Wednesday, July 11, 2018

Farming and Solar Power: Complimentary or Mutually Exclusive?

Photo taken June 24 in Allendale.  Plants with white flowers are White Clover.  Plants with yellow flowers are Birdsfoot Trefoil.  They both fix nitrogen.  If the soil has sufficient P, K, Ca, Mg and S there is no reason the land cannot be sequestering carbon and increasing in fertility.
A young orchard.

A twenty acre, mowed yard.
NIMBY activists are using Michigans "Farmland Trust" laws to stop, delay or otherwise increase the cost of solar installations in Michigan.

One account I read (sorry, no link) the activist wept a thousand tears that her grandmother's land was being uglified by solar.  News flash:  The activist could have been spared the ugly if the family had not squandered their inheritance.  It is no longer her grandmother's (deceased) nor the activist's.

But let's give the activist's claim a hearing.
The United States has never experienced a famine due to war.  We have never been cut off from most of our food production base.  But most European countries have and that is why it is so difficult to rezone ag land.  Their collective memory puckers at the thought of paving over their ability to feed themselves.

The Farmland Trust (henceforth called FT for compactness) as set up to slow the irreversible degradation of farmland due to urbanization.  Unwinding a development like this and reclaiming it for farm land would involve legally condemning all of the properties, compensating the owners, demolishing all of the structures, filling the foundations and regrading the soil.  And what would it get you?  Nearly barren subsoil.

Sprawling suburban housing is slightly better.  It would be easier to convert a 20 acre lawn back to ag but you would still have one pissed off cowboy regarding the owner.

Back to agriculture
One reason the United States has very productive agriculture is that we irrigate our higher value crops.

That young orchard uses trickle irrigation.  Each row is about 10' apart and each tree is about 4' apart within the row.  While the apples are easy to pick and of very high quality, the trees don't have long enough roots to be able to mine deep, subsoil moisture.  They require irrigation to remain productive...perhaps to avoid death during dry spells on sandy soil.

Irrigation is power intensive.  It takes approximately 3 horsepower-hours to increase the pressure of an acre-foot of water one PSI.  Said another way, it takes 100 horsepower-hours to raise an acre-foot of water 70 feet up a well.  It takes another 50 horsepower-hours to increase the line pressure to 15 PSI to make the emitters function.

So how much energy would an eighty acre orchard require?

According to the MSU Enviroweather site, the average evaporation rate in Charlotte, Michigan (my nearest station) has been 0.186" (or 0.0155 feet) per day for the last 16 days.  That means that optimally growing plants need to be able to 'find' that much water.

The inverse of 0.0155 feet is 64...suggesting that one acre-foot of water would be sufficient to water 64 acres of apple orchard for one day on sunny, Michigan days.

The real world is messy.  Entropy, friction, rust and leaks never sleep.  150 horsepower-hours is a perfect world number.  Considering that we are talking about a complex system it is prudent to increase the energy requirements by 100% to attempt to comprehend losses.  That takes us to 300 horsepower-hours per day.

How much solar power capacity would it take to churn out 300 horsepower-hours a day in mid-summer?

Figure five hours a day where the solar generation is near peak-power.  Yes, there will be cloudy days but the evaporation rates will be correspondingly lower.  That means a system that is barely adequate for 64 acres must generate a peak of 60 horsepower (45 kW with a bit of rounding) of electrical power for a 64 acre orchard or 30kW (with a bit of rounding) for every 40 acres of trickle irrigated agriculture.

30kW solar power generation for every 40 acres of irrigated farm land in Michigan is a bare-azzed minimum.  That value doubles if the system is not trickle irrigated because it requires 60 PSI vs. 15 PSI.  It goes up if the pumps are inefficient.  It goes up if the pipes leak.  It goes up when the "head" is more than 70'.  It goes up as solar panels age and lose efficiency.

Solar energy is not antagonistic to Michigan agriculture, rather it complements it.  A progressive, forward thinking goal would be to incentivize the installation of a minimum of 30kW of solar power capacity for every 40 acres of irrigated land in Michigan.  The two technologies complement each other nicely with regard to the peaks matching.

Note to Loren, a sometimes reader:  Please double-check my computations.


  1. If there is one way that solar makes sense, it is in the sunny climes where temperatures require A/C, creating peak demand when the sun shines. I cannot understand why each and every WalMart parking lot in the SW USA is not covered with solar panels to provide shade to the cars parked beneath them. Shopping centers are places of high consumption, in centrally located service areas, and even in northern climes, solar could be used to heat water for underground storage and nighttime heat exchange. There is a lot about solar that can be made to really work well - as long as electrical constancy is not a fundamental requirement, and as long as the end user is nearby.

    1. That is a great point. One thing that makes solar a good fit for irrigation is that the soil has the ability to "buffer". That is, it can store moisture for later use, thereby diluting the intermittency issues with solar.

      Thanks for commenting!

    2. I really enjoy your blog Joe, it's a great read. There are many African projects that utilize self-contained solar-powered downhole pumps with a small surface tank for both village water supplies and agriculture. Also, the big ranches in South Texas have long ago started transitioning away from Aeromotor (windmill) rod pumps to solar setups. They are pretty efficient. For your orchard setup, why not go old--school and erect an elevated water tank to provide head for your drip feed, and then use a small solar pump to keep it filled?