Calculating energy cost of lamps and appliances

Conserving energy benefits the planet, while also conserving costs.  With this in mind it is helpful to be able to calculate how much money one saves by replacing an inefficient appliance or lamp with an energy efficient one.  For this example we will look at replacing an old 100 Watt incandescent lamp (which are being phased out around the world) with an equivalent 13Watt 800 Lumen CFL (Compact Florescent Lamp) and another equivalent brightness 10W LED lamp.

First, let's review the three salient electrical properties we are looking at here.  Volts which for the sake of this discussion is the available Voltage at a standard electrical outlet in the US which is 120 V.  Amps is the amount of current, and Watts is the product of Volts and Amps (W = V x A).

13W 800 Lumen CFL

In order to calculate cost, we first need to figure out how much power we will be billed for on a monthly basis.  Electrical power is billed by the kilowatt hour (kWh) which means 1000 W per hour.  Or another way of looking at this would be the equivalent of a 1000 W heater turned on for one hour.  The average cost per kWh in the US is approximately $.10, however that rate varies significantly from state to state and region to region.  Here in Maine we are paying approximately $.15/kWh.  It is also worth noting that the percentage of renewable energy sourced electricity varies significantly.  In New England we have the RGGI (Regional Green house Gas Initiative) that mandates a minimum amount of renewably sourced electrical power.  In Maine about 30% or our power is renewable sourced much of which comes from Canadian hydro, with the remainder sourced from biomass, wind, and solar in-state.

So let's start with an old-fashioned 100 W light bulb and assume that it is on in your living room for 6 hours a day.  To calculate how many Watt hours (Wh) are used per day we simply multiply:

100 Watts X 6 hours = 600 Wh

Which can be expressed as .6 kWh
Since we are billed by the month, we can multiply this by 30 to determine how many kilowatt hours per month we will be billed for:

.6kWh X 30days = 18kWh/month

To determine our monthly cost for this lightbulb, we simply multiply by the electric rate, so let's assume the US average of $.10:

18kWh X $.10 = $1.80/month

That doesn't look too bad does it?  But if you run the math for an energy efficient compact fluorescent lamp you get the following:

13W X 6hrs = 78Wh

.078kWh X 30 days = 2.34kWh/month

2.34kWh X $.10 = $.23/month

So by replacing that old style lamp with a compact fluorescent you would be saving $1.57 every month while also reducing fossil fuel emissions required to generate power for this electricity.  If you do the math for a 10 W LED lamp it comes out at $.18 per month with a net savings of $1.62 every month.  These lamps are so inexpensive now that you will recoup the investment within 5 months and since LED lamps last significantly longer than incandescent lamps it is a gift that keeps giving both to your wallet and to the planet.  Also, LED lamps contain no mercury.

9.99W 800 Lumen LED lamp

If like me, you have been using CFLs for years and are now in the process of upgrading to slightly more efficient LED lamps, please be sure to recycle the CFLs responsibly since they contain an average of about 4mg of mercury.  Lowe's stores have bins where you can return CFL's and also rechargeable batteries and plastic bags right next to their returns counter.

Recycling bins at Lowe's - next ro returns counter

So next time you go shopping for any electrical device from a lightbulb to an appliance.  You should start by looking at the label on the appliance you are replacing to see how much power it uses and do the math to figure out what it is costing you now and how much energy the new one will save.  If the nameplate on your appliance only shows the power in Amps, then just multiply it by 120 V to get Watts.  

Newer appliances are often more efficient.  For instance, it is generally assumed that if your refrigerator was made before 2000 that newer ones will be significantly more efficient.  So you will not only be saving money, you will also be doing the planet a favor by reducing CO2 emissions from the fossil fuels used to generate electricity.

A real-time energy display for my solar power system

Ever since one of my electronic parts suppliers (MPJA) got in a line of cool blue digital meters, I have been applying them everywhere.  See my recent blog posts describing the gauge I added to my solar charged electric lawnmower, and temperature gauges that I added to my solar hot water heating system.

When I give a tour of my renewable energy systems, I point to the circuit breaker panel where the 240 V AC comes in from the roof mounted solar array and feeds out to the main breaker panel.  

Breaker panel, new meter (circled) and Envoy

Next to it (the white oval device) is the Envoy web Gateway for the Enphase microinverters on the roof.  

Envoy Enlighten live web portal

The Envoy allows real-time monitoring of every solar panel and creates a live web portal (that I embedded in my web site) showing performance of each panel and how many watts it is producing right now and over time.  The problem is that the Envoy only shows total wattage in a small hard to read small display, along with a few other statistics like the number of microinverters reporting and the total megawatt hours produced. 

What I needed was something that can be seen easily that shows the amount of power my array is producing in real time.  So I installed a multifunction meter (circled in the image above) that displays  Volts, Amps Watts, and kWH on a clean brightly lit display:

Now it is easy for me to tell people as I show them my system that it is currently generating 4497 Watts, and if a cloud goes by one can see the numbers changing dynamically.  The number at bottom right shows kWh since the meter was last reset (= 1.6MWh).  My system generally produces between 4 and 5 MWh per year.  As a geek, I have to admit that I am a sucker for a sexy blue techno glow display!

A new meter for my solar charged electric lawnmower conversion

Okay, so I am a geek!  11 years ago, I converted an old gasoline lawnmower to electric by replacing the gas engine with an electric motor and a deep cycle 12 V battery that I charge from solar panels.  I wrote a detailed blog about the construction of this mower and many other people have built their own.  While commercial cordless lawnmowers exist, they are relatively expensive, plus it is much more fun to build your own.

The original design included a voltmeter, amp meter, charging jack and circuit breaker power switch mounted near the handles.  The meters are standard automobile components, but they were unreliable and the Amp meter would get stuck often and I never really bothered to look at it very much.

An electronics parts supplier I use a lot (MPJA) has been getting in a line of digital meters that can display multiple properties and I decided to replace the old meters with a meter that can display Volts, Watts,  Amps and Watt hours.  At a cost of around $18, I consider this sexy meter a real bargain.  Click here to get a copy of the manual. 

 The image above shows the meter installed with the motor running before I took the mower for its first major test drive.  So with the blade spinning, it is drawing about 140 W and as I mowed into the taller grass, that peaked at around 250 W.

It took an hour or so to reconfigure the mower wiring to make it compatible with the meter and its current sensing shunt. 

After mowing a section of lawn for 10 minutes or so, the screen above shows that I used 34 Watt hours and the battery voltage slumped below 12 V on my brand-new deep cycle AGM battery.  This is the first time I have been able to quantify how much energy the mower actually uses!  I was watching the Amp numbers ranging from 12.5 to 20 while mowing (or about 150 to 250 Watts).

When I plugged it into the 40 W solar panel mounted to the roof of my garden shed, the voltage came back up to 12.56.  The battery is usually topped off in five or six hours of good sunlight.  Note that the display has a cool blue "techno glow" back light - not something that is very useful for device used mostly outdoors in bright light, but it sure is pretty.  I installed a power switch to the left of the meter to prevent it from draining the battery between uses.  The meter only uses about 2.8mA though, so I could just leave it on.  

6 week later
I recorded the Watt Hours (Wh) for each time I used the mower and found that I am ranging from 28 to 53Wh each time depending on how much area and how tall the grass is.  This is not a lot of power - and of course it's all free from the sun.  I also burn a lot of calories pushing this Beast around!

Solar powered motion sensing yard lights

I live in rural Maine where there aren't any streetlights and on a dark moonless night it can be hard to navigate from my parking area to the front porch.  Recently, I purchased a set of four motion sensing solar powered yard lights that I am very pleased with.  The ones I purchased were made by URPOWER, but there seem to be many manufacturers of nearly identical products that range in price from around $10-$15 each.

These clever lights require only minimal solar exposure during the day to charge up their internal battery.  And like exterior floodlights that come on with a motion sensor, these ones do the same thing but only come on for 30 seconds.  They respond to someone moving from up to 16 feet away and provide a good bright light.  This clever strategy allows these lights to be very efficient while creating a large pool of light.

I have two that are sufficient to light my front porch steps and others placed around the yard to help people unfamiliar with my property to navigate from the parking area to the porch.  I consider these relatively inexpensive lights to be a very good investment and so far they have survived six months through a Maine winter which is a testament to their hardiness.  They get excellent reviews on Amazon.

If you have an area in your yard that needs lighting, but you don't want to go to the great expense of pulling AC wiring, then this may be an optimal solution that is extremely effective.

The benefits of a rain barrel

Rain barrel on the corner of my front porch
with raised vegetable beds visible in the background
and Envoirocycle composter on the right

Over 10 years ago, I installed a rain barrel on my front porch that catches rain from hundreds of square feet of roof on my house and front porch.  While commercial barrels are available, I found that the nearby rural feed store sells used plastic 50 gallon fertilizer barrels for about $15.  All I had to do was paint it a dark color to prevent algae from growing inside and put an opaque cover on top that lets water in.  I added a hose bib at the bottom and an overflow pipe near the top that drains out into the garden. 

hose bib at bottom of tank

It was a simple matter to modify downspout with an angled section that can be reversed to divert water away from the barrel as needed.  Due to my large roof surface area, it only takes a few tenths of an inch of rain to fill the 50 gallon barrel.  I sited the barrel up on my porch in order to have it high enough to drain well into the garden.

From an energy efficiency and sustainability perspective, this reduces the electrical usage of my 1500 Watt well pump.  In a dry summer I can go through hundreds of gallons to water my vegetable beds and flower gardens.  I don't worry too much about the lawn which is mostly weeds that I just cut down as I am less concerned with appearances than I am functionality.  In my small raised vegetable beds, I grow rhubarb, strawberries, basil, chives, nasturtium, sugar snap peas, cherry tomatoes, and some occasional herbs.

Solar water heater dashboard upgrade

 When I installed solar collectors for heating the hot water in my house back in 2006, I decided to add a small "dashboard" in the kitchen to monitor the temperatures.  Since I am an electrical engineer, I was able to cobble together a device that displays collector temperature, storage tank temperature, and a green light to indicate when the circulation pump is running.  A red LED indicates low antifreeze fluid in the collector overflow  tank.

Original solar dashboard

 There is more detailed information about the construction of this dashboard on this page of my website: http://www.arttec.net/SolarDHW/10_Dashboard/index.htm
Basically, it uses digital volt meters with LM34 temperature probes that produce a voltage that directly correlates with temperature so that 78.1° is represented by .781 V.

 Over the years I have grown accustomed to looking at this dashboard to confirm that the system is working, and also to decide when to take a shower, run the dishwasher or clothes washing loads by looking at the storage tank temperature and seeing when it has peaked during the day.  The only drawback is the displays did not include a back light and sometimes were hard to read in the evening and nighttime.

I recently came across a new temperature meter designed for monitoring heat exchangers in high-end gaming computers. They are much more attractive, include a back light and use standard 10K thermistors as temperature sensors so I ordered a few to see if I could adapt them.

Temperature meter for heat exchangers

 These meters are available from MPJA (click the image above for details) and also on eBay for under five dollars.

When I received them, the first thing I did was cut off the computer power connectors and connected 5 VDC from a wall power supply to the red and black wires.

Removed computer power connector

 Then I cut off the temperature sensor and replaced it with a standard 10K thermistor that I sell as an accessory for the solar temperature controller products I manufacture (ART TEC Solar).

Original sensor above and standard 10K thermistor below

 I used an 8 conductor CAT-5 computer cable for the wire run down to my solar heating equipment in the basement.  I used two wires each for the sensors, and two wires each for the LED status monitors.

 I mounted the 2 meters in a standard plastic box and mounted it to the window frame above my kitchen sink in place of the original dashboard.  I find these meters much more attractive and they are easier to read day and night.

Updated solar dashboard

 Here is a larger view of the meter next to my kitchen window, right above the sink:

 I am quite pleased with the more contemporary styling of this new dashboard.

Easy composting using an Envirocycle

Nearly 20 years ago I purchased an Envirocycle composter and have used it continuously ever since.  This elegant and simple to use device has been around for over 25 years and is made in America from recycled plastic and shipped in packaging made from 100% recycled materials.  

I put kitchen scraps in it every week or so and occasionally add dry materials as needed such as sawdust or leaves in the fall.  Every week or so I rotate the barrel 3 full rotations, this mixes the contents and accelerates the composting process.  When everything is in balance, there is little to no smell and I leave the unit off the side of the front porch where it is easy to rotate.  The black drum warms up in the sun which also enhances the composting.  Liquids drain through into the liquid collecting base that can store up to a gallon of compost tea.  In the spring and fall I drain this tea into a 5 gallon bucket and then dilute it about 10:1 and use it to fertilize my blueberry bushes and raised vegetable beds.  When I want to use the compost, I simply roll the barrel across the garden to where I need to empty it and then shovel the compost directly onto the vegetable bed or locations where it will be applied.

adding fresh kitchen scraps

Draining the compost tea from the base

diluted compost tea on the left

Picking up roadside trash

Trash from 3/4 mile of local roads (I removed the redeemables and recyclables).

For the last few years I have been walking around my neighborhood here in rural Maine picking up roadside trash every week.  While there is little to no trash on my small dead-end road with about a dozen houses on it, the moment I get out onto the more widely traveled roads I find a lot.  In fact, every week I fill a 15 gallon trash bag by walking about a half mile in each direction on the three roads that intersect the end of my road.  Generally, I find a lot of beer cans and bottles, miniature liquor bottles, cigarette packs, and general fast food packaging and other trash.  Here in Maine I can redeem most of the bottles and cans for 5 cents each so I often pay myself over a dollar a week.  The rest gets sorted into my trash or recycling bins.  During my walk this afternoon, I was thinking about all the reasons that I do this and I thought I would share them with my readers in the hopes that I can inspire some of you to follow suit and pick up trash in your neighborhood if you live in a neighborhood where outdoor trash is an issue.

• Community service - I value my community, and Maine is known as "Vacationland" so it is important to keep our roads clean and attractive.
• Environmental stewardship - 'nuff said.
• Treasure hunt - as I walk searching for distinctive shiny or bright objects, there is an element of treasure hunting and the reward is often 5 cents.
• Good exercise - I generally walk between two and 3 miles and the roads are hilly enough that I raise my heart rate and work up a sweat even on cold days.  It's not just walking but all the bending and stretching that makes it a good aerobic workout.  I often stray out into the fields on each side of the road where windblown trash shows up and there is some scrambling around to get there and back.
• Visible activism - by being highly visible on the road and picking up trash I am hoping to inspire other people to follow suit, or at least raise their awareness of the issue.
• Grateful neighbors - every now and then a neighbor will stop and say "thank you".  It's not the main reason I do this but it's nice to be acknowledged.

I bought less than 40 gallons of gas last year and drove about 8000 miles!

2012 Chevy Volt

I bought my Chevy Volt back in May 2012 and have over 50,000 miles on it now.  I decided to review my records to see how much gas I have used and was pleased to find that in all of 2015 I purchased only 39.28 gallons of gas and drove about 8000 miles.  My average purchase was for 2.7 gallons because Chevy recommends that you only put in one third of a tank in to keep the weight down.  There's no sense in hauling around gallons of gas that you never use.  So my total expenditure for gasoline last year was $108.55.

My Volt uses around $40-45.00 worth of electricity a month, and in the summer that is more than offset by my solar array.  So for 5 months I am literally driving for free on sun power.  In the winter months when we have less sun in Maine my electric bill goes as high as $70, with most of that going to power the car.  In Maine over 30% of our electric supply comes from renewable sources, so the bottom line is that the carbon footprint of my car is negligible.  That is the main reason I own it.

Tor those that may be unfamiliar with the Chevy Volt, it is unique in the industry because it is an electric vehicle with a built-in "range extender".  My model has an electric range of approximately 37 miles under ideal conditions.  When the battery runs down a four-cylinder gas generator kicks in that maintains a battery level allowing the vehicle to continue driving at around 40 miles per gallon.  Since most of my driving is local, I rarely use gas.  The vehicle does turn on the gasoline engine generator in the winter occasionally to help warm battery when temperatures drop below 20°F.

I recently test drove the 2016 model Volt.  The vehicle has been completely redesigned although it it looks rather similar from the outside - with some sexy improvements to the style lines, the interior is quite different.  There are so many changes in its design that it is essentially a different vehicle entirely.  The driving experience was even more sporty than my model because the 0 to 30 acceleration time has been shortened quite a bit, so it literally surges forward and burns rubber if you tromp the accelerator.  This model has a rated 52 mile electric range and gets better gas mileage when in "range extender" mode.  

2016 Chevy Bolt

I am now struggling  with whether or not to upgrade to the new Volt or to go with the brand new all electric Chevy Bolt that will be released towards the end of this year.  This impressive vehicle has a range of over 200 miles per charge and will cost around $30,000 after the $7500 federal tax incentive.  It is amazing that GM has managed to trump Tesla and bring out an affordable electric vehicle well before the much-anticipated Tesla model 3 has been released.  The real issue for me is whether or not I want to deal with the range anxiety issue when taking a long road trip.  I have grown so comfortable with the idea that the Volt offers me a no-worry option of driving as far as I want without any concern that it may be challenging for me to accept the limitations of an electric vehicle range.  I sometimes take trips down to Boston which is around 170 miles away.  While there are more charging stations available in the city, it would be inconvenient to have to take many hours to charge the car up.  Not to mention having to take a cab or public transportation between the charging station and my desired location.

More fun with time-lapse photography

In my last blog post, I had just started getting to know my new Brinno TLC200 Pro time lapse camera.  Since then I have made a number of videos under varying conditions, all of which have turned out really well.  Here's a picture of the camera:

(Click here to purchase on Amazon - As an Amazon Associate I earn from qualifying purchases.)

Once you own a time-lapse camera, you think of all kinds of uses for it.  I have always wanted to see a day in the life of my cat.  She is over 12 years old and relatively sedentary and she likes to sit in her window seat and sleep and then watch the birds at the bird feeder outside the window occasionally.  So I set up the camera to document her from mid-morning until dusk.

Click image to see YouTube video

I have been making wood bowls from freshly cut trees for the last few years.  When an apple tree blew down in a storm recently I was able to harvest some beautiful wood and made some bowls from it.  The rest of the tree will be harvested for firewood.  I set up the camera to take images once per second and got this great video.

Click image to see YouTube video

Update Feb 5, 2016:  I always wanted to see myself clearing snow using my Craftsman snow thrower and we got 7" today so I set up the camera outside with it's waetherproof housing.

Click image to see YouTube video

These videos were all shot in 1080 P high-definition video, so you can view them full-screen and they look great.  Stay tuned to my YouTube channel to see more videos as I put them up.