Generator vs batteries

[GeorgeF]

Im wondering what is more cost-effective:

Suppose a house needs max 1Kwh per hour, max 6 hours per EVENING. Thus total +/- 6Kwh.

What is more cost-effective?
1. generator or
2. deep cycle batteries charged with solar panels

[SunEagle]

You can do the math yourself but IMO for a 6kWh load a generator will always be cheaper to run.

[J.P.M.]

Which one is more cost effective depends on the application, what factors you take into consideration in the cost analysis, and how long into the future you're planning takes the analysis, usually in terms of years.

Short answer:
Short term, the generator option will probably cost less.
Long term, at some point, PV/batteries will be more cost effective.
The questions are: What factors to consider in determining cost effectiveness ? And, for how long is the analysis to run in terms of time ?

If you're interested, read on. If not, go the last sentence of this post

Solar energy utilization is generally characterized (and justified) by (sometimes much) high(er) first/initial costs for the equipment with low(er) operating costs than for other, usually more conventional means of meeting a duty.

One way to see that - and perhaps justify it - is to consider the high initial cost of solar equipment as sort of prepaying future operating (including fuel) and maint. costs associated with the alternatives to solar with perhaps an additional advantage for the solar option of some insulation from future price fluctuations in those future conventional (non solar) operating costs, particularly if those future costs are thought to have a higher probability of increasing rather than decreasing.

So, in it's most basic terms, an economic analysis that involves solar energy equipment against other alternative methods to meet a duty is often done by comparing an initial known investment with estimated future operating costs.

That analysis is then done for each method of meeting a duty. For such cost analyses - if the most cost effective method is the goal - the option with the lowest combination of in initial and operating costs on a NPV basis is chosen.

When comparing solar as a means of meeting a duty with any other means of meeting the same duty (goal(s)), both alternatives (or all alternatives if more than two options are being considered) are compared using the same criteria. Sometimes there are many factors, sometimes few. Sometimes the analysis period is short, sometimes long. Whoever is footing the bill ought to be the one who decides the criteria for the analysis and how complicated it needs to be.

The alternative that produces the lowest NPV in terms of all costs associated with that alternative is one way to define the most cost effective alternative.

The common reality these days, and as its been for a long time is that for short periods of, say, a few years or less, and if the economic criterion chosen for the analysis make any sense and are not slanted in the solar option's favor - as solar peddlers and the greenwash media often/usually do - the solar option is not usually the most cost effective.

For what you describe, given the relatively small load of 1kW, if you don't put a high $$ value on piece/quiet, short term, the relatively low(er) generator initial cost will probably make that option more cost effective than the PV/battery option more cost effective for any reasonably short analysis period.

As the period of the analysis gets longer, the fuel for the ICE generator will probably be the biggest factor impacting the NPV of the long term costs of the generator option.
As the period of the analysis gets longer, the operating costs of the PV panels and associated equipment will be pretty low, maybe --->>> 0$, but the batteries may have some operating/replacement costs, as well as perhaps some maintenance PITAs.

The point in the future when the NPV of the costs for the two alternatives are equal is when they are equally cost effective.

So, for the simple analysis described above, if your period of analysis (that is, how long, years maybe, you plan to be meeting a 1 kW load 6 hours/day) is shorter than the point in the future when the alternatives are equal, one option will be more cost effective - I'm guessing that's the generator option.

If your period of analysis is longer than that breakeven point, the other option - I'm guessing the PV/batteries - will be more cost effective.

One way to go might be to get a generator and see if the PV/battery option gets more cost effective

Take what you want of the above. Scrap the rest.

[Mike90250]

i'd make a hybrid system. medium size battery bank, small PV array, and a generator. If you run out of solar, fire up the generator to run loads and recharge. After a year you will know your usage and costs and can decide to purchase more fuel or more solar PV.
For this use, I'd get a propane conversion kit, the generator will run longer and cleaner from propane

update:
strike: the generator will run longer and cleaner from propane
insert: The engine for the generator will last longer and run cleaner on propane. (note, propane is not as dense as gasoline, so you need about 10 gallons of propane to replace 7 gallons of gasoline)

[GeorgeF]

Thanks for all the replies above.

In the country where I am now i can buy 3kg LPG for only +/- 1.50 USD .

I have read another thread here, Honda 5Kw generator = 1 gallon lpg per hour.

So, in an offgrid situation here perhaps wise to use a generator in the evenings for some heavy loads, like aircons just for a couple of hours.

[J.P.M.]

Thanks for all the replies above.

In the country where I am now i can buy 3kg LPG for only +/- 1.50 USD .

I have read another thread here, Honda 5Kw generator = 1 gallon lpg per hour.

So, in an offgrid situation here perhaps wise to use a generator in the evenings for some heavy loads, like aircons just for a couple of hours.

So, consider a modification to Mike's suggestion: Get a generator and a battery bank sufficient to meet your needs as you define them, but hold off on the PV until you've lived w/the generator/batteries for a year or two - or longer. I kind of doubt the price of PV will be going up much anytime soon.

In the meantime, study up on off grid PV. Any system you then acquire will be better designed and constructed for the learning.

[Keylan]

It really comes down to your need. But, I prefer a generator. Also, it provides reliable power compare to the solar panel on the other hand solar creates no noise.

[Riley5781]

RE: What is more cost-effective?
1. generator or
2. deep cycle batteries charged with solar panels

Another way to think about it is that you can't really own/run/maintain #2 (deep cycle & solar) without a generator. The generator is really part of the system and to think that you can get away with off-grid solar without a generator isn't correct. The generator is required to properly maintain the batteries during periods of low sun/winter ect.

So it's either #1 or hybrid of the 2. If off-grid, I would work on the 1KW average demand at night. My off-grid home idles at about 250 watts or 300 with the TV on. That includes a modern fridge and LED lights ect... You can live pretty comfortably at those power levels. You just need to run heavy loads during times of excess power.

[peakbagger]

I have known of several off grid camp owners who used to use generators and switched to batteries to reduce their fuel use, cut down on noise and cut down on lugging fuel to the camp. Solar was an after thought. An idling generator is still burning fuel while a idling inverter uses very little power from a battery.

I was looking at piece of property on a large undeveloped lake, (Aziscohos Lake in Maine and NH) there was a sporting camp next door and then the nearest neighbor was about 19 miles down the shoreline and a few camps a mile or two across the lake. Unfortunately the sporting camp had an idling diesel generator for about 12 hours a day. It really impacted the illusion of a wilderness lake when the generator was running especially during the daytime when folks were out enjoying the lake. They had what looked to be hospital grade silencers but the generator could be heard a couple of miles away on the lake. The camps owners were old school but my guess was if they had gone with a battery bank and solar with diesel backup they would have attracted far more return clients. I walked away from the deal mostly due to the diesel.

[sidpost]

A high-quality generator like the Honda's is certainly easy to use and has a small "footprint". However, you have noise and the hassle of grabbing fuel all the time. If your fuel supply goes away (storms, conflict, shortages, etc.) you lose your power.

Solar Panels to run a small air conditioner a few hours each night will initially cost more but, decouple you from the need for fuel and those recurring costs. LiFeP04 batteries will last a really long time so, are pretty cost-effective. Storms and other things won't take your "fuel" away so you can still charge cell phones, run a fridge, etc. The negative is you need to the space for the batteries and inverter plus a location for the solar panels.

[SunEagle]

A high-quality generator like the Honda's is certainly easy to use and has a small "footprint". However, you have noise and the hassle of grabbing fuel all the time. If your fuel supply goes away (storms, conflict, shortages, etc.) you lose your power.

Solar Panels to run a small air conditioner a few hours each night will initially cost more but, decouple you from the need for fuel and those recurring costs. LiFeP04 batteries will last a really long time so, are pretty cost-effective. Storms and other things won't take your "fuel" away so you can still charge cell phones, run a fridge, etc. The negative is you need to the space for the batteries and inverter plus a location for the solar panels.

Actually storms and clouds will take away your fuel if you rely on the sun and solar panels to charge your batteries or run your loads. And once you have a battery system you also add a "hobby" watching them and keeping them safe and charged.

I understand the drawbacks of a generator but when I do the calculation running a generator that can use different types of fuel is cheaper then having a battery bank big enough to run my loads. Even LiFe type batteries will die and need to be replaced.

[sidpost]

Actually storms and clouds will take away your fuel if you rely on the sun and solar panels to charge your batteries or run your loads. And once you have a battery system you also add a "hobby" watching them and keeping them safe and charged.

Bifacial half-cells are more resilient to cloudy days and shading but, as noted extended heavy cloud cover is an issue. On our systems here in Texas, we average about ONE yearly 4-day cloud event where we don't make power continuously and have only had ONE 7-day event. Single days or half days with no or poor solar activity are more frequent.

Regarding the battery "hobby," modern charge controllers and BMS systems do the vast majority of the work assuming you aren't running lead-acid batteries. Lead-acid batteries definitely need more hands-on attention for things like adding water after an EQ to clean the plates and some Hygrometer monitoring to make sure they are healthy and the specific gravity is where you need it to be.

For me, the cost of Lead-Acid versus LiFeP04 batteries is very similar assuming similar sized systems. In my case, the 302Ah LiFeP04 batteries are significantly cheaper than lead-acid batteries of similar usable capacity.

Then there is the issue of racking for lead-acid batteries for weekly maintenance checks versus LiFeP04 which are essentially hands-free and generally are significantly lighter which makes racking easier. Both have issues with cold temperatures so, that is something to be aware of when using them in areas that aren't protected from low temperatures (modern charge controllers will protect them from cold weather).

I understand the drawbacks of a generator but when I do the calculation running a generator that can use different types of fuel is cheaper than having a battery bank big enough to run my loads. Even LiFe type batteries will die and need to be replaced.

Assuming you don't BEAT YOUR BATTERIES TO DEATH, LiFeP04 batteries are good for 7,000 to 10,000 cycles. If you take really poor care of your LiFeP04 batteries, you should still get ~5,000 cycles.

If my LiFeP04 batteries last 20 to 30 YEARS, how many generators have I replaced along the way? If you are worried about storms in a remote location, what do you do when the LPG, Diesel, Gasoline, etc. run out? I have been there PERSONALLY. Today I am a very strong solar advocate. My "FUEL" may run out when the clouds move in but, after weeks with no way to charge even a cell phone or play a radio after every ounce of gas, diesel, etc. was used up, I'll gladly take my chances with sunshine!

And yes, bad personal experience may make me a little opinionated and a touch hard-headed.

[SunEagle]

Bifacial half-cells are more resilient to cloudy days and shading but, as noted extended heavy cloud cover is an issue. On our systems here in Texas, we average about ONE yearly 4-day cloud event where we don't make power continuously and have only had ONE 7-day event. Single days or half days with no or poor solar activity are more frequent.

Regarding the battery "hobby," modern charge controllers and BMS systems do the vast majority of the work assuming you aren't running lead-acid batteries. Lead-acid batteries definitely need more hands-on attention for things like adding water after an EQ to clean the plates and some Hygrometer monitoring to make sure they are healthy and the specific gravity is where you need it to be.

For me, the cost of Lead-Acid versus LiFeP04 batteries is very similar assuming similar sized systems. In my case, the 302Ah LiFeP04 batteries are significantly cheaper than lead-acid batteries of similar usable capacity.

Then there is the issue of racking for lead-acid batteries for weekly maintenance checks versus LiFeP04 which are essentially hands-free and generally are significantly lighter which makes racking easier. Both have issues with cold temperatures so, that is something to be aware of when using them in areas that aren't protected from low temperatures (modern charge controllers will protect them from cold weather).



Assuming you don't BEAT YOUR BATTERIES TO DEATH, LiFeP04 batteries are good for 7,000 to 10,000 cycles. If you take really poor care of your LiFeP04 batteries, you should still get ~5,000 cycles.

If my LiFeP04 batteries last 20 to 30 YEARS, how many generators have I replaced along the way? If you are worried about storms in a remote location, what do you do when the LPG, Diesel, Gasoline, etc. run out? I have been there PERSONALLY. Today I am a very strong solar advocate. My "FUEL" may run out when the clouds move in but, after weeks with no way to charge even a cell phone or play a radio after every ounce of gas, diesel, etc. was used up, I'll gladly take my chances with sunshine!

And yes, bad personal experience may make me a little opinionated and a touch hard-headed.

So my question would be how long have you actually had those batteries and do you really believe they will give you the 20 or more years that you feel they would. As far as I have heard all batteries require some type of attendance to make sure they are not over or undercharged.

And as for past weather patterns concerning clouds... well I would not use it as a solid based considering how much our climate and weather has changed over the last couple of years.

All I can say is stay safe and make sure you have a way of keeping your batteries charged because solar panels (all types) will be working overtime to provide what people expect them to.

[Mike90250]

Li batteries vs Lead Acid, yes, there is initial cost, and there is the lifetime of the cells themselves. If your battery is for nightly use, every night, then right sized Li may be less expensive, after you have leanred to manage your system. Lead acid can take some mild abuse and still be just fine. Li is very particular about upper voltage and lower voltage, and is unable to be charged when below freezing.

[sidpost]

After running a big 24VDC and currently a large 48VDC lead-acid systems, ownership costs, and routine maintenance to me are a huge hurdle to overcome. With CATL or EVE "Grade A new" ~300Ah LiFeP04 cells being <~$160 on my doorstep, I have a hard time thinking Trojan L16's or recycled Forklift batteries are a remotely good choice for myself personally.

Freezing temperatures are a valid concern but, protection for that condition is pretty simple and embedded in my charge controllers, even the ones on lead-acid batteries! Charging a frozen lead-acid battery isn't a good idea either! Not to mention, the power available really falls.

If freezing temperatures is a concern, I would seriously suggest a heat mat for your batteries that is triggered when the temperatures fall.