Sizing of Inverter

Is the load of a critical nature? Is there any backup planned? Like say a generator or grid power available....What is your geographical location? Is your space limited? How much money is your budget?

http://www.wholesalesolar.com/inverter-system/solar-power-center-2135219.html

http://www.solar-electric.com/1waofsoposyw.html

http://www.bluepacificsolar.com/home-solar/solaredge-3500w-solar-kit.html

Driving a 3500 watt load with a 100 watt panel will be a cute trick, unless the load is active only 1/35 of the time.

You already said PV size.

Battery size for 3.5KW depends on ampacity of battery.

Identify the voltage levels and balance the power on both side. Go for more capacity than load.

It responds to a little arithmetic. So the inverter needs to be larger than 3500W. The panel is therefore too small by a factor of 35 to drive it continuously. It can, however, supply this load continuously for somewhat less than 1/35 of the day. Is this satisfactory?

The panel is not nearly big enough for a 3,500 watt load.
We also need to know the voltage of the load.

I got the impression from the OP that he wants to know how many 100 watt panels he needs. This statement -"I want to know the panel size, battery size and inverter size used in this installation" - appears to indicate that, and then he goes on to tell us what sized panels he wants to use - "The panel rating is 100W panel"

The voltage of the load should be immaterial. The power requirements from the panel and batteries will be identical for a 3500w load no matter what the output voltage of the inverter is. He will need to get an inverter with the correct output voltage and frequency to suit the load, but we would hopefully assume he knows that much at least.

That was my take on the questions, but as the OP has not been back, it's probably a moot point anyway.

We need to know the kwHr load per day

I suspect he meant his total load was 3.5Kw hrs per day.

We need more information. You say you want to know panel size then give the panel rating. Question...do you mean to say that 100w panels are available to you? Is your 3500w load continuous or is it the peak power?

Having some experience with solar, and this would be just a suggestion, for a continuous load I would size my array to produce 3 times the load. This would produce the extra power stored in the batteries for at night and also allows for cloudy days and the reduced power generated in the mornings and evenings.

For a continuous load I would also have enough batteries to store about 4700 amps hours, assuming 12v batteries.

Assuming the continuous load is a motor then the inverter should handle the surge probably a 5000w inverter.

If this is for a residence then an array producing 3500 watts may be just big enough but I would likely want about 5000w to be comfortable. You would need to know the watt-hours all of the appliance need in a day to help calculate the size of the battery bank. I would probably stay with the 5000w inverter.

This is just a rough estimate of what I would do, others may have a better idea. Good luck!

Solar electricity (energy) is very expensive.
A 3500 watt load is far too much.
Turn off the 2,400 watt radiator. Get rid of your 2,000 watt kettle and make your cup of coffee on a wood stove.

Dear Mr. ee.saurav,

You have referred "I want to know the panel size,battery size and inverter size"

For Battery Size, it depends upon the No. of Hours you want to use your electrical load, since if sun shine is not there, the battery has to supply the power through the inverter.

If you assume that you intend to use for 10 Hours 3.5 x 10 = 35 KWHr. For 3.5 KW, if the Batttery is of 24 Volts, the current will be 3500/17.4 = 201.4 Amps say 202 Amps to maintain for 10 Hours., to meet your demands. Hence you need 202 x 10 = 2220 Amp.Hrs rounded to 2500 Amp.Hrs.

DHAYANANDHAN.S

I think you may be a little confused there.

The 17.4v figure that the OP mentions is the knee or maximum power voltage of the solar panel. That voltage will satisfactorily charge a 12v battery via a suitable controller, but it will not service a 24v battery.

Therefore for a 12v system the discharge current will be 3500/12= 291.7 amps.

The panels may be connected in a series parallel array to service 24v batteries, again through a suitable controller. The discharge current would then be 3500/24 = 145.8 amps.

In your scenario, using your figures, drawing 202 amps from a 2500Ah bank for 10 hours would see the battery terminal voltage drop below its rated value (24v, 12v, etc., the battery voltage doesn't matter) in less than 6 hours and the bank would be seriously discharged (1.9v/cell or 10% SOC) at the 10 hour point. The inverter will likely quit on low voltage disconnect before the 10 hours are up.

You can check those figures on any LA battery voltage/time discharge graph, just look for a 0.08C curve or pick a spot midway between the 0.05C and 0.1C curves.

Hey Guys, FAR too much truth and accuracy here, the OP is apparently GONE.....!

If we tell him that it will work (with a little bit of adjustment!), maybe he will come back?

Have a great Good Friday everyone.

It is also possible that the 3.5kw figure is the amount of electricity consumed in a day. (A figure that would cover many homes in the Philippines, for example).

If that is the case then 10 x 100watt panels, a 2-3kw inverter and 600 AH battery storage should suffice.

The sun's radiation, at the Equator, is 1KW/square meter. Since you don't indicate where you are located and the received Solar Radiation number is, an accurate calculation cannot be made.

As previously pointed out, unless you have a means of solar tracking, the maximum radiation will only be when the sun is normal to the surface of the panel. The panel will only produce 100w if the temperature of the panel is =< 25* C. The 1704V panel rating is open circuit and the 6A is short circuit. There is no Power Factor.

The output of the panel is probably 9V under resistive load, < 4A at best.

Clouds, haze, dust, etc. will further reduce the efficiency of the panel.

As to the Battery:

It is recommended that the core battery voltage never drop below 80% of full charge.

That irradiance figure of 1kW/m² is only true for when the sun is perpendicular to the surface, and that can shift from roughly 23° North to 23° South of the equator during the course of the year and is therefore only perpendicular at the equator during the equinoxes. Because equatorial regions are generally hotter and wind speeds generally lower, solar panel efficiency is reduced due to increased panel temperature.

Whilst panel current rises slightly with a hotter panel, open circuit voltage falls considerably, thus reducing overall power output. Typical losses would be 0.5% per °C rise above 25°C so that could reduce panel power by as much as 15% at times.

The 17.4v that you mention is the normal maximum power voltage (Vmp) of a panel used for 12v battery charging. Its open circuit voltage (Voc) will be closer to 22v. The panel will only produce 100w if it is used in conjunction with an MPPT type regulator which will maintain the panel's operating point at its "knee" or maximum power point.

A solar panel produces its maximum power at only one point between open circuit voltage and short circuit current, it produces no power when open circuited and no power when short circuited.

Connecting a 100 watt (17.4v Vmp, 6 amp Isc) panel to a 12v battery that is at 12.1v or 50% depth of discharge (DOD) via an MPPT regulator will produce around 8 amps charge current to the battery. 12.1v x 8 amps = 96.8w

Connecting that same panel to the same battery at the same DOD via a series or PWM type regulator will produce only 6 amps charge current to the battery. 12.1v x 6 amps = 72.6w.

Unless the regulator is faulty (in the case of an MPPT device), or the battery is down to 9v (in the case of a series regulator), or you are erroneously connecting the panel directly to a load, you will never see 9v at the panel during decent insolation.

Whilst I agree that maintaining battery state of charge at never less than 80% is good for battery longevity and works best for standby systems, best economy - ie cost of battery replacement vs Ah till replacement - is achieved by sizing the bank for a 50% DOD. Inclement weather factors have to be considered.

It may interest you to know, that because of the problems you correctly outlined with regard to excessive temperatures of Solar panels reducing efficiency, there are also available in some parts of the world, what are basically "normal everyday" solar panels, but with water cooling added on the back, which keep the cells to a far more reasonable temperature, even in strong midday sun AND furthermore supply warm water for the central heating, baths/showers and the like....it seems that keeping the cells to 85°C or less, promotes/allows higher efficiency.

The warmed water is basically free once the higher cost of the panels has been amortized. Many are installed here now in Germany....

IBM has also made some big strides in further concentrating more Sunlight (using optical methods), onto smaller, therefore cheaper cells, so much sunlight, that in itself would normally cause them to overheat to over 1300°C (which would possibly melt them!), but when force water cooled to around 85°C, produce vastly increased efficiencies.....

The trick is it seems, is to use a very thin quantity of "liquid" metal as the heat transfer "contact" to prevent local excessive heating, as for example the various "pastes" use in PCs do not transfer the heat quickly enough to work properly at the efficiencies required..

Thank you for the additional information. The installations I had seen utilized heat sinks mounted to the back of the panel. Not very efficient for the face temperature.

I am only too happy to assist, you appear to know most of the right stuff already, more than the rest of us put together!!

Nice to make your acquaintance.

Normal is perpendicular

A really good and to my mind totally "real world" post, I thank you (even though I am totally unaffected!) and I give you a GA for it!!

Hopefully a few more here will also reward you for a bit of simple to understand and clear thinking for the OP!

Interesting, at least someone here did not understand why my post was needed and gave me an OT. Nobody else mentioned it, even though the Poster had earned at least 1 or more GAs for a very accurate and correct assessment...

The OT poster of course knows who he is (I have a very strong suspicion too!!), he is also VERY ignorant in any way shape or form with regard to the technology mentioned and apparently simple good manners.... He also has serious personal problems as we have seen demonstrated rather often here on CR4.....

But having broad shoulders, I can handle it.... One could say, "Water off a duck's back basically."

As J.J. always says, "Sticks and stones.......!"

Do remember though, such a person is only to be pitied by us all...!

And I would guess that most of you here know who it is too!! It is not too difficult to work out!!

Happy Easter to everyone!

If I had waited an hour, I wouldn't have bothered to post, but I got the bit between my teeth.......

I have to admit that I have "shot him down" on SO many occasions because of his stupid an inaccurate comments, its just about the only way he can hit back....its actually quite sad....

Its like him going to a gunfight armed only with a knife!!! Each and every time!!