# Sunny Island doubts

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• Solar Expert Posts: 262 ✭✭
Re: Sunny Island doubts

I understand what you want to do (I also have a battery-based system with grid support but no sell to grid). There's something you must think about here though. Your plan seems to be to put a very large constant load on the system when the sun conditions are good. But remember that a cloud can come by at any time, putting the whole load on the batteries. Even if an inverter existed that did what you want in this situation, based on what you said above, which is to start to take the load off of the battery bank to prevent it from falling below a certain voltage, you'd still have a huge load on the bank until it reached that set voltage. So you'd have to make sure the bank was large enough to support that load without being damaged. Another thing is what you'd do with the surplus once the batteries entered absorb and then float (needing progressively less power). If you didn't somehow systematically add loads, it would be wasted.

My point about the charging and absorption is that as the battery voltage falls with a heavy load, you want the grid to come in to help by having a trigger voltage that tells the inverter to start taking power from the grid (I'm taking this from your comment in post 23). But how much power? I'm guessing you have in mind that the grid power would be progressively added to keep the voltage from falling below some set point. So if the set point is 49 volts, say, then when the bank hits 49 volts under load, the inverter adds grid power to keep it from going lower (otherwise the bank will just keep falling as it drains and quickly get disconneted). Is that what you had in mind? If so, then the battery contribution will get progressively smaller as they lose charge (fewer amps), even though the voltage is held steady. This would be the opposite of the absorption stage in the charging cycle (constant voltage, decreasing charging amps).

Here's another potential problem with that idea, although it wouldn't be insurmountable. Normally, if you tell an inverter to disconnect the batteries at, say, 49 volts under load, the battery will not be discharged that deeply. How deeply exactly depends on the size of the load and the age of the batteries. But on my system, for example, with my normal household loads, a cut-off of 49 volts would leave the batteries at around an 85-90% SOC. However, with the idea you have (at least as I've described the details), such a cut-off would lead to a much lower SOC, since the batteries would continue to add a little power until they really couldn't hold 49 volts at all (this would be about 60% SOC on a new 48 volt bank). Now, you could partially mitigate this by basically reversing the absorption cycle here too. Absorption charging can be set to end when the batteries can no longer take charging amps below a certain percentage of their 10- or 20- hour amp-hour rate (like 2 or 3%). And you could likewise have them cut off when they could no longer provide 2 or 3% of their capacity in amps. But it would still be a much deeper discharge, and users would have to learn to change their expectations accordingly.

Maybe this is among the reasons why, to my knowledge, no inverter manufacturer has ever made such a design.

I and some others have gotten close to 100% capacity utilization in a different way: basically by letting the charge controller handle opportunity loads, and especially by using pwm signals from the controller to tell a relay to vary the input voltage on resistive loads like heating elements. Chris Olsen has posted here and elsewhere on how to do this, and it works well because the power to the element is scaled very closely to the available surplus after battery charging and constant loads.
• Solar Expert Posts: 600 ✭✭
Re: Sunny Island doubts
Eric L wrote: »

Maybe this is among the reasons why, to my knowledge, no inverter manufacturer has ever made such a design.

Eric,

See post #13 in this thread. I believe Outback inverters using HBX mode do exactly what he is asking and do it in a way that avoids some of the pitfalls you describe.

I agree that there may be better ways to achieve full use of PV without selling but that is different than saying no inverter can do what he wants.
• Solar Expert Posts: 124 ✭✭
Re: Sunny Island doubts
Eric L wrote: »
I understand what you want to do (I also have a battery-based system with grid support but no sell to grid). There's something you must think about here though. Your plan seems to be to put a very large constant load on the system when the sun conditions are good. But remember that a cloud can come by at any time, putting the whole load on the batteries. Even if an inverter existed that did what you want in this situation, based on what you said above, which is to start to take the load off of the battery bank to prevent it from falling below a certain voltage, you'd still have a huge load on the bank until it reached that set voltage. So you'd have to make sure the bank was large enough to support that load without being damaged. Another thing is what you'd do with the surplus once the batteries entered absorb and then float (needing progressively less power). If you didn't somehow systematically add loads, it would be wasted.

My point about the charging and absorption is that as the battery voltage falls with a heavy load, you want the grid to come in to help by having a trigger voltage that tells the inverter to start taking power from the grid (I'm taking this from your comment in post 23). But how much power? I'm guessing you have in mind that the grid power would be progressively added to keep the voltage from falling below some set point. So if the set point is 49 volts, say, then when the bank hits 49 volts under load, the inverter adds grid power to keep it from going lower (otherwise the bank will just keep falling as it drains and quickly get disconneted). Is that what you had in mind? If so, then the battery contribution will get progressively smaller as they lose charge (fewer amps), even though the voltage is held steady. This would be the opposite of the absorption stage in the charging cycle (constant voltage, decreasing charging amps).

Here's another potential problem with that idea, although it wouldn't be insurmountable. Normally, if you tell an inverter to disconnect the batteries at, say, 49 volts under load, the battery will not be discharged that deeply. How deeply exactly depends on the size of the load and the age of the batteries. But on my system, for example, with my normal household loads, a cut-off of 49 volts would leave the batteries at around an 85-90% SOC. However, with the idea you have (at least as I've described the details), such a cut-off would lead to a much lower SOC, since the batteries would continue to add a little power until they really couldn't hold 49 volts at all (this would be about 60% SOC on a new 48 volt bank). Now, you could partially mitigate this by basically reversing the absorption cycle here too. Absorption charging can be set to end when the batteries can no longer take charging amps below a certain percentage of their 10- or 20- hour amp-hour rate (like 2 or 3%). And you could likewise have them cut off when they could no longer provide 2 or 3% of their capacity in amps. But it would still be a much deeper discharge, and users would have to learn to change their expectations accordingly.

Maybe this is among the reasons why, to my knowledge, no inverter manufacturer has ever made such a design.

I and some others have gotten close to 100% capacity utilization in a different way: basically by letting the charge controller handle opportunity loads, and especially by using pwm signals from the controller to tell a relay to vary the input voltage on resistive loads like heating elements. Chris Olsen has posted here and elsewhere on how to do this, and it works well because the power to the element is scaled very closely to the available surplus after battery charging and constant loads.

That's why first talked on soc and not voltage, but in 90%of the days I will have enough sun/batts to not need grid on the loads that will be in the inverter ...
On the night/winters I think in some days I will have to fail to the grid and on the night it could be a complete grid change over (no batt charging from the grid) what I want is these would be managed completely by the inverter no need for DIY/bricolage components.

Soc> 60% take all from batts/solar.
Soc<60% change to grid ( full or partially)

Adding loads when the Sun is producing at high rates is something that i already do +/- manually:
Manually: everyone knows that when the led is green put the machines to work
Auto: when battery enters float hot water system turn on, second batt bank start charging from a dc dc charger controller....
Have to think a few more....

This weekend the full PV will be ready and next week have to think on the inverter, my studerxpc2200 + USPS are not enough to use all this power ... And even if my studer can cope with "parasite 400w" I can't risk to put that circuits on the current inverter because If someone remember to connect hair dryer or a vacuum cleaner on the plug... Cabum...

Im almost decided by the victron going talk to them to see if I can connect the bvms to the inverter and so use the soc....
• Solar Expert Posts: 1,925 ✭✭
Re: Sunny Island doubts
fca1 wrote: »
Soc> 60% take all from batts/solar.
Soc<60% change to grid ( full or partially)

That would keep your batteries at 60% SOC all the time. Under this regime, your batteries will die very soon. You need to cycle them, so they regularly (at least once per 10 days) go to full charge.

You probably wanted something like this:

- Soc < 60% switch to grid
- Soc 100% switch back to batteries

This may not be good neither. If it is cloudy for a long time you may be sitting on grid while your batteries are at 60% and nothing is charging them. If it lasts for few days, it may cause suplhation. To prevent this, you must charge them somehow, may be manually.

Other consideration is that charging from 80 to 100% SOC is very inefficient. Batteries will only take very little. The rest of energy is lost unless it goes to loads. You can avoid using grid for these bad periods:

- Soc < 60% switch to grid
- Soc >80% switch back to batteries

But this does not ensure that the batteries are going to be fully charged often enough and we're back to circle one.

I think that you need to figure out what exactly you want to do, how it's going to minimize energy losses and at the same time maintain your batteries in a state of good health. Once you figure that out, it's time to think how to implement your strategy.
• Banned Posts: 17,615 ✭✭
Re: Sunny Island doubts

He need time of day factored in too, so the system doesn't expect to charge (or run loads) when there is no sun available. Ideally it would be nice to have an "available power" option on the charge controller (similar to MidNite's "waste not" feature) so it would also use grid to charge if it weren't sunny.

So ... IF SOC <70 (60 is too low in my opinion) AND time is -after charging hours- OR available solar <sufficient THEN switch load & charging to grid.

See? It gets pretty complicated quite quickly, especially if you want to minimize battery cycle and minimize grid use.
• Solar Expert Posts: 963 ✭✭
Re: Sunny Island doubts

fca1
Soc> 60% take all from batts/solar.
Soc<60% change to grid ( full or partially)

I do believe that what mtdoc posted from outback on "HBX mode" does that.

I half remember tallgirl on the outback forum having software that tried to use all the battery while in sell by learning charging and load trends. She didn't like it cause it seemed to cycle the battery too much.

In hbx mode she said it was easy to end up with cronic under charging.

I believe I got that right.

mtdoc
An extra thanks for taking the time to answer the questions I ask you

I have really injoyed this thread. Eric L I have learnt from your imput also.

I can't wait to put some of this into practice, at least untill I ruin my first battery bank.
It won't be so fun then.
Cheers
gww
• Solar Expert Posts: 963 ✭✭
Re: Sunny Island doubts

mtdoc
As you have the same inverter as me, do you sell to the grid?
Thanks
gww
• Solar Expert Posts: 600 ✭✭
Re: Sunny Island doubts
gww1 wrote: »
mtdoc
As you have the same inverter as me, do you sell to the grid?
Thanks
gww

Yep.

But I have turned selling off (while still grid connected) for short periods and of course during grid outages I have been in "off grid" mode so no selling then. Also - selling is turned off when the generator is connected as the AC input source.
• Solar Expert Posts: 1,571 ✭✭
Re: Sunny Island doubts
He need time of day factored in too, so the system doesn't expect to charge (or run loads) when there is no sun available. Ideally it would be nice to have an "available power" option on the charge controller (similar to MidNite's "waste not" feature) so it would also use grid to charge if it weren't sunny.

The Sunny Island can do the first bit, but not the second. So he could set one SoC level to connect to grid during daytime and a different SoC level during nighttime, but it doesn't know anything about available power.
• Solar Expert Posts: 1,973 ✭✭✭
Re: Sunny Island doubts
stephendv wrote: »
The Sunny Island can do the first bit, but not the second. So he could set one SoC level to connect to grid during daytime and a different SoC level during nighttime, but it doesn't know anything about available power.
The Sunny Island charges the batteries from the AC bus. It cares not whether it is grid power or PV inverter power or some combination thereof; it's determined by the state of the internal transfer switch and how much power the PV is producing relative to the loads on the protected loads panel.
• Solar Expert Posts: 1,571 ✭✭
Re: Sunny Island doubts
ggunn wrote: »
it's determined by the state of the internal transfer switch

Right. And what I'm talking about is programming that internal transfer switch to turn on and off at different SoC levels at different times of day.
• Solar Expert Posts: 1,973 ✭✭✭
Re: Sunny Island doubts
stephendv wrote: »
Right. And what I'm talking about is programming that internal transfer switch to turn on and off at different SoC levels at different times of day.
I interpreted what you said to mean that the Sunny Island cannot "use grid to charge if it weren't sunny". The Sunny Island charges the batteries off the AC bus, whatever it's connected to.
• Solar Expert Posts: 124 ✭✭
Re: Sunny Island doubts

Hi there now I'm bit lost...
I need an inverter that will be at center of my system it will be the main "distributor" of power in the house and should be able to choose from where it gets power ( grid/ batts/ other) .
And this decision should be done based on rules coming from soc,loads, time of the day, available power etc...

Re reading all your helpful replies ( thanks) I see no unit does it all I want but what is closer ?
I need to have ~5kw of power as its my worst case loads....
So I have the victron Quattro 5k, the sunny island and maybe the out backs

I'm in Europe so units must be 220v 50hz..
As im Several weeks away from home some times, it must be something that works very autonomous, as my family don't have the knowledge to changing things manually or even checking batts stats etc....

Victron seems a very robust unit and have 5kw at 24v have. A nice remote display .... Just dint get yet how to program it to work as I need, the local distributor knows less than me

edit:

Found someone who knows about victron and after all it can do almost what i need..

check the configuration tabs and it have more options it can ... very flexible

• Solar Expert Posts: 124 ✭✭
Re: Sunny Island doubts

Hi there reading the SUNY island 8h manual I found this

This what I want but it's no clear how to set I up and also if the transfer between sources is non interrupt like an ups or if I will have a break when shifting

I would like to say that any loads bigger than 2000w will be "assisted" by the grid but that 2000w will always come from batts until soc is >50% ..

Not getting many help from local sma people they know a lot about SUNny boy and grid ties etc but very little on offgrid sunny island ..
Others question does it have a mod us Ethernet interface ?

Regards
• Solar Expert Posts: 1,571 ✭✭
Re: Sunny Island doubts
fca1 wrote: »
I would like to say that any loads bigger than 2000w will be "assisted" by the grid but that 2000w will always come from batts until soc is >50% ..

No inverter on the market offers this option. Both victon and sunny island will let you power 2000W from the inverter and have the excess assisted by the grid, but it's not SoC dependent- it's a permanent programmed setting.

Sunny island has serial based RS-485 protocol and it's an open protocol, they've even released an open source software library so that you can write your own software to talk to any of the sunny products. Victron uses a closed protocol, so you can only use Victron's own software and accessories to talk to their inverters.
• Solar Expert Posts: 1,973 ✭✭✭
Re: Sunny Island doubts
fca1 wrote: »

Not getting many help from local sma people they know a lot about SUNny boy and grid ties etc but very little on offgrid sunny island ..

SMA tech support is very good. 916 625 3552
• Banned Posts: 17,615 ✭✭
Re: Sunny Island doubts

I think the SOC statement is from evaluating the point at which the inverter would shut down and go to charge mode. This will be based on battery Voltage, and that is not a reliable measure of SOC. It shouldn't be expressed that way.
• Solar Expert Posts: 1,973 ✭✭✭
Re: Sunny Island doubts
I think the SOC statement is from evaluating the point at which the inverter would shut down and go to charge mode. This will be based on battery Voltage, and that is not a reliable measure of SOC. It shouldn't be expressed that way.
I don't think the Sunny Island determines battery SOC from voltage.
• Banned Posts: 17,615 ✭✭
Re: Sunny Island doubts
ggunn wrote: »
I don't think the Sunny Island determines battery SOC from voltage.

That's not what I meant. It does determine whether or not it needs to be charging the batteries from Voltage though. If the Voltage is too low it will not invert.
• Solar Expert Posts: 124 ✭✭
Re: Sunny Island doubts
stephendv wrote: »
No inverter on the market offers this option. Both victon and sunny island will let you power 2000W from the inverter and have the excess assisted by the grid, but it's not SoC dependent- it's a permanent programmed setting.

Sunny island has serial based RS-485 protocol

That's start so it can assist the inverter with the grid by load and if voltage/ soc go bellow 50 complete change to grid ?
Does the Si have a input, I mean I can make my monitor to activate a relay when soc is at x% so if SI can read this as a order to switch to grid is ok for me ..
Can we disable the charger in the SI ? May be I'm not reading the correct manual but victron have a more clean and easy to follow docs...

Stephen, does the SI. Have Ethernet connection ? Any modbus output ?

Regards
• Solar Expert Posts: 1,571 ✭✭
Re: Sunny Island doubts
fca1 wrote: »
That's start so it can assist the inverter with the grid by load and if voltage/ soc go bellow 50 complete change to grid ?

Apologies, what I wrote earlier is not correct. When the SI or Victron switch to the grid then the base power comes from the grid and you can configure them to assist the grid above a certain power level. E.g.
- Switch to grid if loads demand more than 2kW
- Assist the grid if loads demand more than 3kW

So if the loads demand 4kW, then 3kW comes from the grid and 1kW will come from the inverter. If loads demand 2.5kW, then 2.5kW comes from grid and 0kW comes from the inverter. If the loads demand 1kW then 1kW comes from the inverter.
fca1 wrote: »
Does the Si have a input, I mean I can make my monitor to activate a relay when soc is at x% so if SI can read this as a order to switch to grid is ok for me ..

I think given the complexity of what you want to achieve your best bet is going to be program the SI with a very simple rule: if the grid is present then connect to it. Then use your own external monitoring and control system to switch the relay between the grid and the SI. This way you'll be freed from the limitations of the SI programming and can program grid connect or disconnect however you want.
fca1 wrote: »
Can we disable the charger in the SI ? May be I'm not reading the correct manual but victron have a more clean and easy to follow docs...

I guess so. You can configure the maximum charging current for the batteries, don't know if you can set this to 0, but you could just set it to 1A.
fca1 wrote: »
Stephen, does the SI. Have Ethernet connection ? Any modbus output ?

No, not ethernet. RS-485. Not modbus, they have their own protocol which runs over RS-485, I think they call it sunnynet or SMAnet. The specs are open and their library for talking to it is open: http://www.sma.de/produkte/monitoring-systems/yasdi.html
I modified someone elses open source software to talk to the SI which you can download here: https://github.com/stephendv/IslandManager
You need the additional RS-485 piggyback for the SI and you need an RS-485 interface on your PC. I used a USB-RS-485 converter for the raspberry pi which works fine.

I know you're a mango fan, so the way I've set my system up is that a program runs on the PI which fetches data from the SI every minute and dumps it into a MySQL database. Then mango goes and fetches that data and pulls it into it's own database using the SQL datasource.
• Solar Expert Posts: 124 ✭✭
Re: Sunny Island doubts
stephendv wrote: »
Apologies, what I wrote earlier is not correct. When the SI or Victron switch to the grid then the base power comes from the grid and you can configure them to assist the grid above a certain power level. E.g.
- Switch to grid if loads demand more than 2kW
- Assist the grid if loads demand more than 3kW
That fits what i want...

stephendv wrote: »
I think given the complexity of what you want to achieve your best bet is going to be program the SI with a very simple rule: if the grid is present then connect to it. Then use your own external monitoring and control system to switch the relay between the grid and the SI. This way you'll be freed from the limitations of the SI programming and can program grid connect or disconnect however you want.

This what i have now i was looking for more integrated soltution..
stephendv wrote: »
I know you're a mango fan, so the way I've set my system up is that a program runs on the PI which fetches data from the SI every minute and dumps it into a MySQL database. Then mango goes and fetches that data and pulls it into it's own database using the SQL datasource.

you send one PM i was looking how to get mango fetching values from sql source or even a web page and not finding the solution..

By the way first quote for SI 8.0h 4.4K € is a price inline with the market ?

regards
• Solar Expert Posts: 1,571 ✭✭
Re: Sunny Island doubts

Not sure whether your fork of mango supports SQL datasources.... The version I use has an "SQL" option when adding a new datasource, do you have this too?