Building a backup power system

Alternative energy sources
Forum rules
The usual. As I have two large solar PV systems here, and my lab assistant just put one in, and others are interested in things like this, here's where that stuff goes. This is mostly for things that work now, not "gee someday a fusor will do this" -- we know that, but it's not someday yet.
The hope is to save anyone embarking on this sort of thing a lot of wasted time and money, as at least I have been off the grid since 1980 and have had a lot of practice (and made mistakes you won't have to).

Building a backup power system

Postby Joe Jarski » Tue Dec 06, 2011 6:43 pm

I've been contemplating how to implement a backup (for now) power system, with a distant goal of eventually being mostly self-sufficient. My power here goes out quite often, usually not for long periods, but it goes out almost every week, if not more. I've been lucky so far because I've been able to borrow a generator as needed from friends or family when I didn't have power because they usually did. Sooner or later though, we're going to get hit with a big ice storm or something else that'll take things down for several days. I was without power for ~4 days when things went dark in the Northeast a few years ago, but that was in the middle of summer - not really a big deal, except that you had to drive quite a while to find anyone that did have power if you wanted to buy gas and other supplies. This is a longer term plan (due to cost) to get *nearly* off the grid and be able to function normally without grid power for extended periods. So, here is what I've been thinking and wanted to get some input form others...

The first thing for the near term is a small ~2kW inverter generator that can run the essentials in rotation. I'm thinking small for the fuel efficiency (less to store) and then use it as a backup for the rest of the system down the road. The next thing would be batteries for longer term power storage and peak load handling that would be needed for normal daily operation rather than a minimalist emergency situation. The last thing would be to add solar and/or wind generators to maintain the batteries rather than using grid or generator power on a regular basis.

This seems like the most logical approach to building a system that would still be useful during a "widespread" power outage. I suppose an argument could be made for adding batteries and solar/wind genny at the same time and just increase capacity as you go. The need for a generator is obvious, but there may be a better strategy for building the rest of the system over time. Any thoughts?
User avatar
Joe Jarski
 
Posts: 231
Joined: Thu Sep 16, 2010 8:37 pm
Location: SouthEast Michigan

Re: Building a backup power system

Postby johnf » Wed Dec 07, 2011 1:41 am

Joe
Although the inverter gensets are of better efficiency than the usual genset I would consider a slow revving diesel genset. Look around for an ex boat type house generator Kohler, Lister/Petter enclosed (silenced) type. Several brands exist and at low loads an oily rag is all they need to run.
Iknow Diesel is expensive in the US but with a biocide in it, it will last for years unlike petrol (gas) which goes stale pretty quick. These units usually have an alternator that is oversize compared to the engine output to allow a power facor of up to 0.8 either way without burning the alternator up.

If going for something new check out the whispergen for bat charging and heat very efficient stirling technology --I have posted on these before on this site
johnf
 
Posts: 433
Joined: Sun Aug 08, 2010 3:51 pm
Location: Wellington New Zealand

Re: Building a backup power system

Postby Doug Coulter » Wed Dec 07, 2011 11:22 am

John's points are well made even to this guy who HATES diesel fumes and the noise they always make. BillF's Lister setup is most impressive as well - we'll see how it works in practice, should be good but probably will need some tweaking once real operational experience is had. At the moment, I believe his thinking is just a power company replacement for an otherwise unmodified lifestyle. But we might be getting the cart ahead of the horse proposing solutions without a well enough defined problem here.

What are your essentials? How many motor-start loads are there? Those are the worst, especially if there are more than one that might try to start at the same time. Unlike the big power company, we can't have the inherent load leveling of large numbers here, so we have to sweat that more than they do. Also once you've handled your surges, you need to define some average as well, as that's what will have to be delivered most of the time - your system should be set up to be happy doing that - if it groans a little on peaks, no big deal.

Inverters have finally gotten to the point of handling surges well, but at the limit, their source has to have enough inertia at some point to keep up during the surge. My little 1kw inverter genset will start and run my 3kw electric chainsaw, but will eventually bog if I push it too hard, for example - and it works better if I set it to run full rpm instead of throttling down between loads for that use. A 3600 rpm genset will have more stored inertia due to the E=mv2 thing, but will wear quicker in use. If you're not going to pile on the hours - you get a different winner. Since all mufflers are low pass filters, consider that higher RPM's are actually easier to make quiet. It's just run life that suffers.

Anticipated use is really important to minimizing overall costs (which probably need to include your time for preventative maintenance). You might not care much what the running costs are if they are only going to happen infrequently in a general power outage, but care a heck of a lot if, like me, you're always in that state. So the capital vs run cost equation is one that affects all the other decisions.

As far as fuel storage goes, consider that you'd run a generator some anyway as part of the maintenance program, and that you probably have a reservoir of fresh fuel around all the time - your vehicle! It's not that hard to add a tee and a valve to get it to pump its fuel out into something else, and by its nature it's usually pretty fresh. I've done this and it's a good solution and a lot less messy than a bunch of cans - and easy to transfer from the gas station to the end use by comparison. A little bit of piping and valving means never having to carry (and spill) fuel.

Any fuel based generation system is most efficient running wide open on the torque peak - the problem is, if it can handle your peak loads, it's then almost never in that state, and usually at a much lower output - which is why inverter gensets exist as a partial solution to that one. So at some point, you start thinking about batteries, as even with their losses, you win in fuel/KWh.
This implies a way to get to AC from batteries of course. I've had great luck with Trace/Xantrex inverters (their name keeps changing) on that, but those things aren't cheap. Most battery tech you don't want indoors with you - the gases always entrain some electrolyte, and whether that's sulfuric or hydroxide, it makes a mess of things around them. However, you do want some temperature moderation on them to make them perform best. A decent solution is a basement with venting, or a little "energy shed" built onto the side of the building. I've not had troubles with H2 buildup myself - it's pretty good at getting away on its own. Nearly all the newer inverters will act like a grid-tie UPS and maintain batteries when there's grid power - or sell it back to the grid if you've got extra. The sine wave ones are really nice...

Once you go the battery/inverter route (which sadly does cost more money) then the flexibility of the system increases dramatically. You can have any number of ways to charge them, accept charge at whatever rates and times work best for the sources, and take it out as needed (within battery capacity of course). You can also have more than one inverter to handle the "what if" a bunch of surges want to happen at once. I'm doing that here with some machines on different inverters - the batteries can handle enormous surges that any one inverter can't. Deep cycle batteries can't do as much surge as the more short-lived batteries, but you either just use more, or use some trolling batteries across them like bypass capacitors - this actually works, and I do it here. The trolling batteries take all the gaff, and die in a year or two - but are light and cheap and easy to replace, allowing the "submarine" batteries to last forever.

A large advantage of this is also that you can then size your genset to only have to handle the average and run it in its most efficient part of the envelope. I was sort of surprised at the realization that most of the available ones are now too big! That 1kw one is running now - second day of dark here, and snow about to fall - and it's making net gain into the batteries while loafing. IT wouldn't keep up with my lathe, but if I just made a few parts, it would catch up again by the end of the day easily. My 3.5kw one is getting less and less use these days. I did use it once to charge up the Volt - inefficient compared to other ways, but I wanted to do a battery range test on a day I didn't have another way (no sun).

And on that one - the Volt is by far the most efficient fuel to KWh converter I've come across. Kinda an expensive way to get there (you do get a sexy car out of the bargain), but the tech in that engine generator is the absolute best man has come up with yet. My best guess at this point is that it gets me about 25% more output energy per input gallon than anything else I've had here. And it knows how to get it's own gas (fun!), I don't have to touch the fuel, and due to the nature of the thing, the engine gets run enough to preclude the need for the odious preventative maintenance you have to do on a fixed-plant generator. (Trust me, if you skip that, you'll find out - you have to at least test-run your generators weekly or they won't be working when you need them - and you should run them long enough to bake the blow-by water out of the oil each time and really give them a test under load).

So far, I've not had the chance to test the Volt as my prime system backup. The reason is weird, but it's going to get solved soon. The Volt can put out up to about 200 amps into a 12 volt load, enough for my purposes, without having to get into the 360v main battery, and will run the IC engine - wide open - in cycles, to keep its main battery above 45% if you tell it to. All good, max efficient. But their "12v" output is 15.1v! Which happens to trip the overvoltage self-protection on the inverter I have put in there to use for this (pipe 120v over to a battery charger on my 24v system). So, I'm going to have to come up with a dodge there to reduce the volts to the inverter, or fake out it's overvolt trip-out. Otherwise, this should wind up being my main go-to system here, it's going to be the best in all of reliability and efficiency - and convenience. The jury is still out on that one, but that won't be long. Just a simple diode drop in the right place in that inverter should fix that issue.

Well, this has been a bit of a ramble. I guess something important to consider is where you want to wind up, so you don't buy things now that won't fit into the final system well.
If you're going to full alt energy thing - batteries and inverter with tiny generator is where to begin, with room to add to those, if you've got the upfront scratch for that. If not, just doing emergency backup, then probably a big honking generator and some fancy wiring does you the most for the money - you don't care how much per hour it costs to run, because the hours are nil.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 3515
Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA

Re: Building a backup power system

Postby Joe Jarski » Wed Dec 07, 2011 4:40 pm

I do like the slow revving diesel idea - it's been years since I considered those (back when diesel was much cheaper than gas) and marine types never crossed my mind. Those should be relatively quiet, and out behind the shop... even better. Years ago I really wanted to use a lister for a genset - something like Bill's is just plain cool to me. I'll have to research the diesel option again. And maybe get a small genset for the interim.

The Whispergen looks like a neat thing, but at ~$20k for a unit, it's not something that I'd be doing anytime soon.

I spent some time today measuring the starting loads of the larger motors in my house and shop. The big (3 phase) machinery is just plain impractical to run off anything but the grid or a large genset. The worst is the inrush on my phase converter ~134A/250V next are the lathe and air compressor which come pretty close to that as well. Power requirements for normal (running) operation with machines and lights would be around 9-10kW. Most other things in the shop could run from my house system as needed.

My longer term plans are to work towards an alt energy setup for my house over the next couple years. The worst motor starting load in my house is the well pump at ~16A. The A/C may be a little worse, but it's too cold to check it right now and it's not a necessity. After doing some back of the electric bill calcs, an alt energy system to run my house would be about the same as yours, Doug. There are some improvements that I could make too, like replacing my big CRT's and turning off the IBM/Unix space heaters that I normally keep running.

Those inverters do have a nice surge rating and though expensive, they aren't as bad as I expected.
User avatar
Joe Jarski
 
Posts: 231
Joined: Thu Sep 16, 2010 8:37 pm
Location: SouthEast Michigan

Re: Building a backup power system

Postby Doug Coulter » Wed Dec 07, 2011 6:43 pm

Bill's Lister setup is really cool. Hopefully he'll report on it in actual use. I think he needs to put a better exhaust system, and maybe a more modern generator/governer on it, but time will tell on that. We started it here by just spinning the flywheel with the compression release engaged, then tripping it off - very cool to have it come to life that easy. He has a minor issue with the water cooling (it's too good!) but that should be easy to fix with a thermostat. I'd rather have that than Paul's new big Generac that runs on propane - it's already failed him due to carb icing when he needed it, and he doesn't use it much. It wasn't cheap, either.

Those Xantrex inverters are seriously under-rated. I've had my lathe running (2hP) and then the 10 hp air compressor start up - no issue whatever lights didn't even blink. Computers don't crash when you do the welders. They're not cheap, but did you notice you can chain them up for any net size? I found out something interesting about them. If you have say, 50 ft of #16 wire off one, and short the end, it'll just fry the wire - most spectacular. But 20 feet of #10 - short it and the inverter shuts down in mid cycle, not even a spark. Kinda freaky how well that works.

The advantages of going that way are several. If you've got batteries to handle peaks and inrushes, your gen set only needs to be able to keep up on average, not handle the peaks, which means it can run closer to full output and be more efficient. when you need it to run at all. (The Volt uses this scheme too) The inverters can use the power company to keep batteries charged and gracefully maintained when you have mains power, so for short outages, you might not even need a generator at all. And from experience, it's nice to have the power tools, lights, and soldering iron working to fix a generator you only find out needs it when you, well, need it.

I've seen 100 amp peaks out of the "40 amp" Xantrex SW4024 I use here, and 70 out of the "30 amp" one. They really kick butt. They just work. Of course you need real fat and real short wires to the batteries to get those kinds of numbers.

FWIW, those big sub batteries cost me ~$6k delivered. Wish I'd gotten twice as many...they're really nice, and I can now say that with a few years experience on them - they are much superior to the "cheaper" L16 class things most people begin with - worth the extra cost. They lose a lot less going and coming for one thing, and didn't have the rapid performance fall off after new that most other ones seem to have.

What's nice about the battery/inverter UPS system is the the computers don't crash in a switchover - it's completely seamless. That's hard to beat, especially if you have motor loads that can dump a big inductive surge back into the line in a power failure.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 3515
Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA

Re: Building a backup power system

Postby Joe Jarski » Thu Dec 08, 2011 2:15 am

I did some searching and found that you can still buy the Listeroids for about ~$1300 (I thought the EPA had put the kibosh to those) which would be good for about 4kW. I have a 16kW propane powered Generac genset here that was ripped out of it's installation. The only thing left is the generator and engine - no electrical. Way overkill, but it may be salvageable for a project if I can find some documentation. I'm not even interested in using the propane engine to power it - it's bad enough using propane for heat. I sure wouldn't want to put all of my eggs in that basket.

Wow, if you didn't have any issues with you compressor starting while the lathe was going then I may be able to run my machinery too. Might be worth a try if I don't have to worry about frying the inverter. Being able to parallel them is cool too - nice feature for adding capacity. Am I correct in assuming that it's best to run the DC system at the high side of the allowable input voltage to reduce the current in the switcher during surges?

I'd like to install the inverter/battery system in the spring and then add the solar within the following year. I was sizing everything for my projected loads, but I guess it can't hurt to have excess battery capacity if I can afford it.
User avatar
Joe Jarski
 
Posts: 231
Joined: Thu Sep 16, 2010 8:37 pm
Location: SouthEast Michigan

Re: Building a backup power system

Postby Bill Fain » Thu Dec 08, 2011 9:27 am

Hi, My Lister system is still on the trailer. Have been waiting for a time that the ground was hard enough to drive it to the backyard; for installation behind the shed. I also need a couple of guys to help move it into place. I have considered what loads I can actually run when and if I need it. They are few as the max output from the engine/generator would be about 5KW. It should have no problem handling motor start up as it has two one hundred pound flywheels. Using the radiator to heat the house would be nice, but I don't think my better half would like it sitting outside the window.
It was my understanding that the EPA had banned import of these things, but glad to see you have found a source. Supposedly, people were importing them as "air compressors" and adding the necessary external parts later. The Employee Prevention Agency, sorry, EPA actually saw through that and stopped it. I know they are available in Canada, no problem; and could be "hauled" into the US. Someone I know on the board lives real close to Canada. -bill
User avatar
Bill Fain
 
Posts: 90
Joined: Sat Jul 17, 2010 10:23 am

Re: Building a backup power system

Postby Doug Coulter » Thu Dec 08, 2011 9:31 am

A neighbor has that Generac, I might be able to borrow his manual for you. His only troubles with it are carb icing in winter, and well, what it costs to run it.

The Xantrex inverters seem poof-proof, I've pretty much done almost everything nasty you can do to one, other than hook the output to the power company (which they claim to handle as well).

The tradeoff with battery voltage is the old set of issues with any series string - the more junk in series, the old "if one's bad, the whole thing is bad" comes up more. I'd not go above 48v myself just yet. With solar panels, of course that means one of two in series in the shade means two not giving you anything - 24v output is about the sweet spot for single panels. Most charge controllers won't step up - but just about all will step down (switching supply), so in a system the solar array is usually the highest voltage thing. I stuck with 24v because of all the mil surplus stuff (including nice big motors) you can get for it - now and then I find that handy to just direct drive things. I'm thinking about adding shop hydraulics for example, and power packs for that can be had 24v. But that does tie one to using some real fat wire in the low voltage stuff.

Since you live up north, the shipping for those Rolls batteries ought to be less - they are a product of Canada. Shipping a few tons costs.

I doubt you'd have much trouble running your machinery off this kind of thing, I don't. I do only use one machine at a time (at least on purpose, the compressor has a mind of its own), since I have no CNC anyway. All my machines are 5hp and down, no phase converter is involved, but I do use a transformer to get 240, which might kind of isolate the peaks from the inverter due to transformer internal impedance - hasn't been an issue, it weren't broke so I din fix it. I think you can get phase converters pretty cheap that are all solid state - those are more efficient than the rotary ones anyway. I see them surplus now and then for attractive prices. Using more than one inverter is a certain cure - you don't have to chain/parallel them, you can just have more than one circuit, so no matter what happens on one, there's no effect on the other. Since I've not tried the new ones, I have no clue which would be best.

Dave Knight, who built a superset of my system with the newer inverters - and the good max power point tracking solar controllers (30% more power gained), is running a bake shop off his - ovens, industrial dough mixers....zowie. Since he's not managed to post up his system here, I'll have to go bug him and bring my camera to get some pix of a really maxed out one.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 3515
Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA

Re: Building a backup power system

Postby Doug Coulter » Thu Dec 08, 2011 9:46 am

Bill, my 8kw Onan was such overkill for my house - all loads combined, that I couldn't keep using it, too much fuel wasted. All you should have to turn off is electric heating/cooling, the rest should be fine. I'll be glad to help move the thing into place, just let me know - I can probably bring PaulS along, or one of my other strong pals with a good record of "getting 'er done".
I'd bet that Lister will do more than you think, if the ancient generator you have on there is up to it and has decent load regulation. New units 10kw size aren't too expensive (and weigh a tithe of what that one does). It's good to have a generator rated higher than the engine can drive, as this gets you less copper and iron losses. And brush-less.

For those who don't know - Bill lives in just about the perfect solar location - so I'm raggin on him to think along those lines...when you do that, the first thing you do is get off electric heat (including water) and onto propane, anyway. And cook with gas - you know the saying - it's really better, anyway.

What DaveK did, was just move circuits from his power co breaker box over to solar one by one as his system grew, and now he's selling them power back most of the time.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 3515
Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA

Re: Building a backup power system

Postby Joe Jarski » Thu Dec 08, 2011 2:58 pm

Bill, good point about Canada - I'll have to check on that also. Unfortunately, it's too heavy to sneak across the border in a plane. That method works well for importers of other "goods". :) ...for awhile anyway.

Doug, good information about the system voltage and series hookup. I've been looking at 24V, but I would have been inclined to go higher if I was going to run the machines. Paralleling the smaller inverters if necessary would be a better option, but it sounds like I won't have too. I can work on any 3 phase issues as I go since it's not my primary concern. Having fewer cells per battery is probably a more "fail-safe" method of doing the battery bank rather than use the higher voltage, multi-cell batteries that I was leaning towards.

I've thought about the tracking systems, but I didn't like the added complexity. I was considering just making tilt adjustable mounts that I could set a few times a year to maximize the power in a "fixed" system.

This is my Generac generator. I could probably find an aftermarket regulator for it to use in a new system. I'll have to work on getting it apart to check the overall condition.
Generac.jpg
16kW Generac generator
User avatar
Joe Jarski
 
Posts: 231
Joined: Thu Sep 16, 2010 8:37 pm
Location: SouthEast Michigan


Return to Alt energy

Who is online

Users browsing this forum: No registered users and 7 guests

cron