Computing stuff tied to the physical world

Solar at last

In Hardware, News on Oct 20, 2012 at 00:01

As mentioned recently, last step was getting the SMA 5000TL inverter and hooking it up:

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Here’s the before-and-after shot of the hookup:

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Three pulse-counters to help me measure what comes in, what goes out, and the induction stove (measured separately). Still a minor wiring error, but that’ll be fixed soon.

So that’s the end of the story for now. Let the sun shine!

  1. wow, you only have single-phase mains power. Is the wiring error in regards to the solar power coming in after the RCD (protected side)? Seems odd at least to me.

    • Yeah, single phase has always been enough in this house (incoming mains is going through a 35 or 40 Amp fuse).

      The error is that solar is being fed into the RCD while the leftmost new counter is placed after the RCD, so it can have current going either way. They need to reconnect solar to its own RCD and route directly to the central mains switch, so that each counter has current going only one way. Otherwise those pulses are meaningless.

  2. That’s the weirdest looking fusebox I’ve ever seen! I assume that’s normal for the European mainland? I honestly don’t know what I am looking at in most of it! What are the round things? I see they come in big and small flavours. Are they pop-out fuses, or rotary switches?

    I don’t think I’ve ever seen 3 phase to a residential property. Over here on our little island. The main fuse is normally 60amp. At 230-240volt that’s more than enough watts for anyone outside of the Frankenstein family!

    Anyway, good to see it all come together, now you’d better get off to bed or you won’t be awake early enough to be sitting in front of the meter when the sun comes up so you can watch the disk slow down, stop and then reverse :-D

    • The big round things are pop-out fuses, the smaller round things above them are switches to turn off a complete group. These kind off fuse-boxes are a bit old-school but are still around in the Netherlands.

    • The big round things are lead fuses as they were commonly installed up to the 60s of the last century. You have to replace the ceramic cartridge every time one blows. The small round things look like switches to me. I don’t know about the Netherlands, but in Germany, it is quite common to have three phases in a family home.

  3. I’m curious how it works financially. Suppose there was no subsidy (I suspect there was one in NL) – how long would it take to recover the cost of this installation? Just roughly, assuming you keep consuming what you did last year and at current electricity prices. Years? Decades?

    • Break-even point comes after 7 or 8 years, assuming a 7 %/yr energy price increase and unchanged pricing for production (in NL, same price is paid for energy production as for production, so you can treat the net as one huge all-year battery). Subsidies were dropped a few years ago, but this summer there was a one-time bonus which ended up being about 7% off the total price.

  4. Left counter counts net use, middle counter shows solar yield, right counter has cooker usage right? Does the left counter count up and down, or up regardless of direction? If regardless of direction, why is solar counter wired ‘reversed’, as if the utility connection is a load? If left counter goes up and down, I think you can calculate total use: left plus middle. If it only counts up, then left counter should be in pace with Ferraris meter. If it counts up with current going back or forth, you have a wiring oddity with the middle meter… @Tankslappa: the green or white ’round things’ are switches. The ‘eyed’ round things are fuses; eye (supposedly) pops out when blown. Socket base diameter determines max #Amps. Does the inverter act like an RCD too? I can see a circuit fed by the inverter without passing through the RCD, as Stephan already noticed. But then, I’m not an electrician…

    • No up-and-down counting, and that wouldn’t work with the pulse output anyway. See my earlier remarks about the error in the wiring. What I want is three circuits straight into the central mains switch. House + cooker through existing RCD, solar counter wired the other way around due to negative flow, with its own RCD, still to be added. Then all the current flows are unidirectional, and I can do the math.

      These are 2000 pulse/KWh counters, so I’m hoping to get about 6x more detail than with the Ferraris wheel. Haven’t been hooked up yet – looks like these are phototransistors, i.e. polarity matters, but hopefully bounce-free.

  5. Here in DK we use 3-phases in the household extensively for “Power” .. aka. Induction-stowes (Kitchen cooking units) , washing machines , etc.

    It might also be caused by , the wire’ing in the walls are usually rated @10A for normal usage (outlets) , and @16A for “Power/Heat”.

    So if you want to use the oven @300deg , and at the same time boil potatoes & vegetables , you would draw more than 16A , and therefore you’d usually install a 3-phase 3x16A outlet to the cooker. If you use 3-phases for the washing machine , it’s usually just for being able to heat up quicker (faster washing cycle).


  6. Whether or not you have 3-phase power to your house depends on the other energy sources you have available. If you have a natural-gas line and your house is older then 20 years, you will probably have only 1 or 2 phase power to your house. If you don’t have gas, you will probably have a heat pump (like I have), you will have 3 phase power to power that thing. Also it started to be common practice to wire up every new house with 3-phase capabilities somewhere in the 90’s in the Netherlands.

    Furthermore, what you see in the pictures: The big round things are old style fuses that you have to replace when those break, the small round things above them are switches to turn one group on or off, and the rotating switches are (probably) the main switch and the resicual-current-circuit-breaker.

    • Hey! Am I reading this correctly: the RCD needs a trip level of at least 100 mA for these types of transformer-less inverters?

  7. Hmm, more likely 300mA (reaches for Wiring Standards guidelines….) A lot depends on how/where “earth” (tagged PE for Protective Earth) gets defined. Is there a stake in the ground feeding the distribution box?(likely that yellow wire wandering off to the left in its own conduit) Or a strap to the incoming neutral and/or sheathing of the incoming armoured cable?(modern practice, tagged PME)

    Transformerless inverter designs can’t avoid some inherent imbalance which sets a floor on the sensitivity of protecting with an RCD.

    Interesting how different standards evolve for basically the same function. That distribution board would fail U.K. inspection on several points (inadequate cable cross sections, conductor separation, mixed colour codes etc.) though it was not intrinsically unsafe as wired. Partly the medieval Guild mentality – let’s make it seem really hard and have lots of rules so that we protect the livelihoods of Guild members.

  8. I wonder how the RCD works; looks like a brown bus bar to the left and a blue bus bar on the right circumventing the RCD entirely? In the original wiring only the green labeled switches were protected. Now the non-green labeled solar group is also connected. Imho residual electricity can flow from solar to green labeled groups undetected. The PDF only mentions 100 (300?)mA in order to prevent false trippings due to internal resistance of the inverter and capacitance to ground. It does not state a RCD functionality being offered by the inverter?

    • Yep, that’s the wiring error which needs to be fixed.

      The SMA docs that came with the unit do mention a built-in RCD in the inverter, but I’m probably going to ask for a 100 mA unit to be added when that wiring gets redone.

  9. It’s not clear in the first photo, but there doesn’t seem to be a DC breaker in the feed from the PV strings. A failure inside the inverter risks a continuous energy dissipation from the panels with no mechanism for interruption.

    Perhaps a more worthwhile investment than the “missing” RCD which duplicates functionality in the inverter.

    Fun to install after the fact – either have to work “live” or at night ;-)

    • There’s an “Electronic Solar Switch” in the unit: the bulge at the bottom left can be pulled down and removes a long plastic bar, which breaks the DC feed deep inside the unit and prevents arcing when attaching or removing the DC-side plugs. Incoming voltage can be up to 700V, so I suppose this is not a luxury with long strings. Here there are two strings of 5 and two of 6 panels, with a nominal voltage of about 150 and 180V. I’ve seen the unit briefly produce over 2500W, but will probably have to wait until next summer to see what the actual maximum level will be. Cloudy and misty now, drat ;)

  10. Hi, I’m following this blog for a while but rarely post comments as my level in everything you’re talking about is ten steps behind. However I’m so surprised by your picture that I felt obliged to react: your electrical installation looks disco, I mean very 80’s style!! Look at a how it has to be in France: (that’s not mine). Why aren’t these fuses compatible with DIN rails, they are so user-friendly! Why not circuit breakers instead? And by what I can see, no DC breaker?? Installations were very amateurish a few years ago, but everything got very strict since 2010 here, I can send to who’s interested the texts that control new installations now.

    2nd Point, I installed 2 SMA 10000TL inverters at home, they indeed DON’T work with 30mA RCD, don’t keep it or you’ll pass the rest of your life pulling it on again. 100mA (my choice) seems to pass the test, except one or two times a year when weather is extremely humid (but no chance for earth leakage, so what? Air leakage??). 300mA would indeed be perfect, but that’s not 100% safe anymore… BTW, 30mA are compulsive in France in residential houses, so I bought a 30mA RCD just for a few days before being controlled, and I’m selling it now on ebay ;o)

    Sorry for my poor english Chris (official trainer for photovoltaic installers)

    • Yes, its is from end 70’s. Simply has never been upgraded. It works…

      Thx for the note on RCD’s. My proposal to the electrician will be to simply hook it up without RCD, since there is one built-in. But it’s his decision.

  11. Sorry JCW … what type of pulse-counters is here ? maybe i cam put on my SMA inverter. Thanks

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