Ever on the lookout for creative applications for tech, [Andres Leon] built a solar powered battery system to keep his Christmas lights shining. It worked, but — pushing for innovation — it is now capable of so much more.
The shorthand of this system is two, 100 amp-hour, deep-cycle AGM batteries charged by four, 100 W solar panels mounted on an adjustable angle wood frame. Once back at the drawing board, however, [Leon] wanted to be able track real-time statistics of power collected, stored and discharged, and the ability to control it remotely. So, he introduced a Raspberry Pi running Raspbian Jessie Lite that publishes all the collected data to Home Assistant to be accessed and enable control of the system from the convenience of his smartphone. A pair of Arduino Deuemilanoves reporting to the Pi control a solid state relay powering a 12 V, 800 W DC-to-AC inverter and monitor a linear current sensor — although the latter still needs some tinkering. A in-depth video tour of the system follows after the break!
All the electronics are housed in a climate-controlled box which kicks on when the Pi’s CPU heats up — this is in a Florida backyard, folks — and powered off the battery system, with a handful of 40amp breakers between the components keep things safe. [Leon] has helpfully provided links to all the resources he used, as well as his code on GitHub.
We love homebrew solar power systems, but if only there was some way to take them on the road with us.
33 thoughts on “Innovating A Backyard Solar Battery System”
That’s funny, an hour ago I was selecting deep cycle AGM batteries for a 3kW solar array. Flooded lead acid is better but only if you keep it watered properly, which is a pain for off-grid stuff. LiPo4 is arguably the best but it’s gonna run you at least $20,000.
Whoops, I mean LiFePo4.
Nissan Leaf cells are going for about $200/kWh, making them cheaper than lead acid after accounting for lifespan and derating.
But can I expect them to have a long life outside of the car?
why would their lifespan be worse when out of the car?
as long as you treat them according to specs they should if anything have a longer life off the road, simply due to the lessened mechanical stress, i also doubt most stationary solar cell uses would draw as hard on the batteries as the multi kw draw/charge cycle of common driving with regenerative breaking.
I wonder why nickel-iron batteries are not more popular for home setups?
Because they are VERY HEAVY and VERY EXPENSIVE and THE ENERGY DENSITY STINKS ON ICE.
Other than these minor details, a pretty good solution.
Long life span though.
I want to make an LED solar light with one as a steampunkish project.
Cool, I was thinking of making an active diode from a relay instead of using a shotki diode. Anyone try this?
Do you mean you’re switching the diode in and out of the circuit? Is there an advantage to that?
I think that he means closing the relay when blocking is required, instead of relying on a diode for blocking. However the relay will need to be timed to make sure that it conducts when it’s needed. The benefit is the lack of forward voltage drop that would be present if a diode was used.
Use a perfect diode. Example: http://www.ti.com/lit/ds/symlink/sm74611.pdf
Damn! Now I’ve actually got to read to find out what the catch is. An 8-amp diode with a 26 mv. Vf? Right!
(Thanks for the info, LB9MG; looks VERY intriguing).
Its a mosfet with a comparitor that uses the RDSon of the mosfet as a current shunt. When the current starts flowing backwards, it turns off the mosfet.
It also has a charge pump to drive the circuitry when the mosfet is on, that will occasionally switch from 0.026 Vf to 0.6 Vf to charge a cap so the comparitor and mosfet gate have power.
Better still, beefy MOSFET with low on resistance.
Damn! Now I’ve actually got to read. Again!
(Thanks, [Elliot]; looks like a very good article.)
Last time I looked into Mosfets as a diode, I read that they leak if the voltage was too low on the blocking side…iirc.
I read the article and now remember more:
I was considering the mosfet at a time when I wanted to charge a 3v battery pack. I wanted to avoid the diode drop, but the 3v battery couldn’t always be assumed to be above 2v to cause the mosfet to act like a diode.
Thanks for the link!
And here i thought that florida has some humidity in the air….
how is the system going to survive ONE summer?
depends on the electronics enclosure he uses and the moisture rating of the inverter.
the number one solution for remote marine power is solar cells, from buoys over weather platforms to small sensors, perhaps it isn’t as fragile as you think?
We used to tell our customers–who wanted to know how we tested our product for 85/85 (85°C/85% RH) compliance–that the product operates successfully, over-night, on the patio of our Florida hotel room. Never had an argument.
Extreme humidity is definitively an issue. I am noticing that my battery poles are getting oxidized even after applying silicon rubber on them. The container holding all the equipment is as sealed as much as I can, but I notice that it is till damp inside possibly due to condensation. I am planing to add more fans to help remove some of that humid air. I’ll provide an update in a few months.
What about using Vaseline on the battery posts? I used that on my car battery.
Ps wet air will still suck in when the box is cool from the night (unless it is vacuum sealed which is almost impossible).
Better not seal any lead acid battery.
They will vent hydrogen gas.
Better to use a sealed box for all the electronics, with an air to air exchanger made out of a pair of PC Heatsinks.
Have the outside fan tach monitored and PWM controlled (4 wire), profile the fan when new, and you get longer life by only spinning when and as much as needed…
The inside fan can just be tach monitored.
Goto your auto parts store and get battery terminal cleaner/acid neutralizer and terminal sealer (2 separate spray cans) they should last a while in a non-automotive setup..
Go someplace which sells stuff for electricians and buy a gooey, conductive paste for use on aluminum wire, in order to ensure a good connection of the Al wire to whatever you’re hooking it to. Use this stuff on your batteries and associated connectors–AFTER cleaning very well, first. Works like magic. I started doing this when GM came out with their stupid side-terminal batteries, and have NEVER had a corrosion problem since. That’s been a long time, folks.
An example of this goo is “NOALOX” (for ‘No aluminum oxidation’. Cute, huh?) by the Ideal Company/Corp/Group. Others make a similar product
Go to a junk yard, a used battery pack from a Prius is cheap and easily reconfigured. I’m foregoing the battery system and just have my 4 100 watt panels connected to a synching inverter that is tired directly into the house power. during the day I offset about 340watts of draw constantly which makes a significant dent into the AC costs. My inverter is capable up to 1500 watts so I just need to keep buying a new panel every 3 months and soon I will have free Air Conditioning during the day.
That’s a good idea! I may start looking around for such batteries. Thanks!
I’ve been thinking the same. The main issue is that all the required hardware is several months worth of electrical bills.
Yeah you’re right man.
This is a really cool update and post. Although, I am not able to find your like button.
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