With IRMA threatening to hit the east coast I sat down and took a look at my position and what backup options i had.
The main area i had no real backups was power. I decided this was a good time to give solar a try as its been something i wanted to play with for a while.
So i did some poking around and bought a 100w monocrystaline panel and a 30amp pwm charge controller from amazon.
join me on this journey into the world of solar.
Step 1: Bill of Materials
- Solar Panel kit 100w with 30a controller 168usd:https://www.amazon.com/gp/product/B018ZU2KQS/ref=o...
- Batteries - i used some Sealed lead acids i had around the house
- Fuse kit - NEEDED!!! 12.49usd https://www.amazon.com/gp/product/B01E5MM63C/ref=...
- Wire of correct gauge for power and distance you need to run it.
- Digital Power Energy meter 16.99usd: https://www.amazon.com/gp/product/B01JOUZELG/ref=...
- Automotive 12v bus 6usd - note this was really poor quality, would not reccomend: https://www.amazon.com/gp/product/B0732Z72WG/ref=...
- Clone of adafruits ina219 breakout. adafruit was Out of stock :(
- 6.89usd x3 https://www.amazon.com/gp/product/B01ICN5OAM/ref=...
- ESP8266 node mcu 7.99usd: https://www.amazon.com/Laqiya-Version-NodeMCU-Int...
Step 2: Location Location Location
With solar panels, location is key, you want a location that will have full sun for as long as possible.
Thankfully google has a tool that can help us: https://www.google.com/get/sunroof
just tap in your address and it will show you a heatmap of the best place to put it.
Tilt is also important. this site does a great job explaining it: http://www.solarpaneltilt.com/
because i wanted to be able to get to the panel and i didn't want to drill a hole in the roof of my house just yet, i put mine on my shed.
the downside it it only gets about 3 hours a day of usable sun, during that time i'm seeing about 4-5amps off the panel. the rest of the time i'm only seeing 0.25amps.
Other consideration is volage drop and current handling on your cables. ideally you want the shortest possible and the correct gauge wire. in my system i ended up with a wire length that was much longer than i wanted. but i will improve this going forward.
Step 3: Batteries and Charge Controllers + Wiring
Let me open with this, Fuse everything.
Put inline fuses ont he input from the panel, battery leads and to your load. the fuse should always be before anything else in your circuit so that it can blow if there is a short.
Lead acid batteries can deliver a lot of current, so treat them with care.
with that out the way this is fairly straight forward.
My panel came with a wiring diagram. i made a few changes as i wanted to use an inline power monitor on the load, and add in the IoT power monitor too.
I've mocked up a wiring diagram of my system. just remember that the panel is always generating power when it sees light so be very careful not to short anything out.
The shunt resistor is used for the current monitor. basically it drops a known value in line and lets you monitor the voltage. because the value is known we can extrapolate how much current this equates to. more info on these here: http://www.rc-electronics-usa.com/current-shunt.html
My controller allows you to monitor voltage and current from the panel, battery and load.
Step 5: Adafruit.io Integration and Power Monitoring
Very quickly in this project i realized i wanted to be able to see the metrics of the panel, so being a maker i grabbed some parts and built one. This board measures voltage, current and watts of the panel, battery and load.
this uses an esp8266 nodemcu and 3x ina219 i2c power monitors (you need to change the shunt resistors or they can only do 3amps).
i soldered them to a board and then push it to adafruit.io. you can take a look the the live stats here:
The code is attached and here on github: https://github.com/raptordemon/SolarTrack
Adafruit has written a great article on these boards. here: https://learn.adafruit.com/adafruit-ina219-curren...
I simply wired the i2c bus together and set the addresses on the boards and boom, 3 channel power monitoring.
Please note that this requires different shunt resitors to allow the ina219 to handle more than 2 amps. on top of that i had to modify the libray with the calibrated values for the new shunt resistor. i have included this in the zip file but you will need to copy it to your libraries.
Also don't forget to include your adafruit.io key and wifi values!!
Step 6: A Word on Efficiency
During my testing i needed to bleed of some power stored in the batteries as i wasn't able to get a decent charge current going because the batteries were full.
I did this by plugging in a 40w incandescent bulb into my inverter. what happened was i saw about a 4.5amp draw off my batteries for just one light bulb!!
a 40w replacement led bulb uses just 6 watts of power and uses 84% less energy than standard bulbs. that means your power will go much further.
so if you are going to do solar. start by making things more efficient first.
Step 7: Conclusion
This was a really fun project that i intend on continuing with.
One thing that is really clear that at 1usd per watt of power just for the panels, and the cost of the batteries (100ah lead acid deep cycle batteries are 140usd approx) that this is an expensive way to generate and store power.
you can buy a 5500w generator from 500usd https://www.harborfreight.com/engines-generators/... that is 9cts per kw not including gas.
that same output for solar is going to cost 5,000usd just for the panels. This doesn't mean that solar is useless, far from it. but make sure you set expectations.
This 100w system is perfect for charging my cell phone, running some lights and a fan in an emergency. It could even be used to run some low current devices all the time. I have enjoyed this project and have learned quite a bit about solar.
please let me know if you have any questions or tips you would like to add.