Aug 06 2020

Ubiquitous Solar

If you follow any science news aggregator you will see a ton of solar power news. The industry is clearly advancing quickly, and this is translating to the field – to actual production of commercial solar panels. It seems likely that the solar news of today will be the solar energy of the not-to-distant future. So what’s on the horizon?

One of the advances that seems likely to at least add to the way solar is produce is semitransparent tinted solar panels. These are basically windows that capture some frequencies of light to produce electricity while allowing other frequencies to pass through. The efficiency (percent of light energy converted to electricity) of these photovoltaics is in the 17-18% range, which is right in the range of current commercial solar (15-20%). Of course, advances are also increasing the efficiency of silicon-based solar panels, which should reach the mid 20s. There is also the promise of perovskite solar panels which can top 30%, at least theoretically. Finally there are organic solar cells which are less efficient, in the mid teens, but are really cheap.

Essentially, there are lots of options coming when it comes to solar power, and this means the best option can be applied to many different situations. One interesting idea is agrivoltaics – combining farming with photovoltaic energy production. This uses tinted semitransparent solar panels in greenhouses or other covered farming. The color of the panels results from the frequencies that they allow to pass through, while the other colors are used to generate electricity. The idea is to choose the frequencies most important for growing specific crops, while using the less important frequencies to generate power.

The study linked above looked at orange tinted solar panels used to grow basil and spinach. In both cases the net profit for the farmer increased, although much more with the spinach. Using the tinted glass crop growth did decrease due to decreased total solar energy for growing. However, the decreased grow was more than offset financially by the electricity production.

The study found the saleable yield of basil grown under the tinted solar panels reduced by 15%, and spinach reduced by around 26%, compared to under normal growing conditions.


The combined value of the spinach and electricity produced using the tinted agrivoltaic system was 35% higher than growing spinach alone under normal growing conditions. By contrast, the gross financial gain for basil grown in this way was only 2.5%.

The reason for the higher profit from the spinach despite a greater decrease in production is because basil is a more valuable crop, selling for about 5 times the cost of spinach. Also, while total crop biomass was decreased, for the spinach the biomass shifted more to the leaves to capture more sunlight. This is good because the leaves are the part of the crop that is sold and eaten.

Such a system is good for farmers. They increase their profits, while also diversifying their production, which will make their business more resilient to market fluctuations. However, we have to think carefully about the net effect on the food production system. Reducing productivity by 15-26% may not be sustainable given the global food demands. On the other hand, we would be making double use of the land, for both food and energy, and therefore overall land use efficiency may not be as bad. We need a systems-wide analysis to predict what the impact would be of wide adoption of agrivoltaics.

Hopefully more research will also improve the trade-offs. We need to find the optimal match between the color of the solar panels and the crops being grown. There may be a way to capture some energy while having a minimal negative effect on plant growth. Also, we may eventually be able to adapt plants to these new growing conditions – to develop varieties that are optimized to take advantage of frequencies that are allowed to pass through. The numbers, therefore, are likely to get better from here.

Semi-transparent solar panels also would allow for architects to design buildings with solar power generation built in. Eventually, all buildings could theoretically be designed to produce most or all of their energy requirements through built-in solar power. Even our electric cars could generate some of their power through onboard solar.

Advances in solar voltaic technology, which is rapid and practical, are making it increasingly possible to have ubiquitous solar power generation. There is more than enough energy from the sun to power our civilization, if it could be efficiently harvested.

But regular readers of this blog should know what is coming next – the real limitation we are already running into in areas with high solar production is grid storage. Producing solar is cost-effective while total penetration of renewables, and specifically solar, is low. The greater the percentage of total energy production that is from intermittent sources, the less able the grid is to take in that energy. More and more of the intermittent energy is therefore wasted or left idle due to overcapacity. What is that percentage? There is no clean cutoff, it is just that the higher the penetration, the less efficient each additional solar panel is. But something like less than 30% there is essentially no problem, from 30-60% there is increasing inefficiency, and north of 60% intermittent energy sources become very expensive and impractical.

The solution is to have constant energy production to cover the remaining 40% or so. Or – we need massive grid storage. The advantage of grid storage is that it allows everyone to benefit individually from the financial gains of having solar. Farmers, for example, can only benefit from agrivoltaics if there is a market for their excess solar power.

There is also a technical limitation – the grid needs to have the capacity to accept this production, which requires local transformers. When I put solar on my house I was essentially the last house in the development that could do this without having to pay 5-10 thousand dollars to install an additional transformer so that the local grid could accept more solar power generation. There are 4-5 houses with solar out of 40 or so – so that is a significant limitation. Right now, in CT at least, there is no requirement for the power company to pay for the installation of extra transformers.

What all this means is that in addition to grid storage, we need to massively upgrade the grid itself – it needs to be adapted to highly distributed local power generation. Otherwise, we will have lots of options for cheap and efficient solar power, but will lack the capacity to use it. Early adopters will flood the market, and everyone else will be blocked out. I suspect this is exactly what will happen, because our government does not seem capable of anticipating and dealing with such a problem before it occurs.

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