Solar Array Critter Guard

With no clear consensus on the value of critter guard, the decision of whether to invest in it can be a tough call.  There are stories from homeowners who’ve dealt with roof leaks and expensive repairs due to squirrels, and then those who’ve had no animal issues after decades of PV system ownership. Some solar installers include a protective animal barrier on every PV system they sell, while others sell systems without even mentioning it (or they charge extra to install it).

Is it worth installing if the money it saves (by avoiding nest removals, repairs, and lost production) exceeds the cost of installation?

In this report, we are focusing on the cost of the critter guard install in comparison to the what ifs. The average residential PV system owner could be liable for about $875 (net present 2023 value) in animal-related costs over the lifetime of the system without installing a critter guard. These costs would include removing nests, inspections, repair of damages caused by animals, and the PV production lost due to animal damage.

Simulations show a standard deviation of $1,300 in liability from damages, with the best case resulting in zero costs and the worst case over $10,000. About 60% of PV systems will likely experience at least one damage event caused by animals over a 30-year lifetime, with any such event requiring professional inspection and remediation.

Factors for Damage

• Amount of squirrel/bird activity
• Accessibility of PV system to animals from overhanging trees, roof height
• Local contractor rates for inspection and repairs

Four different ways the year could play out:

Easy Peasy

No animal activity/damage. 

Lucky Break

An animal nests under the array and is detected right away. A service tech is brought to the sitefor nest removal. Because nests frequently result in damage to the roof or PV system, the technician must inspect the nest area for damage, which involves temporarily shutting off the PV system and removing several solar panels for access.

Bird nests can restrict airflow under the solar array and increase PV cell temperature, so the system power output will have suffered during the presence of the nest – but only for a short time.

Houston, we have a problem!

An animal builds a nest, resulting in minor damage to the PV system and/or the roof. Repairs often include replacing wires whose insulation has been chewed through by rodents, replacing an individual panel whose backsheet has been scratched, and re-roofing portions of the roof where a nesting animal has scratched through the surface.

Worst Case Scenario

An animal nest goes undetected until secondary damage has occurred. Secondary damage includes water damage and mold due to a compromised roof surface, long-term performance degradation of the PV system, and fire and electrocution hazards due to compromised electrical insulation and PV hot spots. All of these would require extensive repairs.

Likelihood of Damage

Having established these four possible outcomes, how likely is each to occur for a PV system without critter guard? We’ve been unable to track down reliable statistics around this, so let’s make some conservative guesses:

Event; Chance of occurrence (over 1 year)

Nesting; no damage 2%

Nesting; minor damage 1%

Nesting; secondary damage 0.1%

No damage 96.9%

Estimating that in any given year, there is a 1-in-50 chance (2%) that an animal nests under the array but is removed with no further consequences. These figures will certainly vary by location, but the numbers above represent a normal area with moderate critter activity.

Cost of Inspections & Repairs

Consider the estimated costs of dealing with each of the outcomes listed above. 

If live animals are nesting under an array (or there is an extensive animal mess that needs proper PPE to clean up) it can result in needing to hire animal control since service technicians are not armed with the knowledge or PPE to deal with this sort of issue.

Truck roll – In contractor-speak, this means having to send a qualified person (e.g. a licensed electrician) and helpers to the job site– which costs money regardless of any work performed. Average cost: $200

Panel removal/inspection – If any animal activity (or debris buildup) is detected under the array, nearby solar panels must be lifted to inspect for roof rot and damage to the PV wiring. Average cost: $200

Minor roof/PV repairs – Removing nests, replacing chewed wires and compromised roofing, re-commissioning system. Average cost: $800

Major repairs – Interior mold remediation, PV module or electronics replacement. Typical cost: $5,000

Lost production – Reduced PV output and downtime due to hot spots over nests and chewed wire insulation. In a 2020 report based on observing 100,000 PV systems, NREL found that “damage caused by animals may not occur often, but… can have substantial impact on annual production.” This is because damage that reduces PV performance, but does not actually shut the system down, may go undetected for years. We’ll assume lost production equals 25% of expected production during the year in which animal damage occurs. For the average residential rooftop system, that is about (9,000 kWh)*(25%)*($.14/kWh)= Typical cost: $31

Let’s round out our hypothetical situation with these parameters:

Remaining PV years of service – For this demonstration, we’ll assume we are a homeowner considering adding critter guard on a new PV install which we expect to be producing electricity for 30 more years. (If the system is a decade old and you’re considering a retrofit, you might reduce this to 10 or 20 years.) 

Discount rate – We’ll discount future costs using this rate to reflect the time value of money. Our results will all be stated in terms of today’s dollars. Note the discount rate represents opportunity cost, but not inflation – since solar service costs are likely to rise with inflation.

Contractor profit – In our example situation, we are a homeowner who expects to pay a 20% premium above the contractor’s direct labor & materials costs. 

Putting it all together, we have the following model:

Our spreadsheet performed over 1,000 simulations of the 30-year lifetime of our model PV system, calculating the costs incurred for each year and summing them in terms of today’s dollars. The histogram indicates the odds of a single PV system’s lifetime animal-related costs falling into various bins.

The first indicator tells us there is a ~50% chance that our model PV system will incur <$500 in animal-related costs over its lifetime. The second indicator tells us there’s a ~20% chance those costs will fall in the $500-$1000 range – and so on.  Based on our calculations, there is a decent chance that lifetime costs will be less than $500, but a significant “tail” of higher-cost outcomes. 

Analyzing the results further:

The key figure here is the mean, or expected value, of lifetime animal-related costs – $875. According to our initial equation, we should install a critter guard if it can be done for $875 or less. However, consider two scenarios:

We do NOT install a critter guard:  We will probably incur $875 NPV costs over the lifetime of our system. However, the actual cost could be slightly lower (as low as $0) or significantly higher (our simulation’s worst case was ~$9,300).

We DO install a critter guard at a cost of $875: Assuming a quality installation, we have little risk of animal issues for the lifetime of the system.

Choice #2 involves the same expected cost as choice #1, but with less variation (or risk), making it a better investment all else being equal. For most investors, it would make sense to pay some premium over $855 for animal guard in order to eliminate this uncertainty.

Another interesting result is that while the odds of having zero animal issues in any given year are 96.9%, the odds of getting away scot-free for all 30 years are only 39%. In other words, the majority – 61% – of PV systems are expected to have at least one animal-related event during their lifetime.

Other Factors to Consider

Raccoons have been known to scratch holes clean through roofs.

Homeowners looking to buy a new PV system may stand to gain the most from critter guard installation, because it will protect the system for longer. Those seeking to retrofit critter guard onto an existing PV system may still find the job worthwhile.

Will homeowner’s insurance help cover animal damage under your PV system?  If a homeowner can prove that the damage was incurred by specifically a raccoon, repairs may be covered under homeowner insurance, but they do not cover bird, squirrel, or rat damages.”

Some homeowners will look at the numbers in this report and think it is a no-brainer to leave their system unprotected; after all, there is a decent chance they’ll have zero animal problems, so why not avoid the up-front cost of installation?

Others will see animal guard as an obvious winner, since it eliminates potentially huge costs and stabilizes the return on investment of their PV system.

After reviewing these different perspectives, I hope you choose to go on the 'safe' side.  It's just like a little insurance policy for your solar system.