Assembling reliable off grid power system for emergency preparedness

Many advocates of unreliable power sources like wind and solar blithely toss out the concept of “storage” as the panacea that makes their favored energy sources viable competitors in the potentially lucrative business of supplying on demand power.

I’m skeptical because I have some experience with operating and budgeting for power systems that use batteries and emergency diesel generators to ensure reliable operation when there is a major power outage. However, my spreadsheets for that work were not my property. Even if they were, there have been several intervening years, so my numbers would be out of date.

Recently, however, I was privy to an email from an associate in California who is an Amateur Radio operator (ham) who takes his hobby seriously. Gene feels a personal responsibility to ensure that he can stay up on the air as an information relay during major disasters. In support of that strong sense of mission, he has invested in a system that ensures his radio will remain powered even if the grid is down for several days.

He gave me permission to share the email describing his system and possible alternatives. It does not offer a short, glib response to those who says that they will simply “store” excess wind or solar energy for use when those weather-dependent sources aren’t available, but it sure puts some perspective on the challenges that must be overcome first.

Note: I edited the original email slightly for improved clarity.

By: Gene Nelson, Ph.D.

As an Amateur Radio operator (KE5HXX) who is an advocate for emergency preparedness in California, there is an advantage for disaster preparedness for those whose solar PV system includes energy storage. I own such a small-scale system in addition to owning a propane-powered 5 kW emergency backup generator. Solar PV systems with storage can supply emergency power, subject to the limitations of their storage systems. Unfortunately, the majority of residential and commercial solar PV systems in California lack any energy storage system for reasons of economy and reduced maintenance. Theose systems are constructed such that they will NOT produce power even when the sun shines if the the grid goes down, as would occur following a large-scale disaster. (See How Rooftop Solar Homeowners Can Prepare for El Niño from PG&E for details.)

I would urge anyone who owns a rooftop solar PV system without energy storage to consider the purchase and installation of such an energy storage system and an automatic transfer switch if they have concerns about disaster preparedness. Current lead acid battery based systems will require a concrete mounting pad, since the energy storage system has substantial weight of at least a ton and will cost several thousand dollars. The lead-acid batteries will need to be replaced every 5-7 years. Installation should be by a licensed electrical contractor. (The less-expensive approach would be to purchase an emergency backup generator powered by natural gas – with the additional-cost option of propane power as a backup.)

To obtain an understanding of the cost of a modern lithium-ion based energy storage system, consider the following.

Amazon carries Li-ion cells and charging systems. Here is an example set.

    Eastshine Li-ion

  • Bundle: 4 Packs EASTSHINE E35 3500mAh 3.7V 12.9Wh Protected 18650 Rechargeable Li-ion Battery for… $58.95 Sold by EASTSHINE and ships from Amazon Fulfillment. (Free shipping)
    Nitecore charger

  • Nitecore D2 Digicharger Bundle with Eastshine EB182 battery box and car charger: $19.00 Sold by EASTSHINE and ships from Amazon Fulfillment. (Free shipping when ordered with the above battery bundle.)

For a 12.5 kWh energy storage system, you would need 250 of the above sets using 12.5 Watt-hour batteries for the battery and charger components of the system. (The pre-tax price of these 250 sets would be $19,487.50 from Amazon) One should not scrimp and purchase a low-quality system, as lithium batteries have an unfortunate tendency to explode and burn if charged or discharged improperly.

According to the Wikipedia article about Lithium-ion batteries, the Tesla Model S electric automobile requires 7,104 cells rated at 11.965 Watt-Hour per cell. The list price for this Tesla Model S starts at $79,900.00 per with the 85 kWH battery, per the Wikipedia article about the Tesla Model S. The battery cost is about 21-22% of the cost of the vehicle. The batteries are currently guaranteed for 8 years.

The recent problem with the Boeing Dreamliner lithium-ion batteries was traced to wiring errors and a charging circuit that attempted to charge the batteries too quickly. The result were some fires and a grounding of the Dreamliner fleet during part of 2013 until the charging circuitry was redesigned.. See the Wikipedia article titled “Boeing 787 Dreamliner Battery Problems” for additional details.

This email provides documentation regarding the substantial purchase and maintenance costs of energy storage systems for low-duty-cycle generation technologies such as solar PV and wind. I invite your feedback.

Concluding thoughts

Though there is room for improvement in battery technology and there may be room for lowered costs with even larger scale manufacturing, the asymptote is not far away. Highly motivated engineers and scientists have been working on chemical storage batteries pretty steadily for more than a century. Lithium ion cells like those that Gene describes are already being manufactured in highly automated, mass production facilities to serve a market that is quite large and price conscious.

Lead-acid batteries have already achieved an even larger scale market in cars, trucks, and boats along with systems that have been installed to back up telephone networks and to provide uninterruptible power supplies to a wide variety of loads.

Another big challenge that a system using batteries to attempt to make wind and solar into reliable power supplies is that the batteries can only hold a finite amount of electricity. When they are depleted, they must be recharged. Blackout is the alternative. Consider what happens if the battery depletion arrives and there is still no wind or usable sunlight.

Finally, please consider our environment. The effects of extracting the materials required to increase battery capacity by several fold and the need to safely recycle or discard depleted materials after they are no longer capable of retaining a charge are not trivial or solved problems.

Hardy souls who are willing to tinker and cobble together a variety of power sources can go off-grid, but hooking wind and solar to storage is not a prescription for powering the population.

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