I recommended to my friends, who have very little technical knowledge, in Sep 2022 a Bluetti system consisting of an AC500 and four B300S batteries. They were just keeping it for backup and I suggested they add solar panels to their system. I’ve completed the design with three solar panels in each of the two DC strings and am interested in confirmation on the DC input limits and how firm the max wattage is.
The AC 500 manual states: 3000W max (was told on another call this is 1500W max per DC input), 12-150VDC max, and 15A max.
CED Greentech here in San Diego offers 23 different solar panels. I did the design using STC Isc and Voc and also Voc adjusted for record cold, which is -2 degrees C in Oceanside CA. Only four panels fell below the maximum for the 1500W power maximum at STC and one of the dropped out for power adjusted for low temperature.
Three Silfab SIL 400 HC+ panels are within the voltage and current limits for the AC500, even at the minimum low temperature and would add a hundred watts per string if I could use those rather than the REC REC365NP2 Black panels. In addition, the max power for the Silfab panels under NOCT conditions is 298 watts/panel or 898 watts per string. The REC panels under NOCT conditions is 276 watts/panel or 828 watts per string.
I’ve read that the max Isc and max Voc (adjusted for low temperature) are hard and fast limits for solar charge controllers (SCC) and I assume that’s the case for the AC500. Some have said that the “Watts” limits aren’t actually limits, but that they do affect self-heating of the SCC and lifespan.
Designing using STC is definitely the safe, conservative method. However, for the Silfab panels this shows exceeding the AC500 max wattage, even though staying below the AC500 max voltage and AC500 max current.
So the question(s): how hard and fast is the max wattage limit on the AC500 and what damage may occur to the AC500 SCC if the stated max wattage is exceeded?
The max wattage is the MOST it will receive, any excess is not used.
In fact, when it comes to solar panels, you will likely have to “overpanel” to get to the limit because you won’t get the rated output from them. A 100 watt panel will produce around 80 watts.
I started with 15 100W panels, expecting to get 1500W into one of the two PV inputs. I got only 1200W on a good day. I ended up with 18 100W panels, and I average 1490-1495W. Overpaneling is also useful for rainy cloudy days, gathering up whatever light they can get.
Besides the 2 pv inputs, you can also connect the B300s batteries to solar panels using the provided cables with each battery. These will add to the total overall wattage input. (These have only a 60 Voc limit.)
You can also buy a special 30 AMP connector to charge the AC 500 from a Tesla outlet plug, if you have a Tesla.
So bottom line, excess wattage doesn’t matter. It will take only as much as it needs and ignore the rest.
Correction, the charging cable is 50 amps, not 30.
Also, like wattage, you don’t have to worry about Current; it will only draw up to the 15A limit and no more, which is also how you determine wire size to the PV Panels. 14 gauge wire is rated up to 15 amps; 12 gauge for 20 amps if you want to splurge for thicker wire.
Naturally you want to get the most power you can to the charging inputs, so in wiring up a panel array, you can wire panels up in Series or Parallel or a combination of both.
Voltage adds in Series.
Amps add in Parallel.
As an example in my 18 panel array, I have 3 strings of panels wired in Parallel. Each string has 6 panels wired in Series. That’s the way the math worked out to keep Voc below 150V.
6 x 24.3Voc = 145.8V
3 x 5.21 Isc = 15.63A
The theoretical wattage is 2187W, but 1500W or less is the real world wattage.
There is no Current limit and also no Watt limit.
The power station Regulates how many Amps it wants to pull and therby the Max Power in watts.
You only have to look out for the maximum Voltage.
(but a view volts over won’t instantly kill it. there is some headroom and it will warn you if you have over voltage)
You can and shuld “overpanel” your solar input so get maximum charge rates even at non ideal weather.
its very common practice to add around 1,5-2 times more PV peak power than your charge controller can handle.
Thank you St8kout and lambda,
That’s great to hear that the AC500 will only draw up to 1500 watts and 15 amps. I’ll definitely make sure the design stays below the Voc, including the temperature coefficient of Voc.
CED Greentech here in San Diego is currently offering these panels. Based on your feedback I’ll look to overpanel the system with the SilFab SIL 500HM panels. These are the largest available to us. I used these panels and ran through the calculations with PVWatts calculator (PVWatts Calculator) and it showed about 5,250 kWh/year.
I would love to incorporate more panels but I’m dealing with placement constraints. Due to HOA restrictions, my friends’ solar panels must be ground mounted rather than roof-top mounted. They also must not show from the street. They also must fit between a driveway, two fences, and a raised garden bed. This limits the design to two separate rows of three portrait mounted solar panels. Unfortunately one array of two rows by three portrait solar panels would bring the solar panel height above the top of the fence. The inter-row spacing I calculated has the north row very close to the fence and the south within a couple feet of the raised garden bed.
I did mention to my friends that if they were concerned about a long grid down situation they could buy some smaller solar panels, lay them in the back yard, and use them to directly charge the B300S batteries.
St8kout, thanks for the information on the wire gauge. I’ll probably recommend the 12 gauge wire since the wiring run from the location of their Bluetti system in their garage and the solar panel array is about 100 feet and 12 gauge will have 1.3 volt less drop, according to the voltage drop calculator at http://www.calculator.net/
The design does include the 50 amp AC charging cable to connect the AC500 to a NMA-50 socket that will be installed in the garage to charge the AC500 from the grid. The design will also include connecting the AC500 from the NEMA 14-50R outlet back to the main house circuit panel through a Reliance Control PRO/TRAN2 manual transfer switch (actually six individual transfer switches).
Thank you again,
Update. Here’s the reply I received from Tony from Bluetti technical support in response to the same question: “how hard and fast is the max wattage limit on the AC500 and what damage may occur to the AC500 SCC if the stated max wattage is exceeded?”
AC500 has two PV ports (DC1 and DC2) and supports two strings of solar panels, and the open circuit voltage of each string should be within 12-150 VDC, and 1500W ± 50W / 15A ± 0.5 A MAX for each DC port, and total 3000W±100W MAX solar input for AC500.
AC500 will limit the input current to 15A MAX from solar panels and no impact on the AC500 and solar panels, and AC500 has both overcurrent and overvoltage protection mechanism, it has been widely used all round the world and it is safe and reliable.
I’m going to stay below the Voc (including low temperature) and the Isc, but will overpower the panels.
If interested, here are two great threads related to overpaneling:
How do MPPT charge controllers curtail the power if the load is less than the solar generation?
Excess energy from my off grid system
For DIY you want the panels on the ground. If roof mounted you’ll have to get permits and inspections, and notify your Home Owners Insurance. (Not sure if the HOA can ban roof panels professionally installed by Grid Tie system companies.)
Anyway, you’ll need to allow for changing sun angles throughout the year. I set up mine last spring, and now I had to move one array (which is on wheels) to another part of the yard because part of it ended up in the shadow of the house, severely lowering the output.
I’m waiting on a delivery of those new Bifacial 500W panels which I’ll mount against my block wall facing South far away from the house shadow. I placed the order almost a month ago and the truck delivery got delayed until next week.
Thanks for the feedback. My friends checked with their HOA and home owners insurance and there are no issues and they have a green light to do a roof install. Even with permits this will be cheaper than the panels on the ground. They are not technical at all and having them out of sight will be an advantage. They were not going to bother with making monthly or quarterly adjustments throughout the year with the ground mount anyway. I ran calculations for solar production for their roof using the PV Watts Calculator https://pvwatts.nrel.gov/pvwatts.php and also the California Solar Initiative Incentive Calculator https://www.csi-epbb.com/. The latter calculator allows you to select the solar panels and inverters from a large list of panels and inverters. The solar production is a little lower than the PV Watts calculator. Another nice feature of the latter calculator is that it also provides the solar production for the panels and inverter selected if the panels were at optimum tilt and facing south. This gives a nice comparison.
I used a sun path chart program at University of Oregon to help look at sun azimuth and elevation throughout the year when I was working the the ground mount solution. http://solardata.uoregon.edu/SunChartProgram.php
I used solar angle calculator to get the best solar angles throughout the year, but again this was for the ground mount approach. https://footprinthero.com/solar-panel-angle-by-zip-code.
It sounds like you’ll have quite an efficient system when you get your new 500W Bifacial panels installed!