How to Design Homes to be Solar PV Ready
Many homeowners might be building a new home or doing renovations and they want solar, but not right now. The following is a guest post from Jamie Leef, an expert builder and solar installer at S+H Construction that will be helpful to general contractors and architects that are advising their clients. Jamie is also teaching a course for architects and engineers on design considerations for integrating solar in urban areas.
If you’re an architect or engineer advising clients about solar PV in urban areas, click here to sign up for Jamie’s course “Solar PV Design Considerations in Urban Areas”
By making a few changes to the building while construction is under way, you can make installing solar MUCH cheaper when they finally decide to invest in solar.
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Enter Jamie Leef
This is standard document we provide to firms we work with to advise their clients. In any place where I say “we” you can substitute with “solar contractor”
If you’d like me to BID on a solar project. Here is my contact information
Renewable Energy and Green Building
Design Homes to be Solar PV Ready Summary.
PV systems have three key components: Roof- or ground-mounted panels, DC-AC power conversion equipment mounted either at the panels or in a mechanical space, and balance-of-system gear that measures, controls, and connects the parts to each other and to the electrical grid.
Keep these things in mind when designing or analyzing a residence for a solar PV project:
The roof needs solar access! This generally means an area of flat roof, or pitched south-facing roof, that is unshaded and large enough for the panels. A typical 4 kW array is about 270 SF. Modules are in units of approximately 40” x 66”, though other sizes can be found.
The roof structure needs to be able to handle an additional load of 3 to 4 pounds per square foot.
Your client should like the way the panels and proposed layout look.
The roof cladding should have a standard manufacture’s detail for attaching something to it. All typical materials do – fiberglass/asphalt, EPDM, TPO, slate, etc.
The building should have an electric meter owned by a customer who uses a good amount of electricity. Condos, for instance, can get complicated.
The building should have electric service from a utility that offers net metering and PV interconnection. Some space should be set aside near the main electric panel for solar power equipment. The amount of space varies by system type, but is usually about 4’ x 4’
A conduit will be run from the PV equipment location to the PV panel mounting install area. This can be inside the building, on on the outside.
Other Kinds of Installs
Okay, so your project does not look like the other cookies that the cookie cutter created. Here are some other scenarios to consider.
Consider a ground-mounted system if your roof can not take panels
Within some utilities and areas you can share net metering credits with other meters, which can allow for installs in condos, for instance, to pay back to several residents.
If you can not get an interconnection agreement, consider going off grid! We have even done this in downtown Boston. Ask us how.
Remember that solar hot water takes less space on the roof. It also works very well in multifamily buildings where there is a shared water meter and hot water distribution system.
Solar Ready Details.
The following are things that should be done to design or prepare a residence for a solar PV project.
Ensure the roof has the structural capacity to accommodate the panels
Rough-in an unbroken metal conduit from the PV equipment location to the PV panel mounting install area. There are to be no accessible pull-boxes or ways to access the DC conductors. Please refer to section 690 of the NEC, and to the local AHJ for the conduit material options. Large systems with a central inverter might have several DC conductors in this conduit. Micro-inverters will have conductors designed for AC. Size the conduit accordingly. If you have questions about sizing conduit call S+H Solar HERE
Label the conduit with “Solar PV Circuit” labels as per 690 NEC
Please discuss the specific site requirements for future access to cathedral ceilings, attic spaces, and the possible exterior conduit paths.
For exterior conduits we strongly recommend metal pipe or flex rather than plastic pipe for durability and temperature correction reasons, even if code does not require it.
Provide a 4’ wide ¾” plywood mounting panel adjacent to the main electric panel that is at least 4’tall and centered at 4’ AFF, but can be taller if possible. Ensure there are similar electric code restrictions to this space, such as no water above, 3’ clearance in front, and free air above and below, etc. Micro-inverter systems do not require this much space, but it will never go to waste.
Ensure that the proposed PV system back fed breaker rating is no more than 20% of the bus-bar rating of the main electric panel. For example, for a 200 AMP main breaker, the maximum overfeed is 40 AMP. There are other optional interconnection points, depending on the utility and the service details. If you there are multiple breakers, if this is multi-family home, or a small service and you have questions, please contact S+H Solar:
Leave a two-pole breaker blank space at the bottom of the bus-bar reserved and labeled for use as the PV back-feed breaker (or the section of bus that is opposite the service cable feed lugs or breaker).
Endure space for a small AC side-arm disconnect next to the exterior service entrance (assumed to be an electric meter cabinet). Install a capped, waterproof conduit to that location for future AC wiring from the PV equipment panel if that location will be otherwise hard to wire to in the future (for instance, complicated foundation finishes insulation, or finished basement).
Provide a terminated CAT5-E or better, data cable to the main house router for monitoring at the PV equipment mounting location.