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Grid tie vs storage PV system

gfretwell's picture

I am looking into this and I still think I want some storage.
Unfortunately the rebates are only for grid tie systems.
Grid tie looks like "buy high, sell low" to me since they pay a small fraction of the usage charge when you sell power back to them.
Grid tie also lacks the "back up" capability I desire when the grid is down.
Has anyone seen a hybrid system with a grid tie meter and some storage?
Is there any good reason not to build one that way?

Greg

(post #157779, reply #1 of 13)

I'm not sure about Fla, but utilities in NC pay more for incoming than they charge for outgoing. 2k of battery storage is around $6000... so is a 17K propane powered generator.

We started out building homes with the Out Back system, which sounds like what you are looking for, but now, our systems a feeding everything back into the grid.

www.tvwsolar.com

We'll have a kid
Or maybe we'll rent one
He's got to be straight
We don't want a bent one
He'll drink his baby brew
From a big brass cup
Someday he may be president
If things loosen up

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The Village Woodworks, Inc

Chapel Hill, NC

 

We'll have a kid Or maybe we'll rent one He's got to be straight We don't want a bent one He'll drink his baby brew From a big brass cup Someday he may be president If things loosen up

(post #157779, reply #2 of 13)

Snort,


utilities in NC pay more for incoming than they charge for outgoing.


How long do you figure the utilities can afford to do this?  Are you sure "somebody" isn't subsidizing this arrangement?


Generally you buy at retail and sell wholesale.  Netmetering is better.  TOD metering may allow you more than break even, depending on your usage pattern.


Fret,


Yes, you can tie to the grid and also have storage.  But batteries and storage really complicate things.  If you want cloudy/night power off-grid you need storage.  If you want emergency backup then you don't need storage, you need your inverter to work with your generator.  Check with the inverter makers to determine if their equipment will work with the waveform from a small emergency generator you might use - I've never done this but it may work (with a proper transfer switch of course!).  You'ld need to figure out what happens when you shed the load and your PV system tries to motor the generator.  Someone must have already looked into this.


Jim x 3


 


Edited 9/7/2009 3:38 pm ET by jimjimjim

(post #157779, reply #4 of 13)

I am not sure why storage is $6000 ???
My emergency power needs are fairly small and that is why I thought a storage system would be a reasonable thing.
If I could use a 36v inverter I would have about 7.2kwh in my golf cart alone. (about $600 worth of batteries)
All I really need to power is a fridge and my well pumps, maybe a TV and a few CFLs.
I have a "kill a watt" I am looking at my loads with as I speak. The fridge is surprisingly small, particularly since it is outside in the pool bar.
I am looking at a direct drive DC pool pump system in addition to the 120/240v system and solar hot water.
It looks like I still need the grid tie to get any guv'mint money but I wouldn't mind intercepting all of that I can for my own use before I start selling it back to them at 3-4 cents a kwh.

Greg

(post #157779, reply #9 of 13)

I assumed that each state had something like this:

http://www.ncgreenpower.org/

www.tvwsolar.com

We'll have a kid
Or maybe we'll rent one
He's got to be straight
We don't want a bent one
He'll drink his baby brew
From a big brass cup
Someday he may be president
If things loosen up

www.tvwsolar.com

The Village Woodworks, Inc

Chapel Hill, NC

 

We'll have a kid Or maybe we'll rent one He's got to be straight We don't want a bent one He'll drink his baby brew From a big brass cup Someday he may be president If things loosen up

(post #157779, reply #3 of 13)

Use the advanced search and look for post from CAP with Storage or Batteries in in them. If not true Solar.

I believe that he has comment on the cost difference and why it is rarely done where you have grid power.

If you net metering it does not deduce electric cost any, has limited capacity, has maintance cost.

A generator would be more practical.

.
William the Geezer, the sequel to Billy the Kid - Shoe
. William the Geezer, the sequel to Billy the Kid - Shoe

(post #157779, reply #5 of 13)

For the infrequent number of power outages we have, a generator is pretty expensive and you still have to "feed the monster" during the outage. A storage system would pay you back every night and twice as much during an outage.

Greg

(post #157779, reply #6 of 13)

It does not pay you back at night if you are on net metering or you have time of day metering.

IIRC one of the reasons for the extra cost is the type of inverter system that is needed to both sync with the power line and run independing and also not back feed.

One of the problems with your scheme is that if use the batteries to supply power to reduce external consumption and then the grid goes out you have all ready used up your storage.

I think that a separate inverter and some batteries is what you needed for the limited emergency capacity that you need.

.
William the Geezer, the sequel to Billy the Kid - Shoe


Edited 9/7/2009 5:17 pm by BillHartmann

. William the Geezer, the sequel to Billy the Kid - Shoe

(post #157779, reply #7 of 13)

No timed metering here

If my storage is enough to run the selected loads overnight, I wouldn't really care if the poco was there or not.

The separate inverter, battery backup is what I have now with a 100a DC alternator to top up the batteries. I would just replace that with solar charging.
During Charlie and Wilma I used the batteries in my cars, starting them now and then to top up the battery. That ran the TV and a computer.

Greg

(post #157779, reply #8 of 13)

The go standalone. Cheaper inverter system.

.
William the Geezer, the sequel to Billy the Kid - Shoe
. William the Geezer, the sequel to Billy the Kid - Shoe

(post #157779, reply #10 of 13)

Hi,
You can get systems that do grid-tie with battery backup.

Outback makes a line of inverters specifically for this.

Some sample systems of this type here:
http://www.builditsolar.com/Projects/PV/pv.htm#Grid%20Tie%20+%20Battery

It costs more to do this than a grid-tie alone, and the systems are not as efficient, and you have the battery replacement costs to add in.

These systems do qualify for the fed rebate, since they are grid-tie, but they also provide power when the grid is down.

A lot of utilities pay full retail for power you generate up until the time you zero your bill out -- a very bad deal for the utility, since this is well over what the pay for electricity wholesale. But, I guess in your area they pay less.

Gary

(post #157779, reply #11 of 13)

Thanks for all the tips.
I am scheduling an appointment with the only state sanctioned dealer in my area to see what they say.
The way the deal works here is the state will rebate most of the collector cost ($4 a watt). I am thinking I will be collector heavy at first and then divert some from the grid tie later.
The direct drive pool pump is a separate system and the state won't rebate anything for that.

Greg

(post #157779, reply #12 of 13)

http://www.csindy.com/colorado/stranger-than-fiction/Content?category=1064385


Denver's power company wants to charge solar-energy users for electricity even if they don't use any. Tom Henley of Xcel Energy told 7NEWS that the proposed fee would level the playing field for electricity users who are currently subsidizing connectivity fees for solar users, who some months use no electricity. Henley later admitted no Xcel customers pay extra to fund connectivity fees and that the proposed fee, which would add $2 a month to customers' bills, would all go to Xcel. He said the fee is intended to ensure that down the road solar users don't get free rides.


 


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(post #157779, reply #13 of 13)

Generally batteries will be expensive ... relative to the occasional use they might have during outages. Generally, the buy back rate is the same as the rate you pay ... normally a net meter simply 'runs backwards' so you don't pay for kwh excess you generate and put back into the grid. If you have time of use charges like in commercial applications, PV goes well with it since your peak generation usually matches any peak charges (e.g. 12 noon to 6 pm).


Yes, you can do battery backup, but not sure if it's worth it ... unless of course you have frequent (and relatively long) outages. You will need a charger controller and then the batteries.

There ain't NO free lunch. Not no how, not no where!