Am I just special…?

New joiner…. Hoping the experts can provide some insight!

We purchased a home in Northern California earlier this year. One goal is get the house “off grid” using solar. We’ve had 2 solar companies come out and - to be honest - the bids are staggering (~$100k).

Our situation:
We only have 5 months of energy usage at the house. We are in Northern California (Bay Area) and - as such - our weather is not severe by any means. We’ll get a few hot weeks in the summer (high temps in the 90s) but it still cools off every night. Winter highs are in the 50’s/60’s, with lows in the 40’s.

The house is a single-story mid-century modern. We’re currently connected to the local utility provider PG&E. Most of the house is electric - especially after a few recent upgrades (removed the central air/heater and replaced it with a heatpump; removed the 2 water heaters - 1 gas, 1 electric - and replaced with a gas on-demand unit). Working through replacing/upgrading all the lights to LEDs.

Power consumption in Jan/Feb (our coldest months) was ~1500kwh. March/April power consumption (after some of the upgrades) is materially lower - getting closer to ~1100kwh.

With logistics and trees, we’re looking at a ground-mount system. Our area gets a minimum of 5.2 h of sun in the winter. We’d like battery back-up for evenings as well as enough power (in case of a blackout) for 24-36 hrs. (Guessing that’s ~2 batteries).

The estimates (so far) have 28 - 42 panels, 1-2 inverters, and 2-3 batteries. Any suggestions, thoughts, insights would be appreciated!

1.5kWh base load, what is the surge load when the stove and dryer etc are on?

For CA I think they are pretty specific on what is "approved", maybe something like a solark 15 with some Pytes batteries

TRSmith99 said:

Power consumption in Jan/Feb (our coldest months) was ~1.5kwh. March/April power consumption (after some of the upgrades) is materially lower - getting closer to ~1.1kwh.

Click to expand...

First off - welcome to the forum @TRSmith99 !

something not correct here, or we don't understand what you are trying to say - do you mean 1.5kw steady x 24 hours per day = 36kwh per day?
or you mean 1.5 - 1.1 MWh per month perhaps. your utility bill will tell you monthly consumption.
Maybe start with the total monthly load per month in kWh (tyically 900-1200 per month for a full home)
Then as @Brucey says check for the largest single load to get an idea of the peak load you would want to support. Keep in mind motors often need x 3 or more for starting compared with running current.
For the PV side - go to PVWatts (look it up online) and input your location and 1kW of PV use your latitude as the tilt angle and see what the calculator spits out per month per kW of solar PV - use this to scale the total array you might need.
Come back with some more info and questions and we can help you.

You are on the right path with the above line of thought. What is needed is to quantify your power needs. Would recommend getting a something like a Emporia Vue 3. They are a good value and are available in 2 Circuit (mains only) version up to 18 circuits total. Prices start at $99. There are other products on the market with better graphing and historical data but for the price Emporia will give you what is needed to design a system.

Clarification: You mentioned Off-Grid, I believe you actually meant "self consumption". Realistically you probably do want to keep the grid connected. Of course in addition to the building/electrical permits, there is also the NEM 3.0 approval needed from PG&E.

With the amount quoted by the 2 solar installation outfits (~$100K) and the proposed number of panels (wattage?) I would guess that you have a fairly substantial household load to cover. You really need to get a handle on what loads you have in order to know if what they are quoting is adequate or more than needed.

Mattb4 said:

With the amount quoted by the 2 solar installation outfits (~$100K) and the proposed number of panels (wattage?) I would guess that you have a fairly substantial household load to cover. You really need to get a handle on what loads you have in order to know if what they are quoting is adequate or more than needed.

Click to expand...

or they are up-selling him, and just figured out the PV based on what will fit the roof area with a plan to sell back to the utility - even if the sell back doesn't pay what it used to.

I'm guessing your 1.5 kWh is really 1,500 kWh, which is about 50 kWh per day. Abought right for a large house, and consistent with the quotes you mention.

3 Days of batteries is 150 kWh, or 10 eg4 powerpro. About $30,000.

At that level of usage, you nay need two Sol-ark 15k, or another $14,000.

About $6,000 for 36 400w panels.

Add labor.

With the drastic decline in solar in CA, you should be able to get a good deal.

DIYrich said:

I'm guessing your 1.5 kWh is really 1,500 kWh, which is about 50 kWh per day. Abought right for a large house, and consistent with the quotes you mention.

3 Days of batteries is 150 kWh, or 10 eg4 powerpro. About $30,000.

At that level of usage, you nay need two Sol-ark 15k, or another $14,000.

About $6,000 for 36 400w panels.

Add labor.

With the drastic decline in solar in CA, you should be able to get a good deal.

Click to expand...

Do not forget to add mounts, wires, breakers, fuses, distribution panels, battery cables, fires suppression equipment, test equipment, tools to do the installation with, bandages, aspirin and the beer budget.

Next time the solar sales people come by, hide the Rolls in the garage and take off the Rolex.

TRSmith99 said:

One goal is get the house “off grid” using solar.

Click to expand...

How "far" off grid?

Some possible answers:

1. No grid connection, no backup generator

You will need a big battery and also the ability to, on rare occasions, have no power. North CA is blessed with lots of sun, so this kind of works.

2. No grid connection, backup generator

The generator covers the times when the battery would be depleted, so the battery can be smaller and you need to provision for the generator. Propane is usually the best option here (versus gasoline or diesel).

3. No grid connection, but have EV with V2L, V2H or V2X.

If you have an EV and it has some way for it to provide power, you can use it as the "generator". For example, my Ioniq 5 can output 1.8 KW and has 77 KWH of storage. When/if the sunshine isn't enough, plug it in and have it charge the solar battery. When the car gets low, drive it to a fast DC charger ("refuel") and then bring it home again to run the house. The car doesn't have to output the house load, just put back as much energy as the house uses in a day. 1.8 KW x 24 hours is 43 KWH per day, probably enough if you do even just a slight amount of conservation during this mode (delay dryer use, say). And you won't be charging your car, either.

4. Grid as backup

Maintain a grid connection but only use it when the solar system is near depletion. Basically treat it as a generator. Incurs monthly meter/minimum charges but is generally cheaper than maintaining a generator. Doesn't protect you from long duration grid down situations (like a major earthquake that took out electrical towers).

Personally, the EV car V2L option is my favorite, though I have not actually done that myself and you have to have an EV with the V2L, V2H option. to make it work. EVs also make a great load dump for when you have excess solar energy and no place to put it otherwise. Plus solar EV means another economic win for the system.

TRSmith99 said:

We’ve had 2 solar companies come out and - to be honest - the bids are staggering (~$100k).

Click to expand...

It is hard to find honest solar companies form what I see.

TRSmith99 said:

We only have 5 months of energy usage at the house.

Click to expand...

Presumably you want some things to remain powered the other 7 months? Like fridge, HVAC, etc?

During this dormant period, the solar + battery will likely be able to take care of everything without issue.

TRSmith99 said:

(removed the central air/heater and replaced it with a heatpump; removed the 2 water heaters - 1 gas, 1 electric - and replaced with a gas on-demand unit).

Click to expand...

If you have natural gas, then a natural gas generator is an option for backup.

Water heating is a great load dump option instead of the gas. I've seen too many houses blown up by gas to be comfortable with it.

This happened just a year ago in my town:


This is at least the third house to be blown up since I have lived here.

Ironically, the same people who express fear of LFP batteries in their house think nothing of the gas appliances they have. I'd rather than the LFP batteries any day.

TRSmith99 said:

Working through replacing/upgrading all the lights to LEDs.

Click to expand...

Huge win. Saves money in replacement cost and in energy usage.

TRSmith99 said:

With logistics and trees, we’re looking at a ground-mount system.

Click to expand...

Usually cheaper since it has fewer rules. Your ground mount system can have an inverter and battery shack to keep that out of the house, too.

TRSmith99 said:

The estimates (so far) have 28 - 42 panels, 1-2 inverters, and 2-3 batteries. Any suggestions, thoughts, insights would be appreciated!

Click to expand...

Check out pvwatts.nrel.gov for power estimates.

I ran 42 panels at 400 watts, 16.8 KWH, 95404 zip code, 180 azimuth, 45 tilt. Came to 25 MWH per year.



The 45 tilt is not optimal for total energy, but produces more energy in the winter. You can tweak the tilt to get the yearly distribution to suit your loads.

If you are not grid tied (meaning you don't export), you have more freedom from the rules.

There are a number of low cost 10 KW class string inverters that could apply to your situation, you likely need two. They can share a battery bank. I'm just now starting with the Amensolar N3H-X10-US (10 KW, $2200) and EG4 Indoor Wallmount battery (14.3 KWH, $3400). It is a bit too early to say this combination is recommended, but there are other similar offerings out there.

Mike C.

Mike - thanks for the detailed update! Truly appreciated!

A couple updates…
Our “off grid” goal is somewhere between #2 and #4. The house has a Generac (powered by natural gas) already. Our thought is stay connected to the grid, use the generator as an alternative source, pull from grid only as a backup (or a backup to the backup). We’d also likely sell some back into the grid - but that’s really not a motivator.

Since we just bought the house, our energy consumption history is only 5 months long - we don’t have a full year yet. We’re living here full time. ; >

Thanks for an honest look at the numbers and the url link. If I look at the info you shared, it seems that this was created to match our monthly 1500kwh consumption - with December & January being the lowest performing months..?

Assuming that’s correct, 2 Q…
1. Pricing
For the 25,250kw system, it would need 42 panels + 2 inverters ($2200-ish each) + 2 batteries ($3400-ish each)?
42 panels + $11,200 (plus other misc materials, permits, and labor).

2. Resize
I’ll check the URL you shared. The 2 peak months of power consumption (so far) for us have been Jan/Feb at 1500kwh. As mentioned, we’ve been doing upgrades on the infrastructure. As such, the monthly power consumption number is going down overall.

You are making my brain hurt with your units confusion, but as @BentleyJ said, get an Emporia or equivalent and do an energy survey to determine what you need.
Only then can you start looking at tradeoffs between panels, inverters, batteries, and grid interface.

TRSmith99 said:

The house has a Generac (powered by natural gas) already.

Click to expand...

Since you already have that, it is the natural choice for your system. There are two concerns, of course, natural gas leaks and explosions risk, and the fact that in a major earthquake, the natural gas lines will likely be inoperable. Outside of those concerns, you already have it, so you should build around it.

TRSmith99 said:

Our thought is stay connected to the grid, use the generator as an alternative source, pull from grid only as a backup (or a backup to the backup). We’d also likely sell some back into the grid - but that’s really not a motivator.

Click to expand...

There is a regulatory cost to touching the grid, it activates a bunch of requirements, inspections, etc, particularly if you want to export.

Given you are already paying for gas for hot water, then the marginal cost of running the generator is relatively low. I'd give some thought to going off grid entirely.

One thing to note is that the generator will run far more efficiently than when it serves as a house backup. Instead of it running at low power for long periods, which eats fuel, it will run for shorter periods at higher power while it charges the batteries back up. This makes the generator more efficient.

Many inverters have a generator input and a generator control signal. When the inverter senses the batteries have reach a low state of charge, the inverter signals the generator to start. Once the batteries reach a suitable state of charge, the inverter signals the generator to stop.

TRSmith99 said:

Thanks for an honest look at the numbers and the url link. If I look at the info you shared, it seems that this was created to match our monthly 1500kwh consumption - with December & January being the lowest performing months..?

Click to expand...

Dec and Jan are often the lowest performing months. The tilt of the array determines if you want the most total power per year, or whether you want the most power in the worst month. For off grid, it is usually best to go for most power in the worst month and have excess at other times.

TRSmith99 said:

1. Pricing
For the 25,250kw system, it would need 42 panels + 2 inverters ($2200-ish each) + 2 batteries ($3400-ish each)?
42 panels + $11,200 (plus other misc materials, permits, and labor).

Click to expand...

There is not enough data to define your system.

Inverter sizing needs to be aware of your peak power demands. Any means you have to lower the peak demand will be useful (such as soft start for HVAC, avoiding simultaneous loads, etc). Two 10 KW inverters is 20 KW and that might not be enough, or it might be. For scale, a 200 amp service is 48 KW and most houses never come close to that load.

Battery sizing is highly dependent on the uniformity of your daily usage and the weather. It also is a function of what percentage of usage do you want to cover without using the generator. For a 1500 KWH per month house, 50 KWH per day, you probably would like to have 50 KWH of battery so you can do 1-2 days. More will make your power last longer. With a generator ready, it may be more cost effective to let it run periodically (which is good for it, too) than to get a huge battery.

Panel sizing has a lot to do with how much you want to generate in the worst months. If you expect 4 hours of good sunshine in winter, then a 50 KWH house probably needs about 16 KW of panels, roughly divide the energy required by 3. More isn't wrong, but at a certain point, you are wasting money generating energy you can't use.

Making some assumptions:

2 Amensolar inverters (20 KW): $4400
4 EG4 Indoor Wallmount batteries (57.2 KWH): $13,600
42 Canadian Solar CS6R-400MS-HL panels (16.8 KW): $7,000

There are a lot of other bits and pieces plus labor to build a system so just adding up the big items isn't enough.

One disclaimer: the Amensolar inverter is very new and I have not used it enough to solidly recommend it yet. The EG4 18KPV is much more widely used, but also considerably more expensive.

TRSmith99 said:

2. Resize
I’ll check the URL you shared. The 2 peak months of power consumption (so far) for us have been Jan/Feb at 1500kwh. As mentioned, we’ve been doing upgrades on the infrastructure. As such, the monthly power consumption number is going down overall.

Click to expand...

And it can go up, like if you buy an EV.

With a generator, you can try on size and then expand later if you want more panels, battery, or inverters.

Mike C.

You can't legally run a standby generator when there's grid available except for maintenance. I'm not saying I wouldn't do it too, but you should be aware there are laws on the books against doing that.

If you switched from gas to heat pumps after winter then you're missing key data on that consumption. You could approximate it from historical gas consumption.

I've roughly figured that I would need 16kW of solar to mostly off grid with heat pumps, and that's with ideal ground mount placement and no shading. There would still be plenty of backup days too.

hwy17 said:

You can't legally run a standby generator when there's grid available except for maintenance. I'm not saying I wouldn't do it too, but you should be aware there are laws on the books against doing that.

Click to expand...

And check the total cost per kWh of utility vs generator charging, include maint. costs.
I would recommend the order of power supply as: PV, Battery, Grid, Generator.
in my own location each kWh from the generator is about 10x the cost of the utility rate.
To maintain an off-grid set up, the utility can charge via EG4 Chargeverter during low ToU rate periods (assuming OP has ToU rates).
For poor winter weather days I like to use the grid to "top up what was missing today" during low utility rate periods; if the house consumes on average 50kWh per day, and say you collected 30kWh on day in December - then charge off peak with the Chargeverter to "top up" the missing 20kWh the sun didn't provide that day.
I control my chargeverter with a 'smart plug' powering the control side of a 240v relay, this way I can set a time schedule for the smart plug to switch on and off the Chargeverter based on what I see from Solar Assistant as the daily solar collected.
You can just set it and forget it at a certain number of hours per night of charging, or you can play with time settings based on actualy solar collected and what is in the next day forecast - depending if you want to play with the solar or not.

Generators should be the last line of power supply - the most expensive (and noisy) option, only the case when solar, batteries and grid are not an option.

OffGridForGood said:

And check the total cost per kWh of utility vs generator charging, include maint. costs.
I would recommend the order of power supply as: PV, Battery, Grid, Generator.

Click to expand...

This. My generator fuel cost is more than 10X my crazy expensive grid power, not including maintenance and amortization (cuz sunk costs).

OffGridForGood said:

Generators should be the last line of power supply - the most expensive (and noisy) option, only the case when solar, batteries and grid are not an option.

Click to expand...

+1.

There's a lot of Bay Area people on the forum who have done fully DIY permitted systems with PG&E (me, ampster, hedges, hwy17, agarg, fafrd, probably missed a few. some have done multiple...)

There's also decent local forums with people that know solar and the local prices. I found a few on NextDoor, and theoretically you can also network with SunWork.org volunteers if you are savvy enough.

If you're going to pay $100K, at least let it be from one of the cadillac companies that have been installing solar since the 1990s instead of paying a ton for bad service for a new outfit.

You should be able to request energy usage from PG&E from before your purchase. Unless it is new construction (but you said midcentury and your power usage numbers, noisy / weird as they are, are commensurate with some minimally updated 1950s-1970s construction).

Your project cost numbers are way off. The inverter and battery costs are for non-code compliant stuff. mciholas has posted some deals he saw on some bleeding edge equipment. Though I'll note that the Amensolar and EG4 Wall Mount interior are probably NOT code compliant as a pair, and California is maximally picky.

Without batteries I did 11kW of rooftop HoyMiles microinverters in Q3 of 2023, for $19K pretax (I'm looking at my spreadsheet for tax deduction right now). I did buy the panels at the peak of NEM2 craziness, the prices have since crashed.

Just the big ticket item invoices totaled to $15K, and then there's the nickel & diming of small parts from eBay, distributor, home depot, etc. Add up $50 here and there and it suddenly becomes real money. Subtract maybe $150/kW for string inverter + RSD vs the cheap microinverters I specced.

I also agree with investigating the V2L approach. I drive a Hyundai and basically all of the new Hyundai/Kia/Genesis have it. 15A at 120V goes a LONG way in a power outage compared with not having it. I haven't fired up my generator since getting that. That said, 120/240 would be a lot less janky of a power source. V2L is allowed to operate down to 20% charge. When I have widespread power outages I can typically still find a fast charger that operates, my local one is literally across the street from the substation. So I've seen 1000 dark houses in adjacent neighborhoods, while substation still hums along

Well, it might be down if it was like the apocalypse and the transmission lines and generation were... threatened, but usually it isn't

mciholas said:

If you have natural gas, then a natural gas generator is an option for backup.

Water heating is a great load dump option instead of the gas. I've seen too many houses blown up by gas to be comfortable with it.

This happened just a year ago in my town:

This is at least the third house to be blown up since I have lived here.

Mike C.

Click to expand...

Mike, what the heck is it with Indiana and gas explosions? I left Indiana in 1985 to join the military and swear to god, we had three gas explosions just while I was in school. the second one happened one block off of the square and took out the Sullivan daily times and one of the paper boys was injured. (we were later classmates in high school).

zanydroid said:

Though I'll note that the Amensolar and EG4 Wall Mount interior are probably NOT code compliant as a pair

Click to expand...

How so?

Each component meets code so they can be used together.

I am not aware of any code incompatibility in the system design and neither is the engineering firm that produced PE stamped plans for the system.

Don't cast vague accusations of non compliance, be specific. If there is a problem here, I want to know about it.

Mike C.

You really need to wait for a full year of consumption data before you can properly size an offgrid system. I'll bet it will be August that defines your sizing, not the winter.

mciholas said:

How so?

Each component meets code so they can be used together.

I am not aware of any code incompatibility in the system design and neither is the engineering firm that produced PE stamped plans for the system.

Don't cast vague accusations of non compliance, be specific. If there is a problem here, I want to know about it.

Mike C.

Click to expand...

Depends on your code requirements. UL9540A means the batteries won't burn. UL9540 means the inverter and batteries have been tested together as a system, and certified to work together.

I have no idea what the chances are that Amensolar and EG4 got together to certify their gear to UL9540, but if I cared about that certification, I'd go with a consistent vendor. [I don't care about UL, but I do care about compatability, so I went with the EG4 ESS.]

mciholas said:

Don't cast vague accusations of non compliance, be specific. If there is a problem here, I want to know about it.

Click to expand...

UL9540 has traditionally qualified the inverter and batteries as a paired listing. It is a system level listing

UL9540 V3 added an option to qualify the battery as a DC ESS, which is then broadly able to convey 9540 as long as the inverter is 1741 and able to comply with installation requirements (comms, wiring, etc) listed in the manual for the DC ESS

I only know of one DC ESS thus far, and very few people other than me have been making internet posts about it.

cosmicosmo4 said:

You really need to wait for a full year of consumption data before you can properly size an offgrid system. I'll bet it will be August that defines your sizing, not the winter.

Click to expand...

There are microclimates around SF that are heating dominated and probably at best it goes to neutral. My house is definitely heating dominated. I only need 5kWh or so per day to get AC past a heatwave but I need 10 kWh-15kwh per day, continuously, during winter heating season

AC was optional in many counties until like past 15 years with the increase in heat waves.