Design outfit for zero export w storage, integrate into existing Grid Tied PV

[bjbjustin]

Been looking all over but coming up with zeros - figured I'd ask ya'll experts for help on a referral.

Is anybody aware of a design consultant which can layout a zero export storage system...that integrates with an existing Grid Tied PV?
(Utility in San Diego wont allow existing system expansion without changing rate structure - Net Metering 1.0 to NEM 2.0/3.0/etc, no question we want to stay on NEM1.0)

Supplementing the existing PV with Zero Export & Storage - everythings is gravy - but all the info I've been able to research doesn't take existing PV arrays into consideration. I'm sure with enough time on this forum, and plenty of questions I'd eventually get there...but kids, life, work - I don't think wife will give me a free pass to knock it out over a couple years.

Install isn't the issue, it's the initial design and component selection/wire sizing etc...just like in my day to day work, I can have a designer layout a chiller plant based around my specs quicker than I could for a consultant fee - shortening a projects timeline is well worth every penny. The few design outfits I have reached out to weren't quite up to the task (one even said 'hmm, contact Tesla, they'll help you out.' oddly enough I did, no surprise they didn't jump at the opportunity to supplement their existing system with a competitors offering) Any referrals are greatly appreciated - already diving into the wealth of knowledge around systems and componets that weren't around even 10 yrs ago - all hail solar!

 

[RCinFLA]

It is the existing GT inverter that will most likely to be the issue. Check to see if model has the add on option to accept zero export kit.

The GT inverter must must have variable output power capability or a load dump. The kit amounts to adding a current sensor and line voltage measurement with phase info at the main breaker grid input with a controller box that determines incoming power and as it approaches zero incoming grid supplied power sends a signal to GT inverter to cut back production so no power push is made to grid.

It is possible to make any GT inverter into a zero exporter with a load dump equipped controller. Dumping excess PV power to a hot water heater is a good option. If the hopefully rare situation where load dump is max'd out it would just relay disconnect GT inverter.

 

[Hedges]

I don't think OP wants to convert existing GT inverters to zero export.
He says he wants to add move PV, and use storage to avoid export.

I don't think that is what he actually wants. Rather, to let 100% of existing PV export, and have added PV supply the house plus charge battery, but not export anything.

I think he might get away with a bit better. Let's say existing NEM agreement is for 5kW.
Add more GT PV, coupled with current transformers and limiting to not have any export in excess of 5kW.
That would actually let added PV export, if existing PV falls short of exporting 5kW.

Batteries can be part of such a system. However, I think they will cost more than value of power they will supply.
I think it is cheaper to just buy power from the grid than to use batteries.
I also think it is cheaper to install excess PV and curtail unused production, rather than buying from utility (up to a limit, some 66% or 75% of production wasted.)

 

[bjbjustin]

Spot on (the 2nd assessment).

I want to leave the existing system as is - GT, export excess under Net Metering and 'spin the meter backwards' Although when summer comes around, its almost a net zero. I understand we're not always going to Work From Home (at least not for the next 15 yrs), but as it stands now...my system is undersized by about half.

In a couple months we'll be adding an EV, and I expect more conversion to electric...likely swapping stove for induction, and was looking to ad patio heaters but if I can forgo gas for electric, without Sempra/SDG&E making jackpot noises every time they turn on - then lets de-carb it up.

My NEM is for 3.0 kW. I'm allowed to add 1.0 kW - but - I'd have to swap my inverter as it's maxed out...that doesn't payback.

I'm in San Diego, home of 2 things when it comes to solar. 1) The most expensive utility rates in the US (HI & NY fight for that honor), and 2) SDG&E, a virtually criminally negligent IOU. I have the "pleasure" of working with them closely in my day to day capacity - and top to bottom, they are out of touch...with everything. And at this point, I'd almost rather spend $2 on PV than give SDG&E $1. They're that bad. But their crazy escalation, it'll end up paying back at even a $2:$1 ratio.


- Ultimately, I'd like to keep the 3 kW PV array. Add an additional PV array with a battery storage system, but keep just that system behind the meter' and zero export. What I'm unsure of is how the 2 systems would interact, how they'd be tied together/interconnected (at all?...or are they landed on the circuit breakers like a normal circuit?). And then of course - how do I keep the Energy Storage PV system from backfeeding the grid (inside the inverter, an exterior controller, a controller on a different part of the system? ...along with all the other fun stuff like wire sizing, layout, safeties, fusing, disconnets, etc etc. Disconnect in the event of a power outage, or automatic transfer switch so we can still use solar/battery backup?)
If there's a design outfit, solar supplier, or hell - even savvy inverter manufacture I'm all ears. I'm definitely not opposed to learning, and have done so throughout my lifelong journey & career in engineering and construction...but GD, I can see the rabbit hole I might go down with analysis paralysis...



Rough sketch
- With 3 kW I produce ~ 5 MW/yr. Utility bills show I burn 3.8 MW/yr...(roughly 50%, esp if you take into account I was changing over our AC system to Heat Pump VRF in the Spring and didn't go live until September, so I'm missing a month or tow of cooling...and we haven't seen heating...but SD is pretty mild) Adding an EV (which I'm sure will end up being 2 within the next 5 yrs) at 40 miles/day and 2.7 kW/mile - our system is undersized by 1/3. So...if 3kW is enough for 1/3...then I'm in the ballpark with 7 kW system.

 

[Hedges]

Except for DIY batteries, use of a battery to store electricity will cost more (by the time battery is worn out) than buying the same kWh from your utility. Consider the price of a battery, divide by (capacity x claimed number of cycles x depth of discharge for those cycles). Commercial lithium batteries I calculate $0.50/kWh, and that's only if they last that long.

If you added a sub-panel fed by your main one and moved loads to it, you could add zero-export PV system to that panel, with the current transformers on wires feeding sub-panel. That would only supply loads on the sub-panel.

If you could move connection of existing PV system to before the main breaker by adding a supply-side tap, then additional PV could go to main breaker panel with current transformers between main breaker and the supply-side tap.

But best would be a grid-tie PV inverter that can be configured for either zero-export or 3kW export (maybe you can get away with 4kW export if allowed to add 1kW). That wouldn't require rewiring anything existing. The current transformers need to fit on input to main panel. Does it have accessible wires between meter and main breaker? Or, does it have exposed wires in the utility drop from overhead lines to your roof?

Assuming you can attach current transformers somewhere, just need to select a GT PV inverter which can use them to limit export to target kW value. The inverters I use are SMA Sunny Boy, which don't support that directly but use communication to a separate controller and a 3rd party measuring device.

If you can find a hybrid inverter (ideally batteries optional) with this feature, you can hang it off your existing panel and get the added benefit that it can disconnect from grid during power failures and feed a protected loads panel. That gives you backup for some loads.

Do you have a roof orientation available different from where existing panels are? If so, production peaks at a different time, so you can backfeed more kWh without exceeding 3kW limit.

If you do put panels on the roof, probably required to have arc-fault protection (built into most inverters). Also rapid-shutdown, a box per PV panel (not needed for microinverters.)

I think Enphase offers current transformers and uses powerline communication to control inverter output.
Growatt has export limit according to the following link

Export Limitation Solution-growatt - Growatt

Export Limitation Solution-growattexport limitation,solar system on grid,power solar

growattinverters.com

 

[bjbjustin]

Thx for the detailed response...you'd be surprised on the cost of energy storage in SDG&E. As it stands now, it's $0.41 per kWh. And that's not reflecting the 2 rate hikes approved but not yet transitioned...and not to mention the other rate hikes they're lobby for. With a few incentive programs, solar + storage actually ends up being cheaper than buying it from the utility. If you factor in the historical rate increases over the last 30 yrs from SDG&E of 6%-10%...solar PV with storage actually becomes a good investment to shelter from future increases. Plus, on the proforma there's a line item I have to account for 'cost to user to not send $$$ to SDG&E'. I'd actually pay money to not give them a penny, its worth at least 10% of the project cost.

There's enough here I'll dive into this tonight....trying to run different configurations to ground with a short day at work (minimum day for kids at school)...more effective if I concentrate on making a dollar rather than saving, creating, and storing a kW. Ha.

Long and short - we do have a subpanel, with part of the VRF system on it. Also has the hot tub, and would likely get the space heaters...and no problem dropping in the future EV charger....but would need to account for the draw of the charger & ability of batteries to supply the amp draw. Doesn't help if the sub panel is packed with high draw loads, and the battery system + inverter aren't able to account for the rate of high draw and just kick over to grid power.

Power is delivered to the house via sail, so adding CT's isn't a problem...there's likely space in the panel as well...been a while since I pulled off and took a close look but a few years ago we swapped to a 200 A panel and it has a substantial amount of space vs. what was existing.

It feels like one of those strategies above would make sense for our application...also trying to take into account utility will likely change the legislation and invalidate the net metering 1.0. They tried to previously and lost. They also sent out an email 'hey, nothing to worry about here, hope everything is well. (btw, unless you read to the bottom of this email and elect NO, we're going to automatically transfer you to NEM 2.0...and once you do that there's no switching back). So anyway, hope all is well, thx from SDG&E! You can understand the pure disgust residential customers have for this utility...it's not just the commercial side. But at least they're consistent.

 

[Hedges]

Thx for the detailed response...you'd be surprised on the cost of energy storage in SDG&E. As it stands now, it's $0.41 per kWh. And that's not reflecting the 2 rate hikes approved but not yet transitioned...and not to mention the other rate hikes they're lobby for. With a few incentive programs, solar + storage actually ends up being cheaper than buying it from the utility.

Do you mean there's a spread of $0.41/kWh between credit for exporting power and charge for buying power?

Here are my estimates of battery cost divided by kWh of lifetime cycling (battery inverter not included):

$0.50/kWh AGM
$0.50/kWh big-name lithium
$0.25/kWh FLA
$0.05/kWh DIY LiFePO4

off-brand and repurposed used lithium batteries may approach DIY.
Everything has a cost. Including labor, unreliable products, and top name UL listed batteries that burst into flames and burn the house down.

If you can, plan for future big battery bank but start with small or no battery.

 

[bjbjustin]

With NEM 1.0 - If we purchase a kWH, it's $0.41. We only get paid on the commodity rate for production if it's overproduced, which is effectivly zero (a few yrs back SDG&E was actually paying negative rates for consumption...but they make it all up on the demand). So, for almost all of your power its about $0.41 kwh - until you hit the +400% of baseline (which is an abritray number, based on not your baseline, but what SD&E defined as average, and generally the industry accepts a a completely made up and substantially below what the average rate of consumption is). Adding an EV will bump above the 400% baseline, and then it can be up to $0.61 kwh, but they also have a speperate rate which can tack on an extra $0.20. Yeah, they're that screwed up.

It'll likely be balancing the additional consumption with what keeps us on the edge of that 130%-140% borderline. Hitting the 0%-130% baseline is insane as it's only 200 kWh. Using an EV less than 20 miles a day alone will bump it out of that baseline, no sweat.


Given the tax incentives, the low cost HELOC, and what I expect our savings on EV to be - I'm surmising it'll make sense for partial storage, with our spendi still landing in the 130%-400% baseline tier. First off I have to finish building the pergola that I tore down which has a roof dimension of 12' zx 33'. Project isnt taking of now...but it'll be right around the corner as in summer time work gets so busy I won't have time to dedicate to a solar project. Already got the free pass with backyard COVID renovations and converting our Gas/Electric to Heat Pump VRF...I'll crank out the numbers for partial storage an optimize around that.


Definitley ping you here in next couple weeks...the framework is starting to clear up, just need the actual implementation plan & line item diagram to procure materials. And then just let SDG&E keep raising those rates, just like taxes. Jerks.

 

[Hedges]

At $0.41 or $0.61/kWh, I don't think most batteries can compete. But it looks like DIY LiFePO4 can.
Is an EV rate offered? You might be able to add a second meter for EV charging with low rates at night.

Other than that, extra PV with zero or capped export. If that costs $0.05/kWh, you only need to use 1/8 or 1/12 of production to break even. More than that and you're saving money off the bill.
How much of your consumption is when the sun shines? A/C is the easiest to match with PV.

Buy two EVs, and alternate charging one during the day while driving the other?
Do you get any deals on charging at work? V2H

 

[hellosf]

Thanks for the conversation and advice. I expect that many folks (myself included) may soon start asking similar zero-export questions once NEM 3.0 is finalized in California.

I believe that there may soon be a large CA market for grid tied, zero-export customers based on the proposed CPUC plan for new solar installations that may see a monthly fee assessed as non-bypassable charges (NBC) on all customer’s gross consumption, which would include assessing NBCs on both imports and consumption behind-the-meter.

These changes would add a proposed $0.05/kWh to all customers, whether they own solar or not. The charges would even apply to power generated by the customer’s home solar system, which is unconventional considering the utility does not have ownership over the solar array, and did not invest in it. While this revised NBC proposal may be superior to the previously proposed "solar tax" of $8 per kilowatt/month to cover the state’s cost of maintaining the grid, it still makes adding solar less economical.

I am also not sure how zero-exporting systems will be permitted in most jurisdictions in California. Can or will they be treated as a separate off-grid systems by municipalities?

We find out soon what the CPUC has in mind as they recently reopened the NEM 3.0 proceeding with comments due by tomorrow, 6/24/22...

 

[Hedges]

At $0.41 or $0.61/kWh, I don't think most batteries can compete. But it looks like DIY LiFePO4 can.

The prices and cycle life I've recently seen for "server rack" batteries (e.g. from Signature Solar and others) appear to be around $0.05/kWh amortized over 16 year life. If they do achieve that, could help address the costs of new solar-unfriendly PUC terms.

$0.025 to generate power, $0.05 photon tax from PG&E, $0.05 to store in a battery, $0.?? for suitable inverter to run off battery and manage power flow. It probably still beats off-peak utility rates (about $0.25/kWh), definitely beats on-peak (about $0.50/kWh).

The $8/kW/month was almost exactly $0.05/kWh

Wild card is how they determine kW capacity or kWh on the customer's property. Utility personnel get to enter without a warrant? Satellite photos, same as we use to determine enemy capabilities? Some installations meter solar production separate from consumption (including self-consumption), but most existing consumer installations don't have that.

Anybody got a tar pot and some old chicken feathers?