Going off grid soon, electron harvester needed

Bjammin

Howdy from central Virginia.
My wife, kid, and I are taking to the woods in a 30' yurt and we need some help figuring out our energy design.

My main question is what size solar system you think we can get away with on a budget, although here is the whole scenario:

We have good sun exposure from 10am until 2pm, roughly. More in the summer.
The sunny spot is 130' from our yurt site. Would you ideally run 24V DC line to house, then have all the gadgets and battery bank?

-I have a grasp on our water collection situation, but it requires some electricity for the pump from the below ground cistern. There is a hill behind us, but I'm planning on putting the cistern right near the yurt because that's our collection surface. So the pump will be 3 feet in the ground in the cistern and pumping water to a propane on-demand water heater, through some filters, and to a sink and low flow shower/bath. The rise is about 4 feet to yurt deck, plus some more to faucet height. The heater requires around 30 PSI. I'm thinking it will be a 3-4 gpm DC pump, but still researching and open to insight.

-The other big electric need is refrigeration. We are doing a chester freezer to DC fridge conversion for under 200 dollars (google it if interested, several sites with instructions). This little guy should only use about .2-.3 KWH per 24 hrs.

-A fan for circulation would be ideal. Any recommendations on efficient fans? The yurt is 700 sq ft and round. 14.5' in center, so heat gets lost up top and needs recirculation in winter and needs to be pumped out of the dome vent in summer. 2 computer fans enough?

-Charging/running 2 iphones, 3 headlamps, 1 macbook, occasional inkjet printing

-2 or 3 LED lights... if that is best option.

Would this system fit the bill?
http://www.bluepacificsolar.com/off-grid-solar/midnite-1560w-kit.html
Because it fits my budget!

Or would I have endless maintenance and be replacing parts in a few years?
Should I stay away from kits? I like the DIY aspect and the less 'figuring' part.
It would be great if the system was expandable, for in the future when we want MORE! However, if this effects overall cost too much, we may just keep it simple.

I'd say my budget is $5000, but I'd like to be under. Is this possible?
Thanks for any help! It's much appreciated.

Ben

BB.

Welcome to the forum Ben.

Boy--You are really jumping in with both feet! It sounds like what you want can be done, but shading and trying to stay at 24 VDC may be an issue.

First--Know your loads. Both average/peak Wattage (or xx amps @ yy volts) and hours per day of use (like deciding a 5 gallon or 100 gallon fuel tank is needed for your reserve power).

In general, the refrigerator is the main driver for sizing your system. I am not quite sure--Is this a 120 VAC chest freezer to refrigerator conversion? If so, you will need an AC inverter. And standard AC refrigeration pumps are pretty efficient--But have really high (ugly) starting current requirements--That usually requires a 1,200 Watt AC inverter (unless you have a 12/24 VDC freezer/fridge--And DC compressor systems are not usually cheap).

The rest of your power power needs are very reasonable for a small solar system--Get a 300 Watt AC Inverter (like this one) and run a 12 volt battery bank (using 6 volt "golf cart" batteries--Rugged and cheap).

So, can you tell me a bit more about your Chest Refrigerator setup? AC or DC system (the power requirements of ~0.3 kWH per day are typical).

You might need to make a trade off:

• 120 VAC chest freezer (cheap/reliable) + larger Off Grid power system (larger AC inverter+larger battery bank)
• 12/24 VDC chest freezer (expensive) + smaller DC power system (small AC inverter may still be very handy).
• Propane powered fridge/freezer (salvaged from RV) + smaller DC/AC off grid power system

A propane powered fridge may run 1/2 to 1 lb of LP per day (guessing--not my field). At this point, propane is much cheaper and will help you keep the off grid power system small.

Also--What is your plan for water pumping (small DC pump)?

A big issue with 12 volt (and 24 volt systems to a smaller degree) is sending power long distances. In general, you either put the 12/24 volt battery bank next to your "large" DC loads and run the solar array at higher voltage through a (not cheap) MPPT solar charge controller. Or, you put the panels+batteries in the sun, and run a 120 VAC inverter from the battery "shed" to the point(s) of use...

Your thoughts?

-Bill

Dave Angelini

Ben,  I always tell folks to live there for some time through all the seasons. The hardest in that area is the summer with the heat and humidity.

If this is long term and you want to be successful, you are under budget. For a year or two there are many ways.

You probably are young and might make this happen by growing into the home powerwise. Good Luck!

kaipo_boy

Wow! I applaud your commitment, the wishy washy people in the world could learn a thing or two from ya.

I did the fridge-to-freezer conversion, too. Mine is 14.7cu ft and my measured draw was exactly .500kwh per 24 hour period, in Hawaii with about 90 degree days and 75 degree nights, plus 2 kids who open the door then stay planted there drooling at the contents for inordinate periods of time.  I also have a 7 cu ft chest freezer which is being used as a freezer, and it draws significantly more, I measured it once but can't recall the numbers, but think it was around 3x what the fridge drew, at half the size.  I didn't much care as I was going to do exactly what BB recommended above, find a DC powered freezer (Sundanzer) but so far the one I've wanted has massive shipping costs associated with it. My chest freezer is probably 10 years old, though, with the old style coils on the back and I know it leaks cold everywhere, the seals are slightly green from algae due to being constantly wet from condensation (so I know cold is getting past them regularly, another reason to upgrade to a Sundanzer). Both appliances draw huge amounts when the compressors kick in. Its the only time my Cotek 1.5kw inverter's fan comes on, then when they drop to normal running the fan on the inverter stops.

My attempts to go solar slowly, piecemeal, were only begun after coming upon the freezer-to fridge concept; a normal fridge just drew too much power, in my opinion, to make it possible to emigrate off grid without huge cost.  But the freezer-to-fridge conversion was pivotal.  Now that I have reduced the costs to welcome-to-merely-poverty-level instead of completely-destitute-level, I'm sure I must have my head examined by a professional soon.  If I could afford it.

Good luck,

walt

Bjammin

Thanks ya'll! And yes, my family thinks I am insane and way under budget... but we have a firm grasp on the situation. Meanwhile 2/3 of the worlds population has it rougher than we will and they walk 20 miles a day or more for water.

The chest freezer conversion is a DC conversion. The articles I've looked at have the fridge wired to the battery bank and this person had a 4 panel system and its been on for 2 years.

12/24 VDC chest freezer (expensive) + smaller DC power system (small AC inverter may still be very handy).

This is what I was planning. The AC inverter would be handy for using energy when it is available for charging/stereo...etc.
As for the water pump, it would be a small DC pump.

I've been rethinking the water situation. Actually, over the last day I have been rethinking the approach for everything after talking with a friend and getting responses from off grid and solar forums.

The hill right behind us is probably 15-20 feet up. I want to see what PSI I get with that and see if there is an on demand water heater that will operate with that PSI. If not, I want to build a 10' water tower on top of the hill and that should be enough.

For the pumping I could then just have a cistern at yurt level to catch water, then pump up the hill to big cistern when the sun is shining. This could also just be gas/diesel generator powered to cut costs.

I'm actually now considering the idea of no solar at first to save money, and just using a generator to pump water when the tank is emptied (1000 gals probably, so that will last awhile between pumpings). 

I could then use a propane refrigerator instead of DC/solar. 

For the lights, fan and misc. charging, couldn't I charge a battery or two with the generator every few days? No idea how long 1 battery would power those items, and I know it depends on what the usage is, but rough guess? I haven't researched generator with battery banks. Is that a thing? Seems like a good idea. Gas is cheap and I am in a bit dire situation. It would be really cool to get a generator that can later be used with an inverter in a solar system. Any thoughts with that? I'll go do some research.

Thank you for input!! Very helpful and exciting to hear back.

Ben

BB.

If you already have the DC chest "freezer"--You are doing well (lower cost DC power system running DC fridge).

Is the DC fridge 12 or 24 or 12/24 volt setup?

For the rest of your system, a 12 VDC 300 Watt AC inverter would be a nice fit--The unit I linked to had both a remote on/off switch and a "search" setting (basically, inverter blips ~1 per second, and if it "sees" a >~6 watt load, the inverter then switches on--Either is a great way to save some energy usage--A nominal small inverter will draw 6-10 watts or so just "turned on with no load").

A 24 volt inverter will probably be larger and use a bit more power. But deciding on the size of your loads--May be appropriate (loads usually grow with time). And finding a "smaller" 24 VDC inverter (with some of these remote on/off and search modes may be difficult).

For the water pump--If you can install it (and the inverter+refrigerator) near your battery bank--You are better off (keep the 12/24 volt DC cables short and heavy). If you need to send power longer distances, using 120 VAC and/or Higher Voltage solar panel array and MPPT controller can make things a lot easier.

Using a simple RV type DC pump (12 or 24 VDC) should be just fine--You do not need to look for a high power AC pump unless you are pumping a lot of water (such as irrigation pumping--Typically, AC pumps and induction motors last longer than DC brushed motors--And there are other options too).

An older member here "Icarus" has posted a fair amount about using tankless water heaters off grid:

http://forum.solar-electric.com/discussion/3386/paloma-tankless

OK---Some math and guesstimates about your power usage (relatively conservative):

300 WH per day (fridge)
30 Watts * 10 hours per day (working at computer)=300 Watt*Hours per day
20 Watts * 5 hours per day LED lighting = 100 WH per day (12/24/120 VAC LEDs--Any is fine)
2 phones * 2 charges per day * ~10 WH per charge = 40 WH per day
1x water pump * 8 amps * 1 hour * 12 volts = 96 WH per day
Misc AA or AAA Battery charger ~ 10 WH per day
====================================================
816 WH per day (~1,000 WH per day is pretty nominal for a small off grid cabin, and very good if DC fridge)

So, lets say 1,000 WH per day. First size the battery bank. 1-3 days of storage with Lead Acid deep cycle battery--Around 2 days of storage is "optimal". 50% maximum discharge for longer life (note: 12 or 24 volt battery bank does not really matter at this point of the design phase--try 12 volts to keep things small/inexpensive--DC fridge will probably set Battery Bank voltage).

• 1,000 WH per day * 1/0.85 AC inverter eff (yes some power is DC fridge) * 1/12 volt battery bank * 2 days storage * 1/0.50 max discharge = 392 AH @ 12 volts
• Note, a 24 volt battery bank would be 196 AH @ 24 volts (same size of battery bank, just different series/parallel connections)

OK, that would work out to 4x 6 volt @ 200 AH "golf cart" type batteries (2 series x 2 parallel for 12 volt @ 400 AH or 4 series for 24 volt @ 200 AH battery bank). Please ask for clarification if I am confusing you.

Next, we need to size the solar array--Two calculations. One based on the size of the battery bank (larger battery bank needs more solar charging). And second calculation based on the amount of sun the system will receive (note--must be full sun--Any shading will reduce solar panel output by ~50-100% while shaded):

• 400 AH battery bank * 14.5 volts charging * 1/0.77 panel+controller losses * 0.05 rate of charge = 377 Watt array minimum (weekend/seasonal system suggestion)
• 400 AH battery bank * 14.5 volts charging * 1/0.77 panel+controller losses * 0.10 rate of charge = 753 Watt array nominal (full time off grid system suggestion)
  
• 400 AH battery bank * 14.5 volts charging * 1/0.77 panel+controller losses * 0.13 rate of charge = 979 Watt array "typical cost effective maximum"
  

And then based on hours of sun per day... Fixed array near Lynchburg VA:

http://solarelectricityhandbook.com/solar-irradiance.html

Lynchburg
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 53° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
3.34	3.79	4.53	4.82	4.97	5.00
Jul	Aug	Sep	Oct	Nov	Dec
5.02	4.83	4.74	4.75	3.65	3.12

Assume you will use a generator during some of the dark 3 months of winter, use 3.79 hours of "equivalent noon time sun" for February "break even" month:

• 1,000 WH per day (AC power) * 1/0.52 off grid system eff * 1/3.79 Hours of Sun (Feb) = 507 Watt array for "break even February"

So--somewhere around a 507 to 979 Watt array would meet the requirements--And a >=753 Watt array would give you a bit more operational headroom.

And you would like a 10-20% rate of charge battery charger (40-80 amps @ 12 volts for suggested 400 AH battery bank)--Running a Honda eu2000i genset can (as I recall) run an Iota 45 Amp @ 12 volt battery charger pretty handily (and fuel efficiently). Just run the genset from ~50% to ~80% or so state of charge when the sun is not shining/array is in shade--Do not bother trying to charge to >90% SOC with the genset every time--That will be a waste of fuel.

Anyway--Some quick and dirty numbers.

-Bill

Thank you vtMaps--Fixed the typos. -Bill

Ralph Day

A friend of mine has a Takagi Jr demand water heater htat operates at about 22psi.  That pressure is developed by an 8foot (at the bottom) water tower at the top of a 20 foot or so hill.  No problems with the operation at that pressure.  The shower doesn't push you against the shower wall, but works fine none the less.

I have a small booster pump that brings cistern water to 30-50psi range and only uses about 150 watt hours per day (big pressure tank).  Either scenario works. Mine is more teck dependant than using  a hill.

Ralph

Dave Angelini

" Meanwhile 2/3 of the worlds population has it rougher than we will and they walk 20 miles a day or more for water."

When I hear this I think, right, but you don't do that and your family does not. They might be use to air conditioning in Virginia and as long as you are doing this with open eyes, go for it!  Just keep in the back of your mind there is a pretty high chance that this will not end well. 

oil pan 4

$1000 got me enough solar and battery to run a refrigerator while the sun is up, but I am using Morningstar charge controller and AGM batteries.

You can get a small surflo agricultural diaphragm pump that will pump between 0.5 and 1 gpm if you want to lift water up several feet. My 1gpm surflo pump says "1gpm" but it really free flows closer to 0.5gpm and draws 2 amps.

Each foot of water column will give you 0.43psi.

If you are going to run the generator much you could heat water with generator exhaust heat if you were to circulate water through a repurposed diesel EGR cooler. 

I talk about doing something like that here:

http://ecomodder.com/forum/showthread.php/fast-warm-up-ideas-exhaust-heat-exchanger-29085.html