Calculating Module Wattage

[tag]

I really appreciate all the good information on the forum. I am new to solar energy. I've only made one panel, the usual, 36, .5v cells giving an 18 volt panel.

I quickly discovered that if I could use higher voltage cells I could get a panel with higher voltage and wattage. But before I make one I want to calculate what the wattage would be if I used 9v cells, 30 of them in the panel. That way I could save on the cost of glass and frame and encapsulator, etc. Each cell has Peak Current of 70mA and Short Circuit current of 75mA. Can anyone help with what wattage that panel would be?

Secondly, would you have to use heavier tagging and bussing wire? How about the diode?.....and anything else that I would have to take into consideration. Thanks in advance.

Tag

[Sunking]

Watts = Voltage x Current every day of the week

[tag]

Thanks for the quick reply Sunking. I am familiar with the formula but I'm not sure how to handle the amperage. Do you use the 70mA or 75mA once or do you increase it by the number of cells (30)???

What about the size of wires, diode, etc.?

Tag

[Mike90250]

.........I quickly discovered that if I could use higher voltage cells I could get a panel with higher voltage and wattage. But before I make one I want to calculate what the wattage would be if I used 9v cells, 30 of them in the panel. ......

I'm not clear what you mean about "higher voltage cells". Solar PV cells are only 0.5V. Cells that have been wired together, make a "panel" and those are only limited by how many cells you wish to wire up. There are commercial panels for grid tie use, that run at 90V, 200W, but their amps are only 2.2A. Same wattage and square inches as any other 200W panel, but cells are wired in series, instead of series/parallel to develop lower voltages and higher amps. It all revolves around your end use, do you need more volts for grid tie, and lower amps (smaller copper wire) or more amps at lower voltage for battery charging ??

The individual cells are all rated 0.5v, and the size determines the amperage they produce. When you buy cells, their spec sheet should say all that.
Cells in series increases voltage, amps stay the same
Cells in parallel, increases amps, volts stay the same
DC watts = volts x amps You can get 200W with high volts & low amps, or low voltage & high amps, but it's still the same square footage of PV, just wired differently.

[tag]

Hi Mike,

Thanks for replying. My aim is to get as many watts for the fewest amount of $$ as possible. Why use .5 volts cells if you can use 3v or 4v or 6v or 12v cells (PV CELLS, not panels, there are cells bigger than .5vs). You would string these higher voltage cells together just like you string the .5v cells into a panel that would have a much higher voltage (270v) instead of the 18v panel that you get from using .5v cells. Is that not possible?????

I am trying to find out what the wattage of a panel would be if that panel was strung in series, with 9.0v cells that had a peak current of 70mA or a Short Circuit current of 75mA.

Using Sunking's formula: (I am trying to figure out how to use the amps in the formula)

W = V X A

W = 9v X 30c X 0.075A = 20.25 Watt Module
or
W = 9v X 30c X 0.075A X 30c = 607.6 Watt Module

Which would it be or am I totally wrong?? If my math is wrong please correct me.

Second question has to do with the wiring.....would you have to use a heavier tagging and buss wire, diode, etc.?

Thanks again guys, sorry to be such a bother.

Tag

[Sunking]

One little problem, cells are .5 volts.

[Mike90250]

Why use .5 volts cells if you can use 3v or 4v or 6v or 12v cells (PV CELLS, not panels, there are cells bigger than .5vs)

Please show me some info about the multi volt cells you are speaking of - AFIK, unless, there was a MAJOR breakthrough in the last 24 hours, all cells are 0.5V. Someone may be pulling a fast one on you, and selling panels, or pre-tabbed kits of higher voltage, but there are no cells higher than 0.55V. Show Me !

[Sunking]

All individual solar cells produce approximately .5 volts @ Voltage Maximum Power Point. Does not matter what the physical size of the cell is.

Current is the variable unit in a photovoltaic cell, and the current is directly proportional to size in square area and the amount of light. As a general rule of thumb it takes 6 square inches to produce 1 amp. For example your 3" x 6' cell produces 3 amps of current with 1000 W/m2 iradiance input. A typical 6 x 6 cell will be around 6 amps.

So when a panel is designed they generally fall into two categories of either off-grid or grid tied design.

Battery panels in general use 36 cells in series to produce about 18 Volts Maximum Power Point ofr a 12 volt battery system. So the power is completely dependent on the size of the individual cell size used in the design. So for the largest 6 x 6 cells will yield about 114 to 120 watts

Grid tied panels will use more cells to run higher voltage, but the cell size still determines the current value

So in other words it is the nature of the beast. Wattage of a panel is directly related to its physical size. You cannot put 10 pounds of crap in a 1 pound box. The law of physics cannot be violated.

[russ]

There are some companies that are claiming breakthroughs with higher output - Off Grid Solar being one.

They seem to be a scam type of company with a long history of shady practices.

Like Mike and Sunking said, no such thing on the market today.

Russ

[tag]

Thank you guys, Russ, Sunking and Mike for your responses. I am a accountant/ecomonics guys by education so I tend to look at everything from a $$$ perspective. When I made my first panel I realized that it was too costly in time, material and $$$ for the watts that one panel produced.....sooooo, I started looking to reduce the costs of the panel and the common demonimator for reducing costs is more watts/$$$$ or cells that produce more watts or volts.

I found a company at futurlec.com that cells higher volt cells....the design is a little different but the principal for string them together is still there so I bought some.

I want to make 270v panels out of these cells. Can I do it???????

Israel and Spain are both producing a "concentrated" solar cell that are 1mm X 1mm and produces a tremendusly more amount of power (I want to say 1000Xs more but I might be mistaken) than the traditional cells.

Reminder. You guys still haven't addressed my orginal question about watts that a 270v panel produces if the cells are 9v with a peak current of 70mA and Short Circuit current of 75mA. How about my formula calculation which one is right or are they both wrong?????? What is the wattage????

Thanks guys I really do appreciate your time and effort.

Tag

[russ]

Hi Tag - You have probably heard most of the bad names engineers call the bean counters (accountants) when they try to get involved with the selection and materials side. I can remember someone telling me but it is all stainless steel - what difference can it possibly make whether it is SS 304 or SS 316.

1) There is no (as in NO) cell 1000 times better than sold in present day solar panels. Maybe you are thinking about the solar towers where they use mirrors to concentrate light on a tower to make steam.

2) I'll let Mike or Sunking tell about the cells on futurlec - basically, when something is too different and goes against all practices it is a scam.

3) As the cells are not 9 volt I don't understand how the calculation can be done.

Russ

[Mike90250]

Voltage range from 0.5V to large 18V Solar Panels.

http://futurlec.com/Solar_Cell.shtml

It's a scam. Any parts listed over .5V, are, if you look closely, chips of small cells,
bonded together into a PANEL. Some I recognize from solar path lights. These are likely surplus or 2nds, and from the 50% failures I've had from pathlights, I never realized they could have 2nds to sell.

So their largest one 12V @ 80mA, produces a whopping 0.92 watts, for $10 ( and when you read the fine print, at 11.5V, it is impossible for it to recharge a 12.5V lead acid battery.

Really, these are not what you want, to produce actual amounts of power.


So, for your 270V, @ 0.07A that gives you 18.9 watts That's from 30, 9v modules at $6.90 each, you made a "20 watt module" that cost $207. $10.35 per watt. Warranty not included. Your mileage may vary. Would you like to buy a bridge?

For $207, you can buy a UL certified, 25 year warranty 45W panel !

http://www.solar-electric.com/spm040.html

If you needed 2, the economics of scale really start working for you, and you can get a 185watt panel http://www.solar-electric.com/kyocerakc170gt.html Now we're at $2.70 per watt, and I've not even gone shopping at sunelec.com yet.

Your move.

And what is the reason you want 270 volts ? That's not enough for grid tie, and too much for most MPPT charge controllers.

[tag]

Okay, Russ and Mike, I get the picture, I think. They have increased the voltage and in the process the amperage must come down.

I will see if I can return the cells I've already bought. It's not what I wanted to hear but I understand W = V X A !!

I still need to have a solar system to power my freezer and refrig. ... that is my goal. I will gather wattage requirements for both and I will probably be back with more questions.

Thanks,

Tag

[SteveC]

Okay, Russ and Mike, I get the picture, I think. They have increased the voltage and in the process the amperage must come down.

I will see if I can return the cells I've already bought. It's not what I wanted to hear but I understand W = V X A !!

I still need to have a solar system to power my freezer and refrig. ... that is my goal. I will gather wattage requirements for both and I will probably be back with more questions.

Thanks,

Tag

Now that the original question is all worked out, consider just figuring out what you need and purchasing the commercially-built parts and start making electricity. Don't get me wrong, I am all in favor of homemade stuff and/or going it for less money than otherwise.

However, number cruncher that you are, you might wanna focus in on the Fed. tax credit of 30% that is supposed to be valid for a few more years. It probably will be valid for that time, I don't recall how much longer it is set for, but one never knows whether the Congress will try to cut that time shorter for budgetary considerations.

That 30% might fuel an argument to go ahead and jump in now, at least with a starter system, and get to using PV.

On the other hand, if you decide to make your own, keep us informed as to how it all goes and works out.

[Sunking]

I want to make 270v panels out of these cells. Can I do it???????

Reminder. You guys still haven't addressed my orginal question about watts that a 270v panel produces if the cells are 9v with a peak current of 70mA and Short Circuit current of 75mA.

Tag I am a Licensed Professional Electrical Engineer with about 33 years of design experience. We have not addressed your question in the context given because what you speak of does not exist. There are no 9 volt cells. What they might be offering is 18 cells pre-built and calling them cells, but that is misleading

As I stated before wattage in a solar PV cells is a function of the physical size, amount of radiance falling on the area, and the efficiency of conversion. So since you are a bean counter is is some numbers to crunch.

The theoretical limit of 100% efficient solar cells is 1000 watts per square meter (1 kW/m2) Average solar panels today are 12% with 17 to 19% of products made by Sanyo and Sun Power systems. So that means the most power you can get out of a Square Meter of area is 120 to 190 watts. It does not matter how the cells are arranged to either yield 18 volts @ 10.55 amps or 70 volts @ 2.7 amps, it still comes out to 190 watts either way. With energy the law of physics cannot be broken or the books cooked to get the numbers you want like accounting.

I know that is not what you want to hear but how would you tell someone who makes $2000/month net who borrowed on credit cards to the point the minimum monthly payment of interest only exceeds their monthly income? Same thing the world banks are about to tell the USA, you are finished, hire a good lawyer and file bankruptcy!