Clean Up Your Solar Before A Bushfire Does It For You

With record-breaking heat and bushfires sweeping the country, times like these serve as a sobering reminder of why we need more solar – and also as a reminder that those of us living in at-risk areas ought to prepare and maintain our rooftop PV arrays appropriately.

I recently heard a conspiracy theory, purportedly from the USA, about how Australia has made fires in California a million times worse. It’s not your usual argument about our massive fossil fuel exports and world-leading carbon pollution though.

Americans have found we’ve planted incendiaries all over their countryside.

We already know, but after a hundred years or more sowing them, Californians have figured out that eucalypts are flammable. Without the native pests, gum trees do really well in a SoCal climate, I’ve seen first hand that they actually grow taller than trees you’d be familiar with here.

I’ve also seen first hand the batchit crazy timber shingle roofing they use but, the point is, we all need to be careful about how we build and look after our homes.

BAL Is The New Black

Bushfire Attack Level (BAL) is the planning jargon used to describe how you should build a new house if there’s any chance it might be subject to fire. Broadly speaking the rules are justifiably more stringent the further into the bush you decide to build.

Having worked on houses that are designed to the highest standard, the golden rule is to get everything millimetre perfect. When you’re done, there should be no more than a 1mm gap in any finished surface, and behind that mineral fibre (rockwool) insulation fills the voids.

For the solar on your roof there’s not much change from an average suburban house, but there’s three details really worth getting right.

This array had a number of issues, but leaves were one of the worst problems.

Penetrating The Roof

Getting the DC wiring from the roof down to your inverter requires mechanical protection under the Australian Solar Standard (AS 5033). For a BAL rated installation, this means using what the electrical trade calls an “anaconda” which is a flexible metal conduit inside a protective plastic sheath.

The hole in the roof must be a tight tolerance to meet the 1mm gap requirement. The practice we found best was to install the conduit, wiring and weatherproof rubber flashing (often referred to be the trade name Dektite) with urethane sealant.

Black plastic sheath prevents this flexible metal conduit from corrosion.

On the following day we stretched the flashing enough to put a calking gun nozzle down the outside of the conduit and then proceeded to pump intumescent sealant into the the void between the fashing and the roof.

This “fireproof” caulk isn’t a good adhesive or sealant – it’s difficult to use because it doesn’t stick anything together, but it does fill gaps so even if the rubber flashing is burnt off, the caulk will still offer some protection.

If you really want a bombproof system and you’re as keen as I am on an industrial aesthetic, putting the DC wiring into metal conduit and running it outside the building is the best idea.

This house in the bush has copper pipe used for a fire sprinkler system. (highlighted in green) To avoid drilling the asbestos eaves & roof the DC conduit is run externally.

Mounting On Vertical Rails

Keeping the roof clean is key, and it is easier when the mounting rails run parallel with the roof rather than across it.

Average houses have a roof pitch of 22.5° and anything more than that will help rubbish and wildlife slide right off.

Solar rules call for 4mm² earth cable for mechanical strength, this offers a good support for DC cables but even better practice is to use a plastic coated steel catenary cable.

In my experience the worst problem in cleaning under solar arrays on a relatively low pitch is actually spider webs.

Not even a petrol powered garden blower will break the threads of silk which entangle leaves & bark, so you need a broom of some sort to move everything along. It’s slow, laborious, fiddly and awkward even before you consider the roof angle.

If your array is on horizontal rails and more than a few metres long, then it becomes impossible to clean without disassembling parts of it.

Modern panel frames are often only 30mm deep, which makes it difficult to run conduit or earth lugs (arrowed) on top of the frame. If you can find 35mm frames they can offer more options for tidy wiring

Cable Management Is Crucial

If it’s one thing that the AI hyperbole of the last few years has taught me, it’s that the word crucial has been overused.

However I really mean it here. If there’s any sort of obstruction under your solar, leaves and twigs will get stuck and it only takes one to cause a buildup of others. This is why Australian standards insist that none of your array wiring is allowed to droop down and touch the roof.

Earth connections must be sprayed with “cold galv” paint to prevent corrosion.

It really takes some planning and some pride to get a proper result, but you really must drill it into your installer that dangling cables aren’t acceptable. They’re often quite anal about making it aesthetically nice and straight from the top side, but the functional cable management you can’t see is more important.

While this conduit is good practice, it runs under the rails, close to the roof, meaning it could easily catch rubbish.

One of the best ways I know is to run catenary cables across the array framing before the panels go down. This gives your electricians a nice tight path for wiring to be tied up out of harms way.

If you can look up from the bottom and see straight through, you can check and clean easily

While it’s not always possible, one of the cleverest ideas I’ve seen for solar maintenance was just a very long broom that simply allowed the roof to be swept from ground level. The biggest trick was to make sure the wiring wasn’t going to get hooked up in the process.

It’s worth noting that not every part of the array will be the same, the wiring disconnection point may be a bit messy

For guidance on what to do with your solar and battery if you need to evacuate due to a bushfire, read my detailed guide.