GETTING BUILDINGS READY TO RUN ON SUN

Solar Ready Buildings Planning Guide
L. Lisell, T. Tetreault, and A. Watson, December 2009 (National Renewable Energy Laboratory)

SUMMARY
Simple question: In this time of climate change and the transition to a New Energy economy, why in the world would anybody build a building that is NOT solar-installation ready?

Simple answer: Because they think it costs too much or they don’t know how.

Simple solution: An instruction manual, describing affordable solar-ready construction methods.

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Solar Ready Buildings Planning Guide, from researchers at the U.S. Department of Energy (DOE) National Renewable Energy Laboratory (NREL), describes how buildings can be designed and constructed to streamline the after-purchase installation of solar photovoltaic (PV) systems, solar thermal hot water (ST) systems and solar ventilation preheat (SVP) systems.

Builders always need to keep costs as low as possible. And because of high upfront solar costs, contractors do not want to build in whole systems. On the other hand, new incentives and financing make solar system purchases more appealing to home and building owners, especially as solar PV system technologies become more efficient and grid-supplied electricity gets more expensive.

The compromise for builders and contractors is a solar system-ready structure that costs little or nothing more than a non-ready structure but promises reduced system installation costs and improved system efficiency to potential buyers.

The NREL paper identifies PV, ST and SVP system requirements that can serve as guidelines for solar system-supportive building codes, building design and building- or community-related regulations.

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COMMENTARY
General guidelines for any solar system:
(1) Know where the planned system is to be placed.
(2) Avoid shade. Trees and other structures impede sunlight and compromise system output. If shade cannot completely be eliminated, it should at least be eliminated during peak sun hours.
(3) Build where zoning laws prevent the rooftop system from being compromised by shade from future adjacent construction.
(4) Take special care to prevent any sloped, south-facing part of the roof from being obstructed by shade or other obstacles.
(5) Plan for minimal placement of other equipment on the roof to maximize the open area available for solar collectors.
(6) Build a sturdy roof that accommodates a solar system’s installation.
(7) For a PV system, the roof structure must carry a load of 3-to-6 pounds-per-square foot; for an ST system, it must carry a load of 2-to-5.5 pounds-per-square-foot.

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(8) Consider the rooftop’s wind loads, based on the American Society of Civil Engineers (ASCE) international building code 7-05.
(9) Architectural plans should include all roof specifications and drawings.
(10) Safety equipment on the roof will allow easier access for solar installers.
(11) Pre-plan for solar collector mounting and consider the mounting strategy options. If the collectors are to be mounted with penetrating hardware, it could be pre-built into the roof with flashings at every penetration for extra strength and durability.
(12) If the collectors are to be set on the roof, the roof’s warranty should include terms for a solar installation.
(13) All equipment should be National Electrical Code compliant.

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Additional Guidelines for Solar Thermal (ST) Systems:

(1) Know the building’s hot water load and the water temperature needed so the structure is built to accommodate an appropriately sized system and components. Residential hot water use calculations can be made from Building America Research Benchmark Definition.

(2) Pre-identify and designate where system components (controllers, heat storage system, shutoff valves, etc.) will be located.

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(3) Pre-plan plumbing and water line pathways to link the solar collector, the heat storage system, and the building’s hot water system. Also, lay out the water distribution system and mixing valves to maximize the ST system performance.

Additional Guidelines for Solar Ventilation Preheat (SVP) Systems:

Solar PV and solar hot water systems work in most buildings. SVP systems, which capture the sun and preheat the air entering the building, only work in buildings with high ventilation requirements and moderate to cold and sunny climates. Potential candidate buildings: industrial buildings, warehouses with continuous ventilation, laboratory facilities, gyms, aircraft hangars.

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(1) Minimize the windows, doors, other openings and irregular surfaces on the south-facing wall to avoid limiting the system’s effectiveness and maximize the exposure of the collector to direct sun.

(2) Pre-build direct access (through a knockout) from where the collector will be on the south wall to the outside air (OA) intake duct of the air handling (HVAC) unit to avoid the cost of extra ductwork.

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(3) Install a bypass damper in the air handling pre-ductwork for when the building cooling system is in use.

(4) The air handling unit fan should be big enough to handle the increased resistance from the SVP system and the associated pressure drop from the outside to the air-handling unit.

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(5) Design the HVAC control system with extra control points to control dampers for the SVP system.

(6) Sufficient space must be pre-planned between the collector and exhaust vents, loading docks, parking lots, on site generators, etc.

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(7) The collector mounting must be fire resistant and the wall must meet fire codes because of the high temperatures the collector can hold.

Additional Guidelines for Photovoltaic (PV) Systems:

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(1) Pre-plan PV system inter-connections into the electrical panel and leave space for a PV circuit breaker.
(2) Specify a panel capacity 20% bigger than the building’s total power, which is the PV system power plus the size of the main panel’s breaker. This is the NEC-allowed panel rating.
(3) Pre-plan locations for an inverter and balance-of-system (BOS) components. Review interconnection standards at D-SIRE make sure the building’s inter-connections for the grid-tied PV system meet the standards.
(4) Pre-place electrical conduit from the solar collector location to the electrical panel and other system components.

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(5) Consider (a) special load needs (such as some buildings’ need for an uninterrupted power supply) and (b) the need for storage.
(6) Avoiding shade is especially crucial for PV systems because even a narrow strip of shade, as from a lightning rod or an antenna, could significantly limit the current from the entire array.
(7) Pre-plan all construction based on what the PVWatts calculation tool indicates about the parameters of the system size appropriate for the building.

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QUOTES
- From the guidelines: “This document was designed to be concise and hence accessible to users. When implementing the strategies outlined here, other resources must be consulted. The National Electric Code and local jurisdictions have specific requirements that apply to solar and must be considered. Local solar installers will be valuable resources at this early stage.”

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- From the guidelines: “This guide was written with the focus on new construction. While many of the considerations are similar for retrofit or renovated buildings, there are other considerations to be made for retrofit projects…”

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- From the guidelines’ conclusion: “A few simple considerations when designing buildings will facilitate a smooth and cost effective transition to solar later in the building’s life. In cases in which solar is not economically feasible during the initial construction phase, making the structure solar ready will help reduce the carbon footprint of the building over its lifetime and lower power costs when the solar system is installed. Furthermore, a solar ready building will position the building owner to take advantage of falling renewable energy prices in the future. Implementing policy that requires some or all new construction to be solar ready is a simple way community leaders can promote solar in their jurisdictions…[and] city planners, policymakers, and developers will be able to lay the foundation for Solar Cities.”