Solar power/fuel generator + arduino

[atomix1040]

Well my dad bought a house far away form any civilization. No power, so i got him some solar panels, a battery and a solar charger, he also has a power generator (diesel). Now i'd like to make some kind of control panel, simple enough for an average joe (no mad skillz, just some basic on/off, he is over 60 and my mother will probably want to control it).

Solar source is 12V the generator is 220V but i can easily buy a nice encased AC-DC converter that will give me 12V from the generator. So the assumption is that i have two 12V power sources.

The idea is to have Arduino connected to both power sources (solar and fuel), and have i think 3 operating modes.
- automatic, arduino decides witch power source to pass through based on the voltage levels (two voltage meters with resistor voltage dividers and a relay on output to switch the lines)
- manual, you tell arduino witch power source to use
- off, arduino cuts off power to the house, and just waits or gets turned off, this mode might also include a raspberry PI that starts to monitor some cameras for security (off means everybody is out of the house, watch for intruders)

Theese are my assumptions. Some questions i have:
- if the relay circuit, how do i switch between two power sources each 12VDC, what about ground connectivity etc, i saw a project where someone turns 220V lights on/off but that's one power source
- how much juice will arduino take on it's own doing what's it doing, power usage is very important here
- is the idea a good one anyway ? maybe there are better one for this situation.
- i don't know much about power generators, the one my dad has (i consider buying a new one and this question will help in that case) is turned on using a button (no cord to pull), i'd like to connect that button to the panel/arduino, though i don't know how does that work (if at all)

Any advice links, docs are welcome, i'm a serious newbie but want to help my parents. I need to make it as user friendly as possible

Thank you.

[Tumbleweed]

atom,
Well actually your battery should power your 12v cicuits, your solar controller will keep the battery charged as well as it can, then you just sense when your battery gets below 50% State Of Charge to determine if the generator needs to run. A 3-stage RV converter will be the most economical charger for long term running, but you maybe could find a heavy duty charger elsewhere that will "pump" more in faster. No need to disconnect one when charging with the other.
Actually, voltage measurement is a very poor way to determine battery SOC, total amp hours in and amp hours out of the battery will tell you a lot more accurately, check out Hall Effect sensors or "shunts" for the Arduino.
It sounds like all of you need a lot of education on solar power and "off grid" living, check out these forums
http://www.solarpaneltalk.com/index.php
http://www.wind-sun.com/ForumVB/index.php
or Google for sites
Here,  for some easy to understand info http://handybobsolar.wordpress.com/the-rv-battery-charging-puzzle-2/
Didn't mean to be condescending, but after 40+ years in electrical and electronics, I was amazed at how wrong I was about a lot of solar info, and how little I actually knew.
Your brain will hurt! There is a lot of info out there, make sure it is right by double checking as many places as you can. Some sites are only interested in selling their stuff, others have no actual knowledge of electronics, some both.
Spend a little more for reliable equipment, you'll never be sorry.

[atomix1040]

Well for the solar charger controller i was considering:
http://www.stecasolar.com/index.php?Steca_PR_10_30_en

It seems like a good choice, it's not a cheap chineese crap you can buy.

I know that the controller will keep the battery running as best as it can, but once it's depleted it will disconnect the load cicuit, and this is when arduino should kick in and switch to the generator (that's my idea). I know there might be some time between the switch (the generator needs to start and it might take a few seconds) but that's ok. Now arduino should also know when the battery is ready and switch back to it, and disengage the generator. I know i need to read a lot about charge levels of the battery, i don't know how to deal with that.

I can't switch back to the battery as soon as the charge controller re-connects the load circuit, since it will discharge very quickly, i'd need to know if the battery is charged at a certain level (let's say 75%) so that when switching to it, it will work on the battery for a significant amount of time.

[gardner]

What are the loads you want to run on this system?

One of the key components of my off-grid setup is an inverter-charger with an automatic transfer switch.  This is wired into the building wiring.  When the generator runs, the loads are switched automatically to the generator.  As long as the generator is running my batteries are charged through a 20A 3-stage charger.  I recommend getting one of these.

With all this in place, the only thing you need to program is when to run the generator, which could a function of the battery state-of-charge.  To a first approximation, it is possible to estimate the state of charge of a lead acid battery if you know the cell voltage, current draw, battery capacity and temperature.

[Tumbleweed]

Atom,
OK, first, your loads to the house do not go through the solar charge controller, that load circuit is only for extra loads that are needed to keep wind generators from spinning to fast when the controller disconnects from the full battery, or diverting extra solar power to a w/h or other resistance load to use up "extra" current when the batteries are full. As I read it you have no wind generator, you would need a separate controller for one anyway.
Also, you made no mention of an inverter, just 12V loads in the house, which can be done, but are you?
An inverter is a whole other set of requirements, you are really getting into a lot of design now.
As gardner said an A/C transfer switch will be required then. There are inverter/chargers out there http://www.xantrex.com/power-products/inverter-chargers/overview.aspx for example, that have built in transfer switches, some even have auto start circuits for the generator, and charge the batteries automatically too.
Got to say, that little 30 amp charge controller isn't going to be near enough (and <400 watts of panels it is capable of running) to charge a whole house  system running off of a large inverter, needing >500 AH of 48V batteries, ect.
Check out the "Off Grid" sections of those forums I gave you, read books on solar designhttp://www.amazon.com/s/ref=nb_sb_noss_1?url=search-alias%3Dstripbooks&field-keywords=Solar+system+design, get ready to spend $$$$.
As I said, lots to learn.  Many sites out there that will show you solar is not a cost effective way to supply power to a house UNLESS you are miles away from the grid, which you said you were. Personally, I think the independence is worth it, just can't talk DW into spending $10,000. She'll be sorry when the giant solar flare wipes out all electric grids on Dec 21, or was that the magnectic poles will shift. The sky is falling, the sky is falling!!
TomJ

[atomix1040]

I got my parents an inverter once, but it was a cheap (about 100$) unit, it has two 220V sockets and a 12V input, don't remember how much power it could take.

As for the load for the house, i think that about the same as a RV, i was reading this article http://handybobsolar.wordpress.com/the-rv-battery-charging-puzzle-2/ (great source of information) and i think the a large RV would take the same load. For start i think 4 light sources for 4 rooms, a small fridge and a TV.

That said, i though about supplying just the 12V without the inverter, but now that i have read all the info i think that the inverter is a "normal" situation (i thought that those devices were very power hungry and it would be a big waste to use them).

So my plans have changed now:
The solar charger would be recommended by the author of the article a MorningStart TriStar: http://www.oeko-energie.de/shop1/product_info.php?info=p861_morningstar-tristar-mppt-12---48-v-60a-solarladeregler.html
I think some kind of meter is a good idea (need to find one close to Poland) one of those: http://bogartengineering.com/products/TriMetric
Some good batteries, i was under the impression that GEL batteries were better, but after reading the article it seems better to get the liquid (acid?) based ones. I need to find some good ones in my region too (most of the products mentioned there are either not available or double priced in Poland, for ex. the TriStart costs 140$ in poland it's about 300$, i'm trying to get one from Germany it will be still cheaper).
Now the inverter, i don't know of any manufacturers or properties a good inverter should have, what are the parameters to look for ?

But the arduino role is important, since the power generator will be there, so now i think arduino should switch those power sources anyway (maybe not?)

I was looking the all in one Xantrex devices they look great as it's a complete solution, but it's expensive, but the question is, is it worth it ? Also i was wondering what other manufacturers are available, Xantrex is hard to get from what i see in Poland, maybe there are some European companies that make similar devices ?

[gardner]

For a complete off-grid setup, you're going to spend some money alright.

It is more efficient to run 12V loads directly, if you have 12V compatible things to run.  But there will be lots of things that are just not convenient or exhorbidently expensive in 12V form.  For example CFL lighting for mains voltage is practically free.  For 12V,  CFLs are hugely expensive where they are available at all.  If lighting is a significant part of your requirement, use an inverter to power fluorescent lighting.

Another downside to 12V loads is that you might find you want to run the DC charge and inverter circuits at 24V or 36V, and then 12V loads are just not compatible at all.

I would really be leery of running a fridge from off-grid electricity.  My fridge is LPG.  They cost a bit, but they work great and no electricity at all is needed.

Definitely go with flooded lead acid batteries.  Gel and AGM are great and all, but for a large capacity stationary application, they are not cost effective.  Also do not get automotive cranking batteries, as they cannot handle deep discharge and do not have the Ah capacity of a "traction" battery.  Cranking batteries will not last.

[atomix1040]

Well i got some good 12V based lighting, led based bulbs with a wide angle do the trick i think. There are many choices now for 12V lighting in my local hardware store.

I'm more worried about other stuff like TV, power tools, fridge, water pump (did i mention no running water only a well outside the house ?)

[atomix1040]

Is it possible (or is it a good idea) to distribute 12V DC over cabling that's been prepared for 220V AC. I'm worried that the voltage drop will be much to high with 12V DC. I'm asking cause the house already has 220V cabling with sockets and light switches, and using 12V DC would either require me to re-cable or use the existing infrastructure. I just don't know if it's possible.

I still will need the arduino to switch the power source from the generator to the batteries, the all-in-one solutions that do that are too expensive. I found some products that do just that, but they are ATMel based switches that cost a lot, i can easily do that with Arduino i think.

[majenko]

Is it possible (or is it a good idea) to distribute 12V DC over cabling that's been prepared for 220V AC. I'm worried that the voltage drop will be much to high with 12V DC. I'm asking cause the house already has 220V cabling with sockets and light switches, and using 12V DC would either require me to re-cable or use the existing infrastructure. I just don't know if it's possible.

I still will need the arduino to switch the power source from the generator to the batteries, the all-in-one solutions that do that are too expensive. I found some products that do just that, but they are ATMel based switches that cost a lot, i can easily do that with Arduino i think.

You have to remember that current, voltage and power are all interrelated.  Change the voltage, and the current will change for the same power.

For example, a 5A load at 220V:

P=VI = 220*5 = 1100W.

Drop that to 12V, and keep the 1100W:

I=P/V = 1100/12 = 91.66667A.

It's not just the losses (yes, they will be 18 times more), but it's also the heat.

91 amps pumped through cables designed for no more than say 20A will get rather warm - and melt.

Barbecue anyone?

You WILL have to re-wire for 12V.

[michael_x]

You WILL have to re-wire for 12V.

...if you need > 200W power.

Our house wiring (230V) uses 1.5 mm² and 16A fuses, so I'd set my limit to rather less than majenko's 20 A per wire.
If you just want to power a 12V TV and eventually 3 * 20W halogen bulbs on one wire, I don't see a problem.

With 2.5 mm² wiring, your limit might be higher, but a water pump or your "Power Tools" (?) running at 12 V might be something different.
Also check the switches for their current rating.

Perhaps you feed the battery power into your existing 16A wiring, but have a more powerful 220V supply by your generator, if you temporarily need more power ?

Or the generator feeds 220V into that existing circuit, and you add a separate 12V wiring ( with different plugs and outlets, of course )