> , I can’t simply combine the 12 panels into one string, > because even though the voltage would be very good, > the total power is higher than the inverter can handle on a single string > (3.7kW max per string).
I was under the impression that you can connect an oversupply of solar to most MPPT inverters, because they will simply max out at their rated power no matter how much solar is available. In fact, I have heard that many installers add about 20% more solar panels on the input to make sure the inverter is operating at max on the 95% of days that are less than perfect. Yes, the added 20% cost of solar panels is wasted on those 5% of days, but on average the higher efficiency makes up for it. My system actually DOUBLES the solar input power to the inverters. Each of my three 3 kW inverters are connected to SE and SW facing arrays since both are not fully illuminated at the same time (trees inbetween) and so I get two 3kW periods for twice as long during the solar day. In the winter both arrays can be illuminated at the same time trhough some twigs, but the MPPT just delivers its max rating and does not complain. (90 degrees apart can equal 1.414 times 3 kW or 4 kW or so) I did it this way because inverters are the highest cost in a system, and I can get DIY colar panels for 20% the cost of the original contractor's so I was able to double my annual output with only a 20% increase in cost (And it is DIY since I already had a net meter and all the permits and inspections.. So, I have three 3Kw inverters and each one is connected to TWO 3kw arrays each (facing separate East and West directions). And I make sure to have 14 panels in series on each, since around here, that is the max you can have and stay below the 600V max rating on the best winter day. My MPPT inverters still hang in there down to 195v DC input (compared to 450 to 500v normal) so this means as long as about half of the solar panels in any string are still in sun, then the MPPT is still able to produce max power from the remaing 7 panels. Bob -----Original Message----- From: EV <ev-boun...@lists.evdl.org> On Behalf Of Tom Keenan via EV Sent: Thursday, May 28, 2020 11:16 PM To: Electric Vehicle Discussion List <ev@lists.evdl.org> Cc: Tom Keenan <tnan...@yahoo.com> Subject: Re: [EVDL] : V2g for DIY EV's (economics) For those interested, here is a slightly more detailed write-up of my solar power system at home. The supplier for my system is Electriq. They provided a Darfon(Panasonic) charger/inverter and the Panasonic batteries. I believe the battery cells are similar to the ones used by Tesla, but am not sure. The inverter itself runs at 48v (nominal). I have six sets of 48v batteries wired in parallel to the charger/inverter input. Each of the individual units of the six pack is rated around 3 kWh, but in practice they are kept to about 2.5 kWh by limiting how far up and down they can go while charging and discharging in order to maintain the health of the overall battery system. Thus gives me around 15 kWh at about 48 volts for the battery. The solar array is two strings of six panels, for about 2kW (@240v) for each of the two strings, making it a 4kW (nominal) system. Depending on the sky clarity and temperature, I’ve seen the array put out up to 5kW for brief periods of time. More normal to see it around 3.8 or so kW. If I had to do it again, I’d have two strings of 7 panels to make the MPPT more robust. But putting up two more panels and this point would only add to the amount of ‘credit’ I’ll lose at the end of the year, so I’ll take the efficiency hit. As it is, the voltage of six panels is on the edge of being able to use inverter-based MPPT or not, depending on how much sun they are getting. Generally the voltage is just a little bit (1 or 2 volts) too low to work consistently. With an extra panel in the string, it would normally be in MPPT mode. Unfortunately, I can’t simply combine the 12 panels into one string, because even though the voltage would be very good, the total power is higher than the inverter can handle on a single string (3.7kW max per string). The inverter is rated at about 5.7(?) kW continuous, but will peak higher for certain brief periods. I saw it around 8kW once when I plugged in my EV without first checking the charge amp limit, and it handled it gracefully. I will be charging the Kona tomorrow because I drove it about 50 miles this evening. I’ll plug it in around 10:30 am after the house battery has finished charging. Depending on how sunny it is, and if it is warm enough that I want to turn on The A/C in the house (not likely), I’ll set the car charge amps somewhere between 10 and 20 amps (@240v). Tom Keenan > On May 28, 2020, at 7:11 PM, Willie via EV <ev@lists.evdl.org> wrote: > > Thomas's post didn't make it to me. I'm pleased to see it completely > quoted here. > >> On 5/28/20 8:09 PM, Alan Arrison via EV wrote: >> Tom, could you give some specifics on this system, or point us to a web >> page? >> What battery? What inverter? >> Thanks, Al >>> On 5/28/2020 1:24 PM, Thomas Keenan via EV wrote: >>> Where I live, the local utility has some odd rules, but I do get >>> credited $0.06968 for each kWh given back to the grid. I have a >>> permitted 4 kW array that feeds a Darfon/Panasonic inverter/charger for >>> a 15kWh (useable) battery that was commissioned in January. The battery >>> covers times when the panels aren’t putting out enough to power the >>> house, such as overnight. Overnight, the house uses two or three kWh >>> that comes from the battery. In the morning the battery recharges, and >>> is typically done charging around 10:30 in the AM. After that, any >>> excess is sold. >>> >>> This inverter/battery setup has been working very well. The battery has >>> not been below about 50% so far, and that was during a three-day rain >>> event where the system wasn’t producing much. Aside from those >>> (somewhat rare) rain events, I generally have around 10-20 kWh excess >>> that is sold back to the grid daily. > > This is much the same as my PowerWall set up which has been running about > 15 months. The PW allows me to avoid all electricity purchases. But the > PW cost can not be justified by the savings. > > I sell over production for $.0645/kwh and buy at about $.10. The PW > allows me to not buy about 10kwh each night. So, my daily savings from > using the PW is only about 10 x ($.10-$.0645) or less than $.50/day. I > don't buy the 10kwh at night but I have to use 10kwh during the day to > charge the battery and thus do not sell that 10kwh. The PW cost $13k. I > justify that cost with grid down security. > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > ARCHIVE: http://www.evdl.org/archive/index.html > INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org > Please discuss EV drag racing at NEDRA > (http://groups.yahoo.com/group/NEDRA) > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20200528/c227fd30/attachment.html> _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub ARCHIVE: http://www.evdl.org/archive/index.html INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA) _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub ARCHIVE: http://www.evdl.org/archive/index.html INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
