How to Design an Off-grid Solar Power Array Wire Configuration

in today's video we're going to learn how to design a wiring configuration for an off-grid solar panel array and what i want my viewers to do is to know how to combine various types of solar panels regardless of size or manufacturer to satisfy the needs of their solar charge controller these have specified working voltages for the input and the output and a maximum wattage rating these are also rated in amps and if you're designing an entire system from scratch depending on the charge and discharge rate of your battery please check out my book or my other videos in this video we're just going to learn how to satisfy the needs of the solar charge controller circuit so let's get started so first for our example we're going to figure out the power that this solar charge controller can handle from a solar panel array and there are three variables that we need to make this as simple as possible first variable is the battery bank nominal voltage second variable is the maximum pv input voltage and third is the max pv input wattage if you have these three variables you should be able to design a wiring configuration with any type of solar panel that you have available so first battery bank nominal this one can handle 12 to 24 volts now the max pv input voltage you can find it on the data sheet or typically it's written on the back of them this one has it at 150 volts open circuit so let's write that down now the next variable is the max pv input wattage and this is variable to the battery bank nominal because we need to take the battery bank voltage and multiply it by the output current instead of doing all of that if you're a beginner just read the manual or the data sheet or on this one it says it on the side it says max pv input power is 520 watts for a 12 volt battery bank and then 1040 watts for a 24 volt battery bank so let's write that down and if you do not have this in your data sheet or your manual you can calculate it yourself just take the nominal battery bank voltage and multiply it by the current rating of the controller so that would be 12 times 40 would give me the max pv input wattage so at 12 volts we can connect 520 watts of solar panels and at 24 volts we can connect 1040 watts of solar panels notice that this number is larger than if i were to calculate this myself 12 times 40 amps would be 480 watts but typically these can handle a little bit more so it's best to read the manual and figure out what they recommend so 520 watts 1040 watts is going to be our solar size array for these two voltages and we need to string our panels in series to create a voltage that is under 150 volts when the solar panel is not connected to the controller that's called the voltage open circuit open circuit means that the leads are not connected to anything you're doing a direct measurement of voltage or energy potential right at the solar panel leads so let's try to figure out what kind of solar panels we can combine to create this 150 volts open circuit and while still satisfying this wattage rating so let's say i go on the internet and i find a good deal on 350 watt solar panels and each one produces 45 volts open circuit let's say i string these panels in series what that will do is increase the voltage so i have to add all of these voltages together to figure out what the series string would produce and if i were to string these together i would create 135 volts open circuit and it would create 1050 watts so we have satisfied the controller at 24 volts open circuit voltage limit but we have not satisfied the wattage rating and this is actually 10 watts over the maximum recommendation but this can actually handle some degree of over paneling you can actually connect like i think 2 000 watts to these so check your manual some of the higher quality ones can be over paneled so technically this is safe to have and very ideal for this solar charge controller when charging a 24 volt battery now let's say that we are trying to use this solar panel array to charge a 12 volt battery and at 12 volts you are actually going to have problems because this wattage rating is more than what this is rated for at 12 volts for 520 watts so you cannot use this combination now let's say that we are trying to charge a 12 volt battery with four 100 watt solar panels and they have 20 volts open circuit if you string these together in series you need to add the voltage and guess what we have 80 volts open circuit and this is less than 150 volts so this is good to go and then the max wattage is 400 watts which is less than 520 watts so this is perfect if you have a 12 volt system a 40 amp mppt could easily handle four 100 watt panels no problem with this one in particular you could actually have 500 watts so it's also smart when you design your system to oversize your solar charge controller in case you want to add more panels later on so typically when i design a system i always have a little bit of headroom when it comes to wattage so i could add solar panels if i need it now for the next example we're going to figure out what kind of wiring configuration we can use with this mpp lv2424 this is an inverter charger with a built-in mppt that's rated for 24 volts battery nominal a maximum of 145 volts open circuit and a maximum wattage of 1920 and what's nice about the mpp is there's actual wiring configurations in the manual but a lot of people do not understand how they work or their solar panel size is different than the recommended one in the manual so we're going to figure it out ourself instead so let's imagine we have six 300 watt panels and we're going to connect them in series and each one produces 45 volts open circuit so let's add up all of the voltages and figure out what the wattage is with these panels in series we will create 1800 watts which is perfect for the lv2424 but it will create 270 volts open circuit and that would destroy the mppt circuit in this inverter charger system so we cannot use this configuration so what we're going to have to do instead is put another string of parallel panels so that we still have the same wattage but we drop the voltage so let's reconfigure these real quick now i've reconfigured these solar panels so that it will not burn out the circuit so now we are creating 1800 watts and 135 volts open circuit and how i did this is i took the three panels over here and i created their own series string and i put them in parallel with the original series string so now we have two parallel strings with three panels in series and we can write this kind of configuration as 3s to p because we have three panels in series and two in parallel but this presents a new problem when you have multiple parallel strings problems can actually occur if one of these panels were to short or to fail one of these could feed the faulty string and it could cause a fire and all sorts of other things so typically higher potential this side right here you're going to want to put some kind of ocpd for every individual string typically these are easy to find these are mc4 connector inline fuses and i put them on my website but if you do not have multiple parallel strings typically you do not need any form of ocpd and that's as you guys will notice on my blueprints on my website anything with over two parallel strings i always add inline fuses to that package but if it's a single series string you typically don't but i need to mention that you have to have at least two parallel strings for ocpd to be required and if you have a small array there is actually a limit that you can calculate that you don't need any ocpd at all even with parallel strings for a lot of people that are building systems that are under 400 watts or a thousand watts it's not really a big deal and you can put the solar panels in whatever configuration you want there is potential for failure if you have like five solar panels in parallel um that is enough to create enough power to go against the blocking effect of a single solar panel and it could cause a fire if one of them were to fail so in that instance you do need inline fuses but yeah if you have like a 400 watt array with like four 100 watt solar panels and you put them into a series series and then a parallel configuration like this positive and negative if this string were to fail this cannot create enough power to cause a fire in this one these have their own like resisting or blocking effect it's like a massive diode but if you have a lot of solar panels in series like this then you put these all into parallel and you have a short in this panel these two strings could feed into this one and cause a fire at the weak spot so in this instance yes for larger arrays you need ocpd and you usually have a combiner box with a disconnect or with circuit breakers for whatever code compliancy you're trying to satisfy but yeah for smaller arrays it's really not a big issue i usually don't put any ocpd on any of my strings at all because at the size that i'm working with under a thousand watts um typically the solar panel will have enough of a protection effect built into itself you just need to make sure the conductor is the right size but yeah it's pretty interesting when you make bigger arrays you definitely need to make sure that you follow the code with ocpd for all of this stuff for the next example we're going to use a pulse width modulation controller and create a solar array for it so this is an interesting kind of controller because it says switching regulation to modulate the voltage what that means is there's a switch going on and off and that means that the input to output voltage differential will give you the power availability and the efficiency typically these will give you 70 percent because these do not track the power point so that means that we need to match the input voltage to the output voltage that means that for a 12 volt battery we can only connect 12 volt panels and if i want to connect the full 400 watts that this is rated for we're gonna have to put these in parallel so let me show you so let's say we have four 100 watt panels and they have an open circuit of 20 volts and a working voltage of 15. so they'll work perfectly with this but we need to put these all into parallel so that means we need to connect the positive over here and then connect it to the controller and then we need to take all the negatives and connect them over here and this part right here where all the positives come into a single conductor and all the negatives come into a single conductor is an mc4 branch adapter so for these you need a branch adapter if you were to put all of these into series you will not have much power availability you'll have like the power of a single 100 watt panel i think when you use these you need to put them all into parallel and you cannot use a 24 volt panel to charge a 12 volt battery with the pulse width modulation controller even if it says that it can handle 24 volt batteries you still need to use a 24 volt solar panel so very important the input to output differential will determine the power availability in other things and on the back of this one it says they can handle 30 amps and a max pv input power of 400 watts and because we're putting these all into parallel and you have 30 amps going through this conductor and 30 amps is the max for an mc4 adapter that means that you cannot exceed this that means you cannot add any more panels you are limited significantly with this because you are pushing a lot of current but when it comes to an mppt you want to keep the voltage very high to increase efficiency and maximize output under various circumstances such as low light if this has low light and the voltage is high enough you will get an amp boost in the morning you can still charge your batteries with this for this one you need to wait until the voltage of all of these reaches a point and current can flow enough to actually charge the battery at its nominal another thing to consider is the temperature coefficient of the material of a solar cell the output will increase if the temperature is cold so if you're in a very very cold environment and you have a long series string it's best to have some headroom for the voltage open circuit like if it's 150 volts i would like to keep it under 130 volts so i'm not going to push that limit i want to have some extra safety headroom a lot of these systems can actually handle a little bit more voltage but if you were to exceed it and it doesn't have any over voltage protection it will destroy these so it's best to err on the side of a lower voltage open circuit also a lot of these have over current protection at least in my testing even if it doesn't say that it does in the manual it will have it in practice and it will reduce the output of the controller to its maximum if you were to exceed the current from the input that's not all the time it's usually on the higher quality units but it's something to think about and i might be over complicating some of this stuff if you have a small solar panel array it's not going to be that hard just read the manual look up the wattage connect them check the voltage make sure it's not too high and then hook it up and you're good to go but i've seen a lot of people and they'll find higher voltage panels for really cheap and they're used and you can still use those but you might have to add another parallel string or something to reduce that voltage so i think the number one most important thing that you guys can do is check the voltage before you connect it to your solar charge controller but be very careful when you're testing higher voltage if you're messing with 140 volts dc it can kill you instantly a safe way to check the voltage before you connect the solar charge controller is if you have a disconnect switch or a combiner box for your solar strings you could test the voltage there before you turn it on for the solar charge controller but yeah if you do the math and you just add it you should be fine anyways i hope you guys like this video it's a hard complex topic because all of these vary so much so yeah please read the manual and yeah if you find some cheap panels they're higher voltage you should be able to use them just do some quick math and you'll be alright alright i will talk to you guys soon thank you so much for watching bye

Channel: DIY Solar Power with Will Prowse

Views: 694,777

Keywords: off grid solar, will prowse, diy solar, rv solar

Id: C-k0WHJ4RxQ

Length: 15min 4sec (904 seconds)

Published: Thu Aug 06 2020