SF Bay Area solar system planning: help me avoid making dumb mistakes

[Sunking]

Understood, and I can come up with a hypothesis as to why they are designed that way (primarily, there's likely to be a mismatch between what your house requires in power and what the array can deliver.) The "unacceptable" part comes from my wife who says, if we're paying for solar we damn well better have some power to the house when it's sunny and the grid's down.

Well your hypothesis is half baked, but not correct. A GTI system is a current source and is required to operate into infinite low resistance of the grid. Your home is an infinite open resistance compared to the grid. If you did not shut down with the grid would likely burn everything electrical in your house up, and be a clear and present danger to utility workers.

To make your wife happy is another $30 to $100K add on option. Plus she has a new part time job requiring 7 days a week no days off job. See if that makes her Happy Happy.

I was looking at AGM batteries instead, as we're sloppy when it comes to maintenance.

Well now we up the option to $60 to $200K, plus replacement of batteries every 2 or 3 years. That will make you Happy Happy paying for something you rarely if ever use. Kind of like my wife, I never use her much anymore and still paying for it.

Think Grid Tied with whole house generator using diesel, NG, or LPG if you want emergency power.

[Blammar]

A couple of things
You will not be deep discharging them on a regular basis as they will only be used during the odd outage unless this occurs every day.
Lead acid batteries are almost 100% recyclable and are recycled regularly ( Why do you think the auto parts store charges a core charge if you dont bring in your old battery when you buy a new one. Almost none of a battery ends up in the waste stream.
I do not know about lithium Ion and their ability to be recycled.
$2000 a KWH sounds about right for the Lithium batteries

Oh. Interesting. My model was that the batteries would be charged via solar during the day then discharged every night. I'm not seeing a time of day option on my power bill, so I get charged the same amount per KWh regardless of when I consume it.

If, on the other hand, I go to a time of day option (assuming it's even available), then I want to use solar during the day as much as possible, and the grid at night. In that model, the batteries behave as you describe.

Okay, if I don't deep discharge the AWG batteries, what am I looking at as their replacement time? 10 years?

[Naptown]

Oh. Interesting. My model was that the batteries would be charged via solar during the day then discharged every night. I'm not seeing a time of day option on my power bill, so I get charged the same amount per KWh regardless of when I consume it.

If, on the other hand, I go to a time of day option (assuming it's even available), then I want to use solar during the day as much as possible, and the grid at night. In that model, the batteries behave as you describe.

Okay, if I don't deep discharge the AWG batteries, what am I looking at as their replacement time? 10 years?

What you are actually looking for is a grid tie system with net metering and battery back up.
A TOU plan may help to some extent but for the most part you will be tier shaving (I assume you are on a tiered rate system in Caliland)
I would expect 5 or more years out of the batteries depending on what quality you buy (I generally use Concorde Sunextenders)

[KRenn]

I'm finding that grid-tied systems will shut down when the grid goes off, even if more than enough power is coming in from the solar panels to energize my house. Clearly, that's unacceptable.

It looks like SolarCity is the only vendor that has the Tesla Li-ion energy storage I want to use (I do not want to use lead acid batteries at all.) So I've put in for some of their free consultation. I'll post here once I get more information.

So you want absurdly more toxic and expensive batteries without a great measurable improvement in performance? Why not just go with some AGM's, stable, maintenance free, reasonably priced...etc. It seems more like you are buying into a marketing gimmick then what is actually the best combination of performance and cost-efficiency.

[KRenn]

Well your hypothesis is half baked, but not correct. A GTI system is a current source and is required to operate into infinite low resistance of the grid. Your home is an infinite open resistance compared to the grid. If you did not shut down with the grid would likely burn everything electrical in your house up, and be a clear and present danger to utility workers.

To make your wife happy is another $30 to $100K add on option. Plus she has a new part time job requiring 7 days a week no days off job. See if that makes her Happy Happy.

Well now we up the option to $60 to $200K, plus replacement of batteries every 2 or 3 years. That will make you Happy Happy paying for something you rarely if ever use. Kind of like my wife, I never use her much anymore and still paying for it.

Think Grid Tied with whole house generator using diesel, NG, or LPG if you want emergency power.

This. The best answer. I never understood the obsession with people wanting to have a dedicated battery system in case of a power outage. Realistically, how often do power outages even occur? If you were to jot down every single power outage for the past 10 years, and calculate whether its worth the additional $30,000-$60,000 for a battery backup system, basic logic and math would dictate that it isn't. If outages are a concern, a cheap, generic generator is a FAR more reasonable and less problematic investment.

[Blammar]

So you want absurdly more toxic and expensive batteries without a great measurable improvement in performance? Why not just go with some AGM's, stable, maintenance free, reasonably priced...etc. It seems more like you are buying into a marketing gimmick then what is actually the best combination of performance and cost-efficiency.

Relax -- my initial belief was that Li Ion batteries were ready for prime time, and had much better life cycle costs than lead acid. I've come to learn otherwise.

[KRenn]

Relax -- my initial belief was that Li Ion batteries were ready for prime time, and had much better life cycle costs than lead acid. I've come to learn otherwise.

Beware of slick salespeople pushing marketing nonsense, its utterly endemic to the solar industry.

[Blammar]

This. The best answer. I never understood the obsession with people wanting to have a dedicated battery system in case of a power outage. Realistically, how often do power outages even occur? If you were to jot down every single power outage for the past 10 years, and calculate whether its worth the additional $30,000-$60,000 for a battery backup system, basic logic and math would dictate that it isn't. If outages are a concern, a cheap, generic generator is a FAR more reasonable and less problematic investment.

Understood. The planning here was to be able to handle the aftereffects of a large earthquake that cut power off to us for two weeks. The number of outages we've had over the past 10 years have been on the order of one a year, for a few hours at most, and that arguably doesn't justify a $30K additional cost. (By the way, how did you get that figure? A 18KWh battery is only about $4k; what am I spending $26k on?)

So Plan B appears to be: go reduce our daily power draw by 50%, look into generators, and decide if solar is actually cost effective at all. (Funny enough, my original plan I had 10 years ago was to purchase a natural gas fuel cell generator... for some reason, they are still not being made.)

[Naptown]

Go propane on the fuel for the generator.
Natural gas could be shut down in the event of a broken line due to an earthquake.

[SunEagle]

I can recommend Generac as a very good propane generator. I have one of their 3250w cont - 3750w peak portable units and it does a real nice job. If you want to have a true back up go with a whole house type with a large anchored propane tank.

You may also want to add a second generator using a different fuel type (gas or diesel). That way you will not be depended on just one fuel source for long duration outages.

[inetdog]

I can recommend Generac as a very good propane generator. I have one of their 3250w cont - 3750w peak portable units and it does a real nice job. If you want to have a true back up go with a whole house type with a large anchored propane tank.

You may also want to add a second generator using a different fuel type (gas or diesel). That way you will not be depended on just one fuel source for long duration outages.

On the other hand, I have been seeing comments on other forums (like MH) that if you want to do your own generator maintenance or do not buy through a local dealer Generac's customer support really sucks.

[SunEagle]

On the other hand, I have been seeing comments on other forums (like MH) that if you want to do your own generator maintenance or do not buy through a local dealer Generac's customer support really sucks.

I hadn't heard that. Generac seems to be a pretty big supplier with distributors at HomeDep. I would think they would yank some chains if there was a customer service issue or stop distributing them. Don't want to make a bad name for themselves.

Since i have a portable I didn't really worry about a service call. I would just take it to someone that works on generators although I don't expect issues anytime soon.

[Blammar]

I can recommend Generac as a very good propane generator. I have one of their 3250w cont - 3750w peak portable units and it does a real nice job. If you want to have a true back up go with a whole house type with a large anchored propane tank.

You may also want to add a second generator using a different fuel type (gas or diesel). That way you will not be depended on just one fuel source for long duration outages.

The 20kw Generac is only around $4500, which surprised me. Is it true that if you draw say 5kw from a 10kw generator, it's able to consume less gas? I.e., it's more efficient to buy a larger generator than you need, correct?

I assume you need to hire a propane truck to come and refuel your tank. Just say no to sparks when that's happening.

[Sunking]

The 20kw Generac is only around $4500, which surprised me. Is it true that if you draw say 5kw from a 10kw generator, it's able to consume less gas? I.e., it's more efficient to buy a larger generator than you need, correct?

I assume you need to hire a propane truck to come and refuel your tank. Just say no to sparks when that's happening.

Optimum is 75% at full load like the HVAC running with a few lights. But in SF I doubt yu really need AC. Coldest place I ever went was SF to Candle Stick Park for a baseball game in summer.

[SunEagle]

The 20kw Generac is only around $4500, which surprised me. Is it true that if you draw say 5kw from a 10kw generator, it's able to consume less gas? I.e., it's more efficient to buy a larger generator than you need, correct?

I assume you need to hire a propane truck to come and refuel your tank. Just say no to sparks when that's happening.

I know that most generators have fuel consumption rating based on the % load that is being used. I don't think it is linear. There has to be a certain % of waste depending on how lightly it is loaded. The smaller the load the lower the efficiency and the higher the waste. I would check out what the manufacture rates their equipment.

And yes you would need a fuel truck to come by every so often. They should have all of the proper tools (usually brass) when they make the fuel transfer.

Before you purchase the gen set check out what the cost is to refuel as well as the tank sizes. Some places give you the tank as long as you purchase an amount of fuel each year. You don't want one too small but too big has other issues. Hopefully you can get more than one quote on that.