March 30th 2016
LearnThis has always been about discovering and learning new skills and helping others to do the same. Those skills can be learned in a variety of formats, where a blog normally consists of reading and writing, I’ve always been an advocate to practice skills, learn by doing and whenever possible, put those learned skills into action on a regular basis. I do exactly that by building things and fixing things that I can learn about myself. Home repairs, renovations, handyman. I’ve done a lot of carpentry, metal work and several times now, small solar energy projects. In this three part series, I’m going to outline 3 home solar projects I’ve done. Hopefully they serve as an example of how you can use a do it yourself (DIY) approach to learn a lot about a subject.
First DIY Solar Experiment – Battery Backed Photovoltaic
The first solar experiments I did about 15 years ago with a small solar panel that I used to mount on my home’s roof to power a vent fan that would help to cool the attic, using air exchange anytime it was hot and sunny out. I used a 15W 12V panel, to drive a 12V high volume fan and wiring it up to an old mercury thermostat. The cool thing about an old mercury thermostat is that it works on gravity, so you can mount it upside down to reverse its operation. What normally activates the heating cycle if the temperature drops, upside down it behaves as a cooling unit, activating the cooling when it gets above a specific temperature instead.
I quickly realized that my 15W panel was a LOT more power than the 5W fan was using for air exchange. I figured I could try to extend the use of this power with a battery pack. I did quite a bit of research and was a regular reading the magazine “Home Power” to find some ideas and sources of information. I looked at and purchased a simple circuit board kit that I could solder and build myself, since it was only about $20 to buy. The board was a charge controller, with low load protection and over voltage protection that I hooked up to a small 7AmpH 12V gel battery.
The additional 10W took a few days to fully charge the battery, but then I was able to use that to operate several compact fluorescent lights in my basement laundry room. I used a small 175W inverter that was nearly zero no-load draw. I was able to drop the wiring down from the attic along side the house plumbing vent stack right to the basement so I could put the charge controller, battery and lighting in the basement for the roof mount solar panel.
I ran it for quite a few years and it kept the attic at least 5-10 degrees cooler with the active cooling fan and the added light in the laundry room was great to operate for essentially free from the battery. Overall, it was a great experiment and fun to build, yet I never proceeded doing photo voltaic again, due to the high cost and low efficiency of the panels. I sold the panel and battery used when selling the house, to another solar experimenter to hook up and play with.
Second DIY Solar Experiment – Active Solar Air Heater
I’ve always been interested in efficient energies from the sun. The most common is solar photo voltaic, however it continues to be a fairly costly solution. Capturing the sun’s energy with photo voltaic unfortunately has very poor efficiency. However, cost of panels has reduced rapidly so for DIY-ers, they have become much more affordable. Commercially installed PV systems are still very expensive still with around 20 year payback periods. One problem with PV panels is that their energy efficiency is only around 15% for most commercial panels.
I looked into building a passive solar air heater for additional heating on our tack room / barn. It is heated by electric baseboard heaters to keep the room from freezing (and the cats warm) in the winter. I found some examples of home built popcan solar air heaters on youtube so I decided to start with one of those. I picked up a bunch of free windows being given away on a local classified site, and so had a 2 foot by 3 foot glass panel to start a small heater from.
Next, I built a simple plywood box to house aluminum cans which when painted black, could collect the sun’s heat nicely and act as a heat exchanger. This DIY concept is very simple, cold air comes in the bottom of the box or panel, which has a glass front facing the sun, with black cans inside to absorb and radiate the heat into the air inside the panel. That hot air rises so can exit out a top vent to create continuous heat output.
I built and tested this in the sun and while a passive design worked to raise the temperature of the air by over 30°C (86°F) continuously, the air flow was very low. I decided to add a couple of small 12V computer fans to blow the hot air out into the room where I needed the air. It worked great and I exhausted the hot air into the barn through a window which I built a sealed panel for with insulated air ducts to reach it.
The heater’s fans were mounted in a series circuit with a $2 snap disc I found on ebay. These engage the circuit whenever the temperature was above 25°C (77°F). A cheap 12V power supply (also from ebay) ran the fans whenever there was heat in the box. I enclosed the end with tin to seal it all up from weather and to connect my air duct vents to the barn when it was actually installed.
Overall, the heat was great on a small DIY device like this, considering I didn’t even insulate the box. Its surface area gets about 660W of sun radiant heat (about 1KW/m2). My estimate of efficiency after doing some math on the air flow and heat increase as well, was about 65% so this device was able to output a continuous 400W or so. Not bad, for a diy experiment that cost me about $20 to make since I had most of the parts already.
Outputting 400W for 5 hrs a day, meant it produced about 2KW per full day of sun. Saving $0.18 per day of operation, it only needed 111 days of operation to pay off. I installed and had it operating for 4 yrs. This equals about 125 days per year of sun so it more than paid off and even saved me an extra $70 on electric heating for the barn. SWEET!