More people are switching to Solar Water Heaters. After all, solar hot water heaters are 
old and proven technology. Everyone living in Israel has been using those for the past sixty some years, so why not?
Of course the Philadelphia area does not get the sun exposure of the Mediterranean climate. So after having installed a solar water heater, the question that comes up is what is the most efficient and least carbon intensive conventional water heater that can fill in the gaps during cloudy winter days?
If you are facing the decision of what kind of supplemental water heater to install, make sure you read this article all the way to the end.
The question:
I installed a solar hot water system in my house this past year passing the 6 month mark December 26th.
So far it has covered close to 100% of my hot water needs. I imagine one of these days I won’t have enough hot water and I’ll have to switch over to fossil fuel. I have two options:
- I could switch over to a 30 gallon electric heater, or
- to an oil furnace with summer winter hookup.
I thought it would be cheaper and more efficient to use the 30 gallon electric rather than the oil heater. Then again I’m not an expert. Can I get an opinion?
The answer can from Sean Crane:
Sean is a practicing certified energy rater and auditor. See more details on Sean Crane below
He can be reached at: info@hometowngreen.net.
His website is: www.hometowngreen.net
FINANCES:
1. Usage cost of a supplemental oil water heater
- There are 140,000 btu hrs of heat in a gallon of oil.
- A summer winter coil has a typical efficiency of .65. 140K x ..65 is 91000 btus.
- A gallon of gas-oil is $3.48 This is roughly .00004 cents per btu
- Assuming an inlet water temp of 60 degrees and an outlet temp of 120 degrees (rise of 60 degrees)
- The math then is 91000/ 60 / 8 pints per gallon = 189 gallons of water heated
2. Usage cost of a supplemental electrical water heater
- A kilowatt of electricity is 3412 btus.
- A typical electric hot water heater is .89 efficient so 3412 x .89 = 3037 btus perkilowatt
- A kilowatt is $.1736 .1736 / 3037 .000057 cents per btu.
- To make things equal, let’s assume you use 30 kilowatts of electricity and produce 30 x 3037= 91110 Btus
In this example Electricity is financially more expensive
CARBON:
see: http://www.earthlab.com/carbon-calculator.html
- Roughly a gallon of heating oil releases 22.84 lbs of CO2
- Roughly, a PECO kilowatt generates 1 lb of carbon x 30 kilowatts = 30 lbs
RESULTS:
For equal amounts of heat, the grid electricity is filthier and costs more money
ALTERNATIVE SOURCED ELECTRICITY
The problems with grid based alternative electricity is loss. In truth the grid loses 1 out of 2 kilowatts placed on it, so grid based ALT E is socially expensive, and still has a footprint
Locally produced electricity is ideal, and if solar, would likely be impacted when your water heater is, unless you had batteries, which of course have a footprint of their own.
OTHER ALTERNATIVES
1. You could look at a heat pump hot water heater which, on the surface, is 2.2 times as efficient as your present electric heater. I own one. Do not take this plunge without dropping a note: there are finer points.
2. Indoor Wood or pellet stove boiler… see http://nationalstoveworks1.clickforward.com/hotwaterstoves.html
3. ALT STREAMING:
When we install a solar hot water heater, we offer an option to run the cold water line through the ducting or adjacent to the stove pipe to the heating system or to Exchange it with boiler heat. This means the water going into the solar system is preheated by your heating system. Doing this can raise the input temp into the solar collector or the hot water tank depending on what type of system you have. Doing this can reduce the amount of run time for your backup system and can turn low output days into days with enough to get you by. Alt streaming, when coupled with GOOD evacuated tubes can often limit your back up on time to less than 10 days a year. Usually those days can occur in short light from DEC 7 to Jan 7, and they can occur after 2-3 consecutive intensely cloudy January days.
Sean Crane is a practicing certified energy rater and auditor. Sean endorses ONLY professionally designed, and installed hot water systems and HVAC systems based on load calculations made by a certified, practicing energy rater, professional thermal engineer, or ASHRAE engineer. The author specifically discourages Do it Yourself (DIY) calculation, design, and installation as DIY is seen by the author as an unsustainable and unsafe approach to the problem of giving energy upgrades and alternative energy installations the positive reputation we as a society need them to have, so that the use of more sustainable technologies can increase.
