Before I get in to the nitty gritty progress of Green Glamping Girls, I’d like to thank Matt and Mariah from the Comet Camper for coming all the way from New England to Texas. They were a great help and I learned so much!
Alright, so we’ve got less than two weeks to get this project done, and then we’ll have some time to put together the presentation for the professional panel of engineers, very sophisticated. So far, my team and I have the design of the trailer mostly laid out and a majority of the materials chosen. One thing that Matt and Mariah really helped solidify in my head was the concept of solar panels. I learned about AC (alternating current), DC (direct current), photo-voltaic cells, and watt hours.
Prior to Matt and Mariah’s arrival, I was really unclear about how many watts were necessary for the solar panels, how many solar panels were necessary and how it all worked. First off, two main types of solar panels exist: monocrystalline and polycrystalline. Mariah recommended that monocrystalline solar panels should be used for this project because of its efficiency. The key step to determining specifics of a solar system is adding up all of the appliances that will be used in the system and how much energy they will consume in one hour. The camper is required to go off grid for 2 days and the appliances that are the most likely to be used are LED lights, fan, computer, cell phone, iPad, vent fan, and water pump. With Mariah’s help I found the watts that these electronics use in 1 hour and then multiplied that by the hours it would be used in 1 day. The total amount of watts/hours for 2 days off grid totaled to 2522 watt/hours (refer to spreadsheet). It’s always better to be safe than sorry, so this number was rounded up to 3000 watt/hours. As I learned from Matt and Mariah, in construction always buy 20% more than you need and this rule of thumb also applies to solar power. Watts are the unit for power, so to sustain all of the trailer appliances for 2 days; it’s estimated to use 3,000 watt/hours.
To determine the number and specifics for solar panels like wattage, 3000 watt/hours is divided by the wattage of a solar panel. Since the watts cancel out during division, the dividend equals the number of hours necessary to charge the battery bank with the solar panel(s). For example, if my team and I wanted to buy a 200 watt solar panel, this would take 15 full hours of sunlight to charge the battery bank (3000wh/200w=15h). 15 hours of direct sunlight could take as many as 3 days to fully charge the battery bank. The Green Glamping Girls have decided to purchase two 190 watt solar panels from Home Depot totaling 370 watts. These solar panels would take about 8 hours (1 ½ days) to charge the battery bank.
As mentioned above, the solar panels will be charging a battery bank. The battery bank consists of batteries(wired in series) from which the appliances being used get their electricity needed to function. Using the equation P=IxV (power=amps x volts), the watt hours are divided by the voltage of an individual battery (3000wh/12V=250i). 250amps is what all of the 12volt deep cycle batteries should add up to. It was recommended that we purchase four 75 amp batteries or two 150 amp batteries (it’s OK if the total amps exceed the required amount). In short, buy batteries in even numbers, odd numbers make it more difficult. In effort to prevent battery corrosion, a charge controller is necessary to communicate to the solar panels when the battery bank is at full capacity. This is another necessary piece to the electrical system.
Solar Panels use direct current (DC) which is more dangerous, but more efficient. Instead of having to convert the DC to AC which is done by an inverter, the trailer will run appliances that are plugged into cigarette lighter/car chargers and USB outlets for our design as opposed to a standard outlet (3 holes) which requires AC. Right now, the trailer has 3 car charger outlets. In order to use a standard outlet, an inverter is necessary to convert DC to AC which sucks up energy from the battery bank when off grid. Although we already have an inverter that came with the trailer at time of purchase, it is inefficient to buy more solar panels to power the inverter. All appliances that run on DC will be able to run off grid, and those that run on AC will work only when the trailer is plugged in at a trailer park or camp site with electrical hook up. Because of its convenience the trailer will run on DC when off grid.
In physics last year, I learned about electricity and it has been a great experience to take that knowledge even further and apply it to a real world situation like Project VENTURA.
solar panel- http://www.homedepot.com/Electrical-Alternative-Energy-Solutions-Solar-Power/h_d1/N-5yc1vZbm18/R-203079641/h_d2/ProductDisplay?catalogId=10053&langId=-1&storeId=10051#.URHj9KU1mSr
standard outlet- http://images.wisegeek.com/standard-us-power-outlet.jpg
car charger- http://image.made-in-china.com/2f0j00lCIaThcsvgkE/3-Way-Car-Cigarette-Lighter-Charger-Adapter-USB-Model-CG12-.jpg