solar system design

[Sunking]

SunKing,

You're taking DoD as a per-day figure.

Hush girl, we got to keep the communist confused.

There are technologies that will handle very deep cycles. Many of the larger traction batteries will do 50% DoD on a daily basis and last for years. The HuP Solar-One batteries are rated 2,100 cycles to 80% DoD. 2100 / 365 is several years. It's all about plate chemistry, thickness and the rock well.

I understand that as I have worked with the manufactures for decades. However designing for 50% DOD on a daily basis is a poor idea for RE applications. That same battery discharged to 50% DOD each day lasting 2000 cycles can go 10,000 at 20% DOD. It is all about cost, location, and backup which has to be factored in.

[greenHouse]

Hush girl, we got to keep the communist confused.

I dunno if he's a commie, but he's keeping himself confused

[greenHouse]

ya mike sorry i forget to give time.
I want to design for 5.5 hours.
Total load 450 W*5.5 h = 2475 Wh
so Total energy demand per day is 2475 Wh.
Now pls go ahead

And for battery sizing take DOD 70% and battery efficiency 85%
sunshine availability in India is about 5.5 Hours

Got a few minutes, then coffee and annoy some solar installers.

You need to provide us with more accurate, as well as more realistic, information. Very few places average 5.5 hours per day. You'd have to be in the tropics, which much of India is, but then you have to allow for the rainy season, which much of India has.

Also, there is no such thing as an 85% efficiency, measured in full-cycle watt-hours battery. For a stand-alone system, efficiencies are a lot lower because they have to be designed more robustly. You gain some efficiency when recharging from a discharged state, but we don't even know what that is for your system, because 5.5 hours for winter (Northern India) or rainy season (the rest of India) doesn't happen.

You =can= decide that 70% DoD is your design point, and there are valid reasons to do that, but it's a lousy design point, especially since foul weather tends to last more than one or two days, and that gets back to "rainy season".

Anyway, time for coffee!!!

[vikas maurya]

Two problems here. Unless this is a AGM battery, efficiency is around 80% at best. You say 5.5 hours? Is that average, peak summer, or low winter. In a battery system you have to design for worse case or the shortest Sun Hour day in the year. Very few places receive 5.5 hour in winter or rainy seasons.

it's average sunshine availability in a year

[russ]

What city are you near? I'll look up the insolation on PV Watts

Russ

[Sunking]

it's average sunshine availability in a year

You should not use the yearly average on a battery system, otherwise you will likely go dark in the shorter daylight months.

[vikas maurya]

Got a few minutes, then coffee and annoy some solar installers.

You need to provide us with more accurate, as well as more realistic, information. Very few places average 5.5 hours per day. You'd have to be in the tropics, which much of India is, but then you have to allow for the rainy season, which much of India has.

Also, there is no such thing as an 85% efficiency, measured in full-cycle watt-hours battery. For a stand-alone system, efficiencies are a lot lower because they have to be designed more robustly. You gain some efficiency when recharging from a discharged state, but we don't even know what that is for your system, because 5.5 hours for winter (Northern India) or rainy season (the rest of India) doesn't happen.

You =can= decide that 70% DoD is your design point, and there are valid reasons to do that, but it's a lousy design point, especially since foul weather tends to last more than one or two days, and that gets back to "rainy season".

Anyway, time for coffee!!!

Don't worry about the average sunshine hours, coz there is Grid which is also available nd my inverter is able to take grid input as its a bidirectional inverter. and for battery DOD and efficiency check this

http://www.hbl.in/brochures%20pdf/TubularGel_VRLA.pdf

[greenHouse]

Don't worry about the average sunshine hours, coz there is Grid which is also available nd my inverter is able to take grid input as its a bidirectional inverter. and for battery DOD and efficiency check this
http://www.hbl.in/brochures%20pdf/TubularGel_VRLA.pdf

Oh-Kay, so ... what do you really =want=? Playing 20 questions isn't getting anywhere and I think some of us are losing patience.

(And you need to believe us -- 85% full-cycle efficiency doesn't exist, regardless of what the ad hype says.)

[vikas maurya]

Solar panel Wattage = [2475 x 1.5] / 5.5 hours = 675 watts if using MPPT controller and you actually get 5.5 Sun Hours which I doubt in winter.

No way should even consider taking a battery to 70% DOD, that is suicide, your battery would be worthless in a few short months, and just 1 cloudy day and you go dark. Try 20% DOD or 5 day reserve which is equivalent to 2.5 days real reserve to 50% DOD. You did not say what voltage you wanted the battery, or was it 48 volts?

At 48 volts the battery AH capacity needed is [2475 wh x 5 days] / 48 volts = 257 AH @ 48 volts.

Charge controller size assuming MPPT is Panel wattage / nominal battery voltage = 675 watts / 48 volts = 14 amps minimum.

In finding out solar panel wattage you take 1.5 i think its fudge factor.
but you didn't consider the losses.
and in calculating battery capacity i think DOD and battery efficiency should be considered.
and as there is availability of grid and my inverter is bidirectional so i'm not worry about battery life coz it can also charged by inverter when Grid is available. so it will rarely go in deep discharge level.
as load is very small, is it not good to design system on 24V system?

[vikas maurya]

Oh-Kay, so ... what do you really =want=? Playing 20 questions isn't getting anywhere and I think some of us are losing patience.

(And you need to believe us -- 85% full-cycle efficiency doesn't exist, regardless of what the ad hype says.)

As you people are very experienced and professional so i don't think you should lose your patience.
i'm new to field and in learning stage so i have to clear my doubts.

[Mike90250]

As you people are very experienced and professional .....

Sometimes we smell a rat. Advice is being given, and you keep saying,

oh, no matter, I'll do it this way. BTW, is this XYZ a good idea to 35% ?? Please you must tell me yesterday, as our reliable grid power is off.

[greenHouse]

Sometimes we smell a rat. Advice is being given, and you keep saying,

I had a client who refused to follow my advice.

Then things went wrong and they blamed me.

Then they told me "We were paying you to be the expert".

Except, they stiffed me over $600.

So, I'm going to be suing them. They can explain to a judge why it's my fault they neglected to follow any of the advice they were given.

[greenHouse]

As you people are very experienced and professional so i don't think you should lose your patience.
i'm new to field and in learning stage so i have to clear my doubts.

It's not that you're trying to learn, it's that you're telling people you acknowledge as very experienced and professional that we're wrong.

I've worked with a fair number of people from India, so I know there are cultural differences that can sometimes cause miscommunication. Rather than simply disagreeing, you'd do better to ask "Why is that the case?" For example, the reason that 85% full-cycle efficiency is unrealistic has to do with the voltage elevation during charging, and the voltage depression during discharging. A battery, such as the one you referenced, that is 95% efficient on an amp-hour basis isn't going to be 85% efficient in a real-world installation on a watt-hour basis. And the reason is that the voltage is 0.5 to 1.0 volts higher (per 12 volt monoblock) during charging, and 0.5 to 1.0 volts lower during discharge.

For a real example, my batteries "Absorb" at 57.6 volts, but they "run" at 49 to 50 volts. That voltage difference -- 86% lower during discharge -- is multiplied by the 95% amp-hour efficiency to yield a net 81% watt-hour efficiency. In your case, the discharge rate is higher, so the voltage depression will be greater and the full-cycle efficiency lower still.

Had you asked "Why?" instead of questioning us about our expertice, you'd have gotten that answer, and then you could have asked still more questions and gained additional knowledge.

Something to consider in the future.

[greenHouse]

wow you really giving the americans a good name with those comments, thanks for not letting my opinions down of yall

I dunno. I thought his post was rather funny.

I also suspect Sunking knows that there is no way R.E. system design and construction can be outsourced to commie workers. Pretty hard to be an underpaid worker in Bangalore or Pune when the physical work is in Dallas or Houston!

[Sunking]

Riffraf if not for Americans, you would be Japanese my friend. Now who is going to save you from the Chi-Coms?