by Marcus Marino
These past few weeks have made it clear to almost everyone that we have a problem on earth. The climate is different, and we are all heating up. Trees help reduce the “island heat effect” in and around cities.
When trees are in a parking area the temperature of the parking area is 10 to 20 degrees cooler. They help shade us, our cars and more importantly the pavement so that it does not reflect the heat.
Can solar panels and trees co-exist on the same site? Well, the short answer is yes. Of course, if your house in always in shade and you planned to put the solar panels on your roof you will not 
get enough power from the solar panels to pay for themselves in a lifetime. However, the standard philosophy that solar panels and trees cannot be placed near each other is nonsense.
Here in Davis we have before us a prime example. Sutter Hospital Phase 2 Project’s consultant proposes removing all the trees in the parking lot so that solar panels can be placed above the parked cars. City Council will be voting on an Appeal by Sutter Hospital from the approved City plan to permit the trees to be removed and NOT relocated as the City had required them to do so in its approval.
However, there is a solution that will save the trees AND provide even more solar panels. The solar panels can span over the driveways in the parking lot thereby allowing the trees to remain on the island median between the parked cars. The trees would be far enough away from the solar panels so as not to shade them. The shade from the trees will still shade some of the cars, and the solar panels will shade some of the cars as well. The accompanying drawing shows where the solar panels can be located, a sketch comparing our recommendation to the Sutter Hospital consultant’s approved plan and a sectional drawing showing the shading of the trees and solar panels on the cars. This recommended plan also protects the solar panels from possible future car fires in the parking spaces.
Marcus Marino is an Architect whose firm has prepared an alternative that will permit even more solar panels than the hospital has planned for and KEEP ALL of the existing trees.
I appreciate this effort, but I think it would need to be carefully reviewed by solar experts to see if the trees and panels would truly be compatible.
The species on site include sycamores or plane trees (Platanus hybrids) and, I recall, Zelkova serrata.
Both species easily reach 40 to 60 feet tall and wide at maturity. This is one of the reasons they are popular for shading large asphalt areas such as parking lots: properly planted and watered, they can provide quick shade over large areas. The illustration doesn’t appear to have these species at their correct mature sizes.
It is very likely that trees of that size would shade solar panels from one direction or another to a significant degree at various times of day and year.
Platanus trees are pretty high litter with very large leaves, seed balls, bark exfoliation, and a propensity to drop small branches. This would be a factor in the longevity and maintenance costs of the solar panels.
The likeliest outcome would be severe pruning of the existing trees as they begin to encroach on the panels.
I think this is an outstanding example of how to install a new parking lot, with trees chosen carefully for their compatibility with the solar panels. There are a lot of issues with how trees have been permitted for parking lots, and a concerted effort to improve the success rates, coupled with consideration of implementation of solar power, would be a very practical and useful endeavor for the commissions that are jointly reviewing this issue.
IMO the panels themselves would need to be 20 to 30 feet up off the ground to allow for the growth habits of small to medium size shade trees. It’s easy to come up with a species list for that situation. But in this instance we are dealing with very large species that already have about twenty years of growth and are, if properly irrigated, just about to really hit their stride in fulfilling their job of shading, mitigating pollution, and sequestering carbon, not to mention the other general benefits trees provide.
EXACTLY!… And the ordinances should be modified to recognize that solar panels in parking lots can achieve the basic shading goal, avoiding heat island, local air ‘heating’, etc.
Trees good… solar panels good. Retrofits trying to optimize both? Not so much… what may look good in theory, pretty computer generated pictures, might be a total disaster in practice… Don points out of some of the biggest issues, including the very biggest…
You just can’t have a good canopy from a tree that is planted in a constrained space like we’ve seen done for 50 + years… again, look at Oak Tree Plaza, Oakshade plaza… the plans looked great for 50% shading… reality is much different, and deficient… most trees need ‘ground-space’ proportional to their eventual canopy… rule of thumb I’ve heard for many tree species is that the root zone is close to 1:1 as to canopy… the roots need air and water…
Root zone will actually go well past the canopy in most cases but in a paved situation you just want to optimize the soil area as best you can to allow for infiltration of water and air exchange for the roots. Trees can be chosen that live without irrigation once established, but that is a pretty short list and most are rather slow growing. So we usually choose trees that can be watered deeply and fairly infrequently, and sycamores and Zelkova certainly fit those parameters.
There are real issues with how parking lots have been landscaped. Results are quite variable, as you can see in the picture of four parking lots around Davis. The weird concrete planters that were used in the parking lot near Nugget in north Davis (upper right in picture below) simply don’t work. It would actually be pretty easy to figure out how to do this if plant professionals were occasionally brought into the process.
I fully agree Don… but the reality for 50+ years that “so called” experts (landscape architects [“plant professionals”?) who submitted tree planting plans for shading, for City staff/public review, ‘convincingly’ showed, with ‘pretty’ graphics, showed 50% or more shading in the time frame required by the tree ordinance. An inconvenient truth.
Even PW engineers knew that it was ‘bogus’… but we and the City arborists were ignored, by Planning Staff, the public, Commissions and the electeds, because they met a ‘checkbox’ on the plan submittals… another inconvenient truth.
Landscape architects are design professionals, not plant professionals. The BS program in LA at UC Davis only requires two courses in plant materials. My experience with the plan check by staff when we went through it a couple of times for customers was that it was pretty cursory.
Parking lot shading plans, including species selection and installation specs, should be reviewed by the Tree Commission, IMO.
Most LA “professionals” aren’t, in my experience. Professionals bring in team members who can fill in their gaps in knowledge, and/or continue to grow/learn before they submit ‘professionally’ prepared plans.
As it stands, I believe it is correct that what’s common in college (LA) is a BS program… the “S” is supposed to stand for ‘science’… but often it stands for another noun… my understanding is that Cal Poly SLO actually turns out ‘professional’ LA’s, as a rule…
The landscape architects that I have worked with locally have generally been highly professional and very good at what they do. It’s important that people understand what their skill sets are, at least by training.
I hope that the subcommittee of Natural Resources and Tree Commissions will give this proposal due consideration and have it vetted separately by a solar engineer and a consulting arborist or professional equivalent. My quick impression is it won’t work or will be problematic, but I’d be more than happy to be proved wrong.