Friday, September 17, 2010

Solar Electric Upgrade

While my 4.4kw solar electric system was performing to specifications, size does matter.  Unfortunately, my budget and choice of suitable locations were limiting factors.  As a result I had a system that could only deliver 620kwh/month when I was using 1800kwh during our hot and humid July.  My solution was to create a new mounting site over my southern facing coal bin.  In addition, I designed and machined my own mounting system.  This greatly lowered the cost, and it also gave me a system that I could not find anywhere:  One that is both roof-mounted and has adjustable tilt for summer and winter.
Fortunately for me, my PV Powered 4800 inverter had the ability to handle the 5 extra panels, bringing my cost per watt down to a very reasonable $2.50, installed.  The result was a substantial 31% increase to 5.58kw and a summer monthly output averaging 812kwh.  While still far short of July's 1800kwh, it will produce a surplus in the spring and fall, when demand drops into the 600's.
Close up of the hinged mounts.  I used the identical design for both the top and bottom rows.
However, only the top row mounts function as
hinges.  The bottom row mounts are separated at the hinge pin and a 24" piece of square tubing is
placed between the hinge halves.  Bolts are then inserted through the hinge pin holes to lock the tubing in place.
These hinges allow for 22° of movement, a few degrees less than ideal.  However, achieving more movement would have required taller hinges, which would have put more stress on this design than I desired.

Panels in the winter position.  I designed the 
coal bin roof with a 45° angle.  Not the optimum
winter angle for our latitude, but a good compromise between the requirements for the coal
bin and the solar panels.

Panels raised 22° for the summer months.  Not the optimum setting, but close enough.  Overall, I'm pleased with the design.  The tilt can be changed in a matter of minutes, and even 22 degrees gives me a significant advantage over fixed systems.

After panels are raised, a link with tapped holes
ties adjacent panels together. The bolts now serve
2 purposes, attaching the legs and linking the
panels. The result is an extremely rigid structure
that does not move even in the strongest winds.

The system has been in operation nearly one year, and has performed very well, even through our cloudy winter.  The winter output is surprisingly good, given that the system had to cope with snowstorms and fewer daylight hours. Below are charts of the electric production, my consumption, and the amount the system is saving me at our current rates of $0.15/Kwh.
Under my current agreement with my utility, excess production gets rolled over into the following month.  That reduced my November bill by $15. The May surplus was $13. That, along with the 800kwh the system made in June, reduced the bill from what would have been $161 to only $28. Since the system was installed, it has made 76% of my electricity. 
Last year, the propane hot water heater failed, and I decided it was more cost effective to use a 60 gallon electric water heater as the backup heater for the Reynolds Solar heater.  This has proven to be a good decision, for my propane use for hot water dropped to zero, while my electric bill remains low, if not zero. 


  1. Hi Robert, I enjoy your posts on the Reynolds solar water heater and on your solar electric upgrade. Really fascinating all the data you how shown. I have the Reynolds solar water heater and never have been able to determine its value. How did you gather the data? Are their meters that can be fit to the solar tank or did you manually log every day. What was your process?

    1. Dean,
      I have a temperature gauge on the solar water storage tank, which is a Whirlpool electric hot water heater with the heating elements not connected. As a result, the water temperature in the tank is 100% solar. The inlet temperature is typically 60 degrees, so I would subtract 60 from the tank temperature to calculate the solar contribution to the water temperature. If by the end of the day, the temperature exceeded 120 degrees, I would record this as a 100% solar day. If the solar temperature was 90 degrees, then I would record this as a 50% day. I had to manually record this every day. This method only works because I had two separate water heaters. If you are using the electric elements in your solar heater, than this method will not work. In that case, I would put an hour meter on the electric elements and record the amount of time the elements are on. You could get a rough estimate that way.