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The majority of our customers still prefer batteryless systems, as
in most parts of the country. Battery-based grid-tied systems are
less than 10% of our residential installations. But I find myself
speaking with more people who inquire about GTWB systems out of a
growing and fundamental lack of confidence in the social
infrastructure in the future. It's very small still, just as
grid-tie in our region was very small ten years ago, and it's the
early adopters, with interest and means to investigate investing in
some type of long-term energy security. These people are looking to
be able to run part of their home on PV for an indefinite period.
The systems are set up as standard GTWB, but with larger backup
energy storage capability. The systems aren't necessarily huge. We just completed one on an urban residence with only 2.2 kW of PV and 600 A/hr @48V of VRLA Concordes, that the customers carefully calculated would serve their essential needs if the grid went down permanently. They are purchasing a sense of security against an uncertain future. These are by no means the bunker-mentality fringe that we have all read about; this latest is a retired professor and scientist wife; another last year was a conservative retired couple with small livestock and garden on one acre; he was a utility lineman. The systems are inherently difficult to design, for two fundamental reasons. First, they must serve three functions, two of which are almost mutually contradictory: provide the economic benefit of grid-tied PV as long as the grid is up, which could (and likely will) be for the life of the system; provide backup power to protected loads during a typical short utility outage; and immediately behave like an off-grid system (but without a backup generator) in the unlikely event of long-term or permanent loss of the grid. Second, taking an on-grid home off grid is one of the most difficult tasks: in 15 years I have never done it, and have turned it down as impractical numerous times. But if the loads are carefully selected and moved to a separate panel, and it's understood what is possible to run and what isn't, and there's a good monitor in the system, it works. We are very clear with clients what to expect; this is the place to be very conservative in explaining how the system works, how long batteries may be expected to last, the need to go without electricity if there's a week of cloudy weather, etc. It helps that this is the sunny Southwest, of course. We are very careful not to encourage fear. The desire to install a system with this capability has to come from the client, and I make sure that they understand the costs and limitations of this approach. These systems run in the ballpark of $15-20/W installed - about 3X a batteryless system. And we also make sure that they understand that while we can't predict the future any more than they can, if indeed the worst happens and the grid fails, we likely not be able to support them, as transportation fuel may also not be available and social upheaval will be unpredictable. For this customer, a generator isn't a solution, as it's limited to the amount of propane in a tank. And natural gas isn't an option, as the natural gas distribution system is also dependent on the grid. I would think that this approach would also work for medium-term natural disasters, such as ice storms or Vermont floods, but with a generator and large propane tank for backup battery charging as part of the system. Are the rest of you Wrenches getting these inquiries? I haven't seen much on this list about the topic of long-term or permanent loss of grid power. Allan
Allan Sindelar
al...@positiveenergysolar.com NABCEP Certified Photovoltaic Installer NABCEP Certified Technical Sales Professional New Mexico EE98J Journeyman Electrician Positive Energy, Inc. 3201 Calle Marie Santa Fe, New Mexico 87507 505 424-1112 www.positiveenergysolar.com On 9/4/2011 6:28 AM, Christopher Warfel wrote: One should also factor in the availability of generator fuel if an extended outage occurs. In some communities, the fuel will be scarce or non-existent, especially if significant damage occurs to fuel transporation and storage infrastructure. |
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