Introduction: Micro Solar Power System
The best way to learn about renewable energy and solar power is to get hands on and build your own system.
Here is a small solar photovoltaic (electricity producing) solar power system which includes charge regulation, monitoring and fused outputs all within a laser cut enclosure. Its designed to be a entry level solar power system to recharge small devices such as mobile phones, mp3 players and power small sound systems.
This has been designed to be put apart with very little soldering, using mainly connector block and crimp terminals.
Step 1: Parts Required
- 10Wp Solar PV panel (cost £20-30)
- Such as this:
- Check eBay
- Cable (£2-5)
- 0.75mm2 or 1mm2 diameter (enough to take 2 to 5A).
- In red and black if possible.
- I used 3 different types - twin core for the solar panel, thick tri-rated for the battery cable and thinner cable for internal wiring, after the fuse.
- Battery (cost £? depends upon size of battery. I got some used but OK UPS batteries for free)
- Rechargable lead-acid
- I used a sealed gel lead acid battery taken from a UPS system.
- Capacity (Ah) of the battery is dependant upon the load and solar resource
- Charge regulator (£6)
- This stops the battery being over charged by the solar module.
- 2A rated 12V DC.
- I used this Chinese one: http://www.ebay.co.uk/itm/Solar-Power-Panel-Charge-Battery-Controller-Regulator-/380359116665?pt=LH_DefaultDomain_0&hash=item588f2b8779
- Here is a UK-made unit: http://www.256.co.uk/?cat=3
- 12V voltage monitor / Voltmeter (£3)
- To easily measure 12V DC
- Such as this: http://www.ebay.co.uk/itm/DIGITAL-LED-VOLT-METER-RED-BLUE-GREEN-DC-4-5V-30V-No-Power-Needed-Panel-12V-/251094347641?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&var=&hash=item3a7663af79
- You could also use a small cheap multimeter.
- Small push button switch (£0.50)
- This is for the voltmeter so that it is not left on, which would drain the battery.
- 12V 'cigar' lighter socket (£4)
- This is a standard 12V DC socket
- Lots of loads are available that will fit this style socket
- 5A resettable fuse (£2)
- This protects the everything from the high currents the battery can supply.
- Rated for 12V DC
- Terminal connector block (£0.50)
- 2A rated plug and socket (£2)
- This is for the solar PV panel connection
- Insulated crimp spade connectors (£0.20)
- M3 20mm long machine screws and nuts x approx 20 (£1)
- Both countersunk and pan head can be used
- Laser cuttable 3mm birch plywood A4 sheet (£3 + £2 for laser cutter time)
- This is for the enclosure
- You could also use any enclosure you have to hand, but I like the wood aesthetic.
- Cable cutters
- Laser cutter - if making your own enclosure (try visiting your local hackspace)
- Soldering Iron + solder
- Terminal crimpers
- Small pliers
Step 2: Cut and Build the Enclosure
I decided to use a laser cut plywood enclosure. This looked nice enough to be on display, could have logos and images etched onto it and have all the holes and bolt fittings cut out precisely for easy fitting together.
The box was designed initially using boxmaker from Rahulbotics. I used this as the basic dimensions. I also wanted the box to be re-openable, so I decided to use t-nut holder notches. I saw this on Make, so not quite sure who to credit that design to. So the .dxf pattern is a mixture of slots and t-nut holders.
The problem in making this enclosure is access to a laser cutter. Please try (and support) your local hackspace, which might have access to a laser cutter. My local hackspace is Nottingham Hackspace in the UK. Thanks go to Dominic, 'cause he bought the laser cutter at Nottingham hackspace.
You could also put all the components into any enclosure you like, just cut appropriate holes in the sides (I would use holes saw and 'fir tree' hole cutters). You could also just screw all the parts down onto a piece of wood. But I wanted it to look pretty darn good.
The enclosure is held together using nut holders and notches. This works really well. I think I saw it first in an issue of Make magazine.
The .dxf file is attached here. Please feel free to use, adapt, modify it to your needs.
You might need to countersink the holde on the base of the unit. This means that, using counter sunk head machine screws, there will be nothing pertruding from the back.
Step 3: Add Wires to the Voltmeter and PV Panel Socket
The LED voltmeter I used had very fragile wire connections to a circuit board. I strengthened these using hot melt glue over the wires onto the circuit board. This means the circuit board is now impossible to repair, but it was a tiny surface mount board, so I'm not too worried about that.
There are three wires from the voltmeter - red, green and black. Black is ground. Red is the power supply, which can be 12V, and Green is the voltage to detect. I dont want to run this all the time as it will use all the solar power up.
So we wire a switch into both the power supply and the voltage detection cables. Wire the red and green wires together and they go to one side of the push switch. On the other side we have just one cable which will go to the positive of the battery, Check the wiring diagram for more information and detail.
Also solder a short piece of red and black cable to the socket for the solar panel. The socket you use is up to you - but it must be able to cope with around 2A. I used a loudspeaker-type connector, which ensures the polarity is correct.
Check out the wiring diagram step for more information.
Step 4: Wire the Solar PV Module
The solar panel I used came with short cables with MC4 type connectors. These cables are double insulated and rated for 600V DC, as if it would be added to a grid connected system. These were a bit over-kill for this system so I decided to remove them and add a longer twin core cable.
The connections were in a clip closed junction box.
I removed the supplied cables.
I used 2 x 1mm2 cable (actually mains cable). Strip away the cable and crimp and solder on some ring connectors. These can be then re-attached to the + and - terminals of the solar panel.
I used a 4m long cable so the solar panel can be mounted outside and have the cable running to the charge controller box and battery, which can be inside.
I used the standard cable colouring of brown = positive and blue = negative.
I then added the plug to attach the solar panel to the charge controller box. Make sure that the polarity is the same as the socket.
Step 5: Insert Components
Now we have the box built we need to fill it with components.
The wiring diagram is attached to this step. Please follow this.
I am using 7 way connector block so that most of the connections just use a screwdriver.
You will need to fit all the components in the relevant holes. Mostly they are held in place using 3mm machine screws.
The only slightly annoying part is using a glue gun to hold the LED voltmeter in place. Any ideas for doing this beeter would be greatly appreciated.
Step 6: Wiring Diagram
Use the connector block to wire up all the sockets and fuses as shown in the wiring diagram here.
Its easiest to wire up before bolting down the connector block.
Use spade connectors to attach cables to the fuse, 12V 'cigar' socket and also to the battery. (Connections to your battery depend upon the type of battery used). Do not push the connections onto the battery yet.
When finished bolt down the connector block. Carefully fit in all the cables - this might be a bit fiddly, but there should be enough space.
Then fit on the front panel and screw in to fix (using the t-nut holders).
Step 7: Test and Place in the Sun
Connect up the battery. Ensure correct polarity. (Do not plug in the solar panel yet).
You can now check the battery voltage. Press and hold the voltmeter push switch. This will read the battery voltage. Hopefully is it around 12-13V. A fully charged sealed lead acid battery at rest is around 12.8V, a fully discharged battery is around 12V.
Next take the device into the sun, along with the solar panel. Push the voltmeter switch and check the voltage. Keep it pressed and plug in the solar panel plug. The voltage of the battery should rise realatively slowly. This means the solar panel is recharging the battery.
Loads can be plugged into the 12V socket. Devices such as mobile phone chargers, small sound systems and small laptops can be powered.
If you have any problems with either of the above steps then check your wiring. A multimeter would help here.
Thats it done - You can now take some devices off-grid and harness the power of the sun.
Ensure the battery is maintained well and the battery voltage does not fall below 11V DC (keep it higher if possible). Ensure the battery is re-charged to 100% often by leaving in the sun with no loads attached.
More information on doing a load assessment, solar resource assessment and the details of battery and cable sizing can be found on my solar PV design sheet.
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