How to design and build a solar lunch box

Transcription

1 How to design and build a solar lunch box Presented by May 2016 The North Texas Renewable Energy Group () is the North Texas Chapter of the Texas Solar Energy Society. The mission of NTEG to educate North Texans about the power of renewable energy. This is the little sister to the solar cart Build a Solar Lunch Box 1

2 Why Build a Solar Lunch Box? Developing world mission trips Electrical power fights poverty Electrical power improves health and happiness Emergency power during electricity outages Why Build a Solar Lunch Box? Educational what is done for this is scalable to larger systems. The basics are the same It is Fun Build a Solar Lunch Box 2

3 Needed materials Box PV solar panel Outlet Wires Crimp connectors Switch Fuse MC4 connectors Industrial Velcro Battery Mounting Needed Tools Drill Drill bits Solder iron Knife Tin snips Wire strippers Multimeter Crimper Be sure you have the right size bits Build a Solar Lunch Box 3

4 The next few steps follows the handout brochure Planning, design, construction, and operation Some steps take longer than others Some of these steps have been done for you Step 1: Identify the electrical devices that you want to service. This is the expected load of the system or what is needed to be powered. Light? Phone charger? Fan? Battery? Build a Solar Lunch Box 4

5 Step 2: Estimate how much power is required for each device. Light for how many hours per day? How many times to you want to charge the cell phone per day? Step 3: Determine when you want to provide power. This is typically at night --- since the sun does not provide power at night, all the power must be provided by a battery. How many hours of light per night? When do you want to charge the cell phone? Build a Solar Lunch Box 5

6 Step 4 Note: many lights have watts recorded on packaging Calculate the power requirements of the system in watt-hours Remember: Amps x Volts = watts 5.07 volts x 0.10 amps = 0.5 watts 5.06 volts x 0.22 amps = 1.1 watts 5.04 volts x 0.47 amps = 2.4 watts Step 4 cont d Multiply watts by hours needed to get watt-hours Examples 5.07 volts x 0.10 amps x 10 hrs = 5 watt-hrs 5.06 volts x 0.22 amps x 10 hrs = 11 watt-hrs 5.04 volts x 0.47 amps x 10 hrs = 24 watt-hrs More light = more watts Longer time = more watt-hours Build a Solar Lunch Box 6

7 Step 4 cont d Phone requirements vary by type See manual See packaging See internet Note often see milliamp-hrs (mah). So multiply times voltage to get watt hrs Battery banks have power stated on unit Examples: Small Battery Bank: 1000 milliwatt-hrs Simple Phone: 4.2 volts x 1500 mah = 6.3 watt-hrs Iphone 6: 7 watt hrs Smart Phone Backup Battery: 2900mAh x 3.7 v = 10.7 watt-hrs Step 4 cont d Add up the power requirements For this example: Light 1: 5 watt- hrs Light 2: 12 watt-hrs Battery bank: 1 watt-hrs Iphone: 7 watt hrs TOTAL: 25 watt-hrs needed Build a Solar Lunch Box 7

8 Step 5 Calculate the required battery. Typical rechargeable batteries are 12 volts and rated in amp-hrs Sealed lead acid rechargeable batteries should not be fully discharged. Sealed lead acid rechargeable batteries should not be discharged more than 50% between recharging. To be on the safe side, assume that the target is 33%. Ask how many uses before recharging. Example calculation 25 watt-hrs/.33 = 75.8 watt-hrs 75.8 watt-hrs / 12 = 6.3 amp-hrs Assume a 10% loss: 1.1x6.3 = 6.9 Choose next size up so pick the 7.2 amp-hr battery If you want to use it twice between re charging the battery, (2x6.9=13.9) then choose the 20 amp-hr battery Step 6 Calculate the required solar panel Look on the back of the panel for the working current (Iop) 100 watt pv panel Iop = 5.29 amp 20 watt pv panel Iop = 1.14 amp 10 watt pv panel Iop = 0.57 amp Build a Solar Lunch Box 8

9 Step 6 cont d A solar panel can be assumed to generate the rated power for 4 hours a day* (if properly placed) Calculate watt-hrs of available panels Compare to requirement Ask how many cycles between charges For example: If you think that you can charge every day that you use your system then the 10 watt PV panel is sufficient. If you want to be able to use it twice, then pick the 20 watt panel. 100 watt pv panel Iop = 5.29 amp 5.29 amp x 12v x 4 hr = 254 watt hr 20 watt pv panel Iop = 1.14 amp 1.14 amp x 12v x 4hr = 54.7 watt-hrs 10 watt pv panel Iop = 0.57 amp 0.57 amp x 12v x 4hr =27.4 watt-hrs *in Fort Worth, 6 hrs/day summer, 4.8 hrs/day winter. Step 7 Select an appropriate solar charge controller. The solar charge controller is the brains of the device. It keeps the solar panel from overcharging the battery during the day and the battery from draining back through the panel at night. A simple PWM solar charge controller should have an amp capacity of 50% more than the solar panel. For example: The 20 watt pv panel would need a 1.5x1.14 = 1.7 amp controller The 10 watt pv panel would need a 1.5x0.58 = 0.9 amp controller Most cheap controllers are more than this Build a Solar Lunch Box 9

10 Step 8 Select an outlet. Since the light and the phone can be powered with USB outlets, select a marine/automotive outlet that has a voltmeter and a USB outlet. Note that the back is marked with negative and positive Black is Negative or (-), Red is Positive or (+) PV Step 9 Construction switch USB Volt Meter Charge Controller 12V Battery V fuse + - Build a Solar Lunch Box 10

11 Step 9 cont d Trim wires on controller (about 6 inches) Remove insulation from end (about 3/8 inch) Step 9 cont d One 4 inch black wire One 4 inch red wire Assemble red fuse line (9 inch length total) Remove 3/8 inch insulation from ends of each Insert into disconnect and tightly crimp For as much as we can, we are going to use red wires for positive and black wires for negative Build a Solar Lunch Box 11

12 Step 9 cont d Look at switch: If it comes with wires, trim to 4 inch length and remove 3/8 inch insulation If no wires are on the switch, add and solder Twist to end of 4 inch red wire Solder wires Attach disconnect and crimp 4 inch wire disconnect Wire about length of barrel Step 9 cont d Solar charge controller Cut one 12 inch black wires Remove 3/8 inch insulation from ends Twist to end of short black wire and other to black line (battery side) of solar charge controller Solder wires Insert into disconnect and crimp 4 inch wire Battery side PV side 12 inch wire To battery negative Build a Solar Lunch Box 12

13 Step 9 cont d Solar charge controller Slide 1 inch of shrink line over switch wire Twist one side of switch wire to battery positive side of solar charge controller and to fuse line Solder wires Use flame or heat gun to shrink To battery negative Battery side PV side Connect three wires switch Just enough flame to melt the heat shrink but not the wire To battery positive Fuse Step 9 cont d To outlet - Examine the assembly Dry fit components together - Assemble the system on a table so you can see all the parts and can determine that they operate correctly Solar charge controller To Volt meter Battery side PV side To battery negative To battery positive Fuse To outlet + Build a Solar Lunch Box To Volt meter + switch 13

14 Step 9 cont d Cut solar exterior wire at 12 inch long Remove 3/8-1/2 inch insulation from ends of wire Assemble MC4 connectors - large insert into male, smaller into female Crimp around ends Twist end to finish Note: male end is negative Step 10 Prepare the box for the solar materials Carefully mark the location of the holes for the outlet Drill holes as appropriate for the outlets and switch Drill 1/8 inch holes on side of lid for vents. Build a Solar Lunch Box 14

15 Step 10 cont d Trim around the holes as needed Remove interior webbing as needed Make sure the pieces fit Step 11 Place and attach components within the box. Attach solar wires (connected to MC4) to the solar charge controller Male is negative, female is positive Tie a knot on end of wire Use wire nuts. Negative line from battery to voltmeter Positive line thru fuse from battery to switch USB outlet Volt meter switch Build a Solar Lunch Box 15

16 Step 11 cont d Tighten nuts Use Velcro to keep the battery and charge controller from shifting within the box. Put extra fuses and spec sheet into box Step 11 cont d Secure lose wires Turn on to be sure it works Build a Solar Lunch Box 16

17 Step 12 Note: The solar charge controller needs to be connected to the battery first. Then after 30 seconds to the PV panel 30 degrees and south Mount the panel in the sun Charge the system. Not a good mounting Operation Batteries should not be drained beyond 50% of their capacity. The state of charge can be estimated by measuring the voltage of the system. For an AGM battery, the 50% state of charge is 12.3 volt. The voltage can be checked with the voltmeter in the system. If it measures above 12.3, then the system can be used without over taxing the battery. If below 12.3, the system should be charged. Build a Solar Lunch Box 17

18 Your assembly. The soldering and drilling has been done for you Dry fit your system together at first Then assemble in the box using the connects and wire nuts Ask for help from volunteers Remember. This solar lunch box is for education but it is also useful Basic principles apply Large system or small systems work can work like this Can be scalable.but use the design approach to be sure the materials will work Build a Solar Lunch Box 18

19 Safety Safety is JOB #1 Do not short battery terminals Some wire will have sharp edges Plyers can pinch Ask for help Go to For more information To learn more For downloads on this project and others To see meeting topics and schedules For more solar fun! Build a Solar Lunch Box 19