Multiple off grid systems

14 Posts
Oct 15, 2006 05:26 pm
Multiple off grid systems

Hello again

I'm working on a project to build a off grid vacation complex. The complex will be 15 cabanas. My big question is....

Is it more economical to have a single system and run wiring from unit to unit or am I better off with each cabana having a seperate system??

Carlos Cabanas
 
30 Posts
Oct 16, 2006 01:07 pm
Re: Multiple off grid systems

Hi Carlos - the answer to your question is "yes".  What I mean is, depending on the specifics, it may be better to have individual, stand-alone systems vs. one large system (or maybe it's several systems, each serving a 'cluster').  In particular we need to know the expected load at each cabana and the basic geometry of the complex (arrangement and accurate distance between units, etc.).  If you could provide that kind of information then the engineering trade study becomes possible.  One interesting consideration with so many units is load diversity; sharing of available power between systems can provide real design and life cycle cost benefits.  If you could post some additional info I can provide more details (including where is this compound going to be located?)

Best Regards -

Tom Hardy, PE
HVTA, Inc.
 
14 Posts
Oct 16, 2006 03:59 pm
Re: Multiple off grid systems

Tom
Once again thanks for the response!!

The complex will be located on an island in Belize. There will be 15 rental cabanas plus three for a restaurant and a couple for staff accomadation. Actual distances between the cabanas are not actually known, however the plan is to cluster them. Some will have joined galeries (probably a distance under 12 feet. The load at each cabana is also in the planning stage.. e.g. the florescent lights!

Carlos Cabanas
 
30 Posts
Oct 16, 2006 04:38 pm
Re: Multiple off grid systems

Hi Carlos, glad to be of help.  Are you planning other loads in the guest cabanas, namely ceiling fans (not bad), small refrigerators (big load), etc.?

The restaurant will probably be the biggest overall load and obviously you need to plan that very carefully. 

Let me know if I can be of any help in any aspect of your design or implementation. 

Best regards -

Tom Hardy, PE
HVTA, Inc.
 
578 Posts
Oct 16, 2006 07:51 pm
Re: Multiple off grid systems

I think we have talked before, but here are my two cents.

I vote for separate systems.  Economies of scale and interchangeable parts.  Like tom says, keep loads low, maybe even dc.   if you want "normal" appliances and "normal" wiring with servicing done by "normal" electricians, perhaps a small inverter per cabana is possible, say 600 watts or so.  obviously, no blenders or toasters, but in the case that someone does something silly, it does not knock out several rooms at once. 

the physical distances, the battery charging means, and the loads list are crucial for what you end up deciding.

- james Alt-E staff

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14 Posts
Oct 16, 2006 10:07 pm
Re: Multiple off grid systems

Tom

The other loads in the Cabanas are the water pumps... (If it's necessary to have one per Cabana, I think not with your idea of pressurised starage tank.) yes a fan, probably a T.V. and DVD  as well as 120 ac outlets for the guests personal appliances. For example charging an mp3 or the dreaded hair dryer. Obviously that one is causing me lots of problems on the watt planning! Right now I'm planning on 6 125 watt solar panels with 2 12 volt batteries per cabana. That gives me a battery bank of 700 amp hours. The restaurant is actually the easiest in the sense that I don't have guests in there!! Almost everything will be gas powered... don't really think solar is viable for a restaurant. So it comes down to the lighting and a couple of AC outlets for very moderate use of kitchen gadgets. (no microwave!!)


James
I don't believe we have ever talked before (unless your on other forums?) I thought the idea of clustering the systems would help me deal with the peak loads? If every cabana is separate then every Cabana has to be able to deal with the peak loads individually! Wouldn't it be better to have a bigger system so that no one load taxed the system? I'm hoping to keep the lighting DC and the ceiling fan as well. I agree that separate systems would insure smaller problems at a time!!

Carlos

 
30 Posts
Oct 17, 2006 04:27 pm
Re: Multiple off grid systems

Hi Carlos - you bring up some interesting points.

I am wondering how you are planning to heat water for the various cabanas; one central heater or ??  Is it going to be solar or gas, etc.

Also, you mentioned hair dryers - they require about a kilowatt of power to run (not a big deal from a total energy point of view since they would only run a few minutes per day). But that size load will drive the size of the inverter you need at each cabana.  This not only increases cost but also the standby losses are higher with the larger inverters.  You only need a 200w (or so) inverter to run a reasonable TV and satellite receiver. 

The quick model I generated for a cabana with lights, fans, TV/sat and estimated usage time for each results in a approximately 100-120 amp-hours per day (at 12 volts nominal).  Running the solar model for Belize (including long-term weather data from the airport) indicates that you would need 500W equivalent solar panels to break even. So your number of 6 panels of 125W each gives you plenty of margin.  The 700 A-hr battery bank (if that's at 12 volts) might be just a little big but it would give you over 3 days of storage without going below about 50% capacity (so your battery bank should have very long life). So your numbers are pretty good!

Overall you have a good systems engineering problem to determine how to generate/distribute power as well as the hot water (as that affects the electrical system design (how many/where to place pumps, etc.)).  The system architecture considerations considering clustering and power sharing also adds challenge and potential opportunity for an overall reduction in system cost and improved reliability.  One approach we have taken is to use a distributed 120V ac network for a cluster (to allow load sharing) and individual unit DC systems.  As James mentioned, a lot depends on how the various units are located, what the load diversity is, etc.  Other important considerations are the anticipated occupancy rates (especially in a cluster architecture) since that reduces total energy requirments.  Anyway, a real engineering evaluation and trade study would let you know what the optimum approach would be.

If you have any more definition on what you are planning I could probably give you some additional recommendations.

Best Regards -

Tom Hardy, PE
HVTA, inc.


« Last Edit: Oct 17, 2006 04:43 pm by Thomas Hardy »
 
14 Posts
Oct 19, 2006 03:41 pm
Re: Multiple off grid systems

Tom

Once again thanks for the information.

O.k. here's my new concept. What if I was to run just the lighting and the fan for each Cabana with and individual system. No need for an inverter at each cabana and the system could be even smaller!! So far I have between 12-16 lights per cabana depending on the model. Hopefully the lights will not all be on at once as well. Guests will have to be "educated" upon arrival.

 The AC would be one central system from the restaurant or service building, as it can travel the distances easier. I'm sure the chances of 15 hair dryers at a time are very slim! So let's say I plan for a load of a three hair dryers and all the TV/DVD/SATand the rest of my equipment waterpump and desalination etc.

Is this viable, and would I save by joining these systems, or is the cost of one big inverter that much more? I could run a smaller number of solar due to being able to use wind at a lower cost per watt. When the loads become too high for the charging mechanisms I would have a back up gen anyway.

Tom I'm a little confused as to the purpose of pressurized water tanks. I was told that I would need a pump capable of pumping my maximum GPM and pressure. So what's the purpose of storing water under pressure?

The water heating will either be solar or 30 gallon gas heaters. The cabanas will be clustered in groups of four or three, so if it is gas one heater per cluster.

Carloscabanas
 
30 Posts
Oct 19, 2006 08:58 pm
Re: Multiple off grid systems

Hi Carlos - it sounds like you are making good progress in your design.

The pressurized water tanks I refer to are simply standard pressure tanks used with domestic water systems.  They are used so that the pump doesn't cycle as often when small amounts of water are taken from the system.  If you have a central pressurized (cold) water system feeding the individual hot water systems, you don't need additional pressure tanks.  All hot water systems do use some type of expansion tanks however (they may only be a gallon or two).

If you'd like, I would be glad to send you some sketches of various configurations for the DC and AC power systems. Let me know if that would be of help.  Let me know how I can reach you.

Regards -

Tom Hardy, PE
HVTA, Inc.
 
1 Posts
Oct 19, 2006 10:11 pm
Re: Multiple off grid systems

Have you considered the use of grid-tied inverters in every structure to share power in your own little power grid to share and spread all of your loads including those of your restaurant with full appliances. if you need information on how to do this you can contact me at teamnemesis1 @ msn.com
 
14 Posts
Oct 20, 2006 01:22 pm
Re: Multiple off grid systems

Tom

Thank-you for the explanation of the water pressure tanks. Makes sense!! I would really appreciate the sketches!!  I don't know what I did in my first calculations, but I've taken the tv and dvd out of the systems and somehow I need more panels than I did in the beggining?

The salesman for the desalination machine that I need told me that it uses 9 kw an hour 24 hrs a day! Two 5hp single phase motors, 3 phase motors are optional but unfortuneatly I'm not really sure what that means! Anyway that's alot of juice! Can I put that kind of machine on a wind generator?

I can be reached at carlossettle @ ccapcable.com


Have you considered the use of grid-tied inverters in every structure to share power in your own little power grid to share and spread all of your loads including those of your restaurant with full appliances. if you need information on how to do this you can contact me at teamnemesis1 @ msn.com

Would this save on solar panels and what is the cost of all the grid tie invertors compared to the panels and batteries saved? What is the risk of a guest doing something that takes my whole grid down?

Carlos
 
30 Posts
Oct 20, 2006 02:13 pm
Re: Multiple off grid systems

Hello again Carlos - Just a few notes about the past two postings.  David has an interesting idea but grid tie systems are designed to connect to large (huge) systems that have multiple large generating systems interconnected in a managed network.  The amount of alternate energy pumped into the grid is almost infinitesimally small compared to the energy (OK power) flowing in the grid.  That is certainly not the case in your design (a large percentage of the power would be generated by the solar systems).

Most inverters do not like being backfed (i.e. seeing voltages on the grid generated elsewhere). I have seen inverters destroyed by this.  However, it is possible that there may be something available for this (David, if you could post some candidate inverters we can look at using them).

Right now I'm thinking that you have a large power/energy problem with the needs of your desalination unit.  You are talking about over 200 KWhr per day!  You can't do that with a reasonable solar system.  A large wind power system will be quite expensive and is just by itself a large project.

Do you really need that much desalination?  Just as with your comment of educating guests about the use of energy in the cabanas, can you make the same plan about reduced water use?

Typically motors are used to run pumps for reverse-osmosis desalination. If that is the case, there are other options for getting the pressure needed (i.e. DC motors are more efficient and if we can reduce the amount of water you need per day, might get you back in the game).

Let me know what you are looking at for desalination as the rest of the loads are second-order compated to this one (i.e let's see if we can solve this one first).

Tom Hardy, PE
HVTA, Inc.
 
14 Posts
Oct 20, 2006 04:27 pm
Re: Multiple off grid systems

Tom

Look's like I'm going to have to forget about being totally Eco!! It seems the only way to run this thing is with a generator, unless I cover Nevada with solar panels! : ) Anyway the water desalination is mostly for back up in case of dry spells as our plan is to use recuperation of rain water. Maybe we'll start up the Gen for half an hour a day to have pure drinking water.

Let's get back to the DC systems in the Cabanas and an AC system large enough to run tv,s and DVD as well as some restaurant equipment!!

Carlos

 
22 Posts
Oct 25, 2006 09:09 pm
Re: Multiple off grid systems

Carlos,

I manage a private, 45 acre island 65 miles SE of Nassau, in the Exumas, Bahamas.  I am currently doing a major AE installation, and I've opted for several "stand-alone" units for the following reasons:  I am totally against the cost and complexity of running wireing in conduit all across the island.  I WANT the redundancy of multiple systems, so that if any one location gets hit by lightning, the whole shebang ain't zapped.  Each location will have a bank of Absolyte II batteries (or, perhaps the Deka Unigy II's...), and inverter (most likely by Outback--they provide a TRUE sine wave, and are SEALED against the elements!), an appropriate set of panels, and a Whisper 100 windmill (am considering a Bergy or two for comparisons...).  Your battery bank is the HEART of your system.  Like with cistern size, no one has ever said, "Gee, I sure am glad I let them talk me into the SMALLER unit...!".  Consequently, the more the better.  Each location here will also have it's own small (8kW) diesel generator as back up and emergency power (this also allows A/C in the hot months...)  Each generator is "semi-portable" (built in, but permanently mounted on a small trailer), to enable pulling duty at different locals.
  Here, I have one owner, his immediate family, and a precious few "mainlander" guests.  These are all "dialed in" to the alternative energy lifestyle.  This is a MUCH bigger issue than folks here have implied.  ESPECIALLY if you have a coupla dozen bungaloes loaded with tourists (or, as I inaffectionatly call 'em, "turroids").  Folks on vacation will smile, nod their heads, agree wholly, then go ahead and plug in their hair dryers, take loooong showers, and leave the friggin tap running whilst they brush their teeth.  Believe me, the laundry doing TOWELS alone will drain an astonishing amount of precious h20...   Which brings us to your watermaker demands.  At my warehouse, I have two Watermakers brand 2500 gpd desal units.  I also have a cistern with 70,000 gallons capacity (additionally, I have an island-wide capacity of +/- 120,000 gallons).  And, we USE it!!  My intent is to run "mr. stinky" for a day or two here and there, to top off the tanks.  DON'T simply "run it for a half-hour a day", as this is not good for the watermakers (btw, what brand/size desal do you have?).  That said, I have just been notified of a watermaker motor retrofit that WILL run on AE.  Check the Danfoss SWPE for info... 

So, there's my fifty-seven cents worth.  Cheers!

J. Chris Cloud
 
22 Posts
Oct 25, 2006 09:14 pm
Re: Multiple off grid systems

PS-- it never hurts to also dial the water pressure down to roundabout 15 psi....  that helps with the water consumption....  Smiley
 
14 Posts
Oct 26, 2006 11:49 am
Re: Multiple off grid systems

Chris

Thank-you for the information. I don't actually have a desalination unit as of yet. Suggestions are always welcome. I've been looking at the aquapura 7500. How do your guests react to their 15 psi showers? As for the wiring my Cabanas will be relatively close together, so I figure I can save by having a joint AC system, with seperate DC systems to protect at least the lighting from mishaps! I figure that I would save on invertors doing this and possibly on panels and batteries by having one larger bank that provides the peak demands instead of every bank having to deal with those high demand items.

Tom

I'd be interested in seeing any sketches you have as to the wiring of the systems. I will look into the desal pump that chris talked about but for now I would like to base the system on the fact that the desal will be run with a generator.

Carlos 
 
22 Posts
Oct 26, 2006 12:57 pm
Re: Multiple off grid systems

Carlos,

Perhaps a compromise is in order.  Say, each "cluster" of cabanas could be on it's own system?  I agree, if the runs are not long, wiring isn't an expense issue.  See, here, I'm faced with 3000' runs, which mandate at lease #8 wire, and pumping 480, three-phase electricty to lessen "line loss" in voltage.  So, to do that, my AE system would have to be 480 three phase, then I'd need transformers at each consumer end.  Muy Complexo!

As for the water pressure, they get over it.  It becomes part of the "out-island charm", without realizing the alterrior motive of water conservation  Smiley

jcc
 
14 Posts
Oct 26, 2006 03:18 pm
Re: Multiple off grid systems

Chris

Where are you located? Curious!!

Carlos
 
22 Posts
Oct 26, 2006 05:40 pm
Re: Multiple off grid systems

Carlos,

Send me an email at islandmanagers @ aol.com.  Kinda sorta gotta keep "under the radar", as it were...


jcc
 

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