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For a start, let’s be clear. This is not about measuring the financial returns of any solar power generated by the panels.
The focus is on pasture growth – losses and gains due to the light and rain shadows caused by the panels. Also, the trial involves sheep only, not cattle.
On two small paddocks adjacent to the main Palmerston North Massey campus, Wilson’s research team has set up five look-a-like solar panels. Look-a-like because they are not real panels, they are made of iron, but are made to the exact dimensions of normal panels that would be placed in a paddock. They face north to get the maximum sunlight and are spaced three metres apart – the same as if they were normal solar panels. One paddock is the ‘control paddock’ with no panels so a comparison between the two situations can easily be drawn.
The paddock with the panels in it contains a huge range of data-gathering devices that measure, rainfall, wind, light, soil moisture and temperature and these are placed strategically under, around and outside the panels. There are also small ‘cages’ over the grass in similar strategic locations to capture any differences.
Wilson began the project just on a year ago and some preliminary results have come through, but he says they plan for at least another year of trials to ensure the validity of the data.
“In a previous pilot study we did in Taranaki we found there was an 84% reduction in pasture growth under the panels but a 38% increase between the panels. This site is aimed at putting more explanation around why those differences were occurring, hence the extra measuring devices,” he says.
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Wilson says the panels are in effect creating shelters from wind, rain and sun resulting in a series of ‘microclimates’ at various points around the structures.
Not surprisingly, there is a variation between summer and winter. In winter he says the angle of the sun is lower and this combined with cooler temperatures caused a 25% reduction in pasture growth between the panels.
“But in summer when the sun is higher, about 90% of the light gets through to the middle of panels and there is an increase in pasture growth of around 30%,” he says.
The light loggers placed around and under the panels form an interesting aspect of the research project. Dr Wilson says this measures photosynthetic active radiation, which is the light that is available for the plants to use. But in the summer the shading effect of the panels slightly reduces this by about 10%.
“However, this is not a problem because we know that pasture plants don’t necessarily need full sunlight all day to grow at their maximum potential rate, and in fact, if they get too much sunlight, it can be harmful. So, 90% availability of sunlight caused by the shading is likely closer to the optimum level for the pasture to grow, particularly in summer,” he says.
This effect, along with the extra water that this area receives from rain running off the panels, are the most likely drivers for the extra growth in summer.
One of the first things that strikes you when walk into the paddock with the panels is the bare patches underneath them, clearly caused by the lack of rain and sunlight, but it isn’t entirely all bad news. Sam Wilson says, during lambing, the shelter provided by the panels is great for the lambs. He says it protects them from wind, which can be a major cause of lamb losses, is dry and warm and allows the ewe to leave her lamb under the solar panel and feed herself.
So, in the end, it all becomes something of a trade-off. Probably a lower stocking rate may be offset by benefits during lamb with shelter and seeing how the various microclimates perform in terms of pasture growth. He says there is an obvious loss of pasture growth in winter, but a potential gain in summer.
Other research on the use of solar panels is being done at Lincoln University and there are extensive studies being done in Europe and there is some work being done in Australia. Wilson says in Europe they are looking at planting arable crops between the panels which are spaced wide enough for a combine harvester to get through.
He says in a couple of years’ time, similar trials may be done in NZ. The aim he stresses is to give farmers some hard data on which to base their decisions around installing solar panels, rather than relying on anecdotal evidence.
