In coming up with a design, we were able to draw upon the experience of our friends at V3 Power, who had already built a similar trailer that they'd taken to a few festivals with their DIY wind turbines. Combined with our experience of off-grid energy projects, we were able to draw on a fairly well established knowledge base for a project of this kind.
The initial concept for the project was to build a clean, green mobile power source to use at community events in and around south-east London, to support SELCE's community engagement around energy issues. It's pimary use would be to supply off grid renewable power for events with sound, lighting, film projection, food refrigeration, and so on. In emergencies, the trailer could also be capable of providing mobile power if needed when grid power is not available.
Luckily for us, our project caught the eyes of the M&S Energy Fund panel of judges whochose a number of projects to receive funding based on their innovative and inspirational qualities. Now we had the money, we had to get on and build it!
About the energy system:
Energy is stored in a deep cycle battery bank that can supply continuous power to a 1500W load for 4 hours, even with no energy being generated from solar panels or any other power source.
A large pure sine wave inverter provides grid-equivalent 240V AC power. A more efficient secondary inverter is included to use for low power appliances, either separately or in combination with the main inverter as needed.
The battery bank is charged by an array of solar panels, through a MPPT charge controller. A system display panel allows users to easily monitor the power generation, power consumption and state of charge of the system.
The battery bank we ended up choosing was based around wanting to go with a 24V system, and needing to stick within tight weight and size constraints. The Rolls 4000 S605 batteries that we eventually settled on were the most suitable fit with the demands of our design. We used four of them to create a battery bank that could hold a respectable 10.8kWh of total energy.
The key component that took a while to decide on was the main control interface, which needed to provide clear, easy to understand visual information about how the system was performing. After a while researching display panels for control systems, we came across the Victron Colour Control GX, which seemed to offer all the features we were looking for, including a link to an online portal that would store real time info on how the trailer was being used.
Once the decision was made to use this control panel, we were able to build the rest of the system around it, using compatable Victron components that were able to communicate with each other directly to give us an accurate picture of how the system was performing. For our main inverter, we chose a Multiplus 3000. For our solar charge controller, we chose a BlueSolar 100-50. For our secondary inverter, we chose a Phoenix 350.
Building the trailer began with aseembling all the parts of the energy system in our workshop to check that it all worked.
Then we built the interior compartments for the trailer using plywood sheets and lengths of standard 2 by 4 timber. The placement of each component was carefully worked out to make sure it all fit in with enough room for cables to run, etc.
The trailer was just the right size to accomodate some 175W solar panels, which slotted snugly in to be stacked on top of the rest of the system when not in use. The panels had custom made mounting frames added to them so they could be quickly set up on the ground when being used to power the trailer.
Once the trailer was ready to be used, we gathered a group to take it out on a trial outing on Blackheath Common, to put the energy system through its paces and show it off what it could do to all those who had helped put it together. With no problems encountered, it wasn't long before the trailer was out bringing clean solar power to community events in the area.