DE Quest for Net Zero

The Energy Equinox Is Coming…

Design Engineers turned on our 102.6 kW rooftop photo-voltaic array on 9/5/2016 with the audacious goal of making our Cedar Rapids offices Net Zero Energy use. It’s been about 18 months, and what happened? Did we achieve our goals? Were our calculations correct?

The 102.6 kW grid-tied electrical system supplies power back to offset our usage and billing. This symbiotic approach allows limitless access to power any time we need it while contributing to the grid’s daytime capacity and reducing the peak demand on central power plants. To achieve Net Zero Certification, we have to prove we are making more energy than we are consuming. And that particular number changes every day and is influence by a number of factors.

Check our project’s status in the top-right corner of this page. 

The Short Version

Design Engineers Rooftop Photo-voltaic Array

The process of taking our offices to a Net-Zero status has been a journey of a thousand light bulbs, changed by each of us at DE, one at a time. Our initial calculations for our array left little room for error or variation, but accounted for seasonal shifts. Our array was designed to provide just 5% over what we consume. However, as certain as the change of seasons, energy use fluctuates. This tight margin meant everything needed to work as planned to hit Net Zero in our first year. Of course, one of our inverters had other plans.

Hardware Factors
A Failed Inverter Resets the Clock

Our system uses multiple solar inverters to convert the direct current generated by the solar panels into utility-grade alternating current. One inverter chose the month of April to stop working, and the failure decreased the overall amount of power we generated, stalling our certification until its replacement. A key rule of thumb for system efficiency demands tight tolerance. Specifying a system that could do more if you need it to wastes a lot of capital and energy. So we waited for the new inverter patiently, and moved our start time back just a little. The replacement arrived on April 24, 2017, and the race to zero was on… can we get to zero faster than a year?

Annual Cycles & Weather

Dwight clears snow from the rooftop PV Array

Obviously our array will create more power in the summer than the winter. Since our system is grid-tied, we work with our utility to find an equilibrium. This flexible relationship helps utilities to reduce peak loads and production while minimizing our system complexity and cost.

Our ballasted array is hidden beyond our roof’s edge, invisible from the ground. This is the most affordable approach, and does not damage roofing membranes, but it fixes the array’s tilt, making it sensitive to snow accumulation. The sun would eventually take care of the snow, but we wanted maximum power, so Tim Lentz coordinated the “snow patrol” to clear snow from the array; roughly 6 times in the 2017-18 winter.

The Alex Meier Initiative

The snow clearing (and Dwight’s monthly updates) was a very visible effort to both save and create energy, and ideas like that are infectious at Design Engineers. Everyone got into chasing watts down. A mysterious dorm fridge went back to the garage it came from, unused gadgets were taken off light support. And Alex Meier, a 20-year veteran of our electrical department, had an idea about lightbulbs.

Design Engineers Cedar Rapids offices opened in 2008, and the LED light revolution didn’t show up in commercial offices until a couple years later. Today we rarely specify commercial fixtures that aren’t LED-based. “What if,” Alex mused, “we swap out all the already efficient fluorescent lamps for replacements made with LED?” The result of his bright idea was a savings of 4,500 kWh a year, and the results can be seen in the Energy Efficiency Measures slide.

Measure Thrice, Cut Emissions Infinitely 

Alex was pretty motivating, up on a ladder changing bulbs with a smile. He got all of us on a quest to find every spare watt and return it to the system. We tuned and evaluated our own energy use and dialed in temperature and lighting to a tighter fit. Unoccupied or less-used rooms with independent thermostats went even quieter, task lighting got a little more task-oriented. Homework completed, we checked with the experts.

We evaluated our building performance with the Energy Star, ASHRAE Building EQ, and The Weidt Group’s B3 Benchmark. The results are detailed in the following slides. What did we find? According to the Weidt Group, Design Engineers’ Cedar Rapids office ranks the single best performing of 466 similar sites in a 400-mile radius. We’ve included the pre-solar and post-solar calculations below. Solar power is the last mile of our journey; a long trip that started in 2008 with the design of our building and continues every day.

Weidt Group B3 Benchmarking    PRE  |  POST

Energy Star Building Rating   PRE  |  POST

ASHRAE Building EQ    PRE  |  POST

2018 Plan to Achieve Net Zero

Before adding PV, we were one of the top performing small office sites in country with an Energy Star rating of 98 out of 100. So you might think Net Zero would be a snap. And in theory it could have been. Specify a great big PV array with lots of safety factor and turn it on. But efficiency, in both cost and performance, keeps us working on the BEST solution, not the easiest. So we installed a system just large enough to meet our expected load and are carefully managing our way to Net Zero. As we start the final countdown to zero we find ourselves checking the Solar Edge Dashboard for Design Engineers habitually.

Avoided Energy Costs & Emissions, 2017

This is our 2018 plan: We are closely monitoring our energy use and solar production, turning off the lights when we leave the room and letting our PV system make electricity. That’s the whole plan.

And as of 3/30/18, it’s a plan that worked. We love it when a plan comes together.