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Jeremie Francois
Works at TecRD
Attended UTC, France
Lives in Montpellier
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Jeremie Francois

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A very interesting SAMD21 (32bit, 48MHz) super minimalist board for 25€ shipped worldwide, by +Albert van Dalen. I shall get a few of them for both pro & hobby uses, as they are probably one of the finest options out there!
(via +Jean-Luc Aufranc)
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Jeremie Francois

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Incredible & condensed stuff to know for solar + batteries setups (below, not my own stuff here!!).
Ours is differing mostly because we have no batteries... yet. I.E., we are still attached to the grid. When deep-cycle batteries become cheap enough, we will probably jump, and add another set of panels.

For now we have 12x 260 watts solar panels, equipped with individual enphase microinverters (this is more expensive than one big and hardly extensible inverted, but it gives better results (b/c/ they optimize each panel individually), and/so we can spread the arrays and flatten the production through the day (~16+kWh). Check my previous post on the matter:

Then, a raspberry remote-controls the heaters thanks to a few sonoff wifi switches (see The active heater combination are chosen to make the best of the actual production, which I read directly on the (crappy) tiny page that the enphase "central" broadcasts on the local network. As the latter updates the production only every 5 minutes, I plan to bypass it completely by reading the current closer to the solar panels (with some Arduino and a RF link, contrary to the existing powerline networking). Right now, the enphase "envoy" gives useless values for sunny days with scattered clouds.

For now I only can switch between 4 levels because of our various heaters. So I am considering using PWM on one heater at least so as to optimize the production. I also have to redo the water heater (e.g. for this role): for now it runs on a standalone bluetooth controller (!), which behaves better and cheaper than the former "industrial" day/nigh 80+€ controllers that kept on dying every two years!

All this stuff is incredibly cool to control :)
Well, I mean, warm.
Lessons and Tips I have Learnt on my Solar Installation

Some lessons I have learnt over the last year after having to replace one or two components are:

1. Save now, and you will replace later. Also you need to decide if you want a full system to power everything, or just want something to power the lights and some essential equipment.

2. Try go for 24V as it is more efficient, and cheaper cabling too. So buy batteries in pairs so that you can create a 24V system.

3. If you want remote management, make sure what system each device can report to. It won’t help buying one Victron inverter but using an Ellies solar charge controller as you will have to go to two or three places to look at what is happening.

4. The heart is the batteries:
a. You only get to use 50% of the stated capacity as you cannot run the batteries down to below 50% - so a 300Ah battery capacity is going to give you 150Ah of real use.
b. Work out what you want to power – the max load (peak) at any time, will determine what size inverter you need. The total amount of power used during the night for everything with some spare left, will determine what capacity of batteries you need.
c. Lead acid is fine for backup or UPS functionality, but if you intend to cycle the batteries down to 50% daily, you will need better batteries. It will be deep discharge batteries needed.
d. You can wire batteries in serial and parallel to get your 24V and enough capacity – but total capacity is is determined by the total number of batteries you buy.
e. You are not supposed to mix different capacities, brands, and old/new batteries, otherwise you stand to kill your newer batteries. So try buy the right number to start with.
f. Don’t connect the inverter and solar charge controller all to a single battery's terminals. Connect their negative to one battery, and connect their positive to a battery on the other end of a parallel setup – this spreads the load more evenly across a parallel setup.

5. Solar panels can also be wired in parallel to get more current, and with a 24V system you can even put them in serial to get 24V. You need to buy enough so that it can run your daytime usage (normal current used for a sunshine day, plus to charge your batteries. So four 120W panels are charging my 300Ah batteries and running other stuff in the day. But 600Ah batteries will likely require 8 panels. Obviously and extra panel or two is going to help for overcast days.

6. On the solar charge controller (this regulates the power from the solar panels to be safe for the system and the batteries):
a. Luckily they often are dual 12/24V output so you only have to consider their maximum Amps and Volts they will handle, and the type of controller.
b. Maximum Amps will determine how many solar panels you can add to it (look at maximum output of the panels eg. mine are about 6Amps per panel.
c. Maximum Voltage input is important because it also determines how many panels you can connect in serial (as the Voltage is higher, which is more efficient and cheaper cabling again).
d. The PWM controllers are cheaper, but are also slower to respond to partly cloudy weather so you lose efficiency. The MPPT controllers cost more but are much faster and more efficient (and recommended that you wire the panels in a 24V configuration for MPPT controllers, as they will start charging quicker in the mornings).

7. On the inverter (converts your battery voltage to 220V) they are often a set input voltage (12V or 24V) so your battery setup helps determine this choice and then you stick with it unless you want to replace the inverter later on. But consider also:
a. Continuous power rating (in Watts) – this is the constant load it will support. In my house the LED lighting, a pond pump, lounge TV, a computer, and the Internet modem and router all draw about 300 Watts at 220V. But kettles, geysers, etc are going to be at least 2kW each and remember they can run together. Someone did say that electricity is not the best way to cook and heat – and gas may actually be better for them, which lowers the cost of your solar system.
b. Their peak power rating (this handles short spikes like for a fridge motor switching on – if not high enough, a fridge will trip your system). So often you will see 600/1200 as a spec which implies 600Watts continuous power and short peaks of 1200 Watts can be handled.
c. You get standard inverters (just invert the power to 220V) and you get inverter/chargers (where the latter will also supply 220V to charge the batteries on say cloudy days, and they will often also act as automatic UPSs where they will switch to batteries if the grid power is off, or vice versa. It all depends on the battery type and how the inverter/charger can be setup and programmed so it is worth discussing these expectations to be sure of what is possible.

8. Wiring:
a. You do need a registered electrician for any 220V that connects to the house. And get an electrician who has experience with solar as from the above, you will appreciate their are nuances over and above what an electrician knows about 110/220V systems.
b. You do want a separate distribution board installed so that any circuits running from the inverter, are separate from any direct Eskom fed 200V circuits.
c. If you are mixing grid and Inverter power, you may find that some of your plugs and lights share common negative, and these will need to be separated by the electrician.
d. You do need to have fuse/isolator switches fitted to isolate power from the solar panels, from batteries, from inverter, and also for any power going into the sub-DB.
e. There is also usually a switch fitted to select between inverter and grid power supplying the new sub-DB so that if there is any fault on your solar setup, you can switch to just using normal grid power to those circuits.

9. Management: With systems like the Victron you also need something like a Color Control GX (CCGX), which is essentially small Linux computer with a status display – it pulls the data together and transmits the data to Victron’s cloud (where you can monitor it remotely or have alarms sent to you). Some of the individual devices will connect via Bluetooth devices but a single central monitor is better.

I hope these tips will help newbies before they start out, to ask the correct questions when planning a system. If anyone else has additional tips, or corrections, please add them in the comments.

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48 comments on original post
Michael Gebetsroither's profile photoJeremie Francois's profile photo
+Michael Gebetsroither wow I will have to re-read the figures... The switch may come earlier than I thought :)
For some time I somehow eyed second-hand EV batteries, but they are hard to find. I have space in my attic for less-than stellar batteries. Destroying lead-acid batteries because I discharge them too much is probably impossible with a proper controller anyway, but I do want a long life indeed ;)
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Jeremie Francois

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Heh learning everyday: what are these ubiquitous, funny-looking, round windows on ships? Spoiler: some are rotating as fast as 1500 rpm (!).
This is one of the (few) interesting things I knew existed but that I never asked about myself enough [the order of the words is important here: there are certainly (exceedingly many) interesting things I am not aware of at all]. May be I could start a specific "random knowledge" collection :)
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Jeremie Francois

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Variations of particles in a vector field. The (now) usual idea is to illustrate winds dynamically, according to actual weather data and better than with ugly arrows. Pretty easy to make (I am an old demomaker so it is just awesome to be paid for this kind of work!). It is barely slightly harder to optimize and make it pretty. The movement of the second picture is extremely soothing, while the first one draws an interesting map of the Earth. this is due to the fact that low altitude winds are significantly slower on earth than on oceans, hence the shorelines often show up. The background colors shades are the wind speeds.
I cannot wait to see this being used on my client's own maps (which is the most satisfying part of the work to me!).
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Jeremie Francois

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I was a backer of the first OpenMV camera ( It can easily be programmed in micropython with a nice IDE, but it is a tad slow, and barely usable for real-time analysis (imho). Even though the latest model is an improvement over the first version, I will not buy it because there is a killer one on kickstarter right now: the exceedingly tiny $49 QuadCore 1.3GHz JeVois camera. The specs are much, much better on all points of comparison and it is even $15 cheaper! It also embeds a full little linux OS (that boots in 5 seconds), and it comes with a serious and functional set of algorithms in C++, made by, and used by scientists. The video seems to prove how smooth real-time analysis can run:
I just hope they will not fail on the production, as it often happens on kickstarter. Note that it is already funded and 17 days are left.
NB: it is obviously a French guy... but working in Los Angeles, sigh. Our country really has issues keeping smart people :'(
Open-source quad-core camera effortlessly adds powerful machine vision to all your PC/Arduino/Raspberry Pi projects
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Jeremie Francois

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For some reason artistically hand-drawn stuff always appeal to me :) Check, e.g. GreatScott! on YouTube for electronics, and you will understand what I mean. Is it only because it stands out? Or more work on the presentation means better selection on the details? 
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Jeremie Francois

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April fool before the day? YES, after 6+ years of jail (only because s/he revealed some serious abuses by the state), he should be released free! :) This is ridiculous nonetheless, that presidents may have opportunities and free hands to do this, and that they do it only on their last days. What kind of justice is this when whistle-blowers get jails without a proper (public/regular/non-militray) trial, a proper sentence (no parole), and being able to get freed by one person afterwards ... three decades early?!!
I wish Snowden is next, even though but he might want to wait a bit before returning to the USA anyway... At least he could stop risking being extradited by allies and start having a life again (
Oh and there is Assange btw.
And there are a few prisons to close (as expected, eh?), namely those that were settled outside of the public territory (how?! I ever wished I knew the kind of super-ugly deal there are with the hosting countries... They ought to be illegal by the most basic international human right standards).
Free but limited time to clean some year-long mess? Amazing country :(

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There was an article on one of the news orgs which kind of explained the diffs to Mannings vs Snowdens release of info, the kind of info, and then the subsequent surrender/trial/sentencing/imprisonment which they indicated why snowden isn't likely to get clemancy from obama since he fled to an advesary who then that country is suspected to have manipulated the last election.

Personally I find it more appalling that there were plenty of "tax evaders" and other rich people found guilty of white collar crimes, and then given pardons, vs those who were perhaps wrongfully railroaded by a penal system to oppress minorities in a greater number than white counterparts.

but yes its all a bit absurd.
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Jeremie Francois

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Actually I find it pretty hard to find palettes anymore because the good ones are all re-used or recycled. It used to be a good source for building furniture imho also. And well, it was super heavily treated against the elements, as most of the wooden electric poles and public fences are: chrome + copper + arsenic afaik. This became illegal years ago for obvious reasons and they now no more last as much outdoors :/
Peter van der Walt's profile photoJeremie Francois's profile photo
The support structures are 12 year old, and they start to crumble only now (too bad, I liked the benches a lot). Only the table itself was made out of pine, and I had to replace it twice (we have nasty cycles of freezing/heating in winter).
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Jeremie Francois

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In my experience, normal people will simply never cope with the markdown syntax. In fact I dislike it also: the "nonstandard" one from dokuwiki is more readable, more consistent and easier to remember imho (check how to do italic, underline etc...
So how could we make their life easier? The little tool below is a nice little wysiwyg-otrsots editor, where "otrsots" stands for "on the right side of the screen" ;)
It is very light and sleek but it still too big for my needs right now though (I wish to have a basic support with a few Kb only and without libraries).
cc +Luc Yriarte
Pat Cummings's profile photoJeremie Francois's profile photo
BTW you made me realize that "vorpal" sword comes from his poem! :)
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I think we have set our optimal real-life production goal yesterday for winter (this is an array of 4 groups of 3 x 260Wmax hi quality solar panels with individual enphase micro inverters). This curve will be a reference for any subsequent hack. Most importantly, my homemade support structures allow for seasonal setting (i.e. the panels have an horizontal axis of rotation -- something which would be impossible on a roof). I did not try to add a vertical axis of rotation to track the sun through the day as it would have been complex and probably not that useful: in winter, the sun mostly stays low on the horizon and it has a shorter path (we are 43° latitude). In summer we have more than needed anyway.
One thing to stress out is that we are not selling our production, and it changes what is "best" for us. Instead of trying to maximize the overall quantity of energy throughout the year we try to "flatten the curve", i.e. get the maximum average production throughout each day, including in winter.

So I do not think we can get much better than this (see how fast it raises on the morning!). I positioned each of the four groups of solar panels on a slight (vertical) curve so as to get more energy on the mornings and on the evenings (and it is prettier imho).

We do not care much about the (mostly useless) peak at noon, even though it is always hard no to consider it as a goal. In the latter case, a flat array would get "better" results, but it would take more time to catch energy on the remaining of the day.
electrodacus's profile photoJeremie Francois's profile photo
+electrodacus great info, thanks!
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Jeremie Francois

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Until today I forgot about this excellent calculator that I used years ago (Debian 4?). I just tried in vain to install it or to compile it again on a recent linux distribution. QT makes it horrible in my opinion together with the qmake ecosystem: with time, I think it kills old projects like these. Also, things might have been better if the project was hosted on github instead of the ad-bloated sourceforge, for others developers to fork and keep the project alive more easily :/

BTW: interesting story on the bad moves Sourceforge did, before it was bought again by another company. As they say, there is a long way for them to regain what they lost due to greedy malvertising though with the former owner.
Extcalc Description · Concalc Description · Screenshots · Features · Sourceforge · Download · Binaries · Extcalc Documentation · Concalc Documentation · Examples · Contact. The calculation window of Extcalc The graphics window of Extcalc 3D-Graphics in fullscreen mode. Tables window of Extcalc
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Seems this one could do the job, but it is way more than a calculator (i.e. I would better stick to octave or scilab). - Genius Mathematics Tool and the GEL Language

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Jeremie's Collections
An open-minded technophilic iconoclast driven by curiosity.
If you know me and you cannot tell exactly what my real job is, then you probably found the right Jeremie. Check for some pointers.

I am self-employed and I help start-ups, research centers, small companies with their needs related to computers, sensors, data processing and mechatronics. If you have a project and know what "R&D" is, then you already sparked my interest ;)
Bragging rights
Coded an award-winning pinball game on palm. Published R&D papers in IEEE. Drove my motorbike deep into Sahara sands and in freezing Iceland. Wrote a popular blog by chance (featured in wired and hackaday!). Swam in a warm volcano lake. Kept all my friends so far.
  • UTC, France
    computer science, 2000
    PhD + engineering degree
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Whatever I can that I did not try yet!
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  • TecRD
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