This page describes the development progress and the history of the Campus Center for Appropriate Technology's (CCAT's) Mobile Energy Operations Wagon (MEOW). Specifically, this page describes the work that took place on the second version of the trailer (MEOW V2) after the first version was stolen in 2010.
Background[edit | edit source]
In December 2010, CCAT lent their Mobile Energy Operations Wagon (MEOW) V1 to a local eco-hostel. While away from the CCAT house, the 720 W photovoltaic (PV) trailer was stolen and vandalized. Some days after the burglary, CCAT received a call from the local police who said they had found the MEOW V1 abandoned on the side of a nearby highway. It turns out that the vandals had broken the hitch lock, attached the trailer to their own vehicle, and drove it miles away where they could remove all the components of value (i.e. the 720 W array, batteries, charge controller, and inverter) in a less conspicuous area. After the vandals stripped the trailer of all high-value components, they covered the trailer with a patchy coat of black spray paint to make it seem as though the trailer had been deserted by its owner (Fig 1)
. The MEOW V1 had been one of CCAT's most effective tools used to disseminate knowledge of renewable energy and appropriate technology to students and community members. The theft of the MEOW V1 was a disappointing, but not a devastating, blow to the employees and volunteers of CCAT. It took nearly 18 months of hard work spent designing, fund raising, building, and repairing, but the CCAT house was finally able to get their beloved MEOW purring again. So was born, the MEOW V2 (Top Photo).
Funding the MEOW V2[edit | edit source]
CCAT operates on a very limited budget (roughly $6,000/year for ALL projects). The most difficult task of bringing the PV trailer back to life, by far, was acquiring funding for the new components(e.g., PV modules, inverter, etc.). After two rejected proposals to the Humboldt Energy Independence Fund (HEIF) committee and many phone calls/emails to community members and local solar companies, it was David Katz of AEE Solar who was the most helpful at getting us what we needed. David donated four REC 230 W panels as well as his personal Outback GVFX48 inverter to CCAT. For the remaining components, David put us in contact with the Trojan Battery Company and Outback Power Systems from whom we were able to procure a battery bank at cost and a refurbished charge controller at no cost, respectively. We at CCAT would like to extend a hearty thank you to David Katz of AEE Solar, Outback Power Systems, and The Trojan Battery Company, for without their support, this project would not have been possible.
MEOW V1 vs. MEOW V2: The Advantages and Disadvantages[edit | edit source]
The components for the MEOW V2 that we received from our donors have several advantages and disadvantages from those of the MEOW V1. For starters, an advantage of the MEOW V2 is that the new PV array has a slightly higher wattage (920 W as apposed to 720 W), which allows us to harness more of the sun's energy. The second (and probably most significant) advantage is that the new Outback GVFX48 can operate in both off-grid and on-grid applications. Technically speaking, this inverter can be programed to divert any excess electricity to the utility grid when no primary load is detected. What this capability means is that when the MEOW V2 is parked in CCAT's driveway, the system can inject electricity into the PG&E grid and based on our existing net metering contract, CCAT (Associated Students) will receive a certain dollar amount per kWh that MEOW V2 produces. This feature is an obvious improvement since a key issue identified with the previous MEOW was that the available electricity was not put to any useful function when the trailer was parked in CCAT's driveway (which was most of the time); the Outback GVFX 48 solves this problem.
A disadvantage of the MEOW V2 is the amp-hour (aH) capacity of the new battery bank. Due to CCAT's budget, we were only able to acquire a 48 V, 102 aH battery bank (i.e. four 12 V, 102 aH (C-20) GEL cell batteries). This set-up will provide roughly 25% of the energy, or autonomous run-time (ART), that the MEOW V1 provided. However, when CCAT finds new funds, the MEOW V2's aH capacity can always be increased with sets of four 12V batteries placed in parallel with the existing battery bank. An advantage to the new Trojan GEL batteries is that they are maintenance free as opposed to the previous sealed led acid (SLA) batteries, which required employees to frequently monitor the electrolyte levels. Furthermore, there was always a risk that the sulfuric acid inside the SLA batteries would spill when the trailer was being towed. This is no longer a risk with the sealed GEL batteries.
A list of the component specifications for the MEOW V1 and MEOW V2 are given in the Table below.
|PV Modules||Astropower 120 W||6||REC 230 W||4|
|Batteries||Trojan L-16 (6V, 350aH)||8||Trojan 31-GEL (12V, 102aH)||4|
|Inverter||Trace 4024||1||Outback GVFX 48||1|
|Charge Controller||NA||1||Outback FM 80||1|
The Reconstruction Process[edit | edit source]
This section summarizes the main tasks that were performed to get the MEOW running after the theft.
Interior and Exterior Cosmetic Fixes[edit | edit source]
The theft and vandalism left our beloved trailer looking like a hideous piece of rotting garbage, so the first task the CCAT family worked on was getting a fresh coat of paint on the MEOW. Once the exterior was made presentable we proceeded to renovate the interior. The vandals had completely sawed of the system hardware panel where the previous inverter, charge controller, and battery monitor were mounted; we constructed a new system panel and maintained a compassionate attitude toward the thieves as we worked (Fig 2a and Fig 2b).
The PV Rack[edit | edit source]
The PV rack turned out to be one of the most difficult components to rebuild. Although the bandits did not take the PV rack, in their mad dash efforts to remove and steal our valuable PV panels, they did manage to leave the rack system horribly mangled and more-or-less useless to us. Due to a lack of mechanical and structural expertise, our preliminary designs for the new rack weren't fully functional (each panel weighs roughly 40 lbs. and must be able to safely travel down the highway at speeds of 65 mph; headwinds encountered on the highway must also be considered). In the name of safety and a long lasting system, we decided to work with local professional John Davis at Solar Racks to build the new PV rack. For John's efforts, we traded him a couple of 60 W monocrystaline PV panels that had been lying around the CCAT house and had not been put to use in some years; because we are a worthy NGO, John also gave us a good deal on materials. By working with John we were able to give several students the opportunity to work in a metal working shop and receive hands-on experience with building solar racks (Fig 3 - 3b).
The final design for the rack was a stationary flat-mount (i.e. 0° tilt) rack (Fig 4a). This design was ultimately chosen for three reasons. The first reason is that a flat mount simplified the design and minimized materials cost. Second, we figured that a flat-mount rack would be much safer than a tilted or adjustable rack for the mobile system. The logic here was that if we were to make an adjustable rack, we would run the risk of someone accidentally leaving it 45 degrees during transport (which is likely since CCAT has a very high turn around rate of employees who don't always know the finer details of h