We live in an exciting time with respect to electrical power, one in which it has never been easier to break free from mains electricity, and low-frequency AC power in general. A confluence of lower-power appliances and devices using low-voltage external switch-mode supplies, readily available solar panels and electronic modules, and inexpensive high-capacity batteries, means that being your own power provider can be as simple as making an online order.
But which parts should you choose? Low Tech Magazine has the answer, in the form of a guide to building a small solar power system. The result is an extremely comprehensive guide, and though it’s written for a general audience there’s still plenty of information for the Hackaday reader.
Perhaps the most important part is that it’s demystifying the subject, there in front of us are a set of pretty straightforward recipes for personal power. The computer this is being written on spends a significant proportion of its time on the road with the ever-present company of a very hefty USB-C power pack for example, and the realization that a not-too-expensive solar panel and USB PD source could lessen the range anxiety and constant search for a train seat with a socket for a writer on the move is quite a powerful one.
Take a look and see whether your life could use bit of inexpensive off-grid power, meanwhile we’re quite pleased that the USB-C PD standard has eased some of the DC problems we expressed frustration at back in 2016.
I see a lot of DIY solar, but I rarely see anyone just wire a panel to an indoor DC outlet (Anderson PowerPoles?) to charge off the shelf solar generators.
They have amazing features at low cost, Lifepo4 versions are available, they’re portable, and if you’re a hacker, you can probably swap the battery when it wears out, if we still use the same battery type by then, although you might have to build a new case to fit it.
Even if you want to do it all yourself, for a small system, the flexibility of building the battery part as a portable unit seems like a big benefit.
The problem with doing this is that the voltage output of a panel fluctuates depending on the amount of light striking the crystals, so a DC-DC converter of some kind (either PWM or MPPT for further reading) is used to regulate the voltage to an appropriate value.
There’s no reason this functionality couldn’t be integrated into a BMS inside the battery unit, but modularity makes for better serviceability, and with larger systems the units tend to be fairly large with external heatsinks.
I think they are referring to the battery, USB-PD, inverter and solar charger units you can buy – for instance an Ecoflow Delta (though there are many others, I just happen to have used an Ecoflow). But talking about the self contained units that have everything you need it seems to take almost any DC source or wall AC and turn it into energy in the inbuilt battery, while often also having the inverter and USB outlets to power almost anything.
In which case I can agree its a neat idea, and one that is very much inline with something I’ve been thinking anyway – those thinner folding solar panels would make a good awning to provide some shade for the summer months while being easy to pack away when they are not of much use. So having an easy socket to indoors to connect them to the varied battery you might want to use would be nice – though very low priority as a project here right now as the big battery has been living at the grandparents for a prolonged period now.
Yep, those are the ones I was talking about! They have the MPPT built in for direct connection to panels.
> the voltage output of a panel fluctuates depending on the amount of light striking the crystals
More properly, the photoelectric current changes with more or less light. There is a slight change in open cell voltage because the threshold of the PN junction isn’t linear with respect to the photoelectric current. That makes the maximum power point shift around, but not by much.
The simplest MPPT controllers simply use a fixed voltage set point and vary the load current to keep the solar panel at that voltage.
the simplest(semi manual) voltage regulator for a pv solar panel is a battery,as long as the open circuit voltage for the panel is higher than whats showing on the battery,the panel will just work at the batteries voltage and keep trying to drive the voltge up,its semi manual and must be watched as it will end up over charging a battery that is unloaded ,I have used this method and also run
alternators with no voltage regulator,just battery
voltage to the field winding,and a lightbulb as a
crude volt meter,as in “ok thats getting BRIGHT NOW” and pull the wire to the field
techniques such as this are fine,as long as you have a blase atitude towards things catching on fire and friends who know when to start backing
away slowly
Transmission losses. Voltage sag over long distances. If its a ’12v’ solar panel you can do the math on the length of your run and the voltage drop. Unless you have a source of welding cable (or other low resistance wire) nearly free the wire can easily rack into the 100s of dollars.
Look up a chart of voltage drop for DC and wire guage.
Now if you wanted to start upping the voltage by putting panels in series and use a DC DC step down at the outlet. You could save a lot depending on the scale of the system.
Its a balance depending on the cheapest component you can source. Cheap panels? Just let the wire have losses, as long as it doesn’t heat up unsafely. Cheap wire? Perhaps wire it direct at 12v. Neither is cheap? Maybe spend an extra $20-50 on a step down DC DC and run higher voltage.
The current in these kinds of very small systems is only going to be a few amps. Some larger solar generators even support 60v, but most are 30v max input it seems.
Low voltage safety regulations may apply. If it’s something a consumer can install by themselves, something between 48 – 60 Volts is usually what is legal to sell. Higher than that may require licensed installers.
A lot of modern installations have “inverters” in each panel, converting to AC. One question I’ve asked but haven’t gotten an answer to is how multiple panels’ phase is synchronized. Obviously you can’t just combine a bunch of out-of-sync sine waves.
Those are normally called “micro inverters”. They require an existing AC power source (mains, house battery+inverter, etc) to sync to. If they don’t detect a power source or the power source’s sine wave is too noisy (most generators) then they don’t output power.
So they all stay in sync using the same AC power source as reference, if they were to somehow get out of sync with each other then they would stop outputting power because there wouldn’t be a clean sine wave to sync to.
Why not make a contest for the longest running Linux on solar panels every year
Because you can run Linux on an ESP32. i.e. Running Linux is a very generic target.
Doom?
Crysis?
I’m a huge fan of the USB-C Power Delivery standard, especially in an off-grid setup. It makes things so much more efficient when dealing with anything up to a laptop, rather than having to use an inverter to step up to high AC voltages then back down in a power brick to the DC ranges used on many consumer electronics.
I even run a gaming laptop off a 100W 12V PD supply – it does still run the battery down over time but you can get a decent few hours gaming with fairly high video settings before needing to let it recharge for a bit.
You could just take the Vbatt straight into a DC-DC converter for your device, you really don’t and never needed to step up to AC and back down again for most things – about the only thing I know of that would be fussy on that is those awful Dell laptop powersupply combinations that refuse to charge the battery if they can’t talk to the powerbrick or the powerbrick isn’t seen as official. The solution to which is not to use a crappy Dell product, or hack the crappy lockdown for no reason out of it…
Not that I disagree with the convenience of USB-PD when it works right having the devices make sure the idiot human can’t plug the 48v barrel jack into the 19v device and that you don’t in theory even have to consider which cable you plug into is nice. Though in practice it isn’t really that perfect – so many things will really want something that this PD power source doesn’t do (either newer vs older versions with higher voltages, something that is only optional in the spec anyway, or just incomplete support), or the supply does have the ability but can’t right now as its total power budget is already consumed/ it doesn’t like the cable. And if you are not careful you might find a supply that has a USB-C end but doesn’t bother with PD and just dumps the 20v the device it shipped with wants right into your poor 5v only device…
Very nice resource. I wish I had it when I started configuring the solar for our trailer. I’m *still*a little uncomfortable with the idea that the battery could be getting charged from three directions (solar, shore AC, tow vehicle –obviously not the latter two at the same time)) but I know it’s all fine, I just wish someone made a reasonably priced solar+AC controller/fuse box/distribution panel, as I’m sure there is a lot of redundant circuitry, and the Bluetooth remote monitoring is part of the solar controller, meaning i can’t monitor the charge state when plugged into shore power.
We went with Renogy for the solar components (they supply 6ga wiring which is overkill and rather stiff when trying to hide your wiring), and a lead acid battery, knowing that lithium will be cheaper when this one reaches its lifespan.
Shouldn’t be too difficult, run an isolator between Solar and the other. ‘Other’ here being a relay on the Truck/Shore power. Ideally only switching on with engine running/charging (or key on if you are keeping it simple). Or feed one isolator into another? Not sure. Aren’t mosfet based shore power smart enough not to charge with the truck running?
It’s a bit old, but not irrelevant.
Those common lead-acid solar charge controllers are actually quite wasteful for small solar systems. The standby current is usually something like 5-6 mA which is a huge amount when you add it up around the clock, day after day. It can become an issue if your solar setup is only tens of Watts peak panel power instead of hundreds.
Until you mentioned it, I hadn’t considered hooking our Jackery up to our 9 Horror Fraught solar panels.
Even easier:
Connect, say a 100 watt panel, to a jackery (or other brand) solar power station (hundreds of these available on Amazon at various sizes and prices).
The power station has charge controller, battery, inverter, DC and AC outlets – all in one unit.
Really, along with a spot of sun, those 2 items are all you need. It’s easy and almost anyone can do it!
Check the specs of the device. The one I can find was 12-30 VDC and 42 Watts max for the DC input. That means the MPPT simply won’t apply enough load on a 100 Watt panel and you’d be wasting money.
All good in theory until you find out you need a proprietary adapter cable to connect the panels to the jackery. Jackery won’t sell it unless you purchase their panels at significant cost. Just another greedy company extorting the do good consumer
I have an interesting twist on my system. The load on the mppt controller can typically be programmed to turn on or off at dusk. You can also set the load on all the time. I use the load to drive a relay which switches the inverter on and off (load on, inverter odd / load odd, inverter on). I simply use the relay as the on/off switch for the inverter. So by turning off the load I also turn on the inverter.
The advantage of this is it gives me remote control of my inverter through the wifi app which controls my mppt controller. It’s nice to be able to use my computer or phone to control my inverter, which I only need intermittently.
What I’d like tot see is a cheap wat tot run my solar in case of a blackout.
Due to rightful regulations my inverter now shuts off, instead, i would love tot keep it running in case of whatever.
There are these mains auto switches, for generators n stuuff and that helps, but the inverter need ac to sync too. Using a tiny ups would do the trick, but appearantly its bad to feed to much current back into it or something.
Don’t use the grid tie inverter. It’s not safe to disconnect the panels from that inverter; it would probably be cheaper and more legal to install a generator circuit on your house and build a solar trailer with some battery backup. A used golf cart or forklift battery is a great way to do it if you can source cheap. Get salvage panels and batteries, should be less than $2k for the whole setup and 3,000 watts of solar. (Local FB market prices: 6v 150Ah Golf batteries $300, 116w 30-39v panels $20 each. Trailer from HorrorFreight $300, structure from tractor supply/HD $200-400. Add your own solar charger/inverter $500-600
That was 6x golf cart batteries for $300, adds up to 36v-40v
Rich, but I have already 5k of solar on my roof :) I live in NL with tiny back yards and tiny row-houses. So I’m not looking into reinvesting to go off grid. Just prepare for the zombie Apocalypse, and random blackouts.
You need a safe arc free way to tap the panels then. Or a system with power wall. I’m in CA and talking with folks who get solar installed many systems seem like a scam, overpriced and no way to use without grid.
I am wondering about this too, I’m thinking with the grid tie inverters you just need a “master” inverter to feed your house wiring, and a switchover switch (commonly used for generators) so you can isolate the house from the grid and then run autonomously.
Probably a UPS would be sufficient as a master inverter. But you might also consider a small diesel generator powered off used vegetable oil.
I should hasten to add a 24v or 36v system might be wise given you can source panels for grid-tie obscenely cheap. EG my local marketplace has 116w (39v open circuit) ‘panels*’ for $20 each. (*They are rolled up panels 1.5′ x 16′ long). Easy enough to do with 2 or 3 12v nominal batteries. And sometimes the 36v inverters are much cheaper in the large 1000w to 3000w sizes. You can use much thinner cabling and suffer less transmission loss as well.
Now to modify the 900w step up DC supply I got for $18 into a MPPT, just tie the current limited function to the solar panel voltage and tune it so it only sags the panel voltage into the sweet spot.
This is an area ripe for hacking.
100 W solar panels, HF 35 Ah AGM battery attached to ~$20 charge/load controllers [several tested] successfully powered Raspberry Pi 4B.
~12V output of controller connected to a drok buck regulator with usb type A connector.
5.3 V fed into Pi.
Charge/load controller impressively compensates for solar panel erratic/intermittent output.
No Pi 4B power glitch resets res .
Question: Charge/long controllers used have LCD displays. Allow settable values inputs.
What software technology used in these charge/load controllers?
Erratic solar output caused Springerville AZ coal/solar generating plant to have to use coal
backup 100% of the time!
PNM solar erratic/intermittent DATA illustrates issue. https://prosefights2.org/irp2023/windscammers18.htm#erraticsolar
I hang out in a DIY solar group and OMG every night I walk away thinking
there are an awful lot of fools with money out there
I am amazed there are not a lot more fires
Newbie here! I am running a handyman business and I am wanting to learn/add a small solar energy system to my enclosed work trailer (to power 3/8 electric drill etc, charge my 20v power tool batteries, maybe charge a cell phone or two). Any advice and or plans are much appreciated! Thank you. Curt πΊπΈβ€οΈπΊπΈ
Get on endless sphere and look around. Can go cheap or expensive. Used EV batts or new deep cycle trolling batts. $20 charge controller or a good renogy or midnight commander. 1000w inverters are $80-200. Keep DC cables short and get panels from local marketplace is cheapest.
I have put a solar panel on my teardrop trailer ( renogy 100w flexible ) I have that connected to a pwm solar controller and made a 100amp LIFEPO4 battery ( next time I would just buy one the savings are not worth it). I charge my dewalt batteries ( for my electric bike) from it using a RC car battery charger which takes the 12volts to the 21volts required. If the LIFEPO4 batteries drop below 12.5 ish volts the battery charger cuts out with a low voltage warning. So to do this reliably a 24 volt system would be better but the rc charger I have gets upset over 18 volts and cuts out with an overvoltage warning.
You could use an inverter to take the 12 vols up to 240 then plug a standard dewalt charger in but that isn’t a great way to do it.
I have a Chevrolet EV car, I need to build a small solar system that can be able to charge it.
I need a guide.
A small solar system?
Would Proxima Centauri work for you?
The linked article is useful but really seems aimed at small scale DC. I do like the mounting ideas though, I haven’t really been considering so much wood, but treated timber shouldn’t rot.
I’d like to be self-sufficient (currently I’ve got about 800W max on microinverters plugging into the ring main) but really need to increase the number of panels markedly, get some battery on there to dump excess power into, and as a second string dump excess power into the immersion heater (could be DC into that below 200V). I need about 2.5kW max output from the batteries to power heavy use items, cooker, or kettle, or washing machine, or tumble dryer, but not all at once.
An off-grid isolation feature would also be nice, as mentioned above, for apocalypse scenarios. I already have the pitchforks and other weapons to fend off the zombies!
Tres bon guide, Merci a vous. J’aimerai utiliser des panneaux qui permettront de recharger des portables et des ordinateurs. Et j’aimerai savoir est ce qu’il existe des cartes electroniques comportant des ports USB de type A et C qui pourront etre alimentes par le panneau et oΓΉ les appareils seront branches ? Dans ce cas quels types de cartes electroniques me conseillez-vous ? Merci d’avance !