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Installing Solar Systems in Historic Architecture

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There is a move afoot to retrofit existing homes to make them more energy efficient. Solar energy is a popular choice because it's sustainable, renewable, and quiet. Once installed, solar panels require minimal maintenance. As a result, historic preservation commissions have seen an increase in the number of applications to retrofit buildings with solar energy systems inside designated historic districts.

If you own a historic property and are considering installing solar systems, the challenge you face is to balance the objective of conserving energy with preserving the historic nature of the building. One key issue is the visibility of the solar equipment. When installing solar tiles on a historic structure, it's important that the tiles don't look unsightly or otherwise detract from the look of the building. In addition, the solar installation shouldn't replace or damage the original construction materials.

We'll take a look at the solar tiles currently available and recommended ways to install them in historic buildings.

Types of Solar Systems

Understanding the types of solar systems will help you decide which option is best for installation in a historic property. There are three types of solar systems currently in use:

  1. Photovoltaic: A photovoltaic system (also called a PV system) uses an array of solar panels to convert sunlight into electricity. The system is made up of a number of components, including solar panels to absorb sunlight and convert it into electricity, a solar inverter to convert the electric current from DC to AC, and mounting equipment.
  2. Solar Shingles: First commercially available in 2005, solar shingles (also called photovoltaic shingles) were designed to look like traditional asphalt shingles, and were used by those seeking a more traditional roofline. Solar shingles were once more expensive than photovoltaic panels, but they have become more popular as prices drop.
  3. Freestanding: Freestanding panels are typically used where PV systems would mar the roofline or alter the building. They are also used in places where the roof provides little or no access to direct sun, such as where the sunlight is blocked by trees. Freestanding panels are located away from the structure and connected by underground cables.

The Secretary of the Interior's Standards for Rehabilitation

The Secretary of the Interior is responsible for advising federal agencies about the preservation of historic properties. The office developed ten Standards for Rehabilitation, which show how to protect a historic a property by preserving its historic materials and features. We'll concentrate on the two standards relevant to solar retrofitting.

  • Standard Two: The historic character of a property shall be retained and preserved. The removal of historic materials or alteration of features and spaces that characterize a property shall be avoided.
  • Standard Nine: New additions, exterior alterations, or related new construction shall not destroy historic materials that characterize the property. The new work shall be differentiated from the old and shall be compatible with the massing, size, scale, and architectural features to protect the historic integrity of the property and its environment.

In short, this means the addition of solar panels shouldn't change the character of the building, and the historic features of the property and the surrounding area should remain intact.

Recommendations

If you're considering a solar retrofit of a historic building, avoid installing solar panels on the property's primary façade, since this will have the greatest effect on the character-defining features of the building. The following are recommendations for primary elevations, secondary elevations, accessory structures, and freestanding solar panels.

For Primary Elevations, Secondary Elevations and Historic Accessory Structures

  • Limit the visibility of solar panels by placing them behind architectural features such as parapets, dormers, and chimneys.
  • Solar panels and mounting materials should be similar in color to the existing roof. Equipment related to the solar system should be treated so it's not noticeable.
  • The solar panels should be installed flush with the roof so they don't change its slope or appearance. The installation must be removable, and shouldn't harm the historic nature of the building or that of the surrounding area.

For Primary Elevations

  • Use low-profile solar panels for primary elevations. Original or historic building materials shouldn't be replaced with solar shingles or laminates. Avoid using solar panels in windows or on walls, siding, and shutters.
  • For secondary elevations, solar panels should be mounted on rear slopes or locations that can't easily be seen from public areas.
  • On buildings with flat roofs, solar panels should be set back from the edge of the roof to hide them from view. The slope and height of the panels should be set back in a way that minimizes visibility from public areas.
  • Solar panels installed in non-historic windows or on walls, siding, or shutters should be mounted in a way that limits visibility from public areas.

For Secondary Elevations

  • For secondary elevations, solar panels should be mounted on rear slopes or locations that can't easily be seen from public areas.

For Secondary Elevations and Historic Accessory Structures

  • On buildings with flat roofs, solar panels should be set back from the edge of the roof to hide them from view. The slope and height of the panels should be set back in a way that minimizes visibility from public areas.
  • Solar panels installed in non-historic windows or on walls, siding, or shutters should be mounted in a way that limits visibility from public areas.

For Freestanding or Detached Solar Panels

  • Freestanding solar panels should be installed in locations where there's minimal visibility from public areas. The freestanding panels should be concealed from view with fencing or vegetation that fits in with the character of the neighborhood.
  • The design and placement of the freestanding panels shouldn't get in the way of the historic character of the site or the surrounding landscape.
  • The visibility of freestanding solar panels from neighboring properties should be taken into consideration.

Not Recommended

The following are actions to avoid.

  • When installing solar systems, don't remove historic roofing materials.
  • Don't remove or alter historic roof features, including dormers and chimneys.
  • Don't install anything that will damage or permanently alter any historic features or materials.

The Last Word

Opinions as to what is considered unobtrusive or unaesthetic can differ. The National Park Service has an outstanding website featuring photos of successfully retrofitted historic properties. In addition, the National Trust for Historic Preservation has an excellent booklet, Developing Sustainability Guidelines for Historic Districts, which can be downloaded as a PDF document. The booklet discusses how local historic preservation commissions can incorporate sustainability concerns into their design guidelines.

Because technologies and regulations change over time, there is no one permanent solution to balancing energy concerns with historical considerations. Owners of historic buildings should aim to achieve reasonable energy savings at an acceptable cost, while at the same time preserving the character of the structure and the surrounding area. 

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