Our EntropyPawsed cabin solar electric system is small and simple, yet the learning curve for us was considerable. When designing the remodeling and finishing of our cabin, we incorporated solar electric into the design. Our theme of simple and low energy included a desire to be able to do most of the work ourselves.
The discovery of the "Sandia Report, Photo voltaic Power Systems and The National Electrical Code: Suggested Practices" after fits and starts of reading and research, provided me with enough information on how to wire a system that I could proceed with growing confidence. When I started the installation, gaps remained in my ability to conceptualize it. However, upon completion, it now seems very straight forward and easy to understand.
While we looked at and considered cabin systems from various alternative energy suppliers, in the end we decided to piece the system together ourselves from several different suppliers. This saved a lot of money; our entire system cost less than $3,000. The Photo voltaic (PV) panels, deep cycle batteries, distribution panel, system controller, inverter, charger, generator, LED light, ceiling fan, and exhaust fan, were purchased from various on-line suppliers. The wire, connectors, junction boxes, conduit and miscellaneous hardware was purchased from local retail stores.
Our PV system consists of one GSE 60 Watt thin film panel, and two Sunwize 55 Watt polycrystalline panels. After purchasing the GSE panel, I read that most of the “25 year” polycrystalline panels purchased over 30 years ago were still producing in excess of 90 % of rated capacity. For us, longevity trumped new technology in the form of thin film.
The panels are mounted on a treated wood frame attached to the front of our south facing deck. I constructed the frame in a way that I can rotate easily to three positions; winter, spring and fall, and summer. Having the panels four feet high allows us to clean them of pollen, dust, snow and ice.
The panels are wired into a junction box where the three sets of leads are combined into one set of heavy 6 gauge wire. One can consult charts to determine the voltage loss at certain distances to determine the gauge of wire necessary. The 6 gauge wire runs 20 feet through conduit under the cabin and into a junction box, then into the cabin to a circuit breaker/cutoff.
From the inside cutoff, we use smaller 10 gauge wire to go 12 inches to our Morningstar Sunsaver 20 Photo voltaic System Controller. This inexpensive yet nifty little device acts as a charge and load controller. A particularly valuable function disconnects the load when battery bank voltage drops to 12.1. This protects the batteries and helps to maximize their life. As the saying goes, “Batteries don't die, they are murdered.” The Morningstar device works with panels producing less than 20 amps total. However, for larger systems, more than one device can be used in parallel.
The battery bank consists of three “no name” 12 volt, 75 amp hour glass mat lead acid batteries wired in parallel into a safety cutoff, and then into the Morningstar Controller. All devices powered by the system are referred to as the “load”. We purchased a 12 volt pre-wired distribution panel from New England Solar Electric for load distribution. Each of our four load devices are on a separate 10 amp Square D “QO” breaker circuit. Only this breaker reliably works with 12 volt systems.
Our four load circuits/devices are an LED light, a ceiling fan, and exhaust fan, and an inverter. Our inverter is an AIMS 1250 watt truck inverter, the kind normally plugged into a cigaret lighter, but hardwired in ours. Since it is much larger than needed, the inverter works very efficiently. The inverter is located near the load center to minimize 12 volt current losses. A back up inverter is stored nearby, as the inverter can be a weak component in PV systems.
A dark green extension cord (matches our trim) goes from the inverter window seat location near the front of our cabin to the office alcove at the rear. It plugs into a three-in-one adapter. Plugged into it are two 6-outlet power strips. This arrangement powers our DSL modem, our laptop computer, computer speakers, our printer, Bonnie's cell phone charger, our AAA battery charger, and our cordless phone. We have found it important to be very diligent in completely turning off everything when not using the system. Our stored photons are very precious.
When it is cloudy and our battery bank voltage falls below 12.1, the system cuts off. Then we must run our generator to recharge our batteries. Our generator is located in a shed far enough from the house to preclude exhaust fumes. We run a heavy red (14 amp) extension cord to a small box on the outside of the cabin where we plug into our Xantrex 40 amp charger located inside next to the battery bank. It takes about three hours to fully charge the batteries. During this time, we use a second extension cord from the generator to supply the power strips in the office alcove.
We have been using the system for about a year and a half. We are using the wired LED light, ceiling fan, and exhaust fan very infrequently. We use the modem and computer a great deal, and the other devices in our office alcove as needed.
We vigorously debated the merits of doing PV versus no electric (our cabin is “off grid”). In researching solar electric energy returned on energy invested (EROI) results range from 0.5 to 20. If we trust the low end of the range, that means solar electric is unsustainable. If we trust the high end, the energy returned is better than fossil fuels. Only time will tell if such systems are sustainable. I think perhaps they are not, but are rather a bridge to a low energy future for those of us who have grown up in the age of electricity.
The PV System has afforded us the opportunity of transitioning our EntropyPawsed project to a perhaps more sustainable remote learning basis. From a Permaculture perspective, whereby we take advantage of fossil fuel inputs to implement a sustainable system, we can justify the resource investment in PV, while knowing as we proceed into the future, these inputs will grow increasingly scarce.
Here are the most important lessons learned through our relationship with PV:
- Climb most of the learning curve before purchasing expensive components and attempting installation
- Buy polycrystalline PV panels
- Do not use Romex (solid AC type wire) or AC components. 12 volt must be wired with braided wires, mechanical connectors, and special spring loaded switches.
- Make sure your wires are suitable gauge
- Do not add a battery to your Glass Mat battery bank after it has been in use for more than a month or two.. Carefully size your bank initially. Wait until replacing the entire bank to add capacity.
- Don't add other significant loads to the generator when running your deep cycle battery charger (You might melt your charger wires/connectors)
- There is nothing so complicated that an American cannot further complicate it.
- The PV system is never big enough in a West Virginia winter
- We like oil lamp and candle light. Bonnie doesn't miss television. Frank only does a little during football season:)