Oil

[leehljp]

Loring,

Something is lost between my post and yours. (but I am not in a logical engineer mindset )

That little 2 inch by 8 inch solar cell in my pickup kept enough trickle going that the battery was not drained (dead) after 11 months of setting up - when I returned home. The normal clock and whatever drain - did not drain the battery like it had the previous times.

IS this a miniscule amount? So what is the difference in power of a dead battery versus a fully charged battery that is kept that way ONLY because of a small trickle charge solar panel over a year's time?

THAT raises the question of just how much Amperage that the solar panel is providing over 11 months of non engine use . . . and indirect sunlight at that? We are not talking about one day, but a whole year. The solar cell is providing the difference in a dead battery and a charged battery that starts the vehicle.

No, I am not inferring that it needs direct sunlight. My little truck battery stays charged with indirect sunlight when in the past it would be dead every year - and I would always purchase the largest that would fit - or rather take the dead one back for a warranty exchange.

Now to hybrids - when compared to a small solar panel as mentioned above, how much energy could a 3 ft by 4 ft solar panel on the roof of a hybrid provide over the course of a year? How much will that transfer into miles for a city hybrid?

[LCHIEN]

hank, the little solar panel will put out something in the range of 10 or 50 milliamps even in indirect sunlight.
This is probably enough to make up the running current of the clock and what are called parasitic items, as well as battery internal self-discharge. Self discharge varies with age and temperature among other factors, but is probably only a few milliamps.

As you stated it will more than makeup the charge loss from a battery in a parked car for a year - a little at a time, same as the loss rate.

A car battery left with the parasitic loads and self- discharge will be discharged in about 1-3 months. Discharged means some or all cells reach zero charge, Dead in my lingo means it can't be recharged because its bad. Which can happen if a discharged battery is left connected so it tries to further discharge.

Amperage is a measure of instantaneous current flow. Amp-hours is a measure of charge, which are time-related. An analogy is how fast the water is poured from a bucket and how full the bucket is. Left long enough, the small solar panel might charge the battery but may will take weeks. Watt hours is an amount of energy - takes the voltage into account.

Going back to the analogy, you bucket is left full when you drive it and the alternator charges it. The bucket has a small hole that trickles out, after days it will be empty. The solar charger is a small inflow trickle, As big as or slightly bigger than the out-trickle. This will keep the bucket full and able to start your car. Any excess will just heat the battery which is pretty large so you don't notice this extra heat.

Starting the car will take out a few pints of water but the alternator will put it back after a few miles - car batteries are generally kept topped off (full charge).

My points vis-a-vis your truck battery are:
1. left alone, it will discharge in a matter of weeks or months
2. left alone, it may damage the battery - make it dead-bad- through excessive discharge
3. with the solar panel you are preventing discharge(1 above), and eventually (2 above). - this is a good use for those small panels. You did a smart thing.
4. the small panel does not have enough trickle to fill up a battery in anywhere near a useful time.
5. And the battery for starting a car is not sufficient to propel it anywhere.

for how much a 3x4 panel will help:
3x4 solar panel puts out 150 watts with the sun directly overhead, no clouds on a mid-latitude location, and the panel ideally pointed at the sun (perpendicular).
Assuming the panel is flat against the roof top and not aimable and charging occurs throughout the day (average of 10 hours ) and the average angle to the sun is around 45 degrees (0.7 factor) no clouds and the panel is perfectly clean. Also Charging efficiency (ability to put electricity into the battery is less than 100% due to heating, voltage conversion etc) is probably no more than 75%. You'll get maybe 780 watt-hours energy in a days exposure.

A Prius on flat ground and city driving conditions takes 250 watt-hours of energy to drive a mile on the average.

So you might theoretically under the best possible conditions drive 3 miles on a days solar charge, provided the location is at a favorable latitude (e.g. not Alaska or Canada) and no clouds, and no shade - (even temporary) on the car - has to be in an open location.

By contrast, the power your little panel puts out, lets say you car battery uses 20 milliamps total for leakage and parasitic ops, amounts to about 5W per day.

[leehljp]

Loring,

You are a good friend to have! Thank you for the time you spent in getting those figures.

Ironically, I was watching the Discovery channel tonight and they had a special on a solar panel driven tractor. Well the solar panels charge a series of batteries and was impressive. I don't think it was for a daily use work horse but occasional few hours use.

[cgallery]

Loring, if you're still reading this thread, I have another Q for you.

What is the "efficiency" of current solar panels like Hank is referring to? That is, if you compute the amount of solar energy with which they are bombarded, what percentage of that is converted into electricity? Is there room for improvement?

[LCHIEN]

Loring, if you're still reading this thread, I have another Q for you.

What is the "efficiency" of current solar panels like Hank is referring to? That is, if you compute the amount of solar energy with which they are bombarded, what percentage of that is converted into electricity? Is there room for improvement?

the amount of Solar radiation falling on a panel that is convereted to electricity for the most common high efficiency panels commercially available is generally rated at 12-18% range. Usually use 12 or 15% as the number.

That leaves about 85% for improvement... you can make it 6 times better.
But, its been a problem worked on for years without breakthru, only a percent or so improvement here and there - I doubt a breakthru is imminent.

Even if there is a breakthru, it may involve exotic processes or materials that will drive up the price. Would you pay 5X for a panel that was 25% efficient?

So goes the economics of development. For a few mobile items with need for small footprint it would, but panels are already too expensive for many potential uses.

[JR]

Another alternative is fuel cells, and in fact several well known auto manufacturers are on the verge of producing them. Of course, there's no fueling infrastructure yet

I like this technology, too, but a couple of miracles have to occur before it can displace our gasoline/diesel-based model.

I saw a program on TV recently where they interviewed scientists at two different MIT labs. Their work was very preliminary, but promising. One of them has the idea that very-small-scale conversion might be feasible. This would enable home systems, perhaps using solar, wind, or hydro-powered methods. The homeowner would be able to create enough hydrogen for his own needs. This would theoretically mitigate the huge infrastructure-development problems associated with hydrogen production and distribution.

edit: I misremembered the facts slightly. Here is the 60 MInutes article, which explains the idea more clearly.
JR

[natausch]

A little less than a dozen years ago we had an inkling that we could turn Corn into a biofuel.

Today we're working on scaling production of Algae biofuels that have 10-50 times the capacity of corn biofuels.

Give it another decade and two and we should be able to replace petro as the main supply of portable fuel.

[jackellis]

As Loring points out, the beauty of petroleum is that it's easy to transport, it has a very high energy density, and it doesn't require a lot of exotic technology.

The biggest problem with most forms of renewable energy is that they are of relatively low density. Petroleum and coal are essentially a few million years worth of renewable energy in compact, high density packaging. One gallon of gasoline is the equivalent of about 30 kilowatthours of electrical energy, which by Loring's calculations (see earlier post) is the amount that would be produced per day by about 480 square feet of solar panels. So for most detached homes, the choice roughly boils down to producing the equivalent of a gallon or two of "gas" per day, or producing enough electricity to power, heat and cool your home. Average-sized homes probably can't do both with any degree of reliability even if you ignore the effects of clouds and seasonal variations.

I'm not suggesting we should forget about developing alternatives. Quite the opposite in fact. But there are some practical limitations.