I’ve noticed when people are using generators to power a tool or appliance, they always directly plug into the generator. Then the generator is burning fuel reguardless of consumption.
How can that waste be reduced? A simple approach would be to plug your tool into a UPS (uninterruptible power supply) which is then plugged into the generator. This would help capture some of the excess energy when you are not pulling the trigger on a drill. Correct?
Possible flaw in this thinking: lead-acid batteries can only be trickle charged. So putting a battery in series only captures a small slice of the energy waste. Better than nothing, right?
I’m asking because I may need to install a generator for a whole house, and it’s not just for incidents. It will run daily in an off-grid house. So I’m trying to work out how to keep the fuel burn at a minimum and also how to fully exploit the available energy when fuel is being burnt (which should generally be during low sunlight times).
(edit) The UPS idea could backfire. IIRC, some UPSs are designed to always draw power from the battery while charging it at the same time. This is a superior design because it ensures that your appliance gets clean power that closely resembles a sine wave. UPSs that directly power the appliance from the mains and only tap the battery when mains go down have the disadvantage of sending potentially quite dirty wall power with surges and brownouts to the appliance. I think the always-use-battery design becomes self-defeating if using the UPS just to avoid generator waste. Correct? Though I’m confused because I don’t quite grasp how a lead-acid battery can charge as fast as it dissapates energy… I would think the charging would be slower than the consumption and power to eventually be lost.
I was under the impression that inverter generators already did this. Because it uncouples the engine speed from the generated electrical frequency, it the engine can run at much lower speed when not under load. They’re expensive though. I bought one for camping and it’s only 2000W and cost $600.
If you’re talking about a stationary application, you should seriously consider solar.
Lead acid batteries don’t only take trickle charge. But lifepo4 is better these days anyways.
This is what inverters with built in charger and transfer switch are for, when the generator is running they bypass the loads and charge the batteries, then when the generator stops they run the loads off battery. They also often have gen contacts for auto start/stop.
The simple approach is a LiFePO4 battery bank with a charge capacity (A) and charge controller that is appropriately matched to your generator’s output. Fire up the generator to run heavy draw appliances such as electric stove, or when batteries are low.
It’s somewhat frustrating to me when I’m running the generator to charge my laptop and run internet (150w) and the thing is rated to 5kw. Worse yet if you were running only lights. This can be mitigated, somewhat, by having an inverter generator which responds to load.
There’s many problems with a UPS:
- UPS are designed to handle short term load. That is, a brief power interruption as a cable is relocated, or the time between an outage and the generators starting. Therefore, even if it has the capacity to run the home in current, it’s not likely to have the batteries behind it
- UPS usually charge very slowly after discharge.
- A UPS sized for a home - even off-grid cabin - is going to be obscenely expensive.
- UPS usually use lead-acid batteries which, while by far the cheapest option, lag behind lithium based alternatives significantly in terms of depth of cycle, cycle count, and charge/discharge current.
Depending on your projected load, those “solar generators” may be a good fit. Ecoflow, for example, has a “smart generator” which hooks up to their inverter/battery pack and fires up when the battery is low. You can easily connect some solar panels as well. However, if you consider your money worth more than the ease of use or you need capacity exceeding what is readily available, there’s more affordable solutions.
Personally, unless you have a strong need for it, I would strive to find a solution using solar generation as the primary source, with the generator only providing backup. It’s regrettably the “expensive” option.
LA batteries don’t “only trickle charge”, but a) the cost per kW of UPS equipment is usually significantly higher than the generator, and b) the generator has a much higher surge current capability than inverter-based sources, and c) the power that actually goes through the battery loses anywhere from 10-30% in the round trip, so you get less usable output by routing power that way. If the cost issue becomes a smaller obstacle and you can be clever about bypassing the battery when appropriate, then like hybrid cars you can overcome those challenges… but not everyone or all affordable equipment can do that.
Another aspect of UPS, they may not like the dirty power from a small gas generator and spend some of their time discharging while the generator is on. They can be pretty sensitive to frequency especially.
I think you’d somehow have to make it team up. If the generator runs even when the battery is (almost) charged, you’d be in a similar situation as before. No device consuming the energy, but the generator runs nonetheless. With a bit of loss on top since the whole battery charging/discharging isn’t 100% efficient. And trickle charging doesn’t do a lot, it’s mainly a waste to let a generator run just for that. So I believe the way it needs to be set up is, the generator only kicks in if the battery is beneath some level and/or enough electricity is currently being used. Then it runs until the battery is charged again and turns off automatically. I’m not an expert, though.
You’re pretty spot on there! Wouldn’t be hard to program a controller to measure the voltage on the battery, then send run signal to generator to turn on. The when it hits a mark 80% charged, probably, send kill signal to the generator. With this controller, it would also pair nicely with solar, which it sounds like OP is pursuing as well
OP, for maximal efficiency and integration with solar, batteries are an absolute must. Much higher startup cost, but much less expensive in the long term.
I would have thought there were some ready-made products out there, like hybrid diesel generators with a battery?! I mean the use-case doesn’t seem to be far off to me. That’s also kind of how hybrid cars work (minus the solar)…
There might be some products available, but your power output and storage requirements might be vastly different, and it would be complicated to size both in one package. It makes more sense to buy the generator you need and then buy the batteries you need.
Also, I would use a transfer switch rather than a ups because of losses in efficiency between charging and discharging. You can use a small ups for electronics or computers, but you want to charge the batteries with excess generator power and then turn off the genny when the batteries are fully charged. Then, depending on how deeply you want to cycle, you turn the generator back on when the batteries need more charge. You can also run the generator under higher loads, if your battery bank cannot handle spikes in demand.
Was thinking about this very topic, although I plan to catch wind.
So far the best ideas I’ve got are:
- Scavenge old Toyota hybrid Ni batteries - those are surprisingly reliable long after they are not giving enough power for a car, and have quite good charge-discharge capacity
- Build Fe-Ni base batteries - messy but cheap
- Switch part of equipment to compressed air, run compressor for storage, spin generator with air on demand, possibly bubble air through some kind of bioreactor (kelp, mushrooms, etc.). Maybe same thing with vacuum line.
- Electrochemical synthesis on spare power (pretty much open battery loop; just a little bit - by making materials to be used in non-rechargeable batteries - or completely - make something useful elsewhere like metal coatings; I could extract stuff from local minerals, or barrety broth, or some kind of local goblinite). Anyway, something that wouldn’t care about random schedule, as opposed to, for example, greenhouse lighting or heating.
Home power storage is very hard to design. Ballpark-wise, I found that energy storage could be as profitable as renting space for living, normalized by square meter; thus it’s bound to be at least about as expensive to run. If possible, you should consider making smart grid with neighbours.
You could also use the excess power to heat up water in your house or for AC. In well insulated systems, you could keep constant temperatures for a while.
Well, in Finland, this kind of setup is deeply default. It becomes the main power consumer in November though.
Some types of solar charge controllers and battery managers have the capability to start a generator.
Steps:
- charge controller: raises or lowers GPIO pin (3.3 or 5 V, current: a few milliamps)
- relay board (needs 5V power): amplifies the GPIO signal and actuates a small relay
- small relay: switches 12V power to actuate the starter relay (current: maybe 1 amp)
- starter relay: powers the starter motor (12V, 10+ amps)
In an ideal world, your generator is well designed and already contains the starter relay, and the charge controller has a relay board, so you get to skip steps 1, 2 and 4 and just run a “start signal wire” between the two units.
Now, after getting your generator started, what you care about is load. The maker of the generator should have published a chart of efficiency vs. load. Too little load, and you’re wasting energy to overcome mechanical drag. Better stop the generator. Too much load, and you’re reducing the lifetime of your generator and risking accidents. Better reduce charging current.
Regarding UPS: a typical UPS comes with a lead acid battery that is not intended to be deep discharged repeatedly. If you end up doing that, expect dramatically reduced battery lifetimes.
If you’re new to electric circuits, your safest bet is probably an industrially produced LiFePO4 battery bank with balancing, alarm and emergency disconnect circuits built in.
However, if you have a manually startable generator, you better just get a big battery pack and find out what the optimal load for your generator is (note: might depend on temperature and cooling). You would want to start the generator rarely.
P.S.
If you can’t find a suitable product combination, this functionality can be DIY-ed with a Raspberry Pi, analog digital converter, voltage divider and cheap Chinese relays. But then it requires some electronics skills.
