nwdiver
Well-Known Member
True... but no one has the opportunity if they don't have grid access and that opportunity can be greatly expanded with a broad HVDC grid.
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Plan: Off grid solar with a Model S battery pack at the heart
- Thread starter wk057
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- Energy Environment Policy
True... but no one has the opportunity if they don't have grid access and that opportunity can be greatly expanded with a broad HVDC grid.
beeeerock
Active Member
Certainly there is a significant seasonal variation. As well, you will see significant variation within seasons. I agree with the previous posts suggesting the system you propose is going to produce more power than you can use in the summer, but may not be able to keep up during the darkest days in winter. If you could store annually rather than day to day, then maybe, but clearly that's not even close to possible!
I would suggest you look at the cost of the grid tie (granted, you've indicated it's going to be expensive) and include it in your calculations... then decide how much solar you can afford. I saw days on end this winter where snow covered the panels and I generated absolutely nothing. Sure, I could have removed the snow, but I am at work during the daylight hours and the roof is precipitous to say the least. If I was away for a week, who would look after the snow removal?
My thinking is that you offset as much of your consumption with solar as you can afford, but not attempt to rely upon it as your only source. You may find after a year or two that you're installing the grid tie anyway, and so much for the savings...!
I would suggest you look at the cost of the grid tie (granted, you've indicated it's going to be expensive) and include it in your calculations... then decide how much solar you can afford. I saw days on end this winter where snow covered the panels and I generated absolutely nothing. Sure, I could have removed the snow, but I am at work during the daylight hours and the roof is precipitous to say the least. If I was away for a week, who would look after the snow removal?
My thinking is that you offset as much of your consumption with solar as you can afford, but not attempt to rely upon it as your only source. You may find after a year or two that you're installing the grid tie anyway, and so much for the savings...!
beeeerock
Active Member
I think that depends on your definition of 'good'. Where I am (and likely where you are too), that's a more carbon-intensive way to generate your power than what would come from the grid.
As well...
- you'd likely only need it on the dark, cold days of winter. The typical conditions where a propane engine doesn't want to start. Murphy dictates that this will happen around 3 AM in a driving snowstorm.
- you'd likely have to be around to start the generator, unless you build an automated fail-over system (costly, I'd expect).
- you'll have to swap out the propane tanks... will you be around when the tank empties?
- what happens if you want to go away for the weekend, or worse, a few weeks?
- you'll need to stay on top of a maintenance and testing program to ensure the generator remains in good running order and will start when needed.
So the questions begs to be asked again... is your intent to offset carbon or simply feel more self-sufficient? I think it's important that you be aware that in the planning process, idealism often attempts to trump pragmatism...!
nwdiver
Well-Known Member
If the grid is totally cost prohibitive some form of co-generation would likely be your best bet. Any ICE generation is going to be extremely inefficient <20%... scavenging the heat would would make it a less terrible option.
IMHO the only valid point above is the first one - combustion engines don't like to start in very cold weather. However, gaseous fueled engines are less susceptible to this than liquid fueled engines. The reasons that the rest are invalid in my mind:
- off-grid power systems have a generator auto-start function
- people who use propane in rural installations don't use BBQ cylinders, they use fixed tanks that are hundreds of gallons
- when you leave the property, the electrical usage is very low, so it's much more likely that your renewable generation can keep up
- most backup generators have automatic self-test that starts the engine on a weekly basis if they didn't run during that interval.
beeeerock
Active Member
Well, having lived my entire life in a climate that includes an actual winter (most years, anyway...) my observation has been that the poor suckers who drive propane conversions invariably have problems getting them going in cold weather. I've also had natural gas gensets included in larger civil projects (backup power for lift stations mostly) and they have generally been reliable, although never put to the real test Murphy requires... 'coldest day with no human around to convince it to start'. They also have a 24/7 maintenance crew available and budgets to build really nice stuff. Some (quite a few) public works guys don't want to see anything that isn't diesel (which must be the worst for cold starts), but how much their stance is based on fact and how much is preference I've never decided.
The question of how large the tank would be is really a variable. It would depend entirely on just how big a system he's proposing and how long he wants it to run. My impression was that he'd use it only when necessary, or a few days a year. I wasn't envisioning a BBQ tank... more likely a few 40 or 100 pound units tied together. I can't imagine he's planning the heat the house with propane - way too expensive!
Auto-start would be ideal. At least a mechanism to attempt an autostart. A cold generator out in a shack that hasn't been tested in a few months wouldn't give me enough confidence to be happy about going to Maui for a few weeks. Automatic testing capability adds more cost. I inferred that the genset would be simple to reduce costs, so even autostart might be more than he's intending.
During the winter period, electrical consumption is typically higher for me, but I run a geoexchange system which is more efficient that the typical A/C unit in the summer. More lighting, more heating requirements (hopefully not baseboard electric, but even forced air requires the fan to keep turning).
Most importantly, losing the ability to heat your home when the temperature falls below zero is a big concern. No power means no HVAC. No heat means the house will eventually freeze and water lines will rupture. I'd walk away from my place in the summer with no concerns. The winter? Not a chance. Someone always checks on it daily.
If the system is substantial enough to require a big fixed tank, big genset, building, automatic transfer switch etc... the cost to install AND maintain is likely to make the pole line from the street look more affordable.
I was thinking a bigger tank for propane just so it didn't have to be filled very often, and because I believe propane can be stored longer without going bad. In Seattle the winters don't get all that cold typically, but I would like to get an auto-start feature and the ones we've looked at automatically turn on once a week or so just to keep things lubed up. Would really like to have it as part of the battery bank such that, based on charge level and time and perhaps weather forecast, it kicks on and charges the battery bank to hopefully extend battery life.
As far as using it...shouldn't have to use it much. 30KW a day from the solar array in December on average with the cloud cover should be plenty, but for those strings of non-average weather days/weeks it would be great as a backup. Won't take much to heat our place with an R-value of 60 I don't think. Plus it's not a huge space, only 800 square feet or so as it's planned now. Hasn't yet been built so our mileage may vary.
As far as using it...shouldn't have to use it much. 30KW a day from the solar array in December on average with the cloud cover should be plenty, but for those strings of non-average weather days/weeks it would be great as a backup. Won't take much to heat our place with an R-value of 60 I don't think. Plus it's not a huge space, only 800 square feet or so as it's planned now. Hasn't yet been built so our mileage may vary.
beeeerock
Active Member
Well, my opinion (whatever it's worth!) is that you're embarking on a journey that will become more costly than you expect... that it will impact the way you live, and actually increase your carbon footprint above what it would be with a grid tie. With the tie and all those panels (or fewer), you'd presumably be net negative... with the generator and no tie, you'll be net positive as soon as you fire up the generator.
Granted, Seattle is warmer than where I am, but freezing temperatures are still possible I think? Climate change might mean higher average temperature, but also wilder fluctuations, so all bets are off.
Bottom line, it would have to be A LOT cheaper to install the generator with all the bells and whistles before I'd personally forego the grid tie.
It's often a fine line between 'idealistic' and 'realistic'... ;-)
Granted, Seattle is warmer than where I am, but freezing temperatures are still possible I think? Climate change might mean higher average temperature, but also wilder fluctuations, so all bets are off.
Bottom line, it would have to be A LOT cheaper to install the generator with all the bells and whistles before I'd personally forego the grid tie.
It's often a fine line between 'idealistic' and 'realistic'... ;-)
Freezing does happen in Seattle from time to time. I think you're right, the road from idea to implementation is going to be a steep one and that doesn't tend to be a money saving journey. I'd hate to see an investment of this magnitude turn out to be a bad one. I definitely need to do more homework. I appreciate the inputs from those of you who've actually gone to work implementing these technologies and sharing.
adiggs
Well-Known Member
I encourage you to continue posting about your journey and what you're learning. I think there are many people here who are also thinking about variations of the theme (I know that I am), and I like reading about what everybody is doing.
You might even go crazy, and start up a new thread (we DO like new threads around here). Heck - maybe one of these years, it'll be me starting a thread about being a self-sufficient year-round energy producer, at least on the homestead.
You might even go crazy, and start up a new thread (we DO like new threads around here). Heck - maybe one of these years, it'll be me starting a thread about being a self-sufficient year-round energy producer, at least on the homestead.
Has anybody, other than WK, used a Model S battery pack or other lithium batteries for the heart of their system? Any pointers on resources to learn how to make a battery bank from salvaged lithium batteries? I think I saw where WK indicated his huge bank cost roughly $40K. I'd love to make a smaller version of that.
nwdiver
Well-Known Member
The biggest problem with WKs system was the fact that it's 48v... you need crazy currents to meet most household power demands with a 48v battery. Then there's then problem that EV batteries are typically ~350v (for the same reason)... but there really weren't any off-grid inverter systems that could accept ~350v at the time.
That's changed. SolarEdge now offers an off-grid capable inverter; Fronius and SMA also plan to start offering off-grid capable inverters that accept ~350vdc. You should be able to buy a used LEAF battery for <$5k that's 24kWh and use it directly without rewiring the pack to get 48v.
Sunny Boy Storage
Under max load (~64kW) my setup only pulls about 1500A from the battery side. That's enough to power two HPWC plus basically everything else in my house. Sounds like a lot, but wired correctly it's perfectly fine and not a problem at all. I agree, a higher voltage pack would definitely make wiring *easier*, but that doesn't make a lower voltage system a problem. On the contrary, I consider the lower voltage setup to be a hair safer and easier overall. No risk of HV arc flashes, no need for HV PPE when working with the system, etc. There's also a whole section of code in the NEC of requirements for disconnects and maintenance disconnects, and all sorts of stuff once you go over 50V nominal battery voltages. Probably most integrated commercial storage packs in the future would probably include these things, but repurposing a vehicle pack at HVDC off-grid setup would mean meeting all of those requirements as well.
*shrugs*
nwdiver
Well-Known Member
Right... and 64kW @ 350v is <200A. Voltage loss is I²R so your wire size requirements go down A LOT; For the same size wire pushing 1500A generates >50x as much heat as 200A. My only point is that as high voltage options become available they're generally the better choice for loads >2kW. The other huge advantage is you can use EV packs as they come without rewiring them.
I have a 48v off-grid system too... that's all that was available. But if I had to do it again today I would either go with the Solaredge 'Storedge' solution or a Fronius Symo when they get released later this year. Smaller, lighter, cheaper and more efficient.
After I started reading WK057's posts I bought one 4kW Outback inverter and purchased some 160Ahr batteries. I have an En[phase inverter on my solar so there was no way to integrate the solar system. Mine is very inefficient but my price differential is $0.26kWhr during the summer and it also doubles as a back up. I run it during the peak rate period from 2PM until 8PM through a critical loads sub panel and charge it from the grid from 10PM until 8AM the next morning ($0.11/kWhr). My loads are generally one to two kWs and that maximizes my solar generation that goes back to the grid during the peak summer rate of $0.37/kWhr.
Are those batteries lead acid types? If so, how do you like them? Much maintenance involved?
nwdiver
Well-Known Member
You should be able to AC couple them in the event of a grid failure... it's not ideal long-term since the Radian can't control the charge rate of the batteries but it'll work in a pinch. The Radian can keep the batteries from getting overcharged... it will increase frequency to 60.6hz which will cause your Enphase inverters to trip off.
Outback AC coupling
