I am trying to build a system to augment my grid power for day to day living and to act as a backup system indefinitely if the grid goes down. Obviously in the backup mode it would be for "essentials" only. I consider the essentials to be as follows: A newer model (energy star) freezer, a newer model (energy star) fridge, some small lighting and the blower for my furnace. As far as the blower goes, we are planning on switching to a 97% efficient furnace with a DC blower for our main (propane) heater before next winter. We also have a wood fired central furnace the has a blower and is piped into the HVAC. I am working on getting that up and running. I am not sure what the blower motor is on that, but I could easily install a DC on there as well I imagine. In back up mode we could lower the temp inside to reduce the load from the blower. As it is we only keep it at 60 in the winter. I have a number of questions, and I am sure there are things I should know that I won't even think about so feel free to chip in with any info you can. As for my questions here are the big ones. Solar panels: How do you figure out how many you need? I understand I can consult my electric bill or a kill-a-watt meter and figure out how much I am using and compare that to the ratings of the panels. But I assume those ratings are peak power and I am sure the sunshine is variable. So how do you figure the real life variables? -also, do they all have to have the same rating to be in a system together? My imagination tells me no, that each panel will simply contribute it's share and they should all work together. ?? -also can they be located in different locations and wired together at the box? Battery bank: How do you size the battery bank. Obviously if one of the things I want to power with this is the furnace blower, and it runs more at night than during the day, then I will need a considerable reserve. -also do they have to have the same rating to be in a system together? This seems to be more critical to me than the panels. I just can't seem to figure out why. -also what kind of batteries are best for this application? deep cell, marine, sealed, refillable, 12v, ??? -also, what voltage do you use? all 12v batts in parallel for 12v system or sets of 4 12v in parallel for 48v system? etc to invert or not to invert: Seems silly if I have DC powered fans to invert to AC and then back to DC to run them. I also know there can be significant line voltage lost in DC wiring. I don't know where one overrules the other. Same question for DC lighting? I will have to invert some of it, since I have never seen (or at least don't own) a DC deep freeze. Can you run DC loads direct from the bank and run an inverter. Seems like these should both just be different loads on the bank. leaving room for expansion: I would like to get this size system up and running fairly soon and for as little money as possible. But I can see wanting to upgrade as funds permit. In what areas should I leave myself room to grow? Inverter, battery box ??? Thanks in advance. I have been searching this forum and others to find some of these answers on my own but I appreciate whatever help you can offer. If some of these things are covered somewhere I would appreciate links as well.