Ive been into this for some time now. You can go back and find this thread:
http://reefcentral.com/forums/showthread.php?s=&threadid=550482&perpage=25&pagenumber=1
Since then, the practice has caught on more here it seems (that, or just more people are posting about it).
Anyways, here are my suggestions to save on your electrical bill:
-use natural sunlight. If you can use natural sunlight, go for it. Its more economical and effective than solar power, as solar power has a pretty high startup cost, and even the most efficient systems are only converting about 10% of the light they take in. A skylight or solatube costs a fraction of this, and means you can skip alot of your bulbs, reflectors, etc... and your heat levels are significantly lower since sunlight only provides radiant heating. Even the most efficient bulbs (halides) still waste about 75% of their electricity on conducted heat. Even as far north as I am, its still loads of light considering our tanks are about 2' deep on average, and in the wild the corals are 5-25 meters deep.
-If you cant use natural sunlight, use the most efficient lighting possible... and no, I dont mean LED's (yet). The most efficient bulbs are still 10,000K halides. Dont like all that yellow? Well... going with a bluer halide isnt the best idea either, as outputs tend to halve if not more. Rather, use a bulb that can make blue light more effectively than halide... use T5s. A MH+T5 system is the best combo per watt that you can get. T5s can make blue light better, and halides can make daylight better. Together... whoah. Also, whenever possible, use light movers. Click on my little red house to see how mine is. I love it, and my corals do as well. A few other hobbyists in my club are trying them as well, and very pleased with the results. They make one halide do the work of what 2, sometimes 3 would be required to do. I use mine on the main display, and with the supplimental T5s, it doesnt even mess with the 'viewability' of the tank... I would actually say it enhances it. And as far as bulbs, reflectors, ballasts.... dont cheap out... you will most likely end up spending more later to replace them, and you wont be getting the 'bang for the buck' that you could have otherwise. Use lumenarc3 style pendants, since a larger reflector like this will carry light farther than a smaller pendant. Use quality bulbs and ballast combos for the best output per watt. Also, get a PAR meter. The $300 that they cost is nothing compared to what knowing actual light levels will do for you in the long run. Because of my meter, I was able to figure out the minimal amount of lighting needed for my tank, and still have SPS growing like weeds (Im looking at a frag-a-thon or bust in the next 4 months here... and the tank is new!). I estimate my meter has saved me about $1000, and easily saved those in my club about the same. Having a concrete way to measure light levels w/o having to guess is a huge saver. I dont have to guess how much, or when I have to change a bulb... I know.
-Use low wattage, high flow pumps whenever possible. The only high-head pump on your system should be the return pump, and that doesnt even need to be that large. I use an eheim 1250 for my 125g... things are great. This adds less heat to the tank as well. Use tunze streams/prop driven pumps rather than closed loops. The major argument against Tunzes is that they stick out in the tank... well... not if you plan ahead. Look at Iwan's tank... a 200g with 3 tunzes that you cant even tell are there. I am going to be using a page from his methods and making aragacrete pillars for the back of my tank (to cover the overflow/back as well) to allw the tunzes to sit inside a 'shelf' that will allow them to blend into the back wall as well as a bulkhead and piece of loc-line, if not better. If you must do a closed loop, look into ReefFlo pumps. 3600gph for 140watts with minimal heat transfer is still a great deal. Pair it up with an Oceansmotions or some 'sea-swirls' and that one pump will be hitting more spots in the tank with its output than a fixed output.
- Vents. Use a canopy, or seal the room your tank is in from the rest of the house. Heat and humidity wont show up on the electric bill from your tank, but your AC will be working double time if not more. I have helped a buddy seal off his basement sump room/frag tanks and it dropped his monthly bill by a couple hundred dollars right there... just from the AC. I use a canopy that is designed to be vented to the outside via a 100cfm fan and a 4" duct. That way, all the hot and humid air goes right outside (spouses like to note the smell has been removed as well).
-Use evaporative cooling, and a good size top-off. Use fans to remove heat from the tank's surface. The amount of heat that a fan can remove through evaporation is more than you might think because the phase change allows water to absorb more heat energy than the body of water its coming from... so you can actually cool water to 80 degrees F in a 90 degree room with fans alone. Just be sure your ATO is up to the task. Also, due to my low electrical use, my 125g doesnt even have fans running yet in the middle of summer, and it stays 80 24/7.
-use efficient skimmers. That dual beckett skimmer thats using 250 watts of electricity might be replaced by something smaller, as well as 1/10th the wattage.
-use aragacrete. Its cheaper than live rock. Its more adaptable than live rock. Its lower 'impact' than LR. Reef Ceramics are all the rage in the EU. Then you just pick a few nice pieces of 'show' LR to 'seed' the system. You can also buy dry LR by the pound for about $2 from multiple places. Its mined from dry land which was once a coral reef. After a few months in the tank... its 100% LR.
-Use passive systems whenever possible. Got a recirc skimmer? Try to feed it from an overflow. The skimmer can be smaller because it will perform that much better... getting water from the surface and all, and you will eliminate a feed pump. Click my red house for more. My return pump feeds my skimmer, my Ca reactor, my phos reactor, and carbon chambers, as well as circulating the refugium and being the return. Not bad for 20 watts (kill-a-watt reading on my eheim 1250).
AS far as BB vs DSB... I dont see the point of debating. You are going to provide the flow that your corals need. You could have 90x turnover in a tank w/ sand (I have), and a BB with much less because otherwise your zoas and rics might get blown right off their rocks. Besides, as long as you use efficient flow methods with either type, the actual savings will be negligable.