"Paradigm Shift"

[Eric von Kleist]

Well, the last post was December 8th, and today is December 17th. There's a lot less sun lately, as it is dipping lower and lower in the sky. Now there's only direct sunlight from about 11:00am to 1:00pm, and for another 5 days it will get less and less. The cloudy overcast we have been having lately with all the snowy weather is cutting the electrical production. The other day, I averaged about 0.5A/hr for 5 hours. That only produces 2.5Ah for the whole day, which is not enough to meet my minimum demands of about 16Ah/day. On the other hand, when it was cloudy with bright sun in just the right combination, the brilliance in the sky was enough to make as much as 8.7A during the peak sunlight hours, and about 5.0A during much of the rest of the day until it fell off an hour before dark, which is at 4:30pm. I'm watching the Amp-meter on the charge controller very carefully, and using electricity very sparingly. I don't want to damage my battery by running it down low.

If my cheap generator worked, this would not be an issue; however, the $250 3,500W generator I bought last Christmas has burned out its distributor, and you can't get parts short of a 3 month wait from some Mitsubishi licensed Chinese factory -- good luck. If I can find an engine to replace it with, I might have a chance of getting it working, but it'd be cheaper in the long run to buy a decent generator.

Fortunately, the solstice approaches, and then the days will get longer and the sun will get higher above the mountain. The light was still pretty good on the 8th, when I last posted, so by the middle of the first week in January things should be much better...hopefully...if not...I'll have $$ to buy a new generator by then!

I'm going to post some more pictures in the gallery about how I get water out of the well.

[Eric von Kleist]

Well, the Solstice has passed, and all our days will be longer now for a while! On a bright fairly overcast day, I am generating around 15 to 20 Amp hours of electricity. On a cloudy overcast day that is fairly bright, I'm lucky to generate 12 Amp hours all day. A sunny day is around 12-15 Amp hours. The best day is when there are moderately high clouds and the sun is at an angle to shine under them -- then I can generate as much as 25 Amp hours of electricity in a day from what is mostly reflected sunlight.

I'm thinking of building a wind generator this spring. Something with a nominal output of 1-2kW/hr.


I hope everyone enjoys the new year!

[Eric von Kleist]

Revising the above: Sunny, bright day: 8-10 Ah. Bright overcast day: 12-15 Ah. Overcast day: 5-7 Ah.

My laptop takes about 20Ah to charge (because it has a big battery), and it will run about 6 hours on a charge. Right now, I can charge it roughly every other day, and still have enough electricity to run an 11Watt flourescent bulb for 5 hours and the odd amperage drain that my 12V water pump draws (maybe 1Ah all day.)

Life is interesting when you have to really think about what your [bold]needs[/bold] are.

I highly recommend these 12V Flourescent bulbs http://www.solar-electric.com/sol12voldcli1.html. They fit standard screw in sockets, and you can thus use standard light fixtures in your bus. I have wall sconces made out of a disassembled chandelier, and I use these bulbs in my sconces http://www.skoolie.net/gallery2/v/Sk...+_Product.html. They draw about 0.9Ah, and are as bright as a 40W bulb.

[added] Right now, if I have a 5-7Ah day, I have produced enough electricity to run one of these bulbs for 5 to 7 hours during the evening without further draining my battery, i.e. no net gain, however. There is a spot nearby with sunlight for more of the day where I could put the bus, but it is downhill and has nowhere near the commanding view that the current site has, so...I'll opt for the view over electrical power. But the days grow longer...

[Eric von Kleist]

Okay, now it's late February. The Sun has been up over the top of the mountain since about the first week in the month. The bus starts getting direct sunlight at about 9:00 AM, and keeps it until about 4:30 PM. At present the solar panels (390W) are pretty well keeping up with my normal daily demand of about 8-10 Ah per day. On days when I burn 20 Ah charging my laptop, it will take a day or two for the solar panels to re-plenish the deficit, but at least there is enough solar power available on a reliable basis now (as opposed to this winter when it was in short supply.)

I have seen many publications and books that advise utilizing a bank of solar panels with a total output power roughly equal to half the Ah capacity of the battery bank. I would advise differently, at least in a mobile application, because you can never be sure where you will be located, and, thus, you have to incorporate "excess" power in your system in order to be able to operate successfully in less than optimum lighting conditions.

My battery capacity is 265 Ah. The useful capacity (20% of battery capacity) is 53 Ah. The solar panels put out 390W at maximum output. Thus, my output capability (390W) divided by my battery capacity (265 Ah) results in a ratio of 1.47:1. If you look at the output capability (390W) divided by the useful battery capacity (53 Ah), however, the ratio is 7.35:1.

I think that an output (W) to useful capacity (Ah) should be at least 5:1.

Often, you will only be able to generate 10% or 20% of the solar panels' capability, so having significant output capability means that you can still make meaningful amounts of electricity.

When you are either sited well for solar collection, or in a place where the sun shines for many hours, you will have electricity to burn -- literally. Not a problem. The less deeply, and the less often you discharge your battery, the greater the number of charge/discharge cycles it will survive. Having an abundance of power means that often you will be drawing less than the panels are charging -- this allows the batteries to stay closer to full for greater periods of time, and will prolong battery life greatly. Solar panels last longer than batteries, so in a lot of ways it makes more sense to invest in greater solar output than in greater storage (assuming you have enough storage for you daily needs).

Just some thoughts on system design.

[baadpuppy]

Originally Posted by Eric von Kleist

My battery capacity is 265 Ah. The useful capacity (20% of battery capacity) is 53 Ah. The solar panels put out 390W at maximum output. Thus, my output capability (390W) divided by my battery capacity (265 Ah) results in a ratio of 1.47:1. If you look at the output capability (390W) divided by the useful battery capacity (53 Ah), however, the ratio is 7.35:1.

I think that an output (W) to useful capacity (Ah) should be at least 5:1.

Often, you will only be able to generate 10% or 20% of the solar panels' capability, so having significant output capability means that you can still make meaningful amounts of electricity.

This is all great information, and has my mind churning with ideas.

You say the useful capacity of your battery bank is only 20% of the total capacity? How was this determined? Is this a good rule of thumb the rest of us should adhere to?

Since your useful capacity is 1/5th of your total capacity, and you state that your solar output should be 5 times your useful capacity, it sounds like you're basically saying your solar output should equal your total capacity. Is that what you mean to say?

For your 390W of solar panels, about how much square footage is it taking on the roof of your bus?

Thanks,
jim

[Eric von Kleist]

Originally Posted by baadpuppy

You say the useful capacity of your battery bank is only 20% of the total capacity? How was this determined? Is this a good rule of thumb the rest of us should adhere to?

Since your useful capacity is 1/5th of your total capacity, and you state that your solar output should be 5 times your useful capacity, it sounds like you're basically saying your solar output should equal your total capacity. Is that what you mean to say?

For your 390W of solar panels, about how much square footage is it taking on the roof of your bus?

Thanks,
jim

Hey, Jim!

Lead-acid batteries (AGM, Gel, plate&acid) last longer the less deeply you discharge them. Taking a battery down to 50% of capacity on a regular basis will wipe it out after maybe a couple of hundred recharge cycles. Taking it no lower than 75-80% of capacity will make it last several times as long. Thus, for long battery life (i.e. less cost in the long run) you should only use that "top" 20 or 25% of capacity as your "available supply." Otherwise, you will just run your battery into the ground in a couple of years, instead of having it last 5 to 8 years.

I think as a rule of thumb, that for people who have extremely variable solar supply -- like people who drive busses, and may or may not be able to choose a "solar-friendly" parking spot -- for those people, *I* would recommend at a *minimum* a 5X actual capacity (I have about 7.3X actual).

You are right, that my *minimum* recommendation is that battery capacity = max panel output. I would be happy to have a 10:1 ratio, but 7.5 seems to be plenty.

You have to realize, that what I am advocating is, essentially, overkill in terms of what others recommend, but I make the recommendation so that one has PLENTY of power on sunny days, and ADEQUATE power on overcast days. Some folks might say, "well, just use more batteries so that you have more storage," and that is ONE solution. But batteries weigh a lot, and solar panels don't -- and they cost about the same on a Watt (of storage) for Watt (of generation), plus solar panels last longer than batteries, so your money lasts longer....

FWIW, YMMV

Eric