Image: Rendering of Woodbury Tower Drive projects. Courtesy of City of Woodbury and included in the Solar Possible RFP.
The Tower drive request featured a significant renovation to the existing public works building and a soon to-be-built solar-ready rooftop across the street at the Fleet Services building. These sites introduced a couple of unforeseen issues:
A community solar garden subscription. The Public Works building had been subscribed to community solar gardens for 120% of its annual electricity consumption—the maximum subscription under Minnesota’s community solar garden legislation. This 120% also constrains the amount of on-site solar that Woodbury can install. Unless Woodbury were to grow its electricity consumption or transfer the subscription to a different facility, there would be little flexibility for the facility to host a commercial-sized solar array on the available roof spaces.
No individual energy model per building. To size a solar array, vendors require a reliable number of kilowatt-hours consumed in a typical year. Xcel energy requires documentation that the array will not produce over 120% of the annual electricity consumption for its interconnection process. There was no way of knowing what the electricity consumption specifically might be for each building. The Solar Possible team and the City of Woodbury could not supply vendors with an accurate estimate of electricity consumption.
Currently, Woodbury has allocated 20% of the community solar garden subscription to another meter. Woodbury may still be able to host solar at the Public Works building pending more observed electricity consumption data.
Lesson learned: Requesting a bid for a to-be-built or to-be-renovated building is not inherently problematic, but it is more difficult. This solicitation could have been improved with specific, individual electricity models. Vendors did not know how large to bid the projects. The vendors were concerned about submitting a bid that would eventually be rejected by Xcel Energy over a breach of net metering regulations. In this case, the bid could have been improved with either a 12 months of observed electricity consumption (post building commissioning) or a specific electricity model for each building.
In Woodbury’s case, obtaining an energy model this late was cost prohibitive; we’d recommend seeking an energy model early on and pairing the results with a solar bid.
Ojibway Parks Building
Photo: Rendering of the Objiway Parks building, courtesy of City of Woodbury and included in the Solar Possible RFP.
The second site submitted by City of Woodbury was the Ojibway Parks building. This park building is to serve as a community gathering place and warming house for winter sports in the surrounding park. The two key issues are enumerated:
No energy model. Similar to the Tower Drive facilities, there was no energy model from which to scope the size of the project. The building was expected to use very little electricity, but without a good estimate, the vendors faced difficulties in proposing an adequate size; they would have encountered issues in the interconnection agreement process as well.
Structural engineering assessment. The team discovered late in the process that the roof was not structurally engineered to support racking and solar modules.
Lessons learned: With this yet-to-be-built building, an energy model could have improved the accuracy of any bids. Secondly, the team should have requested a structural assessment earlier on. The building’s engineering team should have been consulted before participation in the Solar Possible program.
It is common for the structural engineering assessment to be conducted as a part of the “post contract award services.” This is a common practice when contracting solar for existing buildings.
In retrospect, we now recommend that pre-construction facilities:
Have professional energy models that meet interconnection agreement standards. Late in the engineering process, an energy model can be cost prohibitive. Thus, we recommend incorporating an energy model early on when contracting building design services. Or, waiting to acquire 12 months of electrical use data before issuing an RFP.
Are pre-screened by the engineering and/or integrated design team. If considering a roof mount installation, the structural engineer and electrical engineer should be consulted before issuing an RFP.