Keeping Hot Water Hot

My wife and sons are off visiting with Grandma and Grandpa this week.  The house is definitely less chaotic without two energetic boys running around and I miss that.  But their absence does allow me to do some projects that might otherwise be impractical.  

We will soon need to replace our water heater.  Ours is showing signs of age and better to address before we end up with a leaky tank and a flooded basement.  Part of my research into replacement options is to determine approximately how much energy our current water tank loses to its surrounding environment – the basement.  The best way to do this is to shut the water heater off (we have an electric heater) after measuring the hot water temperature at a faucet.  

Last night I recorded a water temperature of 120 deg. F at the kitchen faucet.  Once I recorded the temperature I was conscious of not using any more hot water, and after waiting an hour or so just to ensure the replaced water in the tank was heated, I turned off the heater at the breaker.  This evening, the hot water temperature was 98 deg. F:

Change in T = 22 deg. F (12 deg. C)
Tank volume = 50 gallons (0.19 m^3)
Water density = 1,000 kg/m^3
Heat capacity of water = 4.18 kJ/kg_deg. C
Energy loss = (22 deg. C) x (0.19 m^3) x (1,000 kg/m^3) x (4.18 kJ/kg_deg. C) = 9,760 kJ

There are 3,600 kJ in a kWh, and thus over the twenty-one hour observation, my water heater lost 2.7 kWh of heat to the basement.  That is the same as having a 130 watt item plugged in and running all day, every day.  130 watts is not a huge draw, but that accounts for about 15% of our daily electric usage.  And now for the big picture - multiply roughly 3kWhs by almost every house in the nation and that is probably close to the amount of energy we use just to keep our household hot water hot.  

So now the dilemma: purchase another water heater tank and pay close attention to the insulation, or purchase a tankless heater, which poses additional challenges such as proper utility connections.  There are also a lot of good DIY ideas here.  Stay tuned...    

 


 

The Solar Neighborhood

After installation of our solar panels (well, technically we rent them), several neighbors stopped by to talk about them.  This prompted our next door neighbors to further investigate and they eventually decided to move forward with solar. And when I got home from work today, this is how the neighborhood looked:

The neighbor's panel installation will continue tomorrow, and then they'll just have to wait for a new electric meter before switching to solar.

I am very happy with our system thus far.  Since May 9th, when we were able to turn our system on, our panels have "generated" 916 kWh, which is more than 100 kWh than we have used!  The daily output has ranged from 7 kWh (on a day that we got 4" of rain) to 40 kWh.  We haven't received an electric bill since going solar, in fact we haven't received a bill since April.  I like it!
   

Solar Cooking

My wife gave me a solar oven for Christmas a few years ago.  While there are plenty of build-your-own solar oven instructions on the web, let's just say that was one of the many projects I just hadn't got around to yet...Anyway, I like the organization she purchased the oven from.  And it works great, too.  

When sunny, the solar oven usually sustains temperatures of 250-300 deg. F., even in winter

We use it fairly often, mostly on weekends.  Today was a typical Saturday that was full of activities.  We went to the farmers market, then my wife took my younger son to the library's summer reading program kick-off, and I took my older son to the park.  Earlier in the morning, I put a pot of beans in the solar oven and let them cook while we were out.  Until I discovered the wonders of dried beans I usually would just dice some potatoes and slice some carrots for solar cooking.  

My sons are impressed with the steam, especially in the winter

When we all got home for lunch, there was a nice pot of cooked beans to supplement our lunch.  The rest of the beans will last most of the week and be part of several meals.  The solar oven, like a crock pot, is nice for cooking while you are away from home during the day.  Unlike a crock pot, the solar oven needs nice sunny weather.  However, kids won't notice a crock pot, but with a solar oven they get to experience the sun's energy (especially on a cold day) which prompts a lot of good questions.  

Powered by the Sun

Last night I noticed that the electric company replaced our meter so that we could send electricity to the grid and get credit for it.  YAY! We're now harvesting energy from the sun.  And even with today's cloudy conditions, the panels generated* more than 10 kWh of electricity than we used.    

It's been a long process that began last summer.  Interestingly, we are only renting the panels and inverter, making solar much more affordable.  The panels are owned by Sungevity and we entered a twenty-year lease with them.  There are many options available right now, for both outright ownership and renting.  Because we're renting, we are not allowed to claim the renewable energy credits for tax purposes.  Sungevity claims the tax credits and passes the savings, albeit after a profit margin, to the customer.  Purchasing solar panels and the inverter sounded nice, but the ~$30K price tag is just a bit much.  Over the course of our twenty-year lease, we will pay Sungevity approximately $10K, which is a lot of money, however, we've paid the electric company ~$9,100 in the nine years we've resided here.  Sungevity has a kWh performance guarantee.  If the system fails to achieve the guaranteed kWh output, Sungevity pays us the market value of the shortfall.  The total cost of the guaranteed output is $0.083/kWh.  Our current electric rate is $0.087/kWh, but when including the distribution charges and taxes, we pay more than $0.14 per kWh from the electric company.  Plus the guaranteed output will provide roughly 80% of our electric need.        

One of our requests when working with the specifications was that the panels had to be manufactured in the U.S.A. to: (1) support the American worker, and (2) reduce the energy consumed in transporting panels.  At first, Sungevity planned our project with panels from China.  With nothing against the Chinese or their solar products, after asking we were able to utilize panels manufactured in Newark, DE.  That's thirty miles from here.  So not only was the transportation impact low, it's also conceivable that someone living in our county works at the plant that produced the solar panels on our roof.

Going solar doesn't make us super green; there are still a lot of environmental and social considerations.  Mining the raw materials can be nasty business and I am concerned with the disposal or recycle process at the end of a panel's useful life.  Everything we do has some sort of impact on the world, but short of completely turning off the lights, I believe solar is part of a better solution.  And it just so happens that it is also economically advantageous to our household.


*NOTE: technically, the solar panels generate electron flow.