This small solar system involved a lot of work (largely woodwork and wiring) The basic kit was obtained from Amazon.com (https://www.amazon.com/Renogy…/dp/B00BCRG22A/). Later upgrades were purchased separately directly from Renogy.

A home solar system, capable of off-grid operation, generally consists of four parts:

• Solar panels
• Charge controller
• Energy storage (usually one or more batteries)
• Inverter

Not all residential solar systems contain all of the above. Notably, some systems use what’s called a “grid tie” inverter which eliminates the charge controller and battery array and feeds power back into the commercial power grid when your panels are producing more electricity than you’re using, cutting your electric bill. Our system is an “off grid” system, not connected to the power grid, and providing a relatively small amount of power. It’s basically an experimental or “hobby” system.

Solar Panels

Solar panels convert sunlight into electrical energy and come in several flavors with different costs and efficiencies. The panels used in the system here are “monocrystaline” silicon, the most effecient and highest priced type. These 100W solar panels from Renogy can be bought individually (sans the voltage controller) for $136, and the price keeps dropping. It was only a few years ago that my price target for solar panels was $5 per watt. I’ve seen panels for under $1 per watt recently. The panels in our system are “monocrystalline” silicon, the most efficient and most expensive of the several solar panel technologies available. Many solar installations use “polycrystalline” silicon, slightly less efficient and less expensive. These panels are designed and installed to work with a 12 volt system. Commercial home solar installations generally use 24 or 48 volt panels. These panels are wired in series, and the array, in full sun, puts out 80 to 90 volts.

The original solar panel array was the Renogy “starter kit” consiting of two 100W panels and a 20W charge controller. I’ve upgraded it to four 100W panels, as shown above.

Charge controller

The purpose of a charge controller is to adjust the voltage and current provided by solar panels and present the battery or battery bank with voltages which are appropriate for battery charging and maintenance. Abstent a charge controller, batteries would quickly be destroyed by the voltage delivered from the solar panel array. Charge controllers come in two flavors, pulse width modulation (PWM) and maximum power point tracking (MPPT). PWM technology is relatively inexpensive, but less efficient that the newer and more expensive MPPT technology.

The original charge controller was Renogy’s “Wanderer” PWM controller. It’s their least expensive 20 amp controller. The system has been upgraded to a more efficient 40 amp Renogy “Rover” MPPT controller which handles the current and voltage delivered by the four panels.

Energy storage

The big “gotcha” with solar power these days is still energy storage. All batteries have a limited life span, and are not cheap. For this system, I bought a single 12V 100AH (amp-hour) AGM deep-cycle battery (Mighty Max ML100-12), the cost of which was $175 plus shipping (not inconsiderable on a lead-acid battery). This is cheap for an AGM (Absorbent Glass Mat) battery. Better cost/performance can be obtained with regular flooded deep-cycle batteries, but part of my intention with this solar system is to be able to take a minimal sub-set of it with me if I play out of doors somewhere to power our sound system, and unlike flooded batteries, AGM batteries are spill-proof. I’ve added a Renogy 200AH AGM battery to the system to provide more storage capacity, for a total of 300AH. Many small systems such as ours use widely available standard deep-cycle flooded batteries. For a system which isn’t intended to be portable, flooded batteries are the way to go and provide the least expensive solution. All good charge controllers will have a setting to optimize their performance for any one of several kinds of batteries, including AGM and deep-cycle flooded.

A bit of research on batteries shows that the up-and-coming technology for large installations, capable of powering a home, is what’s called “saltwater” batteries. These are currently marketed by a company called Aquion. They’re 48V batteries, the voltage standard for substantial home installations. Saltwater batteries have several advantages over lead-acid (AGM, gel, flooded). They’re environmentally very friendly, using non-toxic materials and chemicals. They can be deeply discharged without damage. On the con side, the energy density of saltwater batteries is rather lower than that of lead-acid or lithium batteries, which isn’t a problem if space and portability aren’t a consideration.

Inverter

In the US, as in most of the world, all household devices from light bulbs and air conditioners to computers use alternating current (AC). The line voltage varies from country to country, but in the US, the accepted voltages are 110V, or 220V for large appliances such as electric stoves and large air conditioners. An AC electric line alternates between positive and negative at a fixed rate, which is 60 cycles per second (60 Hz) in the US. The inverter in a solar power system converts the DC electicity provided by one or more batteries into AC at the proper voltage and frequency required for home use. Inverters come in a wide variety of capacities, and are rated in output watts. Our system here started out with a Power Bright 600W inverter, shown above, and now uses a Renogy 2000W inverter capable of powering a fridge a small AC or a home-shop power saw. Both of these are “pure sine wave” inverters, the output of which is suitable for use with electronics. Pure sine wave inverters are more costly than those which aren’t, but if you plan to use your solar system for more than just running electric lights and motors, the cost is worth it.

Every component in a solar system should be both switched and fused – or controlled by a circuit breaker which serves both functions. 65 years ago I was a teenager in Appleton, Wisconsin – one of the first towns in the country to have commercial residential hydroelectric power. There was a lot of “legacy” wiring in homes around town, a lot of which didn’t measure up to current safety and code standards and had been taken out of service. This old knife switch was in our attic, attached to the wall but unused. I’ve had it ever since. It serves nicely as a cutoff switch for the solar panel array. The 30A fuses, still available in hardware stores, are probably overkill, but the current delivered by the panel array, even without fusing, should never exceed the capacity of the AWG10 wires.

Cost considerations

The return on investment on this small system is definitely poor compared to power from the grid. Even had I built a larger, more cost-effective system it’s pretty difficult to match the cost of on-the-grid electricity with solar power alone. A well designed system which will power your home or farm has a ROI of 10 to 15 years. After the initial cost, batteries have life-spans. Solar panels have rather longer life-spans, but don’t last forever. Our system, as it stands now, will put out 2000W of power (the rating of the inverter) which is well under 4 hours of power without the solar panels. During the day, with the solar panels providing 400W of power, this would go up a bit. With the addition of another battery or two I could probably coax enough power out of the system to power our cable-modem and small gateway/firewall computer 24/7 so we could stay on the Internet in the event of an extended power outage (assuming Spectrum née Time Warner was still operational). Would it be worth it? I really don’t know. You can take a look at the cost stats at the bottom of this page to get an idea of what I’ve put into it so far and what it would take to bring the system up to something which would provide the equivalent of a single 20 amp circuit for a limited period of time each day.

Perhaps the major payback from this project was learning more about solar power. Were we to decide to seriously invest in taking our home off-grid, this small system would be out of the loop. Standard practice these days is for the installation of 24V or 48V panels – a lot more of them, with a combined capacity of