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Solar and Wind Power for Home, Farm & Industry

Some fun with numbers!


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  #1  
Old 07-23-2019, 10:37:57 PM
Railroads Railroads is offline
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Default Some fun with numbers!

It's been almost 25 years since I lived off grid. I decided for fun to do some very rough and crude math as to what it would take in batteries and cost to setup a small system for fun. Quick, Run for the Effing hills now!

I am no math genius and probably have royally screwed up in my calculations someplace?

I really need to find a good book that gives me the formula's and basics in setting up a solar system.

I decided to settle on using my refrigerator as a base load. Most of which seem to be rated 800 watts. My choice of batteries would be 6 volt Crown traction batteries rated 205AH. Cost $98 each. Choice of inverter is 1500 watt high frequency type.

Voltage of one battery = 6V

Rated capacity of one battery : 205 Ah = 1230 Wh

C-rate : 1 or Charge or discharge current I : 205A
Time of charge or discharge t (run-time) = 1h

This C-rate is off, but I don't have a firm grasp on this either?

Time of charge or discharge in minutes (run-time) = 60min at 205 amps.

Number of batteries in a series = 2

Number of series in parallel = 14

Total number of batteries : 28

Voltage of the storage system = 12 volts

Current of the storage system = 2870 ampere

Capacity of the storage system (energy stored) = 2870Ah = 34.44 kWh

For a 1500 watt inverter.

Load Size: 125 Amps (Watts/Volts) at 12 volts

Load Duration: 8 Hours

Battery Type: Flooded lead acid.

Battery Needed is rounded to nearest whole number, and is rated in AH at a 20 Hour rate. If your battery bank is rated atleast this many rated Amp Hours, Your Load will run for the desired amount of time at a safe 50% discharge level.

Battery Needed: 2716 AH @ 20Hrs.

Lets see, 14 12 volts batteries X2 6 volt batteries. 28 batteries in all. Cost for the batteries $2,744 dollars minus commercial freight transport and hazmat fees for transportation.

Life span of these traction batteries, 5-7 years.

Amount of solar power needed to recharge, 2000 watts at 18 volts for a 12 volt battery bank. this is a best guess???

Cost of solar can vary depending on the route taken. More research on the cost of the solar array is needed??? My Australian friends like to build their own panels using the individual solar cells. Might be a cheaper approach. Might not be worth the trouble. I haven't decided yet?


Just the cost of the batteries to setup a proper small system is quite an eye opener really.

Makes me wonder why folks choose to go off grid when it's cheaper to just pay the Po-Co every month?


Robert
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Old 07-24-2019, 01:44:49 AM
Vanman Vanman is offline
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Default Re: Some fun with numbers!

Here are a couple thoughts. For one, I would use the highest battery voltage you reasonably can, probably 48 in this case, and the fewest cells possible, so I'd be looking at electric forklift batteries, and use just one big one.

I want to build a 112 volt nominal system, just like Kohler used to make. It'll normally be in the range 110 - 125, give or take, a little more and a little less at times. But this way I can run most things directly from the battery, with no conversion at all. But I collect antique DC appliances and I'm a little eccentric so...

On the plus side, a refrigerator doesn't use nearly that much power. Oh, some will be more than others, of course, but 50 to 100 watts is probably a closer figure. This is average. More while running, but also off sometimes. I had one at a house I was working on and it was the only thing connected to power. Per the electric meter it uses 50 watts, again average, of course. I think it was around 100 while running, and probably a few hundred while in defrost.

Another thing that can help is shifting demand to coincide with generation, ie when it's sunny. Then you skip the battery usage, wear and tear, and attendant losses for that load altogether.

Keith

Last edited by Vanman; 07-24-2019 at 02:44:12 AM.
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Old 07-24-2019, 03:08:08 AM
mihit mihit is offline
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Default Re: Some fun with numbers!

Quote:
Originally Posted by Railroads View Post
Makes me wonder why folks choose to go off grid when it's cheaper to just pay the Po-Co every month?
It's probably cheaper for you to lease a car than own one... but do you?
Renting a house is certainly cheaper than buying one... but do you?

Not being beholden to said po-co. No blackouts, brown-outs, no market fluctuations/price increases, generally better quality power. One known cost instead of ongoing.

It's not "cheaper to pay the po-co" There will be a return-on-investment period which will be more or less depending where you are, the price of equipment vs price of the po-co etc.
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Old 07-24-2019, 05:34:43 AM
Railroads Railroads is offline
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Default Re: Some fun with numbers!

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Originally Posted by mihit View Post
It's probably cheaper for you to lease a car than own one... but do you?
Renting a house is certainly cheaper than buying one... but do you?

NO. Everything I own is bought and paid for. Leasing things might be cheaper in the short run. But over the long run is more expensive!

Not being beholden to said po-co. No blackouts, brown-outs, no market fluctuations/price increases, generally better quality power. One known cost instead of ongoing.

Being a member of a Co-Op has it's advantages. Power doesn't fail unless a major storm or equipment failure is at the cause of the disruption. Power quality, I see 125 volts unless I have several KW of load switched on. Then the voltage drops to 118 volts. But, my service feed is 200 feet of aluminum cable buried in the ground. There is also 4 structures being fed from the same transformer. I am pretty sure most of them are setup to supply 3 homes at most. The Co-Op will wire 4 or more homes to one transformer. Don't ask me why? But they do end up coming out and replacing a failed xformer every so often!

It's not "cheaper to pay the po-co" There will be a return-on-investment period which will be more or less depending where you are, the price of equipment vs price of the po-co etc.
Yes and no. I realize there are still places in Australia and New Zealand that demand an off grid system or lighting by candles. Here in the states though, power lines run to nearly every corner of civilization. For me, I am lucky in that power stays on 98 percent of the year. The only disruptions are storm related most of the time. I belong to a Co-Op, and have probably the cheapest power possible. If it was not for the 25,000 BTU of AC needed this time of year to cool this less than efficient structure, my power consumption and cost, would be the lowest possible during the year. Winter generally sees higher power bills because my heat is all electric. 11KW of electric heating elements. The furnace tends to run some days when it's cold non stop all day. Those days are expensive!

For me, playing with the RE in any form is purely for fun or academic.

The fact that there is no "real need" for a RE system, coupled with the high cost of components and need to replace the batteries 5-7 years, really doesn't make much economical sense? It's all a hobby and for fun only.

Robert

---------- Post added at 05:34:43 AM ---------- Previous post was at 04:42:57 AM ----------

Quote:
Originally Posted by Vanman View Post
Here are a couple thoughts. For one, I would use the highest battery voltage you reasonably can, probably 48 in this case, and the fewest cells possible, so I'd be looking at electric forklift batteries, and use just one big one.

I want to build a 112 volt nominal system, just like Kohler used to make. It'll normally be in the range 110 - 125, give or take, a little more and a little less at times. But this way I can run most things directly from the battery, with no conversion at all. But I collect antique DC appliances and I'm a little eccentric so...

On the plus side, a refrigerator doesn't use nearly that much power. Oh, some will be more than others, of course, but 50 to 100 watts is probably a closer figure. This is average. More while running, but also off sometimes. I had one at a house I was working on and it was the only thing connected to power. Per the electric meter it uses 50 watts, again average, of course. I think it was around 100 while running, and probably a few hundred while in defrost.

Another thing that can help is shifting demand to coincide with generation, ie when it's sunny. Then you skip the battery usage, wear and tear, and attendant losses for that load altogether.

Keith
Morning Keith, I thought about 48v but would like to stick with 12v for a couple reasons: One, The system dad had was 12v. I have a fondness for 12v. Two, I want to be able to use a Briggs engine driving an alternator to help charge the batteries if needed for what ever reason, Three, 12v stuff is far easier to find and cost less than 48v. This includes the charge controllers, inverters, 12v appliances and even lighting. Forth, If I was going to be living off the grid and on batteries, I would be looking at 48v and Nickel Iron batteries. I have a fondness for the Edison cells, even know they are stupid expensive. If more RE folks would realize the advantages to the NiFe batteries, they would no doubt be made in America once again, and cost less. How to get people to see past those Lithium bats? Those things to me are ticking time bombs. They do explode a lot more than other battery types!

Ideally, I suppose 24v would be the next step up that would allow me to retain most of the advantages of 12v.

About selecting the fridge. My numbers were done using the most extreme conditions. The idea being that if I plan for a larger load, that in reality I would gain maybe a day or two of run time realistically. If things would run two, maybe three days that would be sweet.

Keith, I am also eccentric, and a mad scientist.

Robert

Last edited by Railroads; 07-24-2019 at 03:49:26 PM.
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Old 07-24-2019, 03:26:09 PM
Vanman Vanman is offline
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Default Re: Some fun with numbers!

What I want to find is some land that is still in the US, but is reasonably far away from any power lines. And a stream with hydroelectric potential would be great.

I want to build my 112 volt system with zero electronics, and make it as faithful to the period as possible. Too bad you can't get cells in glass jars anymore.

Keith
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Old 07-24-2019, 03:42:15 PM
Railroads Railroads is offline
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Default Re: Some fun with numbers!

Quote:
Originally Posted by Vanman View Post
What I want to find is some land that is still in the US, but is reasonably far away from any power lines. And a stream with hydroelectric potential would be great.

I want to build my 112 volt system with zero electronics, and make it as faithful to the period as possible. Too bad you can't get cells in glass jars anymore.

Keith
Keith, That sounds more to my style. 112v system eliminates almost all of the problems that electronics can bring about. The only question though, Where do you find a 110v DC to 110v AC inverter? I've got a friend that keeps pestering me about these inverters too. I know they existed for the old glass jar farm/wind generator power systems. I just don't know what is available today?

I'm personally interested in examples of 110v DC to AC inverters from the old days of those old wind power/farm power systems?

I'd like them to make the glass jar batteries too. Closest thing is the clear plastic batteries used in some substation power supply systems. Those are pretty scarce too.

Robert
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Old 07-24-2019, 05:01:35 PM
Vanman Vanman is offline
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Default Re: Some fun with numbers!

I have enough Kohlers with rusted out engines but good generators such that I'm thinking to couple a DC one and an AC one to make a motor generator. And use the Kohler autostart system to turn it on and off based on load. But I want few AC devices.

Keith
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Old 07-28-2019, 10:18:36 PM
Power Power is offline
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Default Re: Some fun with numbers!

Quote:
Originally Posted by Railroads View Post
The only question though, Where do you find a 110v DC to 110v AC inverter? Iday?

I'm personally interested in examples of 110v DC to AC inverters from the old days of those old wind power/farm power systems?

Robert
Robert, you find 110-DC to AC rotary inverters at ship breakers & salvage! The Liberty ships, Victory, older destroyers, etc up until early 1950's had 110/220 DC generators. The radio room and some other equipment required 115 AC. Ac was also run into officer's rooms. There were 2 or sometimes 3 good sized rotary inverters near the radio room. One of my jobs was to maintain them. They were extremely reliable, only needing brushes every few years.
I do not remember spec's, but think were around 2 KW. I plugged in an electric clock, and it kept time +- 1-2 minutes a week.
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