Planning a grid-tie system

[John Simson]

Hi everybody. I am beginning to plan a grid-tie system at my home in Los Angeles. I'd appreciate any direction anybody would care to give.

My experience is with generators and small off grid solar panels, and extensive home and industrial electrical work. However, I've recently been amazed at how cheaply I can pick up new solar equipment in LA, and want to start accumulating the supplies I will need in preparation for drawing up the plans and submitting them to the building department for permits. I know that this is somewhat backwards, but I figure, if I can't afford the equipment, I don't want to go through all the trouble of submitting plans!

I've measured my roof and found that I can fit twelve 270 watt panels on it. I'll want micro inverters because the roof gets shade in the afternoon and I'd rather have each panel feed the most it can into the grid. I can get Talesun 270 watt 60 cell panels for $110 each and Siemans M-190 IQ7 - 240 - s22 microinverters for $80 a piece, all brand new. This should go a good way toward filling my power needs. I've done the preliminary calculations.

I talked with an engineer with the building department who told me that the specs for the microinverters I've chosen will be OK for a couple of years at least (will qualify for plan approval.) The panels don't seem to be an issue. From what I can tell. LADWP buys 100% of the power the system feeds into the grid and will credit any to me that I eventually use. There is the $10 a month fee. That seems to be it, an incredible arrangement, I think, in comparison to other utilities. The engineer qualified his comments on the microinverters with a "Please note you have no submitted plans and nothing has been reviewed at this time, so the equipment you have mentioned has not been reviewed/approved through plan check. Buying products before it has been approved sort of leaves you in limbo on that front."

What I am proposing is backwards, but is it, as my kid would say, "Stuuuuuuuuupid?"

So, my questions. 1) Is the LADWP deal really as good as it seems to be? 2) Is buying equipment prior to approval really not a good idea?

Many thanks for any advice.

 

[Hedges]

State law and various code keeps adding required features to grid-tie inverters.
Microinverters bypasses requirement for module-level shutdown (fireman safety)
"Rule 21" requires inverters to stay on-line and support the grid during disturbance, different from requirement for earlier models.
Mounting arrangement of panels on roof has requirements for walkways for firemen and room near the ridge to hack vent holes.

Typical today is $10/month fee to be connected, generation credited and usage charged at the same rate. Rate probably varies with time of day. Surplus kWh at the end of the year earn a cash credit of $0.04/kWh

Today, you may have a rate tariff which charges more for more total kWh/month, but doesn't vary with time of day.
Required new tariff probably charges you triple the rate 4:00 PM to 9:00 PM (when PV doesn't generate much).
If you generate 2 kWh from PV but consume 6kWh for A/C, could actually increase your bill instead of decreasing.
See if utility has a "what if" calculator that evaluates rate schedules and your usage history.

I suggest checking out the assortment of PV panels available from SanTan solar (not all still have UL labels, required for grid-tied usage) or other liquidators. Some people order 500W panels new direct from China.

I like high voltage string inverters better than micro inverters. Easier to mix and match various choices of PV panel and fully utilize inverter capacity.

Do you want power even during blackouts? Daytime only, or continue with batteries at night? There are several solutions, so plan your entire system.

Another alternative is "zero export", where current transformers are used to monitor utility feed, throttle back PV production so only enough to offset your usage, never backfeed grid. That avoids being pushed onto different tariffs (although that will happen to everyone soon.) Next step will be to control when loads turn on, to fit your production (useful for battery backup systems too.)

 

[John Simson]

Thank you very much for your pointers. I'm getting the idea that power companies are continually trying to find ways to discourage home owners from going solar. Is this right? With the possibility of tables being turned on me some day - would I be safe from LADWP increasing my costs to provide myself with solar power by going the zero export route, or since I am tied to the grid, but not exporting my solar electricity, could they still penalize me for being grid tie? Would it be best, then to have my solar array entirely unconnected to the grid?

 

[Hedges]

Can't know what changes will be made in the future.
Utilities try to make it more profitable for themselves. Even though, their profit is set (capped?) at a percentage of book-value of assets.

A system with fast payback would be good so you start coming out ahead and get the benefits for a while before someone pulls the rug out from underneath.
What are your utility rates? You may break even in 3 or 4 years.
Net metering is the best way to go, unless so small a system it never exports anyway.
You might add zero-export controls or battery storage later.

 

[John Simson]

Here's what I've found out. The cost for installing a system is presently free with LADWP. In the future it may cost $75 to $145. The Building Department charges something like $450 and reports to LADWP that permits are in order. The power company connects the system free of charge.
The monthly cost of solar is $10. LADWP sells power to us for the same cost we are paying now and it offsets that cost with the electricity we send into the grid from our Solar Array. We get 100% credit for the electricity we send into the grid at the lowest rate (Tier 1), I would imagine. Our credits do not expire, but if we generate more than we consume, we'll never see a dime of that. I talked with a building inspector and he said that whatever the arrangement is that we contract with LADWP is locked in for ever (I would suspect that there are loopholes that could intrude on the "foreverness" of this)! I think that there are inverters (hybrid) that can be programmed to be off or on grid, with or without batteries. Might be best to just start out with a hybrid inverter rather than add something later. What do you think? As for pay back. I haven't done the calculations yet. I'll be interested to know what that is, but with Christmas and all - I've still got presents to get! Thanks again!

 

[Hedges]

"Our credits do not expire"
Not bad; ours expire on the anniversary of approved connection every year.
Sounds like you don't get the standard deal offered through PG&E and SCE
Some cities like Santa Clara have had their own power company for years and gave their residents significantly lower rates.
San Jose is now automatically transferring customers to their own accounting. Rates are a copy of PG&E with a token discount. Deadbeat customers will be transferred back to PG&E so they are left holding the bag.

What is your utility rate, cost per kWh? That can be compared to cost of system amortized over say 10 years.

Batteries-optional hybrid inverters, especially with current transformers for zero-export, would be the most flexible.
I'm not up on the selection of such products, but at least some subsets of that feature set exist.
The simplest functions as a UPS, either passing grid through or generating power from PV and possibly batteries, but that wouldn't be good at letting you use PV and still run appliances. Grid-interactive, syncing inverter to grid so all PV gets used, is what you want.

For larger capacity, I went with separate grid-tie inverters. The battery inverters were added later. Very capable, but not inexpensive for the brand I used.

 

[John Simson]

While still recovering from the holidays, I can answer only the questions that require no calculations! kWh cost is $.1771 for the first 1,000kWh. There's a Power Access Charge Tier 2 of $15.80 and $17.63 tax. Tier 2 cost is somewhere around $ .235 - significantly higher. I rarely go into Tier 2, but sure did this summer! We are usually in a cabin in the woods for alot of this time.

I'll post my calculations when fully recovered. Thanks for the help.

 

[Hedges]

If you can get net-metering, credit for generation same as price to purchase power, go for it.
With grid-tie PV you install yourself, will probably break even in 2.5 years.
You can select equipment that will support battery backup as a future upgrade, if you want it to operate during power failures.

 

[John Simson]

All right. I'm stoked! But, I've learned a lot. I'll go forward carefully. I already "stopped buying stuff!"!

 

[Hedges]

All right. I'm stoked! But, I've learned a lot. I'll go forward carefully. I already "stopped buying stuff!"!

First stop is regulations/codes for permit of grid tie.
That will specify what inverter features are required, what sort of shutdown and disconnect, where to be located. And how panels may be positioned on the roof if they're going there.

Your annual consumption and a website estimating production for your location, orientation, slope of panels will let you calculate array size.

Back when my utility rates varied 3 or 4 to 1 depending on consumption, and panels were expensive, offsetting just the higher price tier consumption gave the best return.
Today with your high tier rate being maybe 25% above low tier, and PV costing a fraction of utility rates, it is good to install excess if possible, cover future use and avoid ever paying utility rates that are 4x your cost to make power. If what you're allowed to install is determined by your utility bills, you could just make sure you have a high enough consumption one month to justify what you want to install.

 

[John Simson]

Yes. By my calculations (which were quick and need to be verified) I can put panels on my best roof for solar to produce approximately twice of what I presently need. But, this best roof is west facing, luckily very low slope and I'll have to figure in how west facing effects power production. I contacted a building inspector who is incredibly helpful and patient and verified that my placement of panels will be up to code. I have a big roof and could put panels on my east facing roof, but it has quite a bit steeper slope. I'm planning on a south facing addition in years to come. This home is great for viewing our valley, but stinks for southern exposure. So, I can start with twice the production (if my rough calculation is true), move toward more electricity vs. gas use (heat pump, water heater, cooking) and by the time all that is in, put solar panels on the new south facing roof. I'm about to publish my first book, so bucks should be rolling in . I'm sensing that I can talk with this building inspector to make sure that I am on the right track for inverter features and disconnect, etc. Are these guys meant to be actually helpful? It sure seems like it.

 

[Hedges]

I think city permit and inspection personnel are often pro-energy conservation.
The problems I run into is when by-the-book for some permit types requires extensive drawings and documentation of existing structures.
Rooftop PV is fairly expedited. In the past I did simple layout drawings and a line drawing of circuit from invertor vendor. Haven't done one in a long time.

You may be required to have an inverter with "Rule 21", recent UL 1741 updates for grid support. You may be required to have "Rapid Shutdown", a module per inverter (or some are per 4 inverters) to isolate them for low voltage when a switch is thrown.

Micro-inverter per grid takes care of those requirements. I like high voltage string inverters (I use SMA Sunny Boy); new models support those features with an extra box per panel. That reduces or eliminates the price advantage it would have had. But Sunny Boy works well with add-on battery inverters.

At one point I had to have a visible blade disconnect in AC line between inverter and breaker panel.
Now, utility considers that they could yank the meter (leaving you without power) if they had a concern about unsafe backfeed.

The size system you can install depends on breaker panel busbar rating and main breaker size. Center-fed panels (main drives middle of busbar) usually can't have PV installed. Utility may allow a tap off the meter, by means of an adapter.
A photo of your panel would provide insight, and the model or amps rating (label inside, under the cover where wires and breakers are) would have the data.

 

[mandrews44]

I built my own, small, whole house UPS / non-tie system that I can generate up to 8kw a day.. I used Raspberry Pi's and ODroid-H2's for server and UPS power monitoring. Using a doorbell transformer, full wave rectifier and an ads1115 hooked to I2C to monitor grid voltage and it gives me < 8ms reaction time. Most times we don't know the grid is out until we hear the generator start up. My last project was to build a generator quiet shed using rockwell insulation that makes the 4kw generator quiet enough that we barely hear it in the house. I also invested in 4 400ah LIFEPO4 batteries, (2 home built) for times when I can't run the generator, which is automatically started when the grid is out more than 10 minutes. @Hedges is right on the money when it comes to grid tie systems. During a power outage, you are sitting on all that power that you can't use. It was a fun project to build, one day I just might post pictures.. :D

 

[John Simson]

This is getting fun and I understand a little bit of what you are talking about, mandrews44. So that's pretty good ! I have an Ultimate Power pure sine wave inverter model 0612 - 600 watt with 1800 watt surge. I will have two or three panels hooked up to this with a controller and two 1000MCA deep cycle batteries. It'll start up my big refrigerator and just one panel keeps it going and the batteries charged. This is good for experimenting and for my off grid cabin later. I can go off grid or on grid or hybrid, but need to get permitted. I need to decide which is best. It seems like a hybrid system is looking good now. LA doesn't have many power outages, so I'm not worried about that. A few panels on the side of my south wall will keep me going during a long power outage - and I have a generator.

And yes, post pictures. I'm interested. I started with a 1500 watt APS, and I was about to use it when I found the inverter.

Hedges, I've attached the pictures you requested.

Yes, I am required to use Rule 21 specs. It's no big deal it seems. No more expensive or anything. The inspector said to submit plans and once approvals are in - then buy the equipment. Saves one from dreadful surprises!

Thanks again!

 

[Hedges]

Looks like the 125A breaker top left is the main.
120% rule would mean you can install a 25A breaker for PV, would go bottom right.
25A breaker with 80% continuous means 20A max from an inverter.
240V x 20A = 4800W, call it 5000W.

Here is SMA's offering:

Discover the Sunny Boy 3.0-US - 7.7-US | SMA America

Discover the Sunny Boy inverter 3.0-US - 7.7-US ► PV performance optimization with SMA ShadeFix ► SMA's SunSpec certified shutdown device

www.sma-america.com

If "Rapid Shutdown" is required, they show this device:

https://files.sma.de/downloads/SMASunSpecRSD-DS-en-18.pdf?_ga=2.184790313.146752054.1609806538-621369231.1589916091

I've seen others which control 4 panels rather than one, would be more economical. Don't know whether those are compatible.

 

[John Simson]

Great! Thanks. But, do you mean that this is a 125 amp service? That's tiny by today's standards. I have a 200 amp service at my little cabin in the woods! I sure don't need any more than 125 amps, but some houses around here (OK, they are at least twice as big as mine and have home theaters and stuff) must have 400 amps services!

 

[Hedges]

Looks like it. Is the meter in the same box?
Schematic on label shows main breaker top left.
Breaker table shows the 125A breaker as "In"

200A is common, good especially if electric heat.
My sister's house had 30A, I upgraded 30 years ago to 100A, think she upgraded to 200A.

400A equipment gets expensive.

If you're happy with 125A service and 5000W of PV (probably average 25kW to 30kW/day), good enough.

If not you can get a permit for a panel upgrade, maybe install a new Square-D QO 225A panel next to this one and the utility drops new wires to it.
With 225A busbars and 200A main breaker you can have 70A PV breaker, 56A backfeed for 13.4 kW PV. Or 150A main breaker for 100A PV.

 

[John Simson]

No, I don't need any more, my neighbors be damned! Yes, I replaced my 30 amp cabin's service with the 200 amp one. Had no idea that 30 was probably fine, just wanted something new and I enjoyed the work!

 

[John Simson]

The first step of my home solar plans is to construct a base for my panels on the side of my garage. I've bought the EMT (electrical metal tubing) and plan to use structural pipe connectors from Maker Pipe to assemble the thing. It'll sit above my garage door on the south side at a 30 degree angle. Two structures, one for one 280 watt panel, another for two panels. I can take these panels with me to my cabin in the woods, secure two to a small roof, and the one on the structure for one panel on the cabin's wall. Has anybody built such structures? Any advice? Some other pipe connector used?

 

[Hedges]

EMT is thinwall conduit, not very strong. I was going to say the structural pipe connectors are for heavier pipe, but I see they have connectors for EMT:

Maker Pipe | Structural Pipe Fittings for DIY Builders

We empower you to make something you love. Whether you're a beginner or DIY pro, our products are a great fit for your project. Learn why.

makerpipe.com

For my large array mounts I used rigid conduit, also the somewhat thinner IMT.
I also have a structure with chain link fence for part of it. This one didn't have any top pipes so I used IMT. I think the fence posts are a bit thicker than EMT.

To use EMT, don't count on much torsional strength; they are easy to buckle. Make diagonal braces so everything is triangles.
Channel struts may be useful. I've used bolts through holes in panel frames into slot nuts in some cases. Unfortunately most channel hardware isn't particularly corrosion resistant and the ones that are, are expensive.
I use stainless U-bolts to hold angle aluminum brackets (for unirac rails) or channels on pipes. But for EMT, easy to kink and weaken. conduit clips for struts would avoid the force concentration of u-bolts but aren't particularly strong.