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Solar Energy Generator

A solar energy system up to 500W in power for use with lithium batteries.

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This project was created on 07/20/2014 and last updated 6 days ago.

Description
This platform is designed to be used as a power supply for systems that do not have access to grid power or for taking systems that are normally grid connected off of the grid. Currently it is in a development stage, and circuit blocks have been constructed separately for to make development and testing more manageable.

Some Target applications include:
- LED street lights and security lights
- Weather and sensor stations
- Radio relays and mesh network nodes
- Security cameras and sensors
- Power for sailboats and cabins

General Features:
- Supports panels in series or parallel combinations up to 500W.
- Compact size of 120x120x45mm.
- Dual phase converter allows for currents up to 16A, input FETs and internal rails tolerate input voltages up to 50V.
- Maximum Power point tracking across all temperature and insolation conditions maximizes energy output.

Link to the full System Design Document can be found here: https://nathaniel-verlee.squarespace.com/downloads
Details

The solar energy generator has a buck boost topology DC-DC converter that can either step up or step down the output voltage from the input voltage, which allows the system to operate at the panels peak efficiency known as the maximum power point. The maximum power point is tracked using a current and voltage sensor by periodically changing the input to output voltage relationship of the DC-DC converter and measuring the corresponding changes in output power the sensors. In addition to implementing Maximum Power Point Tracking, the buck boost topology allows the battery operating voltage range to be either higher, lower, or both relative to the panel input voltage depending on the solar panels used. When configured properly it can be used to harness the energy of panels up to 500W in capacity. Batteries capacities can be anywhere from 100 watt hours to a few kilo-watt hours in capacity, and the initial target battery chemistry is lithium iron phosphate due to its high cycle life and increased safety over traditional lithium cells. Other chemistries such as lead acid will also be supported in the future. The generator is composed of the following circuit blocks: a two phase buck boost DC-DC converter, a battery current sensor, a load current sensor, a battery voltage sensor, gate drivers for the converter, a C2000 micro controller, 12V, 5V, 3.3V and 1.8V rails, and a load switch.

A load switch is critical to protecting the battery from over discharge and short circuit. The load switch opens and disconnects the load if either of these conditions should occur. Currently, this portion of the system is not fully defined and may be implemented either with relays or MOSFETs as the switch. Each of the two load switches should be able to handle at least 10A, and more may potentially be added externally.

A Texas Instruments C2000 TMS320F28035 has been selected for the final design of the project, but in the prototyping stage a TMS320F28027 is being used as it is available in a pre made "launchpad" platform from TI, which includes the necessary debugging and programming interface as well as 5V and 3.3V supplies. The C2000 microcontroller was selected because it has many features designed for digital power applications, and configuring it to drive the buck boost converter is not only easy, but powerful, allowing multiple converters to be driven in a phase relationship, and allowing for fast shut down of the converter stage in the event of a dangerous transient event. In the final single-PCB solution, a buck converter will be connected to both the panel input and the battery via a diode or, which will source power from the higher of the two voltages. This 5V rail will then supply power for a 12V rail (boost) for the FET gate drivers and the 3.3V and 1.8V rails for the micro, sensor circuits, display, and various other circuits.

Finally, the converter will include a simple character display, buttons and an encoder wheel to configures various system settings such as battery float voltage, power limiting, a load shutdown timer, display system power output, and allow for future information and configuration features. I selected an OLED display from Adafruit for its high contrast and bold appearance.

In the current stage of development the separate sensor boards, power stage board and the C2000 development board are all connected to each other in a manner very similar to the configuration of the final completed PCB. Some features are not currently available such as the load switches and the supply rails. Much of the last two months of development has been teaching myself to code for the C2000 platforms. The next stages of development will include finalizing the proof of concept with separate interconnected PCBs, finishing work on the final PCB, measuring the performance of the prototype with instruments and searching for possible improvements, and creating in depth documentation of the project. 

Link to the full System Design Document can be...

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Project logs
  • Update on PCB, and a side project...

    6 days ago • 0 comments

    I have been hard at work routing the final PCB, and its coming out quite nicely. It doesn't look a whole lot different from the photo I previously posted because most of the work has been routing, and the placement was mostly finalized. The final design should go out tonight. In addition, I had a nice little distraction that has already been sent off to OSH park. This "Solar Panel Simulator" is a rather simple way to turn a power supply (which must be capable of doing CC limiting) into a panel simulator. The concept is rather simple: you hook it up in parallel with the supply, set in CC mode, and the thing you want to power (my project) and the power supply now appears to the load to have the V-I characteristic of a solar panel. The diodes basically act as a shunt and sink all the current when the load is not drawing anything. This will be very useful for all those cloudy days and late nights that I have wanted to test my system in accurately simulated conditions. 

  • Update on next PCB design

    24 days ago • 0 comments

    I have been pushing forward with the next PCB design where all elements of the system are combined on one board. I have included a screen capture of what the board will eventually look like. You can clearly see the two inductors for each phase of the buck boost power stage, surrounded by 4 Buck FETs on the left and 4 Boost FETs on the right. I am hoping to push this design out to get fabbed next week. Then I will be focusing back on writing code, getting some delrin laser cut to mount this in a pelican case with a battery, and building up a BOM for a parts order. 

  • Video Posted

    a month ago • 0 comments

    Here is an overview video of my project for the Hackaday prize entry: 

View all 7 project logs

Discussions

Nathaniel VerLee wrote a month ago null point

Thank you Bobnova! And thanks to all my other followers! I have been selected as a semi finalist, very exciting! Can't wait to post more details as this project moves forward.

Are you sure? [yes] / [no]

Bobnova wrote a month ago null point

This looks amazing. I want one.

Are you sure? [yes] / [no]