[kylehotchkiss]

This reminds me that utilities can limit the size of your rooftop solar system, which locks you into whatever your usage you had at install time. Because of that it's difficult for me to actually achieve net zero electric usage and it's more cost effective for me to remain on a gas furnace instead of upgrading to a heat pump. This is such a shame. I wish I could just get 2 more KWh.

[hex4def6]

I assume you mean 2kW not 2kWh. And you can; look up "Non-export addition". These are solar panels that are set to zero-export; they will either charge a battery or the current house loads, but never backfeed into the grid.

[quickthrowman]

> they will either charge a battery or the current house loads, but never backfeed into the grid.

I’m not sure I understand how this works unless you split off loads into a subpanel that is fed by a UPS which is fed by solar panels, and also isolated from your utility connected electrical service.

As far as I understand it, you can’t have power generated by solar panels feeding loads in your grid-connected panel without backfeeding the grid, same deal as a generator backfeeding a grid-connected panel. You have to kill the MCB or service disconnect to prevent backfeeding.

If you have links with info on how this work (one-line diagram would be extremely useful) I’d be curious. I sell and run commercial electrical work, FWIW. I’ve done zero solar jobs so my understanding could definitely be wrong!

[narism]

Zero export inverters are grid-tied but monitor the meter/CTs for load changes in order to curtail solar production/shift it to battery charging. I think they can technically backfeed a little bit if load is suddenly dumped depending on the inverter response time. Some have a secondary hard disconnect for additional protection.

https://knowledge-center.solaredge.com/sites/kc/files/feed-i...

[quickthrowman]

Thanks for the info, that clears things up!

[Dylan16807]

> As far as I understand it, you can’t have power generated by solar panels feeding loads in your grid-connected panel without backfeeding the grid, same deal as a generator backfeeding a grid-connected panel. You have to kill the MCB or service disconnect to prevent backfeeding.

An inverter can limit its output, right? So measure current at a few different points in the system, do some math, and use that to set the inverter's limit.

[quickthrowman]

Thanks for the explanation, that makes sense. Monitor some CTs and let the inverter only discharge enough power to satisfy the current demand without backfeeding the utility.

[jaredhallen]

Or mine some crypto with the excess. I'm only half kidding. Having too much power is a good problem to have.

[kylehotchkiss]

Wouldn't it be like

Grid < Primary solar > Battery < Secondary Solar

Where the house is powered by inverter directly on the battery (and maybe a second inverter for primary solar to grid?)

[kylehotchkiss]

You are correct :) Thank you for mentioning non-export additions! I'll give those a look.

[killingtime74]

If you get more can't you disconnect from the grid? Then they can't stop you. You need batteries of course. Or stay connected with existing system and have more solar that is only connected to batteries separately, no grid.

[lazide]

Some places will condemn your house (or at least threaten to) if you don’t have an active grid power connection. so yes, they can stop you.

[killingtime74]

Wow interesting, which country/juridiction? Seems pretty extreme

[lazide]

Most cities require a grid electrical connection as a requirement for habitability. The codes all refer to ‘utility providers’ for building permits, and require utilities (including electrical, water, etc.) be present and provided before the unit is considered ‘habitable’. Even temporary power (required to start construction before you could even install a solar installation, with the way most permits are done) has to be permitted and done a specific way.

Here is one example code from Arizona [https://law.justia.com/codes/arizona/title-9/section-9-467/].

And a lot of unclear discussion [https://www.reddit.com/r/phoenix/comments/4ugdtu/is_it_illeg...]

At a state level they’ve been making it clearer that it is technically legal - but it’s still hard to actually do.

There has been a lot of controversy on this topic, with permits getting denied in cities when the plan was to be off grid (and people just caving), and some utilities explicitly raising connection fees to ensure zero-usage customers were still paying them.

It gets people really angry too of course (at least in the US) because ‘what do you mean big government won’t let me do what I want on my own land!’.

The reality is, the types of folks who actually want to go truly off grid (and don’t feel the need/prioritize the backups provided by an optional grid connection, or think it is too expensive) probably already live far enough in the boonies that building codes are largely optional anyway.

It’s pretty rare that a random city dweller is going to be trying to go 100% off grid in their condo, or would have the physical space or legal ability to do so, regardless of what the city says.

And code enforcement looking too closely at things way out in the sticks tends to find itself in some very dangerous situations - the type people just disappear from sometimes and are never found - especially out in the remote parts of America’s deserts/woods.

[r00fus]

Not sure if your utility allowed for planned usage changes (ie, planning to buy an(other) EV, planning to install heat pump). This is what my installer submitted to justify my 180% over-specced solar install. This is PG&E in CA.

[kylehotchkiss]

San Diego's limit is 150% but if you don't have a heat pump/car charger to start with, you're def going to be at more than 150%. Did you have to show them concrete plans for EV charger or heat pump?