Newbe needs help trying to reduce the power I buy from the power company

[thomBangor]

National Fire Protection Association (NFPA) National Electric Code (NEC).

Even if permits aren't required (my city is the same), they often require compliance with certain standards. Unfortunately, if not installed by a licensed contractor, my city requires a permit.

I checked the city of Bangor permit requirements, and "permits are usually required for the following: Electrical systems"

The permit application references NEC 2020.

690.12(A&B) Rapid Shutdown of PV Systems on Buildings.

Rapid shutdown provides the first responder with a simple method to de-energize the PV system conductors easily and quickly to ensure a safe condition on the roof of a building during a fire.

www.electricallicenserenewal.com

It's purpose is to protect firefighters on your roof from high voltage DC sources.

Thanks!
I do not live in Bangor, I live near Bangor. In my area knob and tube wiring is still common (albeit not with new installations)

I believe the NEC code is wrong in this case. Adding shutoff for every panel means adding a lot of connections to the wiring, and in doing so raising the probability of failure. In short, the NEC code tries to mitigate a risk of electrocution to firefighters by creating a risk of fire. Strange that they did this, because firefighters already have a means to kill power to panels by spraying it to block the sun. In addition, if this were of high concern, it makes more sense to me that they require the panels be wired in parallel instead of in series- that would have been a very easy and simple way to change the code and keep everything at low <48 voltages. Wire would have been more expensive, but putting a disconnect on every panel is expensive.

In short, I will not put my family/home at more risk because NEC doesn't know what they're doing with solar yet.

 

[thomBangor]

Is net metering available, if so what terms?

You can store power in a battery, but only about 1 day's worth before it becomes impractical in terms of size and cost.
With net metering, you can store a summer's worth of production for use in the winter.

If you DIY GT PV, it will cost $1.00/W +/- and make power for $0.025/kWh +/- (amortized over 20 years)
If you buy an economical LiFePO4 battery (e.g. EG4 PowerPro), it will store power for $0.05/kWh (amortized over 6000 cycles, 16 years.)
The inverter with supports battery as well as powering loads and optionally doing grid-tie net metering may make system cost more than sum of the above, or maybe not.

If you do an offgrid system you can make power as cheap, but if you waste it by not consuming, cost per kWh is more.
If you don't waste any but don't make enough so have to buy from the grid, that will cost you your $0.20/kWh or so rate.

If your main objective is to save money, don't dismiss net metering without evaluating it.
The system can also provide backup during grid failures. You might want a backup generator for winter.
If you have gas, oil, etc. heat available, you can use electric and net metering when the grid is up, and have economical backup.

Versant allows net metering, but with the caveat that your system must be signed off on by a licensed electrician. There is another thread about how difficult this is for people in Maine who are solar diy. Essentially, unless you have a buddy or want to pay the $20,000 markup for a solar-install company who has a staff licensed electrician, net metering is almost impossible.

I started with the goal of net metering, but I estimate it will take 3 years to complete. One example is a friend in a town nearby who had solar installed by professionals, following the Versant net-metering pathway. They're at the last step in the process and have been waiting 6 months, and still Versant has not scheduled an appointment to complete that last step. For reference, There are 7 to 9 steps in the Versant process, almost all of which require Versant participation on their timeline.

I still have net metering as a goal someday, but would like to work toward it whilst reducing my power bill.

 

[thomBangor]

So does that mean if the power goes out at an RV park, then all those RVs hooked up to shore power with charger/inverters will be leaking current back into the grid?

If the power is out then those RVs would be trying to power an entire grid (a near infinite draw and essentially a dead short). Presumably there is either a breaker that will trip or inverter-protection circuitry that would switch.

 

[Citlalatonac]

So does that mean if the power goes out at an RV park, then all those RVs hooked up to shore power with charger/inverters will be leaking current back into the grid?

l guess I would have thought they have something that disconnects the connection or something that prevents back flow.
Or do they all take all the shore power make it DC then convert back to AC to send to the A/C panel? That seems like it would loose a lot of efficiency.
And do they all do the same thing. I have Victron so I am especially curious how they work.

There's so many wacky RV setups that it's impossible to make general statements. Many do use an AC>DC charger to get the grid flow in, which isolates from the grid.

There's no such thing as an electricity backflow preventer, I'm not super sciencey but to my understanding electricity moves really fast and it's impossible to detect a backfeed then take action fast enough to slam the gates before any electrons escape.

An RV park will be on commercial electric and I dint know anything about that. I would suspect that there are enough draws to dwarf any amount of solar generation backfeeding. You can't fit anywhere near the same amount of panels on an RV as on a house, some of the RVs won't have any, shore facilities are also using power. I would expect any entire park to be safe from backfeed the way a single residence can't be. They may have an agreement already, especially if the park has a back generator or it's own panels.

 

[thomBangor]

There's so many wacky RV setups that it's impossible to make general statements. Many do use an AC>DC charger to get the grid flow in, which isolates from the grid.

There's no such thing as an electricity backflow preventer, I'm not super sciencey but to my understanding electricity moves really fast and it's impossible to detect a backfeed then take action fast enough to slam the gates before any electrons escape.

An RV park will be on commercial electric and I dint know anything about that. I would suspect that there are enough draws to dwarf any amount of solar generation backfeeding. You can't fit anywhere near the same amount of panels on an RV as on a house, some of the RVs won't have any, shore facilities are also using power. I would expect any entire park to be safe from backfeed the way a single residence can't be. They may have an agreement already, especially if the park has a back generator or it's own panels.

True.

Even without electrical protection, I know of no power source (including RVs) that can sustain a voltage against a near-infinite draw.

 

[1201]

I agree this is the best, for a single person. In my case it is not the best. Solar generated power through my system is going to vary wildly with snow/clouds/etc. My wife has made it clear that this project can only proceed if she cannot tell the difference in the power. It is my belief that using a subpanel one of two things will happen:
1. That subpanel will be at some point underpowered and my wife will never let me do a project like this one again (not acceptable)
or
2. That subpanel will be conservatively designed, so power is not efficiently used, so the ROI time for this project goes up to the point where it makes no sense to do it.

To point 1. There are many inverters that can pass the grid through to your subpanel if the battery gets low. You need to ensure that the loads are not greater than the inverter can handle.

In my case, my sma sunny islands can be programmed to switch to the grid at a certain demand. So, if demand is higher than x watts, they switch to the grid and power the loads.

They also switch to the grid at programmed soc.

 

[thomBangor]

To point 1. There are many inverters that can pass the grid through to your subpanel if the battery gets low. You need to ensure that the loads are not greater than the inverter can handle.

In my case, my sma sunny islands can be programmed to switch to the grid at a certain demand. So, if demand is higher than x watts, they switch to the grid and power the loads.

They also switch to the grid at programmed soc.

Thanks this is helpful.

Does the pass-the-grid-thru-to-subpanel feature have a trade-name I could lookup in spec sheets/manuals?

 

[1201]

Thanks this is helpful.

Does the pass-the-grid-thru-to-subpanel feature have a trade-name I could lookup in spec sheets/manuals?

most all in ones (off grid inverters) have a transfer switch can switch back to grid when the battery gets low.

I don't know if they can switch to grid if the load is too high. its unwise to undersize an inverter.

in the case of the sunny island its called "grid as generator"

 

[Mkgough]

I agree this is the best, for a single person. In my case it is not the best. Solar generated power through my system is going to vary wildly with snow/clouds/etc. My wife has made it clear that this project can only proceed if she cannot tell the difference in the power. It is my belief that using a subpanel one of two things will happen:
1. That subpanel will be at some point underpowered and my wife will never let me do a project like this one again (not acceptable)
or
2. That subpanel will be conservatively designed, so power is not efficiently used, so the ROI time for this project goes up to the point where it makes no sense to do it.

Batteries will keep that power issue at bay, so just be sure to have enough batteries so the power stays constant and grid fallback.

 

[Solar Guppy]

Any idea what the EG4 Manual means on pdf page 33? Protocol P02-GRW?

Likely one of growatt's 48V battery protocols.

Even within the same brand, they can and do have different protocols, same for most inverter manufactures. HV ( 200V+ ) and LV ( 48V and lower ) are totally separate, unrelated products for all manufactures I am aware of.

400V is a very common voltage for HV inverters, I'm currently using the newer Solis S6 S6-EH1P11.4K-H-US, and have some posts about my latest system

 

[thomBangor]

To point 1. There are many inverters that can pass the grid through to your subpanel if the battery gets low. You need to ensure that the loads are not greater than the inverter can handle.

In my case, my sma sunny islands can be programmed to switch to the grid at a certain demand. So, if demand is higher than x watts, they switch to the grid and power the loads.

They also switch to the grid at programmed soc.

Thanks; I think I might go this route.