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#1 Rif

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Posted 28 April 2012 - 07:23 PM

I have a good sized (800 watt) solar setup on my rig. It works very well and meets most of our needs when we are living off grid, something we do about three months out of the year. The rest of the time we are plugged in somewhere. When plugged in, I never turn on the charger section of the inverter because our 12V needs are minimal and the solar panels provide way more than we need to keep the batteries charged. In fact, I have to change the settings in my controller so I don't cook my batteries. And that leads me to ask, wouldn't it be great if I could use all that extra electricity I am generating?

I realize I could use just the inverter for a while each day, but that requires manual intervention an monitoring. I've done it on occasion, but it is just too much hassle. I don't want to draw down my batteries too much because they only have so many deep cycles in them, and I'd like them to last as long as possible. While the solar panels are capable of providing all my electrical needs a good portion of the time, they can't when the sun angle is not right, clouds get in the way or when my power needs exceed their capabilities. I certainly don't want to arrive at the end of the day with batteries that are not fully charged.

I got to thinking about the grid tie systems that are becoming very popular. Wouldn't it be great if that capability could be built into an RV solar setup. I guess it would require a solar controller and inverter/charger that talked to each other. They would have to monitor the batteries and make sure they are kept charged, then feed any additional available power from the panels to the inverter. The inverter would have to have the capability of feeding the load from a combination of solar generated power and the 120V power from the grid, just as the inverters used in grid tie applications do.

A system like this would provide from 1/4 to nearly all of my power needs, depending on weather. There would be some small savings when I am paying for metered electricity, but more than anything it would put to use electrical power that is currently being wasted. I don't claim to be a big environmentalist, but I do know that meeting the power needs of the country in the coming years is going to require some changes.

I'm curious if anything has done any investigation into this. Are there any manufacturers with equipment that could easily be adapted to do what I am describing? Has anyone thought any other way of utilizing this wasted power?
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#2 Jim Seward

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Posted 28 April 2012 - 09:02 PM

I have a good sized (800 watt) solar setup on my rig. It works very well and meets most of our needs when we are living off grid, something we do about three months out of the year. The rest of the time we are plugged in somewhere. When plugged in, I never turn on the charger section of the inverter because our 12V needs are minimal and the solar panels provide way more than we need to keep the batteries charged. In fact, I have to change the settings in my controller so I don't cook my batteries. And that leads me to ask, wouldn't it be great if I could use all that extra electricity I am generating?

I realize I could use just the inverter for a while each day, but that requires manual intervention an monitoring. I've done it on occasion, but it is just too much hassle. I don't want to draw down my batteries too much because they only have so many deep cycles in them, and I'd like them to last as long as possible. While the solar panels are capable of providing all my electrical needs a good portion of the time, they can't when the sun angle is not right, clouds get in the way or when my power needs exceed their capabilities. I certainly don't want to arrive at the end of the day with batteries that are not fully charged.

I got to thinking about the grid tie systems that are becoming very popular. Wouldn't it be great if that capability could be built into an RV solar setup. I guess it would require a solar controller and inverter/charger that talked to each other. They would have to monitor the batteries and make sure they are kept charged, then feed any additional available power from the panels to the inverter. The inverter would have to have the capability of feeding the load from a combination of solar generated power and the 120V power from the grid, just as the inverters used in grid tie applications do.

A system like this would provide from 1/4 to nearly all of my power needs, depending on weather. There would be some small savings when I am paying for metered electricity, but more than anything it would put to use electrical power that is currently being wasted. I don't claim to be a big environmentalist, but I do know that meeting the power needs of the country in the coming years is going to require some changes.

I'm curious if anything has done any investigation into this. Are there any manufacturers with equipment that could easily be adapted to do what I am describing? Has anyone thought any other way of utilizing this wasted power?


You could always add one of these to your system as a back-up power source:

http://www.amazon.com/Wind-Power-Generator-Water-Proof/dp/B006GU5A3K
Jim & Sherry Seward
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#3 Stanley P. Miller

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Posted 28 April 2012 - 11:24 PM

I looked at a diversion load for my old Trace so I could use it as a space heater once the batteries were charged but it looked like I'd need two loads, one inside for heating and one outside when I was warm enough. The price for one load was high enough, two loads and the switching circuitry put it out of the useful price range. I spent a good bit of time trying to find something useful to do with the extra power and never came up with anything that made sense.

Grid tie stuff is interesting but if you do a bunch of digging there are a lot of issues with actually using it that make it less attractive.

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Sell a customer a Linux computer and you'll eat for a day.
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#4 Roadwarrior

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Posted 28 April 2012 - 11:46 PM

You could always add one of these to your system as a back-up power source:

http://www.amazon.com/Wind-Power-Generator-Water-Proof/dp/B006GU5A3K

yes I have one since 1999.
http://roadwarrior.free-man.com/WindGen.shtml
you don't get good charging till there is 15mph winds.
you don't get full charging till 35mph winds.
even as windy as our march is, the average charge per day, is less than 10 watts.

Edited by Roadwarrior, 28 April 2012 - 11:55 PM.

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#5 Roadwarrior

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Posted 29 April 2012 - 12:10 AM

I had such a system till I had a fire, not related.
I am now working on a new version
http://www.rvnetwork...showtopic=97859
The minimum cost if you built it your self from a kit, is about $1K. If you bought it put together add another $1700.
In practicality, you would do best to get a pair of Welding cables with clamps and just jumper to the RV next to you.
Let me know if your interested.
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#6 Dan Zemke

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Posted 29 April 2012 - 06:41 AM

I've not come across anything like you describe, and unfortunately, am not optimistic that I will in my lifetime. To me, the biggest impediment is that our power grid isn't set up to accept distributed mobile power generation. I'm sure you know all this, but just to make it explicit: Even if your site is metered, the meter is only designed to measure power provided to the site. There's no provision for measuring power provided from the site. Folks that sell power back need a meter that tracks power both ways and a billing infrastructure that supports this. If you plug in for a few days and provide excess power, how would you get paid? Then there's the economic reality of how much power you are actually generating. If you could provide 5 KWh a day of excess power, what is that worth - a total of 50 cents at most?

Maybe you could use to power a small still. Your solar-boozer? At least it might be good for some laughs.:D High power 12v cartridge heaters are hard to find, and pricey. eBay didn't have any surplus currently listed but I found these 24v units that would provide 75 watts of heat at 12v and might work.

http://www.ebay.com/...=item3373c293d8

Dan

#7 Rif

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Posted 29 April 2012 - 09:01 AM

Jim and Roadwarrior, I'm not looking to add more renewable power generation. I'm looking to use power I am already capable of generating but which I'm not able to use.

Stan, In the past I've considered things like you describe and have come to the same conclusions. However, a lot of things have changed in the past few years. I'm seeing the kind of thing I describe being used already. My brother recently installed 8,000 watts of solar on his home. His system does include a grid tie that permits him to sell electricity back to the power company, but that option was not even turned on until the power company inspected and approved the installation. During that first month his system was generating most of his power needs, pulling all the power it could from his solar panels, and pulling power from the grid when there was not enough solar available. Dan, it does not have to feed back to the grid. It can be a one way only system.

It looks to me like some of the systems on Back Woods Solar's site might do what I am describing. Some of them even include a battery backup component that comes very close to what I have described. Of course, they are not designed for RV use but they might work. I was just wondering if anyone was actually doing this in an RV application yet.
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#8 Dan Zemke

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Posted 29 April 2012 - 10:29 AM

Yeah, after I posted that, I figured out you probably weren't thinking of trying to sell your excess power back like some grid-tie folks do. But then, of course, the economic value deteriorates of your excess power deteriorates. If your solar system happens to be producing 500 watts of useful power, and your actual use is 200 watts at the time , then 300 watts of that is still wasted. So from a dollars-saved perspective, the most likely result is that the potential savings is under $0.25 a day.

I'm not a strong environmentalist either, but I still feel conservation is a worthy path, within reason. For some, with larger solar systems like you, I suspect an easier and less expensive way to reduce annual grid power usage would be to replace an air conditioner with one you can comfortably run off your inverter/battery bank. Instead of saving little bits over longer periods of time, you could save bigger bits less frequently (and with potentially less management hassle). Yes, you'd have to turn on your inverter, but only on the days you anticipated running the smaller air conditioner.

http://www.rvpartwho...Brisk-RV/Detail

Dan

Edited by Dan Zemke, 29 April 2012 - 10:51 AM.


#9 Roadwarrior

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Posted 29 April 2012 - 10:54 AM

So what to do with solar when there is no demand.
you have not way to give this to someone. so the logic of grid tie does not work.
Unless you demand is great enough when there is not solar to deplete you batteries enough for the solar to run full time, you will always having extra solar. The easiest to is to have a programmable Solar charger the automatically shunts the extra to a dump.

now if you have a large enough bank, you will not discharge the banks to the level to consider a deep cycle (50%soc). more like 1-5%soc.
So the simplest answer is to compute the most you solar's can generate on a longest day of the year, then install batteries to absorb that.
that is about 12 hours at 800Watts. So you generate 66 amps per hour or 800 AH in a 12 hour period.
based on 225AH per bank you need 4 banks of batteries.
however if you want decent usage at 5%, you will need a lot more banks.

At 4 banks
at 5% usage that is 40 amps for 12 hours of night or 3 amps per hour for 12 hours.

during the shortest days you will only charge about 8hrs. or little over 500AH
so you 5% is 25 amps or about 1.5 amps per hour for 16 hour.

if you want to have say 20 amps per hours on the longest night you will need about 80 banks of batteries. which is a little overboard.

one other solution is to switch to Lithium batteries where they have an 80% Discharge for a deep cycle, and would last longer than the Lead acid.
The sticker there is the upfront price.

hope I did not confuse you.
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#10 Hamshog

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Posted 29 April 2012 - 11:04 AM

Hey Rif,

Are you being charged for electricity while you're hooked up??? I'm guessing you are, or you wouldn't be worried about your excess solar going to waste.

Why not move the A/C circuits to a separate panel for utility power and use your solar sysytem for the rest of the coach as you do while boondocking??? Surely 800watts of solar will keep up in the summer, wherever you are for everything but the A/C's, with the 6 to 800amp hours of batteries you must have???

Or you could get some nice custom covers for the panels while your hooked up.... :)

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#11 Rif

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Posted 29 April 2012 - 12:25 PM

Hey Rif,

Are you being charged for electricity while you're hooked up??? I'm guessing you are, or you wouldn't be worried about your excess solar going to waste.

Why not move the A/C circuits to a separate panel for utility power and use your solar sysytem for the rest of the coach as you do while boondocking??? Surely 800watts of solar will keep up in the summer, wherever you are for everything but the A/C's, with the 6 to 800amp hours of batteries you must have???

Or you could get some nice custom covers for the panels while your hooked up.... :)


Yes, I am hooked to utility power right now, although I am not paying for it. But whether or not I am paying for it is not the point. It's the principle. The point is that I am capable of making a large percentage of the power I need to operate my RV, but I am not able to conveniently and effectively use it. It just seems like a waste when you consider the nationwide need to build more power plants. Experts recognize that the answer to the growing energy needs of the country is going to come from many sources, and here I am pulling power from the grid while at the same time throwing away power that is being generated right on my rooftop.

My setup is almost exactly as you describe. I can easily turn off the breaker that feeds the inverter sub panel, and let the solar system provide all the power I need during the day for those circuits, but there are two problems with that approach. First, it requires manual intervention. Second, the circuits on the sub panel cannot use all the power I can generate most of the time. That means power is still going to waste while at the same time I am pulling power from the grid to run the appliances that are not on the sub panel (like A/C, washer, dryer and dishwasher). The point is that I cannot always make enough power to meet all my needs, but I can often make more than I can use on the circuits on my sub panel.

Right now I am in Apache Junction, AZ. The breaker to my sub panel is off and solar is providing all I need to power the circuits there. I'm only using about 25 amps DC at the moment to power all our computer equipment, DVR's, residential refrigerator and other minor loads on the inverter panel. My solar panels are capable of producing 50 to 60 amps in the current conditions, so somewhere around 25 to 35 amps are being wasted. At the same time, my A/C is running and I am pulling power for it from the grid. The 25 to 35 excess amps of 12V DC is not enough to meet that need, but it would certainly offset some of it if the system I have described were available.

Naturally, for such a system to be practical would require a whole house inverter. The difference between a residential design and an RV design is that the RV often does not have grid power available. When operating on solar/battery alone, there needs to be a way to control which circuits are powered. I wonder if the Grid Tie Interactive with battery systems would do everything I'm suggesting? Perhaps they already have a means of supplying selective circuits when operating on battery alone.

As for adding additional battery banks, that's just not practical. I'm trying to avoid cycling my batteries, or even using them at all when they are fully charged and I am on grid power. Besides, the space requirements and weight issues of large battery banks in an RV environment are limiting factors.

I realize that this is mostly a mental exercise, but there's no reason that such a system couldn't be built. It appears they are already doing it in the residential world. All it would take is enough demand for companies like Xantrex, Outback and Magnum to incorporate the technology into their existing RV systems.

Edited by Rif, 29 April 2012 - 12:29 PM.

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#12 Roadwarrior

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Posted 29 April 2012 - 01:00 PM

the system I have is multiple power source in, like generator, shore power, Solar, Wind feed to a DC power buss that feeds a 10KW inverter.
all AC, in the RV, is powered by the 10KW inverter. so your breakers run off the inverter.
there is no manual switches, except a master shorepower circuit breaker.
The shore power is shut off when the solar is meeting the demand, the Generator kicks in if no shore power or Solar, and the demand requires it.
Batteries are buffers or used as source when none of the other power sources are available..
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#13 Rif

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Posted 29 April 2012 - 01:27 PM

the system I have is multiple power source in, like generator, shore power, Solar, Wind feed to a DC power buss that feeds a 10KW inverter.
all AC, in the RV, is powered by the 10KW inverter. so your breakers run off the inverter.
there is no manual switches, except a master shorepower circuit breaker.
The shore power is shut off when the solar is meeting the demand, the Generator kicks in if no shore power or Solar, and the demand requires it.
Batteries are buffers or used as source when none of the other power sources are available..

While it sounds like you are doing what I am suggesting, I don't have the complete picture of your setup. I don't understand how the generator and shore power feed a DC power buss without going through some conversion. Are you are taking AC and converting it to DC to feed a power buss that feeds an inverter to make AC again. And how does the system provide prioritized load sharing between the renewable sources and shore power/generator?
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#14 Roadwarrior

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Posted 29 April 2012 - 02:12 PM

While it sounds like you are doing what I am suggesting, I don't have the complete picture of your setup. I don't understand how the generator and shore power feed a DC power buss without going through some conversion. Are you are taking AC and converting it to DC to feed a power buss that feeds an inverter to make AC again. And how does the system provide prioritized load sharing between the renewable sources and shore power/generator?

I can't take credit for the Idea. I got if from the Cummins-onan Hybrid system.
Mine is micro controlled.
Yes each AC sources runs thought a solid state switch that then feeds a common converter. The solid state switches are controlled by the micro.
The micro monitors the demand from the inverter. when there is a demand it turns on which ever source is priority.
the priority of the sources is programmable through a user interface.
though I don't have a big Solar I have enough to test my system. I am in an area where solar is not feasible.

so in your case,
you would make Solar #1, Shore #2 and Generator #3.
you set up the power ability of each.
when the demand exceeds the sources ability another source, in priority, are added.
Say you unplug shore or it is not available due to blackout. Then the Generator would kick in.
as far as those appliances hook to the inverter they would not see an change since the batteries take up the slack during the change over. Then they are charged once the next source is brought on line.
if no solar or shore power then it would bring the generator on, all automatically.

I have gone one more step with a control unit on the generator as a variable source, so it will run only fast enough to provide the power necessary, instead of a constant speed. this increases the Generators economy.

As a side note I have a 5KW fuel cell that comes on before the Generator.
so in my case, #1 Solar, #2 shore power #3 Fuel cell, #4 generator.

My average use is 100watts, except when using the microwave. Air Compressor, and/or A/C.
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#15 Rif

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Posted 29 April 2012 - 02:36 PM

I'm still confused about one thing. Can you have multiple sources feeding the inverter at the same time? In other words, can the solar feed the buss with all it is capable of, and have shore power supply any additional power needed to meet the demand. Or, is it strictly one source at a time?
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#16 Roadwarrior

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Posted 29 April 2012 - 02:59 PM

multiple sources at once.
In your case the Solar charger would be replaces by the combiner box, for want of a better name.
the Bus to the inverter is dC only.
each source is converted to DC, if it necessary, then passed through the converter that is connected to the Inverter/battery DC bus.
Each source is monitored as to how much Current they are delivering. Then the Current demand of the Inverter is monitored, as well as the voltage of the battery bank.

Edited by Roadwarrior, 29 April 2012 - 03:08 PM.

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#17 DonF

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Posted 30 April 2012 - 01:28 PM

Hmmm,,, this is most interesting.

It sounds like you're "converting" AC to DC (coming from shore source), thenback to DC for the DC bus, then "inverting" back to AC to supply the AC circuits... doesn't give up alot of "power"?!?

I have enough solar to run DC lights *and* invert to AC for TV/radio kinds of things --- BUT, I need the AC, so would like to let the solar run what it can, let the shore (or genny) run the AC or Microwave oven,,, and minimize the "recharge" cycles on the battery bank. (I think this is similar to Rif's OP-query.)

My current setup, while on shore power, I let the Link-1000 bring the batteries into "float", maintaining a full charge (its set-point is around 13.35 while in float); my AM-Solar MPPT solar controller has no settings, it uses its built-in set-point (14.4) to bring batteries up to 85%, but that's it. So, I turn it off, despite having lots of sunshine (here in Mesa),,, just to prevent over-charging. The Link-1000 has a setting for "AGM" battery type, so I use that; it also has a setting to "acknowledge" alternate (ie, solar) source for input charging. I am (just about) clue-less beyond this point; I do watch the Link to be sure it goes into float (ie, to ensure it doesn't get hung-up on the Accept voltage level, 14.x),,, my attempt to ensure not over-charging the batteries. So, observing the charger, I note that despite using (still) lots of DC lamp draw, the float charging seems to hold the batteries' charge level without dropping into bulk or accept). I guess I am a-ok, but I am most intrigued with this thread, and Rif's goal; am still wondering if road-warrior's solution is practical for us... trying to wrap my brain around his config & equipment. Thx!

-Don
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#18 Roadwarrior

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Posted 30 April 2012 - 02:11 PM

Hmmm,,, this is most interesting.

It sounds like you're "converting" AC to DC (coming from shore source), thenback to DC for the DC bus, then "inverting" back to AC to supply the AC circuits... doesn't give up alot of "power"?!?

From AC to DC but not regulated yet, then through a Converter that keeps the battteries charged(DCBus), but supplies enough for the Inverter able to run.
it is about 95% efficent.
The system is built to be like tinker toys.
So if you want to pass the shore AC through to the output of the Inverter and use it direct you can use that also.

I have enough solar to run DC lights *and* invert to AC for TV/radio kinds of things --- BUT, I need the AC, so would like to let the solar run what it can, let the shore (or genny) run the AC or Microwave oven,,, and minimize the "recharge" cycles on the battery bank. (I think this is similar to Rif's OP-query.)

The whole Idea is to keep the batteries from being discharged when possible.
the system manages all the sources automatically.

My current setup, while on shore power, I let the Link-1000 bring the batteries into "float", maintaining a full charge (its set-point is around 13.35 while in float); my AM-Solar MPPT solar controller has no settings, it uses its built-in set-point (14.4) to bring batteries up to 85%, but that's it. So, I turn it off, despite having lots of sunshine (here in Mesa),,, just to prevent over-charging. The Link-1000 has a setting for "AGM" battery type, so I use that; it also has a setting to "acknowledge" alternate (ie, solar) source for input charging. I am (just about) clue-less beyond this point; I do watch the Link to be sure it goes into float (ie, to ensure it doesn't get hung-up on the Accept voltage level, 14.x),,, my attempt to ensure not over-charging the batteries. So, observing the charger, I note that despite using (still) lots of DC lamp draw, the float charging seems to hold the batteries' charge level without dropping into bulk or accept).

as long as your happy doing this there is no reason to change anything.
one of Rifs concerns was having to monitor and change settings manually.

I guess I am a-ok, but I am most intrigued with this thread, and Rif's goal; am still wondering if road-warrior's solution is practical for us... trying to wrap my brain around his config & equipment. Thx!

My system is futuristic by most people standards.
Everything on the Coach is monitored and control from a central point, my laptop, and now my Droid Tablet. the Tablet sits on the Dash. There is a Wifi unit that they both connect to, so you can move around with the tablet if you want.
In 2005 the RV industry caught up with me by Creating the RV canbus specification. These are units that hook to your tanks, Slides, refrigerator, furnace, levelers, tire pressure, Inverter, Generator, and batteries to provide info about what each is doing and being able to change what they do.
Many of the high end coach builders incorporated this into the new builds.
My goal is to have after market units that let someone have this same functionality for coachs that did not have this built in.
So it is easy to add the functionality of an integrated automatic Power source control.

-Don

The bottom line is how much is all the new fangle stuff is worth to someone.
for someone that wants to do it manually, too much.
for someone that want a log of everything and see pie charts of how everything is doing, it may still be alot, but they are willing to pay for it.
the rest comes under
Men and their toys.

Edited by Roadwarrior, 30 April 2012 - 02:23 PM.

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#19 bryanl

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Posted 01 May 2012 - 02:07 PM

wouldn't it be great if I could use all that extra electricity I am generating?


This has been one of the biggest confusions in the 'alternative energy' discussions over the last 50 years or so. It isn't the energy production that is the issue, it is the energy storage. Grid tie systems just offload the problem to someone else (and it does give the power companies headaches).

There have been many inventions towards solving this energy storage issue. Hydroelectric has long roots and works well but needs a large infrastructure. Batteries do OK but their storage capacity isn't all that great. Inertia based devices (flywheels) come and go. Heat storage sometimes works in some situations but the efficiency is usually low. Chemical means, such as water separation, can work but require rather expensive fuel cells (Road Warrior has this covered, though!). Time is also a factor as it'd be nice to average out the energy in and the energy out over a period of a year or more and that sort of thing is not easy to accomplish, either.

Even though an 800 watt system doesn't provide that big an energy harvest (maybe a couple kwh per day), storing that much energy with its accompanying machinery to put it in and take it out is not an easy task, especially if portability is desired.

If you really want to worry about wasted energy, consider the total solar input to the state of your choice from the sun and then add a bit for wind ... but then, we do get something out of that when we get out somewhere with the RV to sit on the beach and enjoy what nature offers.
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Bryan

#20 Rif

Rif

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Posted 01 May 2012 - 03:12 PM

This has been one of the biggest confusions in the 'alternative energy' discussions over the last 50 years or so. It isn't the energy production that is the issue, it is the energy storage. Grid tie systems just offload the problem to someone else (and it does give the power companies headaches).


As I stated in my original post, I am not seeking a way to store any of the energy potential, nor am I seeking a way to feed any of it back to the grid. I would merely like to find an easy and convenient way to use the solar potential that is currently going to waste when I am plugged into the grid, and thereby reduce my draw from the grid. I have no desire to feed any of it back into the grid. I don't understand how that would create any problems for anyone else.

Even though an 800 watt system doesn't provide that big an energy harvest (maybe a couple kwh per day), storing that much energy with its accompanying machinery to put it in and take it out is not an easy task, especially if portability is desired.


As I said, I have no desire to store any of it. My batteries are already fully charged and my 12V needs are minimal. I don't know where your 2 kwh figure comes from, bu my solar system consistently harvests in excess of 5 kwh per day here in the Arizona sun. My average daily usage when I am plugged into the grid and using my air conditioner, is approximately 15 to 20 kwh. When not using the air conditioners or heat pumps, my daily usage is less than 10 kwh. Finding a way to reduce my energy consumption by a a fourth to a half does not seem trivial to me, especially since the solar panels are already in place.
2000 Volvo 770, 500HP/1650FP Cummins N14 and 10 Speed Autoshift 3.58 Rear 202" WB, 2002 Teton Aspen Royal 43 Foot, Burgman 650 Scooter