Looking for Suggestions on: solar/wind system with Auto Start Generator (3,400 watt hrs/day)

Suzanne

Hello, first off, lots of great info here, and thanks for all your help!

I have a 200 sqft cabin "office" that I'd like to run fully off-grid (we plan to move it into the edge of the woods later).

This cabin is wired with 14-2 wire and two 15 amp breakers in a breaker box for 30 total amps possible (not sure if that's needed info).

It will run a total of 5 LED lights, but not all at the same time. It will run a FULL SIZE desktop computer and LCD monitor. Possibly also a laptop. Ideally Id like to leave the desktop running 24/7 but after load calculators I think it will be about 12 max (if I need to upload or save files overnight)

It calculated out to max of 3,400 watt hrs/day, total watts are 1,900/day.

I plan to either use a woodstove for heat or a propane burner. After 2 years this will be transitioned into a mini cabin with NO computer electronics.

I am in mid michigan and we get 2hrs of daylight per day in our "bad" season. However, I ran 2 75watt panels in winter to power a lightbulb and a water pump hooked to two deep cycle batteries and not once did the system struggle to pump. Even in cloudy weather it worked like a charm.

I am looking at doing both wind and solar for this system siince we tend to get a good amount of wind out here on the farm.

I have heard about auto start generator systems that are automatically "turned on" to help balance loads to maintain both batterylife and consisstant power output. I am thinking that might be the best way for me to go considering I'll have sensitive equipment on the system.

Can you point me in the right direction of what components I need to buy or systems I should be looking at?

Thank you so much!

mike95490

un attended auto start generators are a common cause of fires.  I would not use one

You can use a laptop for downloading, and an external Drive if you need extra storage - no need to run a tower for that purpose.
You may need the tower for extensive graphics/cpu processing

But first, get a power meter, something like a Kill-A-Watt and start recording what your actual power draw is.

Could you possibly trench and run a underground power to the cabin ?  Far less expensive and more reliable if you don't have good winter sun.

Suzanne

mike95490 said:

un attended auto start generators are a common cause of fires.  I would not use one

You can use a laptop for downloading, and an external Drive if you need extra storage - no need to run a tower for that purpose.
You may need the tower for extensive graphics/cpu processing

But first, get a power meter, something like a Kill-A-Watt and start recording what your actual power draw is.

Could you possibly trench and run a underground power to the cabin ?  Far less expensive and more reliable if you don't have good winter sun.

I do extensive video editing and currently working on a laptop, husband just upgraded me to a full size PC. My Laptop is a gaming laptop specifically made for high end graphics usage, but I've out grown it.

Currently the cabin sits maybe 100ft from the main breaker box on the house. original plan had been to connect it up and down the road move it out further into the property . . . until husband decided he wanted to build a house this summer, and the spot is exactly where my cabin currently sits.

So in just 5 months it will be moved anywhere from 500ft to 1,000 feet away. So if the underground wire is about $1.50 a foot, that brings the cost just to run wire and piping to about $1200 give or take. That doesn't include monthly electrical costs.

Ideally once the cabin is moved, and the new house built, my office will move into the house and the cabin will be rented out for guests who'd like to stay in an off-grid cabin. Making it off-grid allows me to move it again if needed.

BB.

As Mike says--Cost wise, off grid solar is not going to save you any money. More or less, off grid solar generally costs in the range of $1 to $2+ per kWH, vs $0.10 to $0.40 per kWH for utility power (depending on where you live).

A desktop computer system can use somewhere around 300 Watts (computer, monitor, printer, networking)... 24 hours per day:

• 300 Watts * 24 hours per day = 7,200 WH per day (not including lights, heating, etc.).
• 7.2 kWH per day * 30 days per month = 216 kWH per month
• 216 kWH per month * $0.20 per kWH = $43 .20 per month utility power
• 216 kWH per month * $1.50 per kWH = $324.00 per month solar power

Computers (and anything that consumes a significant amount of energy that runs 24 hours per day) use a relatively large amount of electrical power--And on solar, that is a lot of money. An off grid system that supplies ~7 kWH per day (216 kWH per month) will cost a lot of money to install.

A 7.2 kWH per day system is about 2x larger than a suggested off grid home energy budget (around 3,300 WH per day)... And about 1/2 to 1/4 of the average US home's energy usage (around 500 to 1,000 kWH per month for the average north American Home electrical usage).

To give you an idea of the rough sizing for such a system. For an off grid home, plan on 2 days of battery storage and 50% max planned discharge (for longer battery life):

• 7,200 kWH per day * 1/0.85 AC inverter eff * 2 days of storage * 1/0.50 max discharge * 1/48 volt battery bank = 706 AH @ 48 volt battery bank

To charge such a battery bank, suggest around 10% to 13% rate of charge for battery bank (minimum)--Larger battery bank, larger array suggested:

• 706 AH * 58 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 5,318 Watt array nominal
• 706 AH * 58 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 6,913 Watt array "typical" cost effective maximum

Just to take a shot a sizing the solar array system based on your daily loads and location. Guessing you are somewhere around Flint Michigan, fixed array:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Flint
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 47° angle:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
2.86	3.53	4.20	4.61	4.86	5.15
Jul	Aug	Sep	Oct	Nov	Dec
5.31	4.89	4.61	3.68	2.59	2.53

Running the computer year round:

• 7,200 WH per day * 1/0.52 off grid AC system eff * 1/2.53 hours of sun per day (December) = 5,473 Watt array December "break even"

And you could easily need an array 2x as large to make up for bad weather--And you probably would still need an AC Genset to keep the system running if you have more than a few days of stormy weather in a stretch (roughly $1.00 per kWH fuel costs based on $3-$4 per gallon gasoline costs--Not including genset price and maintenance).

I have made lots of guesses hear... Getting a Kill-a-Watt meter and measuring your actual daily loads of the computer system, lights, fan/heater, support gear, etc. will give you a more accurate load estimate. And a better location for a more accurate estimate of hours of sun per day (if my guess of Flint is wrong).

You are looking at $10,000's of dollars to build out such a solar system (batteries, solar panels, inverter/charger, backup genset, etc.)... Normally, I would be suggesting conservation to save energy (continue with the laptop in the cabin, and network to a server in your home, etc.)... Running wiring from your home (or getting a new utility drop--If cost effective) is usually a better choice.

Your thoughts?

-Bill