12 volts VS. 24 volts for Off-grid Solar Power Systems

today we're going to be talking about 24 volts solar power systems and when it's appropriate to use a higher voltage battery bank and why people do it in some of the pros and cons to using a higher voltage for your off-grid solar power system battery bank here are the pros so first you have a lower cost 24 volt systems are always cheaper when building off-grid solar power systems this is because the cost of the wire in your system can cost a lot especially if you're building a large system and if you have a 12-volt system the amount of amps going through that wire is going to be double compared to a 24 volt system so that means that the wire needs to be twice as thick to carry that load and copper wire is not cheap at all and copper lugs especially big ones are really expensive as well so that's the first cost determinate factor the next cost is going to be the solar charge controller so these are rated in amps and if you have a 24 volt system you can get away with half the size of a solar charge controller as you would a 12 volt system so a lot of these solar charge controllers are rated for 12 and 24 volt systems and so for example if you have a 20 amp controller and you're using it on a 12 volt system you can only hook up 260 watts to it if instead you have this same exact controller same exact price which is going to be around 130 dollars you can actually hook up 500 something watts it doubles the wattage of panels that you can use on your system and solar charge controllers are not cheap if you are building a large system with a 12-volt battery bank you are gonna spend a lot of money on that solar charge controller you will spend double and that's a lot of money but when it comes to the cost of the inverter it is pretty much the same whether you buy a 12 volt or 24 volt they're gonna be the same but 12 volt has the advantage that is readily accessible so local stores sell 12-volt inverters not many stores sell 24 volt inverters nowadays we have the internet in Amazon so it's as easy to get a 24 volt inverter as it would be to get a 12 volt inverter so for most people that doesn't matter but if you're sourcing your equipment locally then that might be a big drawback to 24 volt system have to go with the 12-volt system instead the next advantage is if you are using batteries and strings to create 24 volts a lot of people use four six volt batteries or two 12 volt batteries it is better to have batteries and strings or in series because when they are in parallel if you have more than three batteries in parallel one can start feeding the other one and it can cause one of the batteries to die sooner and then you'll have a shorted cell and you have to remove it or it degrades so batteries do not like to be in parallel and typically especially with like the Tesla battery each parallel battery has its own fuse just in case it shorts so long story short batteries do not like to be in parallel with each other it's better to have them in serious strings or to have bigger batteries if you have more than three batteries in parallel you're probably going to have problems around three to five years but this depends on what kind of chemistry using the health of them how well they're matched if they all have the same resistance if they're used in the same way if the temperature is the same for each battery there's lots and lots of different factors there series connections better parallels worse typically with 12 volt systems I see people parallel connecting in 24 volt systems I see people serious connecting so that's another advantage of 24 volt systems the next advantage is all of the system components like to be at a higher voltage if you have high volt solar panels you have a higher voltage battery there's less work that that solar charge controller needs to do so there will be a marginal increase in efficiency with most things at a higher voltage not all the time but typically it's going to be that way also you're gonna have less wire loss so wires like to heat up when they carry power and if you're running everything at a higher voltage there will be some improvement in the efficiency so yeah it's cheaper more efficient it's better in quite a few ways I really like 24 volt systems now let's talk about the drawbacks so the first drawback is that you need to have a solar panel array that produces a voltage that is larger than the battery banks voltage so that means that you cannot use 12 volt solar panels with a 24 volt system you can use 60 volt solar panels you can use 100 volts solar panels you can Series connect them in any way that you want to as long as your solar charge controller can handle it but it needs to be high enough voltage so that it's higher than whatever your battery bank needs and in a 24 volt system it can go up as high as 32 volts so that means that the open circuit voltage of your solar panel array should be at least 40 volts or more and usually this is not a problem because you can take 12 volt panels and put them in series you'll have an open circuit voltage of 40 volts so that's really nice but if you're in some weird circumstance where you're dealing with a lot of shading with a tree or something and you need to parallel connect a lot of 12 volt panels a 24 volt system will probably not work for you what you can do instead is have in series pairs so that you jack up the solar panel array voltage to 40 volts but you still have some redundancy because all of them are parallel connected the next drawback to use in a 24 volt system is that you cannot run 12 volt appliances unless you buy a converter and so this is where the cost increases for a 24 volt system but the cost is very low so with solar charge controllers it is much cheaper on a 24 volt system you save like 100 to like $400 in that one instance when buying a converter they cost about 30 to 40 dollars for a nice one with overcurrent protection and other safety features like temperature protection so when you buy this converter this takes the 24 volts and it converts it into 12 volts and then you put up your own little fuse box and you can still use 12 volt appliances for it so it really depends on your system if you're building a solar power system that only has an inverter and you do not need 12 volts at all you don't need to worry about this at all if you're an RV and you still need 12 volt appliances to be powered by your 24 volt battery system you are definitely going to need a converter and that's an added cost this cost is very small so I would not say it all that this takes away from the fact that 24 volt systems are cheaper because 24 volt systems are much cheaper than 12 volt systems some people will say but will I have to buy a converter that's ridiculous why should I spend all that extra money I should just stick with 12 volt systems and I'm like no no no it doesn't work that way you are saving so much more from a 24 volt system even if you have to buy a 30 or forty dollar converter it still works out in your favor with a 24 volt system no matter what unless you have a really large 12 volt load all of the converters that I recommend people use go up to 40 amps if you have like a huge water pump or some specific application for a 12 volt big motor or something thing yeah you probably need 12 volt batteries but for most people if you just have 12 volt stuff like a fan in your RV and you know whatever your water pump for the RV you don't have to worry about it a 40 amp converter will work fine and those run in 90% efficiency so they're really good it's pretty much the same as a good pure sine wave inverter the next drawback I mentioned previously but it's how hard it is to get 24 volt equipment locally so if you're buying all of your parts online it doesn't really matter you can find 24 volt stuff just as easily as 12 volt stuff even the batteries whatever you need you can buy it online but if you're sourcing your stuff locally it's gonna be very tough so yeah 12 volt actually is better in that regard you can go to Walmart and buy an inverter a deep cycle battery and all this stuff and hook up a system today with Harbor Freight solar panels but you can't do that with a 24 volt system you have to order it or find some kind of distributor nearby that can sell you 24 volts stuff the next drawback to using a 24 volt system is the fact that you cannot charge it with your car's alternator so if you have a big van or an RV or a bus and you want to charge your 24 volt Tesla battery with your alternator you can't do it unless you use some tricky stuff you need some special equipment like a converter or a battery charger they can take that power and boost it up and this is difficult you have to also use it with a battery isolator so it doesn't back feed the system you might need some diodes I would never do that in a million years because the amount of like kilowatt hours that you can produce from an alternator at the expense of my charging system for my RV that just seems like a bad idea but I know a lot of people still like to do it and if you drive for like six hours a day they want to charge their battery with their alternator if you want to do that though you need to swap out the alternator for something that is designed for charging deeply discharged deep cycle batteries because if you take your lithium battery where you take your sealed lead-acid and it has a lower resistance than your flooded starting battery and you parallel connect them that's just a bad idea I mean why would you ever do that anyways and you can use a smart isolator so that only when the alternator is on it will boost up the voltage but when you have a battery that's at this voltage and your solar battery is down here your alternator needs to compensate between the two and will find the voltage right in the middle and it'll be a high amperage especially when the solar battery is trying to do a bulk charge the resistance is low so you can heat up the alternator and damage your charging system I've said this in lots of other videos and I said this in the book but man I don't know why anybody's doing that there are much better ways of doing this also if you want to do this long term go to a shop that installs extra alternators and get one that's designed for doing this also marine application there are lots of boat alternators that are designed for charging deeply discharged deep cycle batteries if you have an alternator for charging system of your car and then another alternator for 12 or 24 or 48 volts it charges your solar battery that's a smart move to make that way you don't touch the charging system of your vehicle it is designed for only charging the battery for like 1 2 3 amp hours and to keep the engine running in a couple little appliances in the front like 30 to 40 amps I would not personally charge a solar battery with an alternator unless I had its own dedicated alternator that was designed for it but now that we know the pros and cons of using a 12-volt versus 24 volt system we can talk about when it's most appropriate to use a 24 volt battery system and so what I think is that if you have a small system 12 volts is fine if you have a medium sized system you should be using 24 volts if you have a big system or a house system you should be running 48 volt batteries so the 12 volt system you don't really have to worry about these wire loss and all these things because you don't have many wires you probably have one or maybe two batteries you probably have like 300 amp hours of battery max so you don't really have to worry there's not many parts there there's like four parts in your system if you're building a large system anything over like 600 watts or over 300 amp hours of sealed lead-acid that when you need to have a 24 volt battery system so this works well for a tiny home or for large RVs 24 volt systems excel in those situations if you're trying to build a house system or you have an off-grid cabin then yes a 48 volt system is better but safety wise I like 24 volt and this is because 24 volt is still very very safe but it's a high enough voltage that you save a lot of money on your system components for wire loss so with 12 volt system the safety is very good you could put your tongue on that battery practically and it's gonna hurt a little bit but you'll be fine even if your hands are wet and it's storming and you put your hands on the electrodes you'll be okay and you will not die when it comes to 24 volt system you are gonna get a shock but it's still under 30 volts so that's still technically safe 30 volts is considered the threshold anything over 30 volts and things start sparking and you can get shocked when you start hitting 48 volts you definitely need to know what you're doing 24 volt you still get some sparks but they're not that bad and I've watched a lot of other videos of people shocking themselves like a lecture Oh boom he's got a crazy YouTube channel and 24 volts is pretty darn safe he actually put electrodes on his tongue at 25 volts so yeah if you have a small system use 12 volts if you have a medium-sized or a big RV or a tiny home use 24 volts if you have a cabin or a house use 48 volts and that's all I wanted to say I hope you guys found this video useful let me know if you have any comments in the section below and I'll talk to you later bye

Channel: DIY Solar Power with Will Prowse

Views: 1,243,670

Keywords: 24 volt pros and cons, 12 volt vs 24 volt, 24 volt solar, offgrid solar

Id: Vi7eswWwosk

Length: 12min 41sec (761 seconds)

Published: Wed Feb 06 2019