General Doubt : Off-Grid system without Battery

[Mike90250]

There is Hybrid and Grid-tied system, For your requirement, you can choose an Grid-tied inverter, there is no need to install battery.

For off-grid system, The battery or supercapacitor is the necessary components.

Ha ha funny boy. Show me a functioning off grid system that uses an affordable supercap instead of a battery !

There is Hybrid and Grid-tied system, For your requirement, you can choose an Grid-tied inverter, there is no need to install battery.

For off-grid system, The battery or supercapacitor is the necessary components.

[SunEagle]

Hello and Greetings.

I have 44 Dupont 117Watt Apollo Panels system and 2 string wiring configuration. Is it possible to use the Fronius Symo inverter 5.0-3-M and the smart meter to use this without batteries or grid? Any suggestions I would appreciate it. In my location they do not allow putting power back into the grid. I do have an available grid connect. Thx

http://www3.fronius.com/cps/rde/xbcr...8_snapshot.pdf

For that Fronius inverter to work you still need a Grid to connect to. Once that is done then you can program it to not output anything.

If you have no grid then you will need to connect your solar panels to a charger and then that to batteries.

Hello and Greetings.

I have 44 Dupont 117Watt Apollo Panels system and 2 string wiring configuration. Is it possible to use the Fronius Symo inverter 5.0-3-M and the smart meter to use this without batteries or grid? Any suggestions I would appreciate it. In my location they do not allow putting power back into the grid. I do have an available grid connect. Thx

http://www3.fronius.com/cps/rde/xbcr/SID-EE664BA0-3DEE6C59/fronius_uk/Limited_Export_flyer_972848_snapshot.pdf

[jflorey2]

There is one more problem here. I want to keep generator off as long as possible, since what I understand is generator takes lots of fuel even during idling period.

Right. And the amount of time you can leave it off will be determined by the size of your battery bank. Small battery bank = frequent restarts. There's no free lunch here.

One more solution I was thinking is, giving system without batteries and keeping small generator just for reference voltage and frequency. I am not sure about will this work or not, since I am still technically unclear about need of secondary source of energy in off-grid system.

Won't work without a LOT of additional work. If you try that as you describe, you will overspeed the generator and damage it. You would need an additional dump load to ensure voltage/frequency do not rise above unsafe levels, and those are not available off-the-shelf to do what you want.

And in any case, at best all that will do is reduce the load on your generator; as you mentioned, it takes lots of fuel even during idling (or low load) operation.

[SunEagle]

Running a big load directly from pv is taking a gamble due to the dynamics of both the system load and the sunlight to generate power.

There needs to be a buffer in between to handle these dynamics like a battery system or grid connection.

A generator will not be able to change it's out put that quickly unless you have a bank of them where some are on all the time and others cycle depending on the need.

[ButchDeal]

One more solution I was thinking is, giving system without batteries and keeping small generator just for reference voltage and frequency. I am not sure about will this work or not, since I am still technically unclear about need of secondary source of energy in off-grid system.

sure it will work for a very short bit. Till the load drops. So in your example above you would have a PV system producing 30kw, a load using ~30kw, and a small say 10kw generator. The load drops for a bit to say 10kw, PV is still producing 30kw, generator idles down but where does the extra 20kw go???
there are some grid tie that can limit production to not back feed, though I don't know of any rated for off grid use like this.

[shrikantsol]

That sort of design is possible. However:

1) You need to take into account both power needed to run your load and power needed to charge the battery. (Really energy, which is power X time.) That means a larger array.
2) You need very specific batteries that can handle very high charge and discharge rates, since your capacity will be lower. For example if you want a 2 hour battery (i.e. run for 2 hours before dying completely) then you will need to discharge at C/2, and likely charge at C/2. That means lead acids are out. You might be able to find a LiFePO4 battery that could fulfill that requirement.
3) Lifetime will be lower when you charge and discharge at those rates.

Thanks for support

1)Yes, I have taken into account excess power needed for charging batteries.
2)This is my major concern as well, I want batteries to be discharged quickly as well i.e c/2 batteries as suggested by you.

Note that an additional utility of this system will be better generator utilization; overall your generator run time will decrease if you can add storage, and will be better loaded (closer to rated power) while it is on.

There is one more problem here. I want to keep generator off as long as possible, since what I understand is generator takes lots of fuel even during idling period.

One more solution I was thinking is, giving system without batteries and keeping small generator just for reference voltage and frequency. I am not sure about will this work or not, since I am still technically unclear about need of secondary source of energy in off-grid system.

It would be best if you can advice me on same.

[shrikantsol]

Thanks for showing concern. Actually I am purposefully putting more panels to accommodate battery charging. Solar system capacity is almost little more than double of nominal load, so whatever excess will be generated will be put into batteries,which later will be used during energy shortage from panels. I am hope I am making some sense. Definitely I am trying all things to make this feasible, and once I am sure it will be only then I'll start the project.

[jflorey2]

Now coming back to our discussion, I have this query what if I provide only minimal battery? By minimal battery I meant when during morning or evening when solar panels wont be able able to cater complete load I should be able to take remaining power from battery, I tried to give an example as well,Sorry, I wasn't clear to convey my message. So basically if the load is of 25KW ,and my panels producing say 10 KW, remaining is 15 KW, I want battery to provide.

Now let's see the scenario
Load is of around 25 KW
Industry runs for 8 hours.
typically only during 2 hours in morning and 2 hours in evening there could be problem of insufficient energy from solar panels.
So I want to add battery so that only during these 4 hours of insufficient energy,battery will add remaining insufficient energy.
Since Industry has Generator of their own, in cases when there is no sun for a day or something they may start it,but they want to use it as minimal as possible.

That sort of design is possible. However:

1) You need to take into account both power needed to run your load and power needed to charge the battery. (Really energy, which is power X time.) That means a larger array.
2) You need very specific batteries that can handle very high charge and discharge rates, since your capacity will be lower. For example if you want a 2 hour battery (i.e. run for 2 hours before dying completely) then you will need to discharge at C/2, and likely charge at C/2. That means lead acids are out. You might be able to find a LiFePO4 battery that could fulfill that requirement.
3) Lifetime will be lower when you charge and discharge at those rates.

Note that an additional utility of this system will be better generator utilization; overall your generator run time will decrease if you can add storage, and will be better loaded (closer to rated power) while it is on.

[cabindave]

A basic question for you: If you only have enough power to run your plant 4 hours during the day, where would the batteries be getting the power to run the plant during the other 4 hours?

You have to charge the batteries with something in order for you to use the power later. Does that make sense? You are correct in that you should look into off-grid concepts more. I wish you luck in your attempt, but please don't start on it until you know it is feasible.

[shrikantsol]

Kindly guide me to literature regarding same. Sticky is a good option.
Even if it will be little technical and complicated for many, it's best if we have such option so that those can understand, will be benefited.

So looking forward to have understanding of this.

Thanks.

[shrikantsol]

You have to provide a battery period no way around it.

First thing you have to determine is HOW MANY WATT HOURS your plant uses in a day. That is required to calculate panel wattage required. Example lets say the plant uses 300 Kwh in a day, and you have 5 minimum Sun Hours. Since this is a battery system you have an efficiency factor of 66%. That means the panels must generate 300 Kwh / .66 = 455 Kwh in a day. With a 5 Sun Hour day means the panel wattage needs to be no less than 455,000 wh / 5 hours = 91,000 watts or 91 Kw.

Let's just say a 90 Kw system. The demand is 30 Kw from the plant leaving you 60 Kw to hit the batteries with. It takes a lot of battery to be able to absorb 60 KW. Chose the right battery say an AGM that can take as much as a C/2 charge current to make the battery as small as possible. Charge current depends on Voltage of the battery. With a 30 Kw load is way more than 48 volts, more like say 500 volts and at 60 Kw is 1200 amps. So you go shopping for 2400 AH AGM batteries @ 500 volts.

Good luck with that. You are talking about a 72,000 pound battery costing you $500,000 every few years replacing it. Another challenge is there is no solar battery equipment made to do this. All custom designed and manufactured. Everything out there is 48 to 6 volts @ 80 amp max.

Good Luck. It will never happen.

Thank you very much for your clear insight.

I have little peculiar problem though, and I am trying to customize little different solution to it.

Since I know how to provide a solar solution to on-grid system,I am able to calculate solar solution to off-grid little bit, but problem is again battery. Currently Industry runs on Diesel generator. So I don't have to worry about if there is no sun, since they already have generator it can be put into line. Now coming back to our discussion, I have this query what if I provide only minimal battery? By minimal battery I meant when during morning or evening when solar panels wont be able able to cater complete load I should be able to take remaining power from battery, I tried to give an example as well,Sorry, I wasn't clear to convey my message. So basically if the load is of 25KW ,and my panels producing say 10 KW, remaining is 15 KW, I want battery to provide.

Now let's see the scenario
Load is of around 25 KW
Industry runs for 8 hours.
typically only during 2 hours in morning and 2 hours in evening there could be problem of insufficient energy from solar panels.
So I want to add battery so that only during these 4 hours of insufficient energy,battery will add remaining insufficient energy.
Since Industry has Generator of their own, in cases when there is no sun for a day or something they may start it,but they want to use it as minimal as possible.

Reason for all this is very simple, I don't want to unnecessarily burden more battery, as you said it's not even feasible. But if solution like the one I suggested can be worked out,it will be great help.

And as commented on your previous post, I have taken into consideration losses,solar irradiance and insolation into calculating solar panels and system. But need to clear off-grid concepts little bit.

Your help is highly appreciated.

Thanks.

[shrikantsol]

Thanks for prompt reply. I just joined this forum yesterday and I wasn't expecting such prompt replies, so really thanks for it.

Secondly, thanks for pointing it out, but I am very well aware of solar irradiance and Solar Insolation. In my region worst sun hours in a year averages to 3.6 hours and during peak summer it's around 5-6 hours. So I tried to design system accordingly, taking into account losses as well. I am novice to off-grid solar system so I have few genuine doubts regarding it.

I will write complete situation in your battery post, kindly guide me there.

[Sunking]

OK your first wrong assumption you made and 90% before you was: You have assumed a 100 watt panel generates 100 watts with the sun shining on the panel surface, it will produce 100 watts. From that you conclude a huge error into assuming if you have 16 hours of Sunshine is 1600 watt hours. That would be a huge error. It would not work, and destroy the batteries shortly from severe undercharging.

In practice you would discover what you thought was 16 Sun Hours is no more like 4 to 6 Sun Hours You thought you had 1600 watt hours but only get in real world is 4 to 6 Sun Hours in Summer when conditions are best. In winter months than can fall down to less than 1 Sun Hour and 3.2 is nation average So if you thought 1600 and now discovered it is only 500 you learn.

Look at the graph below. On the left vertical axis is % of power of a solar panel. Lets pretend the panel is 100 watts. Bottom or horizontal is Time in hours of the day from morning to night So Sun Rise at 6am power = less than 1 watt,
Come 8:00am power = 3 watts
9:am power equal = 15 watts
10 am power = 50 watts
11am, 12am = 100 watts
1pm power = 75 watts
2 pm = 40 watts
3 pm = 10 watts
4pm = 3 watts.

Conclusion. Panels only produce specified power for 2 hours around Solar Noon. Much less any other time of the day.

So in the bell curve lies Watt Hours and when you add them up = 530 watt hours. We know the panel wattage is 100 watts. So for a 100 watt generator it would have to run for 5.3 hours to generate 530 WH. Sun Hours = 5.3.



So why is a professional asking such simple fundamental questions. Strange!.