Why are more people not doing 120v Solar System/ 120v batteries?

[hayden55]

I was looking at the current way people were doing it. It seems like people were tying their solar panels in parallel to keep the voltage at 48v but increase their amperage and their loss through the wires through increased electrical resistance which is sent to a mppt with an efficiency of 85%, and a transformer to up the power from 48v to 120v for usage with an efficiency of 75%. So efficiency ends up at 1.0*.85*.75= 63.75% efficiency minus the loss for the increased electrical resistance from wiring so many panels in parallel. So many process to go in a circle to produce one task. My idea is I want 10 360w solar panels. Three panels wired in series on each side, then wired in parallel to have a final voltage of 120v. When you do this and create a lithium battery out of the 3.6v batteries you can create whatever pack voltage your heart desires and have a much higher efficiency. 1.0*.85=85% minus electrical loss through resistance in the wires (less at less high amperage... smaller wires not as much loss). Also when you size the unit correctly you could actually read the load on the panel during peak hours for the house and send needed power directly to the house forgoing the battery route to power the house load (think hvac during peak solar hours) then send the rest to the battery... effectively reducing the size of the battery. My method only works for areas where you can legally do this. We can. If you can't oh well. (50v+ systems are high voltage and have more regulation). I'll need a kill-a-watt to start tracking my variables to size my system and maybe by 2019 I can have this system up and running. Currently with the low peak sun hours in the winter and the cheapness of gas heat its looking like a system with an electric AC system for cooling, and a gas central heat system for the winter is the best way to go. Also an electric tankless water heater. So as soon as I take measurements and get my system up to the task solar is going in.
Basically this is what is going on in cars to increase efficiency and decrease weight as well. High voltage systems with less conversions = maximum efficiency.
Give me your thoughts I'd love to hear it. Also mech. engineering guy here so ignore my bad grammar.

[Mike90250]

Because you can't buy a 120VDC microwave or coffee maker. Or light switches. or cell phone charger Or laptop adapter

Currently in production & for sale:
MPPT charge controller 95% efficient
AGM or LFP batteries 95 % & 98% efficient
Modern 48V pure sine inverter 85-90% efficient
I count only 20% as loss for off grid system,

For Grid-Inter Tie systems, it's +95% efficient.

[hayden55]

Because you can't buy a 120VDC microwave or coffee maker. Or light switches. or cell phone charger Or laptop adapter

Currently in production & for sale:
MPPT charge controller 95% efficient
AGM or LFP batteries 95 % & 98% efficient
Modern 48V pure sine inverter 85-90% efficient
I count only 20% as loss for off grid system,

For Grid-Inter Tie systems, it's +95% efficient.

Wow blatantly simple fact I missed. This is why I love forums. VDC not VAC.

I'm not trying to go off the grid or anything so this would be more of a Hybrid system. I'll actually have to check and see if my power company allows power buy back. My city already buys outside power, but my hometown has so many hydro electric dams they actually produce most of their power and apparently don't buy back power.
I'll have to look at what VDC converts more directly to 120VAC 60Hz.
But basically converting 48VDC to two legs of 120VAC is a pretty extreme jump versus say a single 192VDC or 96VDC system which converts more directly.
Interesting still so your system is 79.135% efficient. So somehow being able to send power to the house for amp draw from the house during solar production time is something to be desired since you get your 95% eff vs 79 eff making the system more efficient and your battery wouldn't need to be as big.

[littleharbor]

If you are looking for a high voltage charge controller here's one of the few I've seen. There's 5 versions from 96 volt to 240 volt systems.

https://www.ebay.com/itm/High-Voltage-PWM-Solar-Charge-Controller-Battery-Regulator-50A-for-PV-System/122882103632?epid=23004071547&hash=item1c9c581950:m:mvbdWt8_TQNakTsilKokGNQ

[PNPmacnab]

Why? When I was in college the IEEE had a contest for the best new use for a microprocessor. Everyone laughed when toilets won. That took 50 years to actually happen. You can barely get people to use 24V let alone 48V. I have almost no battery in my system and operate most things directly off higher panel voltage. Boy, did you pick the wrong forum to expound your ideas.

[ButchDeal]

I guess you have not looked at the SolarEdge StorEdge with LGRESU high voltage battery, 350V strings and high voltage battery pared with 99% efficient inverter.

[Sunking]

Why are more people not doing 120v Solar System/ 120v batteries?


Well I see no one has answered your question yet. Pretty simple, electrical codes. Once you go above 50 volts nominal, all the rules change. Above 50 volts requires grounding of equipment and raceways, and all electrical components must be made inaccessible to prevent accidental contact. Panel voltages can run as high as 600 to 1000 volts, but it is all contained in raceways.

Now commercial off-grid systems that Butch is referring to use much higher battery voltages up to several hundred volts. But those systems have the batteries inside cabinets the consumer cannot access.

[hayden55]

Ah high voltage has more regulation for certain situations. I'll have to go look at the SolarEdge StorEdge with efficiency.

[Guest]

Sir
I am from India where generally voltage from grid is 200V but in my area in winters it drops to 120V. I have recently installed grid tie solar inverter of 2KW which does not function because of low voltage.The requirement for the inverter to run is 180V. Can anybody help me to solve this problem?

[Mike90250]

Sir
I am from India where generally voltage from grid is 200V but in my area in winters it drops to 120V. I have recently installed grid tie solar inverter of 2KW which does not function because of low voltage.The requirement for the inverter to run is 180V. Can anybody help me to solve this problem?

You would use a large step up transformer to match the AC voltages, then the GT inverter should work again. The transformer needs to be a good quality, low loss transformer, or it will not pass the inverter startup Line Impedance test.

[citabria]

The AC vs DC discussion goes way back to when the concept of power distribution systems was being fought between Edison and Westinghouse. In short, high voltage DC systems will kill you quick, and has poor distribution efficiency. I have linked to a historical article, while not very in depth does cover some discussion from that era: https://www.smithsonianmag.com/histo...lry-102146036/

[jflorey2]

Why are more people not doing 120v Solar System/ 120v batteries?

Two main reasons.

1) Path dependency. For a long time 12V (cars) 24V (ships) and 48V (telecom) were the most common voltages out there, and thus there were a lot of chargers/inverters/protection devices available for those voltages.

2) 400V. If you want high voltages, 400V systems are now available - and will likely grow in popularity as time goes by.

[Mike90250]

The AC vs DC discussion goes way back to when the concept of power distribution systems was being fought between Edison and Westinghouse. In short, high voltage DC systems will kill you quick, and has poor distribution efficiency. I have linked to a historical article, while not very in depth does cover some discussion from that era: https://www.smithsonianmag.com/histo...lry-102146036/

That was true way back, when dynamotors to convert DC-DC were big, lossy and expensive. But now, with solid state gear, there are high voltage DC transmission lines, more efficient than AC.

https://en.wikipedia.org/wiki/High-voltage_direct_current

Also, for voltages over 48V nominal, the gear is supposed to be well shielded to prevent "dirty bags of water" (humans) from contacting the gear.
And it's more efficient to run a 500VDC line from the solar array to the inverter parked next to the inverter, and use 240VAC for the last 5 feet of connection
High voltage DC arcs are much more troublesome than AC arcs.

[bcroe]

That was true way back, when dynamotors to convert DC-DC were big, lossy and expensive. But now, with
solid state gear, there are high voltage DC transmission lines, more efficient than AC.

Nice article on DC transmission, a niche the rest of us seldom hear about. The world price of mercury
probably went down, when the gigantic mercury arc valves were phased out. Bruce Roe

[tyab]

Nice classic star trek reference!