No Batteries

Grid-Direct pv, Wind & hydro-electric Systems

by Roy Butler, Ryan Mayfield, Jay Peltz & Joe Schwartz

If you have some experience with battery-based renewable energy systems, you're well aware of the power and energy that a healthy battery pack can provide. If you live off grid, batteries make it possible for you to live on that perfect piece of property beyond the reach of the utility lines. In town, being the only one on your block with electricity during a grid failure is an empowering event—cold beer never tasted so good.

But batteryless grid-tied systems have their own set of advantages. They require fewer components, operate at higher efficiency, and are significantly less expensive than battery-based systems. A batteryless system does not need batteries, a charge controller, battery interconnect and battery-to-inverter cabling, an enclosure for the batteries, and all the balance of system (BOS) assembly gear, such as enclosures, circuit breakers, and bus bars. Additionally, the AC wiring is simplified—no critical load subpanel or inverter bypass switch needs to be installed. Finally, because there are fewer components involved, batteryless grid-tied RE systems are comparatively easy for end users to understand and interact with.

These advantages, coupled with the elimination of inevitable battery replacement, make it easy to see why batteryless grid-tied systems are so popular. If your project is off-grid, you'll need batteries—period. If you live on grid, you'll want to consider a few things about your particular application to help you answer the question, "Batteries or not?"

Do I Need Batteries?

If you're considering including batteries in your grid-tied RE system, ask yourself three questions:

• How often does the grid go down at my site?

• How long does a typical utility outage last?

• How much do blackouts affect my lifestyle?

In most places, the utility grid is quite reliable and power outages are infrequent and short in duration. Exceptions are most likely in rural areas that have a lot of overhead power lines and experience regular wind or ice storms. In these situations, grid failures can be both frequent and long in duration—the power company isn't going to prioritize repairing a downed line that services only a dozen families over one in town that services hundreds.

The duration of the power outages you experience is more important to consider than the frequency. If brief power

System Performance— Batteries vs. Batteryless

In terms of performance, batteryless systems will generate more energy than battery-based ones. How much more will depend on the charging source (solar, wind, or hydro-electric), and the power-conditioning equipment (inverters and controllers) used. The condition of the battery pack and how frequently and deeply the battery pack is cycled comes into play too. Some energy, in the range of 5% to 20%, will be lost in the electrical-to-chemical storage process that takes place when charging batteries. But because batteries are rarely cycled in most battery-based grid-tied PV systems, the overall system efficiency hit can be pretty minimal (5% to 10%) if high-quality equipment is used. Batteryless wind systems can significantly outproduce battery-based ones due to some interesting electrical details covered in the following pages.

outages, say less than 15 minutes, are an annoyance when you're working on your computer, buy a small uninterruptible power supply from your neighborhood electronics store. This simple and inexpensive device will keep your computer and Internet connection alive long enough to properly shut things down and wait for the electricity to come back on. If outages last longer, such as a day or two, an appropriately sized battery-based RE system can provide backup for your critical loads, including lighting, communications, refrigeration, and even water pumping. If you experience outages that last for multiple days, a bigger battery-based RE system may be suitable to supply moderate energy demands. If you have significant loads that need to run for several days, the best approach may be to invest in an engine generator that can either meet all your loads or be run periodically to recharge batteries.

The final consideration is how much the power outages you experience at home affect your lifestyle. If the grid only goes down a few times a year for a couple of minutes and you don't consider resetting your clocks to be a big inconvenience, then a batteryless grid-tied system is a great fit. However, if you work from home and need reliable electricity, frequent or long-lasting power outages can significantly impact your productivity. In this case, a battery-based RE system is an excellent option. Finally, some people see the occasional power outage as fun—the kids think it's an adventure and you can settle down to a nice candlelight dinner, which is better than dealing with a bank of batteries any day.

If you decide that batteryless grid-tied RE is the way to go, the next question is, "Solar, wind, or water?" The following pages detail important considerations for each system type.


Joe Schwartz ([email protected]), Home Power Inc. CEO and editor, lives off the grid outside of Ashland, Oregon. All the electricity used on his homestead comes from the sun. He recently swapped out a set of 10-year-old flooded lead-acid batteries (still in working condition) for a bank of sealed AGMs to see how they compare in terms of off-grid service.

A wide selection of batteryless inverters are available to suit your specific grid-tied renewable energy application.

A wide selection of batteryless inverters are available to suit your specific grid-tied renewable energy application.

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