Green Homes

Building for the future, today – combining the best of historical wisdom and modern technology.

Off-Grid vs. Grid-Tied

5/16/2013 9:12:00 AM

Tags: off-grid, grid-tied, renewable energy, Leigha Dickens, Deltec Homes

solar array round houseMany customers who consult with me on green building profess their dream of living in an off-grid home powered by solar energy.  Since solar technology is now widely available and cheaper than it has ever been, this dream is easier than ever for a homeowner to achieve.

However, solar is still a high-dollar line item on a construction budget or upgrade for an existing home, and whether the concept of an off-grid solar array makes sense for a particular home is a more complicated question.  There are multiple ways to set up a renewable energy system to power your home—with “off-grid” being only one possibility. 

So What Does “Off-Grid” Mean?

“Off-grid” means you are on your own: there is no connection to the power company.  The only way to accomplish this in a setting where you want electricity even when the sun is not shining, is to incorporate batteries into your system.  Thus off-grid homes have no power poles running to them, and draw the power they need from deep cycle battery banks.

Grid-Tied: the Alternative

“Grid-tied,” by contrast, means that your house is connected to the grid, and you are still set up to buy your power from the power company when you need it.  But, when your solar array is producing power, you can either sell that power straight to the grid with the goal of financially offsetting the cost of the power you have purchased, or you use that power yourself first, and sell any extra to the grid.  You may not be using the actual electrons you have produced yourself, but you are still contributing green power to everyone’s benefit.

The Pros and Cons

The advantages of one system over the other come down to cost, comfort and independence. A grid-tied system will cost less because it does not require batteries, which form a significant portion of the cost of an off-grid system.  A grid-tied system for a net-zero home will also cost less because fewer solar panels are needed:  When you are not trying to store your own energy in batteries for later use, you do not need to produce quite as much energy in order to offset your yearly energy use.

A grid-tied system is also more flexible, both from a day-to-day use standpoint, and from a down-the-road standpoint.  Since you still buy any excess power from the grid, you won’t suddenly find yourself without electricity if you accidentally leave the lights on all night—although you will have to pay the electric bill for such a mistake.  And since you aren’t tied in to producing all of your own power yourself, you can use a grid-tied system to install as much solar as your budget allows, adding to it down the road as you are able.  Although you can add to an off-grid array down the road as well, if you don’t install enough to meet all of your power needs to begin with, you can’t wait on installing more capacity if you want to have enough power.

Pictured above is a grid-tied solar array installed on this round Deltec home in Virginia.  It produces enough energy to offset ½ of the home’s yearly energy needs, making the home a partial-net-zero home.  Installing the grid-tied array allowed the homeowners to put in as much solar as their budget allowed.

However, for safety reasons, grid-tied systems cannot function when grid power goes down (a live load on the line would present a danger to utility workers coming in to fix power outages), and to many independence-seeking homeowners, that is the biggest drawback of grid-tied systems.  There may be very practical reasons to go off-grid as well, such as a high cost of installing traditional power poles to a remote jobsite or a concern about local grid reliability.  

solar array awning

Pictured, left, is an off-grid array installed by yours truly at Pisgah Astronomical Research Institute in North Carolina  The small research institute had a number of isolated telescope buildings on a high ridge that was prone to summer lightning storms.  Giving each building its own off-grid array made sense to keep this equipment powered even during frequent lightning-induced power outages at the site.

An off-grid system could also be argued to have a lesser environmental footprint than a grid-tied system.  For one thing, it forces you to adopt a more energy-conscious lifestyle, for every decision about electrical usage has consequences for how your system performs.  Additionally, an off-grid system produces its energy on the site where that energy will be used, eliminating the inefficiencies of distribution.  A grid-tied system is typically sized to offset the power consumed at the homesite, but is not often sized to offset the wasted energy from burning a fossil fuel at the power plant level and then distributing that energy.  An off-grid system represents a complete removal of your home from the environmental externalities associated with conventional power production—for some, this is by far the biggest attraction of renewable energy.

Pros and Cons Can Vary by State

How the state in which you live structures its rules and incentives for renewable energy makes a difference to which type of system makes more financial sense.  In general, grid-tied systems can have a dramatically shorter payback period than off-grid systems, as utility incentives for renewable energy or programs to pay homeowners for the power they produce typically speed up the time it takes to recover the up-front investment of solar.  However, in states that have very poorly structured rules for grid-connection, off-grid might be a better way to go solar while avoiding regulatory headaches.

I recently interviewed four Deltec homeowners who have built their homes with solar energy: two who chose to go off-grid, and two who chose to go grid-tied.  For some of these customers, state incentives played a role in their choice.  I compiled their stories into an off-grid fact sheet I use to educate our customers, which you can download from our website here.  

A good place to go to start looking for the rules and incentives in your state is the North Carolina Solar Center’s Database of State Incentives for Renewables and Efficiency: http://www.dsireusa.org

If you’d like to start getting a handle on just how much solar you would need and how much it would cost, I have found several online calculators useful for arriving at ballpark figures:

Alt-E’s Off-Grid Solar Calculator: http://www.altestore.com/store/calculators/off_grid_calculator/

Grid-Tied Solar Estimator:

http://www.solar-estimate.org/index.php?page=solar-calculator

Bio:  Leigha Dickens is the Green Building Coordinator and resident building scientist at Deltec Homes, Inc in Asheville, North Carolina.  Deltec manufactures round, energy-efficient, high-quality and highly wind-resistant homes.  Learn more about green building with Deltec Homes at www.deltechomes/green-building/

 



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Post a comment below.

 

beaty1841
12/28/2013 2:01:23 PM
Thank you JonathanCole for saying what i was thinking. This article is a little bogus.

JonathanCole
5/17/2013 1:52:39 AM

Actually solar energy is not quite so black and white as this article implies. You have to look at costs and benefits, but you also have to look at goals and responsibilities. Because solar energy is variable over time there is the necessity of backing it up with another source of power when it is night or the sky is filled with dark gray clouds. Every solar energy system must have backup which can be in the form of a battery system, a free-standing fuel generator, or the grid. Of course in some ways, the more sources of backup power you have, then the more reliable your energy system is.

As an example, I live of-grid with a modest battery and a backup gas generator. My solar system is sized to meet my loads in the winter when the days are shorter and the weather is darker and more variable. As a result I get better than 98% of my electrical energy from solar. The other 1-2% is provided by my fuel generator. I have uninterruptible power.

In 30 years of living off the grid I have never had a power system failure. The grid has dozens of these every year. And what is more problematic, the grid provides widely variable quality of power. Transient voltage spikes, brownouts and outages are very bad for your equipment. That low quality power causes light bulbs, electronics, small appliances and gadget of every type to have premature failures. You don't get that if you are not connected to the grid, but a generator requires maintenance and fueling and to get a quality generator that will last a long time with little hassle costs a lot. And it has to be installed properly so that it is quiet, protected in the event of fire, far away from the home to prevent the possibility of carbon monoxide poisoning and so forth.

For many people who are already connected to the grid, what makes the most sense is to use the grid as your backup generator.With batteries to act a s a shock absorber, the up and down transient voltages are not nearly so much of a problem.

As far as batteries being a substantial cost, that is simply not true. Only batteries that are unreasonably oversized are expensive, not only because you have bought too much battery, but also because the battery is so large that it is chronically undercharged which substantially shortens its life. In my system which powers generous samples of EFFICIENT equipment, the amortised cost of my battery system is $10-15 a month. But is does require maintenance. Next time I need batteries it will be Lithium Titanate which will last for 20 years and be completely maintenance free.

Right now I am building pre-fabricated, pre-engineered, clustered solar PV systems with batteries that cost $10 per AC watt installed. These systems are modular so you can put together as many modules as you want. The smallest unit, a single module is just right for a two person household with occasional guests. Want to service more people, add more modules. Engineered to be durable for decades, low maintenance and user-friendly, I can say with confidence, the Solar Evolution has arrived. For lots of free information about solar take a look at my web log LightOnTheEarth.blogspot.com If you want to use solar in an intelligent way, you'll have to learn about. I am training the world for free.








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