Featured Post

Plug In Drivers Not Missin' the Piston

This is the Kodak Moment for the Auto Industry. Electric vehicles are here to stay. Their market acceptance and growth will continue....

Saturday, March 10, 2018

Off-Grid or Grid-Tied: Which Is Greener?


If you have solar panels or you are considering them, congratulations you are helping make the world a cleaner place. After deciding to jump in, there are a few questions that you'll need to consider.

One of those questions is "Grid-tied or Off-grid?". In some cases, such as a cabin in the woods, connecting to the grid is not an option. Assuming that you're already on the grid, then you do have a choice whether or not you'll stay on-grid or go off-grid.

There are several factors that you should consider such as your energy needs, how often you have power blackouts, local laws, the energy storage costs...

A friend of mine has an off-grid system and he made the claim that it was "greener" than my on-grid system.

I wanted to examine this claim (heavily biased towards proving him wrong). The particulars of his system and mine are not that important; I'll try to focus on the bigger picture.

System Size and Backup Power

For a grid-tied system, you can install a PV system that accounts for only a portion of your energy needs. Any energy needs your home has when the sun is not shining will be provided by the grid. How green your local grid is, depends on where you live, but most of them are slowly improving. Many utilities have a green power option that supports their solar, wind, or geothermal projects.

For off-grid systems, the solar panels and batteries have to supply 100% of your energy needs unless you have a backup such as a generator. Backup generators are usually diesel or natural gas based. If these were being used, then an off-grid system would be less green than a grid-tied system.

To remove this drawback, let's assume that each of these systems are capable of powering your home 100%.

Which is greener? A minor advantage for grid-tied here since the backup could be cleaner.

Grid or Battery 

With a grid-tied system, during the day surplus energy is feed into the grid and runs your meter backward. This energy is then used by nearby demands (AKA, your neighbors). After the sun has set, a grid-tied system draws energy from the grid, unwinding some of the backspin from the meter.

With an off-grid system, when there is surplus generation, this is used to charge the batteries. The energy from the batteries is then used to power your home overnight. There is some minor loss of energy during the store and retrieve process.

Which is greener? A minor advantage for grid-tied here because it does not have the storage loss.


Seasonal Considerations

I live near the 47th parallel. We have a winter season here. We don't get a lot of snow, but there are many cloudy rainy days in the winter that don't generate much energy. On these days, even with a very large PV system, we would not be able to generate enough energy for our needs.

With an off-grid system, we'd be running generators on these days.

With a grid-tied system, we are able to use those summertime credits in the winter. Our state requires utilities to support annual net metering. This metering starts each year on April 1st. When the meter runs backward in the summer, you have all winter to use these stored kilowatt-hours. Additionally, there is less demand on the grid in the winter (air conditioners are not running) and the utility's wind turbines in the Columbia Gorge spin frantically during the winter months.

Which is greener? Again a minor advantage for grid-tied here.

Batteries

An off-grid system requires batteries. These batteries have to be manufactured and transported. There are some environmental impacts for these activities. It is far less than connecting to a coal-plant, so it is worth it if you need them for a viable PV system.

If you don't need the batteries, because you are connected to the grid, you can avoid these (albeit minor) impacts and you can avoid the cost. You can used the saving to buy a larger PV system.

Which is greener? Again a minor advantage for grid-tied here.

Wrapup 

Solar is great whether you are on-grid or off-grid, you are generating renewable energy from the sun.

There are reasons such as grid availability or reliability that you might consider including batteries in your PV system. However, if your reason to include batteries is that you think that makes it greener, then I disagree. You could even say that you want to have a Tesla Powerwall because you think they're cool, that's great. Feel free to get one (or two, or three). But don't claim that it somehow makes your PV system even greener.

As I said at the start, I might be biased since we don't have batteries in our system, but in every metric I've looked here, grid-tied systems have a slight advantage. The energy that they generate is always used immediately. The summer to winter delta is covered by net metering. And finally, on the cloudy days that don't supply enough solar energy, no generators need to be fired up.

While both systems are "green", grid-tied systems have a slightly darker tint of green.
(Take that Terry! 😄)

All that said, we might just add a Powerwall or two just for the fun tech of it. How cool would it be to have the only house on the block with power during the next winter storm.

http://ts.la/patrick7819