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Jan. 4, 2022

Land Stewardship in the Solar Industry | Rhett Kerby, KerTec | #67

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#67 Successful vegetation restoration and natural landscaping of solar farms is a vital part of the solar industry. Solar farms mean changes in the land and those changes can be good from an ecological perspective - but this requires expert planning, engineering and execution of soil preparation and conservation and proper seed lists and vegetation establishment and maintenance plans/execution.

Today on the Clean Power Hour we bring you Rhett Kerby, co-founder of KerTec and expert soil scientist based in west Texas and working across the Great Plains and Midwest of the US. We discuss the steps involved in properly planning, designing, engineering, and executing smart soil and vegetation restoration plans as they relate to the solar industry.

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Rhett Kerby, Tim Montague 

Tim Montague 00:00 

Today on the Clean Power Hour environmental reclamation and land stewardship, I'm Tim Montague, your host. You know, here in the solar industry, we are putting large solar farms across the United States. And these range in anything from 20 acres to 1000 plus acre projects. We now have some gigawatt plus scale 

solar coming in to places like Texas and Indiana, there's a 1.6 gigawatt power plant being developed in Indiana. That is a 13,000 acre solar farm. And so we need we in the solar industry need to be very concerned about what we're doing with the land both during and after construction, and helping that land to become an environmental good, not just a power generating facility. Of course, there's many positive attributes to power generating facilities from solar wind and battery storage. But the land is a major component of this. And there's so many other positive impacts to converting land from cropping, for example, or grazing to solar farming. So we're going to get into that today. My guest today is Rhett Kerby. He's the founder and principal at a company called KerTec out of Lubbock, Texas. Welcome to the Clean Power Hour Rhett. 

Rhett Kerby 01:27 

Thank you, Tim. Thanks for having me. 

Tim Montague 01:29 

Really great to bring you onto the show. As you know, as we discussed early in our first conversation, I'm quite involved in the pollinator friendly and multi use movement to to use solar farms for agro voltaic, for example, or pollinator friendly landscaping that's as environmentally and ecologically friendly as possible. And so, when I saw you posting some beautiful photos on LinkedIn, you know, I was attracted to your work and, and so give our listeners a little bit of background on yourself and your company. 

Rhett Kerby 02:08 


Sure, absolutely. So educationally speaking, undergrad from Texas Tech and plant and soil science graduate degree from Iowa State in Plant and Soil Science. After after college, actually, during my 

graduate degree from Iowa State in Plant and Soil Science. After after college, actually, during my undergrad work, I had an internship with USDA, which turned into nearly a 10 year career where my sole task was stabilising highly erodible soils for the Natural Resources Conservation Service. And with that, came the use of pollinator friendly habitat, wildlife targeted establishment projects. You know, so, so it was really a, it was really where I had really had on the ground experience in taking disturbed land and, and converting it into something that was ecologically sustainable, and had value from from a wildlife standpoint, or, you know, multiple different goals. From an erosion control standpoint, from a pollinator or endangered species standpoint, there were multiple goals of the projects that that I was involved in. And then after that, in about 2011, I had an opportunity to manage a native seed company. And that's really where I was exposed to, you know, the beginnings of solar and wind and and this, this need for plant and soil science, the discipline of Plant and Soil Science in the construction industry, at the seed company, I was having conversations daily, with engineers, civil engineers, electrical engineers, contractors, civil contractors doing dirt work, I was having conversations with people about their need for seed. And if you follow me much on LinkedIn, you'll know that I break what I do into kind of two different categories yet exoteric and esoteric, and so what I was, what I was seeing from the construction industry was this very exoteric need meaning that it was very, it was very binary, it was very not well understood. It was it was like, I need a seed. And that's the end of what I need. And you know, and as a, as a, as a soil scientist, you know, I asked questions about that seed or about that project, you know, what kind of habitat or or environment are you going to be placing that seed into, you know, much like you would a garden. You know, if you just go buy the vegetable seed that doesn't make you be successful, you really have to tend to that soil to ever end up with vegetables, you have to, there's a whole lot of other criteria to having vegetables, beyond just buying the seed. And so what I was seeing was, you have an industry that has a tremendous impact may have millions of acres of potential impact, and the conversation was about seed. And it wasn't long before, you know, I was I saw seed being used and not being planted correctly. And it was just a bad reflection on, you know, it didn't speak well to the seed industry, it didn't speak, no one was benefiting from these failures. And so it was in 2014, that, that this kind of brainchild, it, you know, kind of came to be between me and my brothers that, you know, we really need to take our, our practical education and practical experience, and try to apply that in a construction setting. And so, you know, we're much more, I say, we, me and my brothers and the people that work here. I mean, we're scientists, but we're also, we also apply the science, and we were we do a lot of Applied Science, and that, to me is what makes us different is that we have an understanding of the background and the need for certain things, but then we have the ability to execute that. And that's really different than what you see in the industry. Today. You see, you see, you see the scientist, and then you see the applicator. And they're two separate roles. And, and I find a lot of conflicting bias when you separate those two, you know, you have a scientist that may have, you know, that they have great intentions, but then you you have a contractor that has a budget, and is always looking for opportunities to, you know, improve their, their margins, and and so, you know, when you when you place those two bias in the same project, it doesn't always have the best and it doesn't position the project for success. Because, you know, the bias are just conflicting and, and so, so by being the scientist that actually is able to execute the science, in a way that's beneficial to the project is, you know, I think that's unique to what we do, you know, we can write plans, we do consulting, we show up, we have the equipment, we can do the work, we monitor, we do all the things that that ultimately provide results for the project. And that model doesn't always fit well. Or fit, I shouldn't say it doesn't fit well, if that's a contracting against a model like that is somewhat challenging because from from a developer or general contractor standpoint, you like to hand off big chunks of, especially as a developer, you want to hand off the development to a general contractor. And, and sometimes the general contractor may or may not have the technical expertise to know how to handle the things that we do. And so, you know, that's really 

Tim Montague 08:10 


Let me stop you. Let me stop you there, 

Let me stop you. Let me stop you there, 

Rhett Kerby 08:12 

Yeah, go for it. 

Tim Montague 08:13 

You've given us a lot to chew on. And so let's let's kind of step into this in a in a stepwise manner. You've got you've got to you've got to site it, it is being developed, the developer will develop a landscaping plan for pre during post construction. And those plans vary in their level of specificity and detail. But broad, broad strokes, there's a plan. And like here in Illinois, we have a pollinator checklist. And, you know, developers are developers and their contractors are hiring, landscaping landscape engineering firms or environmental engineering firms to come up with a species list that meets certain criteria that is going to produce not only good pollinator habitat, hopefully, but also be very constructible have a low cost of maintenance. There's many considerations right in and money is always a constraint and and that gets weighed with value, right? And sometimes you're getting more value for your money and sometimes you're getting less value for your money and, and, and while you might think, Oh, well, if I have to do pollinator friendly, this is going to be more expensive. Well, you might be surprised how expensive turf grass is. In the Midwest. The amount of seed for example required to get turfgrass established is very high relative to pollinator friendly seed mixes, for example. And then for the long haul, you have to think about okay, What are the runoff implications? What are the habitat implications? What are the costs of maintenance implications? You're going to do less mowing, and less maintenance in general of the landscape once you get some native plants established on site in general. So from those from that perspective, though, okay, you have a plan, you have a site. And tell us a little bit about how you approach this. What are the considerations? And what do developers and contractors need to be thinking about as early as possible? Because that's the thing is, we don't like surprises, and we don't want budget surprises, either. So tell us a little bit about that front end? How do you how do you de risk a project? 

Rhett Kerby 10:49 


Yeah. How do you de risk a project? That's a great, that's a great conversation. You know, the plan, as you mentioned, you know, I think it comes depending on who you're talking to, I think it has different titles. But, you know, you can have a reclamation plan, a landscaping plan, you know, you can have it but I think to me, the goal in the planning process to to de risk a project would be that plan, whatever it's called, needs to have a component that's very closely related to what you find in the stormwater prevention plan. And that is the the erosion control component, because there will be a time where that project is exposed to erosion. And that erosion can remove the topsoil that provides that is the topsoil is the vehicle that is going to allow for vegetation to be expressed. So if you're, if you're, if you're not stabilising that topsoil, or you're not taking care of that topsoil during construction, you may have a risk in losing that topsoil. So you have to risk there, you have the risk of that topsoil ending in a river. So that's now you have a compliance issue. But you also that that event, that discharge event of sediment off site, means that that sediment is what I call topsoil. So that sediments now off site when it needed to be on site. And so, so that is a risk of losing topsoil, to de risk that there needs to be some sort of erosion control planning. And that's not in my opinion, that's not sediment, but it barriers like on the edges of say silt fence to catch it before it leaves. That's great as a kind of as a as a last, you know, final measure of protection, but ultimately have a erosion control plan that stabilises the topsoil, where it was originally. And so there, I understand there may be grading that needs to take place. And so as far as de risking the grading work, you have cut and fill 

areas, you have areas that you have material that's cut away, then you have areas where you put this fill material, those are very highly susceptible to erosion and or highly susceptible to not expressing vegetation because you're you're effectively turning the ground upside down you're placing subsoil on the top, which subsoil is effectively inert and not able to express vegetation very well. So there needs to be planning considerations given for your cut and fill areas related to fertility related there again to erosion controls stabilisation and, and so those are those are really a couple of the biggest risks that that I see. In the beginning is understanding what it what does it look like to keep this site stable during construction? 

Tim Montague 13:53 

When you're doing cutt and fill are the are you recommending then that additional topsoil is brought in from off site to counter that problem of the soil being turned over? Or how do you counteract that? 

Rhett Kerby 14:05 

So the best way to counteract that is to harvest your topsoil and stockpile it so if you know you you have an area, you know you've got, say 100 acres that you're going to cut. we'll scrape that off scrape that. First you got to understand what topsoil is. So after you understand what topsoil is and the depth of that topsoil, take that layer, scrape it off and stockpile it to the side, remove your material and then put your topsoil back. And now you've got topsoil and another risk factor is compaction. So compaction is it needs to be defined. I've had this conversation with construction contractors as far as compaction is concerned, and I really had to leverage I really had to kind of go back to the textbook and figure out what what is what is compaction really To vegetation expression, because to a contractor that's out there with heavy equipment, they may have been told why didn't compact it. That means he didn't roll it with a heavy vibratory roller. But it's still compacted just from the sheer nature of driving on it with the equipment that he drove on and on, drove on and with. So, compaction from a soil science standpoint is anything over 200 psi. So, once you hit 200 psi roots, the root establishment begins to decrease, when you hit 300 psi of compaction at the root zone, vegetation cannot exist roots cannot penetrate 300 psi. So 200 points at 200 psi is where root establishment begins to decrease, it will decrease so you hit that 300 psi point and then it will stop. And so compaction is something that must be addressed in these plans. There's an ASTM, I can find it for you. There's an ASTM soil compaction test with us using a penetrometer. To to measure soil compaction, that is definitely one thing to do because you place seed, even in good topsoil, but it's hard that seed, you know that seed doesn't have the physical power to push through compacted soil. So under understanding compaction is important. 

Tim Montague 16:21 


And then on the erosion control side, what is what is the best practice? And how does that best practice vary by region? Because I know that you're working in a pretty wide swath of the Great Plains and down into Texas. And, you know, I don't know if you've gotten into the into the upper grade lakes, but but erosion is a major, a major concern. I'm glad you pointed out the difference between the silt fence versus, you know, treating the entire area in some way. Because really, that's silt fence is a last ditch emergency to to, you know, a emergency preventer to keep soil on site. But you don't want it to move at all as little as possible, basically, right? Soil is gold. And the argument that I'm making about solar farms is that yeah, you're taking corn and beans here in the Midwest, and converting it to steel piles in the ground and glass panels on top. And and after 20 years, you should have organic, you know, farm ground, if you treat the soil well, if you do pollinator friendly and, and low herbicide or pesticide treatments during the course of maintenance. So how do you control erosion? 

Rhett Kerby 17:36 

Yeah, so to me based on where you are in the country, and the criteria that I use, as we work in different areas of the country is really a ratio of evaporation to precipitation. So that that dictates a lot that dictates how forgiving your environment will be. For instance, in Texas, you have a very, Texas exists right in the threshold, from one extreme to the other. And on the west side, you have about 150 inches of evaporation and 10 inches of rain. So you could do the math there, you're a 15 to one ratio of evaporation to precipitation. And as you that that evaporate, that ratio begins to change as you go east, you were you hit one to one is somewhere around at 35. So you've got one inch of evaporation to one inch of precipitation, that that that to me is where things the you're the level of forgiveness begins to change. As you go east of that line, you begin to have less evaporation and more rainfall. So you're you have the inverse in that ratio. So you may have 50 inches of of evaporation and 60 inches of rain or you know, or some number to that effect or 20 inches of evaporation and 40 inches of rain. So you begin to have a different set of challenges with that you may have a higher water erosion potential, but you also have a higher potential for vegetation expression because you have a more conducive more greenhouse like climate, to to establish vegetation. And so depending on where you are in the state, and then that at 35, you can really kind of take that all the way north and use that as a as a line as to what challenges you're going to see where so so as far as from an erosion control standpoint, if you're west of that line, where you have a deficit of evaporation, to precipitation, it's going to be very hard to establish vegetation quickly. It because you're in a moisture deficit nearly all year long. You will be able to establish vegetation, but it's going to be in a very short window of opportunity throughout the year maybe a rainy season. and that sort of thing. So your stabilisation methods may need to consider, what I call mechanical stabilisation like mechanically placing something on the soil like straw or hay or hydro mulch or some sort of mulch material that actually is going to preserve that topsoil in place. As you go east, you may have a opportunity to use vegetation to quickly establish and provide erosion control, you have to take into account your soil characteristics and some other things fertility, you just can't put seed out there and expect it to grow. Which I have experienced that and, and you if there's no fertility or ground is too hard, you know, you can put seed out and it gets rained on it just doesn't grow because the soil now becomes a limiting factor. So 

Tim Montague 20:50 

As you're going West, it's getting more xeric, though, isn't when the wind erosion a major concern also so it's so on the one hand, you know, the drier and dustier it is right, then you've got major dust control problems and wind erosion problems. And then as you go to a wetter climate, you've got water erosion concerns. Either way, it's a it's a it's a major challenge, right and 

Rhett Kerby 21:13 


Tim Montague 21:14 

Yeah. Yeah, 

Rhett Kerby 21:15 


Rhett Kerby 21:15 


Tim Montague 21:17 

So yeah, I know that during construction, for example, in Nevada, we're involved in being a project where we have to provide constant water to the site to keep the dust down during construction. And that's understandable, right? It's very, it's very dry, dusty. So, that's, that's the nature of the beast out west. 

Rhett Kerby 21:41 

Yes, it is. 

Tim Montague 21:43 

So, well, what, let's, let's talk about some of the best practices just real quick, like soup to nuts, we only have a few minutes, but but what is your company practising? Or what are you seeing others doing so to speak that is a full wrap and and providing for long term, you know, low cost maintenance and and, you know, good solar construction? 

Rhett Kerby 22:11 

Yeah, absolutely. That That to me is is that is a service that we want to provide is a is a turnkey solution that offers long term. When I say long term, I'm talking 30-40 year, sustainable practices. And and that can be a combination of, of pollinator species of native grasses. You know, that that that can be a combination of, of whatever the goals of the client are, but ultimately, a couple of things soil stabilisation, decompaction fertility, and then vegetation that that is suitable to the goals of the client. And if I was to ask what my recommendation would be, as far as vegetation is concerned, I'm always going to lean on natives. Because they are the most highest, they have the highest chance of probability highest probability of success and in in being able to express vegetation after construction, and they offer the lowest maintenance costs going forward some of our modelling because we do mowing and maintenance on solar farms too, some of our financial modelling or forecasting shows, you know, anywhere between 40 and 60% savings over the life of a 25 year project. If you front load some of those O and M costs in the proper establishment of a good vegetation or, or project specific vegetation that allows for minimised, O&M, if you front load and provide a good establishment budget, you're gonna see a, you know, potentially 100% return on that by decreasing the cost O and M over time. And so, you know, that's a very, that is a very hard sale, because you have different silos, you have a construction budget, and you have an O and M budget, and I'm talking about shifting one to the other. And that gets really, really confusing, but but there are some of our clients that that do have long term investment, or a vested interest in seeing a project be low, low cost and low maintenance over time, so it makes sense to have that conversation about shifting a little shifting some of those funds to construction to allow for proper establishment, proper erosion control, proper expression of vegetation. And so with that comes the conversations of compaction, fertility, soil health, all of those things that are needed for for vegetation expression, so I kind of gave you a long answer. 

Tim Montague 24:46 


Tim Montague 24:46 

What does it take to get native plants established here in Illinois, we have a rule of thumb that it takes three growing seasons and you're doing mechanical control and chemical control To keep the weeds down, weeds are a major pest here in the Midwest, very fertile soil. And they will quickly just completely take over a site if they're not controlled rigorously, early in the establishment phase. Right? What do you see? What do you see in, in your parts of the country? 

Rhett Kerby 25:21 

Yeah, integrated pest management approach is it that really needs to be part of that plan that you were referring to is, is a pest management plan, post construction or post establishment. And you're right, there is mechanical, mechanical means of weed control and chemical means of weed control. And, you know, depending on you know, your interest level and and herbicide use. If herbicide use is not an option, then then obviously, you're going to have to compensate for that with mechanical use, or mechanical weed control through mowing, and, you know, string trimming and that sort of thing. But, but if if herbicide use isn't, is a tool in your toolbox, that is the quickest way to achieve satisfactory standard native grasses with herbicide use, and in three years, you know, three years is I think that's a standard across the country, you may have weed problems in in, say, the Midwest, but you may have drought conditions in in, you know, farther west, that just prevents you just have minimal growth. So maybe your your three year window in the West is related to stature and your three year window in the in the eastern parts of the US are related to weed control and just management regarding the competitiveness of the vegetation and area. 

Tim Montague 26:52 

So, are there other aspects of stewardship that you want to highlight for our listeners? 

Rhett Kerby 27:02 

Erosion control is, is in my opinion, from a stewardship standpoint. As a as a Land Steward to this practice for a really long time, a erosion, to me is, is kind of the staple of stewardship. erosion control is a staple of stewardship. And that's wind or water erosion. Because depending on where you are, you may have either 

or both and and as a steward, preventing that erosion is an indication that you're on the right path to successful establishment of vegetation. So, to me, it really does begin with stable soils, then you can have a conversation about compaction and fertility. But if your soils are unstable, and they're blowing and washing away, it doesn't even allow for you to have conversations about these other things. So I would say the first place to start is really with stable, non erodible soils. 

Tim Montague 28:03 


Very good. Well, we'll put a link in the show notes to your company website and your LinkedIn profile. Our listeners can find all of our content at the Clean Power Hour at You can find us on YouTube, you can find us on Spotify, Apple, Google, any of the major audio players, so please subscribe, give it a thumbs up or a like and reach out to me. I love to hear from my listeners. And we're always looking for guests to come on the show. So if you know somebody who has an innovative product or solution, please reach out to me. You can find me on Twitter, TG Montague or on LinkedIn. I want to thank Rhett Kerby for coming on the show today. I look forward to learning more about your work and let's grow solar and storage.