Small Off Grid Cabin – looking for feedback

[save_rka]

I'm planning a small solar system to use with an existing generator
system and would like any comments you might have.
I don’t want to start into solar doing something dumb!


Load Analysis: 1000 Watt Hrs average needed per day. Load is mostly CF Lights and a TV. Assuming 80% DC to AC efficiency I’ll need 1200Watt hrs to the inverter ea. day

Inverter choice: Morningstar SureSine, 300 Watt Sine Wave Inverter 115VAC, turned off when not needed.

Charge Controller: Morningstar TriStar 45 amp MPPT solar charge controller, this way I can run a higher voltage (24v) array to feed the 12v battery bank. It will be mounted on a 125 Amp Midnitsolar Mini – DC Disconnect Power Center. and has a battery temp probe

Batteries: Concord Sun Xtender AGM, Start out with either 2ea- 12v 100ah or 2ea- 6v 300ah, drawing them down 40-50% or more if needed. If I end up needing more power I’m thinking I can increase the battery bank. We are using the cabin 6 to 8 weekends and 1 or 2 weeks or approximately 40 cycles per year. Batteries may end up on second floor (hotter location) due to space limitations.

Solar Panels: Keocera, 2ea 130 watt panels, run in series to boost voltage. This should give me close to 800watt hrs per day in the summer. Solar panels mounted on roof of cabin.

Battery Charger: Iota Engineering 45 amp, 12 Volt charger wired to generator

Location: Mountains of Western Maine

Notes: I’m planning this system so that my batteries are charged up when I get to the cabin and I'll be staying 3 days. I’ll run my generator for 2 hours or so each morning while eating breakfast, taking showers etc. The generator is a Honda EU3000 rated at 2800w (with wireless remote nice!). Generator is used to power well pump, microwave, coffeepot, etc. Refrigerator is propane.

.

[BB.]

Using PV Watts for Caribou Maine, Start with 1,000 watts of panels (round number and program does not go lower than 1 kW), fixed array, 0.52 overall system efficiency for an off grid system with flooded cell batteries and an AC Inverter:

"Station Identification"
"City:","Caribou"
"State:","Maine"
"Lat (deg N):", 46.87
"Long (deg W):", 68.02
"Elev (m): ", 190
"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 0.5 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 46.9"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:","12.2 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 3.36, 58, 7.08
2, 4.34, 67, 8.17
3, 5.23, 86, 10.49
4, 5.75, 89, 10.86
5, 4.99, 74, 9.03
6, 5.09, 71, 8.66
7, 5.15, 73, 8.91
8, 4.99, 72, 8.78
9, 4.26, 61, 7.44
10, 3.45, 53, 6.47
11, 2.38, 35, 4.27
12, 2.73, 46, 5.61
"Year", 4.31, 784, 95.65

You will generate (on average) from 35-89 kWHrs per month, of useful energy or per day:

• 35 kWH per month / 30 days = 1.2 kWH or 1,200 Watt*Hours per 1,000 watts of panels in winter
• 89 KWH / 30 days = 3 kWH or 3,000 WH per 1,000 watts of panels in summer

You have 2x 130 Watt panels or ~260 watts:

• 1,200 WH * 0.260 = 312 WH per day in November
• 3,200 WH * 0.260 = 832 WH per day in April

So, you will need the genset... However, you might not need to run it is as much as you are planning---That is a fairly large genset.

If your loads are low, and you can live with pull start, you might look at an eu1000i or eu2000i if the fuel costs for the eu3000i get to be a burden.

For the battery bank, I personally like to have batteries in series rather than parallel (no extra fusing per parallel string, fewer points to go wrong during charging/discharging/sharing of current). But either would work fine.

The battery bank is probably sized fine for your current loads and with plans to use the generator much of the time when you are there.

My 2 cents.

-Bill

[save_rka]

Bill, thank you for the calculation and input.

I like the Honda eu3000is due to it having an electric starter. With the wireless remote starter we leave the generator out by our shed and can just press the remote to turn it on/off. The problem we have it’s so quite we forget it’s running sometimes!

We typically only use the place in the summer so looks like I’ll average somewhere near 800 watt hr on a good day.

I agree with you on wiring the batteries in series. I was not aware that Concord made the SunXtender PVX-3050T until today so I’m leaning that way too.

Anybody have any experience running the Iota Engineering DLS-45 45 Amp 12 Volt charger from a generator?

Steve

[niel]

hmmm. 1000wh/day and used for 3 days is 3000wh. dividing this by 12v = 250ah. assuming the use of the 300ah 6v batteries, 250ah/300ah capacity = 83.34% dod. this does necessitate the use of the generator while there as the pvs wouldn't likely keep pace with the loads while there and that's if the sun is out while there. if you want to not run the generator you would need at least 500ah of battery capacity to do it and that would need a minimum of 25a to charge at the 5% rate. in any case you can opt for a high rate of charge, and if your genny allows, for the batteries will take it.

[BB.]

Iota makes very good battery chargers (our host sells them too).

I really like Power Factor Corrected (reduces AC current) and temperature corrected (remote battery temperature sensor; hot batteries need lower charging temperatures and cold batteries need higher voltage--plus AGM's are very sensitive to over charging)....

Xantrex made a TC 20 and 40 amp series power supply... And they have a new TC-2 version that looks very nice also (includes PFC, RBTS--but so far has been difficult to get. You might ask NAWS (our host out of Arizona) or look around to see if you can find one (they have the 20 amp, but no 40 amp yet).

-Bill

[icarus]

Just FYi, we live off grid, use ~600 wh/day. No TV, no toaster, no microwave, but we pump our water with the solar, propane fridge(s). We have a very nice balance with ~400 watts of panel, 450 ah of battery (12 volt). This gives up a daily discharge of ~15%, a three day discharge of about 40% max, and we can recharge that 40% in one good day. (Almost, but I never let the battery go below ~75% just to preserve longevity.

We supplement charging with a Honda Eu 1000i, running a Xantrex TC-20 charger.

This set up works perfect for us. If you are nearer 1kwh/day, I would consider another 100 watts or so of panels. The nice thing about the Eu 1000 is that it is very fuel efficient and quiet. I wouldn't worry too much about the rope start. (although the remote is nice) The rope start Hondas are VERY easy to pull and they start on the first or second pull nearly every time!

Tony

[Cariboocoot]

We use about 4X what Tony does. This includes electric 'frige, microwave (used sparingly and only under full charge - a whopping 1050 Watts), "full size" water pump (1/3 HP - about 850 Watts for 6 minutes per day), and digester pump (around 1000 Watts for less than 1 minute).

Other equipment includes desktop computer & satellite Internet/phone unit, various lights, radio, occasional power tools, vacuum cleaner, et cetera. Pretty much typical household usage except no hair dryers, electric coffee pots, or big screen TV.

System produces about 2.4 KW hours per day. We have long Summer days (up to 16 hours so 'harvest' is greater than the typical 4 hours) and uselessly short Winter ones (6 hours - barely enough sun to keep the batteries up with zero use).

Just to give you some idea of another set-up.

[save_rka]

Tony, the TV is for the kids, I don’t usually watch it even at home. My load is an estimate with lots of room for the inevitable growth once power is available at night with the generator off.

Our well pump surges to 24a at 120v on start up, then drops to 12a running. That surge current means I need the eu3000is to start my well. With the auto idle on the Honda I’m not using much gasoline, so I’m very happy with the generator. Plus with the wireless remote I can pump water without leaving the cabin. It does start very well with the rope as well (like when I forget to turn the key off and leave for 3 weeks).

My thought on the Iota Engineering DLS-45 45 Amp 12 Volt charger is it will be charging the batteries at a good rate while the generator is running.

Bill, I’m planning on buying most of my solar equipment from our host (I just think it’s the right thing to do)

Steve

[icarus]

Don't misunderstand,, I am not editorializing about TV,, we just choose not to bother, nor the generator for that matter, I am only commenting on my situation.

My neighbour has an IOTA and is very happy with it.

Tony

[BB.]

Regarding generator use---For the inverter/generators (Honda, Yamaha, etc.) you can probably load them with only 25% of rated load and get pretty good fuel economy.

With standard gensets, they use just about 50% fuel flow for 0-50% electrical loading--So folks with large gensets and "small" electrical loads tend to spend a lot more on gasoline that they really need to...

I would suggest a Watt*Hour meter (old utility meter) and/or kill-a-watt type meter to log how many kWHrs per gallon of fuel you are getting... An efficient genset (seems from my little bit of research) to get 5kWH-6kWH per gallon of fuel when running efficiently... If an installation is getting less than 2.5 kWH per gallon of fuel, I would review the setup and see if things can be changed to increase efficiency (either a smaller genset and/or more electrical load). [fuel=gasoline in this comment]

The general idea is to run the genset in the morning and bulk charge the battery set--and once the current tapers down (~80-85% state of charge), cut the genset and let the solar finish charging for the rest of the day.

-Bill

PS: For example a 45 amp Iota charging a 14.4 volt battery with 80% efficiency:

• 45A * 14.4V * 1/0.80 eff = 810 watts under full current...

So, a 1,600 standard or inverter/genset to possibly a 3,200 Watt Inverter/Genset might be the best fit.

And to only run the generator until the current charging current falls off (by a factor of 2 or more????).

my 2 cents worth of engineering...

PPS: "Fuel" above is gasoline---Diesel can do much better, and propane will be less (due to amount of energy per unit of between different types of fuel).