Off-Grid vs. Grid-Tied

| 5/16/2013 9:12:00 AM

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.

12/28/2013 2:01:23 PM

Thank you JonathanCole for saying what i was thinking. This article is a little bogus.

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 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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