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    I am ready to start development on an off-grid property in the Humid Lowlands of Costa Rica. My understanding of electric is only basic and I am having some trouble with the details. I have a few technical questions.

    1) If I know my house will have a constant use that barely varies (fans to assist passive air flow in the house and composting toilet, an air pump for the aquaponics, router, maybe laptop) would it be wise to put it on its own dedicated system. I’m thinking 25 to 100 watts max running at all times.

    2) If I have uses that are predictable but only in the day or night that balance out would it be wise to put them on an dedicated system. I.e. Computer in the day and lights at night or

    3) Is it possible to divert energy: 1) to another battery that only charges when the others are full (to power an AC or something big on the sunniest day or days you did not use it somewhere else) 2) Diverts energy directly to run a energy hog like an AC or Dehumidifier ONLY when the batteries are full and power is being wasted.

    4) Do separate systems make more sense if I am mixing solar/wind or solar/hydro or hydro/wind

    5) Is there some energy catch 22 that makes it inefficient/stupid to have a freezer (propane or solar dc or regular) and use it for both freezer and the ice to keep an Ice box cool. I know freezers are more efficient and I don’t mind living out of a cooler if I’ve got ice

    6) If I had 2 systems and one was DC are the 12v DC appliance (blender/toaster/coffee grinder/radio) reliable and dependable…they look like cheap crap for vacationers that are gonna use it once.

    I am thinking it would be easier/smarter to have a small system to supply the the full time predictable IMPORTANT appliances (approximately 1000-2000 watts per day depending on how much I put on it) and another for day to day luxuries (make a slice of toast and a smoothie, charge my power tools, watch a movie).

    The property I am buying has hydro potential but I am gonna weight until I get down there to see what kinda of “local” engineering can be used to harvest it. I am pretty sure they have come up with something better (cheaper) than the systems on the market (I’ve heard about pelton wheel and ford truck alternator systems). If so…it seems smart to harness the 24 hour power for the basics and the solar for the luxuries.

    The biggest issue I see is the freezer…I might just go with propane…and I would like to able to run occasionally.

    I am planning on a single refer container home under a 1000 sq/ft palm thatch flyroof with non-weight bearing earthbag 1/2 walls for additional solar deflection. The bedroom will only be 100 sq/ft so I can imagine it would take much AC to cool it.

    Any creative ideas how to have a reliable system with another for luxuries or to harness excess power please chime in.


    well lots of variables here. let just eliminate a couple.

    refridgeration: i’m in favor of the sun electric 12 or 24 volt fridge supper efficient very popular in southern hemisphere.

    chowan who post’s here is very pro 12v because the availability of various products and keeping your system up. if you get all fancy with inverters and 24v or 48v systems if something goes down your trapped without back-up until the one piece is replaced. in costa rica i would go with the 12v option. and avoid propane. cost, hauling, and fixing are all expensive.

    your fans, light, computer/router act will be a minimal load if you have 500 watts or more of pv.

    for your ac you will need specs first. i would find out whats available there and plan on using that. but designing the syterm will require the particular units specs first. another route could be to use the water source you mention thats there(future hydo souce) as a geo thermal cooling. again i would build the system with locally available products. items needed would be tubing, heat exchanger,pump, and fan. (you could also build this system to create a fridge.

    as for your idea of sepeate systems with energy dumps? keep it simple go with one system. except your ac choice if you choose not to go with the geo thermal method will require either 120v or 220v and will require an inverter set up.

    so…. since the geo themal can potential be a cooling souce for habitable space and fridge maybe consider the water souce as a primary and the pv and wind as supplemental to that….

    there is a product called ISolar. which is a differential controller for heating and can be programed for many different applications. i.e domestic hot water/hydronic heating and heat dumps. as this controller is set up for heating temps it would not work but there should be a similar product for cooling. search for differential cooling controller.

    also for habitable space have you considered a swamp cooler? see ac is not efficient if you have open venting cause all the conditioned air will escape and constantly need to be replaced. however, swamp coolers use very little power and should be capable of reducing air temp by 10 degree’s more if it is located in the shade and more if the water supply can be kept cold.

    my 2 cents



    Thanks for the reply and ideas.

    As for geothermal…I dont think the water temp is cool enough. Often water in the hot tropics is still cool cause it comes from high mountains but mine is from a very low mountain (700 feet elevation at peak less than a mile away and I’m at 160 feet). Do you have any idea how cool it would have to be? I do plan on surrounding most of the perimeter with a man made “creek/aquaponics system/natural passive swamp cooler”. I will also draw my air in through pipes laid below the water. And I would shut down the passive vents when using AC (although if the ac is automated based on excess power that might be really complicated).

    As for swamp cooler I was under the impression that they did not work very well with high humidity. The area I’m in is a true lowland rainforest and humidity averages about %500 (at least thats what it feels like). I had one growing up in Florida and it was pretty good but it ran of aquifer water that I presume was pretty cool.

    I will certainly investigate both these ideas before proceeding.

    As for the solar…I was planning 2 x 200 watt pv for the dedicated 12 volt system. You said 500 so I figure without the computer I’d be fine. You also said 1 system but if I have one @ 400 or 500 watt that leaves me virtually nothing for everything else. This project is mildly commercial, will include a hobby farm and will see decades of slow development so an addition system (probably at 120v…from inverter based on 12v batteries) is basically mandatory for a freezer, tool charger, occasional tv, blender, a few lights (I’m sure I’m forgetting something). On top of that the first system is so important that if it ever went down I would be ruined (aquaponics and computer HAVE TO have power) so a backup would be nice. I can live without AC and frozen fruit but if the computer goes down my income dies with it and if the aquaponic pump dies my fish die with it (my food and income are priorities). Not to mention the smell of a self composting toilet without a vent fan.

    I have an internet business (the only reason I have the option to move off-grid) I don’t need to be online very often but I spend at least 2 hours a day on my laptop (so its a predictable power consumption like the other items listed but the time of use varies unlike the rest). I also feel having a fruit tree farm and tourists in the same place makes having frozen fruit, smoothies and meat storage really important.

    As for running the AC on excess power. I think you used the term power dump…is that the idea of using “extra” power after the batteries are full? Would one of those AC units you recommended run from the power directly from the panel. Or is there a way to run one directly from the panel.

    I have also considered having an ac unit that I only plug in when the batteries are full charged AND the solar is being generated at full capacity. Is this math close to correct: If a 500 amp 12v battery pack (6000 watts) is fully charged and the panels are generating 500 watts (wasted per hour cause the batteries are full from say 2-3 pm) And I run a 1000 watt AC for 30 minutes (500 watts) then the batteries suffered virtually no drain (assuming nothing else is running on them)? This is a serious compromise because I would only be interested in AC for sleeping hours (maybe I’ll have to adopt to the siesta culture). Basically, I am curios about a technology or controller that would do this for me automatically…but I guess I should confirm that it works in theory first!?!

    Thanks again for the help and I don’t want to act like I am ignoring your advice but I think you underestimated the scale of the system (my needs). I am also pretty clueless about this stuff so I’m probably overly ambitious…lol


    i have 500watt array. i leave my computer/router on daily. i have electric fridge. even right now in a hail storm i have 2-3 amps coming in through pv.

    1000 watt array would be deluxe.

    a mppt charge controler basically will work the system for you. if your battery storage is getting close to full it lowers the charge amps (float cycle) if you turn on a large load it will go back to bulk where the incoming amps will be increased. the simplest may be just a timer on the ac. if you know when your batteries should fill for the day set the timer for after that point . run ac to shut off after sufficient time for cooling / power consumption is where you want it to be.

    for the geo thermal anything more then 16 degree difference will produce cooling. the higher the differential between water temp and air temp the more cooling you will get.

    load specs for aquaponics pump????

    priorities if i get this right

    1 aquaponics

    2 computer



    til next time got go to work



    OK, its making more sense.

    If I understand correctly: 1) A second systems is pointless if one of them needs the accessories (inverter/mppt/etc). Therefore, it seems an extra battery for emergencies is the easiest way to “back up” the important low watt part of the system (unless its the inverter that dies); 2) High loads will “balance” at peak pv production (with proper planning and a mppt).

    The aquaponics pump will almost certainly be an airlift running on less than 10 watts.

    Priorities were almost correct.

    1 Aquaponics/toilet vent(6 watts all day/10 watts all day) and I have not figured out if I need a roof vent yet

    2 computer/router (100 watts 3-6 hours mostly daytime)

    3 fridge/freezer (as low watt as possible without breaking the bank)

    4 lights (10-40 watts 3-6 hours only at night)

    5 Tools/Blender/Toaster(This is flexible…100-500 watts a day seems like plenty…and this would be a daytime need)

    6 Anything I forgot

    7 AC

    I’ve spent a year and half in Central America. The only time I remember the luxury of AC is when I went to the bank (OH…and a really nice hotel the University put me in for a weekend…but I protested that the place was too nice and that the school should not be wasting money treating students like honeymooners…lol). I would only use the AC for 3 reasons 1) It was running on otherwise wasted power 2) If a guest had a heat stroke 3) If I got cabin fever really bad.

    The way I see it, I need a system that runs the basics reliably. If its overbuilt enough for something like occasional AC then its obviously big enough that the basics are not over working the system. That gives me both piece of mind and the ability for a high demand appliance every once in a while (whatever it may be but probably AC).

    Thank again. The timer idea is good and it gave me an idea.

    I don’t know how it would work off-grid but I have seen timers with 2 power sources. First, they are hard wired with mains power to run greenhouse lights or any 110 or 220v appliance (AC) but the timer itself is plugged into a different circuit that only needs a couple watts to run the relay in the timer (this allows a light running at 220 to be operated by a timer relay on 110). If the main current was from the PV/Batteries and the second was from a tiny PV (like the ones used on direct feed solar fans and pumps) then the timer could only trigger the appliances when the tiny PV was sufficiently active (then set the timer to 24 hours a day so its no longer a timer but a solar triggered device). With some experimenting (finding the perfect amount of shade for the tiny PV) you could MAYBE get it where the AC only comes on during the brightest days. It would not take into consideration if the batteries are already charged but after some trial I should be able to confidently assume if the sun is that bright then the batteries are charged. I hope I explained that well enough…Its just a silly idea but it may have real applications for someone somewhere.

    Thanks again for all the help. This is looking more and more doable every day!


    in-between shifts- so real quick- you won’t have an extra battery just sitting around for emergency. it will sulfate and become useless. you can build your battery bank as large as you would like. however, if its too large the 500 watt array will not satisfy the batteries. so first, 12 volt, 24 volt, 48 volt system. as mentioned previously, i would consider the availability of replacement parts. 12 volt will be most accessible. a morningstar mppt charge controller.

    next consideration is pure sinewave or modified. computer= pure sine wave . if you stick with makita battery power tools they will be fine with modified, but craftsman and dewalt require pure sine wave cause they have a diode in the chargers that can’t handle modified sine wave.

    the cheapest inverters i have found are with american van. they have a nice selection for the handyman working in remote locations. there items are not a sophisticated as those in the solar industry but the convert the power just fine.

    i personally think that getting over 3000 watts ideally 4000 watt inverter gives you the most room to grow. you will need to find out the watts and amps at surge for your ac unit. you may want to go closer to 6000 watt with the ac unit???

    so… back to the back up. once you pick a voltage, size of battery bank to mach capability of 500 watt array, you can determine how many batteries you will have in your battery bank. your back up will be a generator. it will provide power and simultaneously charge your battery bank.

    if you know someone down there who can look at what ac is sold and get specs thats the next step

    you can probably get around the fan for the toilet by

    1 extend vent pipe over the peak of roof by about 4-6 ft.

    2 put a concentric vent in that will provide fresh air into compost chamber and force gas out. this would require adding a vent hole. 3 or4 in pvc with hub and silicone .

    also back to geo thermal cooling. your ground temp at 5-6 ft should be about 70 degrees. that would give almost 20 degrees of cooling

    next ac specs.

    getting the back up idea???


    p.s. I’m due for vacation oct- dec and april thru may . would consider a building vacation?????


    Gordos advice is great. A couple of points needs emphasis. Large inverters have more parasotic losses (idling current) than smaller inverters. If you are driving inductive loads such as motors pumps and fans the MSW will consume 20% more energy than sine wave.

    I have sometimes recommended to clients to use smaller dedicated inverters for certain regular or steady loads instead of one big unit wher the load ranges from 215% to 90%. Inverter efficiencies vary according to load.

    It doesn’t make sense to use a 3kW inverter if the main load is a 400 watt icemaker for example.

    On the subject of air conditioning since you have flowing water a marine water cooled air conditioner might be worth while. This is what I spec for boat where the client want air conditioning over night.

    DC appliances are exactly what you describe as cheap consumer jumk! They rarely last more than a year and are often more expensive than mains powered products doing the same task. They are usually more difficult to find repair parts for.

    By comparison think about power them from a low cost MSW inverter. The appliance is usually readily available especially compared to 12V DC models

    We power a small coffee perker from a dedicated inverter. Got the perker froma garage sale and it is 20 years old.


    Gordo touched on battery sulfation. I learned from a battery engineeer that unless you charge a battery with at least 10% of the amp hour capacity you will not completely flush out the accumulated sulfation. This is a common problem with large banks and modest charging from solar cells.

    This is a good justification for a generator set that periodically charges a battery bank at a high amp rate. It flushes out the sulfate and keeps the battery healthy.


    Have a look at something called ‘powerspout’ It seems to be a recent entry into the micro generation foeld. looks to be better than the Harris turbbine.


    enlav- the powerspout looks great. just checked it out. i have water right running through a 6 in pressurized system i’ve been thinking of putting a hydro gen inline. next disposable 1200 bucks could be going their way.



    Thanks again! Its funny how things can make more sense and less at the same time.

    If I am correct:

    1) I would never want 2 systems but 1 system with 2 inverters is a good idea.

    2) If I scored an extra pv and extra battery some day, there is no point in leaving them separate as a backup…just connect them into the system…but don’t expand till I have BOTH the pv and battery.

    I was thinking if a disaster occurred (the whole thing caught on fire or was stolen while I was on vacation or destroyed by an earthquake etc.) then having a 12v 200 2400 amp watt battery charged somewhere would be nice. Correct me if I’m wrong but if that battery was charged and never used then it would stay charged and last a LONG time with just enough PV to account for the daily drain of 2-3% max = 72 watts / 5 hours = 15 or 20 watt PV. When all hell breaks loose at least I can run a cb radio and keep my fish alive.

    3) I will have to look into geothermal cooling more. I have not been to the area for final research yet. I need to get soil and water samples, check ground and surface water temperatures, price a well (might be worth the cost if it gets me my cooling otherwise I would collect the 160 inches of rain we get each year) and figure out how much hydro I can get away with.

    4) I don’t think a passive vent pipe in the toilet would work at night or when it was raining. If I’m gonna have a composting toilet I want it to be a nice one…My guest will probably find this more important than me. I am still open to suggestions here but for 10 watts I think I’ll just get a fan

    5) Are there cons to the PSW other than cost…i.e. appliances that need MSW

    A little about me and the place:

    This property is a multiple use property. 1) Its going to be my home for a long time. 2) It will be a mini fruit tree plantation. 3) It will be some of the most remote tourist infrastructure in Costa Rica 4) I’m gonna try and do it with less money that anyone in their right mind would or should to set an example for sustainable design and off-grid livig. 5) The container and the power are the only piece of the puzzle with any serious budget.

    If I can develop a DIY hydro or wind turbine/alternator it would reduce the cost a ton, so I am planning a simple starter PV system just to get the ball rolling when I get there. At the same time I am doing the needed research in case wind/hydro doesn’t work out. It sounds like a 400 watt PV and PSW inverter starter system would be a pretty nice one (freezer/computer/aquaponic pump/toilet fan/blender) if I use a generator for the early construction needs and backup.

    It will be a VERY modest place built with all local and recycled materials (unmilled timber frame, pallets, earthbags, earthen patio floor and palm thatch outdoor space surrounding/protecting a single container house). It will start with the container. I like the containers because they are easy to secure if I need to abandon the property temporarily. Putting the container under a thatch roof eliminates solar gain and create tons of outdoor living space for very little money. I will also elevate the container off the ground so I can draw cool air in from underneath it. Because I am into aquaponics I’ve decided to put a “creek / pond” around the perimeter of the roof to catch the water and eliminate the potential for roof water leading to erosion. This will act like a swamp cooler if I can keep the sun off it and transfer the heat somewhere (I am thinking with a deep area under the container and/or a waterfall somewhere… a waterfall uses a lot more energy but less than a roof vent) but might just make the place ultra humid if I can’t. I could also lay the air intake pipe below the water but I think it might fill with condensation and need drained periodically.

    Does anyone know how a flyroof effects passive cooling…I know it will be cooler under it but it seems like it will disrupt the thermocline in the container. I think it will create the need for a roof vent to power the ventilation in the container. That’s probably a question for another forum but you guys seem knowledgeable about more than just solar.


    casey- sorry to disappear on you. so i think your getting it on the solar. again just a reminder. a battery sitting around will not be much of a back up. it needs to be exercised. if you acquire extra batteries just make sure you equalize the whole bank together when you incorporate the additional batteries. equalizing is a controlled over charge that raise the specific gravity of the water( distilled)that acts as electrolyte.

    i have a little concern about the pond so close to the structure. water collection can be diverted. anyway guessing that the soil is already very wet and loose make sure its re-enforced/ and lined well. since you into aquaponics i’m sure you ability to control water quality is good. but what about attracting bugs and other living organism’s if this water is to potable??? storing the water on the down hill side of the container.

    i think the flyroof is a definite. with a floor vent and strategic placement of upper vents you will get convection cooling. like when the back porch door is open and you enter the front door and then porch door slams shut. also depending on local wind you could construct the roof to create a draft with its shape.. same with the shape of the ground around and under the container for creating draft. on the interior you could put a duct that comes from the floor vent the roof and discharge high. to cool air will sink cooling on the way down. this discharge should not be located near the roof vendor it will just escape.



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