We just had solar panels installed on our roof of a new house and they were turned on in January. The local city/state and utilities have a big influence on how cost effective it is. In Austin, the city has had some very aggressive rebates but they are slowly reducing them each year. Our system cost just under $20,000 and Austin Energy had a rebate good for 50%. Then you get another 30% federal tax credit. We did a 12 month interest free loan to get the tax return. Cost to us was $6500. Our system has a total of 26 panels at 260 watts for a total of a 6.76 kW system. Our energy bill has dropped from $130 to under $10. In the summer, when the ac kicks in we are hoping for about 50% to be produced by solar. Also the billing method will vary by your location. I think the two most common ones are net metering and cost of solar. Net Metering is where you are billed for the net difference of the power you get from the grid and what you produce with the panels. Austin uses a "cost of solar" method. You get billed for the total amount of power you used and then you get a credit for the solar production. This allows you to pay the normal fees and taxes that help support the grid infrastructure that are outside of the actual electricity rates. The cost of solar is a complex algorithm calculated each year, but 75% of it is based on estimated future cost of natural gas. Apparently they can arbitrarily modify this each year instead of going thru an electricity rate adjustment process that usually takes a few years.
There are a lot of things to consider:
Age of roof needs to be rather new (maybe less than 5 years) or most companies won't install on it.
Need mostly sun, ideally no shade at all, on your roof with the panels facing south, southeast or southwest (in the northern hemishphere). West might work also with the amount of power produced being limited for a full day. Pitch of the roof should be ideally close to the latitude of your location. Any shade on the panels can significantly affect the power production (see inverters below).
An inverter is required to convert the DC power from the panels to AC. I think two of the more common inverter companies are Aurora and SMA Sunnyboy. Usually you will have one inverter for the system. If you have any shade, you can get micro-inverters on each panel. The micro inverters will allow each panel to produce the maximum power. If you use a single inverter and have any shade on a panel/panels, the entire sytem drops production to the lowest producing panel. Any solar power you produce is directed to the immediate needs of your home. Any extra power produced over what your home needs "right now" is directed to the grid and available to the utility.
Poly crystalline or mono crystalline panels. Mono panels are the more mature manufacturing process where the silicon is grown from a single crystal. Poly panels are a less expensive, newer process that grows the silicon from multiple crystals. I think the actual power production of each are very similar now. Probably the biggest difference is the poly panels will have a blue color to them and the mono panels are black. If you, or your HOA if you have one, are concerned with the aethetics (panels will be seen from the front or side of the house) you may want to go with the mono panels. Also both come in a black on black frame that eliminates the silver grid that are common to the panels. If you have seen any small solar panels along the road powering a sign or cross walk signal, they are usually the blue poly panels.
Most panels are probably around 15% efficient. Sun Power produces some of the most efficient panels (in the low 20%) but they are very expensive and usually don't make sense financially. Where they help is if you have a limited amount of roof space.
The "name" rating (in watts) of the panels is based on some standard lighting/temperature conditions. You want to look at the PTC rating which was developed at UC Davis and is a more realistic estimate of the power the panels will produce. Our panels had a STC rating of 260 watts and a PTC rating of 233 watts. On a perfect sunny day they produce about 43 kWh of power and we are using about 20-30 kWh hours in a 24 hour period.
The panels wear out. The industry standard is panels will keep 90% of their capacity within 10 years and 80% within 25 years. The panels are estimated to reduce about .5% per year. Also the inverters are expected to be replaced after about 12-17 years. They are around $2,000-$2,500, depending on the size of your system. Some inverters now come with a receptacle that you can plug an extension cord into if you lose power from the grid and your panels are still producing energy. Not sure how effective this really is in practice.
There are hundreds and hundreds of panels to choose from but you may be limited on what each installer uses. You need to look at the financial viability of the company also as many go out of business. Many installers or panel companies have re-insurance policies to "protect you" if a company goes out of business. Many Chinese panels are very inexpensive but there have been a few bankruptcies. And yesterday, there was a warning from China that they expect a lot of bankruptcies in general across China in the next few years. Here is one list of recent panel companies that are no longer in business:
http://www.indianadg.net/gtm-updated-list-of-bankrupt-solar-companies-what-is-the-formula-for-success-for-solar-companies/
They seem to have good construction to prevent damage due to hail (or weight of snow). It helps that they are usually at about a 35-45 degree tilt so any hail hitting it is a "glancing" blow and there are some industry warranty standards against hail damage. Since they are attached to your home, most insurance companies probably cover it, but you may want to adjust your total $ coverage in case you had a catastrophic loss to your home. I have seen virtually nothing about reports of storm damage on the web but I imagine it happens.
Trying to do an off-grid system is very expensive due to the cost of batteries and many utilities won't allow it. So this is probably not an option unless you are in a more secluded area.
You want to get a company that is concerned with a good engineering design, good products (panels, inverter, mounting system) and good installation. Many "solar" companies in Austin are just roofing companies that sub contract everything out. We ended up going with a company called Circular Energy which I believe is limited to Texas.
Look at other installations your company has done and the type of roof mounting system they use. We looked at one house where the panels were not lined up properly. They should fit snug, not sag and all be on the same plane.
It helps to have a year's history of your energy bills to estimate the real savings. Generally, I think most people go for a system that provides 50-80% of their annual energy.
There seems to be quite a bit of hype around how much value solar panels add to your home. There are formulas based on the amount of your energy savings but it probably is more like the value of a pool. Some people will be attracted to it and some people will be turned off by it. It seems the younger generation starting to buy their first of second home is more interested in it.
There is a website called PWATTS that is used to estimate power production. It is based on about 20 years of local weather records and has variables for things like size of system, inverter efficiency, tilt and direction of panels, amount of sun you get locally, etc...It will give you a monthly estimate of your power production. These results will probably be used by companies in quotes you receive. Be sure you know if your quote is based on the DC or AC rating of your system. The AC rating will probably be about 90% less. Most companies will probably go with the default settings but some will jack up the inverter efficiency from the default 75% to give you a higher power production estimate. Be aware of what they are using when you are comparing quotes. You can play with the setting to get a better comparison.
http://www.nrel.gov/rredc/pvwatts/grid.html
There is a lot of links/forums on the web. This is one forum that may be helpful:
http://www.solarpaneltalk.com/forum.php?s=4d9a88d719a0c894c3d79a76ecfec7b3
Hope this all helps.
