Need advice for remote solar power

System · October 2007

I am considering a solar system to power some scientific equipment in a back country setting. Our equipment draws 221 Amp/hours per day and will run continuously, 24hours a day for 4-5 months. Half the equipment requires 24V to operate, the other half 12V. Is this obtainable?
Thanks
Mark

niel · October 2007

Re: Need advice for remote solar power

first let me say that nearly nothing is impossible if you can afford it. you probably could do it, but i'm guessing it may be easier to run different systems to operate the 12v section and the 24v section rather that have one large system and converters, but that could be done too.
now that 221ah/day divided by 24hrs is about 9.21amps per hour on average. the power needs to be generated by the pvs in the span of time you get sunlight and that varies depending on where you are, but let's say for arguements sake you get 4 hours of full rated sun hours. that means 221/4=55.25amps in pvs cec rated minimumly. something this big would also benefit by mppt controllers too and you'll need at least 2 of them even if for one large system, but because there is a need of 2 controllers the possibility of 2 seperate systems is also very workable.
of course you will need batteries to store this power. you show 221ah in your needs so you must double that so as to not exceed the 50% dod on the batteries. you are up to 442ah in minimal battery capacity needed on a daily basis so if you need any buffering for cloudy days and such you can add more to it, but be carefull as you don't want to have so much battery capacity that you'll have trouble in charging the batteries.
this is only a rough overall view of what can be done. if you can afford it you must decide on the particulars. we can help there too if you'd like.

GreenerPower · October 2007

Re: Need advice for remote solar power

To add to Niel's comments, you'd need roughly
221 AH/day * 24V / 4 sun-hours/day = 1326 Watts worth of PVs.
Factoring in the efficiencies, you'll need slightly more.
And for "rainy days", you might want to consider an autostart generator in your plan.

GP

BB. · October 2007

Re: Need advice for remote solar power

And, have you made sure that the equipment is as efficient as possible? Can you swap out a "laptop" with a dedicated low power controller? Flash drives instead of disk drives? Does it need run 24x7, or can it run 1 minute out of 60, etc...

Is there wind available? Can you truck/fly in th equipment or must you pack it in. Is it "out of the way" of vandals?

4-5 months--is that winter or summer?

A solar power system makes a lot of sense for year round use (or at least 9 months out of the year). If this is a one time deal and the solar panels/equipment is not transferable to other projects--then cost wise it might make more sense to install a fuel efficient generator on the site with batteries than try to do it with (relatively expensive one-time use solar panels)...

A Honda eu2000i generator (granted, this is not an electric start generator) gets about 5kWhrs per gallon of fuel or:

1,326w*4h per day /5,000wh per gallon = 1.06 gallons per day or 32 gallons of fuel per month. (with inefficiencies--charger, batteries, etc.--might need 50% more fuel than calculated--call it 32-50 gallons per month).

If you can find a similar small, rugged, remote start generator (preferably diesel--you might even be able to cut the fuel use by 1/2) or even propane... And only use 1 day of battery storage (instead of 3+ days).

Makes for a smaller (and possibly cheaper overall) package than 1,500-2,000 watts worth of solar panels (plus mounts, wiring, 3+ days of battery storage, etc.). A solar system is probably a good $15-$20,000 (panels, controller, batteries).

If you are monitoring emissions (CO2, smoke, pollution, etc.) the fuel driven generator may be an issue...

Here is a nice page that shows systems about in the size range you are asking about (for microwave repeater sites, remote cabin power, etc.).

Depending on where you want to installed this station--you may or may not be in an area that has good amounts of sun (world map here).

Bergy makes good wind systems--here is a page that talks about their "hybrid" systems (wind/solar).

I enjoy reading and researching about small generator/electrical solutions--but I usually don't find to much with an internet search. There are lots of larger solutions (6-15kW or more), but not so much in the 200-500 watt range unless you look at fuel cells or TEG type units. A Honda eu3000i (3kW electric start generator) seems to be one of the smaller/commercial units out there.

Generally, a good solar or solar/wind system is expected to have a 2-5 year payback in remote sites... Perhaps you can find a place that would rent a small power package for 5 months (solar or fuel based)...

I would be interested in what you have found so far, and what solution you eventually settle on.

-Bill

crewzer · October 2007

Re: Need advice for remote solar power

I am considering a solar system to power some scientific equipment in a back country setting. Our equipment draws 221 Amp/hours per day and will run continuously, 24hours a day for 4-5 months. Half the equipment requires 24V to operate, the other half 12V. Is this obtainable?

Mark,

Tell us more about which 4-5 months (April - August? October - February?) as well as the general location. If possible, select a location from this list.

Also, please be more specific about your daily energy (Ah/day x V) needs. Does "221 Ah/day... 1/2 @ 24 V and 1/2 @ 12 V" = 111 Ah/day x 24 V and 110 Ah/day x 12 V?

More later,
Jim / crewzer

System2 · October 2007

Re: Need advice for remote solar power

First off, thanks for all the feedback. Here are some finer details.
The site location is near Davenport, CA, so it looks like WBAN No: 23234 (San Francisco) would be appropriate. Fog/Rain is going to be an issue as our site is less than 2 miles from the coast at ~30ft above sea level. The power supply will be used from January 1st to May 15th (peak of the rainy season) There are some open fields to place panels in, so we have a wide-open sky.
Here is a breakdown of our equipment (see attached jpeg)

This is a Hydro acoustic camera system used to monitor salmon migrations.
We have tried to make our system as efficient as possible. For the most part, the laptop screen will be off, which should cut down its draw. I don’t know anything about ‘dedicated low power controllers’. (BB can you tell me more?) The computer must run the equipment software (windows based) and manage the external hard drive. The 300GB external drive is necessary as we will accumulate ~30GB of data per day!
Wind is available, and we can truck in equipment. It is on private property, but security from vandals may still be an issue. The panels could be transferred to another project, so we don’t need to recover the cost right away.

Generators are an option. I assume you would use the generator in place of the panels – to a charge controller – to a battery bank – to the equipment.? I already have 4 12V 100Ah sealed lead acid batteries from another project. If I had 6 of these batteries wired in parallel/series, that would give me 24V and 300Ah. How quickly can a generator like a Honda eu3000i charge a bank of this size?

Thanks for the help
Mark

Solar Guppy · October 2007

Re: Need advice for remote solar power

You can do much, much better than this by building a window PC and being smart with the software

I have built a few PC's and use to run my web-site on a mini-itx based platform .. the PC used only 11 watts active running windows XP and running disks tests using a laptop internal IDE drive. It was the 533mhz fanless mother board.

next, on the software, you could have it cache the data in memory and only spinup the hard drive as required to write to the drive ... BIG savings as you'll need as few percent run vs off time to store the data and its automatically handled by windows

Its a very simple thing to build the PC, better yet, they can run directly off 12 volts with an optional switching power supply that plugs into the power header of the mini-itx PC. Its also cheaper that a store bought PC. You can also use the ITX box an mount a second drive, elimating the need for the external hard drive power supply

Also for hard-drives, notebook drives are now 200GB for only 121.00 bucks ... if nothing else, you can change the HD in the laptop to one of these .. average power is only about 1 watt, maybe 2watts under non-stop seeking

http://sdd.toshiba.com/main.aspx?Path=HardDrivesOpticalDrives/2.5-inchHardDiskDrives/MK2035GSS/MK2035GSSSpecifications

best price check out ..

http://www.pricewatch.com/notebook_drives/200gb.htm

One last thing is most off the shelf video recorders have lots of setting to reduce disk usage. I have allot of experiance with Geo-Vision products .. 30 GB/day is outrageous amount of storage. 16 channel DVR system's I've built and are in use at commerical sites average about 10 GB/day with 16 acitve 530line color hires cameras ... the key is using the motion detection ( totally configurable ) and the GeoVision Mpeg4 codec.

Hope this ideas help ... checkout www.mini-itx.com for some ideas ... all the major internet shops sell mini-itx motherboards and cases .. my personal favorite is www.newegg.com

westbranch · October 2007

Re: Need advice for remote solar power

FYI, just looked at an old 40 GB IDE drive I have spare (and set up as a external HD using a USB port) , and it is a 12 VDC .75 A. Perhaps you could save some energy losses by using 12 v directly rather than a transformer, on an external HD.

In addition to what SG says about caching, is it necessary for 24/7 "recording" of the digital images as opposed to 'snapshots' over the same time period?

Who is going to review all this video???? Sampling theory is not this advanced/comoplex as far as I am aware. Dont you just need the data at the sampling points/time?

thoughts for the grist mill.
Cheers

Eric

BB. · October 2007

Re: Need advice for remote solar power

Wow--that is an 80 watt laptop... My old laptop running XP (that I am typing on now) is only about 20 watts with the screen off (but if you are running a 300 GB disk drive, that will eat the power too)...

Using Windows may limit the use of STAMP or other industrial PC type controllers... It has been decades since I have worked with, or needed to look at, low power controllers--but I was thinking of PC/104 standard devices like this. Also, look for large capacity disk drives designed for laptop computers--they will be much more power efficient (and slower access times)...

To be honest, this does not sound like a solar panel application unless you are in a valley that blocks the marine layer... Just as an example, I have a 3.5 kW solar array (grid tied, 3 kW rated) in San Mateo California--and the winter output is highly variable--depending on weather... I can PM you an Excel file of my daily output for that last 2 years.

For me, December can be a really bad season for Solar Power (my December numbers where half January, and sometimes averaged less than 1 kWhr for several days at a time)--January seems to be better--usually I got around 265-300 kWhrs (8.67 kWhrs/day average) from my array... Working backwards with your numbers:

3,400 WattHours per day 3,500 watt panels / 8,667WHperday = 1,373 watts of solar panels...

But since you are on inverters and batteries, I would use a 60% overall efficiency estimate (93% charge controller, 80% batteries, 80% inverter = 60%)... So:

Panel Watts = 2288 watts of solar panels

...to reasonably power your system (in San Mateo CA, just south of highway 92 and El Camino Real)...

But I don't get the marine layer--you could easily see your average power output drop by 1/2 or more because of fog/marine layer (I grew up on the coast just south of San Francisco, and I could set my clock by 4 days of fog and 2 days of sun during the summer, winter may not be as bad)...

It seems you need to go by there at least once every 7 days...

Just purchasing two Honda eu2000i generators (manual start, 1,600 watt continuous--about one of the most fuel efficient small gasoline generator I have seen), and running them one at a time (backup/maintenance), they will run (from the manual) about 15 hours on 1.1 gallons of gas (internal gas tank)--people take the fuel cap and put a metal barb fitting and a plastic tube and filter--and connect them to a five gallon gas can and the generator draws enough of a vacuum it can siphon and can run days at a time... All for ~$900 per generator and a few bucks to build your own siphon setup (or buy a pre-made kit for ~$100)...

Charging the batteries is a bit more problematic... Generally you are limited to about 10% (1/10 * C) of battery capacity to prevent overheating of the battery... Also, depending on battery type (flooded cell or AGM) you will want to limit the total discharge to 50% or 20% state of charge (50% discharge for flooded cell or 80% discharge for AGM)...

Working backwards, currently you draw about 3,400 watt*hours per day, at 1,000 watts of battery charging power, the eu2000i would have to run about 4 hours to make up the battery usage. That would mean you would want about 1/0.1C * 3.4kWH = 34 kWHours of battery storage (at 24 vdc, that would be 1,410 amp*hours (at 24 vdc) of battery. That is probably way to much battery for your needs (that would give you 5-8 days of no-charge at 50%-80% of depth of discharge)...

But the eu2000i is also pretty fuel efficient at 400 watt of output (1.1 gallons for 15 hours)... Since 15 hours is less than 1/10 C rate--you can charge your system at 3,400 WH / 15 hours = 227 watts... And if you go out to check the system once per day (fuel and start the generator), you can use 1/50% * 3,400 watt*hours / 24 VDC = 283 amp hours of batteries...

There are lots of options if you use a generator--there are inverters with built in battery chargers and fail over switching (connection inverter to your generator AC, when generator is running, passes AC to loads and charges batteries, when generator stops, switches--like a UPS--to inverter, if electric start generator, when battery is drawn down, will restart generator and run the cycle all over again)... And some of these inverters/chargers also have programmable charge rate control.

Lots of variations... How would you like to proceed? I will stop typing here as I will probably just confuse you (and me) with more options and variations...

-Bill

System2 · October 2007

Re: Need advice for remote solar power

There are lots of options if you use a generator--there are inverters with built in battery chargers and fail over switching (connection inverter to your generator AC, when generator is running, passes AC to loads and charges batteries, when generator stops, switches--like a UPS--to inverter, if electric start generator, when battery is drawn down, will restart generator and run the cycle all over again)... And some of these inverters/chargers also have programmable charge rate control. BB, can you tell me more about these generators?
Thanks,
Mark

BB. · October 2007

Re: Need advice for remote solar power

I am not sure if you are asking about generators or inverter/chargers... I can't spend much time typing right now, but a few links:

Honda Generators: The two that I would (based on my limited experience) would take a look at (leaning towards fuel efficiency) is the eu2000i (hand start) and the eu3000i (battery start). If this will be for long term use, then you should look at larger generators/diesel generators with oil filters. The two small eux000i units you would probably break-in on regular oil, then look into synthetic oil for long term use with regular oil changes.

Inverter/Chargers/AC fail over: Two of the good companies out there to start looking at are Outback and Xantrex. Wind-Sun has inverter/chargers that they stand behind--so it is worth starting there.

In wiring the inverters, you can either operate them in standby mode (AC generator -> inverter switch -> AC load) where the generator runs the AC load and when the generator fails/turns off/runs out of fuel the inverter switches over to internal inverter/battery power.

The other way is to have the generator -> battery charger -> battery -> inverter or the continuous conversion technique.

Both work, the standby one saves energy but can glitch electronic devices on switch over (from my experience, never in the lab, but about 1 out of 10 real power failures a computer would have to reboot).

The continuous conversion runs the inverter from battery all of the time, so no power glitches (unless inverter fails). But, you have about 20-40% more losses because of the charger and inverter operates 100% of the time.

-Bill

SolarJohn · October 2007

Re: Need advice for remote solar power

Mark,

Have you considered transmitting data instead of recording it on-site? I'll bet you could significantly cut your power needs at the remote site by doing that.

John

BB. · October 2007

Re: Need advice for remote solar power

If you have someplace nearby (farm house/pump station?)--perhaps just placing the "camera" stream side a low power RF link back to the house where you plug-in your storage/computational equipment.

-Bill

Need advice for remote solar power

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