Off grid financial model?
Curious if someone here knows of a financial model that evaluates cost of energy in an off grid scenario for a single family home. A spreadsheet was what I had in mind.
I can write my own, but if I can avoid reinventing the wheel at first that might be nice.
I’ve glanced through the site and I’ve found numerous articles talking qualitatively about the perils of off grid living, but nothing yet to a financial model (which isn’t surprising given the challenges). Let me just say that where I live and work (advising others on Energy efficiency) has some different climate and utility cost factors that make the model out, so I’m curious to see how close we are to the edge of off-grid being at cost parity with grid-connected.
(And yes, off grid comes with a litany of potential non-financial compromises– I’m just curious and many people I talk to are as well)
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Luke,
Back in the day -- let's say, 15 or 20 years ago -- the writers at Home Power magazine (according to my memory) said that homemade electricity was at least 10 times the cost, on average, of powerline electricity. Some Americans were spending only 10 cents per kWh back then, while off-gridders had an average cost (including periodic battery replacement costs) of at least $1 per kWh.
Every single analysis I've seen shows that off-grid power is expensive.
Also, everybody lies. Everyone replaces their Honda generator and batteries more frequently than they are willing to admit.
thank you Martin
as context, the electricity rate for when my clients are using the majority of their electricity is $0.82/kWh (and maybe rising in the coming years)
So that's causing me to ask the question about solar/storage cost parity and sharpening pencils.
of course, there are myriad other load shifting, conservation, and efficiency measures to consider. And the nuisance factor of managing your own power system is... err.... non trivial.
as it currently stands, grid defection around here is still rare, and most of my clients are grid connected and mitigating costs with solar and storage
however, there are significant signals that grid connection fees will increase substantially for these systems. Recently, our utility proposed a $16/kw monthly interconnection fee for all grid tied solar. it was not approved this time, but they probably haven't given up on that.
does this context make the question seem more reasonable? if not, that's also interesting to hear. maybe we're still not in the ballpark of having grid defection on the table.
If the utility offers net metering then grid-tied solar is a no-brainer almost everywhere. What's clear is that the economic model of net metering is unsustainable, the utility will go broke if they have users who don't pay them anything. Here's where I think it will land: your power bill has two parts, for generation and transmission. Net metering will apply to generation but not transmission, because when you import or export power you're using the transmission facility. Power generated and consumed onsite won't have generation fees. I also think it would be reasonable to have a monthly connection fee for the utility of being connected to the grid, although $16/kW seems really high.
As of April, net energy metering is mostly dead here. That is, the the value of exported generation has reportedly reduced by 75% (as you might expect, I'd like to build these factors into the financial analysis).
Electricity delivery charges are roughly $0.45/kWh. Generation charges range from roughly $0.10 to 0.30 depending on TOU
in a scenario where a 5kw system is billed $80/month just for being grid tied (which is, I should emphasize, not the case yet), it strikes me that grid defection should be on the table. furthermore, the utility is planning to rate base another roughly $2 billion in transmission and distribution for more utility solar. if that gets rolled into non bypassable distribution charges, then nem becomes even less valuable...
to be sure, there are plenty of other shoes to drop. for example, it looks like there are going to be income based fixed charges coming to allay some of the equity issues in this rate structure.
Agree with Martin, although I would characterize it as more self-delusion than lying.
The question I would ask is what do you mean by off-grid? At one extreme, do you mean relying entirely on energy produced on the property -- solar, wind, wood? Or do you mean not having a utility hookup and instead relying on burning fuel -- propane, diesel, gasoline, kerosene, coal, etc? For the sake of discussion let's call the first one "pure" and the second "impure" (without imparting any value judgment). One of the things you find as you get increasingly pure is that it's not an apples-to-apples comparison. If you were going to be very impure, you could just have a diesel generator. The experience of living in that house wouldn't be that different from living in a grid-tied house. At the other extreme, heating exclusively with wood is a very different experience from just being able to set a thermostat to get warm. So one of the big factors with solar is that it's unreliable. How close you are to the experience of grid electricity -- where you just flip a switch whenever you need power -- is determined by how much storage capacity you have, which is a big driver of costs.
Great question DC,
I don't think there's any purity that needs to enter into this just yet. This is all about eschewing utility hookup-- dollars and cents (and hassle).
The purity element for my clients is always a conversation I have with them. I think your scare quotes are appropriate. That is-- I can see why fossil generation is seen as 'impure', but not how solar and batteries are "pure".
As for a diesel generator, that's probably not on the table for long periods of time for most of the sites. That's because of the noise factor and the neighbors. Most of the projects are in-town, but even the rural ones are in locations where the neighbors can hear most everything. So a 24/7 generator wouldn't just be annoying for the client, but maybe annoy the neighbors enough to call the code enforcement. But an intermittent/quiet system is definitely on the table.
I'd appreciate your take too-- given the cost context (or the scant few tidbits I dangled there), would you think it's at least worth a more elaborate workup?
I think it would be a fun and informative exercise. I would do it as a Google sheet so that it's easy to share and have multiple editors. I'm willing to help with it.
In terms of inputs to the sheet here's the kind of things you'd need to gather:
Environmental factors for your location:
* Annual heating degree-days
* Annual cooling degree-days
* Annual solar insolation
* Average monthly temperatures
* Average monthly solar insolation
Cost factors for your location:
* Gallon of diesel/heating oil (for me they're the same)
* Gallon of propane
* Gallon of gasoline
* Ton of coal
* Cord of wood
Economic factors
* Cost of funds -- what it costs you to finance capital costs
* Anticipated inflation rate
* Expected lifetime of capital equipment
Technological factors:
* Efficiency of burning each fuel
Lifestyle factors:
* Number of occupants of the house
* Maximum acceptable temperature in summer
* Minimum acceptable temperature in winter
* Minimum acceptable availability of electricity
* Hot water consumption per person per day
Then you put in your choices:
* Fuel/technology for heating
* Fuel/technology for cooling
* Fuel/technology for heating water
* Fuel/technology for cooking
* Fuel/technology for lighting
Outputs:
* Capital cost
* Annual operating cost
* Annualized capitalized cost
I think what you'll find is that the cost of the electric hookup isn't so bad after all.
aww DC thank you!!
as you saw in the original post, I was hoping to not reinvent the wheel here-- I'm sure there's a financial analysis out there somewhere. but honestly, reinventing the wheel happens all the time, and literally reinventing the wheel that has happened repeatedly throughout history to useful ends. I think for this question, it would be an educational exercise
for order of magnitude HDD and CDD are roughly the same --1500
I'll start my own spreadsheet and if I get time to actually work something up, I'll share it with you to proofread (which it will need extensively). I'll have 8760 consumption data,so I'll set it up accordingly
* Size (in amp-hours) of needed battery storage, remembering that most batteries should never be discharged below 50% of capacity.
* Cost per amp-hour storage capacity of your battery system.
* Number of years you expect your batteries to last.
* Labor cost to swap out batteries.
* Cost of your fossil-fuel-powered generator (needed for cloudy weather).
* Number of years you expect your generator to last.
Deleted
I’d try to include some estimation of resale value too - I assume you’ll get some of the value of a grid connection back when you sell, and probably have a tougher time selling an off grid house.
Wow - $80/month to have your solar array grid tied coupled with lowered net metering reimbursement. Maybe folks in your area should just stay on-grid, but tie their solar into a battery at the house, without interconnecting the solar to the grid. Self-consume via battery management as much as possible.
In the US, the 30% tax credit on batteries might make this scenario attractive, esp with $0.55-$0.75/kWhr electric rates that you have.
Last time I ran the #s in my Zone 5 area, 20 year life solar cost was $0.12/kWhr after tax credit, and li-ion battery lifetime (5000 cycles) cost was $0.20/kWhr.
But as always you have to run the numbers.
Thanks Amorley,
Yes-- that's also a viable option. Indeed, the NEM structure seems to be (d)evolving to promote exactly that. But the set-up is adjacent to just disconnecting from the grid altogether. And so if a little honda generator can tide you over the cloudy months (which is May and June) then you'd be set. Easier said than done, but how much harder is it, really? (not a rhetorical question)
I've never lived off-grid and been responsible for the equipment, so no help there.
But if the choice was expensive on-grid vs expensive off grid electricity for the balance, I'd pick on-grid for the convenience. Setting up automatic bill pay for the electric bill, vs fueling and maintaining a generator makes it a no brainer for me. But I already have too much equipment to maintain in my life.
Off-grid is significantly harder. Lots of voltage checking, troubleshooting, and maintenance involved. Circuit breakers trip, and you don't know why. Did the inverter overheat? Are all the toggle switches on the generator in the right position? Did the water pump and the washing machine try to start at the same time? And so on.
Grid connection is simple -- if you have the option. Worth every penny. And it's greener.
"But the set-up is adjacent to just disconnecting from the grid altogether. And so if a little honda generator can tide you over the cloudy months (which is May and June) then you'd be set"
Not to pile on to what Martin has already stated, but these two scenarios are really not all that adjacent in that sizing and managing the system becomes much more critical and complicated when entirely off grid. You mention the 'hassle' of *connecting* to the grid, but compared to managing an off grid system, it is no hassle at all. (I don't live off grid but manage some off grid rental cabins).
With a good generator and a willingness to troubleshoot issues and diligently refill with gas, it's certainly doable, but I don't see the benefit of running a personal genny unless you're really remote. Why use a small inefficient gas genny when the grid is there in all its glory?
This isn't to say don't run the analysis. I would maybe suggest running two different scenarios though: one completely off grid, and the other with just an off grid solar system while retaining a main grid tie.
It would also be interesting to consider how battery bank size could be minimized by strategic load dumping. Such as running water heating and maybe space heating with a preference for when solar is actively producing. This is more realistic when grid tied since if the sun happens to not be shining when you need to heat water, you can choose to draw from grid rather than an undersized battery bank.
Maine Tyler--
I agree with you. The 'hassle' I meant was indeed the emotional and financial cost of managing your own system, which is what you're arguing. I haven't done it myself, but I know it's a big deal-- especially when it's Christmas morning and it's cold and the lights are out and all the kids are crying while you're outside trying to troubleshoot the bleeping generator.
As for the completely off-grid vs. grid-tie: Yes-- absolutely.
Strategic load dumping-- also great idea, but I've gotta get a version 0.1 working first.
All the hesitation expressed here I agree with. The reason I'm asking is that all the literature previously mentioned (namely on this site) is that off-grid costs roughly $1/kWh-- that was a number cited 10 years ago. Now that the grid cost is getting close to that, and PV and batteries are coming down in cost, there's a 'parity' at some point. Are we at that 'parity'?
>"he reason I'm asking is that all the literature previously mentioned (namely on this site) is that off-grid costs roughly $1/kWh-- that was a number cited 10 years ago. Now that the grid cost is getting close to that, "
Where are you that grid power is $1/kWh? I'm not aware of it costing that much, even in some crazy expensive areas like some islands in the Caribbean. Somewhere in the 15-20 cents/kWh "all in" is more typical these days in most areas.
I've worked out solar to be around $1/watt for the upfront equipment, without installation, and without batteries. Obviously the operational costs per kWh are pretty low, but not quite zero when you include maintenance. If you add battery storage, you add a lot more issues, as well as both up front and maintenance costs.
I've often advocated in these forums for what I call "peak shave" solar, which means size the system for somewhere close to your typical peak loads, and run that way as a grid-tied system. This way you don't need battery storage -- you run off the grid for heavy loads, cloudy days, night time, etc., and you don't need to worry about net metering being available because you're not trying to sell power back to the grid. Peak shave systems can save you money (I've worked out payoffs for DIY systems to around 3-5 years or so), and don't depend on any special rate structures from the utility to be justifiable. Obviously such a system isn't going to work for an off-grid location, but for a grid connected home, it's a pretty good option.
Bill
here you go Bill
see on-peak bundled rate. this is the rate that I'm on BTW
https://tariff.sdge.com/tm2/pdf/tariffs/ELEC_ELEC-SCHEDS_TOU-DR1.pdf
0.83325 $/kWh
general rate case has been submitted to increase that.
it looks like there will be some 'relief' on the horizon through lowering the volumetric rates and replace them with income-based fixed fees.
to wit-- if you make $100k a year, then you'd get a fixed charge on your utility bill for something like $100/month (number VERY much TBD), but lower in $/kWh
If that number ends up being $500/month (in a soak the rich kind of model--i just made up that number though) how would that change the conversation with your wealthy residential clients who might consider defection?
Utilities have to be careful with pricing like that. Electricity that expensive, even a simple zero export PV setup is great ROI. I would definitely go for this as start.
This does mean some wasted PV capacity but there is no batteries needed.
If you want better, poor man's battery in most cases is an oversized hot water tank. There are controllers on the market for running these so it can take excess PV to heat the water.
Luke.... wow. I think those rates are based on a "soak everyone" pricing model. I had some work with the electric rate on St Croix in the US Virgin islands some years ago, and it was around 50 cents/kWh. They're unusual compared to the mainland since their power generation is primarily sourced from diesel generators, which supply the entire island -- not a very cheap way to generate power, but about all that is practical when you have to ship in fuel to an island. That was, at the time, the highest utility rate in the US.
You appear to have around 83.3 cents/kWh as your on-peak rate, from 4pm to 9 pm everyday. That's 5 hours a day at that rate. Off peak drops down to about 52 cents/kWh from 6am to 4pm and again from 9pm to midnight, then the remainder (midnight to 6 am) is their "super off peak" (I haven't heard of that before) at about 35.5 cents/kWh. That's better than 838.3 cents all the time, but your entire day worth of rates is so much higher than typical, you're in spendy power territory for sure!
My rate here is around 25-30 cents/kWh for on-peak, which is 11a-7p weekdays. The rest of the weekdays and all day on weekends is off-peak at around 11-12 cents/kWh now, and those numbers are after all the different pieces of the rates are added in. Looks like your rate is around 3-4 times higher than ours.
Peak shave won't help you as much, since solar is dropping off during that highest rate time of day, although you could oversize your system to compensate. Remember that with solar, you do not HAVE to send your excess power back to the grid, you can just not use it. The downside here is the need for more solar panels that you otherwise would have for a given kW level for your system.
I'm not a fan of income based electric rates, I think that is a sort of moral hazard situation in terms of overall use efficiency. I can see ridiciulously high electric rates changing the economics of the small scale residential solar systems, but there will be unintended consequences to that in terms of maintenance.
BTW, I don't really work with "residential clients", wealthy or otherwise, outside of people who know me from my commercial work. My typical commercial customers don't have any choice but to use grid power due to the scale of their power consumption. Many of my customers have an average load of over a megawatt, 24 hours a day, every day, all year long. They don't typically have enough land to generate a significant fraction of that in terms of solar power, although they do sometimes try to do some.
Bill
Ha one of the few downsides of living in a place with wonderful weather is that the annual electricity usage per household is really low, jacking up the distribution prices. It's much hotter and much colder where I am, so we crank the AC and the heat. As a consequence, our total rate is $.14/kwh.
Also, Luke, Southern California is in climate zone 3 - I know California has their own special system but usually climate zone 7 is understood as parts of Minnesota and Alaska.
@Paul
(sigh) yes-- I'll cop to being a little disingenuous about my climate. When I created the profile (a long time ago), I was in a peak of frustration after having some question I had at the time dismissed and discounted due to assumptions about my climate. Climate Zone 7 is where I am according to my state code, so it wasn't that I was lying either. But yeah... you're right. I'm in CZ 3 in San Diego, so I could be in Borrego Springs, Mount Laguna, or La Jolla.
“Recently, our utility proposed a $16/kw monthly interconnection fee for all grid tied solar.”
My guess is the engineers that work for the power company did the math and proposed a price equal to the cost of ownership of the home sized batteries on the market today. Seem fair enough to me, they are providing a service and the market has set the value of that service.
Did they really propose 16 dollars a kWh or 16 cents a kWh?
Walt
Walt it was a $16 per kilowatt monthly charge.
so a 5 kilowatt grid tied system would be billed at $80 a month, just a fixed fee. then exported electricity would be purchased back by the utility at some rate that was significantly less than the retail rate.
this latter aspect was retained in final NEM policy. we buy at $0.10-0.35/kwh, but sell back at $0.04-0.08
batteries did not play into this proposal, at least not explicitly. but you can see how the incentives for them change. a PV/battery supplying your home's electricity needs at 4-9m this summer will save you ~0.80/kWh.
Charging per kW of install solar makes sense as apposed to $16 per kWh consumed that made no sense.
I still think the $16 per kW each month is the math for what it would cost to own and operate a battery.
Buy at .35 and sell at .04 sound about right because you need to buy at the peak in late afternoon demand and sell early in the day when they have light demand. My guess is that is very close to the wholesale market pricing at those times.
Walta
"I still think the $16 per kW each month is the math for what it would cost to own and operate a battery."
I was skeptical about this, but the math bears Walta's point out:
7kW rated capacity li-ion battery with 13kWhr storage costs about $13-15k installed. Most come with 10 year or 5000 cycle warranty.
7kW x $16/month x 12 months x 10 years is $13,440.
I'm still trying to imagine the electric market dynamics there that make a utility with such high rates (both energy and transmission/distribution) willing to create so much incentive for customer defection. Super high solar penetration coupled with diesel peakers balancing the system? A shrinking market? Curious and curiouser...
Yeah, I've been trying to figure out where Luke is. Electricity is 0.82/kWh, HDD =CDD=1500. I'm thinking an island in a temperate place, maybe the Carolinas or Pacific Northwest.
Welp-- I'm now having a hard time finding where that $16/kW came from.
The number I'm seeing now is $11.09/kW (but it's indicated as 'illustrative'). I think they updated the number and it's buried in another part of this docket.
I'll see if this link comes through.
https://docs.cpuc.ca.gov/PublishedDocs/Efile/G000/M371/K711/371711892.PDF
"My guess is the engineers that work for the power company did the math and proposed a price equal to the cost of ownership of the home sized batteries on the market today."
I must be missing something. If a consumer pays X dollars to install a PV and/or battery system, what do those dollars have to do with the service the utility is providing? If they are asking for additional money equal to that already made investment (essentially doubling the cost of the system, if true), then they are double dipping and inflating system costs by 2 fold; minus the cost to service the interconnection.
It makes sense for the utility to charge for the service they are providing, but the service they are providing is the interconnection and associated costs, which as far as I can tell have nothing to do with the cost of installing a home generation system. What does the cost of their provided service have to do with the capital cost of the home battery/solar system? I don't see the relationship.
The utility can propose whatever they want to the utility commission, it's up to the commission to figure out what's legal and appropriate.
Clearly net metering changes the paradigm and creates a problem for the sustainability of the grid; if everyone were on net metering there'd be no paying customers to pay for the grid. What we need to figure out pretty quickly is what is a model that encourages good outcomes.
For example, which is a better model, a fixed monthly interconnect fee per unit of capacity or separation of generation fees from transmission fees, and only net metering generation fees? I would argue that the second one is a better policy because it incentivizes customers to align their consumption with their production. But I can see how utilities would prefer the first because it's so much easier to implement.
DC_Contrarian
Behind my question here is exactly the issue you're raising.
What if the Utility is raising costs for interconnection beyond what it 'costs' for people to do themselves. What if the grid gets so expensive (out of bad regulation, or plain-old 'rent-seeking' (see economic term)), that it starts to spiral down?
Are we already there where I am? Depending on whom I ask, the answer is sometimes 'yes', but I haven't seen the financial models to support this.
If the grid costs/policies promote defection (intentionally or not), I think that's a travesty
“If a consumer pays X dollars to install a PV and/or battery system, what do those dollars have to do with the service the utility is providing?”
Tyler the net metering crowd want to use the grid as a free battery they want to make more power than they use in June and use that power in January without paying any money. This idea is something that total impactable with physical batteries.
On a smaller scale they also want to make excess power on sunny days and bank it for use when they have several cloudy days in a row at no cost to themselves. This idea is doable with physical batteries but gets very expensive.
Daily they want to bank excess power in the daylight hours and use it at night again at no cost to themselves. This is possible with physical batteries today. My guess is it would cost more than $16 a month per kW over the life of the battery.
The net metering crowd also get very upset when they are forced to buy power at the retail cost and sell at the wholesale price.
In short the net metering crowd want to use the grid and pay almost nothing shifting all costs people that have not bought solar.
Note the grid becomes totally unmanageable as more people get solar.
Walta
"In short the net metering crowd want to use the grid and pay almost nothing shifting all costs..."
This isn't what I'm asking about at all. I get that the utility is providing a service (a "balancing/transport" service).
What I don't understand is what the cost of that service has to do with the capital cost of installing the home system.
The suggestion is that if I spend $8,000 on a solar battery system I am costing the utility $8,000? Can you elaborate on that logic, if there is any?
Or is the idea that its just an arbitrary way to put a semi arbitrary price on it?
So long as your system relies on the grid to provide backup power when your batteries have been depleted the utility must spend the money to build and maintain the necessary capacity to power your home and all the rest of the homes with similar systems are all likely to go off line when the weather conditions limit solar production.
So yes, it does cost the utility money even if you little or no power they must be prepared for the day when everyone is on the grid and demand triples.
Walta
"Or is the idea that its just an arbitrary way to put a semi arbitrary price on it?"
Kind of. Imagine if the utilities commission tells the power company that it's considering allowing them to charge customers for being net metered, and asks the power company to come up with a recommendation for a fee structure. The CEO goes to the CFO and says, "what's the most we could charge customers and not have them say screw it and just cut the cord?" The CFO goes to the operations guys, they kick it around and decide it's whatever price point makes buying batteries cheaper, they run some numbers and come up with a figure. The CEO then takes that figure to the utilities commission.
"So yes, it does cost the utility money even if you little or no power"
One last try then I'll give up. I'm not arguing against this point. Im not saying it doesnt cost money. I'm merely saying that to suggest the $ amount it costs them is somehow equivalent to the $ cost to install the home system makes no sense. Perhaps some utility has used that to set an arbitrary (and high) price, but in leui of knowing that is what a utility has actually done in real life, I'm not sure why it's being suggested that that is how they developed the rate structure.
Maybe I am misreading this:
"power company did the math and proposed a price equal to the cost of ownership of the home sized batteries on the market today."
Cost of ownership. I took it to mean the cost of the system. Is this not what is meant by ownership?
Martin, what I'm hearing is that no matter the result of the analysis, it's incomplete. and it sounds like there's just intangible costs that effectively make grid defection never worthwhile from a personal financial position.
in short, I hear you, and I give your wisdom borne of nearly 50 years a lot of weight. I know you're right, so I hope you won't be disappointed if I run the analysis anyway. sometimes, it's worthwhile to learn things the hard way.
Doing analysis is the easy way. The hard way is buying all the equipment and then finding out it doesn't work the way you thought it would.
Luke,
By all means, run the analysis. I'm interested in the result.
I can contribute some expertise to this financial modeling exercise. I have excel sheets I've written here to calculate out the electric cost for base (constant) kw loading for my customers, since many of my customers have six figure monthly electric bills (these are big industrial customers). These excel sheets calculate everything using data from the utility's "rate book" that is on file with the state, and includes all the generation and distribution charges as well as all the misc fees that get added in like "bond recovery" and "nuclear decommissioning". I also size battery systems for these sites, so can offer some assistance there as well.
For my customers, I find that their backup generators (usually diesel) tend to be about four times more to run on a per-kwh basis compared to grid power, and that's if we exclude the purchase price and maintenance costs on the generator. Since commerical rates are generally lower than residential rates, I'd expect things to possibly work out a little better for residential installations. For natural gas though (what I use for my own generator), the 4x utility rate price is still about right, since natural gas is cheaper per BTU than diesel fuel here. That is still excluding the up front and maintenance costs for the genset though.
You're likely to find that off grid will always be significantly more expensive than grid power, since the entire point of the power grid is to allow for the leveraging of economies of scale to lower the cost of electricity production. If grid power is cheaper than generating your own, then the power grid is doing it's job :-) Don't underestimate the maintenance costs for an off grid setup too, and remember that you'll have to do all that maintenance yourself, or contract it out. The utilities roll all those costs into your electric rate, so you don't have to worry about it -- if the power goes out, you just call the power co to report it and they fix it for free. With off grid, an outage is entirely your problem to fix.
Bill
Bill,
When you wrote, "You're likely to find that off grid will always be significantly cheaper than grid power, " I assume that was a typo and you meant the opposite. Right?
Yes, I most certainly did! Thanks for catching that, I corrected my earlier post.
Bill
With those prices, I was with DC and guessing you were on some remote vacation island in the PNW where a loaf of Wonder bread at the one general store probably costs $15 due to the remoteness. I had forgotten how crazy SDG&E prices were.
To the original question of to go off-grid or do something else to reduce costs:
Staying grid tied, but not interconnecting your solar is probably your best bet. A while back I read that Tesla Solar was offering discounts on non-interconnected solar arrays, to save on the paperwork and meter swapping hassle costs. I bet other installers can offer a discount for that too.
SDG&E has a baseline monthly usage threshold that if you stay below that, your rates are a good bit lower. Use non-interconnected solar to keep you under that threshold. You will obviously "waste" some production this way, but model your daily usage out to keep it to the min. And program any programmable appliances to run during daylight hours. Or downsize your system to do that, like Bill says.
If you have a need or desire for backup power, get a battery that can also manage your solar production and usage to optimize that. (Most major battery brands have the software to do this for you.) You'll save a bunch of money, while also meeting your backup needs. The SDG&E Time of Use rates can even allow you to arb the super-off-peak rate to charge your battery (if necessary) to avoid using grid power during the very expensive on-peak hours, if your solar production is insufficient on some days or at some times of year.
Plugging some #'s into Tesla's pricing website using a random La Jolla address, you could get a 7.2kW array and 2 Powerwall batteries for $37k, before tax credits. If you can use the tax credit, you are outlaying $26k for the system.
My math (assuming Tesla's pricing is real) shows ballpark solar electricity costs after tax credit (20 year life) of about $0.07/kWhr, and battery cost after tax credits (5000 cycles) of $0.095/kWhr. Pretty good savings over SDG&E's wild rates! Even if you have some maintenance costs, still lotta room between those prices and retail rates.
The non-TOU rates are $0.45/kWhr below the baseline threshold, and $0.57 / kWhr above the monthly baseline threshold electricity volume. That's your price to beat. You can probably save more using the TOU rates too if you have a battery and program it to arb the on-peak / super-off peak pricing delta.
excellent amorley
I had similar thoughts. my OP was to look at the extreme example (full off grid) and then evolve the analysis towards self consumption with grid interconnection in a variety of forms.