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Old 07-27-2009, 08:17 PM   #51
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Re: Solar power questions...

Man that sounds like a nice system Sean!

I was looking at the Trojan batteries, was told there is nothing better! If you don't mind me asking, how much are those batts each? Your DC fridge only draws 25 watts? Thats really good! What size is the fridge?

We were thinking about a wind generator but are unsure how much wind we will get on the property & I would imagine if we were to place it on top of the hill we would have a good wind but the wire run would be way too long to make it efficient...We shall see when we get there!

So what do you do for water & waste disposal while living in yer bus? I am guessing it is just you? Oh yea, your bus looks like it is a bit short... how long is it? The interior is very nice & I am digging the round window door, very cool...
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Old 07-27-2009, 08:56 PM   #52
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Re: Solar power questions...

Quote:
Originally Posted by ezbme
Man that sounds like a nice system Sean!

I was looking at the Trojan batteries, was told there is nothing better! If you don't mind me asking, how much are those batts each? Your DC fridge only draws 25 watts? Thats really good! What size is the fridge?

We were thinking about a wind generator but are unsure how much wind we will get on the property & I would imagine if we were to place it on top of the hill we would have a good wind but the wire run would be way too long to make it efficient...We shall see when we get there!

So what do you do for water & waste disposal while living in yer bus? I am guessing it is just you? Oh yea, your bus looks like it is a bit short... how long is it? The interior is very nice & I am digging the round window door, very cool...
The batteries were about $200 each, bought at a Batteries Plus store.

The fridge is a Nova-Kool R4500, 4.3 cu ft, teeny freezer. After doing an analysis of electrical consumption, for many households, it turns out refrigeration is the #1 electrical load. An inefficient fridge may mean an extra panel and a battery or two, so in that way, a $200 dorm fridge may cost more than an $800 efficient fridge.

For water, I just have to park where there is a water supply. I don't really have a way to haul water (with a motorcycle...would be interesting). Grey water goes onto the ground where allowed, otherwise into a sewer connection, or I use a 22-gallon Blue Boy to lug it if the sewer dump is far away. No blackwater because I use a waterless composting toilet.

Yep it's just me in the bus, along with the cat. The bus is 29' bumper-to-bumper, 23' interior length from rear of doghouse to back wall. A good size for one person, or two people who get along really well.
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Old 07-29-2009, 05:41 PM   #53
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Re: Solar power questions...

Thanks for taking the time to answer all of my questions Sean, it has been alot of help for me to understand solar power a little more! I will check out the battery store next week to see what my options are & to get some advice from them also. You really use alot of solar power for your business, quite impressive! I hope I am able to get ours working efficiently & to our needs but still have so much to learn. I am on some solar forums & so many people have so many different opinions & it really is discouraging sometimes...
I really like your bus, you have done a great job setting her up!

Jonathan
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Old 07-29-2009, 11:27 PM   #54
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Re: Solar power questions...

A couple of things from the older posts:

1. Your homesite looks great. Personally, my only worry in buying something like that sight unseen would be if it had a good water supply. Good luck and have fun.

2. When you used the online battery sizing calculator, you left the second column (which is daily use) at zero for the heavier loads. If you look at the "Total Daily WattHours required" box, its total of 820 is just for the computer and misc loads. The first column is instantaneous loads, and is useful for inverter sizing. The second column is for accumulated usage, and is the basis for the battery bank sizing.

Since you have a Kill-a-Watt, let it accumulate the usage on each appliance for 24 or more hours, and in the second column enter the accumulated watt-hours adjusted to 24 hours (two-thirds of a 36 hour total, one-half of 48 hours, etc). This will come up with a somewhat larger battery requirement.

3. If the photovoltaic panel label in the next photo is the panel you got, notice that it only makes 90 watts at 17 volts! (Max power 17 volts x 5.29 amps = 89.93 watts in 'standard' sunlight) If you have a Maximum Power Point Tracking (MPPT) charge controller, you can get close to the 90 watts, with the panel running at around 17 volts and its output being down-converted to 12 volts for the battery. If you use a simple 'disconnect when full' overcharge prevention limiter, you will get much less power.

Look at the 5.77 amp Isc short circuit current and the 21.5 volt Voc open circuit voltage. The power curve for a panel generally looks like a horizontal line at 5.77 amps starting at zero volts up through maybe 15 volts, then falls off to zero amps as it curves down to 21.5 volts. The maximum output point is on that curve between the maximum current and maximum voltage points.

Connected directly across a battery with no controller, or a shut-off only controller, the panel is loaded down, and you will get:
5.77 A x 10 V = 57.70 watts into a discharged battery
5.77 A x 12 V = 69.24 watts into a half-discharged battery
5.77 A x 14 V = 80.78 watts into a full battery

So, without MPPT, the more you need a recharge, the less you will get. (I have two sites with older disconnect only control, and the result has been disappointing.)

There are charts that estimate average sunlight hours per day adjusted to 'standard sunlight' for different areas. Around here it's about 4.5 hours in winter. So I could estimate that with MPPT your single panel would give me 90 x 4.5, or 405 watt-hours per day. There's obviously more light in the southwest. It looks like the one panel won't make you generator-independent, but will cut a big chunk out of the requirement.
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Old 07-30-2009, 01:42 PM   #55
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Re: Solar power questions...

Quote:
Originally Posted by Redbear
A couple of things from the older posts:

1. Your homesite looks great. Personally, my only worry in buying something like that sight unseen would be if it had a good water supply. Good luck and have fun.

Hey thanks! We can't wait to make the 2,000 mile trek to see it! There is a great water source as the development was a stop off for the cattle drives back in the day & water is still very plentiful. We will have to fill up tanks from the subdivision well (about 3/4 mile from cabin) & then pump the water into the holding tanks at the cabin using a generator.

2. When you used the online battery sizing calculator, you left the second column (which is daily use) at zero for the heavier loads. If you look at the "Total Daily WattHours required" box, its total of 820 is just for the computer and misc loads. The first column is instantaneous loads, and is useful for inverter sizing. The second column is for accumulated usage, and is the basis for the battery bank sizing.

I need to redo the online battery sizing calculator as we have made more changes since I posted that calculation... Here is the very basic needs that we have at the moment:
The house is self sufficient, has solar & is not in the equation. It is completely separate from the bus/office.
The system I am setting up is in the bus & will power the office supplies only...

Laptop = 50w per hour - 4 hours per day
Modem = 50w per hour - 4 hours per day
Inkjet printer = 29w - 2 hours per day

100W x 4 hr + 29 x 2 = 458wh / 5 charging hours = 91.6W Is this correct?

Since you have a Kill-a-Watt, let it accumulate the usage on each appliance for 24 or more hours, and in the second column enter the accumulated watt-hours adjusted to 24 hours (two-thirds of a 36 hour total, one-half of 48 hours, etc). This will come up with a somewhat larger battery requirement.

I will do this...

3. If the photovoltaic panel label in the next photo is the panel you got, notice that it only makes 90 watts at 17 volts! (Max power 17 volts x 5.29 amps = 89.93 watts in 'standard' sunlight) If you have a Maximum Power Point Tracking (MPPT) charge controller, you can get close to the 90 watts, with the panel running at around 17 volts and its output being down-converted to 12 volts for the battery. If you use a simple 'disconnect when full' overcharge prevention limiter, you will get much less power.

This is the panel we got & are lookng at at east one, maybe 2 more 85 watt panels. I am not quite understanding all you are saying (man, I wish I understood this more)

Look at the 5.77 amp Isc short circuit current and the 21.5 volt Voc open circuit voltage. The power curve for a panel generally looks like a horizontal line at 5.77 amps starting at zero volts up through maybe 15 volts, then falls off to zero amps as it curves down to 21.5 volts. The maximum output point is on that curve between the maximum current and maximum voltage points. Connected directly across a battery with no controller, or a shut-off only controller, the panel is loaded down, and you will get:
5.77 A x 10 V = 57.70 watts into a discharged battery
5.77 A x 12 V = 69.24 watts into a half-discharged battery
5.77 A x 14 V = 80.78 watts into a full battery

So, without MPPT, the more you need a recharge, the less you will get. (I have two sites with older disconnect only control, and the result has been disappointing.)

There are charts that estimate average sunlight hours per day adjusted to 'standard sunlight' for different areas. Around here it's about 4.5 hours in winter. So I could estimate that with MPPT your single panel would give me 90 x 4.5, or 405 watt-hours per day. There's obviously more light in the southwest. It looks like the one panel won't make you generator-independent, but will cut a big chunk out of the requirement.


I was told that the insolation in New Mexico in the winter is 6 hours which I would imagine is very good. I really need to learn this more & maybe simplify it so I can understand it. I really just want to be sure I can run what we calculated without power loss or having to run the generator every day to charge the batteries...

I really appreciate your help so far!!

Jonathan
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