What should one consider when buying a small electric generator for home use?
We have annoying power-cuts very often here in Sri Lanka. I would say it happens at least once every couple of days. Each power cut lasts from 5 seconds to 10 hours. Plus, they do weird 'maintenance' stuff very often, and heck, we have a 10-hours power cut 'scheduled' tomorrow. This is bad luck for people like me, whose entire life depends on electricity
I think it's time that I should better be off with some backup electricity source - maybe a fuel-powered electric generator if it costs the least to get done and install. We have different types of generators available in the local market that runs on Kerosene, Diesel, and Gasoline, mainly. All these fuel types are widely available, but kerosene costs very less compared to other fuel.
What do you think I should go for? I think turning on all my essential electric stuff would take it around 1.5 - 1.7 kW, so I probably need just 2 kW one? What would happen if I get something like a 5 kW one, but attach only 1 kW of load? Would it just run slowly saving fuel? I heard that most generators have some sort of energy control mechanism that makes it take less fuel when the load is less. But I wonder if that kind of thing work with small kerosene generators?? What would cost less and be more efficient when running for around 5 - 10 hours?
Well, you need to look at the specs and ask around to figure out how many liters per hour the burn at 2k load and compare the cost of fuel to get an idea of cost per day. We do not get small diesel or kerosene ones in the states, the infernal EPA has to approve any that get imported and the importer has to pay for the testing...
If you are going to keep the load under 2k all the time, then an inverter style generator is great. They sip fuel under partial load and are much much quieter. Absolutely awesome, but they are expensive up front.
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I do not have any experience with a kerosene generators, but gas and diesel I can tell you about. Diesel generators generally run at 1800 rpm .. slow and steady plus very powerful , this would be my choice. The inexpensive gas generators run at an earsplitting 3600rpm and do not have a long life! Do not buy one unless it is all you can afford. A better (but expensive)gas unit has a no load / low load idle down feature that saves on fuel but... when you need power it will speed up to 3600 rpm and make noise / drink fuel . In general slightly bigger output than you think you need is a better choice (say 5kw vrs 2 kw) Sizing a generator bigger than you need insures that it will not be working at max output but at a much easier partial output. Again kerosene may be a good choice but i do not have enough information about them ,but if they run at 3600 rpm I would stay away ! In my opinion a low rpm diesel generator is the better choice. Or... If you are adventurous then look into a 1 hp steam engine to spin an alternator, no fuel but burnables and the byproduct is heat ! And at 200 rpm very quiet ! Of course there is the little detail of a boiler... they have been known to blow up! Maybe solar power is an option ?
To add a little bit, I think 90% of my 2kW load would be electronic items - computers, monitors, printers, and stuff in that range. As I read from Scott's post, I think if I go for a generator, it must be an inverter style one, or I should have some sort of stabilizer to ensure that I get smooth current that doesn't burn up those electronic stuff. I just searched for some inverter style generators, but they all seem to run on gas! I haven't noticed the RPM though, but if I remember correctly, I think I've seen something on web that was rated to be in 60 - 70 dB noise range. Maybe those inverter style gas generators run at lower RPMs as they generate DC?
I liked kerosene generators just because they seemed to cost less. But I took the liberty to research further, and it turned out that these generators are NOT really that good. These generators seem to be eventually run into all sorts of weird voltage problems, or they will just end up not being able to start at all. So kerosene no longer seems to be a way I would go.
thomas rubino wrote:Maybe solar power is an option ?
I think one thing positive on this would be that I live near the equator where we have bright sunshine. I know nothing about the costs and installation of these cells, but as for the biggest downside I think setting up a solar array can utilize 2kW would ridiculously cost and take up so much space, compared to any generator at the same capacity??
Devaka; rpm is one of the things that gas generator manufacturers do not like to talk about. To my knowledge all gasoline generators run at at least 2500 rpm up to 3600 , unless idling.Diesels are 1800 rpm. What scotts post was referring to, I think is a pure sine wave output . This is not DC, but a electrical waveform that is comparable with normally generated electricity, allowing sensitive electronics (computers )to work properly. Some of the small honda generators work this way and also are very quiet , but you must pay quite a bit for it. Sadly small generators are also susceptible to theft. I think that for your location a solar arrangement would work . It sounds like your computer is the most important item that you need running . You only need enough holding capacity in your battery & solar panel to last the time of power outage. Easy to do if the sun is shining. A small deep cycle battery , a small pure sine wave inverter,charge controller and a solar panel and you are online while your neighbors are not AND no loud generator! There is much for you to learn about solar energy. But living where you are it only makes sense to investigate the possibilities and the associated costs. Homepower.com is a site that you may find enlightening.
1) I have seen a variety of low-end diesel generators in recent years that run at 3600RPM. Not a fan of this development at all. Don't assume diesel runs at a nice low healthy RPM, check!
2) The advantage of inverter generators is generally that they will output a decently pure sine wave, along with the ability to adjust to suit the current load. The quality of power output by a non-inverter generator is usually very bad and rather likely to damage your computer equipment.
Some small inverter generators can be connected together to allow 2 to share a larger load. This would provide for some redundancy, but of course cost more.
3) A kill-a-watt meter is fairly cheap, and would help you find out how much power you actually use. 1.5-1.7KW is a lot of power, a nearly maxed out 15amp circuit! Maybe you are overestimating based on max power consumption of the devices?
4) Battery power for 10 hours of 1.7kw usage is very expensive. Assuming a 90% efficient inverter, a LiFePO4 battery bank to allow 80% depth of discharge, and oversizing by 20% to allow for some capacity loss over time... you'd need something like an 800AH 36V battery. Balqon sells 400AH cells; using 24 of them to get 800AH at 36V would cost about $12,000 USD. Then you need cabling/connectors($$$), controller($$$+), inverter($$$$), and solar panels to suit($$$$+).
5) What I wish I could suggest is a smaller battery bank, small solar array to keep it topped off, a big high quality inverter, and then a diesel DC power source to feed the batteries/inverter when a sustained load is needed. Unfortunately, the only options I know of for this last crucial piece are *very* expensive and almost certainly hard to get to Sri Lanka.
My guess is a gas inverter generator is likely the only practical option that will provide decent quality power for 10h. Make sure to check run-time, it's often quite short on a single tank of fuel.
I had not heard of 3600 rpm diesel gen sets... But live & learn, YES they have managed to couple a diesel to a 3600 rpm alternator ... with a belt! gear up to spin a cheap alternator with less copper windings .... Now they have managed to produce a cheap throwaway diesel gen set !!! What JUNK !!! I really am thinking hard about a 3 hp steam motor with a small boiler ... 200 rpm last forever... if you don't blow yourself up...
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