Distance to choose string over micro inverters?

[ButchDeal]

do you not also need to take into account safety? i understood that with micro-inverters you're dealing with AC at 240v (considered low voltage in oz) as opposed to high voltage DC at 600v (depending on your array size) . also, with a string inverter you have a single point of failure which is probably ok in a grid-tied system but may be decidedly inconvenient in an off-grid system.

i'm only just beginning to design a system that suits my needs and scenario and was sold on micro-inverters for those reasons (and the shading issue) but admit i'm a complete amateur. i'm not even sure what i'm thinking for me can be achieved... but very interested in hearing an experts take on it.

i'm grid connected but want to get off when i have enough of my own generation and storage (so slowly). I do not want to feed in to the grid for various reasons so that's not a requirement.

i was thinjing a string inverter supplying my AC load (panels would be at least 100ft from where the power is needed, and ground mounted). That inverter would ideally take in an AC tie to the grid to cover any shortfall in AC produced by the inverter, the inverter itself fed by batteries (DC) also. Even if i can get that product (???), then it comes down to how to charge the batteries. If i have micro-inverters, then i could in theory run the AC into an AC to DC battery charger, but now i'm going DC-->AC-->DC which seems silly? Ideally i'd be able to take a DC feed (pre AC micro-inverter) and feed that to a DC-->DC charger to charge the batteries with spare capacity from the panels, but i'm not sure you can do that while the micro-inverter is also connected to the panel?

So in summary, the grid AC would be there if the batteries ran low (this would also be used to charge the batteries via AC-DC charger in the case it was appropriate (battery damage by being discharged too low)). Once i have enough panels/batteries for that not to a regular requirement i'd be replacing the grid AC input with a generator AC input.

Can all this be done? i don't mind purchasing two inverters to achieve it (and put it down to having some redundancy in the case of a failure). I think it's called AC coupling, but don't quite understand it. I realise i might need some 'smarts' to prevent over-charging of batteries or over-discharge. Ideally i'd wake up in the morning with enough juice left in the batteries until the sun came out and if not, take AC from the grid and put some charge in and/or use the grid AC to satisfy loads.

Sure you could do AC coupling but then you have your single point of failure again so why bother woth the micros.

get a bimodal oe hybrid inverter and connect the grid, batteries and your load.

[buckettea]

do you not also need to take into account safety? i understood that with micro-inverters you're dealing with AC at 240v (considered low voltage in oz) as opposed to high voltage DC at 600v (depending on your array size) . also, with a string inverter you have a single point of failure which is probably ok in a grid-tied system but may be decidedly inconvenient in an off-grid system.

i'm only just beginning to design a system that suits my needs and scenario and was sold on micro-inverters for those reasons (and the shading issue) but admit i'm a complete amateur. i'm not even sure what i'm thinking for me can be achieved... but very interested in hearing an experts take on it.

i'm grid connected but want to get off when i have enough of my own generation and storage (so slowly). I do not want to feed in to the grid for various reasons so that's not a requirement.

i was thinjing a string inverter supplying my AC load (panels would be at least 100ft from where the power is needed, and ground mounted). That inverter would ideally take in an AC tie to the grid to cover any shortfall in AC produced by the inverter, the inverter itself fed by batteries (DC) also. Even if i can get that product (???), then it comes down to how to charge the batteries. If i have micro-inverters, then i could in theory run the AC into an AC to DC battery charger, but now i'm going DC-->AC-->DC which seems silly? Ideally i'd be able to take a DC feed (pre AC micro-inverter) and feed that to a DC-->DC charger to charge the batteries with spare capacity from the panels, but i'm not sure you can do that while the micro-inverter is also connected to the panel?

So in summary, the grid AC would be there if the batteries ran low (this would also be used to charge the batteries via AC-DC charger in the case it was appropriate (battery damage by being discharged too low)). Once i have enough panels/batteries for that not to a regular requirement i'd be replacing the grid AC input with a generator AC input.

Can all this be done? i don't mind purchasing two inverters to achieve it (and put it down to having some redundancy in the case of a failure). I think it's called AC coupling, but don't quite understand it. I realise i might need some 'smarts' to prevent over-charging of batteries or over-discharge. Ideally i'd wake up in the morning with enough juice left in the batteries until the sun came out and if not, take AC from the grid and put some charge in and/or use the grid AC to satisfy loads.

[sdold]

Palmtree: Will the array be ground mounted? I can't think of any advantage to using microinverters or optimizers instead of a simple string inverter on a ground-mounted array with no shading, other than meeting rapid shutdown requirements at the module level. The most oft-cited reason I hear is panel-level monitoring, which you'll probably pay attention to for a month or two, and ignore after that. Until you think you are under-producing, that is, but with a ground-mounted array it's pretty easy to measure each panel with a clamp-on meter.

[J.P.M.]

Doesn't buying optimisers put you over half way to paying micro's?

Any doesn't high voltage DC still require larger cable for 200 feet....I am not a pro so just asking for a friend.

Short answer to # 2 above: Longer runs will increase voltage drop. That may necessitate greater wire thicknesses (numerically lower wire gages). Greater current flows will require thicker wire.

BTW, for a well designed array with the well designed part including not a lot of shade, and because the use of neither micros or optimizers will produce any more electrical power from shaded panels than a straight string inverter, I don't think there's an absolute reason optimizers for micros for most any residential application. The PV police will not get on you for a well designed simple array with a string inverter.

Example, I've got a 5 kW array with a string inverter that has an annual late afternoon shading loss of right around 3%. Micros or optimizers would reduce that loss to maybe 2.5 % or so. Micros were easily available 5+ yrs. ago, but the cost of the micros would have added ~ 1.5% to the cost (~ $280/$16480 after tax credit), saved me ~ $9/yr. in avoided billing, and would have put more electronics on a roof with all the increased probability of failure that goes with more complication. I'd be kind and assume optimizers would net out about the same for cost, complexity and the increased probability of failure.

[ButchDeal]

Doesn't buying optimisers put you over half way to paying micro's?

SolarEdge is cheaper than micros on most systems over about 2.5kW. Most people seem to miss calculating for the cost of the proprietary enphase cabling

Any doesn't high voltage DC still require larger cable for 200 feet....I am not a pro so just asking for a friend.

No. why would it. The higher the voltage the smaller the cable can be for the same amount of power, doesn't really matter if it is AC or DC.

[ButchDeal]

I was thinking that micro inverters would be more convenient and that it would be nice to monitor each module.

SolarEdge allows lifetime free PV module level monitoring. Enphase costs for module level monitoring.

[bcroe]

I operate similar power and distances. The DC running up to 400 feet has max
losses just over 1%, my AC losses over 250 feet exceed 3%. Clearly if you do
not have shadowing problems, its more efficient to make as much of the run at
high DC voltage instead of lower AC voltages. In addition, the overall hardware
(wiring) cost will be way down. Individual unit performance can be checked
other ways, and in fact very rarely need to be after a satisfactory system launch.
Bruce Roe

[NewBostonConst]

Doesn't buying optimisers put you over half way to paying micro's?

Any doesn't high voltage DC still require larger cable for 200 feet....I am not a pro so just asking for a friend.

[J.P.M.]

I was thinking that micro inverters would be more convenient and that it would be nice to monitor each module.

Unless you've got a shade problem micros are of little benefit. Just more electronics to fail. KISS applies. IMO only, for a well designed (including the economics) and appropriately sized and sited array, micros are hard to justify.

Besides, if you're similarly inclined to most folks, chances are you'll quickly tire of the novelty of looking at output.

Not that it matters much, but some vendors I've talked to who seem to be knowledgeable see some owners worried about things that don't need to be worried about like individ. mod. outputs that are a watt or two different from one another. A little knowledge on owners part is very good, but the small amount can make all perceived differences the same in in terms of importance.

[Palmtree]

I was thinking that micro inverters would be more convenient and that it would be nice to monitor each module.

[ButchDeal]

Well if you are just looking at line losses from voltage drop then high voltage DC is better.
But why would you consider micros in the first place for a 12kW? if there are shadows then use SolarEdge and get optimized features as well as high voltage and reduced costs.
Micros cost more the larger the system, they tend to be cheaper on small system under 2.5kw.

[Palmtree]

I am in the planning stages of a 12 kw grid tied system. The best location for the array is about 200 ft from my meter. Should I run high voltage DC to a pair of string inverters 200 feet away or would it be a better choice to use micro inverters and run 240v AC over the 200 feet?
Thanks