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Inverter, Meter, and Shut-Off Mounting Surface for Solar PV Systems

Scope

Include adequate, sturdy wall space for balance of system components when building a Renewable Energy Ready Home (RERH).  Attach a piece of plywood to the wall for mounting solar photovoltaic (PV) equipment including the inverter, meter and shut off switch. Space requirements and layout for solar photovoltaic system components should be taken into account early in the design process. 

DOE Zero Energy Ready Home Notes

The U.S. Department of Energy (DOE) Zero Energy Ready Home National Program Requirements includes in Exhibit 1, Mandatory Requirements, Item 7 Renewable Ready, that all homes must meet the requirements in the Consolidated Renewable Energy Ready Home (RERH) Checklist.

The RERH Checklist requires builders to

  • Install and label a 4 ft x 4 ft plywood panel area for mounting an inverter and balance of system components. 

Alternative: Blocking is permitted to be used as an alternative to the 4’ x 4’ panel. The area designated for the future panel to mount PV components shall be clearly noted in the system documentation.

See the Compliance Tab for related codes and standards requirements, and criteria to meet national programs such as DOE’s Zero Energy Ready Home program, ENERGY STAR Certified Homes, and Indoor airPLUS.

Description

A renewable energy-ready home (RERH) is one that is built with the wiring and plumbing conduit and other components in place to facilitate the future installation of solar photovoltaic (PV) panels and/or solar water heating panels. Some energy-efficiency programs, like the U.S. Department of Energy’s DOE Zero Energy Ready Home Program, require homes to be renewable-energy ready.

Solar PV system inverters can be quite heavy (>80 pounds), necessitating a solid backing to mount the inverter. To meet the requirement for the DOE Zero Energy Ready Home program, a 4ft x 4ft piece of finished plywood should be mounted near the electrical service panel for the PV balance of system components, including the inverter, meters and disconnects. 

The purpose of the plywood backing is to

  • Ensure a dedicated space for these components.
  • Provide a secure foundation for mounting future equipment.
  • Facilitate the future installation of these components by the installer.

The 4 ft. x 4 ft. plywood sheet should be fastened to the wall studs and mounted so that its center is roughly 4.5 feet above the floor. The dedicated inverter area may be located inside or outside the home. In either case, the dedicated inverter location should be free of direct sunlight, excessive heat, or any harsh or extreme weather conditions. It is also recommended that the inverter mounting area not share a common wall with a living space, such as an adjacent bedroom, where slight noise and vibration may be considered a nuisance. In all cases, the builder should conform to all local or national codes when meeting this specification.

The builder should clearly identify the location of the designated area on electrical and architectural diagrams. This area should be labeled as the RERH balance of system component.

How to Designate Space for the Balance of System Board

  1. To meet the requirements of the DOE Zero Energy Ready Home program, designate a dedicated space approximately 4.5 ft above the floor for the future balance of system components, 4 ft tall by 4 ft wide. Consider locating the wall space directly beneath the roof space for the future PV system to minimize the wiring conduit required.
  2. Label the space by placing a water resistant 10 in. x 6 in. label or sign in the center of the plywood that reads “Renewable Energy Ready Home - Solar PV Inverter/Service Panel Location.”
  3. Record the balance of system wall location on the floor plan to be provided to the homeowner.
Complete balance of system board
Figure 1. Complete balance of system board. (Image courtesy of BSC).

The Balance-of-System (BOS) components include all of the electrical, mechanical and hardware elements integrated into the PV system (see Figure 1).  Some of those elements are: the inverter, the charge controller, disconnect switches, the rack and mounting system for the array, and a battery bank.  Many of the BOS components need to be protected from the weather elements.  The parts that are required to be installed in weather-resistant enclosure require proper working and maintenance clearances.  A secure mounting space is required for those components as well.

Inverter

This converts the direct current (DC) power coming off of the panels (or from the battery bank) into alternating current (AC), the convention for household electricity.  Inverters vary in terms of their capacity (how much electrical current they can handle) and the “quality” of the AC they produce (some household loads—lights, appliances—can tolerate lower-grade current, while others—printers, computers—have more exacting needs).

Charge Controller

This manages the flow of electrical power from the panels to the battery bank and household loads.

Battery Bank

PV systems need deep-cycle batteries; this means that they are almost always lead-acid, big, and heavy.  The cost of a battery bank depends on its capacity—just how much electricity is needed in storage to deal with nighttime power needs and cloudy days.  While charging, batteries produce hydrogen gas; therefore, if used, battery banks require proper ventilation for safe operation.  When handling leaky batteries, use care to avoid damage from the sulfuric acid.

Ensuring Success

Ensure adequate utility room early in the house design process to allow for ample space for solar photovoltaic (PV) and water heating system components.  Confirm with local code officials early in the design process what steps are needed to guarantee that installation of PV panels will meet with local codes, homeowner's association covenants, and historic district regulations.

Protect the electrical and mechanical components of the PV system from bulk moisture, high temperatures, and direct sunlight.  The utility room should be properly ventilated and maintain average indoor temperatures.  Proper clearances and working spaces should also be maintained.

Climate

Among other things, the Consolidated Renewable Energy Ready Home (RERH) Checklist is required only under the following condition related to climate:

  • Location, based on zip code, has at least 5 kWh/m2/day average daily solar radiation based on annual solar insolation using the PVWatts online tool.
Map of average daily solar radiation
Map of average daily solar radiation

Training

Right and Wrong Images

None Available

Presentations

  1. Zero Energy Ready Home Training
    Author(s): Rashkin
    Organization(s): DOE

Videos

None Available

CAD Images

None Available

Compliance

The Compliance tab contains both program and code information. Code language is excerpted and summarized below. For exact code language, refer to the applicable code, which may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

DOE Zero Energy Ready Home (ZERH) Program

The DOE ZERH Consolidated Renewable Energy Ready Home (RERH) Checklist states

Install and label a 4 ft x 4 ft plywood panel area for mounting an inverter and balance of system components. 

Alternative: Blocking is permitted to be used as an alternative to the 4’ x 4’ panel. The area designated for the future panel to mount PV components shall be clearly noted in the system documentation.

Homes that already have a solar photovoltaic (PV) system installed do not need to meet the PV requirements of the Consolidated RERH checklist.

DOE Zero Energy Ready Home National Program Requirements Mandatory Requirement 7 (Renewable Ready) shall be met by any home certified under the DOE Zero Energy Ready Home program, only where all of the following conditions are met:

  1. Location, based on zip code has at least 5 kWh/m2/day average daily solar radiation based on annual solar insolation using PVWatts online tool, AND;
  2. Location does not have significant natural shading (e.g., trees, tall buildings on the south-facing roof, AND;
  3. Home as designed has adequate free roof area within +/-45° of true south as noted in the table below. Note that in some cases a house may have insufficient roof area for the Solar Electric RERH checklist, but it may still have the minimum roof area for the solar thermal RERH Checklist and would therefore have to comply with the Solar Thermal RERH checklist. In other cases, the home may only have adequate south facing roof for the Solar Electric or Solar Thermal RERH Checklist, but not both. In that case the builder can decide which one of those two checklists to apply.
ZERH Requirements for south roof area
Table 1. ZERH Requirements for south roof area

2009 IECC

Section 401.3 A permanent certificate shall be posted on or near the electrical distribution panel that lists types and efficiencies of water heating, heating, and cooling equipment, as well as insulation R values, and window U and SHGC factors.

2012 IECC

Section R 401.3 A permanent certificate shall be posted on or near the electrical distribution panel that lists types and efficiencies of water heating, heating, and cooling equipment, as well as insulation R values, and window U and SHGC factors.

2009 IRC

Follow the requirements for solar water heating systems found in the 2009 IRC Section M2301 Solar Energy Systems.

2012 IRC

Follow the requirements for solar water heating systems found in the 2009 IRC Section M2301 Thermal Solar Energy Systems.

2009 International Mechanical Code (IMC)

Follow the requirements for solar water heating systems found in the 2009 IMC, Chapter 14, Solar Systems.

2012 International Mechanical Code (IMC)

Follow the requirements for solar water heating systems found in the 2012 IMC, Chapter 14, Solar Systems.

2014 National Electric Code (NEC)

Follow the requirements for solar photovoltaic (PV) systems found in the 2014 National Electric Code (NEC), Article 690, PV Power Systems, and Article 110, Requirements for Electrical Installations.

More Info.

Access to some references may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

Case Studies

None Available

References and Resources*

  1. Author(s): DOE
    Organization(s): DOE
    Publication Date: April, 2017

    Standard requirements for DOE's Zero Energy Ready Home national program certification.

  2. Author(s): Aldrich
    Organization(s): CARB, Steven Winter Associates
    Publication Date: March, 2013
    Brochure on specifications for PV systems.
  3. Author(s): Brooks, Dunlop
    Organization(s): NABCEP
    Publication Date: March, 2012
    This Photovoltaic (PV) Installer Resource Guide is an informational resource covering basic requirements for PV installations intended for individuals pursuing the Photovoltaic Installer Certification credential offered by the North American Board of Certified Energy Practitioners (NABCEP).
  4. Author(s): BSC
    Organization(s): BSC
    Publication Date: June, 2006
    Report aiming to "de-mistify" technology and economic considerations of residential PV systems.
  5. Author(s): EPA
    Organization(s): EPA
    Publication Date: January, 2011

    The RERH specifications and checklists take a builder and a project design team through the steps of assessing a home’s solar resource potential and defining the minimum structural and system components needed to support a solar energy system.

Contributors to this Guide

The following authors and organizations contributed to the content in this Guide.

Last Updated: 08/14/2014