3Aug

Off-grid Solar Dreaming, Loosing the Boogeyman

Wednesday | Filed in: Off-Grid Solar

Utility companies fit somewhere in my mind between wall street bankers, government oil company subsidies and the boogeyman. Because I sell off-grid solar everyday more than anyone I understand the price and complexity of engineering a system, but there are many cases where the pleasure outweighs the pain.

Before we take a closer look at he pro’s and con’s of off-grid solar, let’s understand the different types. The three basic categories of solar electricity systems available today are:

The first are stand-alone off-grid solar systems that are completely independent of the utility grid. With the exception of direct-use systems like water pumping or PV-powered ventilation, off-grid stand alone solar systems must have batteries to give energy storage during times of low input or high usage.

Battery-based grid-tie systems are quite similar to off-grid systems. They also use batteries, but they are connected to the utility grid, so they can send out to the grid any surplus electricity generated by the RE system, and use utility electricity when needed.

Batteryless grid-tie solar systems are the simplest of all systems, having only the energy generation technology (be it solar modules, or a wind or microhydro turbine) and an inverter connected to the utility grid. They do not have batteries, which points to their primary drawback they have no emergency backup capability. When the grid goes down, these systems also shut down.

Of the custom off-grid solar advantages, independence is chief among the reasons for wanting an off-grid solar system where the grid is available. Off-grid systems are not subject to the terms or policies of the local utility, nor are system owners subjected to rate increases, blackouts, or brownouts.

If you’re shopping for rural property, you’ll probably find that off-grid parcels are less expensive. Most people aren’t ready to take on being their own utility, and the land is priced according to this value system. Being off-grid using solar can also be cheaper than getting a utility line extended to a property. But bear in mind that with off-grid renewable electricity systems, there is up-front and ongoing costs.

Off-grid solar systems may have a slight edge over grid-tied systems when it comes to expandability. While both are modular, it’s often easier to grow an off-grid system as you can afford it. In fact, many off-gridders with limited incomes find this to be the norm gradual weaning from fossil-fueled generators by adding more renewable capacity. With lower array voltages (12 to 72 VDC nominal), one to four modules can be added at a time. Batteryless grid-tie systems run in the 150 to 600 VDC range, and specific inverters have voltage windows and efficiency curves, so that adding to them requires more modules and, possibly, another inverter.

Unless you can afford an oversized system, off-grid solar systems tend to force you to use electricity efficiently. This is a big advantage if you also hold environmental values. Some of the most energy-efficient homes in the country belong to off-grid folks. When you have to make all your energy with only the available resources at your site, you think about how to use that energy wisely.

There are many less tangible advantages of being off grid with solar as well, including the satisfaction and peace of mind that goes with using electricity responsibly. And maybe your neighbors will begin to think you are way ahead of your time.

Off-grid solar disadvantages include when making the decision to go off grid, you take on the duties of the cursed utility you were trying to avoid. My experience is that you tend to curse them less and appreciate them more as you tackle these responsibilities. First and foremost, making all of your own electricity is costly. If you are already on the grid, it’s unlikely that installing an off-grid solar system will provide you with cheaper electricity, unless your area has generous incentives, very high utility rates, or both. (Note that most financial incentive programs apply to on-grid systems and do not apply to batteries.) Of course, if you’re a long-term thinker, this changes the picture. But most people conclude that “going off grid” to save money is not a winning concept. With existing off-grid property, you need to weigh the cost of line extension against installing an off-grid RE system. In some areas, utility line extension can exceed $20 per running foot.

System maintenance and troubleshooting are serious, ongoing responsibilities with off-grid systems. When you pay your utility bill, you’re paying for those hard workers in business suits and coveralls to take care of things. If you are the utility, you have to do the work all by yourself, plus buy the coveralls.

Off-grid solar systems use batteries to store electricity and provide it for your home, but batteries don’t last forever. In fact, they will need replacement every five to fifteen years (typically less than ten, unless you have deep pockets for highquality, industrial-type batteries). A minimal bank of batteries will cost at least $1,000, and long-lasting industrial batteries for the same application might cost three to four times that much. And it’s not just the cost in dollars that’s a disadvantage.

There’s maintenance and replacement time, aching backs from lifting that heavy metal, and perhaps labor cost and then there’s the environmental cost of making, moving, recycling, and replacing all that lead. Batteries have another, less tangible cost, and that’s energy waste. At their best, batteries are 90% efficient. That means if you put in 10 kilowatt-hours (kWh), you will get out less than 9 kWh. As they age, their efficiency drops further, and they are also affected by temperature. All this adds up to more energy waste the larger, older, hotter, or colder your battery bank is.

In comparison to grid-tied solar systems, off-grid stand-alone systems have another serious drawback wasted surplus energy. When a grid-tied renewable electricity system makes more than the homeowners use, the surplus is fed to the utility,creating an energy credit and allowing the system to always run at full capacity. Nothing is wasted, and the grid is figuratively (not literally) 100% efficient you get credited for all that you throw their way. When you’re off grid with solar your surplus must be used or it will be wasted. With most off-grid PV systems, the array simply gets turned off by
the controller when the batteries are full, so the energy is never generated. With most wind and hydro systems, the excess energy is shunted to a dump load, typically an air or water-heating element. Savvy off-gridders are aware of their system operation, and change their energy-use habits when there’s a surplus like choosing to do laundry in the middle of the day. But it’s not automatic, and it takes some social adjustments to switch from energy sipper to energy gorger depending on the weather.

If living off grid with solar sounds like a bit more trouble than you expected, good! I’d like you to be successful with your renewable energy plans, and being realistic is a good first step. The social and familial implications of living with a variable energy source shouldn’t be underestimated! Living off-grid with solar can be satisfying, but it’s also a big responsibility. It’s necessary to be willing to flex your electricalactivities with the changes in the weather, or be willing to start up a fossil-fueled generator whenever nature is not cooperating with your energy plans. If you’re a city dweller who gets impatient when the traffic light takes a while to change, imagine how you’ll handle waiting for the sun to come out or for that mechanic to fix your generator.

Source: Home Power Magazine

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