Off-Grid Power Systems

[tjm73]

Don't know if this is an O/T thing or not, but I can't seem to find a very clear tutorial on how an off grid system is put together. It's almost like the people that do know don't want to tell about it.

I've tried some research but everything I find seems incomplete.  

Knowing their are some pretty resourceful and knowledgeable folks in the part of the web, can someone share a good primer of solid example of an off grid system?

[glenn kangiser]

There are a million ways to do it.  

Depends on what you have and what you want and what your budget is.

Basics

1. A Battery or bank of batteries.

2.  A light or other desired loads -appliances etc.

3.  A way to charge the battery or batteries.

Tell us what you want to power and your budget and we will see what ideas we can come up with.  The fancier it is - the more it costs.  No secret - it is something that can grow so there are few that are the same.  What is pretty well fixed is the equipment you have to work with and the cost of the materials is pretty stable.

[Redoverfarm]

Not trying to sidetrack your train of thought but some of the ideas had been discussed in my post " Alternative Energy" . You might pick up something there.

[glenn kangiser]

There is a lot of info here already for sure, -- seems tjm73 may want to get into - hook wire "A" to terminal "a", which we can do also if need be.

Here is a link to that topic.  Thanks, Redoverfarm.

http://www.countryplans.com/cgi-bin/yabb2/YaBB.pl?num=1192660727

[ak_meli]

I am planning an off grid power system too. (very early stages though)

I have a very good local place that has a wealth of knowledge. This diagram is really helpful.
http://www.absak.com/diagram/general/index.html

The specifics of your offgrid system will depend on a couple of factors:

Watts or Amp. used / day =
number of days =
time of year=?
can you see the sun ?
number of cloud cover days =
average wind speed @ 50 feet=
$$$$ to spend=
Will you have a generator?


For me, solar panels won't work for the majority of the year. Some other alternatives that people employ up here is generator and batteries. A few deep cycle fork lift batteries go a long way and are easily charged by generator. The place above, Absak.com sells a quick charge wall unit to place next to the generator from for charging multiple batteries all at once. Spendy charger but well worth it. Costs about $350 for it. Running the generator for an hour or so would charge them enough for a full day and night.

Home Power Magazine may also be a helpful resource.

The Backwoods Solar Electric System of 1395 Rolling Thunder Ridge, Sandpoint, Id. 83864. These folks will do as much or as little to get you electrified in the best-suited type of system for your needs. They will give advice in the planning stage or build the most eleborate power system for you. They are a big help in just getting up to speed an all the various methods for living on and off the grid. AND, they are living and working their own advice: so, www.backwoodssolar.com

As well, The Lehmans Company [non-electric catalog](www.Lehmans.com)and the Cumberland General Store(www.cumberlandgeneral.com.)

Explore the backwoodssolar.com homepage. It has a wealth of information. Here are some things that might help you get started.

Be sure to check out the backwoodssolar.com Newsletters. Here is the summer 2007 one. There is a Fall 07 one out. They are extremely helpful. Also have stories from users.
http://www.backwoodssolar.com/newsletter/pdf/SUMMER%202007%20NEWSLETTER.pdf

They also have a great page on figuring out how much you need, giving some examples.
http://www.backwoodssolar.com/reference/examples.htm

Here is a page on wiring:
http://www.backwoodssolar.com/reference/home_wiring.htm

Some resources to buy:
http://www.backwoodssolar.com/catalog/books_videos.htm

Also, be sure to check out Coyote Cottage, although their system is for the minimalist

Forgot the link....
http://www.coyotecottage.com/powerplant/system.htm

[MountainDon]

tjm73, can you help and narrow the question down a little...

Do you mean like Glenn suggested, the how to connect one thing to another safely, or how to select components, or what components make a system, or??

[MountainDon]

The diagram at absak is good, but depending on what inverter you choose the auxillqary battery charger may not be needed. And the system meter, is interesting for technofiles, but not necessary. They're only as good as they are calibrated and that changes over time as the batteries age. It's probably the last thing I'll ever buy. My opinion.

And you will need a generator in nearly every installation.

[glenn kangiser]

Welcome to the forum, ak_meli.  

Lots of good info there.  I like the diagram - even if not all options are used.  It is a good overview of what you could do.  

The guy around here sold a lady a system at near double the price with no generator.  35K for a 20K or less dollar system.  It failed the first night they went to use it -- dead batteries and no way to charge them.  He probably got another 10K out of her for a generator.

I guess he figured she was old and wouldn't need it for much longer anyway.  I don't do business that way.

[tjm73]

tjm73, can you help and narrow the question down a little...

Do you mean like Glenn suggested, the how to connect one thing to another safely, or how to select components, or what components make a system, or??

Let me try to get kinda specific......

What components are needed? I know you need batteries, an invertor (of which there are several kinds) and I know that the type f inverter is importent if you run sensitive electronics.
How do you size your battery bank?
How do you wire that battery bank? In series? In parallel?


Let's take a hypothetical situation/example....

Let's say we need monthly service of 3.6 kW/h. My little apartment with all the lights on, the TV on, the VCR on, the DVD on, the computer on, refridgerator, microwave, etc... averaged 3.6kW/h on the bill each month over a year time frame.

I know how to make the power, but not how to safely and efficently collect and store it. We are studying the basics of DC and soon AC electricity in a class at college.



I will look through the provided links as well.

[MountainDon]

3.6 Kwh for a monthly average? That seems to be incredibly low.  :-/  :-?

I use far more than that per day in a 1550 sq ft single floor house, and I'm under the national average.

This calculator gives you a good idea of number of panels and batteries you'll need.

http://store.altenergystore.com/calculators/off_grid_calculator/#

If 3.6 Kwh was the true monthly average a single 85 watt PV panel with 2 - 6volt batteries in series would work. I use more than that in my RV.

:-/

[tjm73]

hmmmmmm.....................it may have been 360 kWh. I was going back and forth on which it was.

[MountainDon]

That sounds more realistic, but that's a lot of electricity. That calculator comes up with 15 x 175 watt panels and a minimum of 8 x 6 volt 420 amp/hr batteries for even sunny NM.  15 x 175 watt panels alone will cost about $11,000.00. Batteries at about $2700. Add freight to all.

Rather than use those actual usage figures you should really do an accurate audit of what you really need to use. A normal refrigerator is a big energy hog, that's why some of us have been talking over what's the best propane gas fridge. There are very efficient electric fridges; google sunfrost.

Cooking with an electric range is a no-no. Ditch that for propane.

Calculate the lights using CF lamps, if you don't already use them.

This calculator will let you easily total up your daily use.
http://www.affordable-solar.com/index.php?file=c-off_grid
It will not help with panels or batteries... that other one will.

[MountainDon]

But back to part of your question... your stated main crux... "how to safely and efficiently collect and store"

Collection:
Have the PV panels as close to the batteries as possible. (shorter and smaller cables)
Use a MPPT type of charge controller.

Storage:
Lead-Acid batteries are what's used. Use nothing less than a 6 VDC golf cart style battery. RV/Marine so called deep-cycle"batteries are not much better than the common automotive starting battery, IMO. The "L-16" type are better with heavier plate construction. Also heavier to handle, a disadvantage. Golf Cart batteries can give an excellent cost to service life ratio is maintained.

There are advantages to using a system wired for 24 VDC rather than 12 VDC, though many have used 12 VDC.

The main advantage to 24 VDC is smaller size cables. Also 24 VDC systems have more batteries in series strings. Better for the batteries in the long run, IMO.

The main advantage of 12 VDC systems is the vast number of 12 VDC "things" available. Lots of stuff from the RV market.

At the PV panels where all their wires come together you need a disconnect for maintenance safety. Also fuses or breakers. If the distance between panels and batteries is great then another disconnect from the panels and before the charge controller is advised.

A big fuse or breaker, able to handle the max current of the inverter is required right after the batteries. The inverter should be close to the batteries to avoid long cable losses. Inverter should not be mounted above or adjacent to the batteries. On the other side of a wall is good. Most inverters don't like really cold temperatures any more than batteries do.

A pure sine wave inverter is best if you will have electronics, or motors running off it. Some battery chargers self destruct on square [so called modified] wave inverters. And some electronics work fine off some square wave inverters. Depends.

The compinents you choose, switches, cable types, etc. etc. depend a lot on whether or not you must meet the NEC. You can't go wrong with NEC / UL approved components, but some things get pricey. And some things can be safely exchanged for non code devices. Some. Not all. Not what I necessarily recommend anyone do.

[glenn kangiser]

I am currently producing and using around 12 kwh per day - for 360 per month -- might even be more but I doubt it's much less.  I don't get into the numbers as much as Don.

If they get short on power  I add more panels or I could go and build racks and add an MPPT controller - tilt up for better angle -- build simple racks and do every few week seasonal tracking  adjusting vertical angle for lower or higher sun as the case may be.

[tjm73]

That helps, but I'm still not understanding how to select the batteries.

Let's say we have a small cabin. In it their are the following electrical devices. (some wattages are guesses)

8 CF lights, each 23W, 300mins/day
1 32" TV, 500W, 120 mins/day
1 VCR, 25W, 120 mins/day
1 DVD Player, 30W, 120 mins/day
1 PC, 80W, 180 mins/day
1 Monitor, 180W, 180 mins/day
1 Microwave Oven, 1100W maximum, 10 mins/day
1 Toaster, 700W, 3 mins/day
1 Stereo, 400W, 300 mins/day
1 Refridgerator, 1800W, 1440 mins/day

My calculations show that's 48.2 kW/h, 120V service

[MountainDon]

Also.....where is the point of use geographically?

[tjm73]

Also.....where is the point of use geographically?

Rochester, NY is the closest city to me.

About batteries....

Say you have 2-6V batteries that are 500amps/hr each. In series they add up to 12 volts, still at 500A/h. In parallel they woudl be 6V @ 1000 A/h. Is that correct am I understanding correctly?

[MountainDon]

Using the calculator at http://www.affordable-solar.com/index.php?file=c-off_grid
Leaving the fridge out of it, that's 5000 watts a day, or 150 Kwh a month.

Using the other calculator at http://store.altenergystore.com/calculators/off_grid_calculator/#
I see your profile states upstate NY. Is Schenecftady considered upstate? That's what I selected. That gives a need for 15 x 175 watt PV panels.

I chose a 24 VDC system. Skipped the charge controller for now.

Battery section of the calculator; selecting 3 days of backup power to allow for clouds. Selected 55 degrees F as the lowest temp for the batteries (inside storage, cool unheated room... battery capacity falls as temp falls).  That gives a minimum of 12 x 6 VDC L-16 type batteries at 350 amp/hours per battery. That would be  3 series strings with 4 batteries per series string. Each series string parallel connected to the others. Calculations assume running the batteries down to 50%. You should try to never draw down more than that;better would be to only draw 25%.

Does that help? And remeber that's without the energy sucking fridge.

All the above may vary depending upon location and the winter hours of usable solar sunshine

[tjm73]

Yeah that helps. Schenectidy is Upstate NY. Not near me, but close enough for the example.

I think I'm kinda gettin my head wrapped around the batteires thing. I'll keep readign and thinking about it.

[MountainDon]

Rochester, NY is the closest city to me.

Oh crap! That means less sun than the above example... more panels needed... like about 24 of them and 16 batteries.

Say you have 2-6V batteries that are 500amps/hr each. In series they add up to 12 volts, still at 500A/h. In parallel they woudl be 6V @ 1000 A/h. Is that correct am I understanding correctly?

Absolutely right! And because the parallel connection doubles the amps the cable size goes way up. That's why I say 24 VDC system is better. With lots of batteries some people would consider 48 VDC systems.

Say 16 batteries, two sets of 8 x 6 volt in series, connected in parallel.

Cutting down on the power use will cut the solar equipment needed. LCD TV's are king. Laptop computer is better than desktop.

[glenn kangiser]

Sounds good, Don.  I am running 12 L-16 @375 ah each.

The fridge must be off or needs to be replaced.  My 1934 GE Monitor Top fridge and 20 cu ft freezer each pull only around 1 kwh per day.  Freezer is modern energy star - GE is an antique with better efficiency than new ones.  It runs for about 8 minutes per hour at under 200 watts as I recall.  

[tjm73]

Rochester, NY is the closest city to me.

Oh crap! That means less sun than the above example... more panels needed... like about 24 of them and 16 batteries.

Yup. We don't get poop for sunlight lots of the time.

We get about a 10 mph average wind when the sun isn't shining though. SO a soalr/wind combo with generator backup could maybe work.

[MountainDon]

The fridge is a killer, but the compressor doesn't run 1440 min (24 hrs) a day.Find the model # of your fridge or pick a fridge that seems similar.

Go to http://www.energystar.gov/index.cfm?fuseaction=refrig.display_products_html  and find that model and see what the EPA says the average Kwh use is. It's listed per year.

For example, a new efficient Kenmore is rated at 480 Kwh/year, 40 Kwh a month.
That calculates to 7 x 175 PV panels and 6 of the 6 VDC 350 amp batteries just to serve the refrigerator!!    

[MountainDon]

We get about a 10 mph average wind when the sun isn't shining though. SO a soalr/wind combo with generator backup could maybe work.

Glenn's the windy guy around here.    But 10 mph doesn't sound like much to me. The wind up above trees and houses tends to be stronger, but you'd have to check wind charts/tables and/or talk to a reliable alt power company with local wind experience.

[glenn kangiser]

Wind tends to be about 3 times higher at 100 feet up, where your wind generator should be.

Note that charts don't take micro-climates into consideration, and while maybe not as efficient as if you were in a super great area, a good wind generator such as a Bergey can do quite well.  You can also build your own.  Watch some of the small commercial ones though.  Many are just crap.