Low-Voltage DC Network Build Incited By Solar Panels

Breakers for the system on a DIN rail, with markings like 48V and 24V and 12V and so on on the bottom, and two hefty devices of some kind on the bottom, probably MPTT controllers, with hefty wires running from them.

Nowadays, some people in Europe worry about energy prices climbing, and even if all the related problems disappear overnight, we’ll no doubt be seeing some amounts of price increase. As a hacker, you’re in a good position to evaluate the energy consuming devices at your home, and maybe even do something about them. Well, [Peter] put some solar panels on his roof, but couldn’t quite figure out a decent way to legally tie them into the public grid or at least his flat’s 220V network. Naturally, a good solution was to create an independent low-voltage DC network in parallel and put a bunch of devices on it instead!

He went with 48V, since it’s a voltage that’s high enough to be efficient, easy to get equipment like DC-DCs for, safe when it comes to legal matters concerned, and overall compatible with his solar panel setup. Since then, he’s been putting devices like laptops, chargers and lamps onto the DC rail instead of having them be plugged in, and his home infrastructure, which includes a rack full of Raspberry Pi boards, has been quite content running 24/7 from the 48V rail. There’s a backup PSU from regular AC in case of overcast weather, and in case of grid power failures, two hefty LiFePO4 accumulators will run all the 48V-connected appliances for up to two and a half days.

The setup has produced and consumed 115kWh within the first two months – a hefty contribution to a hacker’s energy independence project, and there’s enough specifics in the blog post for all your inspiration needs. This project is a reminder that low-voltage DC network projects are a decent choice on a local scale – we’ve seen quite viable proof-of-concept projects done at hackercamps, but you can just build a small DC UPS if you’re only looking to dip your feet in. Perhaps, soon we’ll figure out a wall socket for such networks, too.

50 thoughts on “Low-Voltage DC Network Build Incited By Solar Panels

    1. I was thinking of running some HP DL360 servers at home via solar/battery setup without the inefficiency of DC-AC inverters by using the 48VDC power supplies that suit those servers – but then I saw the price of those 48VDC power supplies …. OMG. ROI well into 2050!

  1. Nice. Only bummer to a setup like this (assuming its significant other approved and situated safely away from pets and children) is once their local energy stores are full the excess is wasted, which when you are so so close to a grid that an interconnect is rather cheaply possible is a real shame. Not that I am blaming them for that situation, they have already done a good job for themselves and can’t magic up legal/safe/affordable ways to solve that one last hurdle… Bureaucrats are perhaps even lower forms of life than lawyers and politicians, though they do all so often resemble each other through their lives perhaps they are all the different states of the same lifeform…

    I will say that to make life simpler on the DC side for the non-techie folks you may co-habitate with or provide support for the best options these days is probably USB power… Much as I hate to say it as USB power delivery is a mess, that seems like a massive pain to implement properly, and is very very unlikely to be nearly as efficient as a 48v rail. Its just so ubiquitous and something the non-techie understands – as it is plug in and it works (if you set it up right). Avoiding the need to find the right DC-DC converter for everything or to actively control the ‘PSU’ voltage before plugging in a new device each time – I do that on my desk and haven’t fried anything yet…

    But as off the shelf battery packs that have solar tracking inputs, and maybe even an inverter for that AC device you/they must have AND the USB power are available if you wish to avoid the effort of making your own, doing that more annoying USB power negotiation stuff for you it doesn’t need to be hard to set up. Plus there is still more than enough work for the hacker in us all getting the solar cells mounted (ideally on sun tracking mounts), providing the status monitor, low battery alarms and sorting out the cable runs neatly to the essential locations that its only cheating a little bit…

    1. A good solution for excess energy is a dump load, like an electric element in your water heater. Once the batteries are fully charged, switch over to heating the water with the available solar generation.

        1. The advantage of solar is that you don’t need to harvest the solar energy. You can safely leave the panels in the sun and don’t use the potential energy.

          Offcourse, this is wasteful and injection of that energey to the grid is prefered if it is of any advantage to you.

      1. As CityZen says it will get filled eventually, its just another form of energy store. Not to mention if you already live somewhere hot you are then making your AC work harder if you have it and you life more unpleasant than needed if not as the tank can only ever be so insulated… Water does make a very good energy store, but most households really don’t need that much hot water, and the bigger a single tank setup is means that when you don’t have excess energy you still have huge volumes of water to heat sufficiently for use through the higher energy losses caused by its huge surface area.

        There really isn’t a good ‘dump load’ at individual scale, a big grid with major industry can easily run some extra shifts and ramp up production beyond demand to make some use of the ‘free’ energy. But for the individual really its just an excuse to play it loud and rock around the clock, being carefree with energy use while it lasts or until the neighbors kill you.

          1. You could also run a small room air conditioning unit with an inverter if you really have a lot of excess power to dump and it’s hot. Maybe with the inverter outside…
            It’d be really interesting to see if it’s possible to DIY a heat pump that uses outside air as the thermal source/sink. Sure, it’s really inefficient, but if your problem is too much energy, inefficiency is almost a help.

          2. @smellsofbikes Just because you could build something inefficiently because you sometimes have too much energy doesn’t mean you ever should. What happens when you don’t have too much energy right now but still need that really inefficient process done? Same as in my giant water tank example above you have to find a sensible balance so the important/useful stuff can get done when you are in the doldrums as well as when you have so much energy you could power a heavy metal concert…

            When you can’t send it away for money or why not even give it away for free**? Then the the excess you could generate is just that ‘could’ a potential you didn’t use, its not the end of the world really, just a shame.

            **Assuming it doesn’t actively cost you anything to do so – which seriously is a problem here the ‘standing charge’ to be grid connected is quite substantial so even though you don’t use much being connected may cost you more than they bloody pay you for the excess you ship them – not that I am opposed to giving away the excess, it will be useful to somebody on this giant grid and I don’t have any need for it. BUT to PAY a company so very much for the privilege of earning them even more money from somebody else…

  2. I’ve been considering something like this for 5v, as USB powered devices have become more ubiquitous. Better yet would be some 5v and some variable voltage USB C ports. From there, you can use the 5v for low power devices and the USB C for higher power demand devices. The downside is that the USB C ports would have to handle voltage on a per-port basis, where the USB A 5v would just be a simple 5v bus.

    If nothing else, I’ll almost certainly eventually setup an office with a 5v USB power network. And I might do a 12v one as well, because my electronics projects that need more than 5v almost always need 12v. (Also, I’m pretty sure every router I own uses 12v, and just having simple custom wall plugs instead of a wall wart transformer for every single device would be extremely nice!)

    1. I’m sorry to be the one telling you, but 5V (even 12V), is not good for power distribution: loss along the cable after just a meter or two are within 10% or more, not really usable.
      Cars have been struggling with 12V but can cope with as they are small, but truck and big boat use 24V for this reason, and yes, 48V is the best value: still a safe range rating as long as you dont lick it, standard voltage, plenty of devices, and can be transported to some length without much loss.

      1. The power conversion losses are more important than the cable losses. For instance, in the article’s case if we assume that each DC/DC conversion ins 90% efficient, what you get out of the 5 Volt USB charger at the end has lost 27% of the power. If the converters are slightly worse at 85% then the loss is a whopping 39%. It’s very typical that charge controllers and converters only achieve around 80% efficiency in practice, so it’s quite common to lose up to half of the energy just for regulating the voltages. If the system has low demand, the idling losses of the equipment can consume nearly all the power.

          1. Except for the standby losses at the converters.

            If you have two dozen USB ports ready to deliver 5 Watts each, you need a 120 Watt power supply. If that power supply has a constant 10 Watt baseline load, its nominal “efficiency” is 92% at the specified load, but when your USB port utilization is about 5% on average, the overall real efficiency of the system is roughly 60%.

            More than 1/3 of the energy is lost simply to idle the power converters.

    2. Anything below maybe 36v absolute minimum should never be run long distance. Especially not 5v. Power adapters are so cheap, and copper is expensive and heavy. Batteries are also expensive and power loss is a problem.

      I personally would not do any kind of low voltage DC micro grid at all(Played around with that kind of thing before, came away hating it enough to make a whole video about it).

      I always say put the batteries right at the point of load, and if you need to run power, get an extension cord. The exception is PoE because that’s basically free with the ethernet you might already need for something else.

      USB-C all your projects, power them from power banks and wall adapters as needed. Remember USB-PD trigger modules exist and you can get 9, 15, or 20 if you need it(12v is deprecated and might not work with new adapters IIRC)

      If you want to do solar, 12v is fine for small runs of a few feet under 100W, and also more common than 5v and 48v and whatever, just use that. Or just get a commercial lifepo4 solar generator, they are amazing.

      Every new DIYer always wants to do the DC bus thing and it usually sucks because consumer gear isn’t meant for that and you lose the “just works” aspect of USB wall warts, wind up with heavy cables everywhere and a bunch of custom connectors and such for your DIY system that don’t match the rest of the world, it’s just a hassle.

      The best implementation I’ve seen is the ARES standards in ham radio but even then…. it’s only good for short runs.

      1. For 5v in an office setup I would just get those wall sockets with the built in transformer and USB ports.

        For 12v for routers and things to clean things up a little I’d just get one big 12v 5A transformer and 2.1mm Y cables(Make sure you get decent ones) or wait until 12v PPS trigger modules are available that can get 12v from newer USB-C ports.

        Or even better, just phase out stuff thar has non-usb power if you can. Spending slightly extra at upgrade time to make everything USB-PD could solve the whole issue, and by the time you need a new router or whatever the higher end ones will probably have USB power.

        If I really really wanted 12v outlets, I’d see about putting a hardwire Mean Well transformer right in a utility box by the outlets rather than actually running 12v. No single point of failure, no heavy cable or power loss in thinner cable, easy and obvious for repair.

        But really I’d just invest in some cable management furniture.

          1. Weird guess.
            My guess would be that the input circuitry is handle some fixed current. That would mean a derating down to 50% when going to 130V to 65V, and below 65 some other voltage lockout circuit cuts in.

        1. In a lot of substations there is a battery bank to supply power to the protection relays and allow the circuit breakers to operate (trip and recharge) when power is gone. The standard there is 115V DC. It’s 100% running on batteries, and there’s a AC->DC charger that keeps the batteries always topped off, so no solar in this situation.

      2. The DC distribution problem has been solved – with 802.3af, aka PoE – Power Over Ethernet. There’s no requirement to actually use the the ethernet part of the equation. Ubiquitous adapters, safe power distribution and great reporting/management tools. It’s not even expensive – data centre quality 100MBit 48 port hubs can be had for £30.

    1. I was going to mention this, they’re using POE. The losses from the runs must be less than switching from DC to AC and back to DC. Also can give you built in analytics on what’s being used.

  3. Sometimes I forget that I am living off grid.
    My set up has a 48vdc to 220v ac inverter good for
    about 5kw contious,though Its never been pushed
    very hard.220 volt water pump,fridge ,freezer,tech,
    tools,lights,all that stuff is bog standard.
    I do have seperate set ups for 12 and 24 volt dc
    and or most any other flavor of electricity.
    Run a metal fabrication business off the same set up
    and pump water for a large horse to drink.
    Batteries are from large UPS systems,that i get when
    the batteries are changed out on a time table.
    Batteries are tested for voltage,seperating out the best
    and then loaded with a resistance heater while monitering voltage again,selecting the best again,
    and buying those.

  4. Yes, most things with a “universal” AC input will run from DC. Multiply the AC input voltage by 1.4 to get an equivalent DC voltage. HOWEVER, their internal fuses aren’t rated for DC. Either replace them with a DC rated fuse or use an external fuse. No house fires, please!

  5. >”This means that the maximum string voltage is approx. 80V. In case of a fire, which hopefully will never occur, this should not pose a significant danger to the the fire brigade.”

    ELV standards considers 120 Volts DC as “safe” when ripple free, but the EU general product safety standards put the limit at 75 Volts DC, and the Low Voltage Directive applies to anything between 75-1000 VDC. You may still be in violation of the law, and require licensing to install such systems, but it’s difficult to find a clear answer or any documentation as to what exactly are you permitted to do as an individual builder without any special training.

    That’s why it’s generally considered “safe” to only deal with voltages below 50 VDC in all parts of the system.

    1. Why 50 volts and not 72 volts then? Plenty of solar stuff is available at that voltage.

      Would if be cos a nominal 72V system could be expected to seem up to 90 volts on when charging?

  6. I have two main reactions:

    1. “Legally?”. Just buy some microinverters and plug them into your mains. As even the cheapest Chinese ones have CE (“China Export”) markings, that’s legal in my book. The ‘suicide cable’ aspect is even neatly circumvented by the fact that they have anti-islanding build in, so no 240V output until they are firmly plugged in and 50Hz synced.

    2. Low voltage DC distribution. in the UK we have Live Neutral and Earth going to all sockets. It struck me that, as Neutral and Earth are bonded together, usually at the mains input to the house, why not use Neutral and Earth to distribute DC around the house? So, for example, put Earth at +5V relative to Neutral. Then you can get rid of a lot of pesky mains adapters. You would need some funky electronics to limit the 5V (or whatever) offset, for example some 500A zeners and/or a reverse-biased diode so the fuse would still blow to protect in case of a fault. This is of course a theoretical concept, because no way would any electrical code condone this, it’s WAY too far out of the box!

    1. Crikey! This really isn’t a good idea, there’s a reason Neutral and Earth are bonded. Look in to RCDs and you’ll see why it’s done this way – the “extra” copper really isn’t redundant.

    2. The China Export logo is not a safety or legality guarantee. It is designed to look like the CE (European Community) logo, which does have guarantees, to an unsuspecting buyer.

      1. I have enforced product safety in the UK. I’ve never seen a china export logo. I have seen lots of unsafe ce marked equipment. Lots of ce marks are self declared by law. Not sure what guarantees are there.The use of notified bodies in CE marks is a good thing and does have an independent check.

  7. I did the same thing but its 12v. I also ran automotive fuse blocks into rooms so I could run 12v lights, phone chargers and such straight of the 12v but I also ran 110v to each room and to some lights but it never touches grid power. I have about 25 panels and 4 wind generators

  8. Cheapest way to do it is realize in NA most lines are 15amp around house. Get used marine batteries online or lifepov4 if you can afford them. Stick 1500 watt inverters on each line your running. Yes you can run multiple 1500 watt inverters on same battery bank. Stick to 12 volt starting out, down road move to 24v then 48V.

    Start out with simple battery charger, then a simple 450w solar panel and solar control charger. Then as you have more money step up to 24V, add more solar panels. Eventually get up to 48V then can add alot more solar panels.

    Only real cost moving up to more volts is an inverter. Batteries can be placed in series as you get more so no cost involved there. As you move up in volts you can support more solar panels on cheaper solar controllers, so this is the reason to eventually do it.

    You’ll find biggest cost is batteries. A simple DIY lifepov4 12V battery at 280AH with 6000 cycles and a BMS will run you about 1k CDN. So start by looking on Facebook marketplace, Kijiji and Craiglist for marine batteries when starting out. Can probably get 2-400ah for just a couple hundred. Always go with your budget.

    Saving up for those lifepov4 batteries ultimately is what will give biggest ROI in the end. A Moe’s transfer switch will allow you to drain your batteries each day and switch back to grid power when they reach a certain amount of volts. Best way to save on your hydro bill.

    Starting out just use a gopower transfer switch till you have enough AH in batteries do do transfer switching in reverse.

  9. I’ve also gotten a 48V home battery because of the energy situation. But I didn’t want to go the route of converting all my stuff to DC. So I got a Victron Multiplus GX.

    It can combine your solar and 230V net without creating issues. I can’t legally export to the grid in my apartment. But the Multiplus constantly adjusts the 230v output it makes. So that it doesn’t produce excess power.

    And it can also charge the batteries when power is cheap if the solar didn’t charge it enough during the day.

  10. As far as reticulation DC voltage around your house. I have a different solution. Convert all lightbulbs to 12v-85v AC/DC led bulbs. (These are quite handy bulbs as they run on a wide variety of voltages)

    Then you only need to feed (in my case 24v battery bank voltage) into your lighting circuit which are usually 5A from the fusebox and if your inverters die you still have lights. Then in each light switch you can put a couple of 24V – USB PD converter circuits and sockets so now you have both lighting and device charging independent of your mains AC power (or inverters if you are off grid)

    It’s what I do and because I use old 24v
    conputer UPS’s as inverters that I get from the IT recycler for about $10 each, and we switch them off when we are not using them. So reticulation 24v on the lighting gives me lights at night and overnight device charging. A very very cheap system and can easily be fitted into any residents lighting circuit at the switchboard/fusebox. Or it can even be powered off mains at that point with a 220VAC -24vDC power supply, or at a pinch an old 19v laptop supply.

    Even a grid connected hose with no solar can do this and then power it with a small solar and battery setup so when the power goes out they still have lights and device charging.

    I only ever use AC device charging bricks when I am away from home and I have to say not being used to needing them, I find them a pain in the arse.

    Let’s turn this question around then, exactly how suitable is reticulating 5a of 240v AC just to run led lights in a modern house, seems like a legacy hangover from incandescent bulbs to me???

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