Question about electricity generation/usage and battery life

[OzarkBrandon]

I know the board has several people with strong electrical / battery experience and I was looking for an answer to some questions I have. 

I like the idea of generating my own electricity (probably solar), but the cost and limitations of batteries are my biggest concern.  If my understanding is correct, battery life depends in large part on the depth of discharge and frequency of discharge.  If electricity is being generated at the same time as electricity is being consumed, will all consumed electricity be drawn from the batteries? Just curious if using electricity during the day while production is high, and limiting use at night could extend the life of batteries by preventing/reducing discharge?  Would different systems handle this in different ways?  If so, which component would be necessary for that benefit?

Thanks in advance to anyone who has knowledge to share.

[MountainDon]

battery life depends in large part on the depth of discharge and frequency of discharge. 

The depth of discharge (DoD) has a very large part to playin overall life expectancy of a battery. Frequency too, as the life can be measured in discharge/recharge cycles.  But also playing a large part is temperature. Batteries living in a hot desert climate won't last as long as batteries that are cool or cold all the time.

Once the batteries are fully charged there is power available from the PV panels but being unused, "wasted". If you draw power from the system I believe the batteries will act as a buffer if the power drawn is less than what is coming from the PV panels. If you need more power, more is drawn off the batteries reserves. But the batteries stay more or less full and do not really cycle much so I believe that will not have much affect on battery life. But on a hot day lots of in and out might result in elevated battery temperatures which can shorten life.   So I'm not sure there is a best case scenario or what it might be. Maybe Dave Sparks will see this and comment.

Our daytime use is quite limited on an average day. Most PV input goes to a recharge. Some days may see some light use for the MP3 player & speakers, maybe use of the blender for a smoothie at noon. Our big use starts later in the day after the power production. That may start with microwave use at dinner and extend through the evening with lights, TV or stereo. I don't see how any of that could be time shifted to a daytime, PV power producing time. Suggestions/ideas on that are welcome.   I could go to bed earlier and save on the lights.

My solution to the DoD issue was to increase the number of batteries. Along with that the number of batteries were increased again to counter the power capacity lost in cold weather. (batteries are in an unheated space.)

Some uses can be made quite effectively on a time scheduled basis. Dave uses excess daytime PV power to drive a heat pump (mini split) for A/C in summer and for heating in winter. That is one of the almost perfect examples for using the PV excess.  Any well designed PV system should have some excess PV capacity to ensure the batteries will reach float every normal day of use. That too will go a long ways to maximize battery life.

... 4 years into our golf cart batteries and still looking/working great...   Not sure what I could do different and still have the same level of service from the system.

[OzarkBrandon]

Thanks Don, I appreciate the info.  It sounds good in theory to use the power as it is generated, but I'm sure it would be easy to fall back into the natural pattern of using more power in the evening just like you have experienced.

[Gary O]

 Well now, my search for a thread on batteries has proven fruitful.....

Getting started (aka; thinking about it).

I plan on experimenting with a small solar system, but just to get familiar with it all (harbour freight cheapy).

Howevah,

right now I'm highly interested in batteries and what all I'd need in regard to charging them with a generator.
We're going to be off grid, so a generator is not a passing consideration.

But

They're noisy things, and expensive to burn fuel thru the night.

I figger I could tap into the generator during the day when I'm runnin' it for saws and such, to charge a bank of batteries.
Just want some lights, computer, coffee pot, things like that.
What battery type, size, converter, cable, etc?

Or am I nuts?

Don?

You there?

[MountainDon]

Here, but in the middle of gluing a bunch of stuff.... 

For now start here...   http://countryplans.com/smf/index.php?topic=6059.0    longish thread.

[MountainDon]

Before thinking about equipment you have to estimate your power needs as best you can. And make an allowance for what "wants" will increase that. There is a calc listed in that thread. Use it to estimate your power use. Or any other method as a different online calc or a piece of paper, the old fashioned way.      Back tonight.......

[OlJarhead]

I live pretty much full time now 'off the grid' (power) and can say that Don's pretty much spot on and I doubt I can add anything except experience.  Here are some thoughts:

Harbor Freight:  Forget about it! Seriously, for the same price or just slightly more you can get a much better system by putting it together yourself.  We bought a 60W system from Costco to power our pump and it now sits in the loft waiting for me to come up with a way to use it (maybe the outhouse light).

Living on solar requires a different way of thinking unless you have loads of money.  For me it means turning off the power to the Modem and wireless router when not in use (who does that at home?), leaving the DVR and TV power off unless being used (I use a power strip that I can switch off and on).  Using only the lights you need, not what you might want (most like more lighting).  Turning off the car stereo I use for music when not in use etc etc.

Batteries require maintenance, don't forget!  I have reminders to check them every 60 days or less and fill with distilled water as needed.

Get a good battery meter (I use a Trilithic) and watch what the power does under use.  It may draw down a lot and then bounce back later (that's why you can't rely on a voltmeter alone since it doesn't really tell you much other than what the volts are under a load or without a load -- which isn't the same as remaining reserve).

If thinking of a generator consider one with an auto choke and start (2 or 3 wire) so you can install an auto start switch if you plan to go fully off grid.  This way you won't have to run out and start the generator in the dark or during bad weather etc and then remember to turn it off.  My system is set to come on around 23.5vdc and run for 3 hours (which is usually all it needs) unless I know I'm going to be drawing a lot of power over the evening, then I might set the switch to 24vdc and 5 hours.

Consider a propane generator.  Mine seems to just sip the propane when running and isn't much of a factor for me.  My heaters use more propane!

Panels should be at the right angle to give you the most solar production, plan to change the angle quarterly at least.  A tracker would be better but for the cost you could just add another panel.

Don't plan to add panels later -- chances are, like me, you won't be able to find them!  Manufacturers just keep increasing the capacity and now I can't find the panel I need to add so I'll be getting an entirely new bank in the future.

On batteries you can go with GCB's (Golf Cart Batteries) which I think are find for the vacationer.  In fact, that's what I'm using now and I have 3 banks of 4 of them to give me 660AH @24vdc.

If you plan to live on solar my suggestion is to make your calculations based on winter sun.  Chances are you are going to use more light and entertainment in the winter and a system designed to provide all the power you need in July will be sadly over taxed in December.

Buy good stuff!  Don't go cheap on Charge controllers.  They are possibly the most important part of your system because they maintain the batteries.

Go with a bigger inverter than you think you need and seriously consider 24 or 48v systems.  I'm running 24v but if I had the funds I'd upgrade to 48vdc.

Propane stove with ovens use a LOT of power when the oven is on -- consider that.

Keeping your batteries warm in the winter will give you more capacity -- having them insulated and above freezing (I think 70F is optimum for capacity).

Plan on ventilating the batteries, they need it (or can go boom).

and above all, realize that you are your own power company so if something goes wrong you need to be able to deal with it so doing the install yourself is probably best -- then at least you will know what you built and can repair it.

Oh, and living off solar means one bill:  the initial one.  So while expensive to start it should pay off.  For me it would have cost about $20,000 to bring in power vs. $4000-$7000 to build and maintain my own system and I would have had a monthly bill with that $20k price tag so I'm pretty happy

[Gary O]

Here, but in the middle of gluing a bunch of stuff.... 

For now start here...   http://countryplans.com/smf/index.php?topic=6059.0    longish thread.

Yeahhhhh, that's quite the bunny trail.
Just looking for initial (pertinent) info first.
But, thanx

[Gary O]

I live pretty much full time now 'off the grid' (power) and can say that Don's pretty much spot on and I doubt I can add anything except experience.  Here are some thoughts:

Great info!

Just what I was lookin' for (a direction).

Darn near answered every first thoughts I have.
Thank you so much, OJ.

I'll be buggin' you guys (off and on) for awhile (like years).

cheers, guys

[MountainDon]

Propane stove with ovens use a LOT of power when the oven is on -- consider that.

Depends.  A range that has pilot lights for the range top burners also has a pilot light for the oven. They require no power at all to operate burners or ove.

A typical home range with electronic range top ignition also has a power hungry glow bar for the oven ignition. The oven will not operate without power and as OLJH stated they (the glow bar)  uses a lot of power. You'd probably have to run a generator. The stove top burners should work fine lighting with a match, but with no pilot that is a PITA.

There are special ranges with range top burner electronic ignition and ovens that do not have a glow bar.  IIRC, look at premier, or maybe it's Peerless.    Also I think Unique is another brand that may offer off grid design.  More $$ than a basic gas range from the big box stores.

We went basic simple pilot light range. In winter the pilot light heat helps keep us warm. In summer we shut the gas off between uses. I plumbed a shut off right handy at the rear top of the range. Lighting the pilots for use is easy with one of those 'fire stick' butane lighters.

[MountainDon]

As for components for the power system, as I stated before, figure out the amount of power required for a typical day. The watt-hours needed.

From there the storage capacity can be determined. There are a few environmental factors to consider; battery temperature, inverter losses, battery chemistry losses, how many days of autonomy (cloudy days).... 

Once battery capacity is well estimated then the size of the PV array can be figured. Then you get out the checkbook / credit card.

IMO, you can learn a tremendous amount without buying cheap hardware to play with and later discard. PV systems, batteries and the electronic equipment that goes along with the batteries do not lend themselves well to growing a bigger system from a smaller "starter" system.

Read, ask questions at any time.  Nobody just knows this stuff unless they work with power, etc all the time.

[Gary O]

 

As for components for the power system, as I stated before, figure out the amount of power required for a typical day. The watt-hours needed.

From there the storage capacity can be determined. There are a few environmental factors to consider; battery temperature, inverter losses, battery chemistry losses, how many days of autonomy (cloudy days).... 

Once battery capacity is well estimated then the size of the PV array can be figured. Then you get out the checkbook / credit card.

IMO, you can learn a tremendous amount without buying cheap hardware to play with and later discard. PV systems, batteries and the electronic equipment that goes along with the batteries do not lend themselves well to growing a bigger system from a smaller "starter" system

Yup
Determining that now

 
Read, ask questions at any time.  Nobody just knows this stuff unless they work with power, etc all the time.

Fact