View Full Version : solar water pumping vs generator in mexico
December 27th, 2008, 10:11 PST
Hello, I have been reading so much I now have brain overload. I have a 1/2 built house in baja. 2 rooms and a bathroom. I had been planning on just getting a honda eu2000 and pressurizing the water for the house with that and using camping stuff for everything else. I cannot afford to enclose my garage for another yr so I am not putting in my pv system until that is done since there is not a secure place for my batteries and electronics. This is a vacation home. Would it make any sense to use a solar setup just for the water pump?? My 2500L cistern is gravity fed from a larger cistern in the developement. So I am not pumping from a well. The pv I will eventually need is still small. Just a few lights, music, and I would really like a small fridge. But I think that is 12-24 mos away. Any opinions or suggestions would be appreciated. Thanks,
December 27th, 2008, 12:36 PST
For such short usage, and vacant premises, I'd pass on expensive solar. How do you plan to secure the Honda while gone?
Mike on vacation in snowy Portland, OR
December 27th, 2008, 13:09 PST
I agree with Mike on this...
Solar makes sense when it is generating "useful power" 9+ months out of the year... The more kWhrs it generates, the "less" the overall costs are.
A small, quiet, and efficient generator--such as the Honda eux000i family is a good choice for this... (the smaller generator you can use, the less fuel you will need to store/pay for).
Other than the initial cost for the genset--its ongoing costs are relatively low (you only pay for gas and oil when you need electric power).
You could also get a small set of "golf cart" type deep storage batteries to have "quite" electricity 24 hours per day--but only run the genset 2-3 hours in the morning to recharge your batteries. And get a small panel (perhaps 10-50 watts + charge controller--depending on the size of the battery bank) to trickle charge the batteries when you are not there.
December 27th, 2008, 14:00 PST
Thank you both,
I was initially thinking the small generator a pump and pressure tank. I will lock the generator up in the bathroom where you can't see it and hope it stays there. I think it will. I was in Honduras last year and the place we stayed just used a generator and batteries for the whole operation. They lost the solar in the last hurricane and hadn't replaced it yet. I had also thought of the small panel idea. I didn't know if that made sense financially. I like the idea of quiet power, hence wind is not in our plan. If we were doing everything at once it would be much easier.
December 27th, 2008, 14:06 PST
What you don't say, or I missed is how are you going to pressurize the house with the eu1000? You could design a pump system that can be powered by the generator now, an PV later, so that you don't have to buy two systems as time goes by. If you are going to go with a love voltage dc pump, you could run it on a small battery and charge that battery with the Honda now. If on the other hand, if you are going with a line voltage ac pump, you would power it with the genny now, and an inverter later.
As with most things, if you think things through you can avoid the ready, fire, aim, and avoid buying stuff more than once.
December 27th, 2008, 15:02 PST
My initial thoughts were to get an ac pump, power w/ eu2000 to pressurized the house when I needed it. When I was not there, disconnect the generator and store it. Hopefully when I can afford my pv system in 18 mos or so I could just wire the pump into my electrical system. I know what I will need for power for my end plan, but I am having trouble figuring our a good growable system. Hopefully in about 18 mos I will only need a small system for a few lights, my water, music, and I sure would like a small fridge. The more I read, the more I see is ou there to figure out. I get the homepower mag, go online and have the sie workbook. I have ++ respect for you guys that have it figured out. I think I need to see some hands on with someone.
I guess I was just wondering if there was a solar option I was overlooking.
December 27th, 2008, 16:32 PST
A couple of thoughts,,,,
You don't say if your cistern could be gravity into the house. If so, then perhaps no pump is needed at all. If all you are going to do is, shower, hand sink, kitchen sink, and perhaps toilet you really don't need pressure at all. There are demand water heaters out there that come in small sizes and require little head pressure to run.
On the other hand, if, as I suspect, you have to pump from your cistern the situation is a bit different. Personally, I would go with a small dc shurflo type pump, mounted next to the cistern, pressurizing a good sized p-tank. The p-tank could be located anywhere, near the cistern or in the house. The pump could be mounted with quick couplings to that you could hide it in the house while you are gone. We use a similar system on one our our remote bush cabins. The shureflo pumps out of the lake into the p-tank using a small deep cycle battery. When the genny runs at night, the battery is on a trickle charger so that it keeps charged. That way they have water regardless of whether or no the genny is running. Very cheap to buy, simple to install, cheap and versitile to use. Remember, the demand for water is pretty small, especially if you use toilets efficiently, you are probably only talking ~2-400 litres/day. (100 us gal) This system could be run off a very small solar system in the future.
My personal system is a shurflo submersible pump deep in the lake. The advantage of this system is it won't freeze (not a problem in your neck of the woods I imagine!) and that it is quieter. (the diaphram pumps can be quite noisy,,,,not like a honda, but they can send a buzz up the plumbing). Another advantage is that the pump is always self priming since it is in the water. My pump system draws ~6 amps (12vdc) and runs about 15 minutes a day depending on usage, for 2 of us. (No toilet)
You would also be a good candidate for a simple recirculating solar hot water system. A simple controller, a 12vdc circ pump, and a either store bought or home made flat plate collector preheating water into a tank to feed a demand water heater would be really simple to build.
As for going PV for the entire house going forward, as has been said so often: Remember that your loads WILL grow with time. A simple light now leads to two, a water pump leads to a solar circ pump, a radio leads to I-pod, to pc to satellite internet. We live in a small cabin off grid with 200 watts of panel and do quite nicely with it, BUT, our system is too small by about 1/2 by any ordinary standards.
Good luck, stay warm, it was -34C at home last night.
December 27th, 2008, 18:07 PST
You will probably find that is is very difficult to design a "grow-able" solar/off grid system...
Small systems use "small" batteries, small controllers, small inverters, and "light weight" wiring...
To a degree, the most difficult part of the system to "grow" is the batteries and your choice of voltages... Your DC loads typically are 12 volt, 24 volt, or 48 volt--and cannot be switched/wired to change their input voltage.
The solar charge controllers, they are frequently switchable between 12/24/48 volts--with the larger ones (typically >~400 watts) having more capabilities-such as "networking" between additional controllers.
The smaller controllers (<~400 watts) are typically stand-a-lone and a bit on the expensive side to put a "bunch" of them in parallel when "growing" your system.
AC inverters... You can get a very nice 12 volt to 120 VAC @ 300 watt True Sine Wave to run your small appliances/electronics... (MorningStar 300W (http://store.solar-electric.com/mosu300wasiw.html) is a good one to look at--very low losses when there is no AC load).
In the end, you need to quantify your loads... AC/DC/voltage/wattage/etc. and figure out how much power you will need... Size the battery bank (probably "small" with "cheap" golf cart batteries for now), and just run your generator + solar panels for trickle charging when you are not there.
Certainly, locking stuff up and/or taking the stuff you can't afford to loose with you until you are living there will help too.
Without knowing your loads, it is very difficult to give you exact answers. But picking devices (12 volt vs 24 volt) with an eye on the future will help reduce your losses later on when you build out the bigger system.
Just as a rough recommendation:
<1,000 watts -- 12 volt battery bank is OK
1,000-2,000 watts -- 24 volt battery bank minimum
>2,000 watts of load--look at 48 volt battery bank
Many people tend towards 12 volts because the devices (appliances, car lighter adapters, etc.) are cheap and easy to get...
However, it is very difficult to run 12 volts any distance from the battery bank (voltage drop) and many 12 volt devices do not do well when operated from 10.5 to 15.5 volts (typical solar battery bank voltage range)... Most 12 volt DC devices are designed to run on a car ~12 to ~14.2 volts DC.
Think about doing most of your smaller loads with efficient True Sine Wave 120 VAC 60Hz inverters -- and if you have some large loads (saws, pumps, etc.)--look at getting the cheaper Modified Square/Sine Wave Inverters...
The losses from the conversion to 120 VAC is not that much, and the appliances+wiring will probably cost you less over the long term (and be more reliable).
Plus, you can run them directly from the generator (when charging) or in an emergency when the solar system is down.
December 27th, 2008, 19:18 PST
I agree that "growing a system" is problematic, which is why I always harp on the ready, fire, aim. Having said that here is what I would differently know then what I know now,,,sort of. (Off grid system)
I would start with a good, large MPPT controller. (MX 60 or so) to allow any system to to grow into it. Even with smaller panel configuration the losses you may have are more than made up for in the fact that you CAN grow into it.
I would buy the biggest battery bank that I could reasonably keep charged with my panels, but with some augmentation by genny if needed. That way as your loads grow you have some extra battery capacity to handle the load without having to add batteries to an existing string.
I would buy a real battery charger (genny powered). To often people don't know and try to get by with an automotive type charger that just doesn't cut it.
I would buy the smallest Honda eu series genny that would do the work. If I need a bigger one to run a shop I would consider a second (non eu type) if I could afford it. EU's command a price but other gennies to run power tools are a dime a dozen.
If one were to be off grid only part time, I would consider a good propane fridge (assuming you can get propane) If you are considering full time, I would look carefully at good energy star compressor fridges instead.
And I would buy as much panel capacity as I could afford. Of course if I could afford all that I wanted,,,
So as we say, it is tough to grow a system, but by starting with good components leaves one better options later on down the line.
December 28th, 2008, 17:21 PST
Thank you all for the info and opinions. You convinced me I am on the right track and gave me more to think about. There is so much info out there for a newbie, sometime I tend to over complicate things, I appreciate your help.
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