Troy,
Unless you are going to be your client's power plant manager, he or she is
going to have to be responsible for at least system operation which means
managing production and consumption - or hire someone to manage the system. PV
systems are automatic and virtually maintenance-free to some extent. A
well-designed, properly installed batteryless grid-tie residential PV system's
operation is transparent to the home occupants and requires very little
attention. However, a battery-based system regularly requires operator
intervention especially in a region with frequent brown-outs and black-outs.
There are several Wrenches who live with battery-based grid-tied PV systems. Do
any of you power your whole house through the main service panel (no subpanel)?
If yes, what size PV array, inverter, and battery bank? Any battery-based,
grid-tied PV systems out there in continuous operation since before June 1998?
Joel Davidson
----- Original Message -----
From: R. Walters
To: RE-wrenches
Sent: Tuesday, June 23, 2009 10:29 PM
Subject: Re: [RE-wrenches] Grid-Connect Inverter with battery,AND auto
backoff?
We've looked at a variety of approaches over the years. My current thinking,
is that you want some non critical loads to shut off during an outage, so the
customer knows they are on backup power. With whole house backup, they never
know till the batteries are gone too. I've found that with creative picking of
circuits, the customer can be signaled that the grid is out, without creating
any panic or hardship. Most houses have so many circuits that its just not a
big deal to have the washing machine not work for a few hours.
I'd back off to a proven design, otherwise your going to spend a lot of time
with them making this work. Manually switchable double throw breakers are
available and work well, but yes, you do have to exert some slight mental and
physical effort to operate them. Automatic anything means the installer is
always to blame. Good system design puts some responsibility on the operator as
well.
R. Walters
Solarray.com
NABCEP # 04170442
On Jun 23, 2009, at 10:30 PM, Troy Harvey wrote:
Load sheding is not a bad idea if the tech exists. Not particularly complex
either with networkable breakers and a smart controller in the inverter. Just
software. Cost isn't an issue, they are willing to pay.
The issue on loads isn't battery cut-off (though that isn't a bad idea),
but shedding the less-important loads to make sure the house does exceed the
inverter power output. A 6kW inverter subpaneled will only give you about four
15 AMP circuits. However a typical house of this size will have 30 such
circuits, yet good chance it won't be drawing much more than 50 AMPs for the
whole house at any one time. How do you select what is important? Either the
inverter is complicated or the electricians wiring is complicated.
Troy Harvey
---------------------
Heliocentric
801-453-9434
[email protected]
On Jun 23, 2009, at 10:01 PM, William Miller wrote:
Troy:
Let me guess... They want it right away and cheap, too. Generally
speaking, this is an impractical request. Electrically operated circuit
breakers or 20 A relays and controllers are expensive and complicated. One
thing to learn in this trade is when to try and talk a client out of a bad
idea, and when a client has such wacky ideas that it is best to walk away.
I could, however, suggest two ways to do this:
1. Use two inverters and set the LBCO for one high. Connect one to
critical loads and one (with the high LBCO) to non-critical loads. When the
batteries start getting low, the non-critical-loads inverter shuts down,
leaving the critical-loads inverter running.
Realize that you now need four load centers: Grid, generator (you have
recommended a generator so they can use their wide screen TV during a wind
storm, correct?), non-critical loads and critical loads. This type of design
gets complicated fast. Will the AHJ be able to track this? Set a clause that
allows you to collect hourly fees when they require three different meetings
and three re-writes of the permit application.
2. Use an Outback with external relays to shut off loads when the battery
voltage falls below a certain point. This is a crude approach, the parameters
are not flexible (hard coded delay values) and it requires custom built relay
panels, time consuming, expensive and a potential service problem.
Either system is actuated on battery voltage rather than loads.
Inverters I am familiar with have relays and internal controls that operate
based a set-able battery voltages, but I know of none that has a programmable
relay to actuate at a certain load level. In addition, loads change so rapidly
that this type of switching would be erratic. Loading is a component of
battery voltage, anyway, so you are including that indirectly.
Good Luck,
William Miller
At 07:41 PM 6/23/2009, you wrote:
Hi folks,
I need an inverter/charger/controller solution for a grid connect
house that:
1. grid-connects (net-meters)
2. Islands off of the battery in outages (whole house UPS)
3. Feeds into the whole house breaker, so the whole house is backed up
4. Shuts down less important breakers as needed, if the load for the
whole house is over the inverter limit
Instead of guessing which breakers are important to put on a battery
backed up sub-panel, my client would like the whole house backed up.
But of course, can't guarantee that the house won't be drawing too
much for a 6000 Watt inverter at any given time. So would like to have
the system intelligently remove less important breakers until the
system is below the inverter operation wattage.
Anyone know of a inverter system that is smart like that?
Troy Harvey
---------------------
Heliocentric
801-453-9434
[email protected]
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