Portable Emergency Power - Inverter

[RumRunner]

Such PV systems work best with motor loads far enough below their nominal rating, or with a built in VFD or soft start capability.

Sent from my XT1585 using Tapatalk

Not all inverters put out "full sine wave". A lot of those on the market are synthesized square wave.
Since VFDs are designed to harness the sinosoidal rise and dips of the AC cycle a square wave would be outside the design premise.

 

[FionaZuppa]

Not all inverters put out "full sine wave". A lot of those on the market are synthesized square wave.
Since VFDs are designed to harness the sinosoidal rise and dips of the AC cycle a square wave would be outside the design premise.

like Samlex pure sine wave inverters, and many others.
if it were just for some basic tungsten bulbs the cheapy HF inverter would work. anything beyond that the pure sine wave inverters is the only way to go.

a small Kohler propane gen is what i would be looking at.

if pv/batts/inverter is the ask, i would seriously think about having a freezer full of ice jugs to keep fridge cold as needed when poco dies, and use inverter to power smaller items.

 

[ggunn]

what?
i worked on US govt contract where we had pv's out in remote fields (off grid remote shelters), during the day the solar panels charged the batts AND ran the electric (+ hvac) during the day, a transfer switch went to batt when pv voltage dropped below a threshold. a propane backup gen was there if batts died down too low. batts and panels powered an array of inverters.

what do you mean solar panels cannot power a load?

Solar modules cannot directly power a load (there are exceptions, like agri pumps where one doesn't care when or how fast they run) because they produce a given amount of current relative to their insolation; they cannot deliver current on demand. The operative word in your above statement is "and". Your batteries have to be able to absorb the entire output of the PV or the array will shut down if the loads are calling for less current than the PV output plus what the battery can take. The way these systems are wired is the PV is routed through a charge controller into the batteries and the loads are powered from the batteries.

The bottom line is that your batteries have to be big enough to absorb the entire output of the PV system and to power the loads on their own. You cannot build a system with a big PV section and a tiny battery and expect it to run sustainably.

I obviously have not seen any electrical drawings for the systems you are speaking of, but I would be willing to wager that there was no transfer switch in them unless they were also grid tied, and PV output voltage doesn't vary with insolation, current does. PV modules are current sources (not voltage sources) over most of their IV curve; hence my first sentence above. To drive loads and keep voltage constant you need a voltage source, i.e., batteries.

 

[FionaZuppa]

i do not know of any batt bank that simply keeps charging because the pv's want to keep delivering, and if pv's cant deliver the pv's shut down.

if i have one pv panel rated output 12v 12w, a 12ohm load will max out pv ability, a 24ohm load will just be 6w, the pv provides all the power and does not shut down. i do open ckt on output, pv just sits there @12v with 0A.

how do large solar farms deliver pv power w/o batts when power demand varies?

maybe i just not understanding what you mean.

 

[drcampbell]

Solar modules cannot directly power a load ...

Um, no. Depends on the load. Domestic refrigeration might be quite suitable for being directly PV powered; the compressor could run when PV power is available and the refrigerator's thermal insulation could prevent the temperature inside the cabinet from rising too much, too fast.

... how do large solar farms deliver pv power w/o batts when power demand varies? ...

Grid-connected PV farms deliver however much power they're capable of, and grid operators reduce the output of gas-fired and coal-fired powerplants so that generation & consumption remain in balance.

 

[FionaZuppa]

Grid-connected PV farms deliver however much power they're capable of, and grid operators reduce the output of gas-fired and coal-fired powerplants so that generation & consumption remain in balance.

i posed to Q but already knew the answer, it was one of those Q's

 

[ggunn]

Um, no. Depends on the load.

Um, you edited out where I said that there are exceptions, and the case you cited is not typical.

 

[jaggedben]

ggunn: Does the battery set up make it uneconomical?

How do you put a price on harnessing power from nature after a disaster where the grid may be out for days (or weeks or months) and there may also be a liquid fuels shortage?

 

[jaggedben]

what?
i worked on US govt contract where we had pv's out in remote fields (off grid remote shelters), during the day the solar panels charged the batts AND ran the electric (+ hvac) during the day, a transfer switch went to batt when pv voltage dropped below a threshold. a propane backup gen was there if batts died down too low. batts and panels powered an array of inverters.

Was this some very early experiment? I have to express some skepticism about the transfer switch. Simply connecting the PV to the batteries through a charge controller in parallel to the load makes a helluva lot more sense. (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.)

 

[FionaZuppa]

Was this some very early experiment? I have to express some skepticism about the transfer switch. Simply connecting the PV to the batteries through a charge controller in parallel to the load makes a helluva lot more sense. (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.)

no, just a few years ago, i did mean to say transfer switch for Kholer gen. the pv's ran everything (hvac too) + charged batts during the day, if at night the batts went too low the Kholer gen kicked on to run things and to charge batts. its more like a backwards UPS system, on batts/pv all the time and if batts/pv went too low the gen kicked on and UPS xfer flipped over. batts/pv were the util side of the UPS, etc. most stuff was 48vdc, hvac was 240ac. if i recall correctly the inverters were on aft side of UPS doing 48vdc to 240ac.

 

[gadfly56]

How do you put a price on harnessing power from nature after a disaster where the grid may be out for days (or weeks or months) and there may also be a liquid fuels shortage?

Easy; when the cost of a generator and fuel storage is 1/10 the cost of a battery bank big enough to power your house for a week.

Let's see:
Tesla Powerwall 2, 13.5 kWhr, 5kW steady, 7kW peak, cost:$6,200, less installation, DoD is claimed at 100%
Average American Home consumption: 30 kWhr/day; lets round it down to 27 kWhr/day
Total Power walls: 2/day x 7 days = 14, 14 x $6,200 = $86,800

OK, you haven't put a single panel on the roof. A 19.5kW generator running NG from HD will run you $4,797 with ATS, less installation.

Gee, I wonder which option makes more economic sense? :roll:

 

[GoldDigger]

Some, particularly preppers looking ahead to SHTF will argue in favor of something longer term, not dependent on fuel storage.
They are free to take that outlook, but I do not invest my money for that scenario.

 

[Barbqranch]

Easy; when the cost of a generator and fuel storage is 1/10 the cost of a battery bank big enough to power your house for a week.

Let's see:
Tesla Powerwall 2, 13.5 kWhr, 5kW steady, 7kW peak, cost:$6,200, less installation, DoD is claimed at 100%
Average American Home consumption: 30 kWhr/day; lets round it down to 27 kWhr/day
Total Power walls: 2/day x 7 days = 14, 14 x $6,200 = $86,800

OK, you haven't put a single panel on the roof. A 19.5kW generator running NG from HD will run you $4,797 with ATS, less installation.

Gee, I wonder which option makes more economic sense? :roll:

However, when there is a power outage, you generally can get a pretty good idea of what the duration will be by how widespread the damage is. If I were in that situation, I would cut back to refrigerator (you can buy one that uses barely more than 1 kWh per day), microwave for maybe 30 minutes total per day (0.75kWh per day), and a few lights for a few hours (.25 kWh per day). Then the Powerwall starts to look a lot better, and no engine to run or not be able to start, no fuel to deal with.

 

[gadfly56]

However, when there is a power outage, you generally can get a pretty good idea of what the duration will be by how widespread the damage is. If I were in that situation, I would cut back to refrigerator (you can buy one that uses barely more than 1 kWh per day), microwave for maybe 30 minutes total per day (0.75kWh per day), and a few lights for a few hours (.25 kWh per day). Then the Powerwall starts to look a lot better, and no engine to run or not be able to start, no fuel to deal with.

Well then, you could go with a Generac 7.5 kW unit from Norwal for $1,877. Your Powerwall 2 is still $6,200 and that will get you a week, where the Generac will get you much longer as long as the natural gas flows. And you're still not charging the Powerwall yet. It still doesn't make any sense economically.

 

[JFletcher]

How do you put a price on harnessing power from nature after a disaster where the grid may be out for days (or weeks or months) and there may also be a liquid fuels shortage?

Buy gasoline in advance. Two Honda Eu2000i generators (~$2,200 for both, plus accessories) in parallel gives you 4kw. One of them can run 8 hours on one gallon of gas, at ~56db, which is very quiet. Not 0db like a battery bank or power wall, but still super quiet. A week prior to a hurricane or the like one could buy a hundred gallons of gas for $250 (current prices). If you dont use that then you just dump it in your vehicle. or keep until next time if you bought Supreme (92-93 octane) and use Sta-bil or the like.

Counting gas storage tanks, extension cords, the generators, and accessories, you're right around $3k for up to 4kw of power and enough gas to run both at full throttle for a week and a half... one unit at half for a month.

A single 250 A-H deep cycle AGM 12V battery can run over $500... best small emergency system would be a hybrid, perhaps a single Eu1000i or equivalent with batteries and panels, however its price will still be several times what a small gas generator would be.

 

[FionaZuppa]

Buy gasoline in advance.

it spoils fast in humid environments. to runs days isnt that in the hundreds of $$?
also, if its city water you can find water powered generator, perhaps not huge watts though, but enough to runs lights and some electronics.

ice in freezer method. additional benefits is that you can also use the freezer as needed for other things, like maybe frozen whatever during holidays or parties, etc.
i went 10yr only thinking maybe thats the lifespan of the freezer, but they usually go longer than that.

10.6cuft GE freezer ~$350


218 kwhr/yr * 11.9c/kwhr (miami) = $25/yr


TCO
0yr $350
1yr $375
2yr $400
3yr $425
4yr $450
5yr $475
6yr $500
7yr $525
8yr $550
9yr $575
10yr $600

 

[jaggedben]

Easy; when the cost of a generator and fuel storage is 1/10 the cost of a battery bank big enough to power your house for a week.

Let's see:
Tesla Powerwall 2, 13.5 kWhr, 5kW steady, 7kW peak, cost:$6,200, less installation, DoD is claimed at 100%
Average American Home consumption: 30 kWhr/day; lets round it down to 27 kWhr/day
Total Power walls: 2/day x 7 days = 14, 14 x $6,200 = $86,800

OK, you haven't put a single panel on the roof. A 19.5kW generator running NG from HD will run you $4,797 with ATS, less installation.

Gee, I wonder which option makes more economic sense? :roll:

Well, those numbers are sort of ridiculous.

You definitely do not need 14 Powerwall units if you have a solar system to recharge them each day, or even every other day. A more realistic installation to provide emergency power would be 1 or two. In any state where the solar system pays for itself as a grid-tied system the cost for that should not be figured into the cost of a backup solution. A 19.5kW generator is nice but will be run way under capacity by most people.

Both the numbers you quoted are less installation costs. What this means is that the $1000-2000 difference between the generator equipment cost and 1 Powerwall is perhaps not reflected in the installed cost depending on the details of a house and how costly it is to run a new gas line to the generator location. (Also a lot of urban houses really don't have a good place for a generator.)

So the real numbers for someone without a huge emergency power need end up being ... about $10-13 grand for the solar charged battery, and maybe $8-12 grand for the generator. So there's plenty of overlap depending on the job details. That's in my neck of the woods for installation costs.

So given that that the real costs are much more competitive, I ask again: how do you put a price on not having to guarantee that fuel is available? Being completely not dependent on anyone else, it's the American Dream. :lol:

 

[JFletcher]

it spoils fast in humid environments. to runs days isnt that in the hundreds of $$?

A single Eu2000i running about 1/3rd load gets 8 hours per gallon, so $8 a day. At full throttle they still only use about 5 gallons a day. I mentioned that 100gal would be $250. if you run a big 6500W 'old school' generator, they can go thru 3+ gallons an hour. Running a frig, a few lights, and a few fans would be ~1/3rd load. A small inverter generator of any type is a heck of a lot more portable than banks of heavy batteries.

Sta-bil gasoline stabilizer will let a 5 gal can of 87 octane that's put away in October still be good in April*. You're probably thinking of a marine environment and the problems boat engines can have with 10% ethanol gas. Gas dryer can fix that to some extent. Most boaters I know drive extra distance to get gas w/o the ethanol in it, which is hygroscopic (absorbs water from the air).

*For years, for the last grass cutting of the year, I get a can of 93 octane and add sta-bil to it. I run it in my equipment and leave the tanks full. Never once had a gummed up carb in any lawn equipment, chainsaw, jet ski, motorcycle, etc that I've owned. Even if the gas degrades some it's still above 87.

 

[FionaZuppa]

Sta-bil gasoline stabilizer will let a 5 gal can of 87 octane that's put away in October still be good in April*. You're probably thinking of a marine environment and the problems boat engines can have with 10% ethanol gas. Gas dryer can fix that to some extent. Most boaters I know drive extra distance to get gas w/o the ethanol in it, which is hygroscopic (absorbs water from the air).

most of FL is "marine" env. wet salty air everywhere.

if you search good you'll find ice energy solutions when it comes to solar renewable. sounds odd, but its out there, a cost effective way.

 

[gadfly56]

Well, those numbers are sort of ridiculous.

You definitely do not need 14 Powerwall units if you have a solar system to recharge them each day, or even every other day. A more realistic installation to provide emergency power would be 1 or two. In any state where the solar system pays for itself as a grid-tied system the cost for that should not be figured into the cost of a backup solution. A 19.5kW generator is nice but will be run way under capacity by most people.

Both the numbers you quoted are less installation costs. What this means is that the $1000-2000 difference between the generator equipment cost and 1 Powerwall is perhaps not reflected in the installed cost depending on the details of a house and how costly it is to run a new gas line to the generator location. (Also a lot of urban houses really don't have a good place for a generator.)

So the real numbers for someone without a huge emergency power need end up being ... about $10-13 grand for the solar charged battery, and maybe $8-12 grand for the generator. So there's plenty of overlap depending on the job details. That's in my neck of the woods for installation costs.

So given that that the real costs are much more competitive, I ask again: how do you put a price on not having to guarantee that fuel is available? Being completely not dependent on anyone else, it's the American Dream. :lol:

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.

One Powerwall is not going to get you the same oomph as the 19.5 kW generator. See below my original post for an even lower cost alternative if you insist on moving the goalposts. You also assume a lot if you think that the solar array is going in for free.
The days of that sort of government incentive program are over in most places and likely to disappear everywhere else soon. Tack on another $20,000 or so to the Powerwall cost.

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: