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Solar W Voltage: V Current: A Peak today: 0 W |
Load W Inverter: Current: A Peak today: 0 W |
Battery voltage: V % |
| Generated this week: 0 KwH | Generated last week: 0 KwH | Used this week: 0 KwH | Used last week: 0 KwH | More ▼ |
This project has now been retired so there is no longer any live data.The solar panels have moved on to fulfil a new life on a self build campervan project.
Thanks for all the comments and recommendations on SolarPoweredHome :)
All the best,
- Matt
SummaryThis project started some time ago when I became interested in renewable energy and built a wind turbine, and since then has evolved into a self-sufficient solar energy system, reporting real energy data to the internet using a Raspberry Pi. The generator inside the 24 foot wind turbine itself was frequently problematic and so it is not currently generating. Instead, the system is currently comprised of 400 watts of solar power, which charge 2 x 110 amp-hour batteries during the day. These power the entire LED lighting fixtures inside the house 24 / 7. Although the system is relatively low power, the project as a whole has been a fantastic learning opportunity, and I hope that anyone fascinated by do-it-yourself renewable energy systems find the details here of great interest. My long term plan is to acquire at least 1Kw of solar panels, and perhaps have the excess energy redirected to an immersion heater when the batteries are charged. You'll find that almost everything was acquired on Ebay, and where possible I have included a price and a link to each piece of equipment required, as well as any useful web resources and source codes. |
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Charging batteries
From the solar panels, the cable arrives at a board on which all of the electrical equipment is mounted. A 20 amp rotary switch seperates the solar panel from the charge controller and is used to cut the power whenever maintenance is required.
After experimenting with some of the cheaper charge controllers and project kits, I eventually decided that I should invest in something a bit more fancy if I wanted to preserve the health of the batteries and have a reliable system. I discovered the MPPT Tracer charge controllers by EpSolar, an affordable but fantastic product that suited my requirements and more. I was specifically excited to learn that these charge controllers have a communication port, which has made the real-time data monitoring aspect much easier than first envisaged. More information on this can be found below.
The battery bank currently consists of 2 x 12v 110ah lead acid leisure batteries wired in parallel. The charge controller uses an MPPT charging algorithm to track to best power point of the solar panels. During the bulk charge phase (when the sun comes up and the batteries are low) the charge controller converts the 40 volts from the solar panels into as many amps as possible. Once the batteries have reached the configured voltage of 14.4, they remain at this voltage (the constant charge phase) and draw less current as they become more charged. When the charge controller reaches its float charging phase, the batteries are kept at 13.8 volts until the sun goes down.
After some research, I learned that it was advisable not to let the batteries fall below a 50% state of charge. In light of this, the controller has been set to cut power to the inverter once the batteries reach 12.1v.
Using the power
Connected to the load output of the charge controller is a 300w pure sine wave inverter, which converts the 12v DC from the batteries into 230v AC. From this the power goes onto a 4-way socket.
Inbetween the inverter and the 4 sockets is a backup relay which switches the sockets to mains power should the inverter ever fail or the batteries run flat. This is a simple DPDT 230v relay that I wired according to a simple guide at REUK.
Plugged into one of the 4 sockets is a cable that goes back towards the house, into the roof, and to the lighting circuit for the entire house. The backup relay ensures the sockets are always live, so the lights in the house never go out!
In order to be able to power all of the lights from just a 300w inverter, all the bulbs, 28 in total, have been replaced with low power LEDs. This reduced the overall power required to light the house from 1.3Kw to just 115w, a 91% reduction!
Getting real-time data
| Fitted inside an enclosure is a Raspberry Pi Model B (the credit card sized computer) running Linux (Raspbian Jessie Lite 4.4). It is powered by the batteries with a 12-5v USB adapter and has internet access via an ethernet cable coming from the router in the house.
There's no screen or keyboard attached to the Raspberry Pi, but instead it is accessed over the network via SSH, with a client such as puTTY. I am also able to access it from outside
of the network using a Dynamic DNS service. These are easy to set up providing you have a router that supports one of these services.
Remote SSH access is useful, because it means I can reboot or make changes to the datalogging program from any location. |
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I used one of these USB to RS485 adapters. After cutting the end from an old ethernet cable, I attached the blue and blue-white wires to the adapter (RJ45 pins 4 and 5).
The program I have written (source) continually requests data from the charge controller (solar voltage, solar current, battery voltage, charge current) and posts them to a web address using the urllib2 library. The PHP webpage, hosted on my web server (source) checks the data, calculates the power being generated/consumed in watts, and inserts it into a MySQL database. This is repeated around the clock approximately 8 times per minute.
The minimal amount of code needed for retrieving data from a Tracer charge controller can be seen below. Please see the modbus protocol for a full list of registers.
from pymodbus.client.sync import ModbusSerialClient as ModbusClient client = ModbusClient(method = 'rtu', port = '/dev/ttyUSB0', baudrate = 115200) client.connect() result = client.read_input_registers(0x3100,6,unit=1) solarVoltage = float(result.registers[0] / 100.0) solarCurrent = float(result.registers[1] / 100.0) batteryVoltage = float(result.registers[4] / 100.0) chargeCurrent = float(result.registers[5] / 100.0) # Do something with the data client.close()As well as requesting data from the charge controller, my Raspberry Pi senses the load current manually using a 30 amp current sensor and an ADC (analog to digital converter). This was necessary because the load current data given by the charge controller itself was very eratic, which made it difficult to calculate power accurately. I can only assume this is because the Tracer was not designed to power a pure sinewave inverter directly. The current sensor connects to the ADC of the Raspberry Pi using 3 wires: 5v, ground, and signal. The signal wire connects to one of the analog inputs of the ADC, and the voltage received at that pin (between 2.5 and 5 volts) is used to determine the current flowing through the sensor (from 0 to 30 amps). This is achieved by mapping the analog reading (2.5 - 5v) to the known current range (0 - 30a)
If you wish to use an ADC to detect current, below is the minimal amount of code needed:
from ABE_ADCPi import ADCPi from ABE_helpers import ABEHelpers def map(x, in_min, in_max, out_min, out_max): return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min i2c_helper = ABEHelpers() bus = i2c_helper.get_smbus() adc = ADCPi(bus, 0x68, 0x69, 14) adc.set_conversion_mode(1) inputPin = 6 # The below values were calibrated for my sensor inMin = 2.485 inMax = 2.7 outMin = 0.26 outMax = 3.63 loadCurrent = round(map(adc.read_voltage(inputPin), inMin, inMax, outMin, outMax), 1)The input-output variables for this function need to be calibrated in each individual application, for the output of the sensors can vary somewhat due to temperature, nearby interference, cable resistance, etc. I calibrated this current sensor by observing its output whilst comparing it to the current reading on a multimeter.
* After experiencing persistent issues with the current sensor I am now taking load current directly from the charge controller until I can find a better way. If you've figured out how to measure DC current accurately with a Raspberry Pi, please let me know!
Handling errors and connection loss
One of the more difficult (and ongoing) tasks is ensuring the datalogger is always running. There is always the possibility of the Raspberry Pi crashing, or the internet dropping. Below is a list of problems I encountered, and the solution I have implemented to reduce the effect:
- The program stopped if there was a HTTP/URL error - I put the data submission in a try/except clause so the program continues even if the data couldn't be posted to the internet. The error information is also saved to a log file.
- Periods of data was lost when the internet went down - When data can't be submitted, it is saved to a text file on the Raspberry Pi, and a seperate program uploads that data when the connection is restored.
- I had no way of knowing if the datalogger was running - A check is performed on my web server to see when the last data was submitted, if it is above a certain amount of seconds, an email is sent to my phone.
- The SD card would corrupt and the Raspberry Pi would just stop working - This seems to be a common problem with the Raspberry Pi. I tried a few things to fix this, such as adding a cron job to force a file system check, and storing temporary files on a usb, but the problem continued. Finally, I reserved a small amount of RAM and used this to store the logs and camera images on. This has fixed the problem!. The Pi now runs continuously.
