Growing vegetables or cereals and letting some sheep graze once in a while can hardly be seen as equal. The former and current agricultural values can actually be assessed with numbers, basing one-self on the revenues generated by these activities [2]. It is then possible to ‘compensate’ any lost value, for example by using a fraction of the PV park’s revenue to invest in the rehabilitation of neighbouring former waste lands into farming land and making up for the estimated loss.

My job on this construction project gave me the opportunity to find out that beyond what you do on the plots of land, it is also very important to take care of what you do with the soil itself. Indeed, uncaring construction methods can definitively damage the agricultural potential of the land : the soil is organized in layers of different compositions and fertilities and savage earthworks can ruin them totally. Inconsiderate use of concrete elements is hazardous as it will leave blocks and fragments on and underground at the dismantling of the plant. Leakages (from the transformers, for example) may produce toxic taints. Cables buried in trenches will also have to be dealt with at the dismantling. There are solutions to all these issues but they must be thought of during the construction of the plant and its planning.

  Bad example : the soil’s top layers have been scrubbed completely, leaving only compacted fertile soil.

 

  A better example : the top layer of fertile soil had been removed and kept apart from the area where the earthworks was to be done, and is later restored in place.

 

By nature, EPC companies and investors tend not to care about anything but their work and their profit. If the land has been rendered sterile, it often does not matter much to them as long as they made a good profit out of it [3]. To this regard, it is the role of governments and the various counter-power organisations (non-profit associations, NGOs, media) to be vigilant.

The project on which I worked had actually received its authorization prior to the previously mentioned circular, but a fair sense of diplomacy from the initial project developers had led them to take commitment to preserve the agricultural potential of the plots of land (ca. 20 ha). We did not use concrete foundations and preferred using sand beds and gravel sidewalks ; we made sure that all cables could be easily removed from the trenches, and had them buried deep enough so that ploughing tools could operate on top of them. The most difficult part was the earthworks, as the subcontractor in charge of doing them did not take in account our instructions seriously enough at the beginning, which led to ‘hiccups’.

Initially this land was actually pretty dry and rocky, with a moderate fertility. The planned cultivations include melliferous plants (for the neighbouring bee keepers) and plants for essential oils. On the areas where the fertility is not good enough, mulching during the next 20 years should hopefully bring improvement and I hope that the land will be returned in a better state than it was !

 

References :

  • [1] Quattrolibri : Report on PV farms on farmland

  • [2] I am really sorry about it, but the standard of evaluation always ends up being the money !

  • [3] Try to blame the petrol industry after that !

Addendum :

A presentation done for the Department Grids and Renewable Energy of the ADEME (French Agency for Environment and Energy).

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