Author Topic: My solar controller project: One Fridge Off The Grid  (Read 4648 times)

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SolarTrap

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My solar controller project: One Fridge Off The Grid
« on: August 01, 2014, 02:13:56 PM »
Hi All,

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 models available: "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 (which is now running for about 400 days) 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.

I am thinking of going for crowd-funding because to make this unit affordable I need to manufacture at least some hunderds of them. Also crowd funding has the customers sort of "built-in". When I look at other solar projects that get successful funding they are either utopistic "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!
Also, I have two units (follow the link above to see them) left that need testers! If you have a spare solar panel, inverter and battery send me an email!


Markus
« Last Edit: August 01, 2014, 02:38:20 PM by Bruce S »

Bruce S

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Re: My solar controller project: One Fridge Off The Grid
« Reply #1 on: August 01, 2014, 02:35:43 PM »
You will notice I removed your link.
Though the site looks nice and the idea is a great one,,, rules state no selling or links until after 50 posts.
The site looks nice and all BUT rules are rules.
A kind word often goes unsaid BUT never goes unheard

DamonHD

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Re: My solar controller project: One Fridge Off The Grid
« Reply #2 on: August 01, 2014, 02:45:52 PM »
And further to what Bruce says, I had warned you before you even finished signing up.

FIELDLINES IS NOT A FREE MARKETING DUMP.

I do understand your desire to get customers and cash; I too am raising finance for one of my projects, but FieldLines is not the place to do it.

Rgds

Damon
Podcast: https://www.earth.org.uk/SECTION_podcast.html

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Mary B

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Re: My solar controller project: One Fridge Off The Grid
« Reply #3 on: August 01, 2014, 05:16:12 PM »
Post more info on the design and what it dos and people who are interested can email you for the website address.

SolarTrap

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Re: My solar controller project: One Fridge Off The Grid
« Reply #4 on: August 01, 2014, 06:43:34 PM »
Below was a functional diagram but links are not working for me. The “heart” is my controller which is monitoring all connected devices: Battery, solar charger, inverter and utility power.  It is a hybrid solution that uses solar power and a battery during periods of high sunlight and switches back to the grid during periods of low sunlight to minimize battery cycle depth. The function is similar to an off-the-grid system during the day, then automatically switch over to mains power during the night. The idea is to gain the environmental benefits of a grid-tie system while retaining the backup power benefits of an off-the-grid system.

OperaHouse

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Re: My solar controller project: One Fridge Off The Grid
« Reply #5 on: August 02, 2014, 10:51:07 AM »
You didn't answer my question about what you had for a pullup resistor.  I was curious looking at the board whether this was MPPT, didn't see an inductor.  I actually run my chest fridge only during the day and store cold for the night.  I use only one car battery, from my truck that I don't bring with me, for the starting surge.  I have enough panels to run the system once started even on fairly cloudy days.  The excess power during the day is used to heat water.  Frankly if you want an innovative idea, that is it heating water.  The average extra insulated electric hot water tank loss is 3200WH a day.  Where else can you use the total output of a solar panel.  A control system that can switch in and out the lower heating element and anticipate usage would be the real winner.

SolarTrap

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Re: My solar controller project: One Fridge Off The Grid
« Reply #6 on: August 02, 2014, 06:42:19 PM »
I am using internal pull-up of the ATmega2560.

> whether this was MPPT

The concept of the board is more modular that that. You "plug-in" the charger, that means you can use MPPT or PWM and also be flexible with 12V or 24V. Solar chargers vary in price and quality a lot. You can connect almost any charger.

Using excess power to make hot water is clever. But to just run a fridge one 200+ Watt solar panel is enough because you have the battery for startup surge. There is little information about a typical power draw pattern from a compressor published. I had to measure this myself: about 150W once it is running. (used a kill-a-watt on 4 "ordinary" fridges)

OperaHouse

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Re: My solar controller project: One Fridge Off The Grid
« Reply #7 on: August 03, 2014, 12:27:35 PM »
If you have real switches, I would suggest using 330 ohm pullup to get rid of the noise.  Internal pullups do not really represent a load.  If that works the resistance could actually be a lot higher.  My chest fridge which I would consider worst case draws 121A from the 12V inverter at startup and 13.4A running.
« Last Edit: August 03, 2014, 12:32:24 PM by OperaHouse »

SolarTrap

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Re: My solar controller project: One Fridge Off The Grid
« Reply #8 on: August 03, 2014, 01:29:37 PM »
I have the same numbers for the compressor  :)
only that in my case they are half the amps because I run the system at 24V