DIY net metering system for under $8,000.00 United states.

Bob The Builder

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48 x 280 = 13440
$2300/13440 = $0.17/Wh
That's $170/kWh of capacity.

How many cycles can you get out of them?
If they do last 3650 cycles (a decade of daily 100% cycling), it comes to $0.05/kWh of use.

(of course you would cycle a bit less than 100% each day, maybe 80% or 90%.)
The wild card is whether these cells really last 2500 or 6000 cycles as advertised.
One independent test of many brands of batteries, 95% failed and had to be repaired or replaced. So I wouldn't bet on more than 20% of claimed life, and consider anything above that a bonus.
Maybe it's BMS that fails and cells are OK, in which case it can be repaired economically. So long as the failure mode doesn't let cells over/under charge.

PV on the other hand can reasonably last 25 to 40 years. Although, some have issues which cause degradation far earlier.
Inverters ought to last 10 years, will likely do 20 years.
I came up with $0.05 assuming 10 years, $0.025 assuming 20 (I miss-stated 10 years earlier.) If inverter needs replacement, $0.03/kWh over 20 years.
The math is $1/watt, and 5.5 hours effective sun per day.
Very good advice. I never would have thought! Thanks!
 

Hedges

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House meter connected to underground from utility co. Next is Shed sub panel.

Because the house meter isn't built into main panel, you could add a 200A fused disconnect (or breaker) between utility meter and main panel.
Of course you would have to have the utility isolate the power while you installed it.
If you had a 200A fuse/breaker disconnect, after that you could have 200A main panel (with its on breaker), and in parallel a 100A fused disconnect feeding shed and PV system.

Or, you could replace your main panel with one having 225A busbar and 200A main breaker. Then you could have a 70A breaker in it feed shed and PV.


(I'm assuming your T&B panel has 200A busbar not 225A, but double-check that)
 

Hedges

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@Hedges Look at what I posted here, is this what you posted about the 120 rule, well is this why it's adding and not subtracting ?

That adding/subtracting is just for accounting. Maybe the meter is wired backwards, or maybe it counts "VA" not watts, doesn't pay attention to polarity.

If you connect two batteries to one end of a string of Christmas lights, their current adds.
If you put one battery on either end of the string, each puts its current in the wire (flowing in opposite directions, and some where between they drop to zero. If one (representing PV) is higher voltage than the other (representing grid), the higher charges the lower.
 

Bob The Builder

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That adding/subtracting is just for accounting. Maybe the meter is wired backwards, or maybe it counts "VA" not watts, doesn't pay attention to polarity.

If you connect two batteries to one end of a string of Christmas lights, their current adds.
If you put one battery on either end of the string, each puts its current in the wire (flowing in opposite directions, and some where between they drop to zero. If one (representing PV) is higher voltage than the other (representing grid), the higher charges the lower.
So Hedges, you are saying that it could be the way my efergy e2 is reading and not the utility's smart meter charging me for power I'm producing? If so how can I know for sure?
Also I only see 200 amp. max on my house panel sticker!
 

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Hedges

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Utility has smart meters, and has smart meters for net metering. Difference may just be "calibration", confirming accuracy. Or, the version not for net-metering might charge for power regardless of direction.

Turn off your PV. Note the direction of flow indicated by meter, or that kWh consumed climbs over time.
Turn on PV and turn off all loads. See if meter indicates opposite direction.
Regardless of which, if you set up zero-export which limits PV production when consumption is less, at the main meter it would just register reduced consumption.

Did you say an extra meter you added for PV is your own, nothing to do with the utility?


Yes, that panel says 200A. With a 200A main breaker, that limits circuit to shed to 40A breaker, if backfed.
So either upgrade to a 225A busbar panel, so 70A allowed to shed. Or, add a 200A fused disconnect after meter, and branch to the 200A main and to a 100A fuse or breaker feeding shed (not through main panel.)
 

Bob The Builder

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Thanks a lot. I will add a disconnect as you describe. I don't have net metering yet. When I fire up my bootleg, cheap Amazon grid tie inverter on just 4- 100 watt 12 volt panels hooked up series then parallel to get 24 volts. My meter in my Shed that I installed to show KWH. Well it indicates I'm producing power. But I found out this meter reads eather way. Anyway it's a 120 volt meter hooked up to a single pole 120 volt breaker for back feeding. All looks good until I hooked up a efergy e2 meter to my main house meter 100 foot away. The efergy e2 read 1.300
 

Bob The Builder

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The 1300 watts are with the grid tie inverter Off. When I turn it on. The efergy reads 1600 watts instead of 1000 watts. This is without getting anywhere close to what the house is using.
 

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Bob The Builder

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Also the Kill A Watt meter shows I'm putting in 300 watts and it indicates how much KWH I'm putting in!
 

Bob The Builder

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Utility has smart meters, and has smart meters for net metering. Difference may just be "calibration", confirming accuracy. Or, the version not for net-metering might charge for power regardless of direction.

Turn off your PV. Note the direction of flow indicated by meter, or that kWh consumed climbs over time.
Turn on PV and turn off all loads. See if meter indicates opposite direction.
Regardless of which, if you set up zero-export which limits PV production when consumption is less, at the main meter it would just register reduced consumption.

Did you say an extra meter you added for PV is your own, nothing to do with the utility?


Yes, that panel says 200A. With a 200A main breaker, that limits circuit to shed to 40A breaker, if backfed.
So either upgrade to a 225A busbar panel, so 70A allowed to shed. Or, add a 200A fused disconnect after meter, and branch to the 200A main and to a 100A fuse or breaker feeding shed (not through main panel.)
Hedges I posted to you but not in reply!
 

Bob The Builder

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How would it work if I ran copper wires underground the 100 foot from the solar panels to my home meter! Make that 125 foot.
 

Ampster

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How would it work if I ran copper wires underground the 100 foot from the solar panels to my home meter! Make that 125 foot.
Underground, overhead or in conduit is not the issue. Wire size and distance are the issues in how much voltage loss there is. Voltage loss is the issue that will drive how it would work. The reference above explains that and more.
 

Hedges

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Voltage drop is an easy manual calculation.
Find a chart that gives resistance per unit length, and do some math.
For AC, best to keep voltage drop under 5%, under 3% or something like that.
For DC from PV, similar percentage is a good goal to minimize power loss. However, you can design for 10%, 15%, or even more voltage drop at max power from panels. That is only a percentage of peak wattage that is lost (so long as voltage doesn't drop below minimum required by MPPT.)

Also, follow NEC chart for ampacity. Obey ampacity limits as well as IR drop.
 

Bob The Builder

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Voltage drop is an easy manual calculation.
Find a chart that gives resistance per unit length, and do some math.
For AC, best to keep voltage drop under 5%, under 3% or something like that.
For DC from PV, similar percentage is a good goal to minimize power loss. However, you can design for 10%, 15%, or even more voltage drop at max power from panels. That is only a percentage of peak wattage that is lost (so long as voltage doesn't drop below minimum required by MPPT.)

Also, follow NEC chart for ampacity. Obey ampacity limits as well as IR drop.
Thinks for your help. I'm learning a lot!
 
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