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RE without batteries or the grid?

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  • Wed, May 13, 2009 - 08:28pm

    #1

    davidm

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    RE without batteries or the grid?

 Does anyone know if there is a way to use a RE home system off grid and without batteries?

One thought I had was to simply use the power when you have it and not when you don’t. But no systems seem to be designed that way. 

Another thought was about alternative ways of storing the energy produced. For example, a PV system could pump water uphill while the sun is out, perhaps to a tank. When power is needed later, the tank would release water that would flow through a hydro generator.

I’ve got a stack of pv books, but they don’t cover this. The assume that we will be either be tied to a working grid and/or have a supply of batteries.

Thanks for ANY help or links!

David

  • Thu, May 14, 2009 - 02:50am

    #2
    Peak Prosperity Admin

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    Re: RE without batteries or the grid?

Not sure what you mean with the "RE home system" statement, David. But I am glad to explain some science to those so interested.

One would be much better off to just store the PV energy in batteries and use it directly. Since 100% efficiency is never achieved in any system and introducing two stystems, pumping the water up, then running it back down hill through a hydro generator is really two systems, one would halve the efficiency of that system.

If you want to use the power when you have it and also when you don’t, you have to store it.

Storing that energy within the same system that creates it is much more efficient.

  • Thu, May 14, 2009 - 06:58am

    #3
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    Re: RE without batteries or the grid?

In a word…..  NO!  It can’t be done.  Why?  Renewable Energy, whether wind or solar, varies CONSTANTLY.  So when the sun first rises, no energy will be generated until enough light can produce the 12V the panel is designed to produce, but the current (Amps) will be negligible.  As the sun gets stronger, the A will rise, but eventually so will the V, up to as much as 14V or more.  Wind turbines are even more erratic, they won’t produce anything at all until the wind reaches a design minimum speed.  Then, the power output increases with the cube of the wind speed!  Any gusts, and the V and A coming out the machine will be all over the place.

When the A are insignificant, you won’t be able to run anything, but once they ARE significant, you might even fry what it is you want to run.  Basically you need a BUFFER between the vagaries of the PV/turbine output and the appliance(s) you wish to run.  Other wise they may not run at all, or you might fry them!

Battery storage is REGULATED by "white man’s magic" gizmos, such that if you want 100W, no more no less, then the grid, or your batteries will provide 100W (Watts, BTW are V x A), and UNREGULATED solar panels/wind turbines cannot do this.

So I’ afraid, you have no choice in the matter.  Some things, like lights, will run unregulated.  They’ll just go dim when there’s not enough juice, and go really bright when there’s too much, but they will blow if you overdo it.  CFLs will NOT do this.  Some motors will either speed up or down, but they won’t like it and you will shorten their life.

  • Thu, May 14, 2009 - 11:23am

    #4
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    Re: RE without batteries or the grid?

Thanks DtM. I have never understood electricity and appreciate the expanded answer. I have a couple follow ups, if you don’t mind…

In a grid tied RE system, isn’t there some way that current is controlled, so that the right amount of juice gets to the house panel and the rest goes to the grid? Couldn’t the same method be used, except that the excess would go to somewhere else other than the grid? Perhaps even to a motor (pump) designed to run with variable current, or even to someone else’s house. How about some kind of regulator that would stop (divert) the flow if there is too much, or not enough?

Thanks also Jerry for your reply. The issue I’m trying to solve is how to use renewable energy in the home at a time when the grid is down and batteries are not available (these 2 things would likely coincide). And in any event, an energy system that needs a bank of new batteries every 5 to 10 years is not very useful over the long term. 

David

  • Thu, May 14, 2009 - 12:47pm

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    Re: RE without batteries or the grid?

That’s what the grid connect inverter does.  It turns the mish mash of variable DC (Direct Current, ie one that ONLY flows in one direction) into a steady flow of 110 or 240V AC (Alternating Current, power that changes direction 50 or 60 times a second – depending on which part of the planet you live on!)

Generally, in a grid tied system, ALL the renewable energy goes to the grid, measured through a meter.  Then, if you need some at the time it’s being generated, some of this current will do a U turn back into your house via another meter that measures your consumption.  At least that’s how our system works.  Some utilities will make you fit just one meter, so that when you are putting out more than you use the meter runs backwards.  Which is kinda cool actually!

If you need MORE than what you’re generating, like running a 2000W electric kettle with a 1200W solar array, ALL of the renewable energy does the U turn, PLUS the extra 800W supplied by the grid.  Once you turn the kettle off, all of the solar power goes back to the grid again…

If you are using less than what you generate, then indeed your neighbours will have access to your excess.

It IS possible to have BOTH grid tied and batteries, that’s what we do.  Of course it costs more, our batteries are worth $1500, and that was cheap through eBay.  The inverter we use is no longer available.  So it’s highly likely that if you want to use backup batteries, you’ll need TWO inverters, one to feed the grid, and one to feed the house from the batteries.  Then you need a special switch (ours is automatic/instantaneous so that the only way you know there’s grid failure is if you hear the switch go klunk or the lights on the inverter tells you you’re in stand alone mode).  Utilities will not allow you to feed into the grid during a blackout in case you kill the guy trying to fix the blackout!  Two inverters gets expensive….

Your comment re batteries is totally correct, I worry constantly that one day all this hi tech stuff will not be able to be replaced.  Welcome to the end of the world as we know it….!

Mike

  • Thu, May 14, 2009 - 01:53pm

    #6
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    Re: RE without batteries or the grid?

Thanks, Mike. That explanation (that all the power goes to the grid first) clears up some of it.

The batteries are certainly the weakness in RE. As we come down the backside of the peak, energy prices will shoot up, and there may likely be shortages. Demand for RE will shoot up, and batteries may become hard to get. It seems a shame that a system intended to be renewable depends on a non renewable element like batteries.

It makes me wonder how power is no managed on the commercial grid. What happens to extra power when it is not called for? I know it keeps getting distributed over a wide network, but there must be some extra somewhere. What I’m really driving at is the possibility of a local grid. There’s got to be some way to generate usable power without replying on expendable batteries or FF supplied commercial grids.

David

 

  • Thu, May 14, 2009 - 04:14pm

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    Re: RE without batteries or the grid?

 David,

 The telecom industry is testing a centrifuge for remote location backup power. The results so far are promising, as they have provided reliable backup for several years.  The plan is to make them available sometime in the near future.

 Permanent magnet and brushed D.C. motors are not harmed operating on variable voltage ( P.V. direct). They just slow down and speed up with the variation in voltage. I have several in operation for a decade now.

 Batteries are the weak link in an off grid system. The best options are nickel-iron deep cycle which have an indefinite life span, if taken care of. Some of your large lead-calcium and lead-antimony batteries have a design life of 25-30 years, again if taken care of. Electronic desulfation may extend that.

 I have a 3800 amp-hour bank of GNB lead-calcium batteries. With a 1.215 specific gravity, I only water them once per year and that is the only maintenance. Quality design and assembly is important. Check out the archives of Homepower magazine for an abundance of battery and related information.

 Having just spent the last six weeks TIG welding boiler tubes in the local coal fired power plant, I can tell you there is NOTHING sustainable about our current electricity grid. In order to maintain a grid of any size, you must have a constant source of energy. There are many alternatives to storing energy, we must develope them on a small, sustainable scale.

 Spencer 

  • Fri, May 15, 2009 - 12:00am

    #8
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    Re: RE without batteries or the grid?

I think the only way to go without batteries is to use power while you make it. The downside with commercial PV systems is that the voltage your panel produces most likeley wont be a usuable voltage. The current systems run real high voltage strings, anywhere from 50 up to 500 volts. Usually for efficiency reasons. Lower gauge wire since less amperage with higher voltage, also the battery chargers are more efficient running at higher voltages, vs lower, the ones with Maximum Power Point Tracking (MPPT) specifically.

My opinion, if you bought a gird tie system, and the grid fails. Your system is basically useless. Try running a 12 VDC motor off 250 volts, see what happens. The other downside, the inverters are meant to run off batteries, usually a voltage of around 12 to 14 volts. If you tried to hook your panel directly into the inverter, it will shutdown on over-volatge, or maybe fry the inverter. I have only come across one inverter that is meant to run off panels directly, but only panels up to 25 volts.

If you are getting a PV system as a hedge against grid failure, you really need to pay attention to what you are getting, and getting into.

  • Fri, May 15, 2009 - 12:42am

    #9
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    Re: RE without batteries or the grid?

SPM wrote "My opinion, if you bought a gird tie system, and the grid fails. Your system is basically useless."

Only if it’s set up this way……

http://www.solarelectricsupply.com/Inverters/inverters.html

The Trace SWPV, UT and microsine, AEI GC and Omnion 2400 inverters are examples of an intertie inverter. Using a multifunction inverter allows you to sell excess power to the utility, and also maintain a battery bank for standby power in the event of a utility power failure.

  • Fri, May 15, 2009 - 12:51am

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    Re: RE without batteries or the grid?

Utility-Intertie Inverters
Intertie inverters convert DC power from PV modules into AC power to be fed into the utility grid.  There are two major types of utility inverters; string inverters and low voltage input inverters.

The SMA Sunny Boy, Fronius and Xantrex GT-3 inverters are string inverters.  The name "string" comes from the way the PC modules are wired together, in series to achieve a higher voltage.  These inverters are designed to run at voltages up to 600 VDC.  String wiring is faster to install, more efficient and allows the use of smaller gauge wire.  DC voltage this high can be deadly, so string inverters should be installed and serviced by qualified electricians.

A utility-tie PV system uses the utility company as a storage battery.  When the sun is shining, your electricity comes from the PV array, via the inverter.  If the PV array is making more power than you are using, the excess can be sold to the utility (power company) through your electric meter.  If you use more power than the PV array can supply, the utility makes up the difference.  This type of system makes the most sense if you have utility power, because there are no batteries to maintain or replace.  Unfortunately, if the utility power goes down, this type of inverter will go off, too.

Multifunction Inverters
Using a multi-function inverter allows you to sell excess power to the utility, and also maintain a battery bank for standby power in the event of a utility power failure.  the Outback GFX and Xantrex SW series are primarily stand-alone inverters that can function as an intertie inverter at the same time but with a slight lower efficiency than an inverter designed for intertie only.  The new Beacon Power M5 is an intertie inverter that is designed to provide batter backup when the utility fails.  The SMA Sunny Island inverter is designed to work with a Sunny Boy inverter to provide utility intertie with battery backup.

In a typical installation, the inverter is connected to a batter bank, the utility power lines, a standby generator and the house load center.  If the utility is available, the inverter will supply the house loads from the utility.  If the utility fails, the inverter will supply power to the loads from the battery.

When the utility is available again, the inverter will switch the loads back to the utility, and recharge the batteries.  If the batteries become fully charged by another power source, such as photovoltaic modules or a wind or hydroelectric generator, excess power may be sold back to the utility.

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