I've finally put together some graphs of my electrical and gas usage. Please note, that I know our electrical usage has gone up considerably because in Sept we had a new baby and we use cloth diapers; i.e. the dryer has been running non stop.
That being said, let's take a look at our gas usage for the past 6 months.
In May, our furnace started leaking gas (it's old). I didn't catch it for a day or 2, so that's the reason for the high gas usage. However, when looking at the rest of the months, it's obvious how much gas we saved compared to traditional water heating. Also, you can see gas usage going up in Oct. probably because I turned up the heater with the new baby in the house
Electric usage on the other hand has gone up, which is to be expected since the system uses an electrical backup. Obviously the colder and rainer it get's, the more we use the backup. If you read my other post, I think I could have tuned the system better last summer .
When the electrical backup kicks in is a mystery I'm just starting to solve. In Nov., I purchased a monitor which just hooks on over ones meter. It works great and has helped us to understand how we can avoid using the backup. It's called a Home Energy Power Cost Monitor and I found terrapass had the best price on it.
One important issue the Power Cost Monitor has brought to our attention is the fact if we just pull up the bathroom sink handle in the middle (for warm water), the water heater backup comes on if the tank is a bit cold. Basically, as soon as there is hot water flow, it will kick in. Most of the time, the water isn't on long enough for us to get the hot water in the sink so we're wasting power and hot water. I think I may switch out those combo knobs for ones with separate hot and cold water.
Finally, since my gas usage has gone way down, but my electrical usage has gone way up, I've taken my electrical and gas usage for 2008 and mapped them to 2007 prices.
Once again, I'm not sure this graph is fair since my electrical usage has significanly increased since Sept due to the drying running much more. Also, 2007 gas prices seemed to be higher then 2008 (which skews the results a bit). But, I'm thinking that if you want a solar water heater in order to save money in the long run, it may not be the way to go due to the high inital cost of the system. However, since I do plan on eventually putting up solar panels to offset my electrical, the cost of the solar water heater in that situation may pay for itself quickly.
I'll keep running the numbers and updating the charts as I figure out best practices over the next 6 months. Hopefully, by next year I'll have a system in place which will make significant difference in our electrical usage. At this point, I think I'm about breaking slightly north of even with my electric bill (when I consider the higher dryer usage).