Over the past 2 years I’ve been working on a project to use renewable energy in a small scale. It started out of the need to create backup energy – my area was hit by a storm and we were out of power for 4 days and I wanted to be prepared for the next one.
I researched the market and looked at available technology and bought some solar panels, inverter and batteries. Hooking that up is very simple and it was ready to use. After spending $500 I had a working setup but now it was sitting there all day fully charged and doing nothing.
I decided to hook my fridge up to it and run it 24/7 on the small solar setup. That worked well until there we had a bunch of cloudy days in a row and the battery did not have enough juice to cover it. So I did more research and found out how you have to design “real” off-grid systems and how deep discharging impacts the lifetime of batteries. I decided that is was not worth it and was looking for other solutions. But there are only two: “big” grid-tie installation or an off-grid system.
So I had a bunch of solar installer over at my house and we got mostly the same answer: your energy consumption ($50/month) is too low to make the numbers work for you. At first I was very disappointed but then I thought it might be an opportunity.
I bought an Arduino and started designing my own controller that should do something very simple: use solar whenever the sun is shining and use the grid at night or on a cloudy day.
After a year I had a stable prototype and I started telling friends about it. They liked it and I started showing the idea on environmental fairs - that got me a lot of positive feedback and I decided to make 5 of the controllers for “field” testing. Here are some pictures of the PCB:
I is currently using an ATmega2560 and runs really well - but it cannot be hooked into the IoT. After discovering the Spark I decided the re-design the PCB and concept and ditch the ATmega and make it a plug in board. It currently holds a slot for the Spark and Arduino Nano.
I am thinking of going for crowd-funding because to make this unit affordable I need to manufacture at least 300 of them. When I look at other solar projects that get successful funding they are either “solar roadways” or small portable smart-phone chargers.
I’d love to hear if anyone has any ideas or thoughts about the concept. Any and all ideas are appreciated!
So the board detects how much you have charged the battery and then switches to Solar/Battery when there is enough Solar/Sun/Battery and then switches off when there isn’t? Sounds like a cool project.
Do you do anything as far as measuring the current power consumption on the AC line? I guess if you are measuring power out to the inverter then you essentially know the AC current consumption value anyway.
Could you perhaps annotate the image you posted with notes pointing out what each thing does? I think people would find that interesting
I am not measuring energy consumption over AC lines. Measuring the DC lines is sufficient (and much simpler). Your assumption about the inverter power is right!
As soon as I am holding the new revision of the PCB in my hands I will post new pictures - including annotations.
You can take a first look at the re-designed PCB here. It is not colpletely assembled yet. Once that is done I will post a better picture with annotations.
Hi MarkusL,
I see you are using ACS75x Hall effect sensors. I would like to use them but don’t have Eagle library for this component. You have professionally made PCB. Could you share Eagle library for ACS75x sensors?
Thank you,
@tdphan: I had it made thru a contractor I found on oDesk - not sure where I would find that library. My latest design is not using that part any more - the hall sensor is more noise sensitive that using a shunt.
Very cool! I don’t quite understand the NIGHT-UPS mode. Also, I would suggest, to make it clearer, that you remove the picture of the wall outlet and replace it with a picture or text that says something like “Grid/City Power”. It took me longer than I care to admit to figure out which was which
@harrisonhjones: Thanks for your comments. To explain the ‘NIGHT-UPS’ mode:
If in the UPS mode the inverter will never be shut down to be able to immediately provide power in case of a black-out. I called it NIGHT-UPS because during daytime the inverter is always on. Otherwise at night it gets shut down to save energy.
All comments about confusing wording or drawings are very welcome because it is so hard to find these things
@MarkusL This is a really great project. I also like the schematic to explain the different modes. Even with this explanation, I am having trouble understanding the difference between Night and Night-UPS modes. Are you saying that the Night-UPS mode would be when you are using battery power at night? In that case you are manually switching to close the circuit from the battery to the outlet?
@mashandburn: Thank you. I should remove the word night. In UPS mode the inverter is simply always on. At night the power to run the inverter is coming from the big transformer you see in the picture. This provides power to the inverter to a max idle load of 20W. If the inverter consumes more the batteries will drain.
OK I think I get it. Thanks for that explanation. In the diagram whne in UPS mode the inverter is connected to the battery, but is there a separate connection not shown in the diagram from the inverter to an outlet load such as fridge?
Sorry for the late answer: If I understand you corretly then that connection is shown by the red lines. The outlet (pictured as a power strip) is powered by the inverter or the utility power (wall outlet). The UPS mode powers the inverter 100% of the time to be ready to switch over in case of a blackout.
