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Choosing the system
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When I was deciding what home automation to choose I knew almost nothing. Every seller recommended their own solution. Home construction exhibitions present a lot but it is hard to find out what is hidden behind the scenes of the offered systems. Despite all of that my half-blind decision about buying a PLC controller and adjusting all the electrical installations to its requirements turned out to be the right one. During last 5 years of using, testing, rebuilding and extending I have not regretted my choice even once. Here are the reasons:
Price – a starter kit from WAGO comprised of the PLC, 2 in/out modules, software, charger and service cable can be bought by some EUR 600-800. 8x in or out modules cost some EUR 80 . For a medium house one needs to read impulses from c.a. 40 inputs and control 40 circuits (lights/sockets/blinds), the whole system should cost some EUR 1500 - 2000.
You, obviously, need to add the costs of the wiring. All outs (lights, socets) are connected just like in normal installations. The only difference is that they all are laid so that they meet in one place. The additional cost is therefore related to the additional wires length. If you assume some 500m of additional wires, you can count with some EUR 250. When it comes to the needed workload, it should be comparable with the traditional installation. Instead of crossing the wires in small boxes in the wall (and preparing them) the electrician just needs to roll out all the wires to one place. The wires to 'ins', i.e. those which connect the PLC with wall-mounted switches might be a source of savings. They are not the traditional YDY but Ethernet cables, which are significantly cheaper. You should, therefore, off-set additional lengths with lower costs. Especially that you do not need to care much about the quality of the cable. There will be no real 'transmission' going through them, just closing some circuits.
You will, obviously, need to calculate the costs of the central junction cabinet. EUR 500 should be enough to buy a big unit. An additional EUR 150 should be sufficient to buy all the internal wires. Please, however, compare wisely. Any automation system requires a central junction cabinet and internal wiring.
The attractiveness of a PLC-based home automation is most visible when the wall-mounted switches are considered. Any simple switch, which closes a circuit will suffice. In my house I used elements of the Hager Polo system, with mechanisms costing EUR 7/each. A mechanism of a better switch (multi-key of Berker) costs EUR 10. You need to add the costs of the frames and keys, but still you will not go much over EUR 15/piece. On the other side a cheapest EIB switch costs EUR 100/piece, the nicer one start at EUR 300. Do your own math. You need to buy a bucket-full of switches to fill your new house...
ATTENTION! The above-presented calculations can be underestimated. If the house is big, the electricians demand a high price for laying all the wires, you do not manage to buy the cables at good price and take a service company to do all the wiring in the central cabinet - all the cost migh increase. Everyone must make their own calculation for each individual case.
Reliability – I happened to do all the worst things to my PLC: I crossed wrong wires, unplugged modules without disconnecting the current. The power collapsed many times at many occasions. I also managed to stick in a powered wire into one of the modules and short-circuit the whole installation. The PLC still runs as new and never, NEVER hanged up on its own. I would like to emphasize this advantage of a PLC. I have heard many times fears of those afraid of core meltdowns and machine revolution, which would close a hose with people inside. The PLC controllers are made for industrial or naval uses where a consequence of a malfunction are grieve and costly. They must not break and they do not break. They work for a dozen of years in dust, heat and vibrations, because that is what they are made to withstand. I have nothing against some smaller-scale solutions offered by small companies. I personally have a lot of admiration that they are able to design and sell their own devices. I am even convinced that such systems are reliable enough for being used at home. If, however, we analyze reliability as such - PLC play in a totally different league.
Simplicity of programming - having no experience in coding PLC I managed to code all the needed functions in quite a short time. I know that others have similar experiences. One of the factors supporting a choice of a WAGO controllers is that they use CoDeSys, which in turn allows to code in many languages, one of which being Structured Text. ST is similar to many other languages like PHP, Javascript etc., it understands loops and conditions. There are also many libraries available, as well as application notes and examples. All of your most sophisticated ideas or actions related to 30+ conditions can be coded with ease.
Multitude of usages – a network controller, besides controlling lights, blinds, heating, garden and gates... it communicates with the outer world. It collects data, stores them in the memory, sends via FTP or to SQL. It can send emails, fetch weather forecast from web. It is a NETWORK controller and can do everything that a desktop computer can. That is really a lot! It can be connected to everything that is able to communicate with the outer world. It might be an alarm system, gate engine, recuperator, solar heating system, another computer, etc. It can also substitute all of such sub-systems.
Easiness of self-construction - it might not be important to everybody, but it is worth emphasizing that a PLC-based automation is structurally easy and transparent. The rules of connecting elements and coding are easy to understand. An average man with a bit of curiosity will be able to do something on their own. It might be a great adventure ;)