complete off-grid small system

manzanita2

Hi,

I've been trying to do solar cheap and piecemeal for 20 years. Often without a necessary balance of system component or two ... with predictable results. And a few accidents like a metal, tarp-covered carport frame flying through the solar system during a high wind event or wind flattening a makeshift structure exposing the electronics to weather..

With somewhat improved finances, I'm hoping to buy and install a complete small off-grid system. I know this is a backwards way to do things, but I'm looking at a complete price in the $20k-$25k range. This would include everything: panels, ground mounts, electronics, batteries and generator ... except building an 8'x10' shed to contain the system, generator and a washing machine.

I'd prefer to switch to 48v to avoid a multi-string battery bank. My current use is less than 2 kwhr/day, but that's not enough power. I've worn out quite a few generators. I'd like to add an efficient fridge and the washing machine in addition to my current uses. I'd prefer to go with a completely new system.

I'm at n35.4 w120.5 location with clear sun from near 7:30am to 4pm and usually above 25 deg F in the winter. This will be a non-permitted install which may introduce interesting problems later, but it is a remote location, so hopefully no problems. I do get high winds with local terrain funneling the wind during storms. (But not enough steady wind to justify a wind genny.)

I was liking the Outback system on a panel but not sure if there is a better option.

I've been looking at the NAWS off-grid kits, but their offerings have a gap right in my proposed budget range if you include the cost of an appropriate generator.

As I said, this is a very backwards way of doing things, but money is the controlling factor. Is anyone willing to advise on a system and generator?

Thank you

littleharbor2

The so called, "All in one" inverter/chargers W/solar charge controllers are a very cost effective option. The forum's host Naws carries the Midnite solar versions. I have experience with these units and can say that the live help you get from Midnite Solar is worth the price by itself. Any questions you may have about these units will happily be taken by the Midnite techs.

manzanita2

littleharbor2,

Thanks for your mention of the Midnite Solar "all in one" products. I haven't been following their product line. Despite the fact that their Midnite Solar 150 MPPT CC has been very reliable. Morningstar's Microsine 300 has also been reliable. (Both from NAWS.) Not having a good generator powered charger hasn't helped my batteries at all, since I've been using that to cover my system's limitations so much. The "all in one" unit you mention could be a very useful core to start over with.

I've been trying to claw my way into a usable PV system. Until their demise I had 1800w of PV, the Morningstar 150, the Microsine 300 and two Trojan t-105s. The PV array is shattered and my way too small storage batteries have probably been overcharged to death using bad chargers via various generators to keep them above 50% SOC. Unfortunately, I've also discharged the Trojans too much a few times when not paying attention, so I can't complain about their present poor condition.

So I need new PV, a charger that accepts 120vac and new batteries. I also need a new generator. I guess that I'm expecting too much system from too little money, since most systems are much more expensive than what I have in mind. Thanks for the Midnite Solar tip.

Dave

littleharbor2

Best of luck getting back on your feet. BTW the Midnite AIO's do accept 120 vac grid or generator for charging.

BB.

Dave, I always suggest that you start with defining your loads (watts, watt*hours per day, location/amount of sun, etc.)...

Then define the battery bank. And finally, the support equipment (inverter, charger, etc.).

Just to give you an idea:

• 500 WH per day--Weekend cabin, LED lights, cell phone charger, etc.
• 1,000 WH per day--Full time off grid cabin, 12 VDC RV Water Pump, etc.
• 3,3000 WH per day--"Near normal" electrical existence for a very energy efficient home. Energy Star Fridge, LED Lighting, Laptop computer, efficient water pump, etc... Use wood/propane/etc. for cooking/heating/hot water/etc.

Conservation is critical for solar. It is almost always cheaper to conserve energy than it is to generate energy.

I can walk you through the basic math to do a paper design for a system that will meet your needs... Once the system is sized, then you can start looking for hardware.

-Bill

manzanita2

Thanks Bill,

Sorry for the delay, I've been away from home for days helping a relative with a project. Haven't made it back home yet.  I believe normally my usage is in the 1,000 -2,000 WH/day range. I guess that usage is too high for a hoped for outlay of $25k. I was hoping that a good generator could support the excessive usage,

BB.

If you want to run a full size refrigerator, and other loads (Lights, laptop, cell charger, washing machine, a "solar friendly" low power RV water pump, etc.)... I would suggest a 3,300 WH per day system.

Is the system to be installed/used in San Jose California or somewhere else?

-Bill

manzanita2

3300 WH/day sounds decent. Fridge doesn't need to be full sized. I'm getting really tired of a 65 qt ice chest though.

Washing machine could be a genny-only load.

Location is San Luis Obispo county not far from Santa Margarita, CA. At least 1.5 miles from grid power.

Access is somewhat problematic, after last winter the last mile or more is 4x4 condition. I haven't had much time to work on it. Can't get road materials delivered onsite yet.

Graham Parkinson

Selecting the most cost-efficient, low energy appliances is much cheaper than buying larger battery banks and bigger solar systems!

A bit of time researching low energy inverter washers and fridges etc. really pays off in the long run.

Saggys

If you purchase an AIO set up, make sure you purchase an inverter generator to go with it, they are very particular about accepting a constant input frequency. 

BB.

Starting with a "basic" lower cost system using Flooded Cell Lead Acid Batteries (many will argue that LiFePO4--Lithium Ion--Batteries are cheaper to run overall--Longer life, more efficient, no matenance, better for warm weather, etc.)--Just start with a simple sizing process.

First, say 3,300 WH per day average load. Assume 2 days of "bad weather/no sun" and 50% "planned discharge" for longer battery life (relatively conservative design):

• 3,300 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max planned discharge * 1/24 volt system = 647 AH @ 24 volt bank
• 3,300 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max planned discharge * 1/48 volt system = 324 AH @ 48 volt bank

Either 24 volt or 48 volt battery bank will work for you... If you ever plan on "enlarging the system", you might just start with a 48 volt battery bank (total battery bank cost is the same as 2x higher voltage and 1/2 the AH = same amount of stored energy).

Next, sizing the solar array... Two calculations. First is based on a 10%-13% rate of charge (or more)--Recommended for full time off grid system. 5% can work for a weekend/sunny weather/emergency backup system. Note that you will get the same Array Wattage if 647 AH * 24 volt vs 324 AH * 48 volt system:

• 324 AH * 58 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,220 Watt array minimum
• 324 AH * 58 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 2,441 Watt array "nominal off grid"
• 324 AH * 58 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 3,173 Watt array "typical cost effective maximum"

The second calculation is based on energy usage per day and hours of sun per day... These numbers depend on your assumptions... Do you one live there 9 months of the year (and spend winter elsewhere). Do you want to use a backup genset during bad weather/heavier loads... Or do you want to run mostly summer (i.e., larger array).

Using PV Watts (does way more than I am using here--But good enough to estimate the size for your system). For a fixed array facing south, tilted to 35 degrees, Santa Margarita CA.

https://pvwatts.nrel.gov/pvwatts.php

Month	Solar Radiation ( kWh / m2 / day )	AC Energy (very rough estimate) ( per 1,000 Watt array kWh/Month )
January	4.56	68
February	5.03	68
March	5.88	86
April	6.64	92
May	7.00	99
June	7.26	98
July	7.32	101
August	7.51	104
September	7.40	99
October	6.15	88
November	4.97	71
December	4.29	64
Annual	6.17	1,038

Lets guess that you want to live there 12 months a year... And use a genset during bad weather:

• 3,300 WH per day * 1/0.52 off grid FLA system eff * 1/4.29 hours of sun per day (December average) = 1,479 Watt array December "breaker even"

Since actual sun harvest is variable (and your energy usage is also variable)--Suggest that you only use 50% to 65% of "predicted" solar harvest (to minimize genset usage):

• 1,479 Watt array / 0.65 energy "fudge factor" = 2,275 Watt array with 65% fudge factor
• 1,479 Watt array / 0.50 energy "fudge factor" = 2,958 Watt array with 50% fudge factor

So, the "minimum" suggested off grid Array would be ~2,441 Watt array (10% rate of charge)--And you could easily "justify" an array in the range of 2,275-2,958 Watts. More than 3,173 Watts on a 324 AH @ 48 volt FLA battery life could be "overkill"--More expensive array/charge controllers than you really need.

Sizing of the AC inverter... The minimum suggested (Energy Star Fridge, LED Lighting, some smaller loads) around 1,500-1,800 Watts minimum. The suggested maximum inverter for FLA batteries is 1,000 Watts per 100 AH @ 48 volt battery bank) would be ~3,240 Watt AC inverter (based on 324 AH @ 48 volt battery bank).

AC inverters are relatively cheap (vs battery bank, solar array, etc.) and people tend to "oversize" their AC inverter... Which can draw more current/power than the battery bank can use... And very large AC inverters can also "waste power" (tare losses--10-50+ Watts just "turned on").

Note that these numbers are estimates only... More or less, anything within 10% of the above numbers (Watts, AH, etc.) is "the same" in solar math.

Please feel free to ask questions. The above is just a stick in the sand to show you how the "Math" works, and intended to  design a system that can "meet your needs".

If your needs are "different" (need larger inverter, want Lithium battery bank, want less genset runtime, etc.)--Please feel free to "adjust the numbers" or run new "math" for lithium options (again please ask--The assumptions are "different" for Li Ion batteries).

Your thoughts?

-Bill

manzanita2

Thanks Graham and Saggys for your input. I'll keep your tips in mind. Midnite AIO systems request inverter type generators? I thought that some people were recommending non-inverter generators for charging batteries. I guess that if the generator is large enough the inverter types will also work.

Thanks for the walk through Bill, it helps a lot. 

I don't know what to think of the newer battery types. I tend to lean toward the FLA type because I understand them better and they are perhaps less temperature sensitive. Yes, I like going with 48v. I'd like to expand the system when possible.

I do live there all year. I don't have a problem with using more genset time during the winter months.

As far as the fudge factor is concerned, I do live in a north-south canyon that is about 340 ft wide and 35 ft deep. The array would be located in the canyon where ever the sun is best.

I would favor sizing the PV array to support charging the batteries at the 13% rate if only to provide more of a buffer before needing the genset.

I'd prefer that the inverter be of the 2500 watt size or larger.

The local terrain makes my location a high wind area during storms. So the PV ground mounts would have to be sturdy.

Not quite certain what else to ask at present.

BB.

If you can mount the solar array high(er) on the canyon, and run 100-200 feet or so cables to your "solar equipment shed"--That should be pretty doable. With a higher voltage array and modern mid to high voltage MPPT solar charge controllers, it makes "remote" arrays much more practical.

Arrays with even partial shading (a few tree limbs, even power lines, etc.), can cut array output by 50% or more very easily.

Also watch for "future" shading... Trees in area, new buildings on property you may not control, etc...

Solar panels (at least for now) are relatively cheap and long lasting (>20 years pretty easily assuming no broken panels from hail, rocks, etc.). Batteries are the costly system component now with possibly short term life...

For a smaller system, you can start with good quality "golf cart/forklift/traction" type flooded cell lead acid batteries. They will probably last 5-7 years with good maintenance--And Forklift/industrial FLA batteries can last 15+ years. Of course, there is adding distilled water every couple of months (checking every month, logging/monitoring specific gravity, checking cables, etc.).

FLA are probably better for most people in sub freezing environments as Li Ion cannot operate much below 40-50F, and not below freezing.

However you are in a warm to hot climate (?) so lithium Ion / LiFePO4 type typically) do have much better life and efficiency in these conditions. Li Ion are now pretty well understood and supported by major Solar Equipment Manufactures. And the "better" systems have closed loop communications between Inverter/chargers and the Li Ion BMS (Battery Management system). And a good Li Ion bank should last >10 years off grid without the cell maintenance of FLA batteries.

LI Ion batteries and BMS (both integrated or as an add-on separate "system") are more "complicated" and the "closed loop" feedback adds even more issues.

The downside is solar is "not cheap" and probably will never be "cheap" in our lifetime. Mostly this revolves around "storage" and cost of storage.

Starting with a "less expensive" Golf Cart type FLA battery (typically 6 volts @ 200 AH or so), is a good start. You can get your full system up and running and figure out if it is sized "correctly for your needs". You could always add another string of G.C. batteries... If you "murder your bank" (forget distilled water/maintenance, over discharge the bank, etc.)--You can replace the bank without killing your retirement savings (not uncommon for first time solar folks to kill their first bank).

Once you are "stable"--You can start looking at other battery options. Given that you have had some solar experience over the last couple decades, you may choose to "skip" the low cost FLA batteries and go directly into better/large AH capacity FLA or into Li Ion directly.

Before you buy anything--Highly suggest going through multiple paper designs.. Perhaps G.C. and Li Ion designs and do a cost/benefit/risk analysis.

-Bill