[RE-wrenches] Trace SW4024 feeding back to grid

[Ray Walters]

Back in the old days, when utilities routinely were a huge pain to work 
with, we just created a backup loads sub panel, and ran those circuits 
off grid, and used the grid in place of a generator.  No way to back 
feed, and the customer got the benefits of a reduced bill and backup 
power.  It was not as efficient though, especially with lead acid 
batteries.

In Hawaii, many of the utility circuits are maxed out for solar 
penetration, and so its literally impossible to do a regular GT system 
on many parts of the islands anymore.  Those customers have to do setups 
like I described.  The trick to improving the efficiency, is having some 
dump loads to take the surplus PV power after the batteries are full, 
either water pumping to a cistern, extra heating or extra cooling, and 
have some thermal mass in the house to hold those extra BTUs (+ or -).  
Here on the mainland, we're going to be doing stuff like that in the 
future.

Ray Walters
Remote Solar

On 1/12/2026 3:32 PM, Zeke Yewdall via RE-wrenches wrote:
> Did the utility say that it was feeding back in 1A continuous, or had 
> fed back in 1A at some point?
>
> With better metering, especially the new smartmeters, utilities are 
> finding a lot of PV systems that are connected without authorization, 
> by seeing tiny amounts of backfed power that used to be invisible.  I 
> had one SolArk system get caught.  For the systems that operate in 
> parallel with the utility doing zero sell it needs to have a certain 
> offset for the minimum amount drawn from the utility, such that it 
> doesn't inadvertently sell a little bit during readjustment during 
> load changes.  In the case of the SolArk system, it was set to 0 watts 
> from the utility, and when the load changed, it would sell a little 
> bit for a few seconds.  This is enough for the utilities to see with 
> the new meters, and lets them know that there is solar that they 
> haven't been told about. I changed it to a 120 watt minimum draw from 
> the utility, and it no longer overshoots zero during load changes now, 
> but also draws power from the utility all of the time.  We do have to 
> get this system permitted and an interconnection agreement in place 
> soon though, because now they know about it, and they are going to 
> pull the customers service if he does not do that, or get rid of the 
> solar completely.  This is something that everyone should know, that 
> operating in parallel with the grid without having an interconnection 
> agreement is a risk.
>
> The only way to safely do solar without getting an interconnection 
> agreement (and I think the only legal way) is to never have the solar 
> operating in parallel with the grid, but have a transfer switch such 
> that the solar is never connected to the utility.  For many of the 
> newer systems, connecting the grid to the generator input port instead 
> of the grid port can accomplish this (though it varies from system to 
> system -- some systems can operate in parallel with the generator 
> too).  But almost all of the new systems (all in ones, some operating 
> modes of the Radian and XW) operate in parallel with the utility 
> rather than switching back and forth, so when the grid is connected to 
> the grid input of the inverter, it can potentially backfeed the grid, 
> even if for only a second or less.
>
> The HBX/LBX modes of the SW and the Outback switch back and forth, 
> rather than operating in parallel, and so should not have this issue.  
> I think... I am not 100% certain even with these modes, although I've 
> never seen them have an inadvertent sell issue, due to the inverter 
> being off anytime it's connected to the grid.    The transfer switch 
> in this case would be inside of the inverter.
>
> Zeke
>
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