General Doubt : Off-Grid system without Battery

[SunEagle]

We need a good sticky to just answer this repeated question: Why do I need a battery if I only want to run my load when sun is available?

Good idea. Unfortunately even with a really good sticky most people may still not understand because they have been misled into believing that as long as the sun is shining your solar panels will generate all the free electricity you need all day long. Which as you have learned is a false belief.

[SunEagle]

I am designing a system for small industry where load is of around 25-30 KW.
Since the industry works only in day time, I want to provide a complete solar solution to it.

I have two question, it will be best if someone can guide me technicality of it.

1)If we have to design a off-grid system(Solar Panels,Inverter) do we always need to provide battery for it? Even if load will be catered only through solar generation during sunny hours.If yes, then why?

2)Can I design a system where battery will be very small and act like a supplementary source when there is insufficient solar irradiance, e.g if load is of 25 KW and solar panels producing 10 KW remaining load can be catered through battery, so battery required will be of 15 KW here. I am well aware of battery calculations, DOD factor,losses all, I am just giving simple example here as Diesel generator will be there for backup when solar is not present. But I want to cater most load through battery and solar only, that too only during sunny hours.

Kindly guide me in these two conditions.

Regardless of the size of your load what you are being misled about is the amount of sunlight you get daily to power something from solar pv. Just because the sun is up does not mean there is enough sunlight to make the solar panels work. Depending on where the system is in the world the best you can get is maybe 7 hours a day in the summer but usually less. The worst could be as little as 2 hours a day in the Winter.

So unless you want to shut down your business after only a few hours each day or not have anything work on the days it is too cloudy you will need some type of energy storage system to run the loads. The most available storage system is a battery. The problem is that batteries do not last more then 5 years on average and are very expensive. The bigger your load the more you have to pay for batteries and charge controllers.

What you are asking about generating 30 kw all day long to run a business will cost you many hundreds of thousands of US dollars. Less if you connect the solar pv system to the grid.

And without the grid a solar battery system will never pay for itself compared to other forms of electrical generation at that scale.

[cebury]

We need a good sticky to just answer this repeated question: Why do I need a battery if I only want to run my load when sun is available?

[Sunking]

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.

[shrikantsol]

I am designing a system for small industry where load is of around 25-30 KW.
Since the industry works only in day time, I want to provide a complete solar solution to it.

I have two question, it will be best if someone can guide me technicality of it.

1)If we have to design a off-grid system(Solar Panels,Inverter) do we always need to provide battery for it? Even if load will be catered only through solar generation during sunny hours.If yes, then why?

2)Can I design a system where battery will be very small and act like a supplementary source when there is insufficient solar irradiance, e.g if load is of 25 KW and solar panels producing 10 KW remaining load can be catered through battery, so battery required will be of 15 KW here. I am well aware of battery calculations, DOD factor,losses all, I am just giving simple example here as Diesel generator will be there for backup when solar is not present. But I want to cater most load through battery and solar only, that too only during sunny hours.

Kindly guide me in these two conditions.