PV Gap

Mitchell Said:

solar panel help needed!!!!?

We Answered:

It depends. If you are off the grid what you don't use or store goes away. I live in the suburbs and my electric company will buy what I don't use. So during the day when I'm generating electricity it goes into my home, all my extra electricity goes out to the grid and my meter runs backwards. Other homes are using what I generate. At night when I'm not generating any electricity my meter runs forward. My system isn't large enough to zero out my bill, so I always use a little bit more from the city than what I sell back. My electric bill went from around $200 a month to about $20.

Dean Said:

How long will it take a 100 Watt solar panel to charge a 55 Amp hour car battery?

We Answered:

Mike, I'm assuming the solar panel in question is wired for 12 volt battery charging, which means it actually peaks out at 18 volts if the circuit is open. Panels are rated in watts, which is found by multiplying the panels open circuit voltage by it's short circuit current, or amps. A 100 amp panel wired for 18 volts would have a short circuit current of 5.5 amps. My guess is the question is using a 55 amp hour battery because it is exactly 10 times the amp rating on such a panel.

You might see the answer already, but I'll explain further anyway. If a battery holds 55 amp hours, that means you can start out fully charged, and draw 55 amps out for an hour before it is dead. Or you could draw out 1 amp for 55 hours, and end up at the same place. So if the panel can feed in 5.5 amps for 10 hours, then it would replace 5.5 X 10 = 55 amp hours.

In the real world, the panel would actually put out a bit less than 5.5 amps, since it would not actually be at short circuit amps with a 12 volt battery in front of it. The battery is not 100% efficient, so each 10 amp hours you feed in might yield 8 amp hours of storage, and so on. But I'm guessing the question you are trying to answer is theoretical, so they are probably looking for 10 hours, in direct sunlight that is. Good luck, and take care, Rudydoo

Leslie Said:

Will a 100-watt solar panel (measured at 1000 w/sq m/d) produce 600 watts at 6000 w/sq m/d insolation?

We Answered:

No. Increasing the insolation by a factor of six will heat the standard solar panel, increasing its internal resistance and decreasing its efficiency. At some point there is a maximum amount of power that you can derive from a panel, but that depends on the technology.

Beverly Said:

If a solar panel creates 100 watts does it mean 100w a day, hour, or sec?

We Answered:

A watt is a unit of power, which represents one joule per second. This means a watt is already a rate of energy per unit of time. So a 100 watt solar panel produces 100 watts, meaning 100 joules per second.

Energy can also be measured in kilowatt hours, which represents the production of 1000 watts for 1 hour. So over the course of an hour, this panel would produce 0.1 Kilowatt Hours of energy, or 360,000 Joules.

Harry Said:

How many kwH does a 100 watt solar panel produce each day?

We Answered:

if you live in the lower 48 states, you get about 12 hours of daylight on average over the course of a year. 100 watts is 0.1 kwh. there are 8,760 hours in a year, so there are about 4,400 hours of daylight a year.
equation is,
4400 hours x 0.1 kwh x (days of sunlight/365) x cost /kwh x panel unit efficiency = $ produced
then,
$600/$ produced = simple payback
you may then do a net present value analysis (which makes the payback worse)

notes:
days of sunlight may be obtained locally from your weather bureau
cost/kwh can be obtained from your utility bill
panel efficiency can be obtained from the manufacturer data
equation does NOT include any cost for equipment upkeep or repair.

solar energy is NOT economically viable without extensive government subsidy. i think you will find your payback to be over 10, closer to 20 years, depending on utility cost (vary in the us between about $0.07 and $0.25 per kwh).