Battery or Generator Back-Up Power?
I live in a rural area which gets its share of both cold temperatures and power outages. I’m considering investing in a back-up power system, and was wondering if any of the house-wide battery back-up systems would be a good alternative to a conventional standby generator with automatic transfer switch.
The house has oil heat with blown hot air, and the hot water is heated by the furnace via a closed-loop set-up. It is my assumption that the furnace and air handler do not use all that much electricity and perhaps a battery back-up system –which is completely silent and requires no fuel storage or engine maintenance– might be sufficient.
I travel frequently and am mostly concerned about keeping the heat running should the power fail when I’m away.
Any opinions/experiences?
Thanks,
DM
Replies
I forget to mention that keeping the fridge and the well pump running would be nice, too...
DM
Go with a generator with a auto start & transfer function. You can buy a generators that run on either propane or natural gas. Many of them can also be set up to where they start every week and get up to operating temperature, just to make sure that things are in good shape.
Battery back ups (uninterrupted power supplies) that could provide power for extended periods of time are probably out of your price range. I used to work as a Mechanical Engineer for Yuasa (a battery manufacture) and we made a lot of back up power supplies. Most of the UPS systems that are sold to the general public are the type that give you the time to shut down your computer when the power goes down. Powering a household would take a system more like the style that is used for tetecommunication, operating rooms, & power plants, you don't think that nuclear plants just shut themselves down when the power fails? All of these systems cost big $. One cell G battery is only 1 1/2 volt but puts out enough amperage to blow a 1/2" breaker bar like a fuse (that got my attention) and costs over $1000 each and you need a bank of them. You get the picture.
You can buy backups for your backup generators and still have less money invested than you would spend on a battery system that would have the capacity to power a house for a few days.
By the way battery systems are not maimtenance free. To get the maximum life out of those batteries they need some TLC. The electrolyte level needs to be maintained, specific gravity needs adjusted, the batteries need to be charged and discharged. There are some of the requirements.
Battery backup makes sense if outages tend to be relatively brief (generally under 30 minutes) and if the load is fairly small (maybe 2KW max, below 500W being better). You didn't state clearly how long outages tend to be, but the load you have (especially with water pump) is probably too large for a battery system to be economical.
Get a clamp-on ammeter and measure the current your furnace draws. I'm guessing it's 3-4 amps. The water pump pulls several amps when running (measure it), and probably spikes to 20-30 amps when starting (try to eyeball that as well). ALso note whether the water pump is 120V or 240V, and make sure that's taken into account.
Calculate the average load, maximum steady-state load (ie, furnace, water pump, and whatever else all running), and startup load (mainly water pump startup peak). Multiply average load by max outage length to determine amp-hours or watt-hours of battery storage capacity needed. The max steady-state and peak loads will determine the size of the inverter required.
Thank you, DanH and Abe. This was the battery-based system I was looking at, designed for home use and installed the same as a stand-by generator with an automatic transfer switch:
http://www.backuppowersource.com/index.html
Northern Tool sells it also.
Outages in my area are typically a few hours. The longest we've had in four years was 36 hours. However, temperatures in the winter go below zero F and are routinely sub-20F.
The manufacturer claims 24 to 72 hours of continuous back-up, but without knowing the specific load --as DanH said I must measure-- it would be a wild guess to know if this would work for me. It's a small, well-insulated house, and our electric bills are typically $50-$60 per month, despite paying 18 cents per KWH (Connecticut). I could look up my KWH usage per month to get a rough idea.
Thanks again,
DM
Figure 36 hours at 5 amps (600W). That's 50 amps from a 12V battery if you ignore conversion losses, or maybe 75A with those losses. 75A times 36 hours is 2700 AH. A standard auto battery is typically in the neighborhood of 100AH, so you'd "only" need 27 of them. Even if you really trimmed back your power requirements, you'd be hard-pressed to get below 2 amps running an oil furnace, so you'd end up needing the equivalent of 8-10 standard auto batteries.More practical might be a small propane powered heater, tied into the existing ductwork, and with a small battery-powered fan to circulate the air.
Half of the harm that is done in this world is due to people who want to feel important. They don't mean to do harm but the harm does not interest them. --T.S. Eliot
I'm looking at prices and it seems like for comparable wattage, gas/propane generators are less than half the cost of battery systems.
found a good site to help compare/price/size units:
http://www.electricgeneratorsdirect.com/catalog/pickperfectemergency.php
Yeah, that would be my expectation, and the runtime of fueled systems is essentially unlimited.
Half of the harm that is done in this world is due to people who want to feel important. They don't mean to do harm but the harm does not interest them. --T.S. Eliot
All,
Thanks for all of the tips. It really looks like a stand-by generator with auto transfer switch provides better value overall than any battery system. A small 7000 watt model would be sufficient to run the furnace, air handler, fridge, well pump, water circulator, and a few lights.
Since I'd have to get a propane tank installed (there are no gas lines out here), it might make sense to convert our electic cooktop to gas at the same time. That would remove the drag on the generator of electric cooking during a blackout, and gas stoves are better for serious cooks anyway, providing pinpoint temperature control and instant heat.
Now the really hard part: selling it to my wife :=)
Happy New Year to all.
DM, Litchfield County, CT
Too add to the last post, I use my place every other weekend or so in the winter, therefore I don't want to winterize it for a long term vacancy. I leave the thermostats around 58 degrees, enough heat to give some time if before the house freezes up completely. I do have low temp sensors connected to my alarm system and I turn off my well pump, so that if a pipe does burst it will only empty the bladder tank and not run water continuously. I also switch off the hot water heater when I leave. In addition I have a service contract with my oil company that will go to my house and deliver emergency oil or get the furnace working on temporary power if need be.You are correct in going to a propane fired stove (and possibly clothes dryer and water heater), you could also hard plump your outdoor grill to that tank also.
How are you going to run the blower, fridge and sump pump on DC? They all run on AC. It'll take a bunch of batteries with a good sized invertor to run that stuff till the power goes back on unless it's a very short time. Probably better to get a generator that will handle everything.
The OP was looking at inverter systems.
Half of the harm that is done in this world is due to people who want to feel important. They don't mean to do harm but the harm does not interest them. --T.S. Eliot
I just read that.
"I cut this piece four times and it's still too short."
You have gotten some really good answers here. Including numbers.
I can't give you all the numbers or technical specs or any of that. But I can give you some opinions and ideas based on real world experience.
You ask, generator, or battery, and I say both.
Generator to run during the day when you have the heavier loads, and to recharge the battery. And battery/invertor to run at night when all you need is a couple lights, and the blower on the furnace.
Natural gas water heater, furnace, clothes dryer and range will serve you the best in a power outage. Propane being second best.
Propane would be first best, if there were a major disruption that affected even the gas lines.
I like Dan's idea of a secondary propane heater plumbed into the existing ductwork. Get one designed for a larve RV, and you'll be able to run it on a couple of ten gallon propane bottles and 12v power.
You don't even need an invertor for that. Get yourself a gel type golf cart battery, and you'll be able to run that furnace for a long time...
Close off the least important vents and you'd be surprised how well that little furnace will keep your house warm.
Get over it....... The angry going eat you up. ~Brownbagg '06
I would think a generator would give the most bang for the buck. My question would be; how many types of fuel do you want to have to have deliveries for? Your post said that you have an oil furnace. I don't know of any gen sets that run on heating oil but that doesn't mean they don't exist. A gasoline or diesel generator will have a limited run time if you're not there to refill the tank. My guess is that natural gas isn't available since you're in a rural area. To me, that leaves propane as the fuel for the generator along with a tank somewhere in the yard. May or may not be a concern to you but something to think about.
What ever you choose to install, make sure you have the proper transfer switch and equipment so that you aren't backfeeding power onto the grid. You're local utility linemen will be a lot happier and safer when they don't get zapped doing line repairs.
Home heating oil and #2 diesel fuel are very much similar, the main difference being additives. It's possible to use one for the other, if you aren't too worried about warranty issues, and if the genset doesn't need #1 diesel for wintertime operation.But for lowest maintenance I'd go with propane, if natural gas isn't available.
Half of the harm that is done in this world is due to people who want to feel important. They don't mean to do harm but the harm does not interest them. --T.S. Eliot
I have almost the exact same criteria for a back-up system for my house (Eastern Long Island) and have decided to go with a propane fired generator,(Generac's Guardian for example). I feel a 7kW unit will handle my needs (not concerned about A/C) and can purchase one from HD for a little over 2K. As for the sound, I will build an acoustic rated enclosure (acoustic CMU possibly), but during longer power outages, I will inevitably here other people fire up there portables anyway. Since my concerns are the winter outages, I probably won't even be there to hear it.
Edited 12/31/2006 9:46 am ET by TGNY
When one is concerned about freezing when the structure is unoccupied, the two critical criteria are reliability and run time, and the "reliability" one is concerned about is maintaining a temp comfortably above freezing, not keeping the place toasty warm, the water running, hot water hot, etc. (One might also be concerned about keeping a fridge and/or freezer running, but those should be emptied before the structure is unoccupied for long periods.)In terms of reliability, you need to be concerned about "total system reliability" -- not just the standby power but also the heating system itself. Even if power doesn't fail, there's a non-trivial possibility of heating system breakdown. Any solution to the problem should take this into account.Similarly, there's a chance of water pipe rupture, unrelated to power/heat failure. And of course there are security issues with unoccupied buildings.There's no simple formula to appraise these various hazards, since the likelihood of each will vary with location, age and condition of structure, etc. But it's imprortant to think these points over, or you can end up spending a lot of money on the wrong solution.Most any approach should include some sort of alarm system (even if it's only a neighbor who watches your window for a flashing light). Once a redundant system is activated it becomes a single point of failure.
Half of the harm that is done in this world is due to people who want to feel important. They don't mean to do harm but the harm does not interest them. --T.S. Eliot