John D's posts

Thanks Thomas,

I'd really like to go totally off-grid but my system is small.  I plan to add two or three panels a year and hope to go off-grid eventually.  If I want to keep my wife and kids, I'll have to stay grid-connected a little longer. My wife is supportive of my efforts, and is enthused about the new Power Save program.  She's already adjusting her laundry schedule, and is more aware of energy use.  These things are good practice for the conservation efforts we'll probably have to maintain once we do go off-grid.  The kids will both be in college in a couple of years, which will also help.  They don't yet share our enthusiasm for cutting our electricity usage. 

John

The new meter went in today.  It looks like "Gorilla Solar" is out of the question now.....

John

My electric utility company now has a real-time pricing program, and I've just enrolled.  A new meter will be installed, allowing my electricity use to be monitored by time-of-day.  Instead of a flat rate for electricity, my rate will vary, depending upon demand.  I'll minimize my electricity use during peak demand times, and use more when rates are low.  I'll do laundry, for example, at night when rates are lowest. 

I'll use my PV system as much as possible when rates are high, typically during the day.  That also happens to be when the PV system operates most efficiently because it is not storing and retrieving energy from batteries. 

I welcome comments from others who are already enrolled in similar plans.

John

I have one of those.  I've been using it for about a year, and I love it.

John
   

My point is that even a small amount of resistance heating, operating 24/7 requires quite a bit of energy, and therefore a substantial PV system and batteries.  On the other hand, running a small pump would require much less energy.  What I've suggested is much more work of course, but less costly for materials.  Would a small resistance heating element, mounted in a small-well insulated tank be a better solution?  I don't know. 

John

What you're suggesting is a solar PV system to be used for resistance heating.  That is usually an expensive way to go.

You might consider circulating water from underground (to warm it), maybe through a series of burried pvc pipes.  A small pump wouldn't use too much energy, and could be powered by a modest solar PV system.  If you decide to pursue that approach, first look into pumps.  Find the power requirements for the pump you choose.  Then it's a simple matter to design a PV system large enough to supply that much power.

John

Steve,

I think you'll find my blog post of 4/20/2007 helpful.  It includes a simplified wiring diagram of a small system.  When you purchase the charge controller it will come with instructions concerning connecting the solar panel(s), batteries, and load.  If you're going to use an inverter, connect it directly to the battery just as my diagram shows. The picture you saw on my October 31st post includes some extra wiring and stuff.  It need not be that complicated.  I would, however, suggest that you include a fuse between each solar panel and the charge controller, and a lightning protection device if there is a danger of lightning strikes where your panels will be installed.  Also, be sure to use the appropriate wire for the amount of current that will flow.

If you have any specific questions, I will try to help.  You'll also find great information on websites such as http://home.altenergystore.com/

http://solarjohn.blogspot.com

John
 

Steve,

I have several entries on my blog about starting small.  If you look through my archives I'm sure you'll find some useful information.

I suggest that you start out with a "real" solar panel, (not something from a gadget).  You'll be able to add panels as your budget will allow, and eventually have a system will provide a useful amount of energy. You'll also have a sealed unit that will be able to survive bad weather.  But whatever way you choose to start out, at least you'll be learning.

Keep us posted on your progress.

http://solarjohn.blogspot.com

John

Wally,

I was glad to read your comments because I've been considering that issue as well.  However, my situation is a little different.  I have a sweet-gum tree that provides some great shade for the house and backyard, but it also shades my solar panels late in the afternoon.  My case is different in that the tree produces these spikey balls each fall that are a real pain if you step on them.  I've already cut the tree back, almost eliminating the spikey-ball production, and I'm considering taking it down altogether.  I think I'll lessen my guilt by planting one or more new trees in a better location. 

John

Chester,

A good quality PWM charge controller will also help to remove/avoid sulfation, at least the Morningstar products claim to be able to do so.  And since the charge controller is in use all the time (as opposed to a desulfator that is used periodically), I believe they are the first line of defense against battery sulfation.

John

Hi Jeremiah;

I noticed from your profile that you're 18 years old.  If you're like my son of about the same age, cash is an issue.  If that's the case, you can build a good battery bank from gell-cell batteries that computer departments discard.  These are batteries used in UPS (uninterruptible power supplies) that have been replaced because of age, not because they're worn out.  You can connect several of these in parallel, if necessary, to get the desired amount of storage capacity.  Check with the IT department of any mid-sized to big business in your area.

John

You have 80-watts of PV and expect 5 hours of sunlight each day.  80 X 5 = 400wh X 0.65 (for system losses) = 260wh.  At the load you've specified, you barely have enough power for one day.  If you doubled PV and batteries, you'll have the capacity to compensate for one full day of clouds.

Having said that, I would also add that I wouldn't want to cut it that close on batteries.  Chronic undercharging, or leaving batteries discharged for more than a day or two, will shorten their life. 

If you want to become an off-grid "expert", study batteries.  The rest is easy.   

John

No problem Vincent;

You choose an inverter that can handle all of the loads you intend to connect at the same time.  If the most you'll run is a 15-watt light, and a 75-watt tv, and a 25-watt fan, you'll need an inverter that can supply 115-watts (as an example).  Keep in mind that some motors and other devices have high starting current, so your inverter needs to be able to handle that as well.  But a 250-watt inverter would be a good choice for the example I've stated here, since it exceeds your 115-watt needs.

If you'll play around with the power formula I provided in a previous message, you'll notice something interesting:

Power (in watts) = Volts X Amps

120 Watts = 12 volts X 10 amps
120 Watts = 120 volts X 1 amp

It follows then that to power a 120-watt, 120 volt, light bulb you'll have about 1 amp (at 120-volts) at the output of the inverter, but 10-amps (at 12-volts) going into the inverter.

This is just an example, and doesn't take into consideration inverter inefficiency. 

I hope this helps to clear things up.

John

Vincent,

It looks like your math is correct, except that you didn’t take into consideration system inefficiencies.  To simplify my answer to your questions, consider an off-grid system with batteries to be only about 65% efficient overall.

Concerning the inverter input current that flows to provide 75-watts out, use the formula:  Power = Volts times Amps, and then consider inverter inefficiency, or:
10 (amps) times 12 (volts) times 0.65 = 78-watts.

To compensate for cloudy days, you’ll need more panels and batteries (obviously), and you can use that 65% efficiency factor to do your math.

I hope this helps.

John

More information about the panels can be found here:

http://www.solar-tec.com/SiemensSolarModules.htm

I agree with James, $2.50 per watt is too good to pass up.

John

As the sun warms my roof and panels, the snow does indeed fall off.  In the winter I adjust the tilt (angle) of my panels to about 51 degrees which also helps.  Some pictures can be found on my blog:

 http://solarjohn.blogspot.com

John

Or get your wife to climb up on the roof and wipe the snow from the panels.

(I'm kidding, I'm kidding!)

John
 

Nathan,

The primary function of a charge controller is to efficiently charge batteries, and prevent overcharging. 

Your next question might be; "which charge controller should I buy?"  If your pv array and battery bank is small, you might consider one of the Morningstar products.  Prices start at around $50.00.  For a larger system, the Outback MX-60 would be a good choice, but it runs around $600.00.  When considering a charge controller, it would be a good idea to get one with a built-in meter, since the ability to monitor your batteries is very important. 

John
http://solarjohn.blogspot.com

We need more information roberto.  How much energy is needed for how long?  For example:  If you said that you wanted to run a 75 watt light bulb for 4 hours every day, we would have a good starting point.

John

I've heard that the motors used on large computer tape drives make excellent windmill generators.  Check with a computer/electronics surplus store.

John

I like the idea of adding a meter to the charge controller, or getting a battery monitor.  I use a high-quality digital voltmeter to keep close track of my battery condition. 

The point is; it's important to have some way of monitoring your batteries, since they can easily be damaged if you don't. 

John

Here's what I would suggest.  But these are only rough calculations:

1 - 75 Watt (or bigger) solar panel
1 - 100ah Marine Deep Cycle battery
1 - 125 Watt (continuous power) pure sinewave inverter.
1 - 10a (or bigger) charge controller

You need 75 Watts times 3 hours, or 225 Watt/Hours.

If you get 4 hours of sunlight each day, you'll get 4 times 75 = 300 Watt/Hours.

Since you don't want to discharge your battery more than 50%, you have 50ah of usable stored energy.  The inverter will draw just under 10a (DC) to power the 75 watt load.  Therefore:  50 divided by 10 equals 5 hours of TV viewing, but allowing for system inefficiencies, expect 4 hours at the most.

I have more system design information on my blog:  http://solarjohn.blogspot.com

Hope this helps, John

You might consider a rechargable battery manufacturer such as Altairnano (ALTI), or Electro Energy (EEEI).  One of these might do well if/when PHEV's become popular.

John

Don't know if this will help or not, but Exeltech makes stackable inverters.  It's their MX line.

http://www.exeltech.com/

John D.

James,

Please consider moving to Southern Illinois.  I have a 3-bedroom house for rent, and I'm into renewable energy.

John

Depending upon what you have, you may have to replace your charge controller and inverter when you go from 12 volts to 24 volts.  That could be an expensive proposition.

If the equipment you currently have is not expesive, and if you intend to expand later, you might be better off going with 24 volts now, rather than replacing expensive equipment later.  (I hope you understand what I'm trying to say).

John

I've been reading about recent advances in rechargable batteries lately, and believe that practical plug-in electric vehicles (PHEV's) are coming soon as a result. I look forward to someday being able to recharge my PHEV with my solar PV system, and therefore be driving on free power from the sun.

One company claims to soon be producing a car with a 350 mile range and a 10 minute recharge time.  http://blog.wired.com/cars/2007/06/is_zap_a_flimfl.html
I doubt that they'll be able to accomplish that, but it will be interesting to watch nevertheless.  I'd settle for a 100 mile range and an overnight charge cycle if it eliminates my need to buy gasoline.

As I understand it, PHEV's will have a gas-powered generator that is only used to recharge the batteries, not to drive the wheels. This extends the range of the car.

It all sounds great to me.  And even if I can't provide all of the power needed to recharge via my PV system, it will still be cheaper to recharge using grid-supplied power than it is to buy gasoline for an ordinary ICE car.

Is anyone else as excited about this as I am?

John

As a safety precaution I would slip a piece of heat shrinkable tubing over the bars between batteries.  If you don't, sooner or later you'll drop a tool or something conductive across the pos and neg bars.  It is amazing how much current flows when that happens.

John

First:  Don't allow the batteries to become discharged. 
Second:  Get a charge controller.  A 20 amp PWM type will do nicely.
Next:  Wire is expensive, so mount the panels as close to the equipment as possible.
Next:  Shop around for an inverter unless you want to run everything on DC.  Go for a true sine wave inverter if your budget will allow it.
And Finally:  Check out my blog archives.  I think you might find it helpful.

http://solarjohn.blogspot.com

Good luck, and let us know how it works out.

John

I'm excited about lithium ion batteries.  Once the price comes down, plug-in electric cars will become a reality.  Hopefully, the US government will get behind them this time, instead of what they've done in the past.  (See the movie "Who Killed the Electric Car"). 

http://solarjohn.blogspot.com

John