Hello - I am trying to figure out how many solar panels is required to charge either the A300 or A500 in timely manner (under 8 hours). I need these only to keep my 1500W full size maytag fridge on during a potential power grid blackout or other extended outage. This means I can only charge these with solar. I have limited space and renting so any installation cannot be permanent… I can place up to 4 panels on my flat roof but not sure how I would connect the bluetti units as these will be positioned next to my fridge and lugging these up 3 flights to the flat roof area is not realistic. I do not want to spend $$ to wire through the electrical box as I rent not own the house. Thanks for any suggestions!
Hello @cricci ! To make sure I understand the situation correctly, can you confirm the refrigerator power consumption? For example, my large kitchen fridge normally uses 100 watts, maximum is 545 when it is defrosting.
I will assume for the moment that yours is a typical fridge, and tell my experience. I have an AC300 and I started with 2 B300 batteries, and now have 4. However, I am running a lot more than just one refrigerator, specifically I run 2 refrigerators, two freezers, and the home water pump (just 120 volt pump, not 240 volt), and have been running these for 2 years.
I have 3,000 watts of solar panels, in two arrays of 1,500 watts each since the AC300 has two MPPT controllers. The AC300 can only use 2,400 watts, but as long as the maximum voltage (Voc) is in the correct range it works very well.
My large refrigerator uses 2,400 watts per day average, and that’s with all day use as I have family members at home always. Don’t forget that the AC300 or AC500 uses some battery power to run itself. But one battery, with 3,072 watt-hours, should last more than 24 hours. In your case if you can do it I’d recommend getting two batteries for longer runtime during bad weather days with poor sun.
So, normally you get around 5 hours of good solar charging time (but it does depend on where you live. I’m in the midwest, so I don’t get the northwest rainy weather, but not the southwest desert sun either). So if you would get consistent sunshine every day, then take the approximately 3,000 watts, divide by the 5 hours, and you need to get 600 watts per hour. But solar panels are about 80% efficient, and clouds happen, and so does rain, so at a minimum I would suggest 1,000 watts of solar, better to get as close to 1,500 watts as you can. Most of the time you would have enough power to charge phones and a laptop, and have a light on, etc., as well as running the refrigerator.
Your biggest challenge for solar, in a rented home, will be where can you put solar panels, and how can you get the cabling from those panels to the AC300. If your only solar panel location is up 3 flights of stairs then is it even possible to run wires from those panels into your home?
Assuming you are able to, then you’d need to get panels. For my system I got twelve used 250 watt fixed panels (the type that would be mounted on a home or rack), and paid less than $1,000 including shipping. So if you could find used panels, you could start with enough to get 1,000 watts worth. Do realize that these fixed panels are large and heavy to carry.
To use the panels it will be necessary to wire them up. Whether to use parallel or series depends on the “open circuit voltage” of the panels, called “Voc”. If wiring them in series the number of panels times the Voc must be less than the 150 volt maximum of the solar input of the AC300, and best to be less than about 140 volts. If you get to this point then feel free to ask and we here can tell how best to wire the panels you find, and how many to get.
Then you’ll need to get the proper solar extension cables to be between the AC300 or AC500 in the length you’ll need, you can normally buy these from Amazon.
Hopefully this will be a good start to your quest, and if you have questions ask away!
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Thank you very much hnymann. I am very appreciative of your suggestions.
My fridge is 25 Cu say 614 w for the defrost.
So my big question was: so I DO NOT need equal solar watts (in the A300 Case) 2400 watts of solar. Its more about the watts you get per hour to keep the battery charged. (correct?) which is why you say 1000 watts of solar could suffice.
My roof area is 12 feet by 5 feet so I think I could get 3. However, there are smaller squares too that would be easier for me to manage, maybe I could get more in that space. I have a full roof deck too that would accommodate a few more but trying to avoid that. I’ll be the installer.
May I ask where you purchased your panels? I would be placing them on the roof, not securing. Do you recommend the mono panel style and rigid (not flexibles or portables?
I would need 80-100 feet of cable to connect them to the first floor near fridge. What are those cables called that would allow me to do that or does it depend on which panels I buy?
I could charge it with good sun in about 5-6 hours. Second battery is smart (thank you for that suggestion). I live in Massachusetts.
Regarding solar, yes you can have less than the maximum solar power as long as the ~ 5 hours will be enough to replace the 24 hour power demand on the system. And then add additional solar panels to make up for poor sun conditions.
You would have the option of smaller or larger panels, as long as they physically fit, but you also need to take into account the Voc, the maximum panel current, and determine how many panels and how to wire them (series, parallel, or a combination), and then if there’s room on that roof for that number of panels. Sometimes the voltage will affect what power of panel is suitable (this calculation is actually the most complicated part).
I got my used panels from SanTan Solar. They’re good to work with. Yes, they are the rigid style of panel. The picture below is 6 of the panels when I was testing them in my yard. For reference, these are 250 watts each, have a Voc of 37.6 volts, and max power of 30.3 volts at 8.27 amps. I use 3 in series to get the best voltage configuration, and then put another 3 in parallel to get 1,500 watts, and put that on one of the AC300 solar inputs just as you see them in the picture, then duplicate all that for the 2nd solar input.
Rigid panels almost always come with MC4 connectors, and the AC300 or AC500 also uses those, so this cable or similar would be what you need for the extension cable. You will need only one set if you’re only using one of the solar inputs on the AC300/AC500.
https://www.amazon.com/Temco-Solar-Extension-Connector-Female/dp/B071NPT6LR/ref=cm_cr_arp_d_product_top?ie=UTF8&th=1
Hello Again~
The price difference between A300 and A500 is small so I am considering A500 + B300S so down the road when I move next year I can really scale these. Will a solar array of 1950W suffice to charge this?
I really do not want to deal with 79 inch solar panels (not feasible) so I am looking at the RV roof models like this one: 195W 12V Monocrystalline Solar Panel | ECO-WORTHY
I could fit 10 on my roof. Is this doable with the Series connection scenario?
Thanks again for your insight! I am very appreciative.
Christina
Yes, this set up will work nicely, and will fit in your space. As your diagram indicates, you will wire 5 of the panels in series, and then the other 5 also in series. The voltage is nicely in range, and the current is as well to get as much out of the panels as possible. If we use the 80% rule for the panels, you’ll get 80% of the 1950 watts, or 1,560 watts per hour, 5 hours maximum assuming good sun coverage, for 7,800 watts per day to charge the batteries in the best case scenario. Even on a low sun day you can get 33%, or 2,500 watts on that day, plus what’s in the batteries.
Assuming your refrigerator uses about 2,500 watts per day, you won’t have any trouble keeping that going, and you’ll be able to use some other tools and appliances as well, especially during the day with the solar available.
You’ll just need to get two sets of the solar extension cables to connect both arrays to your AC500.
Thanks so much. I decided against A500 (not enough 120 outlets). So back to the A300 and a second one to handle the cellar boiler which maxes at600watts (looking at A200L). My quick question (and again thank you!) Confused about Series vs Parallel?
Series means they connect to one another via and mc4 connector (male/ female) like this: Rich Solar Y Branch Parallel Connectors 2 To 1 - Off Grid Stores
- If I linked 6 in a series would that add EACH panel’s voltage so 24vOCx6? - What is Parallel then?
- Is it okay to lay flat on the roof without a rack?
Ready to pull the trigger but want to be really clear.
Hello @cricci !
Series connection mean, that you connect Solarpanel 1 (+) with Solarpanel 2 (-).
In this case, all the voltages of the panels will add and the current remains the same. If one panel does have 24 VOC, the voltage on the remaining minus and plus would be 72 VOC.
Parallel connection on the other hand, works by bound all the minus and all the plus connectors to a single one.
In this case, the voltage will stay the same (24VOC), no matter how many panels you add. Instead the current rises with each panel.
greetings
Erik
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@Selfmadestrom has provided some very useful pictures of series and parallel. And regarding the Y-branch connectors you linked to, you will notice they also are called “parallel connectors”, and they do actually allow parallel connections. When you want to connect in series you simply plug one panels’ MC4 into the appropriate MC4 on the next panel, etc. Once they are all linked you will have one of each type of MC4 connection available, one on the first and the other on the last panel linked, and those you connect via the solar extension cords to the AC300’s MPPT solar charge converter MC4 connectors.
For parallel connections you would need a pair of the parallel connectors like the Rich Solar ones you linked to. Those would be good to parallel two panels or two sets of series panels. It is possible to buy parallel adapters that allow paralleling of 3, 4, or even more panels, or sets of series panels, together.
For example, in my case I wanted two arrays of 6 panels. The most I can put together in series is 3 or the Voc becomes too much for the AC300 input. So I made two sets of 3 panels in series, and then put those two sets in parallel with each other. By using both series and parallel connections I was able to make a 1,500 watt solar array that had a Voc of 111 volts (each panel’s Voc is 37 volts). I can safely connect that to one of the solar inputs to my AC300 (and then I made another one just like it for the other solar input to get 3,000 watts of solar panels).
But here’s an interesting thing you may have noticed. The AC300 can only take up to 150 volts on the solar inputs. Also, the AC300 can only take 2,400 watts of solar input, and it can only take 12 amps on each solar input. But I have a 3,000 watt total solar array! And that won’t hurt anything. The voltage is a hard limit we need to design our array for because the panels “push” that voltage. But the wattage is determined by the voltage and the current from the array, and the current is managed by the charge controller. In my case my arrays can each supply over 16 amps, but the charge controller will only take up to 12 amps. So when the sun is really bright in the middle of the day then I can’t use all the solar power available from the panels. On the other hand, my array will be able to supply the maximum the AC300 can take for longer periods of time in the day, and in cloudy weather. Doing this is what is called “over paneling”, and this can be beneficial!
Getting back to your diagram, since you will be creating two arrays of 5 panels in each, and they will all be in series, then you will not need to get any of those parallel connectors.
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Regarding laying the panels on the roof, that’s more of a judgement call. It won’t hurt the panels, but if there is the potential for high winds it is possible they could be lifted up and thrown around.
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Thank you @Selfmadestrom. The diagrams are very helpful and now clear for me. Thank you for taking the time.
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Ahhhh…yes, that is something to consider…wind and lift-off. I appreciate all the additional info as well. Very helpful…I feel much more confident about this DIY project!
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I have 8 panels connected to AC500 (2x4 in serial connection) 400W each panel. Works like a charm. 2B300S batteries charge from 20% to 100% in about 2 hours in Belize sun.
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wow that is fast charging - thank you!
Hello again! I’m ready to set my 10 panels on the roof and will connec 5 in a series (waiting on bluetti). I am not quite
clear on the wiring. Please see attached photo.
How do I know which is - or + and the red/black connector cables? Is one positive or negative?
Thanks so much for your guidance!
Christina
Yes, one of the MC4 connectors will be positive, and the other negative. However, there is only one way to connect the panels to the extension cables, and only one way to connect the extension to the Bluetti adapter cable too. Normally they are all in agreement with their polarity between the panels and the Bluetti cable, so you should be OK to plug it all together.
Thank you. But won’t there be one panel that connect to nothing? So are you saying: the red will plug in at the end of the series (for example. Panel 5) and the black cable to the start of the series (Panel 1)??
Hi hynmann!
Almost there! I laid out my panels and was able to get this configuration. See photo.
I have 3 Questions:
-
The bluetti 300 has 2 MPPT controllers that I plug into so I do not need to make these parallel connections?
-
I have 4 cords with no connection (shown in red). So now I’ll use the 2 red long solar extension cables and the two black solar extension cables to connect to there empty male/females AND then connect those to the Bluetti cord? The goal is to funnel down the side of the house to the kitchen area where the bluetti will be.
-
Each Series will get same number of hours of sun but not all at the same time. Does that mean I will only see 975 Watts of charging at a time if set up as a parallel? Little confused here.
Thank you!
Christina
Thank you. But won’t there be one panel that connect to nothing? So are you saying: the red will plug in at the end of the series (for example. Panel 5) and the black cable to the start of the series (Panel 1)??
Yes, exactly right. 
Very nice! I see you’re going with the B300K batteries too. That’s a good way to go as their price point per KWh is better than the B300. So, for your questions:
- The bluetti 300 has 2 MPPT controllers that I plug into so I do not need to make these parallel connections?
True, you do not need to make the parallel connections. And actually, since you’ll have different hours of sunshine on each set it is better to connect them separately to each of the MPPT controllers.
- I have 4 cords with no connection (shown in red). So now I’ll use the 2 red long solar extension cables and the two black solar extension cables to connect to there empty male/females AND then connect those to the Bluetti cord? The goal is to funnel down the side of the house to the kitchen area where the bluetti will be.
Yes, that is correct. Make sure to label your cables so you know which pair is connected to which set of panels, primarily to make sure you connect the matched pairs from the panels to the pairs used for each MPPT controller.
- Each Series will get same number of hours of sun but not all at the same time. Does that mean I will only see 975 Watts of charging at a time if set up as a parallel? Little confused here.
Since you will have these panel sets (arrays) in different shading/sun conditions it will be best to not parallel them electrically. Also you will not use the “parallel” mode in the AC300 configuration either. By not having them paralleled each MPPT controller will independently handle each panel arrays’ power output. Regarding what you will see on the AC300 – if both sets of panels are fully in the sun at some point in the day you could see something along the lines of 1,600 watts coming in, since the MPPT controllers will add the incoming power together. The level of solar power coming in will vary as the day progresses, and that is as it should be for your setup as shading begins or ends. Even in my own case where I have two 1,500 watt arrays (I will only get a maximum of 1,200 watts from each), with each connected to one of the MPPT controllers, my solar input on a good day will start off at as little as 10 watts early in the morning, rising as the day progresses to as much as 2,200 watts (better in cold weather) around 1:45 PM. At some point in the day the batteries get full and then solar charging stops. As the batteries get down to 99% again the solar charging will start, and that will stop and start as needed to keep the batteries charged fully, with the amount of solar dropping as the day gets towards the evening. I’ll attach a screen capture from the Bluetti app that shows what that looks like on a particularly clear sunny day.
