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In Reply to: RE: Our system would have a battery, no mention was made of posted by oldmkvi on March 17, 2017 at 21:12:25
Our ROI on the last system is only a little over 5 years. I just paid for it from our home equity credit line. The savings on the electric bill is double the cost of the payment. After 5 years, we have no electric bill and no payment
These free deals are expensive financing scams, IMO. They put in the solar for free and they get a 30% discount on the tax credit up front. Then, they give you a guaranteed rate with a reduction from your current bill. However, they're designing the system to cover the bill and charging you a reduced rate for power for 20 years. Over time, it will cost you at least twice as much as buying it and you'll still be paying for power long after you would have paid off the system.
All systems are grid tied. Batteries add a lot of cost, require maintenance and aren't reliable in the long term or even in the short term. For example, if you get a week of clouds and rain, the system won't produce enough power to charge the batteries fully to provide power at night.
You also don't get two bills for power. With net metering, the system runs the meter backward when you produce more than you use and then, the meter goes forward when the system isn't producing enough. At the end of the month, you get a bill for the net usage or a credit for excess power. Monthly, you don't have to pay the bill. It doesn't become due until your annual 'True Up' date. At that time, the net usage versus the credits are totaled up and you can pay once a year.
In our case, we rack up credits from April to October. Those offset usage in winter. Sometimes, I'll pay a $100 in November, December and January which about covers our annual net usage or I can just pay once on the True Up date in May.
BTW: A friend of ours took one of those free solar deals and is now complaining that he's still paying the same amount on his bill. I tried to tell him.
downtime - Night/Bad Weather, add to the cost?
Seems like it only works half the time at best.
How big a system is need to guarantee enough over-production to balance out the down-time?
Obviously, you get more production in Summer than Winter because the days are longer. Bad weather does kill production, but overall, everything tends to average out, so it's not something to worry about.
First, you need to pull your old bills and find out what your average usage is per month and annually. Then, you can figure out how big a system that you need. A caveat is that your location is a variable along with the orientation of the panels. South facing is by far the best. We have both south and west facing panels. The southern panels product nearly 35% more power because they get sun all day long. Your installer has a program to calculate these variables. Or, the free solar guys should have the specs on what they guarantee the system will produce (in kW), and the number of panels and locations of the panels.
You can see the difference in the image below of the layout and production since January. The panel on the lower right side of the top grouping have partial shading in the morning which also shows in the production numbers.
The next two images are of daily production in February 2016 versus 2017. We had a lot of rain and totally cloudy days this year. But over the course of the year, those issues tend to even out.
Finally, the last image is annual production. We started with an 8.4 kW system with 40 panels. In September of 2014, we added another 18 higher rated panels or another 4.5 Kw which shows with the bigger production and since they were all south facing, they're more efficient than initial installation which was half west and half south.
Overall, on an annual basis, the production is fairly consistent. We were getting about 13,000 kWh per year from an 8.4 kW system and it went up to about 19,800 Kwh for our current 12.9 kW system.
So, the key question is what is your average monthly usage or total annual usage over a few years? Then, what would be the orientation of the panels? Other variables are potential shading issues along with where you live. Seattle gets more cloudy days than San Diego.
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