Portable Emergency Power - Inverter

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costs to everything.
in general it like this

you want auto-switch, power everything = $$$$$$
you want auto-switch, power some stuff = $$$$
you want isolated power system, minimal stuff = $$

a freezer full of ice jugs + a couple of smaller solar panels + small batt bank + inverter(s) = low cost solution
not needing to power heavy power items is key to when poco dies for days.

why would you need a heavy gen to keep fridge and toaster working when after days w/o power the food in the fridge is gone, and store shelves remain about empty? i of course assume here that no poco for days means something bad happened, thus even stores have failed fridges/freezers and truck delivery has pretty much halted.

but then again, back in the day, candles, bottled water, canned foods, and a small fire pit lasted a week+ when a hurricane hit where i was and poco was dead for that time. cost there is about zero.
 
jaggedben said:
With such a setup it's also a little useless to discuss if the PV is 'directly' powering loads in any given moment when the sun is shining.
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When the sun is shining the output from the PV varies with the intensity of the sunlight, while the current to the loads is supplied by the inverter on demand and kept constant for constant loads. It's the batteries that enable the inverter to do this, so to my mind the power from the PV to the loads is at least somewhat indirect. If the loads are consuming exactly the same amount of power as the PV is putting out, then I guess I'd call it direct since there will be no flow into or out of the batteries, but I don't think that would happen very often.

But you know all that, right? :D
 
ggunn said:
When the sun is shining the output from the PV varies with the intensity of the sunlight, while the current to the loads is supplied by the inverter on demand and kept constant for constant loads. It's the batteries that enable the inverter to do this, so to my mind the power from the PV to the loads is at least somewhat indirect. If the loads are consuming exactly the same amount of power as the PV is putting out, then I guess I'd call it direct since there will be no flow into or out of the batteries, but I don't think that would happen very often.

But you know all that, right? :D
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It is also possible to design a PV powered inverter which does not use batteries but does limit its output to the power required by the load. There needs to be some small amount of energy storage to allow the input power (constant) to be retimed to match the varying output power over a half cycle of the AC.
The Secure Power Supply (SPS) in SMA grid tie inverters is such a beast.
Neither a simple GTI nor a simple battery source inverter can be connected directly to PV to feed a varying load, but that does not mean that the product cannot or does not exist.
As far as taking an off the shelf stand alone inverter designed for battery input, no, it is not likely to work well even if the PV source is wastefully sized to deliver the peak power of the AC waveform.
 
but ggunn, loads are not sized to match nominal power output of a pv panel. i would not attach a 250w light to a pv rated nominal 250w.

if my loads add up to say 1200w, then perhaps i install 7 or 8 250w nominal pv panels so that if there is some drop off in light i have some buffer to still operate my loads.

and although pv's have output related to light density, that curve does not extend for very long, there are thresholds.

the freezer i mentioned runs 120vac @ 5amp, so it needs approx 600w to run. as example, 250w panel that is ~8A at ~37v, three of these in parallel can supply an inverter up to 24A@37v or 888w, should be enough to allow such freezer to start and run via proper inverter (put 10% waste in the inverter, etc).

the investment in panels + inverter + wiring + install + maintenance to say just run the freezer during the day to keep ice in ice mode is still way more $$ than using the $25 per year to run freezer from poco, over 10years just $250 !! $250 is also on the high side because if you dont open the door the unit will run way less.

also remember, all the gen solutions have the same issue, you typically need to oversize them to run the loads, you cannot be smaller. loads that are transient loads (lights, radio, toaster, etc etc) cause items to be oversized, but their duty cycle use is fairly low, but you still need to buy kw gen for max load, in reality you over pay per kw because the gen is not always max'd out when running. this is the same problem in computing, lots of CPU's that are paid for to crunch #'s at 3.2GHz, yet they sit mostly idle doing nothing.


cant i take say 16 250w37v panels into 8 groups of 2 in series, parallel the 8 groups, feed that into a Cotek SK3000-248
the Cotek has low v shutdown so its at the mercy of sunlight, but when sun is good the inverter does its thing.
 
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gadfly56 said:
For the most part, as I understand it, you can't grid tie a battery system without jumping through a lot of design hoops. That's why in a power outage if you have a solar array you are just as dark as everyone else.
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That's really not true, not these days. Adding storage to a SolarEdge system is about as simple as changing the inverter model and hanging the battery on the wall. Tesla's AC coupled solution is entirely independent of the solar system design, as pretty much an AC coupled solution would be.

One Powerwall is not going to get you the same oomph as the 19.5 kW generator.
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I acknowledged that by also pointing out that many, many people don't need that oomph. Again, how do you put a price on not having to have fuel available? If the economics of solutions are even in the same ballpark - and I believe I've shown that they are - then an intangible like that is something that can't be calculated.

You also assume a lot if you think that the solar array is going in for free. ... Tack on another $20,000 or so to the Powerwall cost.
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You're not demonstrating an understanding of my point. If the economics of the solar system as grid tied system are favorable on their own, then the cost of the solar system is not part of the cost of backup power. I'll grant that someone has to already have cash on hand, or access to financing, to make the solar an option. Or already have the solar system on their roof. But around here that's a lot more people than have a backup generator installed.

The days of that sort of government incentive program are over in most places and likely to disappear everywhere else soon.
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You do not demonstrate much understanding of the solar market with that statement. In California we could still sell solar with no incentives at all.

The fact of the matter is that batteries as power for normal household use are not ready for prime time and absent a Black Swan event will likely remain so forever. :thumbsdown::thumbsdown::thumbsdown:
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Depends on the market you're in. And if it's not yet, where you are, give it a few years.
 
FionaZuppa said:
but ggunn, loads are not sized to match nominal power output of a pv panel. i would not attach a 250w light to a pv rated nominal 250w.

if my loads add up to say 1200w, then perhaps i install 7 or 8 250w nominal pv panels so that if there is some drop off in light i have some buffer to still operate my loads.

and although pv's have output related to light density, that curve does not extend for very long, there are thresholds.

the freezer i mentioned runs 120vac @ 5amp, so it needs approx 600w to run. as example, 250w panel that is ~8A at ~37v, three of these in parallel can supply an inverter up to 24A@37v or 888w, should be enough to allow such freezer to start and run via proper inverter (put 10% waste in the inverter, etc).

the investment in panels + inverter + wiring + install + maintenance to say just run the freezer during the day to keep ice in ice mode is still way more $$ than using the $25 per year to run freezer from poco, over 10years just $250 !! $250 is also on the high side because if you dont open the door the unit will run way less.

also remember, all the gen solutions have the same issue, you typically need to oversize them to run the loads, you cannot be smaller. loads that are transient loads (lights, radio, toaster, etc etc) cause items to be oversized, but their duty cycle use is fairly low, but you still need to buy kw gen for max load, in reality you over pay per kw because the gen is not always max'd out when running. this is the same problem in computing, lots of CPU's that are paid for to crunch #'s at 3.2GHz, yet they sit mostly idle doing nothing.


cant i take say 16 250w37v panels into 8 groups of 2 in series, parallel the 8 groups, feed that into a Cotek SK3000-248
the Cotek has low v shutdown so its at the mercy of sunlight, but when sun is good the inverter does its thing.
Click to expand...
I've said all I have to say on this. You guys carry on. :D
 
GoldDigger said:
It is also possible to design a PV powered inverter which does not use batteries but does limit its output to the power required by the load. There needs to be some small amount of energy storage to allow the input power (constant) to be retimed to match the varying output power over a half cycle of the AC.
The Secure Power Supply (SPS) in SMA grid tie inverters is such a beast.
Neither a simple GTI nor a simple battery source inverter can be connected directly to PV to feed a varying load, but that does not mean that the product cannot or does not exist.
As far as taking an off the shelf stand alone inverter designed for battery input, no, it is not likely to work well even if the PV source is wastefully sized to deliver the peak power of the AC waveform.
Click to expand...
Yes, of course there is the SMA Secure Power Supply, but it's very limited. Some folks think that they can just hook up a lot of PV to a small battery and inverter in order to "fool" a grid tied inverter into thinking it's connected to the grid so it will run off grid. They are mistaken.
 
jaggedben said:
That's really not true, not these days. Adding storage to a SolarEdge system is about as simple as changing the inverter model and hanging the battery on the wall. Tesla's AC coupled solution is entirely independent of the solar system design, as pretty much an AC coupled solution would be.



I acknowledged that by also pointing out that many, many people don't need that oomph. Again, how do you put a price on not having to have fuel available? If the economics of solutions are even in the same ballpark - and I believe I've shown that they are - then an intangible like that is something that can't be calculated.



You're not demonstrating an understanding of my point. If the economics of the solar system as grid tied system are favorable on their own, then the cost of the solar system is not part of the cost of backup power. I'll grant that someone has to already have cash on hand, or access to financing, to make the solar an option. Or already have the solar system on their roof. But around here that's a lot more people than have a backup generator installed.



You do not demonstrate much understanding of the solar market with that statement. In California we could still sell solar with no incentives at all.



Depends on the market you're in. And if it's not yet, where you are, give it a few years.
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I don't believe you have. One Powerwall? I'm glad that during any outage you have the sun will shine merrily down at full brightness.

In California they are using smart meters to do demand metering for residential at up to $0.90/kW-hr, so yeah, it makes sense. They are also re-defining peak time to make solar more attractive. I will foolishly settle for power at $0.15/kW-hr.

At $2/kW-hr batteries make no sense for anyone using power the way Americans do today. And no, I'm not changing the way I live to satisfy Gov. Moonbeam's messiah complex. Let's give it three years and will see how it's going then.
 
gadfly56 said:
... I will foolishly settle for power at $0.15/kW-hr.
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We get people residential solar energy for about $0.08/kW-hr, if your interested in getting in on that. (And that's before the federal tax credit, which makes it more like $0.06).


At $2/kW-hr batteries make no sense for anyone using power the way Americans do today. And no, I'm not changing the way I live to satisfy Gov. Moonbeam's messiah complex. Let's give it three years and will see how it's going then.
Click to expand...

If you want to be accurate try $0.40 to $0.50 / kWh. And yeah, let's check in in three years.
 
drcampbell said:
I think you mean per watt·hour, not per kilowatt·hour.
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I meant the levelized cost to charge and discharge a kilowatt hour of energy, which is what I read gadfly's post as referring to. Not referring to the cost to install a kWh of storage capacity. (Granted, the same units for two very different things is confusing.)
 
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jaggedben said:
I meant the levelized cost to charge and discharge a kilowatt hour of energy, which is what I read gadfly's post as referring to. Not referring to the cost to install a kWh of storage capacity. (Granted, the same units for two very different things is confusing.)
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Actually, I slipped the decimal point a few places. It should be $2/watt-hr. That price applies to grid-scale projects. Google the Mira Loma project in CA.

On the consumer scale it looks like the offering is about $1/watt-hr, but it's hard to parse true pricing because that's typically the net price to the consumer, not the true cost, as subsidies may be involved.
 
gadfly56 said:
On the consumer scale it looks like the offering is about $1/watt-hr, but it's hard to parse true pricing because that's typically the net price to the consumer, not the true cost, as subsidies may be involved.
Click to expand...

At my company's pricing, ~$1/watt-hr capacity is the price before any subsidies.
 
jaggedben said:
Now you're confusing power and energy. That's a 2MW system.
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You're right, that is a mistake. However, it gets more interesting when you visit Tesla's website. Their spec for the Powerpack is 50 kW and a capacity of 210 kW-hr. There seems to be a disconnect between the info at Tesla and the web in general.
 
why is Tesla the defacto ?

imho, Tesla is novelty and everyone is buying into Musk's crazy ideas, literally.
 
FionaZuppa said:
why is Tesla the defacto ?

imho, Tesla is novelty and everyone is buying into Musk's crazy ideas, literally.
Click to expand...

To my knowledge, Tesla is the only one integrating battery packs for a grid-size battery storage solution. Everyone else seems to be staying in the consumer arena. That might be just a good PR campaign on Tesla's part but it's working so far.
 
gadfly56 said:
To my knowledge, Tesla is the only one integrating battery packs for a grid-size battery storage solution. Everyone else seems to be staying in the consumer arena. That might be just a good PR campaign on Tesla's part but it's working so far.
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my view is this, there are folks out there as smart and smarter than Elon, and if we are not seeing a jump onto the same wagon from others then i suspect Elon is chasing a falsehood.

consumer market is not really a market for consumers, its a gimmick to get consumers to buy into expensive systems (typically a lease) where the installer (solar vendor) profits and the consumer saves just a little bit.

i know of no POCO who wishes every home in AZ/TX/CA/NM to have 20kW of panels on the roof to power home itself and to feed extra to the grid, actually, they like feeding to the grid for resale, they just wont pay you for it!
 
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