Before you consider investing in a roof mounted solar PV or solar water heating system, there are several things to consider.
The first, of course, concerns the added weight of the solar system. Is the roof structurally sound to accept it? As a rule of thumb a solar power generating system (PV) made up of solar panels and racking weighs around 4 lb/square foot.
Second, can the system be installed to face generally south?
Third, is the area designated for the solar system in the sun (shade free) between 9 am – 4 pm?
Fourth, and this is what we will discuss in detail, should you install a new roofing system?
The typical reaction to the suggestion that a new roofing system should be installed before a roof mounted solar PV system is installed is resistance.
However it is a penny-wise and pound foolish decision not to replace the roofing system almost without exception:
- Most roofing systems will not last as long as the solar system. The possible exception is a metal roofing system.
- The cost and inconvenience of decommissioning, removing and reinstalling a solar PV system to replace the roofing system underneath far outweighs today’s price to replace the roof system before installing the solar system.
Are there exceptions? One has already been mentioned. A metal roof, depending on its type, its age and construction may not need to be replaced. A two year old single ply roofing system (non-residential) may not need to be replaced but should be subject to inspection and acceptance by the material manufacturer who carries the warranty.
For non-residential installations most roofing systems are under warranty by the roofing system manufacturer for at least 2 years and usually longer. ANY work done on them by a contractor not approved by the manufacturer renders that warranty null and void. This would raise the question, if the original contractor or a contractor approved by the manufacturer has no solar installation expertise what is to be done?
Let us examine what the roofing contractor needs to provide before any solar system is installed:
- Inspect the roof structure. If there is any doubt concerning the ability of the structure to withstand the additional weight a structural engineer should be recruited to provide a professional opinion.
- Check the existing roofing system in place – provide recommendations for reroof, recover or repair.
- Install any supports and penetrations and make them watertight
- If the actual solar panel /combiner/inverter installation is by others: Check the roof after the job is completed for damage to the roofing system and repair as needed.
The rack mounted solar PV systems currently being installed generally carry a 25 year performance warranty.
The typical maximum available roofing system warranty is 20 years. Both of these items are reasonably expected to exceed the warranty limits. It can be argued that as the roofing system is shaded by the solar panels it is not subject to as much UV degradation as roof constantly exposed however, the entire roof is not covered with panels therefore there are roof areas that do have constant exposure. It can further be debated that these exposed areas can possibly receive treatment as time passes to keep them protected and match the degradation of the shaded areas. Given that both of these are possible it does not detract from my original premise that virtually all roofing systems need to be replaced before a solar system is installed.
I have first-hand knowledge of an instance where this was not done. The huge cost associated with decommissioning, removing and replacing the PV system does not even take into account the problems we encountered when reviewing this project.
One cannot simply drop in a new PV panel to replace a faulty panel or a panel that gets damaged during the disassembly of the system and the storage. These panels were ten years old and the voltages and amperages were a complete mismatch with available replacement panels even those with the same nominal wattage.
It is possible that the layout of the existing panels cannot be repeated, the Fire Marshall may have current requirements which will change locations, string sizes and so forth. Trust me, this is a situation to be avoided at all costs – yes, even the cost of a new roof. So, bite the bullet when you install solar PV on your roof and install a new, long-life roofing system. Then relax and enjoy the savings provided by your own roof-top power generating system for decades to come.
Would you want to decommission this array, remove it install a new roof and reinstall the PV system? It simply does not make economic sense