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  • Author Author: ralphjy
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Solar System Performance - 2 year review

ralphjy

I installed a solar system on my roof at the very end of 2017.  I have a description of it in a previous post: Solar System Description .

 

I thought that it would be a useful exercise to examine the performance of the system over the first 2 years and compare it against the design goals/expectations.

 

The system that I installed was optimized for cost rather than performance.  It was designed to have around 10% margin above my annual energy usage.  Projections were based on historical averages for solar energy in Oregon.

 

Here is the initial estimate from the design software:

image

We knew the 5902 kWh number was too high because we did not do a detailed simulation for the effects of shadowing from my neighbor's trees and I even get some shadowing from his roof line (chimney) during the winter because of the low sun angle (south facing panels).  We talked about using micro-inverters to to mitigate the shadowing effects but there was a substantial cost increase vs the string inverter that I'm using.  The good news is that I've worked on reducing our energy footprint (LED lights, high efficiency appliances, smart thermostat, solar window shades, etc.) so our annual electric energy usage is about 5400 kWh vs about 8000 kWh for similar homes in my area.  The other factor that we did not properly account for is the loss of panel efficiency due to rise in panel temperature (the panels are mounted on a black composition shingle roof).

 

Here is the original ROI projection which shows the break even point at about 4 years:

image

 

After the first year I readjusted the yield estimates and it looks like we essentially generate what we use on an annualized basis.  So, we're basically running with no excess energy margin.  We have a grid tie system so we only have to pay for excess energy that we use (there's also a monthly infrastructure charge of $12).  With the Net Metering program that we're in, there is no real cost advantage to generating excess energy because they do not pay you for any excess that you generate on an annual basis.  And excess credits do not carry forward year-to-year.  Our true up cycle ends in March.

 

Here's a view of how we've done over the life of the system versus my adjusted yield estimate (5460 kWr/year):

image

 

Here is a energy usage comparison from our power company compared to 100 similar homes (single family residence with equivalent sq footage) within 0.4 miles:

image

 

Our monthly net energy usage is zero because you can utilize energy credits accumulated during the summer months against the winter usage.

 

Summary

So, the design fell short of what we had intended.  We're basically running with no margin so that as the panels age our energy production will fall short of our usage.  Our break even point is at about 25 MWh which will occur in just under 5 years.  The system total to date is about 11 MWh.  The net lifetime ROI will still be about $15K because of the State and Federal energy tax credits and the State Energy Trust rebate on installation cost.

 

My wife asks me if I'm happy with the system because I complain a lot.  Overall, I'm glad we did it.  At least we've done our little piece of reducing our carbon footprint (about 7.6 tons of CO2 to date - if you believe what the inverter reports).  The worst part of having a solar system is that it makes you realize how few days of sunlight we have during the NW winters image.  No wonder we all have SAD.

  • Hi Ralph

     

    Yes, a 5 year payback is pretty damn good. I looked into it here in the UK about 6 or more years ago. Costs were higher but so were subsidies and pay back for excess electricity. Even so, my payback, on the most optimistic calculations, was 11 years - at the age of 66, I decided to keep my money invested.

     

    I was also concerned about total carbon footprint if you take into account manufacturing and recycling costs

     

    Since then, the view from my conservatory has gained a group of wind turbines..........another technology which does not appear to justify itself on total carbon footprint!

     

    Neil

  •   Awesome update.  It's still very impressive that you generate as much as you consume.  I agree with that a 5-year payback is very respectable.  While you don't have optimal sun, you do live in the beautiful, lush green Great North West.  What you don't have in sun you have in scenery.  It's gorgeous up there.

  • Interesting update on your solar panel system. A 5 year payback is pretty respectable, especially given that there is no payment for excess generated.

     

    All subsidies and feed in tariffs for solar are now gone in the UK and they earn their keep by reducing the electricity take from the Grid of payments for the actual energy exported to the Grid when there is excess, so the installation of them appears to be slowing down now.

     

    Kind regards.

  • in reply to dubbie

    I'll need to think about my blog titles more in the future image. 

     

    No idea how to estimate the energy related cost of the panel manufacturing.  I must admit that I'm a bit concerned about the issue of recycling these panels.  They have a 25-30 year lifetime.  With all of the recent investment in solar there is going to be a lot of waste showing up all at once.  Sort of like not thinking about the negative side effects of nuclear energy waste.  It does appear that the industry is giving it some thought since most of the material should be reusable if the processing is not too costly.  Good news or bad news is that the panels may last longer than I do image.

  • I must admit when I first saw this title I thought you had installed a planetary solar system model(?) on your roof and I was intrigued as to how (and why!) you wanted planets on your roof.

     

    It was interesting to see the real-life costings of this system rather than just theory. Your system seems to be doing very well. It is not so widely known that solar panel voltage output drops as they heat up (they have a negative temperature co-efficient) otherwise they would just heat up until they exploded! You can also lose up to 10% of the power if the surface gets dirty so the panels really need to be cleaned regularly - not something always easy to do.

     

    In the UK any excess power can be sold back to the system although most systems are smaller than needed due to the limited grants provided by the government, soon to disappear all together I think. I do not have a set as I am more worried about my roof blowing off due to the extra strain. Technically, if calculating the carbon footprint you have to include the cost of manufacturing the panels, which I believe might be great than any energy related carbon saving, although that might have changed now due to mass production and better technology.

     

    Dubbie