Generator vs Solar Panels

Toonces · June 2013

I received some great info from you guys on my first thread "Solar Power in Ohio for Off Grid Cabin", and have a couple questions again if you don't mind.

In the first thread we decided that I needed about 600AH@12V to run my lights, 12V demand pump, and stereo for a 3-4 day trip. The solar panels were to some distance away from the charge controller so we discussed going to 300AH@24V. But my buddies keep asking me, why I don't just stick with a 12V system and run the 3500W Yamaha genny with a seperate charger to do the charging? And because they keep mentioning it, I figured I better have a good answer for them (and for myself) before I invest in all the solar equipment.

So here are my questions for you all:

1. What type of charger would I need to charge a 600AH@12V system?

2. How long would I have to run the genny to accomplish the charging? I think we figured my DOD should be in 20% range if I'm not mistaking.

3. Would more than 2 parallel strings still be an issue for charging with a generator?
Example: (6) T-105 6V@225AH (batteries are readily available), but 3 parallel strings which isn't ideal for solar charging i know.
or (4) L16 6V@320AH (harder to get), but 2 parallel strings.

I am at the cabin every 3 to 4 weeks for 3-4 days at a time usually, but sometimes leave it for a couple months in winter or mid summer, just to give you an idea of usage.
And sticking with a 12V system allows me to stick with cheap invertors, but I'm always open to other suggestions.

Any thoughts on this would be much appreciated

Blackcherry04 · June 2013

Re: Generator vs Solar Panels

Toonces wrote: »

I received some great info from you guys on my first thread "Solar Power in Ohio for Off Grid Cabin", and have a couple questions again if you don't mind.

In the first thread we decided that I needed about 600AH@12V (per day I believe) to run my lights, 12V demand pump, and stereo for a 3-4 day trip. The solar panels were to some distance away from the charge controller so we discussed going to 300AH@24V. But my buddies keep asking me, why I don't just stick with a 12V system and run the 3500W Yamaha genny with a seperate charger to do the charging? And because they keep mentioning it, I figured I better have a good answer for them (and for myself) before I invest in all the solar equipment.

So here are my questions for you all:

1. What type of charger would I need to charge a 600AH@12V system?

2. How long would I have to run the genny to accomplish the charging? I think we figured my DOD should be in 20% range if I'm not mistaking.

3. Would more than 2 parallel strings still be an issue for charging with a generator?
Example: (6) T-105 6V@225AH (batteries are readily available), but 3 parallel strings which isn't ideal for solar charging i know.
or (4) L16 6V@320AH (harder to get), but 2 parallel strings.

I am at the cabin every 3 to 4 weeks for 3-4 days at a time usually, but sometimes leave it for a couple months in winter or mid summer, just to give you an idea of usage.
And sticking with a 12V system allows me to stick with cheap invertors, but I'm always open to other suggestions.

Any thoughts on this would be much appreciated

With your generator you could run 75- 125 amp charger. You can figure a charger at about 90% + efficient. The first days you only need to charge back to 80% from 50 % dod and don't do a full charge until before you leave. If your not there you only need a panel to maintain the batteries while your gone or to finish the Bulk charge from the sun. So, you probably only need to run the Generator a couple hrs a day. This is how I run my boat. Posters in here like " OPM " other peoples money........ they spend it freely.

If you still have that cabin 20 years from now, a full solar system might look like a bargain. Hindsight is 20/20.

If it was me, I buy a 1500-2000 watt TSW Inverter / Charger it would already have a Charger and Transfer switch. With it and the Generator you can run about anything you want. If down the road you want to add solar, then you can. 1500 watt usually have a 70 amp charger and a 2000 watt will usually have a 100 amp, you have to go to a 2500 watt to get 125 amp. You kind of get what you pay for.
.

BB. · June 2013

Re: Generator vs Solar Panels

The original thread is here:

Solar Power in Ohio for Off Grid Cabin

I am going to suggest to go back and revisit your loads/needs...

There are cheap 12 volt MSW inverters... And some reasonable priced small (300 watt) 12 volt TSW inverters. But, for the most part, large "cheap" 12 volt MSW inverters are not a great solution. If you are into audio, you can get a fair amount of hash from the MSW inverter (RF interference is not uncommon with charge controllers or inverters). And some items do not run well on MSW (noise, motors/transformers up to 20% less efficient--which goes into heat--which can shorten life of some things--especially the smaller power bricks/AC Watt Transformers.

From the original thread. A 300 watt TSW inverter on 4 6 volt Golf Cart Batteries would power your main loads.

The problem was when you throw a vacuum, coffee maker, etc. in to the mix. That makes your peak power loads 5-10x that of the rest of your stuff there.

Plus, those types of appliances are typically only operated for fairly short times during the mornings/day time. So, getting a 1,600 watt or larger Honda or Yamaha small inverter generator to support those loads (and backup charging for the battery bank during bad weather) would, in my humble opinion, be a better match for your needs.

If you go to the "dark side" and attempt to do most/all of your charging with the AC Generator--And size your battery bank/inverter to support the few high wattage loads, then you are going to end up running the generator for 4-6 hours every day or two to keep up with the loads/charging (just a wild guess on generator times).

Vs just needing to run the generator for an hour or less every day to run the vacuum, coffee maker, and microwave (when needed). And run the rest of the cabin off a smaller/quiet/efficient off grid solar power system. And frankly I would be telling you to get a stove top or propane powered Mr. Coffee and a thermos to keep the coffee hot.

Usually, the first appliance that makes going from a small (1 kWH per day system) to a "larger" (3.3 kWH+) solar power system is a refrigerator (around 1-1.5kWH per day). And usually a fridge (or freezer conversion) only makes sense if you are there for 9+ months a year (i.e., near full time). Otherwise, a used propane fridge (from a wrecked RV) is going to be more cost effective (at the expense of a 20 lb propane cylinder every month or so).

We could do some alternative designs here--But until you have nailed down your power needs better (in my humble opinion), avoid buying any major hardware. Solar is not cheap.

-Bill

niel · June 2013

Re: Generator vs Solar Panels

without my reviewing the old thread you state that you need 600ah. now is that 600ah for the loads or for the batteries after accounting for not going below 50% dod as they need a buffer to prevent depleting all of the battery power and killing them? if it is the loads that need 600ah then you need at least 1200ah in batteries to supply this and at 12v that is huge.

Blackcherry04 · June 2013

Re: Generator vs Solar Panels

I don't know if I'd call 1200 amp hrs huge, thats only 10 GC-2's @ 12 V. If he pulls 50 amps per hour for 12 hrs, he'd be covered, that would run 5 refrigerators all night, it depends on the loads. Now if he was going to run a 1500 watt microwave for a hour at a time off his inverter and battery bank, it wouldn't make sense. If he was going to do that he would start his generator and kill two birds with one stone, cook and charge at the same time.

niel · June 2013

Re: Generator vs Solar Panels

Blackcherry04 wrote: »

I don't know if I'd call 1200 amp hrs huge, thats only 10 GC-2's @ 12 V. If he pulls 50 amps per hour for 12 hrs, he'd be covered, that would run 5 refrigerators all night, it depends on the loads. Now if he was going to run a 1500 watt microwave for a hour at a time off his inverter and battery bank, it wouldn't make sense. If he was going to do that he would start his generator and kill two birds with one stone, cook and charge at the same time.

that wasn't my main point here as i don't want to see him having 600ah in batteries with 600ah in loads. that equals a dead battery.

Toonces · June 2013

Re: Generator vs Solar Panels

Lets start from the beginning since there has been many changes along the way. Here are my loads with immediate future loads figured in:

(5) 13 watt CFL bulbs used 5hrs per night (not all bulbs being used at once ofcourse, but let say that for worst case situation) so 5x13x5= 325 WH per day.

(1) 12V car stereo with (4) 50watt speakers being used 8hrs per day (again worst case, but we do like our music) so 4x50x8 = 1600 WH per day.

(1) 12V 84 watt demand pump (not sure on the usage exactly, since I haven't installed it yet, but lets say 3hrs per day) so 1x84x3= 252 WH per day.

I have eliminated the vacuum and coffee pot from my factoring, so the only thing I'm using the invertor for is the bulbs.

Convert to AH:
Bulbs: 325 WH per day /.9 invertor eff. / 12V = 30.1 AH per day
Stereo: 1600 WH per day / 12V = 133.3 AH per day
Pump: 252 WH per day / 12V = 21.0 AH per day

For a total of 184.4 AH per day

My batteries will be kept underground in a vented vault, so temperature shouldn't be much of a factor.
The "# of days of automony" have certainly changed since we are talking about using generator power instead of sunlight, so 0 days of autonomy I guess.
DOD I'm assuming should be only 20% which equals 184.4 / .2 =922 AH per day (I think I figured 30% to 40% DOD before, thats how I came up with 600AH)

And just to clarify again, I'm at the cabin usually 3-4 days at a time, every 3-4 weeks.
And I think I overstated my genny capacity: I have a Yamaha EF3000iSEB

Hope this all helps, please double check to make sure I did the calcs correctly since I am a newbie. Thanks again guys!

BB. · June 2013

Re: Generator vs Solar Panels

Your stereo power estimates may be way high... I would suggest getting a Doc Wattson and/or a DC Current Clamp Meter and measure the power consumed by the radio. I would be surprised if you used 1/10th to 1/4th of your estimated power.

Most audio systems do not output near as much power as their "ratings"--And even if they do, your system would not output 100% power 8 hours per day as it would no longer be music but a constant tone or distorted mess (my guess).

You also may want to look at other audio appliances... Car Radios (at least in the days long gone when I used to care) are not always the most efficient source of music. You should measure your audio system loads at your typical volume levels between your "car stereo" and some others (battery powered boom boxes, and even AC powered systems measured with a Kill-a-Watt type meter).

1,600 WH per 8 hour period is about 3-4x what a typical full sized energy star rated refrigerator would use (the typically "bad boy", at 1.0 to 1.5 kWH per 24 hours, for off grid power systems).

-Bill

Toonces · June 2013

Re: Generator vs Solar Panels

Thanks Bill,
Since I won't be able to get down to the cabin for a number of weeks, I won't be able to test the car stereo. I tried to find some info online but was unsuccesful. I do remember replacing a 15amp fuse on the car stereo, so I would imagine that the maximum wattage would be 180W. I know we are trying to be precise, but would this get us close enough?
And the max I turn up the radio is about half way, otherwise it get distorted. I know this all speculation, but could I say I use roughly 90W?

And you are right, I may not stick with the car stereo. I'm sure a home stereo receiver would provide me with better sound. I tried to find some power info on home receivers to, but so far I have come up short. I understand that stereos are like ovens, the more you turn them up, the more power they use; but you would still think they would provide some type of rating.

BB. · June 2013

Re: Generator vs Solar Panels

Kill-a-Watt meter will be your friend... I don't know the derating for typical stereo--But a 15 amp fuse would carry about (x 0.8 nec fuse derating) ~ 12 amps. 12a*12v=144watts maximum.

I do know that for AM radios (like Aircraft and HAM transceivers), the average transmit power is ~25% of rated power (AM=Amplitude modulation--where peak power would be 100% transmitter output)--So, I would guess that would be similar derating (or even more since you do not run a stereo at 100% volume) for a stereo.

In the "olden days", when boom boxes filled with D Cell batteries were popular--Those were pretty efficient for the noise produced (D Cells always lasted me a pretty long time).

And, if we want to get more "technical"... We "hear" sound (and see light) on a Logarithmic scale.

Basically, our day to day life we measure a 4 foot board and cut it in 1/2 and we have two 2 food boards. A 6 foot person "towers" over a 3 food kid, etc...

With sound and light, our perception is that something that is 2x louder (or brighter) is barely perceptible to us humans. And something that is 10x louder/brighter "overwhelms" the less powerful source.

So--If you measure 4 amps and "crank up" the stereo to full 8 amp input power--You may not even notice a change in the level of the music.

Your "measured" current will probably be in a 10:1 range (say 4 amps to 0.4 amps) if the audio amplifiers were purely "linear"... But most audio amplifiers are not linear... So you may see 3 amps at normal to near zero volume, and 8 amps when cranked all the way up (just made up numbers for the example).

Until you measure, you will not know. A "minor change" in your volume setting could end up with a large change in power consumption.

-Bill

niel · June 2013

Re: Generator vs Solar Panels

sounds like you do long weekend parties over there. a better quality stereo would tempt you to turn it up even higher as the distortion is keeping you from over doing it. it's hard to say if halfway would be 90w consumed and it would be better to actually measure the current drawn. the meter will vary somewhat will the music. know that if it sustains a high draw from a loud portion of the music that it could still approach or exceed the typical 10a rating of most multimeters. clamp on types will have a wider range, but can be less accurate.

westbranch · June 2013

Re: Generator vs Solar Panels

So... that is why I had to keep getting larger speakers (at least till I was happy with what I was hearing i/c 12" woofers) for the stereo as I kept hitting the distortion with my BIG amplifier...

zoneblue · June 2013

Re: Generator vs Solar Panels

Toonces wrote: »

so the only thing I'm using the invertor for is the bulbs.

If thats the case have you thought about LED lighting, which runs on 12vdc. In the last couple of years LED technology has surpassed CFL in terms of efficiency, and the price has like solar, come way down.

Generator vs Solar Panels

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