An Educated Move Off-Grid: Page 2 of 4

Beginner

Inside this Article

Off-grid PV system
A high-tech off-grid system now provides electricity for the twentieth-century farmhouse.
Twentieth-century farmhouse
This twentieth-century farmhouse was originally built by an Amish family; it was formerly electricity- and plumbing-free.
Usage of energy-efficient appliances
Energy-efficient appliances play a critical role in reducing the electrical loads in an off-grid system.
Batteries for energy storage
Two 48 V strings of Trojan L-16-RE batteries provide energy storage for the McDermott home.
OutBack inverter and two MidNite Solar charge controllers
The balance-of-system components include an OutBack inverter and two MidNite Solar charge controllers.
Generac EcoGen 6 kW propane generator
The Generac EcoGen 6 kW propane generator is designed and warranted for off-grid use with an RE system.
Pole-mounted solar-electric arrays.
Much of the 21-foot lengths of the mounting poles are encased in concrete to handle the wind loads on the large arrays.
PV module mounting
Mounting the PV modules.
Olde English Babydoll lamb.
The McDermotts’ off-grid life also includes this Olde English Babydoll lamb.
Teresa inspects her beehives
Teresa inspects her beehives and checks for honey. Notice the solar-powered electric fence used to keep out pesky black bears.
Off-grid family
Off-grid family Mark and Teresa McDermott with their son Dylan and daughter Laura.
Off-grid PV system
Twentieth-century farmhouse
Usage of energy-efficient appliances
Batteries for energy storage
OutBack inverter and two MidNite Solar charge controllers
Generac EcoGen 6 kW propane generator
Pole-mounted solar-electric arrays.
PV module mounting
Olde English Babydoll lamb.
Teresa inspects her beehives
Off-grid family

System Design

Before we designed the off-grid system, we set a rough budget for the house, with two major considerations: We needed to wire the house so that we could use whatever electricity our system would make and we needed a septic system so that we could have indoor plumbing.

Early in the process, I decided on a solar-only system. There was no hydropower source on the property, and while wind electricity is widely used in the area, I just didn’t have the funds to do a hybrid system, nor did I want to go with just a wind system. Once I focused on a solar-only system, I began the critical process of sizing it.

We used about 1,000 kWh per month at our grid-tied home. That works out to be about 33 kWh of electricity a day used (or, mostly, wasted). I had never examined our electricity usage before. All I saw and complained about was the monthly bill.

Defining the Load

The first step in system design is to figure out how many kWh a day are needed. That seems simple enough, but it is very difficult to arrive at an accurate number. I bought a Kill A Watt meter and measured the energy use of the toaster, computer, TV, dryer, washing machine, and everything else in our existing house that plugged into a 120 VAC outlet. I recorded all of the watts and watt-hours used for everything in the house on a spreadsheet.

Some of our appliances were very energy-efficient and other older ones were energy hogs. But knowing how much energy everything used was crucial. Next, I needed to estimate how many kWh we would need per day in our new house. That sounds easy, but it is also quite difficult. How many lights would we use during the evenings and how long would they be on? The same question applied to everything electrical in the house. Going off-grid forces you to be very aware of how you use your energy.

The trick to off-grid living is conservation and efficiency. After looking at many different scenarios, I came up with an estimated minimum of 6 kWh per day. After getting real data from our appliances and deciding that we would be able to change some of our electrical usage habits, I targeted a 3 to 4 kW system. (Since the system was installed, we’ve loosened our conservation belts a little this summer and have used as much as 6 to 7 kWh per day on a couple of occasions.)

Once your average daily electricity use is estimated, the size of the battery bank can be calculated, based on a specific depth of discharge and the number of days of autonomy (no sun) you expect.

Battery Sizing

Since the solar energy is stored in a battery bank, its capacity has to be enough to provide the energy you need without overdischarging your batteries. The battery bank feeds the inverter that converts the DC to AC electricity used by standard household appliances.

Determining the size of your array and battery bank is a bit of a balancing act. An array that’s too small will struggle to keep your batteries charged. An array that’s too large will cost more up-front. I gathered all my data, calculations, and best guesses and came up with a target system: a 48-volt, 400- to 600-amp-hour battery bank and a 3 kW solar-electric array.

We knew that heating anything significant with electricity was going to be too big a burden on our PV system. We kept the two Hitzer gravity-fed coal stoves, and decided to use propane for backup space heating, water heating, cooking, drying clothes, and to run the backup generator. But we would be reducing our electricity usage by nearly 80%—going from 33 kWh a day to relying on a system that in the depths of winter would produce only 6 to 7 kWh. Our grid-tied house used natural gas for space heating, water heating, and clothes drying. We had a very large chest freezer, electric convection oven, two refrigerators, five TVs, three DVR/cable boxes, a large gaming computer, two printers (one inkjet; one laser), incandescent lights, and a bevy of other little electronics. A pellet stove ran 24/7 all winter. Everything was plugged in and powered most all times. Every night, there were fans and other electronics running. I made some drastic assumptions to reduce our electricity usage. That worried me. What if I had made a wrong calculation? And what if I could not install the system in time for our first winter? With those fears, I decided to hire a professional to help design and install our system.

Comments (6)

America Install Solar's picture

Congratulations McDermontt's making your home off-grid!

It's odd how most('grid-tied') people try to justify not going Off-grid, like saying "the Packback is very long"!
so the Q. for grid dependent users is...When are you going to 'pay-off' your utility bill?

A. Never

Ian Woofenden's picture

The McDermotts are off-grid because line extension cost was in the $35,000 to $45,000 range. If the utility line is on site and interconnection policies are reasonable, using renewable energy ON-grid makes more sense, because you can use or get credited for all production. Off-grid systems must be designed to have a surplus, and therefore are fundamentally less efficient than grid-connected systems. The payback may or may not be longer for off-grid systems, depending on the cost of line extension.

I think sometimes people say "I want to go off-grid" when they really mean, "I want to power my home with renewable energy". Sensible renewable energy design will most often use the existing utility grid if it's practical. Unless line extension costs or interconnection bureaucracy or costs are high, a grid-tied renewable energy system usually makes the most sense.

Ian Woofenden, Home Power senior editor

America Install Solar's picture

Good sunny day Ian! (hopefully there, if not soon) With most of what you said, I concur.
That's why I promote use of 'biModal' PV systems (On-grid+stand alone operation), customers get the Best of both worlds...hopefully, as you said, if not a interconnection mess!
With a hybrid type PV system costing less (vs. cost a Grid-Tied Only sys. few years ago) installing a Bimodal is the best & makes the most sense, esp. when the grid fails...like 'victums' of hurricane Sandy with 'grid-dependent' PV systems, looking at their arrays but have NO power from their solar investment!!
For those with a stand-alone (i.e. 'off-grid' PV+ some type of back-up power) energy system, they will never have the headache of a 'Sandy Storm' (unless their array and 'back-up power' flies or dies!) or dealing with all the net-metering misinformation, and unfair (by most utilities) 'credit' as a lower than grid retail rate 'paid' for PV owner's true value of their solar investment, which should be equal for kWh delivered.
note: Minnesota has just declared the 'value of solar' sent to the utility grid at over 14 cents/kWh hour!
see:
http://www.ilsr.org/wp-content/uplo...

Stay cool,
It's Time for Solar!

Ian Woofenden's picture

From my perspective, it all depends on the goals of the system owner.

My experience is that when most people find out the increased cost and responsibility of battery based systems, they opt for batteryless grid-tie. But again, it depends on their motivations. If they are concerned about the end of the world or grid instability, certainly battery-based systems will fill their needs better. But most people in the U.S. live where utility outages are rare and short, and paying for, maintaining, and charging batteries for 364+ days per year to plan for a brief possible outage doesn't make sense to a lot of people.

I _try_ to keep my personal viewpoints and conclusions (I've lived off grid for 30+ years by choice) mostly to myself, and present options to readers and clients while trying to discover and help them achieve their own goals.

And then to throw a bit of a curve into the batteryless-with-no-backup vs. more-expensive-battery-based-grid-tie decision, we now have the limited-backup-when-the-sun's-out option, as profiled in HP159:

http://www.homepower.com/articles/s...

It remains to be seen how this limited product will play out in the real world of people's goals and expectations.

Ian Woofenden, Home Power senior editor

Kolapo Olakonu's picture

Hello Mark,
this is awesome, i'm all excited about off grid living and look forward to it. the "inside this article" links however does not contain the cost table mentioned within the main article. Can we see that also?
Thank you
Kolapo Olakonu
Phoenix AZ

Michael Welch's picture

Hi Kolapo. Off-grid living has a lot of benefits, but also more expensive PV systems. Unfortunately, there is not a cost table with this article to illustrate that, and the reference should have been removed during the editorial process. Please accept our apologies.
Michael -- Home Power

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