Residential Solar Panels, Solar Installer
Written by Lisa Walsh

Solar on Slate Roofs in Washington DC

Residential Solar Panels, Solar InstallerWith Washington DC offering homeowners the best solar incentives in the country – its small wonder that solar panels are going up like hotcakes. In order to meet the demand, most solar installers are adept at designing and efficiently installing solar panel systems on most roof types in DC: namely flat roofs and asphalt shingle. However, homeowners with a traditional slate roof will need to shop around for a qualified, slate-savvy installer.

Slate Roof Challenge

Washington DC Solar,Solar ServiceIn this order, the most common types of residential rooftops in Washington DC are flat, asphalt shingle and slate. Asphalt shingle are generally the simplest type of roof to attach to. They are flexible, soft and flashing/sealing all of the attachments has been fine-tuned to near perfection by the solar industry. Flat roofs are generally installed using no/few penetrations either with parapet-to-parapet rails or ballast-weighted systems. Slate, however, is among the most challenging roof type to work on for the following reasons:

  1. Expertise Tools and Labor Required

    Solar Service, Home Solar PanelsTraining a work crew adept at installing solar on a slate roof takes a significant investment of time, tools and techniques. As slate is a type of stone material – specialized diamond-tipped drills and copper replacement nails are required to penetrate and reattach the slate; drill too fast – and you’re likely to break the slate. Even with the most cautious of installers, a number of slates are still likely to end up broken and spares need to be kept on hand. Ideally – artificial slate can be used for replacing broken slates. Specialized flashings designed for use with the larger slate tiles must be used to seal around the attachment.

  2. Additional Labor

    Due to the fact that slate is essentially a smooth, slippery thin stone – this can be particularly challenging for installers to navigate. Couple this with a steep pitch, and extended hours on the roof due to time-consuming drilling techniques, labor estimates can easily double or triple when compared to an asphalt shingle roof; not to mention a particularly challenging and long day(s) for the installation crew.

The above two points ultimately result in increased costs for the customer. Fortunately, for DC residents with slate roofs, the financial incentives are such that paybacks are still generally under (or around) the 5 year mark – with many years of clear income to follow. Furthermore, as slate roofs can last 100 years or more, the roof and solar combination is set for a minimum 25 year relationship – and likely a good decade beyond that.

Eastern Shore MD,Solar Service, Home Solar Panels
Written by Lisa Walsh

Non-South facing solar panel installs in Maryland, DC and Virginia

The Design

Eastern Shore ,MD,Solar Service, Home Solar PanelsWhen planning a solar panel system for your home, the first consideration for any solar designer is the tilt and orientation of your roof areas.  We need to know which roof(s) will ensure the most optimum solar output – which translates to the best Return on Investment.   For us here in Maryland, the most optimum solar roof orientation is Due South at 180 degrees.  Of course, not everyone has this perfectly oriented roof and our customer base consists of homes that have South, West, East and everything-in-between orientations.  Occasionally we even install on North-facing roofs if the pitch of the roof is low enough that panels are close to flat, or can be tilted southerly.

For homes that face East-West, you may be wondering which roof would best suited for solar.  This is a good question given the fact that the output of your solar panels is directly related to your Return on Investment and how quickly the panels can pay for themselves.

If either East or West favors a more Southerly angle, then that would likely be a more favorable roof.  Assuming that there aren’t issues related to shadingor obstructions caused by chimneys, vents, skylights and other roof-placed items.

If the house has a perfectly split East-West orientation, with all things equal – the next consideration would be roof angle; the lower the tilt (i.e. closer to horizontal) – the more solar energy will be generated over the course of the day.  If the tilt on either side is the same then we would usually favor the West facing side.   Here in Maryland, DC and Virginia we tend to have cloudier mornings, and sunnier afternoons going into dusk.  Therefore we want to capture the late afternoon sun (west facing) more than early morning sun (East facing).  Of course, should you happen to have a tree, chimney or other obstructing factor(s) on the West roof – we’d favor the East.

The Economics

Homeowners looking at an East-West installation often have concerns as to whether or not their system will be profitable enough, compared to its south-facing counterparts.    Disqualifiers for cost-effective solar systems include shading and limited available roof space.  Rarely, however, is a home found unsuitable due to a Non-Southerly facing roof alone.

To illustrate, following is a comparison of a 10kW system’s output respective to East, West and South facing orientations.  Data compiled using the National Renewable Energy Laboratory (NREL) weather data patterns for Baltimore, MD –

10kW system installed on a 20 degree pitched roof with zero shade

 SOUTH (180 degrees)WEST (270 degrees)EAST (90 degrees)
ANNUAL OUTPUT13,224kWh11,389kWh11,328 kWh
*Annual $avings$1853 per year$1594 per year$1586

*Savings based on a conservative $3.00/watt installation, and $0.14/watt BGE rate

Data from PV WATTS

As illustrated, although perfectly South would be ideal, the East and West orientations provide a competitive amount of solar and would add only a few months to the payback period.  If you were choosing between East and West (as opposed to installing on both), the difference is nominal.  The choice of which roof may come down to aesthetic preference, distance to utility meter and regional weather patterns.

Commercial Solar Energy ,Residential Solar Panels
Written by Lisa Walsh

The Ballasted Solar Attachment: Maryland and DC Solar Panels

Commercial Solar Energy, Residential Solar PanelsWays in which solar panel arrays can affix to a commercial building are as many and varied as the buildings they serve.  In this article, we’re focusing on one popular method of attachment – the Ballasted roof mounted system.

Many commercial solar prospects in and around the Maryland/Washington DC area have buildings with flat or low-sloped roofs.  These are generally defined as a roof with a 3:12 pitch or less.  For these applications, ballasted systems can offer a way of attaching solar arrays without any (or few) roof penetrations.   Many building-owners prefer this method of attachment as it negates the risk of leaking, particularly on flat roofs that may collect water.  With a ballasted system, the arrays are held down using the weight of the existing solar panel arrays, racking and – most importantly – concrete blocks.  These blocks are placed methodically throughout the system design to secure the arrays in place, resisting wind loads or other types of disturbance.

The addition of the ballast blocks to the solar system arrays adds additional weight to the roof.   As with any commercial solar project, this weight load is analyzed and approved by a licensed structural engineer as required by the permitting jurisdiction – with some differences in each locale.   Ballast racking manufacturers also specify the amount of blocks required throughout a design.  The number of blocks per panel typically varies throughout design due to array proximity to building edges, parapets, or other inconsistencies that can affect wind and snow loads.

Although ballasted systems have many advantages, as with any design, they have their disadvantages and are not compatible with every type of commercial building.   Let’s look at a generalized comparison scenario between a roof penetrated system and a Ballasted System:

Roof Penetrated System

Ballasted System

Labor Costs and CriteriaHIGH:  Penetrations require flashing and sealing techniques – sometimes requiring coordination with a roofer.LOW.   Labor skills required for installation are fairly straight-forward and require no roofer coordination.
Panel CountINCREASED:  Systems attached to roof substructure require less roof space for mounting.DECREASED:  Ballast-blocks require roof space and can limit the available space for solar panels
Roof LoadingDECREASED.  No concrete/ballast blockINCREASED:  Ballast blocks add weight to the roof
Design CriteriaFLEXIBLE:  Attached racking systems can usually negotiate hatches, HVAC equipmentLESS FLEXIBLE:  Because of the increased space required per panel – designs may be more rigid.  However most ballast racking does have reasonable flexibility.
Roof Pitch5 – 45 degreesGenerally less than 10 degrees

 

Multi-roofed commercial applications may have a variety of racking types for both sloped and pitched roofs. There are other options for flat roofs also, including attached and hybrid solutions that use a combination of both penetrated and non-penetrated techniques.