Different way to have battery backup on gridtie

This idea came directly from my previous post on a practical PV backup system. I have some grid tied modules nearby my battery backup shed and wanted to employ the grid tied modules to help out when the power was down. I decided to switch 6 modules into a 2 x 3 panel series string to feed the charge controller. The above diagram represents one string. It will deliver >100 VDC @ ~8A. My charge controller, an Outback FM80, can take in up to 150 VDC.
By using 120 VAC for the relay coils, it will automatically switch to DC mode if the grid goes down or you turn off the supply switch. Care should be taken switching in full sun/load conditions. It could shorten the life of the contacts in the relays. Disconnect the AC and DC sides of the system when practical.  You could install 4 RC snubbers on each relay or buy solid state relays. Either is kinda expensive. There may be no problem at all.
I'll be installing this over the next few days and I'll let you know how it works, or not...

Sensible Solar Battery System

It's been awhile since I last posted on this blog. We have been quite busy with our PV and electronics businesses, not to mention all the chores.
Anyhow, now that we are fully gridtied with more than our annual electric needs, I decided to develop a DIY kit for either grid backup or totally offgrid use. I knew it had to be kept simple, conservative, yet as a high performance system with quality parts. It is a 1500 watt PV rating, 48 volt 10KWh battery pak, and a 120VAC 2400 watt continuous inverter. We supply the solar specific parts, you supply the muscle and commonly available wire, gear, and hardware. It will provide about 5KWh per day on an annualized basis here in West Virginia. That may sound not like much, but if you are in survival mode or never had grid power, you'll manage. I have installed a six circuit transfer switch to run critical loads. For us, that's preserving food, a few lights, and satellite tv. Others may have different priorities. But how about water with only having 120VAC? In our case we have a spring fed cistern just below grade. This allows use of a 120 RV-type pump hooked in parallel to our regular 240 pump. If you have a deep well or city supply, you too could bury a cistern or two and fill 'em up when things are rosy. When things go down, use a similar parallel pump system. If you have a site that allows the tank to be planted up hill, you could rely on gravity to return the pumped water. Think of it as a hydraulic battery system.
This kit allows you to get involved in some fun stuff and you may be amazed how easy you could make such a useful infrastructure. We intend on using some fraction of the power every day to keep our batteries exercised and in good shape. We'll also reduce our power demand to boot. If you are interested in learning more go to diy-solar-kit  We also will provide technical resources to help you through the project or to evaluate if this deal is for you.

Power Bill

This is our power bill for December 2010 showing that we finally bought some net grid power from Allegheny Power (264KWh) Ever since the PV net meter system went online back in June, our bills have been virtually zip. Its hard to tell what we used per month last winter and spring because of the over-estimates the power company used. They are now required to read the meter every month and the net metering data is hand calculated.
This kind of bill is only possible with a 3600 watt array if you also have your usage under control. Its not hard to do, just upgrade lights, appliances and behavior. It took two years to trim our use so PV made sense.