We recommend between 5kW and 10kW for a typical house. We will use an 8.0kW system for our examples.
Solar systems are usually sized so that they produce enough power to equal your average electrical bill. The system will then produce slightly more power than you use in the winter and slightly less power than you use in the summer.
It is not a good idea to produce substantially more power than you will use during the course of a year because the power company pays a very low rate for the excess power that you generate.
How much money will this save me on my electrical bill?
A typical 8.0kW system will save you about $150/month on your electric bill.
Here in St. Petersburg, we have about 5 average sun hours a day. This means that an 8kW system will produce roughly 40kWh per day. Over the course of a month, you will produce about 1200kWh. If your electric company charges 0.125 cents per kWh, this will save you $150/month on your electric bill.
How much will a solar system cost?
The installed cost of an 8kW system should be around $22,000. ($15,400 after the Federal Rebate.)
The installed cost for a solar system is usually around $2.75/Watt. This means that an 8kW system should cost around $22,000. There is currently a federal rebate of 30% which reduces this to $15,400.
Some things that may increase your cost per watt:
Smaller system size
High efficiency panels
Some things that may decrease your cost per watt:
Larger systems size
Standard efficiency panels
What is the payback period for a solar system?
At $150 of savings per month, it would take between 8 and 9 years to pay back the system cost of $15,400. However, with financing, most people can start saving money from day one.
Most customers will finance their solar system. A typical loan might be for 15 years at 6% interest. The monthly payment on the loan ($125) would be less than the money you are saving each month on your power bill ($150).
You are also insulated from any increases in the cost of energy from the electric company.
Finally, after the loan is paid off, you own the solar system outright.
How long will a solar system last?
Solar panels are usually warranted to produce at least 80% of their original power rating for a period of 25 to 30 years. The panel life is probably much longer than that. The power electronics (inverters) are usually warranted for 15 years.
Should I install batteries with my system so that I can go off-grid?
No. We do not feel that batteries are financially beneficial yet.
Here are some reasons why we think batteries are not a good investment:
1. The state of Florida has net-metering laws that require the power company to let you use the electrical grid as a free battery.
2. Batteries are still quite expensive. (For example: A Tesla PowerWall battery costs about $8000 after installation. You would need several of these batteries to go completely off-grid.)
3. Batteries degrade over time, and will need to be replaced periodically.
4. There are laws that prevent most people from disconnecting their house from the electrical grid.
Will my solar panels run my home when the power is out?
No, unless you install some very expensive batteries. Click details for some upcoming options.
A traditional gas-powered generator is probably the best choice for power outages today. We believe that there will be some better options in the very near future:
If you own an electric car, then you might be able to purchase a Vehicle-To-Home charger that lets your car power your home during a power outage. Nissan has offered this system in Japan for several years now, and is currently expanding to other countries.
Enphase recently announced that their future micro-inverters (2019 release date) will provide power during an outage.
Finally, battery prices are falling quickly, and they should be a viable solution for power outages in just a few years.