Introduction: Portable Solar Power Supply

Hello there. You've probably found this Instructable to gather ideas about making a portable solar power supply yourself. I've always been interested in electronics with this project being my latest idea to come wandering out of my head, why not make a portable box on wheels, that I can plug basically anything into, thats powered by the sun? So therefore I thought I'd share this Instructable with the rest of the world.

Step 1: Start Thinking...

The first thing to do is to think of what you will be wanting to power via the sun, the whole house would be nice, but that's a tad too expensive and not very portable. Our family go away camping many times during the year so I knew what I had in mind. Some 12 volt energy efficient lightbulbs, a 15 inch LCD TV with a free-to-air digital receiver, some sort of radio/CD player would be nice too, a way to charge our mobile phones/sat navs and being able to inflate our air-beds, one which is 12 volts DC and one which is 240V AC.

With all of that in mind I started looking at prices of components on websites such as Ebay and Maplin as price is a very important factor in designing a solar system. Our LCD and receiver draw 2.2 Amps DC on 12 volt, energy efficient lighting draws just under 1 Amp for a 12 watt bulb whilst the phone/GPS chargers draw very little power. Using the TV for say, 3 hours a day max would equal 6.6Ah consumed, lighting used for 4-5 hours a night would consume roughly 4Ah while all the charging of portable devices would be around 2Ah while pumps for air-beds wouldnt run for long so maybe only consuming around 1Ah, totalling 13.6Ah. Deep Cycle batteries shouldn't be discharged below 50% of their rated capacity, the smaller the discharge cycle, the longer the battery will last, therefore a battery of 30Ah would suffice. The UK receives on average 6 hours of sunlight during summer, which is the time of year we go camping and replacing 13.6Ah into a battery would take a 50W solar panel roughly 5 hours to recharge.

(Watts = Voltage x Amps)
(Average solar panel voltage at max power = 17 Volts)
(50 watts/17 volts = 2.94 Amps)

It's easier to draw power from a battery than to replace, requiring usually 10% more power to recharge than what was consumed, therefore:
(14Ah / 2.94 Amps = 4.76 hours of direct sunlight)
In a real world situation this will never happen due to too many different factors such as;
Solar panel shading,
Overcast conditions,
Battery temperature,
Size of wiring,
Other losses.

Therefore it's safer to use a larger battery bank, where power can be used up repeatedly if weather conditions the day after aren't suitable for efficient solar charging to completely recharge the battery.

Step 2: Use Your Imagination for Your Design and Source Appropriate Components.

With that in mind I know I needed an appropriately sized battery of between 50 and 150Ah. Due to my system needing to be portable I decided on a 125Ah battery which I bought of Ebay for something around the £90 mark, then a solar panel rated at 50 Watts or more. At first I settled on one 80 Watt panel to add to my previous array of a whopping 48 Watts, this way I would produce around 7 Amps in direct sunlight, easily enough to recharge my previous night battery drain, costing just over £170.

Suddenly at this point the idea of a car CD player headunit seemed quite appropriate. Again, after browsing the wonders of Ebay, I settled on a Sony MEX-BT3800U, a headunit with FM reception, front aux and USB input and with Bluetooth phone connection allowing calls to be made and audio streaming, costing me £130.

After selecting these main components I started sketching rough drawings of what I wanted my portable sun powered generator to look like. I have included the design that I finally chose, a front panel for all the switches and power sockets, a panel at an angle to mount LED displays on and the car stereo, speakers in the sides, 2 AC outputs and with adequate space inside for wiring. My chosen designs depth was dictated by the depth of the battery, around 33cm, the width allowed the battery, the headunit and two speakers to be mounted in a space of 54cm whilst the height was due to the height of the battery with the charge controller mounted separately above the battery. My particular battery has a weight of 26KGs so pleanty of pinewood bracing was used to strengthen and hold together the 12mm thick MDF. Cooling was required for the battery compartment to vent any gasses and for the main space to extract warm air created by the headunit and inverter.

I chose rocker switches with LED's in to be the controls, generally because they look nicer than other types of switches, their small profile allow many to be used in a small space while their 3 volt indicator light (resistor required for 12v use) shows me when a device is switched on or off. Cost: around £3 for 2, available with red, green or yellow indicators. (Ebay)

The Inverter is a 600 Watt, 1200 Watt peak modified sine wave inverter, although I never plan to use anything higher than 200 Watts max, I fused this with a 20A blade type fuse. Cost: £35. (Ebay)

The majority of the wiring used is 15Amp capable 14AWG except for the main power wires from the battery, to the main switch to the Inverter which are 25Amp capable 11AWG. Each cigarette lighter socket is fused with a 10Amp fuse while the charge controller is fused at 15 Amp before the main system fuse, meaning that if the main fuse blows, the connected devices and stereo are safe from abnormally high voltage levels directly from the solar panels if that was ever to occur.
Cost: around £5 including the 4 way block.

The speakers are Sony XS-F1331, 3-way Xplod car speakers with at peak of 140 Watts, 25 Watts RMS. Cost: £9 (Ebay)

The front panel digital Ammeters and Voltmeter were my first choice for system measuring as i'm not that keen on traditional analogue moving meters. Most of my components were sourced from Ebay except these meters, available from a very nice website . Located in Hong Kong, they offer speedy delivery while their products are top notch, the British Royal Mail lost my two ammeters in the post somewhere while Virtual Village kindly sent two more to replace the lost ones, free of charge. Cost: Voltmeter £6.99, Ammeter £8.99 each. (Ammeters come with 20Amp shunt.)

Cooling fans: 12VDC 'System Blower' from Maplin Electronics ( ) Cost: £5.99 each.

Heavy duty castors and sprung handles, Cost around £15 total. (Ebay)

DC cigarette sockets: Cost: £3 each (Ebay)

20Amp charge controller: Cost ?Came with 80 watt panel purchased off Ebay?

Crimp terminals for all switches, sockets, fuses and other connections: around  £10 (Ebay)

Wood - 12mm thick MDF (Medium Density Fibreboard) 3m x 3m sheet and 1x1/2 inch pine 5m long and appropriate screws: around £15 from Archibalds.

Miscellaneous connectors for headunit connections/solar connections from Ebay at around £5 total.

2 way Household mains socket: Cost: N/A, scavenged from our loft as they were made redundant by replacing with metallic ones.

Battery powered central heating thermostat automatically turns on fans at 26 degrees celsius: Cost £15 (Ebay)

12VDC-12VDC 1W Isolated Convertor: Cost: £6.15 each. (Maplin Electronics)

Low current LED's for State of Charge: Cost £2.49 per bag of 5. (Maplin Electronics)

Step 3: Building Is the Fun Part.

Now that I knew what I wanted my box to look like and what went where I set about making the physical box itself. I lay the sheets of MDF on the floor and accurately drew the box walls and internal shelves so all I would have to do is cut them out. The majority of the cutting was performed using a manual everyday crosscut saw whereas I used an electric Dewalt jigsaw to cut out the holes for the headunit, cooling fans, meters, sockets, speakers and switches. Cutting these small holes is the hardest part of this instructable, requiring lots of attention as the slightest mis-cut can seriously detract the apperance of the final product. I simply pre-cut all the pieces then fitted it all together using 1 inch wood screws but drilled pilot holes before inserting to prevent the MDF splitting.

Step 4: Wiring It All Up!

The easiest part, well, for me anyway, was wiring everything together. The majority of the devices are connected via bus-bars. The digital panel ammeters cant be run off the same circuit that they are measuring, therefore the two DC-DC convertors are vital to the project. They take 11-15 volts from the battery and convert it to an isolated, regulated 12 volt supply. This is why the shunt is before the main fuse in the circuit, I can measure the current going into the battery and there is no danger of a short before the fuse because the ammeter in question is totally isolated from the main supply. The digital voltmeter however can be powered from the supply that it's measuring. I can't really explain how mine is wired because each case will be different depending on your requirements although the circuit diagram for my particular project is displayed here. As long as you wire yours up carefully and correctly and make sure all crimpings are secure, connectors are connected, and that all exposed wires are sufficiently covered up using electrical tape or heatshrink tubing, we don't want huge sparks and a fire on our hands, do we? The charge controller that I used is a bog standard bulk charge, on-off charge controller, nothing fancy. The controller has 4 LED lights that dictate how charged the battery is, 25, 50, 75 and 100 percent state of charge, I opened the controller up and cut the LED's of at their heads, added wires to the legs, covered the exposed legs with heatshrink tubing, then bought some low current LED's from Maplins and arranged them on the front panel. My particular generator has a large amount of wiring in it, as the picture shows.

Step 5: Labels!

To make the generator look the part and so that people can see what switch does what, labels are crucial. I made my labels by designing them on Microsoft Word then printing them off on a bog standard printer, cutting them out accurately, applying everyday stickytape to the front and back, covering the back of the label area with double sided stickytape then cutting the label out again. This method works like a charm and they seem to be long lasting also.

Step 6: Add a Splash of Sun.

Right, after assuring that all connectors are firm and correct, and that the generator works in it's current state of battery power, it's time to connect the panels. My PV array include four 12 watt solar panels and two 80 watt solar panels. Masses of juice when theres blue skies and still generate a good power output on cloudy days. Since PV panels generate DC and DC isn't as efficient at travelling along long stretches of wire as AC is, try to make the wire between the panels and the charge controller as short as possible to avoid voltage drop. My wire is approximately 15 metres long, allowing it to be easily trailed into the house at home, and allowing plenty of available wire for positioning when camping.

My first original 48 watt array used a wooden stand that folded out to prop the panels up, however, wood is not a good material for this job, it constantly gets wet and mine eventually rotted through after one winter, I didn't want to take the chance of it happening again to my expensive 160 watt array so therefore I decided a metal mount of some sort was required. Browsing the wonders of the Interweb, I found that Ebay (yeah I know! ;)) had some pre manufactured ones, made of aluminium and available in different sizes but cost around the £50 mark. I thought "Pah! I'll make some of my own", I obtained lengths of aluminium L bar from my dad's workplace for free, and found some spare nuts and bolts from our garage to use as the hinge. I wanted my panels to be adjustable depending on the time of year it was so I drilled several holes along the supporting legs so the angle can be altered, using some thumb screws (the kind you find on the back of office chairs, but smaller), the bolts can quickly be removed to change the angle, exactly like the ones offered on Ebay for £50 :). 

Finally, to connect all the panels together I made a waterproof junction box so that all three panels can be connected to the end of the cable, and disconnected when they're being moved or transported. I obtained an LCD digital ammeter off, yep, you guessed, Ebay for around £3. It's a school type meter, and when the cover is removed to take the ciruit board out, the LCD screen is physically screwed to the PCB which makes things alot easier whereas many of todays LCD displays use the actual product case to hold the screen to the pins on the PCB. This ammeter fits snugly into my waterproof junction box and runs off a PP3 9V battery. It allows me to see how much power is being produced by the panels without having to venture inside to see the ammeter on my solar generator.

Step 7: Security!

Solar panels, naturally being expensive, and therefore a target for potential criminals, need a form of alarm. I spent days searching for alarm products on the internet to protect my PV panels. I tried a battery powered vibration sensor, the type you use on windows, however large gusts of wind or rain drops kept setting the alarm off so I set about looking into another form of sensor alarm. Finally I had the idea to design a loop alarm, i.e. when the loop is broken, the alarm is activated.

My particular circuit uses two tent pegs which push into the ground, with a wire connected to each. If the wire is broken, or if one of the tent pegs are removed from the ground the 100dB alarm is activated, meaning that the panels can be moved around about 1 square meter but no further so criminals can't steal the panels. My alarm is powered using 6AA batteries at 9 volt, while it only consumes 0.08 milliamps in standby waiting to be activated, this means that the batteries will last for almost 2 year.

The alarm has to be turned off by the keyswitch to be deactivated as if the loop is reconnected, the alarm will still sound. It all fits into a small project box that is siliconed to the back of one of my panels as double sided stickytape wasn't up to the job of daily heat. Each wire to the pegs is around 1 metre long, long enough to wrap around the panel mount but not too long to get in the way while moving the panels around. A small microswitch forms part of the loop that is mounted in the project box as a tamper switch that will sound the alarm if the alarm is interfered with. I also included a small flashing LED that automatically turns on at dark to warm that the alarm is activated. This circuit is very similar to the alarm circuit, simply replace the buzzer with a flashing LED, remove the relay, and replace the pegs with an LDR.

Step 8: Adding Extras.

Several months after finishing this project I still feel the urge to add further functionality to my portable solar generator. Since my headunit has a front USB port I used a traditional 4GB flash memory stick, trouble is that 4GB isn't much space for music and large memory sticks of 32GB or larger are a bit pricy, I thought why not buy a USB powered hard disk drive and incorporate it into my box. I visited Curry's electricals and purchased a Western Digital Bus Powered SE 500GB drive for £39.99.

Being an external box it was prone to knocks and drops so I decided to mount it inside my solar generator with a separate USB port on the side so a separate cable can be connected to this port and then to the headunit, or even to the PC to edit music on the drive. Another problem appeared, with the drive mounted inside I couldn't see the LED indicator to make sure it was safe to unplug the drive, therefore it was necessary to have an external LED mounted on my box. I designed a circuit that uses an LDR blu-tacked to the hard disk drive LED to flash when the HDD light flashed, instead of opening the drive and physically connecting an external LED that would void the drives warranty. The circuit diagram is shown here, designed to run off 12 VDC to power an LED between 2-3 volts in my case, an LED mounted tidily in a 3mm panel mount clip from Maplin's for 34p. Now I can have my music powered by the sun, currently I have 2700+ songs on my HDD, however my particular Sony headunit can only read 128 Albums max at 500 Songs per folder, this is a problem for me because I can't fit all my music on that I'd like to.

Step 9: Have Fun!

Now that the portable solar powered generator is finished, it's time to sit back and enjoy free, clean green energy, when you like, wherever you like! This project cost me in total around £700 when everything is added together and provides me with masses amount of free electricity and unlimited enjoyment. If you have any questions just ask and thanks for reading! :)