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Solar cell 23.5 VDC 1.15 amps.

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gary350

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I bought one 14"x38" solar cell $35 it says, 23.5 VDC open circuit, 17.5 volts under load. Rated 1.15 amps full load.

Is 17.5 VDC too much for a 12 VDC to 120 VAC inverter?

If I put 7 cells in series I get 122.5 VDC. Is it ok to connect 7 cells in series or is the voltage too high?
 

audioguru

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Your solar PANEL was a bargain price maybe because its voltage is odd.
If the inverter produces 120VAC with an input of 13.2V from a charged 12V battery then with an input of 17.5V from the solar panel the output of the inverter will be 159VAC which is way too high and will probably blow up the inverter and anything it powers. But its rated output is only 20W. What do you have that uses only 20W?

If you connect 7 solar panels in series then the output is DC, not AC and the voltage will be anywhere from 122.5V to 164.5V depending on the amount of load current.
 

Reloadron

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Most 12 VDC to 120 VAC inverters are designed for an input voltage of between 12 and 15 VDC as in this example.

NOTE:
Input voltage range: 10-15 VDC
Over voltage shutdown: over 15 VDC
Under voltage shutdown: under 10 VDC
Low voltage alarm: Audible at 10.6 VDC

So they are designed for a wide input voltage range to provide a constant output of a modified sine wave. The output waveform may or may not be suitable for your intended applications. Inverters that provide a true sine wave do exist but are much more expensive than the off the shelf inexpensive flavors.

The next problem as AudioGuru points out is your panel, under load in full sunlight, only delivers about 20 watts. It would take 5 such panels in parallel to deliver 100 watts and that does not consider inefficiency of the inverter. Not to mention the 17.5 volts will well exceed the input tolerance for most inverters. You want panels that will deliver about 14.5 volts under load maximum for everyday off the shelf inverters and even then will need quite a few to get any real amount of power.

Just My Take
Ron
 

gary350

Well-Known Member
The 17.5 VDC solar cell is designed to charge a car battery. The battery is then suppose to be used to power a DC to AC inverter. There is suppose to be 3 of these solar cells in parallel to charge a car battery but I only bought 1 solar cell. There was no information on the box so I had to buy one to find out the volts and amps that the solar cell produces. Now I have 1 solar cell I need to find a use for it.

I have a car battery in the camper that will run lights at night for 7 days before it goes dead. I have 15 watt lights in all the fixtures and all 6 lights are rarely on all at the same time and they only get used maybe 2 hours each night.

Anyway I am trying to figure out something to do with just one solar cell. I bought this just for fun to experement with. 20 watts is not much power. Maybe I can use it to keep my rechargable camera batteries and flashlight batteries charged.
 

ronv

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You should still be able to charge your battery with it. You need to add a diode in series with it to keep the solar cell from discharging the battery when it's dark. Then you could use the battery to run the inverter.
 

audioguru

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A car battery is not designed to be run down much. It is designed to start a car engine in a few seconds then immediately be charged.
If you run it down then it will fail soon.
Inverters use a deep discharge battery, not a car battery.
 

awt

New Member
As said by Ronv, connecting the panel in parallel to the battery will bring down its voltage to battery voltage. While it charges the battery, it also supplies the inverter. Note that 20watt solar panel is just too small for this.
 

gary350

Well-Known Member
The salvage store where I got this solar cell has a truck load. Some of the broken cells are priced $5 each. The glass cover is broken and the solar cell is broken in several places. I am not sure if the solar cell can be solder together with wires to splice the pieces together and I am not sure it is worth the time and trouble. A piece of protective glass to replace the broken glass is $6 at the hardware store. The good panels are priced at $20 to $25 then the fees plus sales tax makes them about $30 to $35 each.

Screwing around with 1 solar cell does not seem practical. If I were to buy enough cells for 750 watts plus a car battery and an inverter that would cost about $1400 + 10% sales tax. I am not going to waste my time doing the math the saving on my monthly electric bill for 750 watts would probably take 20 years to break even.

I would like to buy more solar cells because of the good price but on the other hand what for?
 
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audioguru

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A car battery dies quickly if it powers an inverter until it needs to be recharged. It is not made for that (it is made to start a car engine in a few seconds then be quickly recharged) and is never discharged.
An inverter uses a very expensive deep-discharge battery.

There is an advertising sign in a field beside a busy road. The owner didn't want to pay the electrical utility company $thousands to wire it to electricity so he used a solar panel and battery so the sign lights in the evening.
It didn't work half the time so he added a windmill that doesn't work some of the time.

Count how many solar panels are used by the electrical utility company in this photo:
 

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gary350

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Wind power is much better than solar as far as price goes. A 400 watt wind generator at Northern Tool is $500. 400 watts of solar cells are $2160. This price does not include, the $100 storage battery, the $35 inverter or 10% sales tax.

Looking at the wind mill wind speed chart it shows minumum wind speed is 3 meters per second. At 6.5 m/s the wind mill produces 100 watts. At 11 m/s it produces 400 watts. At 12.5 m/s it produces 500 watts. Here in TN the wind is gusty all the time it is impossible to fly a kite here. Wind will be dead calm for 30 seconds then 12 mph for 30 seconds, then 3 mph for 30 sec, then 8 mph for 30 sec, then dead calm again. I am not sure a wind generator is practical for an area where the wind is gusty all the time. Average wind speed is about 4.6 mph so that means wind mill average power is 50 watts.

3 m/s = 6.7 mph = 0 watts

6.5 m/s = 14.6 mph = 100 watts

11 m/s = 24.7 mph = 400 watts

12.5 m/s = 28 mph = 500 watts

The old farm water pumping wind mills would operate in a 2 mph wind.

Wind speed calculator. http://www.calculateme.com/Speed/MilesperHour/ToMetersperSecond.htm

Hay, I can get 50 watts with 3 solar cells that is a lot cheaper than a wind mill that produces an average of 50 watts.

I expect one of these days if a lot of people start buying these to save money on the electric bill the Government will want them to pay Tax on the money they are no longer spending on their electric bill.
 
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