“Why can’t I just go off the grid?” That’s a question I hear from about a third of the people who call me interested in solar. Some of them are very persistent as well. “If I’m paying thousands of dollars for solar panels I want them to work in case of a power outage.” A reasonable request for sure. One of the more interesting concerns people share with me is a fear that the fabric of society might break down. I’m serious! I get people telling me all the time. “I want to be off the grid in case the sh*t hits the fan! How can I run my house on solar and batteries?” These are not all together irrational fears. With technology changing and the US moving toward a more “smart grid” there are many people working to address the very real threat that hackers might some day take down the grid. Of course if you live in North Carolina like I do you have the added possibility that a big hurricane could cause you to lose power for a week or more.
Getting your home off grid is possible but in many cases not necessarily practical because of many design challenges and system limitations. Here are some challenges you must be prepared to address and overcome before you can consider an off grid system.
1.) Installation cost! Lets just start with the biggest reason you don’t see too many off grid pv systems. They cost alot! In the future I’ll do a post on designing and pricing an off grid pv system but for now just consider doubling what you would pay for a grid tied system, most of those go for between $20,000-$30,000. While the federal tax credit covers 30% of the cost, the NC state tax credit is 35% capped at $10,500. So any cost incurred over $30,000 dollars you will not get the tax credit for. If your local utility has a solar rebate program you likely will not be eligible. After all, why would they want to pay you to stop being their customer?
2.) System design. There is no cookie cutter approach to a well designed off grid pv system. To get your home completely off grid you have to take an inventory of every appliance in the home, determine how many watt hours they use daily, then figure out the homes average consumption and design your system to that specification. This is a job in itself and should not be rushed. The system designer plays the part of the architect and electrical engineer. He has to research and know how every part in the system works. Not many people are pro’s at this. Be prepared to spend top dollar for his expertise if you want a system tailored to your needs. Attempting to go completely off grid will likely require more than just the pv system with battery bank. How are you going to heat your home in the winter or heat your water? A heat pump requires a lot of electricity, more than your battery system can provide if it gets too cold. An electric water heater pulls a whole lot of current as well. Your battery bank will have a max output current that you will not be able to go over. For this reason making a home completely autonomous may require a solar water heating system as well as a wood burning stove or possibly a radiant floor heating system. While solar has attracted many DIY’ers a large off grid project is not a suitable DIY project and would be foolish to atempt unless you have installed pv systems before and have a full working knowledge of the products, system design and NEC. Making one mistake can cost you big time in terms of money, production as well as time and could be potentially dangerous to you and others. Very often people people approach me interested in DIY solar projects. My advice is the same you would give a teenager about alcohol, “Know your limits and don’t be stupid”.
3.) Battery limitations. Batteries are the weakest link in an off grid system. A pv system requires robust deep cycle batteries capable of discharging 50-80 percent of their total power. Common types are sealed gel, flooded lead acid. The most economical being the flooded lead acid batteries. Flooded lead acid batteries should be maintained in a temperature controlled, ventilated environment. Temperature controlled because you don’t want the water in the batteries to freeze if it drops below zeros. And ventilated because they can vent hydrogen gas. Too much of that building up is not good. Ever hear of the Hindenberg blimp? Yeah. So logistically you probably don’t want the batteries in the house or basement. A garage may work or you may have to build some kind of shed to house those batteries. Other limitations are life expectancy and maintenance. General life expectancy depends on how much you use it and how deep you cycle the batteries. You can expect 5-7 years but some manufacturers say 10. Good maintenance involves keeping the water levels in check, keeping it corrosion free and equalizing the batteries every 60-90 days.
In conclusion making your home off grid is possible but will not be cheap. Proper system design is key and may require more than just batteries and pv panels. You should also understand the maintenance involved as well as the limitations of the battery system.