Distance to choose string over micro inverters?

[Mike90250]

You can never generate and store and use solar power via batteries, as cheaply as you can buy it from the grid. Not even in Hawaii. The expense of replacing battery banks is 5x the cost of buying that power from the grid.

What's your grid cost of a KWh $0.20 ? ( cents symbol truncated my post )
Whats your cost of a new battery bank every 3 years ?

If the math works for you, fine.

[buckettea]

In the XW that I have, the Inverter, while it's qualifying the generator, slowly syncs itself to the generator, and likely flips the transfer relay at a zero voltage crossing point. Small glitch, one out of 20 times, it trips my GFIC's and I get to play hunt the tripped circuit (easier in the dark when the orange light shines like a beacon)

It's likely the better inverters also sync to the grid, but as good as they can be, it still has a non-zero effect. Designing / planning a system that will do this several times a day, while the grid is good, I don't understand. Keep the batteries full, let the inverter pump power into the grid, and avoid activating the transfer switches as much as possible.

Off grid with a generator, you do what you can, and reset stuff.

my problem is i can't feed back into the grid, so to make financial sense i need to use all of the solar and then the batteries overnight so i'm not paying for grid power (else it defeats the purpose).

the only interaction i want from the grid is to provide the extra load if i can't get it from the PV/batt and add charge to the battery should it drop below a low-water mark. when i no longer need this (more solar, more batteries, better efficiency) then i'll stop paying the service charge and say goodbye to them.

[Mike90250]

......does make me wonder though, in the case of complete off-grid systems where a generator is also deployed along side the battery bank how do they get around the 'glitching' of the generator kicking in? is it just a case of putting up with it?

In the XW that I have, the Inverter, while it's qualifying the generator, slowly syncs itself to the generator, and likely flips the transfer relay at a zero voltage crossing point. Small glitch, one out of 20 times, it trips my GFIC's and I get to play hunt the tripped circuit (easier in the dark when the orange light shines like a beacon)

It's likely the better inverters also sync to the grid, but as good as they can be, it still has a non-zero effect. Designing / planning a system that will do this several times a day, while the grid is good, I don't understand. Keep the batteries full, let the inverter pump power into the grid, and avoid activating the transfer switches as much as possible.

Off grid with a generator, you do what you can, and reset stuff.

[buckettea]

Nope, the general design and operation is that the Grid supplies all loads for seamless power delivery (and not keep glitching your AC as inverter switches on and off)
The Solar PV first charges the battery up, and when the battery is full, the inverter is enabled and all PV power is delivered to the grid. This avoids needless cycling of batteries and wearing them down prematurely. This can be enhanced with some time of use settings in inverters to use battery power for internal loads during peak use hours, shaving more off your bill. The next morning, PV power is devoted to recharging the batteries, and then back feeding grid begins

thanks mike, ok so i can see the issue of 'glitching'. i was hoping modern inverters could overcome this somewhat. by your post it sounds like there really isn't a product that will do what i want it to do off the shelf.

i do have some flexibility in that my grid input to the inverter will actually be on a dedicated circuit from the mains box and i could potentially remotely trigger that on/off as required. it sounds though like i sort of have to plan for the end goal of no grid to avoid this.

does make me wonder though, in the case of complete off-grid systems where a generator is also deployed along side the battery bank how do they get around the 'glitching' of the generator kicking in? is it just a case of putting up with it?

[Mike90250]

I'm still not sure a bimodal/hybrid will do what i'm after, but then i have no experience with these products. what i'm really trying to do is:

have a solar PV/battery as the main source of power (in AC, obviously) and then use either an input from the grid or an input from a generator to take up any shortfall (preferably automatically) based on a rule as to where to keep the battery level at what time of day.

Nope, the general design and operation is that the Grid supplies all loads for seamless power delivery (and not keep glitching your AC as inverter switches on and off)
The Solar PV first charges the battery up, and when the battery is full, the inverter is enabled and all PV power is delivered to the grid. This avoids needless cycling of batteries and wearing them down prematurely. This can be enhanced with some time of use settings in inverters to use battery power for internal loads during peak use hours, shaving more off your bill. The next morning, PV power is devoted to recharging the batteries, and then back feeding grid begins

[Palmtree]

Cost effectiveness certainly makes a difference to me. 14kw would be a bit oversized I'm really just trying to future proof as Much as possible while some incentives are still in place. My wife drives a Chevy volt and my Prius has 270,000 miles on it. I'm sure it will be replaced with something electric so our consumption is likely to rise in the near future.

[J.P.M.]

Thanks for all the great info. With the savings of string inverters over micro I could possibly bump the system up to 14kw.

Assuming the proposed design is not oversized, does system cost effectiveness have any importance in the design ?

[Palmtree]

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.

Yes. It will be ground mounted. Shading will not be an issue by the time the sun is high enough to really start producing it will be well above the trees to the east. Thanks for all the great info. With the savings of string inverters over micro I could possibly bump the system up to 14kw.

[buckettea]

I'm still not sure a bimodal/hybrid will do what i'm after, but then i have no experience with these products. what i'm really trying to do is:

have a solar PV/battery as the main source of power (in AC, obviously) and then use either an input from the grid or an input from a generator to take up any shortfall (preferably automatically) based on a rule as to where to keep the battery level at what time of day.

[buckettea]

3kw not 3kwh of modules.

usually inverters feed extra power into the grid. If you dont have net metering or cant feed into the grid then you change the configuration and the charge controller will shut off the array so no power is generated or set the MPPT to off optimal to generate only the power level needed.

sorry, i missed your response. that's helpful, i was more concerned about the safety aspect (fire and equipment). i concluded by the reddit article that if there is no demand the panels just won't produce any power. i hope that's right... i guess like many others it's too big or too small and trying to get a nice balance where i can just modify my activities to suit what i have to hand is my goal.

[buckettea]

i found my answer here (i think):

https://www.reddit.com/r/explainlikeimfive/comments/5ncjzx/eli5_where_does_excess_power_generated_by_solar/

[ButchDeal]

thanks - one last question, if the batteries are full and the load isn't using everything being generated what happens to the excess power (not being fed into the grid)? is it just dissipated in heat or something? obviously that's not what you'd want as the scenario, but i'm thinking of if i went away for a few days. my usage now is low-ish, 12kWh/day or so, and the plan would be to only have about 3kWh of panels but then perhaps a 13kWh battery. i occasionally have a high consumption, which is fine while i'm grid connected as well but thinking when i go off grid the battery needs to store at least enough to cover those days of high demand.

3kw not 3kwh of modules.

usually inverters feed extra power into the grid. If you dont have net metering or cant feed into the grid then you change the configuration and the charge controller will shut off the array so no power is generated or set the MPPT to off optimal to generate only the power level needed.

[buckettea]

It is impossible to charge and discharge at the same time... if the batteries are full ethen all the "charge" goes to the inverter.

you would need a bimodal either way though if you want batteries.

you could try the new outback which can work without batteries and add them latter, or the solaredge storedge solution which can as well as having optimizers.

thanks - one last question, if the batteries are full and the load isn't using everything being generated what happens to the excess power (not being fed into the grid)? is it just dissipated in heat or something? obviously that's not what you'd want as the scenario, but i'm thinking of if i went away for a few days. my usage now is low-ish, 12kWh/day or so, and the plan would be to only have about 3kWh of panels but then perhaps a 13kWh battery. i occasionally have a high consumption, which is fine while i'm grid connected as well but thinking when i go off grid the battery needs to store at least enough to cover those days of high demand.

[ButchDeal]

good question but wouldn't that mean my batteries are working all the time (constantly charged by PV and discharged by the inverter) reducing their lifespan? when the alternative is to by-pass that step and take the AC direct from the micro-inverters while it's sunny and it satisfies the load?

and i know at least some of my panels will be in shade, so there was that. but thanks for the response, it sounds like bimodal is probably what i'm going to need.

It is impossible to charge and discharge at the same time... if the batteries are full ethen all the "charge" goes to the inverter.

you would need a bimodal either way though if you want batteries.

you could try the new outback which can work without batteries and add them latter, or the solaredge storedge solution which can as well as having optimizers.

[buckettea]

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.

good question but wouldn't that mean my batteries are working all the time (constantly charged by PV and discharged by the inverter) reducing their lifespan? when the alternative is to by-pass that step and take the AC direct from the micro-inverters while it's sunny and it satisfies the load?

and i know at least some of my panels will be in shade, so there was that. but thanks for the response, it sounds like bimodal is probably what i'm going to need.