Going off-grid is the ultimate dream of those of us here, but if your house is leaking its heating/cooling, using more water then needed, burning extra energy when operating appliances and lights, then you need to fix that first.
You should make sure that your home is as energy efficient as possible before investing in your alternative power. There is no reason to invest more money for a bigger system then you need. Yes, I’m sure we all dream of being a big power company, like Constellation :-( . Okay, that was a little overboard I admit.
A energy audit is the logical first step to making your home self-sufficient. There are some great resources out there to help you do this yourself. The U.S. Department of Energy has a guide to do-it-yourself, as well as the Home Energy Checkup from the Alliance to Save Energy. You can also get a professional energy audit, since they offer the blower door test and may also include a thermographic scan. You can check with state and local governments about locating one.
Also being efficient will lower your monthly cost so you can buy the alternative power system o your choice. Plus you should need a smaller system as you will not need as much power as before you improved your home. Some estimates the annual savings of over $600 a year over a standard home and appliances. This money could be put to great use on taking your home off the grid.