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.