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

Jamie Leef

Division Manager

Renewable Energy and Green Building

Office: 617-876-8286

Cell: 617-901-5522

Jamie@sandhsolar.com

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.

Finish Work to be Complete by S+H Solar, or another Solar Contractor that you work with. 

• Arrange for interconnection and rebates.
• Install the panels and racking on the roof
• Install power conversion, metering, and related system gear.
• Wire the array
• Pray for lots of sun

Specific structural recommendations about the roof 

Please keep in mind that building code changes often effect the calculations that structural engineers use to prove that a proposed array can meet code.  Therefore it may not be worth having a stamped structural letter produced for the proposed system, or having structural enhancements to the building prior to the actual installation permit application.

However, one very important thing to do whenever possible is to document the framing conditions of the roof and related structure.  Complete measurements and photos of rafters and rafter connections, ridge beams, top plate construction, posts and bearing walls can all be very helpful for future analysis.  If  the building is under construction or renovation make sure to gather this information, or have S+H do it for you.

Installation Considerations:

• To turn the system on we usually want the building to be occupied, have access to the roof, and a computer network, the utility and customer electric power in place and accessible by us.
• Switch-gear for backup generators and battery UPS needs to be accounted for by us so please let us know if that is to be part of the project.
• Work on roofs is weather dependent.  We do work all year long, but the schedule can be hard for us to predict.

Requirements for Finish Install

• We can not get a rough electrical inspection until the building is closed in and tight to the weather.  Please consult the local AHJ for specific regulations.
• The final roof finish (membrane, shingles, whatever) should be completed.
• The main breaker panel, electric meter, light and permanent power all need to be installed and turned on.  We can not connect to temporary power.
• A CAT5e or CAT6 cable from a router or network access point should be brought to the PV equipment location and terminated, or wireless signal present, if Internet monitoring is to be incorporated.  S+H needs to be given instructions on how to access the network, either through a password or appropriate means.
• On new construction we prefer to install prior to insulation.  This is not a requirement.

System Turn-on (usually part of Finish Install)

• The building could be occupied, or somehow in use.
• We need access to the roof
• We will do testing and controller programming.
• We will arrange for the utility NET meter
• We will meet the inspector for sign-offs.  Some localities are requiring a mechanical permit additionally or in lieu of the plumbing permit.
• The Commonwealth Solar grant program and some Municipal Light Plants may require additional technical inspections after the regular code inspections

Safety Note:

Roof racking systems need rope anchor points for safe installation and maintenance.  We install this anchor.  Please make sure it is kept in place.

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