On the bank of the Rock River, in Rockford IL, sits the Rock River Water Reclamation District (RRWRD) campus - the city's sewage treatment plant. For most of its existence, the facility paid nearly $1M every year to have solid waste hauled away to a landfill. Now they extract methane from the waste and burn it in a cogeneration (combined heat and power) process. Solid waste is dried and sold as fertilizer. In 2009, one of the campus' buildings became vacant, and authorities decided to turn the location into a living laboratory and sustainable energy proving ground: Freedom Field Renewable Energy (FFRE). Last week I toured Freedom Field, snapped a bunch of pictures, and got a nice overview of the operation. Naturally, I had to share what I learned with my readers.
Thanks to Professor Steve Fleeman, Chair of Sustainable Energy Systems and Electronic Engineering Technology at Rock Valley College. Professor Fleeman is RVC's liaison to Freedom Field, and he was kind enough to conduct tours for myself and my engineering students. Thanks also to FFRE Executive Director Chet Kolodziej, plant manager John Sweeney, and chief engineer Dave Martindale, who all took the time to speak with the students and explain some of the facility's technology.
A Living Laboratory
Freedom Field's purpose is to provide leadership in sustainability through education, consultation, and experimentation. FFRE offers training and internships through affiliated colleges, provides technical support for local manufacturers, advises regional authorities on sustainability practices, and demonstrates a variety of renewable energy technologies. While the water reclamation district generates electricity with its cogen plant, FFRE contributes solar and wind generated electricity. It's grid-tied, so it can sell excess energy when production exceeds demand and buy electricity when needed. All told, the entire campus is a near net-zero energy operation.
Heating and Cooling Provided by Solar Radiation
Freedom Field includes a 300,000 BTU array of evacuated tube solar radiation collectors that can reach temperatures of over 200oF (93oC), even in the winter.
The 600 evacuated tubes absorb solar radiation and convert it to heat. Natural convection causes the fluid in the tubes to rise to the top, where heat exchangers transfer the heat to water flowing through the horizontal pipe. The hot water is used for radiant floor heating in the winter; in the summer, the heat is fed into to an absorption chiller which, through the "magic" of physics, provides cooling in the summer.
Variable Frequency Drives
The pumps that move water through the HVAC system are efficient alternating current (AC) motors. One thing about AC motors: their rotational speed is dependent on the AC frequency, which makes it difficult to vary the speed. They're either completely off, or they're running at maximum RPM using valves to control the flow rate. As Professor Fleeman describes it, this is akin to pressing a car's accelerator to the floor while using the brakes to control the speed - not very efficient. That's why FFRE added a variable frequency drive (VFD) to control the pump. The VFD runs the pump at different speeds rather than running on-off cycles at full speed. It's driven by an inverter that’s capable of varying its output frequency. With the VFD, the pump now uses 40% less energy than the original configuration.
Solar Photovoltaics
Freedom Field has a 12kW rooftop solar photovoltaic array consisting of 56 Universal Solar PV panels manufactured in Rockford IL. The panels face due south for maximum daily energy production. Four grid-tied Danfoss inverters, also made in Rockford, convert the array's DC output to grid-compatible AC. At the time of its installation in 2010, this was the largest PV array in the region. (Larger ones have since been installed in other places in the area, possibly as a result of seeing how well this array performs.)
As part of its mission to serve as a proving ground, Freedom Field also has a few small solar arrays in different experimental setups. Those were designed, built, and installed by students in Rock Valley College's Sustainable Energy Systems program. I'll highlight those, and other student projects, in a future article.
Wind Turbines
As one approaches Freedom Field Renewable Energy, one of the first sights is the rooftop vertical axis wind turbine (VAWT). In even a small breeze, the turbine spins quite rapidly. It does not, however, generate much power. It's a 1200 watt unit, but that's its peak output under optimal conditions. In practice, it rarely generates more than 200 watts. Even worse, the vibrations can sometimes be heard inside the facility.
VAWTs are often touted for their ability to work in turbulent conditions and for their low startup speed. That's all well and good, but to generate an appreciable amount of energy a wind turbine must be exposed to sustained winds at high speeds. I know of one researcher who's doing interesting studies on wind farms made of VAWTs. That may be a great application for VAWTs, but a single VAWT on a rooftop is not worthwhile.
A more productive wind turbine sits atop a tower on a nearby hill. This 10 kW horizontal axis wind turbine (HAWT) spins more slowly, but performs much better, than the rooftop VAWT. Even so, the tower is too short to reach the high winds needed to make this turbine operate at peak levels. The facility's proximity to an airport prevents them from building a larger tower. The turbines look impressive, but the PV array generates much more electricity than both turbines combined. If you'd like to know more about small wind, check out my analysis of small wind turbines.
Load Shifting and Energy Storage
As I discussed in an article about the Tesla Powerwall, load shifting is a technique that allows a customer to use locally generated (or stored) electricity when grid rates are high and use grid power only when rates are low. Freedom Field has a 19 kWh grid-tied battery bank, consisting of sixteen deep discharge lead-acid batteries, charged by a 4kW PV array. The energy storage unit is connected to a grid-tied SMA Sunny Island inverter. Depending on the electric rate at any given time, the batteries can either charge up, provide power to the facility, or deliver energy to the grid - whichever is the most economically beneficial.
SCADA
With all these power generation systems and various loads, it takes a sophisticated control system to "direct traffic" and ensure that power is being delivered where needed. Freedom Field has a Supervisory Control and Data Acquisition (SCADA) system to handle this. Most operations are fully automated, but they can also be controlled remotely by the site engineer.
But Wait … There's More!
What you've seen so far is a sample of how Freedom Field demonstrates the economic benefits of proven energy technology. But FFRE also endeavors to experiment and educate, which it does through collaborations with local institutions of higher learning. FFRE provides internships, student technician positions, and funding for interdisciplinary capstone projects. Here's an overview of some of the projects that students have completed at FFRE.
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