Travel (150W) & Home (1.3KW) power

These photos show the solar systems we use at our “off the grid” home near Madrid NM. This system was designed and installed by a professional solar contractor, Positive Energy, in Santa Fe NM.

The camper we take to Burning Man has 2 – 75 watt panels wired in parallel to charge a single deep discharge battery. Next year we will add a second battery and bring a spare panel for a bit more power.

This is our home power center. 24V nominal comes in through a Solar Boost controller that efficiently delivers maximum power to the batteries. A trace inverter delivers 120 VAC up to 4KW. The power center controls power distribution between the panels, batteries and inverter.

This is the junction box between the 9 pairs of panels and the DC input buss. Each panel is separately fused.

20 deep discharge 6 volt golf cart batteries store about 24KWH of energy for nights and those few cloudy days.

Here are the 18 panels facing the sun. Each panel has a rating of 75watts at full sun so the total is about 1350 watts peak.

The frame for the panels allows for quarterly adjustment of the elevation angle to account for the varying sun angle.

Contact me at BruceMcIntosh(at)StarBand(dot)net for any questions.

1. UniSolar 64W Monolith ~14V,~4A - Usefull for chargeing power tools, AA batteries too!
2. 4.5 KW STC array (Edison Approved Generation Station & online. about 15KWH daily(Summer=20, Winter=10) into the grid),
   

22ea Sharp 208W panels, XANTREX GT3.8 INVERTER

lifted from Sunfrost.com http://www.sunfrost.com/stand_alone_PV.html

Unfortunately, a 1 KW solar array sitting in direct sun for one hour will not produce 1 KWH of useable AC power. There are a number of ways energy is lost in this system. A major loss occurs because the panels produce their peak rated power at 17 Volts and most of the energy input into the battery occurs at a voltage closer to 13 volts. The energy is then taken out at about 12.4 Volts. The voltage mismatch alone results in a loss of over 25%. When analyzing battery powered PV systems, it is relatively easy to take these mismatches into consideration by using a current-based analysis. With this type of analysis voltage mismatches are automatically taken into account. To get a quantitative picture of the losses in a stand-alone system, let’s calculate the size array necessary to produce 1KWH with one hour of full sun. In a loss-less system, it would of course take a 1000-watt array to produce 1000 watts AC power. In a real system there will be a number of losses along the way. The input to the inverter will have to be about 1100 watts due to the inefficiency of the inverter. If this power is supplied at an average voltage of 12.4 Volts, then the batteries must supply 1100 watts/12.4 volts or 88.7 amps. For the inverter to produce 1 KWH the batteries must then supply or 88.7 amps for one hour or 88.7 amp hrs. (An amp hour is a unit of energy like a KWH). Assuming a 10% loss in the batteries the PV panels will have to supply an additional 10% more energy or 97.6 amp/hrs. To produce 1KWH with 1 hour of insolation will then require a 97.6 amp solar array. For each 17 watts of solar panels the panel will produce one amp; i.e., a 34-watt panel will produce 2 amps. The energy required to produce 1KWH of AC power with 1 hour of direct sun then be 17 watts/amp X 97.6 amps or 1659 watts which is a lot more than the 1000 watt array required in a loss less situation. These large losses make stand-alone power more expensive than a grid-tied system. In a grid-tied system the inverter loads the panels so that they are putting out their peak power. In addition, there are no battery losses and no backup system required during cloudy winter months.

from the Big Wiki: http://en.wikipedia.org/wiki/Solar_cells

excerpt: “A solar cell (or photovoltaic cell) is a semiconductor device that converts photons into electricity.”

http://en.wikipedia.org/wiki/Solar_cells#Simple_explanation

Each cell produces about .5 volt, and amperage depends on size. Many are stacked together to make a panel.

Animated (SWF) article about solar cells: http://www.energex.com.au/switched_on/activities/photovolatic/photovoltaic.html

Solar Power for a Burning Man Camp

This is a short, technobabble-lite description of how I designed, purchased, assembled, and utilized a solar photovoltaic system to power a Burning Man camp. This article will tell you most, but not all, of what you need to know to use solar electric power at your own encampment (whether it be at Burning Man or elsewhere). I hope you enjoy this information. Please feel free to contact me with any corrections or suggestions at jason(at)coopersco(dot)com

Design: Basically, you need to figure out how much power you will use, how much you will bring with you (in the form of charged batteries), and how much you will need to generate. My system powered a small water pump (for the Mist Tree pictured with the author here), some Christmas tree lights, a car stereo, and some other lightly used devices. All of the devices I used were 12v, so calculating usage was pretty easy; I multiplied the number of amps the device consumed by 12 (the voltage) and to get the watts used, then multiplied by the number of hours the device would be used to get the watt-hours. I added up all my watt-hours to get the total amount of power I planned to use. (The basic equation that you use in many electrical calculations is amps = watts / volts. You can rearrange this equation to suit your needs, like amps * volts = watts or volts = watts / amps).

Some of you will want to power 120vac devices like you plug into your home outlets. To do so you will need an inverter; this device converts the 12v direct current supplied by batteries into 120v alternating current. I bought a cheap one at Fry’s and it worked well for my needs (charging power tool and AA batteries, powering a stereo receiver/amp).

Next I calculated how much power I would bring in the form of two heavy-duty 6v lead acid golf cart batteries. Each held 360 amp-hours at 6v, for a total of 360 amp-hours at 12v, which we can convert to 4320 watt-hours using our handy equation above (360 * 12 = 4320). In the previous step I calculated I would consume a total of about 6,000 watt-hours during my stay at Burning Man, thus requiring that I generate about 2000 watt-hours (6,000 – 4,320 = 1680).

I selected 6v golf cart batteries because they are much more tolerant of deep discharge cycles than normal car batteries. However, car batteries will work just fine for the short periods that most of us use our solar systems, so if you’ve already got a car battery or two you can use those instead.

To generate this power I used a 120 watt solar panel made by Astroworks. I connected it to the batteries with a charge controller, which also provided me with a panel output meter (so I could see how much of the rated 7 amps the panels were actually generating), a battery charge level meter (so I could see how much juice I had left in the batteries), and short circuit protection (which disconnected everything if anything went wrong). You don’t strictly need a charge controller, but I’d highly recommend one for all but the most simple systems.

The panels were rated to output 7 amps at 12vdc in full sun. I figured that I could keep the panels in full sun for about 5 hours a day, thus generating 420 watt-hours each day (7 * 12 * 5 = 420). I needed to generate about 2000 watt-hours, which meant I’d have to keep the panels in the sun for about 5 days.

As Burning Man progressed, I realized that while I was generating about as much power as I had anticipated, I was using more than planned. I had to connect my batteries to a generator (via a 12v charger normally used to charge car batteries) a couple times. This use of fossil fuels in an alternative energy system was unfortunate, but bringing a 12v charger does provide you with an easy and effective back-up to under-generation/over-consumption during your stay in the desert. A little red wagon was also very useful for moving the heavy batteries to the generator and back.

Hopefully this is enough information to get you started with your alternative energy system. I am far from an expert on this subject so please let me know if I’ve made any major errors!

Thanks for reading!

Jason