Some results

After a few months of working out how to use solar power in my apartment, I'm ready to share some results. I'm hoping that some conservation plus offsetting some grid use with stored electricity (my battery) will reduce my grid usage and electric bill. Check out the simple graph that's reported on my ConEd bill.



There's definitely a downward trend. That may be explained by the dramatic decrease in temperature and less AC/fan usage from the end of Summer to the beginning of Spring. But look at the difference between Jan 08 and May 08.





During May, New York's temperature is significantly warmer than January. But I actually reduced my grid usage by 22%. This exercise is having a positive effect. But it will take a full year to really get a good comparison. So stick around.

Reverse current leakage

Not a bedwetting condition, reverse current leakage can drain a solar charging system's batteries at night or when the solar panel is shaded. I don't know the details, but I understand the absence or even partial shading of sunlight actually causes the electrical flow to reverse. This would explain why my solar panel was not effective when placed on my AC unit. There's occasional shading and of course a good amount of nighttime to deal with.

One solution is to use a blocking diode to allow the current to flow in only one direction.



Most charge controllers provide this protection as well. A while ago I purchased a Morningstar SS-6 charge controller for $44.00. Rather than wire up a blocking diode, I decided to introduce the charge controller into my mini-system.

Here's where I made a big mistake.



I previously followed the Xantrex manual's instructions and wired a DC connector to my 6 watt panel and plugged it into the AC charger input.

Thinking about, it seems strange that this would work....DC to AC? But it works just like the manual says it does.



Following this logic I clipped off the connector with enough lead wire to connect it to the battery connections on the charge controller.



I then wired the solar panel to the charge controller.



Plugging it into the Powerpack did nothing.



No charge...no indications.

Apparently the AC input on the Powerpack cannot handle the DC current coming from the charge controller. This makes obvious sense. But because I had successfully wired up the solar panel to the AC input, I gave this method a shot.



The correct way to do this is to use the DC/DC charging cable that ships with the Powerpack.





I clipped off one end...



...and wired it to the charge controller. The wire connected to the center terminal is the positive connector. When connecting to the battery connections of the charge controller, this connector should be wired to the positive terminal. My cable had white printing on the positive wire and no printing on the negative wire.



I then plugged the DC charging cable into the Powerpack at its DC power socket. The Xantrex manual states that recharging the Powerpack via DC will not light the charging status light. This was inconvenient considering I wasn't too confident I was doing this correctly. However, after draining the battery to 90%, I set it up to charge on my roof. After a half day in the sun, the battery was back to 100%. I'm assuming the charging setup was done correctly. I'm going to use it like this for a few days to make sure.

A hole in my bucket

After two weeks on my window AC unit, I'm sad to report my little panel has not collected enough juice to fill up my Powerpack. The week before I placed the 6 watt panel and Powerpack on my roof. It took 3 sunny days to get a full tank. So this weekend I abandoned the AC unit and returned the team to the roof.

I liked the AC solution because it was so convenient. Just plug in the panel in the morning. Unplug at night. The only thing with the placement....there's a tree and streetlight nearby that eventually cast shadows on the panel around midday. The shadows must be cutting down the efficiency.

After moving the setup to the roof I realized this process is very similar to collecting rainwater for use in an apartment. Sure, you've got a tap that delivers more water in a one minute than you could collect in a week. But efficient collection plus conservation could significantly cut into how frequently you hit the tap. Now it's just a matter of where I place my buckets.