A huge amount of the info on solar PV power on the net is absolute garbage. (I spent 5 years working on the most advanced solar performance optimization and monitoring system developed to date.) I haven't read all of this article, but so far, it looks dead on (you have no idea how rare that is!) Solar is not the panacea many people wish it was, simply due to the way God built the universe - and there's not a thing we can do about that. (And yes, the panels are now only a small part of the cost of a solar system, especially one capable of operating off-grid...)
Looks like I great article. I'll have to defer reading it. During a quick scan I saw a mention of the SMA technology that allows for dedicated outlets to be powered-up in case of grid failure.
I built a 13 kW ground-mount system feeding a pair of SMA inverters. I have tested this feature by disconnecting from the grid and enabling the outlets (one per inverter). I didn't quite get to the 2,000 W rating SMA claims but got close. Which means that with this size of an array and two inverters I get somewhere between 3kW and 4kW of power to run various devices while the sun is up.
Considering that we might have a couple of power outages a year on average (if that), I felt this was a reasonable investment. Going with batteries is just too expensive and not justifiable at all given the reliability of the grid. One way to think about this is that the grid is your battery. A stretch, I know.
Funny that there's a picture of a gasoline generator towards the end of the article. My guess is that I am likely to invest in a 5 kW to 6 kW generator before I ever add batteries to this system. Again, it's a matter of ROI. Also, I would not go with a gasoline powered generator at all. Gasoline degrades with time and could be a nightmare to maintain the system with sporadic use. I think a propane fueled generator might be a better idea. The fuel does not degrade. So long as you don't have leaks it'll be there ready to go when you need it.
I know way too many people who have been mercilessly duped by these solar companies who come in, hook them on some kind of a lease, install inadequate systems and move on to the next victim. Lack of understanding on the side of consumers has created a situation where solar is equivalent to magic and unscrupulous actors can take advantage of them. That part is sad.
> Backfeeding the power grid, according to some lineworkers I've talked to, is really not a big concern for two reasons. First, lineworkers assume lines are live until proven otherwise. And, second, no residential system is going to successfully backfeed a large dead section of grid. [...] it's really not that big a concern from a technical/safety perspective.
This is wrong and dangerous. Suddenly energising a section of grid which has been isolated from all known power sources could easily kill someone working on it. Yes, lineworkers will isolate and test lines before touching them. No, this won't protect them because your inverter could start outputting after they've tested. Yes, your inverter will probably overload and trip out before putting too much voltage into your local section of the grid, depending on where it's isolated. No, it's not OK to bet a random stranger's life on it.
I like to always highlight the difference between a technically correct statement and a public health and safety policy statement.
A thing may be technically correct, but for the health and safety of the public at large we need to adhere to a consistent policy with what we say in the public sphere.
Mains voltage is dangerous and kills kills kills. Never connect anything to the mains power supply unless you are licensed to do so, or employ someone who is licensed to do so. Always assume a circuit is live unless you-personally have checked and locked out the breaker with your own personal lockout device that only you have the key to.
I'm not a lineman but am a generally curious person, which has caused me to watch and analyze their work when I see it.
Any time I see them working directly on high-voltage lines, they connect a device that looks like jumper cables in-between the phase(s) and ground. They also put bright orange flags on this device so that it is easily visible to anyone nearby. It seems to be a great practice and seems to make things nearly fool-proof because this effectively shorts out any power that may occur on those lines.
I don't think I've ever seen a lineman work on a power line in a manner that would cause him to be electrocuted if surprise power were to occur on the line. I'd bet it's in policies and procedures somewhere, possibly even in OSHA requirements.
The requirement of not backfeeding is another layer in this multi-layer protection scheme.
If a system is successfully backfeeding the grid, something is badly wrong. If a linemen is then electrocuted by this backfeed, something is almost impossibly wrong.
When I work on electrical wires at home, I test if they are hot after flipping what I believe is the correct fuse. If I’m right I know it won’t become hot while I work on it because I control the switches and fuses.
If I worked on wires where I was not in control of incoming power, then I can not be sure the wire isn’t hot just because I measured once. This is for example the case when working with stuff with big capacitors.
So my point is: can line workers really assume a wire isn’t hot just because they tested it? They don’t control both ends, since as you pointed out, anyone could have a) a power source or b) a faulty connection, whether it’s allowed or not. So as a line worker I’d basically just not touch anything even in supposedly dead grid sections.
> Yes, lineworkers will isolate and test lines before touching them. No, this won't protect them because your inverter could start outputting after they've tested.
The lineworkers I've seen that aren't working with live wires use a special tool to ground the wires (it's a set of three clamps connected by a thick wire to a grounding rod). Once the wire's grounded, it's going to be hard to put any voltage on it.
I would also expect that a larger residential inverter could successfully backfeed the load side of a single distribution transformer (i.e. just a few houses). If the line workers are repairing a distribution transformer or its associated hardware, this could be a big deal.
I don’t know if the workers make a habit of physically disconnecting all of the houses that are connected.
I guess the point is that if your residential solar setup attempts to backfeed a dead grid, it will effectively see a short circuit which it, try as it might, will be unable to generate any voltage across, trip and your house is as dead as the rest of the grid.
For this reason, I'd be most surprised if there's a single backfeed system in existence which doesn't isolate your house from the grid once the grid goes down.
Edit: Finally got around to reading the blog post to the end and found that the author makes this exact point in the paragraph following the one quoted in the comment above.
Great article, lots of technical details. A simple answer to the 'Why' can be found in the middle under the 'Off Grid Without Batteries' headline.
> If you have a typical grid tied system (microinverters or normal string inverters, so easily 95+% of installed rooftop solar), the system is technically incapable of running off grid (without additional hardware). There's no waveform to sync with,
I agree that there are a lot of good technical details. However, I wish the article had started off by saying, "It's Not Power Companies Being Evilly Evil - It's Homeowners Being Cheap" instead of waiting more than half way through it.
"there's no waveform to sync with" is technically correct and a very poor excuse
A residential no-break has no waveform to sync with as well.
Something capable of syncing to the grid and then more or less keeping pace even if the main grid goes down should cost very little today. (And when the grid goes back it shouldn't have drifted too much unless something ridiculously big happened)
As this article touches on the solar panels are the cheap part of a solar setup. If you want to run off grid the costs skyrocket.
I live in an off grid bus. My whole electrical system cost in the US$9-10000 range with only 810W of solar. The other components cost a lot more:
* ~$900 for 3x 270W Renogy solar panels
* $1500 for 3.6kWh of LiFePO4 batteries (12 100A 3.6V cells)
* $1600 for a Victron 3kW inverter / charger
* $2000 for a Honda EU3000is generator to run my AC
The rest was the Victron solar controller, color control panel (that runs Linux!), breakers, relays, transfer switch, fuses, cable, and all the other stuff you need to hook it together.
This isn't at house scale either. The cost would go up significantly to support a house scale system.
That Honda EU3000is is an 3 kW ICE-based generator, that is, it's not a part of "solar" setup proper.
OTOH not having a combustion-based backup is likely not very wise if you live off-grid. I wonder how often do you need to run it? That is, what part of your energy budget is covered by the solar energy?
Initial cost might be high but this cost would be slowly return as you save on electricity bills. Also, all this equipment is not perishable and you can still re-sell at good price after your retirement or sell them along with house.
Its no different than investing in house upgrades which adds to the house value.
> The only real way to get off grid power without batteries is to go with an inverter that has an emergency outlet. Some of the SMA inverters support this (they call it Secure Power Supply) - you feed the whole rooftop array into them, and they can, if the sun is shining, provide 1.5kW or so to a dedicated outlet - assuming there's enough solar power. So, from an 8-10kW array, on a sunny day, you can get 1.5kW by operating well below the peak power point. If the array can't keep up with current demand (a cloud goes over), the outlet shuts down. It's better than nothing, but this is just about the only way you can get battery-free off grid power. To get any sort of stable battery-free power, you have to run the panels well, well below peak power (30-50% of peak is as high as you can really run), and even then, you have a horrifically unstable system. If the array power briefly drops below demand (perhaps an airplane has flown over), you shut down the entire output for a while. Hopefully your devices can handle intermittent power like this. If the array can source 1300W at the moment and a compressor tries to draw 1301W while starting, you collapse the array voltage and shut down the outlet. That's really hard on compressors (and everything else attached to the outlet).
It's not ideal, but this is so much better than what most installs are built with (nothing).
I thought there were shutoff devices that could detect a grid outage and instantly disconnect your home from the grid allowing your inverter to power your house until grid power is restored. I assumed something like this would be $10K but well worth it, as basically the whole point of battery-backed solar is energy independence.
Super useful. Pacific Gas & Electric (which powers much of CA) recently announced that they may pre-emptively shut off power to certain parts of Silicon Valley out of concern for potential fires. In the article I read, they mentioned that even home solar wouldn't work, which seemed crazy. I can now see why this is the case, and what folks should do (get a transfer switch and generator) to be able to power their home with their solar panels.
My dad has a 7kw system with the SMA inverter with emergency power outlet for 1.5kw. Works ok, as said the main issue without batteries to buffer is stability.
I have a Magnum 3000w Hybrid inverter in my RV with 320w of solar with a MPPT solar controller. The solar controller feeds the batteries and the inverter draws from batteries or charges them with UPS grade change over. Magnum hybrids can do interesting things like if the sun is out and I am running the air conditioner off generator or shore power it will pull batteries down to float voltage and invert excess power to lower draw, I usually get about 1 amp reduction with 320w of panels. You can also dial in your shore amps and if a load needs more the inverter will step in and provide the overage from the batteries. Nice if you driveway surfing and only have a 15 amp outlet but want to run the microwave or whatever. The RV is basically a giant UPS with generator.
> To get any sort of stable battery-free power, you have to run the panels well, well below peak power (30-50% of peak is as high as you can really run), and even then, you have a horrifically unstable system. If the array power briefly drops below demand (perhaps an airplane has flown over), you shut down the entire output for a while
It doesn't seem like a battery or capacitor to handle blips like an airplane flying overhead would need to be very large?
No, but using a small battery means using a battery that get heavily charged/discharged by such events, and therefore has a short lifespan (less than a year, probably, if you used the kind of battery that's in a UPS.) The reason the battery banks for solar are so large isn't just to capture the entire daytime output for night-time use, but also so that they can have a lifespan closer to that of the solar array itself.
That you could do with a super capacitor, but not with a battery.
I know of some railway train setup, which is deployed in Saudi Arabia by Siemens, that uses a combination of battery and super caps to power the train. While the train starts it takes the sparking current from the super caps. While riding it will take the energy slowly from the batteries. While deceleration it will recuperate and will charge up the super caps, because they can be charged easily with a high current. So the super caps are used as a high available energy buffer with very fast charge and discharge capabilities. While the battery is only used during the times of less energy consumption. Also at the stations the super caps are super charged very quickly. With that concept, they can run the train the whole day with only 40% discharge of the battery. The battery is actually way smaller then in a Tesla.
This concept can be applied also locally. The problem: these super capacitors are way expansive so you need to design them to your specific requirements.
Also, while not necessary trivial, it is not hard to throttle consumption of devices, and if it's with two circuits, one for devices that care about voltage, and one for devices that actually brown out. The latter is easy to scale by just reducing the voltage far enough that it doesn't sink too much power, and devices like e.g. desktop or server computers are theoretically easy to rapidly throttle, e.g. by reducing cpu clock to a few hundred megahertz, halting HDD operations or even cutting their power (most are made to handle hot-swap well).
A large, modern CPU with 140 W TDP can cut usage within 10 ms to 10W, but dram can't scale that way due to how it works, or rather, this scaling is not supported in mainstream hardware.
If you use a small supercapacitor, which commonly has a minimum discharge time of about 2~20 seconds (similar to Lithium-ion pouch cells "LiPo", which are available with different "C" ratings, and negatively correlated gravimetric/volumetric energy density and maximum average discharge power (i.e., optimizing discharge current vs time to maximize the ratio of total power extracted divided by time until empty). You need more metal in the electrodes and the plate/foil that aggregates the current of the individual electrodes, leaving less space/weight for the parts that actually store energy.),
you can use much more advanced power reduction techniques for electronic devices, as you have time for something approaching a proper shutdown. Compare e.g. the time your Laptop takes until it is off from the moment you close the lid.
Oh, and yes, these capacitors are cheap. One about 1kg / 1 liter size for about 100$ can provide 20kW average power, for 2 seconds. The main difference is that they don't care (much) if you cycle them at 100% depth of charge, apart from internal losses heating it up and thereby causing damage.
Maybe this applies in normal markets, but in Puerto Rico the grid is both shit-tier reliability and horribly expensive. Rooftop solar and lithium batteries in an off-grid format are both far more reliable and far cheaper than the grid, assuming a 5% cost of capital. I might throw in some LP or diesel generation capacity too, but solar plus battery is an easy choice.
I've read the detailed reports for outages in the West and the North-East, and they touch on alot of the same concepts that were in this (awesome) article.
Does anyone know, what's a good resource for learning more about power generation, grid regulation, etc.? The relationship between frequency/voltage and available vs. demanded current, frequency sync, grid maintenance, etc.…
This is exactly why people need to explore alternative energy options other than solar. The best off-grid setup I’ve seen is a bunch of conductive pipes lay over the ground that heated water from the sun, that in turn was used to generate enough energy to pump water to a storage tank during the day up a large hill. At night the tank was drained and water came back down and the resulting pressure was used to generate power, supply back to the grid. It used minimal components (& simple ones), no batteries, nothing fancy but was enough energy to supply a community of several single family homes in a completely off grid system.
> This is exactly why people need to explore alternative energy options other than solar. The best off-grid setup I’ve seen is a bunch of conductive pipes lay over the ground that heated water from the sun, that in turn was used to generate enough energy to pump water to a storage tank during the day up a large hill. At night the tank was drained and water came back down and the resulting pressure was used to generate power, supply back to the grid.
So, your example of energy options other than solar is solar with hydro storage? Or did you mean “other than photovoltaic” when you said “othet than solar”.
During 2017, I saw a lot of news articles talking about how the Evil Power Companies were being Meanie McMean by not letting people with solar panels use them when the grid was down. The implication (in many news articles) was that these powerless people with solar panels could use them to power their home while the grid was down, if only the evil power company didn't require that solar not work if the grid was down.
I don't remember seeing any articles that blame the power company for home solar not working off-grid... I do remember seeing articles saying that most home solar installations won't work if the power grid is down, but nothing that implied that the power companies were behind it.
My cheap and simple 15-minute UPS device has waveform generation (?) and a battery. Surely with solar you often have to have huge batteries?
In hot climates you have some power use when the sun is up (cooling, pool heating,) but where I live I’d need my power most when the sun is absent in night and winter (power use is probably 80% heating). Any amount of solar power would be nearly useless if only available when the sun is shining.
I'm curious why a large capacitor or inductor cannot be used to provide momentary power for things like electric motor starts, and to smooth out events like a plane briefly occluding the sun.
I built an audio amplifier in college that had a couple of huge capacitors on the power supply (about the size of a can of soda). It would keep the amp running a few seconds after I shut off the power.
Of course, if you want to run off the grid, the first thing is to minimize your electrical appliance. Get a laptop, the laptop will serve as your TV, computer, radio, etc.
No TV, no Washer/Dryer (you will hand wash), No regular fridge, get a small 12v fridge. No microwave, use stove to heat up food. No A/C, design the space to not get hot, high windows, under the shade, facing away from the sun. Maybe a small fan. The biggest optimization begins with your appliances.
We found that even a well made Honda petrol genset was highly unstable feeding volts into a UPS for a machineroom. They are good at lights. They are good at a cooker. They suck at anything which expects regulated, non-noisy volts.
Lots of homebrew 'you can plug this magick cable I made' methods to supply volts across the fence to neighbours houses when the power goes down are really bad: behind the meter is just as lethal as in front of the meter, if you get it wrong.
TL;DR if you need to read a website like this for clue how to avoid losing power, you are putting your life at risk if you don't follow code, and don't know what you're doing.
Inverter generators like the popular Hondas are not good for surges. If you run them at a steady draw they'll give you nice, clean power. If you your demand fluctuates significantly they will stall or cut out and the voltage during or after the stall may be dirty.
You have to read the specs carefully to make sure they are a good match for your use.
There are all sorts of issues with using a regular grid-tied inverter in an off-grid situation; there are regulatory issues besides the anti-islanding (which is a complicated topic all on its own), and technical challenges too. A lot of the technical challenges go back to the inverter effectively being a thing that bolts on to the existing house wiring; I think that if they could be more of a pass-through thing (like a UPS) then the picture would be a lot simpler.
An off-grid capable inverter needs to handle several state transitions smoothly, and some of those are hard. For instance, starting up can be a lot harder when there's no mains voltage. An inverter will have a maximum output current, which is generally not too far from the maximum power output of the inverter divided by minimum mains voltage. If you have a load that presents as a constant resistance, like a water heater, then as the inverter's output voltage goes from 0 to 240V (120V for areas with weenie power) the current will smoothly go from nothing up to whatever the load normally draws, along with the voltage, and there's no problem. But! A lot of loads aren't resistive - things like computers, battery chargers, and inverter-driven motors (as newer appliances often have) will tend to look more like constant-power loads. So, once they decide it's OK to turn on, if the voltage happens to be half of nominal at that point, they will try to pull twice their nominal current. If that causes the total draw to exceed what the inverter can provide, it stops and maybe tries again. It's practically impossible to measure what the load characteristic of something like a house, from the perspective of an inverter, so the best you can do is something like guess-and-check, and that's not a great solution.
Then, how to handle reconnection with the grid; you either need to re-synchronise before reconnecting, or ensure that the intrepid homeowner first shuts off the house before turning the switch to reconnect.
Switches that can handle that job may need to be specified per-installation, and there are all sorts of regulations around how they work and where they can go. They are not cheap, as a rule. Some regions have the solar generation stuff on a separate export power meter from the import one. This means that the switch needs to be on he supply side of both meters, and that could be regulatorily complicated.
What about multiple inverters? These things all need to play nice with each other when solo, or installed with others. Perhaps you didn't design those, and they might try to start up too, then fire up their anti islanding which should promptly trip out again.
Remember this all has to work with variable input power available, and it needs to be packaged up so that installation is straightforward, and operation is basically hands-off. Oh, and inexpensive too!
What I would like to know is, if there was an emergency situation and the grid was going to be down for an extended period of time (I'm thinking 3+ weeks, months, years) would there be a way of altering the system so that the home could have electricity, at least during daylight hours?
[+] [-] dublin|7 years ago|reply
[+] [-] rebootthesystem|7 years ago|reply
I built a 13 kW ground-mount system feeding a pair of SMA inverters. I have tested this feature by disconnecting from the grid and enabling the outlets (one per inverter). I didn't quite get to the 2,000 W rating SMA claims but got close. Which means that with this size of an array and two inverters I get somewhere between 3kW and 4kW of power to run various devices while the sun is up.
Considering that we might have a couple of power outages a year on average (if that), I felt this was a reasonable investment. Going with batteries is just too expensive and not justifiable at all given the reliability of the grid. One way to think about this is that the grid is your battery. A stretch, I know.
Funny that there's a picture of a gasoline generator towards the end of the article. My guess is that I am likely to invest in a 5 kW to 6 kW generator before I ever add batteries to this system. Again, it's a matter of ROI. Also, I would not go with a gasoline powered generator at all. Gasoline degrades with time and could be a nightmare to maintain the system with sporadic use. I think a propane fueled generator might be a better idea. The fuel does not degrade. So long as you don't have leaks it'll be there ready to go when you need it.
I know way too many people who have been mercilessly duped by these solar companies who come in, hook them on some kind of a lease, install inadequate systems and move on to the next victim. Lack of understanding on the side of consumers has created a situation where solar is equivalent to magic and unscrupulous actors can take advantage of them. That part is sad.
[+] [-] taneq|7 years ago|reply
This is wrong and dangerous. Suddenly energising a section of grid which has been isolated from all known power sources could easily kill someone working on it. Yes, lineworkers will isolate and test lines before touching them. No, this won't protect them because your inverter could start outputting after they've tested. Yes, your inverter will probably overload and trip out before putting too much voltage into your local section of the grid, depending on where it's isolated. No, it's not OK to bet a random stranger's life on it.
[+] [-] TheSpiceIsLife|7 years ago|reply
A thing may be technically correct, but for the health and safety of the public at large we need to adhere to a consistent policy with what we say in the public sphere.
Mains voltage is dangerous and kills kills kills. Never connect anything to the mains power supply unless you are licensed to do so, or employ someone who is licensed to do so. Always assume a circuit is live unless you-personally have checked and locked out the breaker with your own personal lockout device that only you have the key to.
[+] [-] sathackr|7 years ago|reply
Any time I see them working directly on high-voltage lines, they connect a device that looks like jumper cables in-between the phase(s) and ground. They also put bright orange flags on this device so that it is easily visible to anyone nearby. It seems to be a great practice and seems to make things nearly fool-proof because this effectively shorts out any power that may occur on those lines.
I don't think I've ever seen a lineman work on a power line in a manner that would cause him to be electrocuted if surprise power were to occur on the line. I'd bet it's in policies and procedures somewhere, possibly even in OSHA requirements.
The requirement of not backfeeding is another layer in this multi-layer protection scheme.
If a system is successfully backfeeding the grid, something is badly wrong. If a linemen is then electrocuted by this backfeed, something is almost impossibly wrong.
[+] [-] alkonaut|7 years ago|reply
If I worked on wires where I was not in control of incoming power, then I can not be sure the wire isn’t hot just because I measured once. This is for example the case when working with stuff with big capacitors.
So my point is: can line workers really assume a wire isn’t hot just because they tested it? They don’t control both ends, since as you pointed out, anyone could have a) a power source or b) a faulty connection, whether it’s allowed or not. So as a line worker I’d basically just not touch anything even in supposedly dead grid sections.
[+] [-] cesarb|7 years ago|reply
The lineworkers I've seen that aren't working with live wires use a special tool to ground the wires (it's a set of three clamps connected by a thick wire to a grounding rod). Once the wire's grounded, it's going to be hard to put any voltage on it.
[+] [-] amluto|7 years ago|reply
I don’t know if the workers make a habit of physically disconnecting all of the houses that are connected.
[+] [-] lb1lf|7 years ago|reply
For this reason, I'd be most surprised if there's a single backfeed system in existence which doesn't isolate your house from the grid once the grid goes down.
Edit: Finally got around to reading the blog post to the end and found that the author makes this exact point in the paragraph following the one quoted in the comment above.
[+] [-] sandworm101|7 years ago|reply
[+] [-] ghubbard|7 years ago|reply
> If you have a typical grid tied system (microinverters or normal string inverters, so easily 95+% of installed rooftop solar), the system is technically incapable of running off grid (without additional hardware). There's no waveform to sync with,
[+] [-] jccalhoun|7 years ago|reply
[+] [-] raverbashing|7 years ago|reply
A residential no-break has no waveform to sync with as well.
Something capable of syncing to the grid and then more or less keeping pace even if the main grid goes down should cost very little today. (And when the grid goes back it shouldn't have drifted too much unless something ridiculously big happened)
[+] [-] driverdan|7 years ago|reply
I live in an off grid bus. My whole electrical system cost in the US$9-10000 range with only 810W of solar. The other components cost a lot more:
* ~$900 for 3x 270W Renogy solar panels
* $1500 for 3.6kWh of LiFePO4 batteries (12 100A 3.6V cells)
* $1600 for a Victron 3kW inverter / charger
* $2000 for a Honda EU3000is generator to run my AC
The rest was the Victron solar controller, color control panel (that runs Linux!), breakers, relays, transfer switch, fuses, cable, and all the other stuff you need to hook it together.
This isn't at house scale either. The cost would go up significantly to support a house scale system.
[+] [-] nine_k|7 years ago|reply
OTOH not having a combustion-based backup is likely not very wise if you live off-grid. I wonder how often do you need to run it? That is, what part of your energy budget is covered by the solar energy?
[+] [-] unknown|7 years ago|reply
[deleted]
[+] [-] ssdd|7 years ago|reply
[+] [-] VectorLock|7 years ago|reply
[+] [-] agumonkey|7 years ago|reply
[+] [-] jefftk|7 years ago|reply
It's not ideal, but this is so much better than what most installs are built with (nothing).
[+] [-] test6554|7 years ago|reply
[+] [-] gnicholas|7 years ago|reply
[+] [-] SigmundA|7 years ago|reply
I have a Magnum 3000w Hybrid inverter in my RV with 320w of solar with a MPPT solar controller. The solar controller feeds the batteries and the inverter draws from batteries or charges them with UPS grade change over. Magnum hybrids can do interesting things like if the sun is out and I am running the air conditioner off generator or shore power it will pull batteries down to float voltage and invert excess power to lower draw, I usually get about 1 amp reduction with 320w of panels. You can also dial in your shore amps and if a load needs more the inverter will step in and provide the overage from the batteries. Nice if you driveway surfing and only have a 15 amp outlet but want to run the microwave or whatever. The RV is basically a giant UPS with generator.
[+] [-] tlrobinson|7 years ago|reply
It doesn't seem like a battery or capacitor to handle blips like an airplane flying overhead would need to be very large?
[+] [-] derefr|7 years ago|reply
[+] [-] PinguTS|7 years ago|reply
I know of some railway train setup, which is deployed in Saudi Arabia by Siemens, that uses a combination of battery and super caps to power the train. While the train starts it takes the sparking current from the super caps. While riding it will take the energy slowly from the batteries. While deceleration it will recuperate and will charge up the super caps, because they can be charged easily with a high current. So the super caps are used as a high available energy buffer with very fast charge and discharge capabilities. While the battery is only used during the times of less energy consumption. Also at the stations the super caps are super charged very quickly. With that concept, they can run the train the whole day with only 40% discharge of the battery. The battery is actually way smaller then in a Tesla.
This concept can be applied also locally. The problem: these super capacitors are way expansive so you need to design them to your specific requirements.
[+] [-] namibj|7 years ago|reply
If you use a small supercapacitor, which commonly has a minimum discharge time of about 2~20 seconds (similar to Lithium-ion pouch cells "LiPo", which are available with different "C" ratings, and negatively correlated gravimetric/volumetric energy density and maximum average discharge power (i.e., optimizing discharge current vs time to maximize the ratio of total power extracted divided by time until empty). You need more metal in the electrodes and the plate/foil that aggregates the current of the individual electrodes, leaving less space/weight for the parts that actually store energy.), you can use much more advanced power reduction techniques for electronic devices, as you have time for something approaching a proper shutdown. Compare e.g. the time your Laptop takes until it is off from the moment you close the lid.
Oh, and yes, these capacitors are cheap. One about 1kg / 1 liter size for about 100$ can provide 20kW average power, for 2 seconds. The main difference is that they don't care (much) if you cycle them at 100% depth of charge, apart from internal losses heating it up and thereby causing damage.
[+] [-] rdl|7 years ago|reply
[+] [-] CaliforniaKarl|7 years ago|reply
Does anyone know, what's a good resource for learning more about power generation, grid regulation, etc.? The relationship between frequency/voltage and available vs. demanded current, frequency sync, grid maintenance, etc.…
[+] [-] throwawaycanada|7 years ago|reply
Electrical Machines, Drives and Power Systems by Theordore Wildi
[+] [-] iamleppert|7 years ago|reply
[+] [-] dragonwriter|7 years ago|reply
So, your example of energy options other than solar is solar with hydro storage? Or did you mean “other than photovoltaic” when you said “othet than solar”.
[+] [-] akeck|7 years ago|reply
[+] [-] Johnny555|7 years ago|reply
I don't remember seeing any articles that blame the power company for home solar not working off-grid... I do remember seeing articles saying that most home solar installations won't work if the power grid is down, but nothing that implied that the power companies were behind it.
[+] [-] modeless|7 years ago|reply
[+] [-] alkonaut|7 years ago|reply
In hot climates you have some power use when the sun is up (cooling, pool heating,) but where I live I’d need my power most when the sun is absent in night and winter (power use is probably 80% heating). Any amount of solar power would be nearly useless if only available when the sun is shining.
[+] [-] WalterBright|7 years ago|reply
I built an audio amplifier in college that had a couple of huge capacitors on the power supply (about the size of a can of soda). It would keep the amp running a few seconds after I shut off the power.
[+] [-] segmondy|7 years ago|reply
No TV, no Washer/Dryer (you will hand wash), No regular fridge, get a small 12v fridge. No microwave, use stove to heat up food. No A/C, design the space to not get hot, high windows, under the shade, facing away from the sun. Maybe a small fan. The biggest optimization begins with your appliances.
[+] [-] ggm|7 years ago|reply
Lots of homebrew 'you can plug this magick cable I made' methods to supply volts across the fence to neighbours houses when the power goes down are really bad: behind the meter is just as lethal as in front of the meter, if you get it wrong.
TL;DR if you need to read a website like this for clue how to avoid losing power, you are putting your life at risk if you don't follow code, and don't know what you're doing.
[+] [-] driverdan|7 years ago|reply
You have to read the specs carefully to make sure they are a good match for your use.
[+] [-] bacon_waffle|7 years ago|reply
An off-grid capable inverter needs to handle several state transitions smoothly, and some of those are hard. For instance, starting up can be a lot harder when there's no mains voltage. An inverter will have a maximum output current, which is generally not too far from the maximum power output of the inverter divided by minimum mains voltage. If you have a load that presents as a constant resistance, like a water heater, then as the inverter's output voltage goes from 0 to 240V (120V for areas with weenie power) the current will smoothly go from nothing up to whatever the load normally draws, along with the voltage, and there's no problem. But! A lot of loads aren't resistive - things like computers, battery chargers, and inverter-driven motors (as newer appliances often have) will tend to look more like constant-power loads. So, once they decide it's OK to turn on, if the voltage happens to be half of nominal at that point, they will try to pull twice their nominal current. If that causes the total draw to exceed what the inverter can provide, it stops and maybe tries again. It's practically impossible to measure what the load characteristic of something like a house, from the perspective of an inverter, so the best you can do is something like guess-and-check, and that's not a great solution.
Then, how to handle reconnection with the grid; you either need to re-synchronise before reconnecting, or ensure that the intrepid homeowner first shuts off the house before turning the switch to reconnect.
Switches that can handle that job may need to be specified per-installation, and there are all sorts of regulations around how they work and where they can go. They are not cheap, as a rule. Some regions have the solar generation stuff on a separate export power meter from the import one. This means that the switch needs to be on he supply side of both meters, and that could be regulatorily complicated.
What about multiple inverters? These things all need to play nice with each other when solo, or installed with others. Perhaps you didn't design those, and they might try to start up too, then fire up their anti islanding which should promptly trip out again.
Remember this all has to work with variable input power available, and it needs to be packaged up so that installation is straightforward, and operation is basically hands-off. Oh, and inexpensive too!
[+] [-] irrational|7 years ago|reply
[+] [-] parimm|7 years ago|reply