off grid cabin in the woods!!!

Re: off grid cabin in the woods!!!

I will try and take your post in a few bites...

First, the BZ 500 solar charge controller was not the best choice... You can read a couple threads here about some of the issues:

BZ MPPT250 and other controllers
BZ Controller thread

Your first issue is you should replace your Solar Charge controller with a different brand/model. Depending on what your other choices end up--there are several good choices out there for you.

Next, you have a 187 watt 24 volt panel... Really need to know the exact specifications for the panel... What is the Vmp (Voltage maximum power) and Imp (Current Maximum power) for this panel (brand and model number may help us too). Basically, to properly charge your 24 volt battery bank, you will need a Vmp that is > ~32 volts (~30 volts minimum to equalize your batteries, and ~1-2 volts for voltage drop across the charge controller and wiring).

Morning Star makes a very nice 15amp 12v/24v volt MPPT controller (~400 watt panel maximum for a 24 volt system). If you end up with larger panels (over ~400 watts), the Outback or Xantrex (or other brands/models) will be a better choice.


Depending on the solar charger you purchase--it may change which solar panels you can use for your particular installation (and how you series/parallel wire them).

The Iota charger and Honda eu2000i are pretty good brand choices--in and of themselves, these should be fine.

Next, you have 4x 6 volt golf cart batteries. Assuming they are ~220 amp*hour rated (20 hour rate), we use a recommendation of ~5%-13% as the recommended maximum charge rate for proper battery charging...

220AH * 5% = 11 amps minimum (for a 24 volt battery bank)
220AH * 13% = 28.6 amps maximum (@ 24 volts)

Watt-wise, that would be at maximum battery voltage of ~28.4-30 volts during charging:

11a * 28.4 volts = 312 watts
28.6a * 30v = 858 watts

Assuming your charge controller is round 90-95% efficient--then you would want your solar panels to be:

312 watts * 1/90% = 347 watts of solar panels (rough minimum)
858 watts * 1/90% = 953 watts of solar panels (rough maximum)

So, just to properly charge your battery bank, you would need ~312 to 858 watts worth of solar panels to properly equalize and mix the acid in your flooded cell batteries (at minimum current) and not overheat (or waste money) on the high current side (for typical batteries--as always, check the requirements for your specific batteries with the Mfg. data sheets).

Now, the above has not assumed anything about the loads you are going to require for your solar system--this is just based on the size of the battery bank you are using.

To calculate how much daily load you can get from your system, use this link to estimate your average kWatt*Hours of energy you can generate.

Note that the above website will require the panel size in kWatts (1kW=1,000 watts) and 1 kW is the minimum you can enter. If your system is smaller, just enter 1.0 kW, and then multiple the answer by your system size (example 312 watts of panel, multiply by 0.312). Also, answer the rest of the question (tilt, tracking type), and use ~0.52 for your derating factor--these accounts for losses in your batteries and AC inverter too.

For example, using the defaults and 0.52 derating factor for Arcata CA:

We get around 50-80 kWhrs per month (1kW of panels) with what appears to be affects from coastal fog cutting down output. Using 312 watts of panels and 30 days per month:

50kWH * 0.312 * 1/30 days * 1,000W/kW=520 watt*hours per day (fall/winter production)

Or, you can run a 100 watt light bulb roughly 520WH/100W=5.2 hours per day during the fall/winter months from just your 312 watts of solar panels with fixed mount panels at 41 degrees from horizontal facing south. Also, if you don't know your loads (and how much power you need, both in Watts and Watt*Hours), get a kill-a-watt meter.

Regarding running your loads/inverter while charging with the generator is fine (may take longer to charge). It might even be better, assuming you have enough power from the generator to run both the charger and your load (say washer or vacuum cleaner) to run the AC loads directly from the generator while charging (more efficient--don't waste power converting from 120 vac to 24 vdc back to 120 vac).

Other recommendations... Get the Trimetric connected--will really help you understand the state of charge of your battery bank at all times. Another is to get a hydrometer and thermometer to check the battery state of charge (not often--after you get your system under control).

And read the Deep Cycle Battery FAQ too.

Anyway, the above is a start and should help you understand your system better.

Good luck,
-Bill

Re: off grid cabin in the woods!!!

Please feel free to browse our host's webstore... Most of the major component listings (solar panels, charge controllers, inverters, batteries, etc.) on NAWS' site include a link to a few pages of Frequently Asked Questions (FAQ)... There is usually enough there to provide you with 90% of the basic information you need--Then come here for to ask more questions on how it all fits together, or if you get more confused (happens to all of us).

-Bill

Re: off grid cabin in the woods!!!

MM,

You really need to figure out how much power you will need (and for the next 3-7 years--hopefully, so you don't end up with an undersized battery bank and the question of mixing old and new batteries together--not a great idea if you can avoid it).

It will also help you size the rest of your system... Your system (if you pay for the install) is probably going to cost you around ~$15 (very rough guess +/- 50%) per solar panel watt to install.

Get a Kill-A-Watt meter and measure all of your AC loads...

Kill-A-Watt AC Power Monitor Meter

Kill A Watt P4320 Power Strip
Kill A Watt power monitor strip with surge protection
Regular price: $99.95
Sale price: $78.85

Basically you will need to create a chart of Peak Watts, and Average Watts, and lastly, Total Watt*Hours per day (week, seasonal, etc.).

The Peak Watts will size your inverter (and as you have seen a Pure Sine Wave inverter is not cheap)... If you have starting loads (pumps, fridge, motor)--you will probably have to get a pretty large inverter vs your average running load... For things that are optional, work to keep the "peak loads" low (for example, run your well to tank pump when everything else is turned off).

And, you need to know your Watt*Hours per day you will be using... For an off-grid system, power is expensive--probably around $1.00 per kWatt*Hour or more (1 kWH=1,000 Watt*Hours). Or about 10x what the typical cost people pay for home electric power (you are building your own power station and paying your own maintenance for batteries and such).

An example for estimating power needs:

10 hours * 40 watt = 400 Watt*Hours (laptop)
10 hours * 20 watt = 200 Watt*Hours (firewire drive)
5 hours * 13 Watts * 5 = 325 Watt*Hours (5 CFL's)
2 hours * 5 Watts = 10 Watt*Hours (AA battery charger)
0.1 hours * 1,000 watts = 100 Watt*Hours (well pump 6 minutes per day)
========================================================
1,035 Watt*Hours per day.

Assume 130 Watts for constant on power... The well pump would be 1,000 watts--but probably need 2x or larger inverter to start (others with well pumps can give better numbers than I).

Here is where possibly getting two inverters--One small True Sine Wave inverter to run your electronics, and a second Modified Square Wave (or larger TSW) inverter to run your pump (assuming pump runs OK on cheap MSW inverter).

Now, at a minimum, you are looking at needing 1,035 Watt*Hours (1.035 kWhrs) per day.

Using the numbers from my first post in this thread, I estimated around 50-80kWhrs per month (winter/fog vs summer/fog if it is like where I grew up).

Assuming you want to minimize the generator use--assume 50kW per month minimum (winter, base on 1kW of solar panels) to run your loads (more available for summer use).

(1.035kWH per day * 30 days per month) /
(50kWH per month per 1kW of panels) = 0.621 KW of solar panels

So, for my "mythical load" you would probably get away with no generator use for 9 months of the year, and some generator use during the winter (probably a few dozen of hours of use--pure guesses).



Battery size:

6x * 1,035 Whrs per day / 24 volts = 258 AmpHours (@24v)

Or, roughly in line with what you have now.

With an MPPT Solar Charge Controller, you can effectively and efficiently use any panel voltage from Vmp =~32 volts to 100+ volts (there are rules to follow--can't just assume).

Take a look at the MX-60 they are offering you--that unit is now out of production and you should be able to get something knocked off--or look at the FM-XX series. Both are very good controllers--but maintenance wise, it is best not to get an end of production unit for top dollar.

And Mike is right about the Generator--Do not get anything bigger than you will need... Normally (from what little I have seen) if you run a genset at 50% or less load, you are still running 50% fuel flow.

Or in your case, a 6kW unit running at 3,000 watts--can you make use of that much power or not... For charging your battery bank, you are looking at ~400-1,000 watts or so (and less, as the batteries are in the last 10-20% of their charging cycle).

You may end up using 3x as much fuel (or more) with the larger genset than you really will need...

In terms of gasoline--a]reasonably efficient genset gets around 5kW*Hours per gallon--A eu2000i running at 400 watts is still >5kWH/gallon (most are not so efficient at 25% load)...

A generic 6kW unit at 3,000 watts will use:

1 gallon * 3kW/5kWhr = 0.6 gallons per hour to generate 400 watts (0-3,000 watts)

The Honda, roughly:

1 gallon * 0.4kW/5kWhr = 0.8 gallons per hour to generate 400 watts (or more than 12 hours on a gallon of fuel--spec if 15 hours @ 400 watts on 1.1 gallons of fuel)

So--unless you can run your generator at 50% load (or at least 25% load), a 6kW unit is probably way larger than you will need for a low-power off-grid lifestyle...

Certainly, electric start (possibly setup for auto-start), propane vs gasoline, larger/more reliable unit, etc., has it attractions... If you need electric start, you may wish to look at the Honda eu3000i -- not as fuel efficient, but better.

Regarding propane fridge vs electric fridge... I would price out your system assuming you get an electric fridge and see how much extra it runs you.

A good Energy Start fridge is already very efficient. And if you are into do-it-yourself, look at converting a chest freezer into a fridge (basically, change out the thermostat, and maybe set up a drain to catch condensation on the walls)... Can cut your usage down to 1/2 or 1/4 of a standard energy star "fridge":

-Bill

Re: off grid cabin in the woods!!!

Also, to add one more place to look... Outback has a nice page of drawings and parts lists to show how everything connects together.

-Bill

Re: off grid cabin in the woods!!!

monamoore wrote: »

Thanks everyone, and happy holidays.

Happy Holidays back to you and your family!

I was really relieved the folks at Real Goods took my whole system back with the exception of the 4x 6volt golf cart batteries and a 30 amp disconnect.

Always happy to hear good things about companies too!

Now i can start again and do some more research. I will definitely assess my loads first then talk to my installer some more.
I have a question for Bill. i am confused about what WH means. like say i call apple and they say my laptop draws 100watts is that per hour? does that mean if i use it for 8 hours that it takes 800 watts a day. how does that translate to watt hours?

Just to be clear, it is not Watts per Hour, but Watts that you are taking about...

Watts is already a "rate" based measurement... It is equivalent to Miles per Hour.

Watt*Hours is the unit we measure "work" in for electricity (really kilo-Watt*Hours or equivalent 1,000 Watt*Hours--there are other units used in your physics and chemistry classes--Jules and Ergs and such--but those are really small numbers so the kWhr was used instead for most utility power).

Watt*Hours is equivalent to Miles Driven (if Watts=MPH)...

Watt = MPH = Rate per unit time
Watt*Hour = MPH * Hour = energy used or miles driven

It is confusing--even for me--first in physics and chemistry--and even here years later when I started posting--it is really easy to mix-up the units...

So, when you call Apple and they say your computer uses 100 watts... That is really 100 watt*hours per hour (if that makes sense).

So, if you use your computer for 1 hours, then 100w*1h=100Watt*Hours of energy used (drive at 100 MPH for 1 Hour = 100 Miles driven).

Run your computer for 10 hours at 100 watts = 10H*100W=1,000 Watt*Hours or 1 kWhr of electrical energy (power is a rate / per unit time, energy is the amount used -- equal to miles driven).

Now, 1,000 Watt*hours = 1 kWhr and a typical electric rate is $0.10 per kWhr, so you have used $0.10 of electricity.

If you are off grid, your costs are probably around $1.00 per kWhr, so your power use would be 1kWHr*$1.00/kWhr=$1.00 of energy used.

Also, the reason a Kill-A-Watt meter is so important is that the "ratings" of appliances are typically maximum/worst case ratings... You need those, but you also need your "average" to size your solar panels and batteries.

Your car may average 65 MPH on the freeway, but when you take all of your time together (stop lights, stop and go driving, etc.), you will find your average motor on time is around 35 MPH average...

Same thing with your computer and fridge--at certain times they take more energy, and other times less (fridge only runs 1/3-1/2 of a 24 hours day, your computer and diskdrive use more power when computing/accessing files, less when not, and less when the backlight is off)--the Kill-A-Watt meter allows you to total all of the energy use and average it over 24 hours, a week, whatever.

I guess when I get the kill-a-watt meter there will be instructions. I am on the grid for a few weeks so maybe i can try to measure my usage and add it all up.

Exactly correct...

And because your electric power will be so "dear" in cost--you will need to see what you can do to reduce your needs.

I think I am heading for 6x175w sharp panels on a combiner box (because some panels will always fall in the shade of the redwoods)

The combiner box will do nothing about shading.

Don't kid yourself--solar panel arrays need full sun to work correctly... Look at your site right now--hopefully, you are getting full sun from around 9am to 3pm--at least. You can do with less (or east, or west, facing panels)--but you have to account for the loss in overall power generation.

Some people have morning fog, so they face their panels west... Others have hot afternoons with thunder showers, so they face their panels east.

Others have limited space and face 1/2 the panels east, and the other 1/2 west... But--when you split panels based on available light--it is very important that a string (a set of series connected panels) all have the same sun... If one panel in a series connected string has even 10% shadow--it is possible that the effective harvested output of the entire string will drop to near zero (if there are two or more strings in parallel).

There are lots of issues that you cannot take for granted with designing/building your own solar power station... And solar panel location/positioning is very important (solar panels only generate usable power when subjected to full sun--shaded panels and panels facing away from the sun will not generate any useful power--no matter what some people post or write articles about).

Also the outback system(inverter charger and charge controller) with the Honda Eu2000 or maybe the 3000 for back up.

Either Honda would be good for a backup and/or low cost entry level system where solar power provides the majority of your electricity (don't run these 24 hours per day and expect long life).

Not sure about more batteries- I thought I couldn't get anymore and still be 24v?

Not quite sure what you mean by this--if your batteries are still in good shape and pretty new, you can add more in parallel (for more energy storage at 24 volts) and/or more in series (for more energy storage at 48 volts).

In any case, the voltage of your battery bank is dependent on how much power you want to draw (I would suggest trying to stay at below 100 amps typical current maximum) to keep your wire size low and so as not to overheat your batteries with high current...

100 amps * 12 volts = 1,200 watts maximum
100 amps * 24 volts = 2,400 watts maximum
100 amps * 48 volts = 4,800 watts amximum

For battery sizing, you want them to be sized appropriately with the charging system... Too many batteries--can't charge well on small solar system... To few batteries, deep discharging will lessen battery life and cause you to run the generator more in bad weather.

The above numbers are recommendations--and other things can be done for the right reasons with the correct parts. Pretty much everything within +/-50% of the above numbers is not a big difference to fret over.

-Bill