Category Archives: Uncategorized

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Resilience

Components of building resilience (the four R’s) from the National Institute of Building Sciences [1] are described below with examples applicable to an energy efficient solar roof:

Robustness. The ability to maintain critical operations and functions in the face of crisis.  Roof temperature moderation with an energy efficient roof allows a smaller HVAC system design, and also a smaller solar and battery system design.  Having solar power with possible electrical energy storage allows backup in power outage conditions. The smaller systems allow construction budgets room to afford other building features. Lightweight tiles, such as the Power Shield Inc. (PSI) metal tiles present less potential stress on a building during an earthquake. The metal tiles are fireproof.

Resourcefulness. The ability to skillfully prepare for, respond to and manage a crisis or disruption as it unfolds. This includes identifying courses of action and planning business continuity; training; supply chain management; prioritizing actions to control and mitigate damage; and effectively communicating decisions. For safety reasons, utility companies don’t want solar systems to be able to feed power into the grid when utility workers may be working on the lines—so there are safeguards to prevent that. In most cases, this means that when the grid goes down, the homeowner can’t draw power from the solar system even during the day in sunlight (anti-islanding). Some inverters allow the use of one AC circuit  (with a hard disconnect from the grid during a power outage) to be supplied with power. Battery backup systems like the Enphase Energy AC or the Tesla Powerwall can be configured to draw power from a solar array without risk that power will be back-fed into the grid.

Rapid recovery. The ability to return to and/or reconstitute normal operations as quickly and efficiently as possible after a disruption. Components of rapid recovery include implementing carefully drafted contingency plans, with people and resources toward the right places. Matching priority equipment with the available solar and/or backup power is important. Recovery will be faster for a building with the PSI system, which does not heat up as much as a building with typical roofing.

Redundancy. This means there are back-up resources to support the originals. Typically for homes, this means a battery back-up or a portable generator.  There can be connection with equipment such as lights, food refrigeration and fans to operate in back-up modes. Redundancy design options are at the lowest cost when a building is built. Control systems can be intelligent enough to take account of available resources, such as solar power, battery availability and potential modes of operation to respond automatically and to allow building supervisor(s) to modify this response based upon available information on the length of the power outage.

Oak Ridge National Laboratory has performed tests on similar tile configurations as the PSI system and demonstrated that a cool roof coating on metal roof tiles with above sheath ventilation (ASV) are effective means to reduce heat transfer from the roof to the building interior [2]. As much as 30% of the cooling energy can be achieved with these measures. These studies are for steep slope roofing applicable to residential and commercial buildings. For power outages or brownouts during the cooling season, occupant area temperatures and comfort can be improved through a cooler roof with low heat transfer.  Air conditioning is typically not a high priority system during power outages because it can take approximately up to half of the building electrical demand and usage.  ASV can minimize the heat loss of cool roof coatings during heating season, because of the insulating gap between the tiles and roof deck.  It can help in preventing ice dams in conditions prone to them.  Blackout and brownout scenarios can be random, for planned maintenance or happen because of programmed outages in fire hazard areas, such as California, where large area blackouts occur because of location, winds and dry conditions. A metal roof tile system is naturally fire resistant and will work well in wildland urban (WUI) interface zones.

An energy efficient roof with solar are often of high priority for authorities having jurisdiction (AHJ) and building efficiency organizations, such as ASHRAE, DOE, ICC, NFPA and others.

[1]  https://www.wbdg.org/resources/building-resiliency

[2]  A Compilation of Home Energy Assessments for Cool Roofs, Above-Sheathing Ventilation, Radiant Barriers, and Other Attic Strategies William Miller, PhD.  ASHRAE 2010 Buildings XI.

BIPV, Solar Cost, Solar Roof Tiles, Uncategorized

A new roof that pays for itself?

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For most people, the home is a significant investment in terms of money, time and effort.  When a new roof is needed, evaluating the available choices of roofs, along with the possible solar options, are important for getting the most out of the money to be spent.

Looking at the various roof types life expectancy, impact on energy bills,  and the effect on resale value over time, all help in making an informed decision.  Adding solar to the roof affects how the home looks and can provide financial returns over time that can pay for the roof and solar.

Graph A

G A

Metal roofs, lasting 50 years and more, have a lower life cycle cost than asphalt shingle roofs, which last around 16-18 years.  Potential buyers can see where the roof is at in its life expectancy and will adjust their offers accordingly.  The graph above shows solar savings and solar savings offset by the cost of solar and the various roofs. Solar and the cement tiles are replaced at 32 years and asphalt shingle roofs are replaced at 16 and 32 years. In the graph below, Power Shield, Inc. (PSI) metal roof tiles with integrated solar (BIPV) are compared with asphalt shingle roofs with solar, both types compared with a cash purchase versus financed.

A 1,750 Square Feet (163 SqMtr) house with 2,100 Square Feet (195 SqMtr) of roof area and 3,000 watts max of installed solar was used for the calculations used in the graphs. The average electric rate is $.21/KWhr initially, with annual increases of 6% used in the analysis. The solar panels have 77% of max power available over an average 5.5 hrs of sunlight per day. The solar panels are calculated to lose 2.5% output the first year and 0.5% thereafter. The 30% US investment Tax Credit was applied to the initial costs in the calculations. The finance rate is 5% annually for 15 years for the graph below, with only the initial installation financed (re-roofing, maintenance, new inverters and new solar all considered on a cash basis).

Graph B

G B

The roof type has a major impact on the amount of unwanted hot or cold energy being absorbed into the home or building. Asphalt shingle roofs directly conduct heat into and out of the roof deck and attic, which increases the air conditioning and heating loads versus a roof with above deck ventilation.  Some roof types, such as metal, ceramic and cement tiles can be installed so hot air is ventilated away from the building through a chimney effect of heated air between the roof deck and tiles.  A ventilated space between the roof and roof deck also acts as an insulating layer during the heating season. Cool roof coatings reflect the heat absorbed from sunlight back into the atmosphere, limiting the amount of heat transferred into the building.

The Power Shield roof system features a cool roof coating, above deck ventilation and is made from recycled and non-combustible, lightweight steel. The graph below shows the additional savings available from air conditioning and heating costs with a Power Shield roof compared to a conventional asphalt shingle roof. The graph shows the same house characterized above and built in the Sacramento, California area before 1980 (1).

Graph C

G C

Another aspect of solar installations is the direction the front (and possibly sides) of the house face and whether the best location is the front of the house.  A big influence on solar is the placement on the roof and the sight lines from the street.  Power Shield tiles with solar can be placed anywhere on the roof and will look exceptionally well.

Power Shield, Inc. roof replacement of 38 year old cement tiles with about 4200 watts of solar:

A roof is a major ongoing expense that, like a mortgage, must be dealt with. Buying a new roof is a decision with 15 to 60 year implications.  A new solar system has a 25-35 year life expectancy.   The decision to go solar provides increased savings every year as the electric utility rates rise.  House values fluctuate depending on the life expectancy of the roof and solar.   Making a bigger decision up front will add to the returns over time.

Kurt Kramer, Power Shield, Inc.

1.   http://web.ornl.gov/sci/buildings/2012/2010%20B11%20papers/64_Miller.pdf

Solar Roof Tiles, Uncategorized

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BIPV, Solar Roof Tiles, Uncategorized

Class A Fire Rated solar & roofs in Wildland Urban Interface Areas

TUV-Rheinland-Fire-Test                                          Courtesy TUV Rheinland

On January 1, 2015, jurisdictions throughout the State of California and elsewhere, with designated Wildland Urban Interface Areas (WUI), will begin enforcing the new Class A & B fire ratings for PV systems and roofing.  Most PV system products have the lower C rating and this enforcement date may prove a disruption for the PV industry.

If the Authority Having Jurisdiction (AHJ) requires either Class A or B fire ratings for buildings in the Very High Fire Severity Zones and WUI Areas, the requirement will now be enforced for roofing, mounting hardware and solar panels. In 2000, the U.S. Wildland Urban Interface contained more than 12.5 million housing units, a 52 percent expansion from 1970 (see http://www.ucsusa.org article “Playing with Fire” 2014).

The 2011 International Building Code (adapted in many jurisdictions) requires that PV systems have a fire rating that is the same or better than the required fire rating of the roof, which in the WUI areas is generally Class A or B. To properly address this new fire rating requirement, the safety standard UL1703, which regulates the safety of PV modules and panels, was updated in October of 2013 with new fire performance test requirements.  As of the fall of 2014, only a few manufactures have evaluated their products to the new version of UL1703. This link provides more info on the new test requirements: http://solarabcs.org/about/publications/meeting_presentations_minutes/2014/pdfs/Guide-FireRatingPVSystems-V2.pdf.  The updated UL1703 test requirements do not affect Building Integrated PhotoVoltaics (BIPV) which are fire rated as a roofing product.

Effectively, for many areas where new homes are built or homes re-roofed, the fire classification requirements will be more stringent and the rating will apply to solar panels and mounting hardware.  As Power Shield, Inc. goes through testing as a roof and a BIPV product, it intends to achieve a Class A rating for the metal roof and metal solar roof tiles.