Year End Results

We've had the solar hot water for 9 months.  We also got a new higher SEER heat pump in April.  We are definitely using less electricity,  Whether this is because of the solar hot water or the heat pump is uncertain.

In 2014, we used 9973 kwh.
In 2015, we used 8858 kwh.

Costs in 2014 were $1141.
Costs in 2015 were $955.

Savings per year: $186.

March Electric Bill

We just got our electric bill for March.  We had the coldest day of the year (below freezing) and the warmest (air conditioning most of the day).  Usage was below our 5-year daily average for March by 3.3 kwh.  The solar system was operational for the entire month.  We had a few overcast days where the water wasn't being heated by the sun, but 90 percent of the time we were getting a few hours of solar heating every day.

Over the past 5 years, April has been the month we use the least amount of electricity.  Next month's bill will be interesting.  We are saving on electricity, but there isn't enough data yet to draw any reasonable conclusions.

Sunshine Again

Finally. a nice day.  It's been cloudy and rainy the past few days.  Today, the 40-watt solar pump ran constantly from about 9:30 until 3:15.  High today was 78.  Water temp from the tank peaked at 107.  I can't believe I am looking forward to getting our next electric bill!

Cloudy with a Chance of More Clouds

I have posted all my past musings so now I'm posting in real time.  We've had the system for a few days and I've been logging temperatures whenever the solar turns on.  It ran a lot the first few days, but as the water in the tank gets warmer and the system reaches an equilibrium, it turns on less frequently.  Particularly on cloudy days.(Duh.)

One nice surprise is that on sunny days, the system is kicking in way earlier than I expected.  There have been days where it turns on as early as 8:15.  The water at the bottom of the tank is 80 degrees, but the panel, in partial sun, is warmer.

On sunny days, it operates more or less continuously from 8:30 until 3:00 PM.  The highest temperature of water leaving the tank was 107, which means the collector temperature was 115.  The high that day was 76 and there were periods of clouds.  According to the Wayne's Solar sales rep, the collector will reach 140 (which is the recommended max) once the weather warms up and the sun is higher in the sky.

Today is supposed to be cloudy all day so we probably won't get much activity.

Even with the cloudy days, we haven't run out of hot water.  We've been able to use the dishwasher set to normal without it switching to pseudo energy boost.

I will be monitoring electricity consumption.  Because we have a smart meter, we can see a graph of our electric use on an hourly basis.  At this time of year, we average between 1 and 1.5 kilowatts per hour.  I'll post more when I have more data.

System is Relentless

2/21/15

Solar kicked on at around 9:15.  Temp from tank was 78, return was 86. My wife took a shower.  I took a shower.  I turned the recirculation pump on at noon so we could wash the dishes in the dishwasher.  Up to now, we have needed to use the energy boost feature of the dishwasher because the water going to it wasn’t warm enough.  We have a “smart” dishwasher so if you set it to normal and the water isn’t hot enough, it switches to a pseudo energy boost.  Instead of running for 90 minutes, it runs for 168.  Energy boost runs for 132.

After circulating hot water through the house, we turned on the dishwasher to normal.  The water coming in was hot enough so it only ran for 90 minutes.  So far, so good.  Right after we turned on the dishwasher, the solar system stopped sending water to the roof collector.  It is cloudy today so the collector isn’t hot enough.  The last reading I took before the system shut down was tank temp = 83, collector temp = 91.  I hope the sun comes out so we can replace the water the dishwasher used.  Energystar dishwashers are only supposed to use 5.8 gallons of water.  Our GE uses only 3.8 per cycle.  That means we shouldn’t lose too much heat from water replacement in the hot water tank on this cloudy day.

The solar system goes off when it is cloudy but as soon as a bit of sun peeks through, it goes on again.  Fascinating.  It is such a simple design, but is relentless at getting the sun to heat the water.

Installation Complete

2/19/15

9:25 - Air temp is 39 with 25 mph wind gusts.  The techs arrived and assessed the situation.  I think we’re all on the same page regarding what has to be done to finish the job.

11:24 - The panel is on the roof.  Temp is still in the low 40s.  They are now threading the soft copper pipe through the attic to the roof.  Lots of shouting back and forth.  No swearing though.

1:00 PM - The copper pipes have been run through the attic and through the garage attic.  They still have to solder them together and insulate the pipes on the outside of the house.  Temp sensor wire also run.  The panel should be nice and warm by now.

They are now adding the freeze valve and connecting the pipes and the sensor on the roof and connecting the pipes from the soffit to the garage.

3:15 PM - They are done.  Still need to install flashing on outside of house.  System is running.  The tech said it would take at least another sunny day for the system to get up to speed.  He turned the hot water backup a bit higher.  The sales rep will be coming with the inspector sometime and will finalize the FPL stuff.  The Pump is set to go on when the collector temp is 8 degrees warmer than the tank temp and shut off when collector temp is 140.  The LED that indicated that the pump was working turned off at around 3:45.  The collector is mostly in shade at that point.

8:44 PM - I noticed that the temp outside was down to 38, so I checked the controller.  All 3 LEDs were on, which means that the freeze protection circuitry is working.  When it gets close to freezing, the system sends warm water to the collector to keep it from freezing. As I watched it, it shut off.  So far, so good.

2/20/15

7:00 AM - 29 outside.  Three LEDs are on.  I checked the roof.  The other valve drained the water out and there is ice on the gutter.  The antifreeze protection is working.  I’m going to monitor the LEDs today to see how much heating we get from the sun.  High today is only supposed to be 50.

8:45 AM - OMG.  2 LEDs are on and it’s 36 outside.  My wife took a shower this AM and used a few gallons.  The panel is mostly in the shade but it’s warm enough to have the water be heated.  Using an instant read digital thermometer, it looks like the water leaving the tank is around 62 - 63 degrees.  I’m going to keep a log to see what it does today.

I talked to the sales rep.  The city inspector is coming today.  If flashing isn’t needed, we should be OK.  The flashing should be ready next week.  The rep is coming on Monday to finalize FPL rebate stuff.

11:15 AM

The city inspector came.  Looked at the tank.  Checked for leaks and signed off.

12:45 PM

Air temp: 49.  Water temp out of tank = 98.  Temp back to tank = 109.  Encouraging.

3:00 PM - one LED lit.  The last reading was temp out = 105, temp in =112.  It will be interesting to see what happens tomorrow.

Incomplete Installation

2/18/15

We ran out of hot water this morning.  After some googling, I found out that the tank we have will only provide 40 gallons of hot water when it is running solely on backup because it only has one heating element.  Regular hot water tanks have 2 heating elements. I sure hope once the solar system is up and running that this doesn’t happen again.

This experience led me to do some research on heat loss.  If we get cloudy days, how long will the water in the tank stay warm?

According to one site, “due to advanced insulation technology, water heated by the sun can remain hot for up to 80 hours after being exposed to sunlight.”

In the owner’s manual for the system we are getting, it states: “During normal operation, without any use of hot water, your solar storage unit should not lose more than 2 degrees per hour.”  That sounds overly conservative to me based on a formula for heat loss at Build it Solar, which is one of the most useful web sites on residential solar energy.  I think I am doing these calculations correctly, but I was an English major so there are no guarantees.

Heat Loss = (Area)(Tin - Tout)/(Rvalue), where Area is the area of the inside of the tank, Tin is the temperature in the tank, and Tout is the ambient room temperature where the tank is kept.

The Rheem tank we are getting has an R factor of 17.3. The area inside the tank is 38 sq ft.  Assuming a temperature in the tank of 120 degrees and room temperature in the garage of 60, you get the following:

Loss = 38(120-60)/17.3

Loss=131 BTU/hr

A BTU is the amount of energy needed to raise (or lower) the temperature of one pound of water by 1 degree.

1 gal of water = 8.3 lbs

80 gals of water = 664 lbs

664 BTUs are needed to raise temp in tank 1 degree.

664/131= 5.06  hrs to lose 1 degree based on the above calculation.

If you assume other factors for heat loss and take a more pessimistic scenario, we could postulate a loss of 180 btu/hr.   Then

664/180 = 3.7 hrs to lose 1 degree

Based on these calculations, it would take 3.7 to 5 hrs to lose 1 degree if temp in garage is 60.  In 15 hrs overnight, the loss should only be 3 to 4 degrees.  Of course these calculations don’t account for cold water entering the system so they would be best case.

If you use the 2 degrees per hour loss mentioned in the owner’s manual, that would be a loss of over 1300 BTU/hr, which seems high.  According to the formula, the R value of the tank would only be 1.7, which is basically uninsulated.  Like ROI, my heat loss numbers have a wide range. Experience with the system will be the true test. However, since we don't have any experience with the system, I spend a lot of time doing theoretical work that may, in the end, be totally off.

Here is some more information about how warm the solar collectors can make the water from Blue Pacific Solar, a California vendor.  

A solar collector consists of a network of pipes through which water is heated. Collectors come in various sizes, with 4 by 8 feet the most common. On a typical summer day (sunny and warm), the fluid in the collectors reaches 140°F to 180°F. On a clear winter day (sunny and cold), it can reach 120°F to 150°F. When it´s cloudy and warm, collectors can reach 70°F to 90°F, and when it´s cloudy and cold, 50°F to 60°F. As long as the temperature in the collector is greater than that of your incoming cold water (usually about 50°F), your solar hot water system is saving you energy.

I hope they can finish the installation tomorrow.