is a gen necessary?

sgtalexmom

it's come up that a generator is recommended when doing off grid design.

just wondering what everyone thinks.

do you have a generator on hand? brand/size/opinions, etc. are greatly appreciated.

i guess it would provide some peace of mind, but is it overkill if the solar is designed and sized correctly?

Cariboocoot

Re: is a gen necessary?

Depending on what the weather is like in your area, a generator can be really cheap insurance against a long stretch of low sunlight. Otherwise you may find yourself spending a lot of extra $ to have enough reserve capacity to see you through the stormy spells.

Some people will recommend three days reserve, but even that gets expensive quick - and you find you've paid for extra solar that you can't really make use of when the sun does shine. My particular plan is to size your battery bank so that 25% DOD is one day; then you have another 25% in reserve for a bad day, and a generator to start if the sun doesn't shine on day 3.

You'll find many off-grid people (including me) have small inverter-generators like the Honda EU2000i. That particular model is extremely reliable, quiet, and fuel-efficient.

icarus

Re: is a gen necessary?

A generator and good battery charger are almost essential for off grid. Unless you disign, build, (and pay for) a system that provides so much reserve capacity that you can weather any bout of not enough sun, or extra peak loads you will pay for it in over drawing the battery.

A generator is invaluable for peak loading as well. You might also want to use a generator for power tools instead of trying to build a battery based system big enough to run them.

Tony

PS, that said, get a good one, sized for the loads. A genny just for charging a small off grid battery system, like mine may be too small for running the kind of power tools you need. A Honda Eu 2000 is a pretty good compromise, as it will run smaller saws, drills etc, but will run a 20-40 amp battery charger fairly efficiently as well. Not that I am suggesting it, but I have a selection of generators ranging from an Eu 1000 (900 watts running) to a 5 kw Lister diesel, to a 10 kw Onan, with lots in between.

Frxddy

Re: is a gen necessary?

I get the impression that a generator is also used to charge the batteries during rainy spells so they don't sit discharged for long periods. About the worst thing for a battery is to sit discharged. Like, if you have batteries enough for two days and you have a week of rain, on day three you use the generator to charge the batteries and THEN use it to keep them charged as you use power.

mike95490

Re: is a gen necessary?

Hi,
My name is Mike, and I have 3 ways to charge with 3 gensets and 2 different chargers

2manytoyz

Re: is a gen necessary?

Weather is the issue here. Doesn't matter how many panels you have when it's raining.

My system is sized for my limited use (I'm still mostly ON the grid) to last a few days before needing to use the generator + 75A Iota charger.

If we have a major event (aka hurricane), all my critical loads automatically transfer to the inverter. At that point, the solar array can only barely keep up if the weather is cooporative. But during/after a big storm, the weather is nasty. After the storm has passed, the generator will be fired up periodically to replenish the battery bank, then back to running on batteries, conserving gasoline, and reducing the audio signature (neighbors running over with extension cords!).







Can't go wrong with either a Honda, or Yamaha quiet series generator. I opted for the Yamaha EF2400iS. It's the lightest quiet series generator capable of running an RV A/C unit (13,500 BTUs) reliably. I've done a fair amount of testing of my generator. Details here: http://www.2manytoyz.com/yamaha2400.html

chevenstein

Re: is a gen necessary?

I live off grid full time and I have:

- a hardwired LP 7kW genset
- a hardwired 6.5kW gas genset
- a portable gas 6.5kW genset
- a portable gas 5kW genset
- a portable gas 1kW genset

...and I'm still looking for at least one diesel genset and possibly a PTO generator for my farm tractors (need more fuel diversity).

So yes, I would recommend a generator. You could probably get away without one in a tropical latitude with a correctly sized system, but what if your inverter dies? What if you need to plug two engine block heaters in overnight for some reason? It's all about preparedness.

System2

Re: is a gen necessary?

Just curious, why hasn't anyone mentioned the need of a generator to run the EQ functions of battery maintenance?

I would think either grid or generator was essential for that.

stephendv

Re: is a gen necessary?

All you need for EQ is a sustained high voltage which can be done through solar/wind/hydro/anything. The need for a minimum current, is in my opinion, exaggerated. Once the batteries have charged passed their absorb voltage current MUST be limited to a MAXIMUM of 5A for every 100Ah capacity. So the vast majority of time spent in EQ will be well under that maximum.

Now if you can't manage to bring your batteries to the EQ voltage in a reasonable amount of time in winter, then yes, you'd need the gen for that. Otherwise, solar can do it just fine.

Cariboocoot

Re: is a gen necessary?

solarbum wrote: »

Just curious, why hasn't anyone mentioned the need of a generator to run the EQ functions of battery maintenance?

I would think either grid or generator was essential for that.

Only essential to have a gen if you don't have enough panel to get through Bulk and Absorb while there's still enough daylight to run EQ. If you're system is designed right there should be enough power to stay in Float for at least an hour a day, and if you can do that you can do the EQ thing too.

Photowhit

Re: is a gen necessary?

Cariboocoot wrote: »

Some people will recommend three days reserve, but even that gets expensive quick - and you find you've paid for extra solar that you can't really make use of when the sun does shine. My particular plan is to size your battery bank so that 25% DOD is one day; then you have another 25% in reserve for a bad day, and a generator to start if the sun doesn't shine on day 3.

I think the most valuable information is what Coot said, it allows you to keep your costs reasonable both in battery bank and array sizing.

...That said I choose not to have a backup, but I'm willing to have an over sized system for my needs and reduce use/increase DOD in times of prolonged weather.

Dave Angelini

Re: is a gen necessary?

If you live in a place that has good solar all year, and have enough money to afford a proper system, a generator is something you buy if your inverter fails.
If you have a spare inverter you probably will never need a generator.

I am working on my 44th offgrid home system and I would say about 30 of them are this way.

The ones that need generators most often have loads that they can't seem to shed in winter. Some for good reason, some just can't wait for that storm to pass.

SCharles

Re: is a gen necessary?

I have a Honda 3500 w. generator I use for running a table saw 220 v and an air compressor which could be run off the batteries/PV but I don't as the generator is right there and the compressor draws quite a current. So the gen. is available for battery charge if needed. However, I rarely use it for that and don't recall doing so in the past few yr. I often go a month without starting the Honda, so it's gasoline use is quite minimal. If I didn't have the saw and compressor, I doubt I'd have the Honda.

In 26 yr. of PV running our home, I doubt there are a half dozen times I would be wanting the generator to help with the batteries. But I am in a very sunny clime. Ask me again if I ever live in a cloudy area.

Whether you need a generator depends on your area, your weather, your PV charging array, and, as in my case, whether you want to operate electrical devices which are inappropriate in PV systems, such as a power-hungry tool. The $20 a year I spend on gasoline to run a saw would translate to many thousands to beef up the PV system to run the same saw. Many thousands.

Cariboocoot

Re: is a gen necessary?

Dave;

Just curious. What's the furthest North you've ever put a system in?
Our horrible 10 hour yearly daylight swing up here would make a 100% solar recharge really, really expensive.

chevenstein

Re: is a gen necessary?

Cariboocoot wrote: »

Dave;

Just curious. What's the furthest North you've ever put a system in?
Our horrible 10 hour yearly daylight swing up here would make a 100% solar recharge really, really expensive.

I'm wondering the same thing. From April through September I have more power than I know what to do with (even if it's cloudy). From December through February even a sunny day won't get it out of bulk before the sun is too low in the sky. Twenty below temperatures don't help, either!

Dave Angelini

Re: is a gen necessary?

Cariboocoot wrote: »

Dave;

Just curious. What's the furthest North you've ever put a system in?
Our horrible 10 hour yearly daylight swing up here would make a 100% solar recharge really, really expensive.

Marc we sailed our sailboat all around most of north and south america. We crossed the atlantic and went out to the south pacific looking for such a place. We wanted over 20 inches of rain, a wood source for heating, and a winter sun resource. To answer your question in this hemisphere it is the northern boundies the southwest US.

I am not saying there are not ways to to work out a strategy in other places but the keyword "work" is not involved in most of the southwest. It is easy there!
I have acustomer in Yellowknife and 2 in Alaska. They definately need generators!

Cariboocoot

Re: is a gen necessary?

You know how much I love trackers. It drives me nuts that in the Summer I could be grabbing 6 kW hours from my tiny array. But the install here would be impossible due to the layout - and the bank account. My last crazy idea was to run a pole up the corner of the cabin and mount a tracker above roof level; out of the way yet in the sun. Could be done but ... pain in the pocketbook.

On the other hand the Winter is brutal. If the sun shines it's only for a couple of hours. The -40 temps are great for super conducting, but it makes for difficult array planning when the Voc can shoot up 30%.

So I have generators. :roll:

TenMile

Re: is a gen necessary?

sgtalexmom wrote: »

it's come up that a generator is recommended when doing off grid design.

just wondering what everyone thinks.

do you have a generator on hand? brand/size/opinions, etc. are greatly appreciated.

i guess it would provide some peace of mind, but is it overkill if the solar is designed and sized correctly?

All the points above are valid, but I also think that whether you need a generator depends on how your are using your off-grid property and if you have alternatives. If it's just for weekend use so your system has a week or more to recover -- then you might not need one.

Our off-grid cabin is used heavily in the summer. We run lights, TV and small appliances. Fridge, stove and backup lights are propane and we can completely live using propane alone (as we did for the past 35 years). We've only needed to use the generator a single time in 6 months when someone got over-zealous with the shop-vac and decided to run it for several hours vacuuming the exterior logs and we had to recharge the batteries. Otherwise, during the spring/summer/fall the batteries typically don't fall below 90% capacity overnight so there is lots of capacity to run things for many days.

In winter and rainy seasons we generally don't stay there for more than a day or two and find that the system has enough time to fully charge without the generator being required.