Monday, July 31, 2006

My Solar Photovoltaic System. Past, Present, and Future.

My solar photovoltaic (PV) system started out small, and is periodically upgraded as funds become available. When power outages have compelled me to use the system I’ve been well pleased with its performance, but at the same time I’ve wished that it could do more. With that in mind, I’ll attempt to outline the past, present, and future capabilities of the system.

Initially, my system components included one solar panel, a charge controller, some gel-cell batteries, and a 600-watt modified sinewave inverter. With the appropriate wiring, panel mounting hardware, and miscellaneous items, the total cost of the system was about $600.00. The batteries were throw-a-ways that I got from the IT department where I work. They were not like new, but still had some life in them.

Using a couple of 75-watt light bulbs as a test load, I found that the battery bank would last for just a little over an hour. While the solar panel was capable of producing more than 400-watts of power on a sunny day, the fully-charged batteries were only able to deliver about 150-watts. Clearly, the battery-bank needed to be upgraded.

I replaced the gel-cell battery bank with two marine deep-cycle batteries. The rated capacity of these is 105ah each, for a total of 210ah. Using the 150-watt test load, the battery bank lasted eight hours. Battery capacity jumped from 150-watts to 1200-watts (150-watts times 8-hours). However, since my single solar panel can only produce about 400-watts of power on a sunny day, it will take three days to fully charge a depleted battery bank. Still, the capabilities are much greater than they were before the battery upgrade. I need not worry about running out of power when the load consists of low-power devices such as compact fluorescent (cf) lamps. The cost of the battery upgrade, including wiring, was about $150.00, and was well worth it.

A recent upgrade included another solar panel and two more marine deep cycle batteries. I now have 800-watts (per sunny day) of charging capacity, and the ability to store 2400-watts of power in the battery bank. The system is limited in that it will take three days to fully recharge a depleted battery bank, but I have an abundance of power. During a recent power outage, I ran several cf lights, fans, a radio, and a cell-phone battery charger. I even connected a TV for a short time. The drop in battery voltage by morning was hardly noticeable.

My next goal is to be able to power our small chest freezer in the event of an electrical grid failure. I’ve measured the power consumption of the freezer, and found that it uses about 0.76 Kilowatt hour per day. This is just slightly less than the total daily capacity of the two-panel array that I currently have. Without another system upgrade, I’ll have very little power left over for lights and other things. Still, running the freezer is better than watching food spoil. And, if you consider that my fully-charged battery bank will supply enough power to run the freezer for more than two days, I should be OK for the short term power outages that we typically experience.

The inverter that I’m currently using may not be able to handle the high motor-starting current of the freezer, so my next step will be to purchase a 1000-watt true sinewave inverter. I’ll also install another solar panel so that I won’t have to skimp on lights and other low-power devices in order to use the freezer. This upgrade will also allow me to use a small microwave oven, and other high-power devices for a short period of time. At this point I’ll have just over two thousand dollars invested. The performance of the system in an emergency will be well worth it.

In the event of an electrical grid power failure in the winter, I’ll want the ability to use the system to provide heat for my home. Having installed a corn-burning stove this summer, the PV system will provide electrical power to the stove’s blowers, and auger. To meet the requirements of the stove, I’ll add one or more solar panels, and two more batteries. I’ll measure the actual power requirements of the corn-burning stove on high and on low settings later this year. The only time I’ll need to conserve power is when cold weather forces me to use the stove for an extended period of time. At all other times I’ll have plenty of power for lights and small appliances.

If I had been thinking only in terms of emergency heat I would have opted for something other than a corn-burning stove. I could have installed a wood-burning stove which could have heated my entire home without any electrical power requirements. However, wood burning is more work, dirtier, and not as safe as burning corn. My previously stated goal is to live comfortably in the event of an extended power failure. All of the chores that go along with wood-burning do not meet my definition of living comfortably.

For a little over $3,000.00 I’ll have a system that will meet all of my basic household electrical needs in the event of a grid power failure. Knowing that I could have opted for a generator for about a third of that, I have no regrets. While the initial cost of a generator would have been much less, the cost of fuel to run the generator would quickly surpass the cost of the PV system. And, fuel is not always available in an emergency. My power source, the sun, is free. It recharges the battery bank each sunny day.

Having met my emergency electrical needs, I’ll next focus on upgrades that will help to reduce my grid-powered electrical load on an everyday basis. I already use the system to provide power to my grow-lights for my plants, but it would be a shame to use the system for that alone. I want to replace grid-supplied power with solar-generated power as much as possible. I’ll run the chest freezer on a continuous basis and add wiring to my computer desk. I’m also considering the replacement of our refrigerator with a highly efficient Sun Frost model. I’ll add that to the solar-powered load. With periodic upgrades, I hope to power my entire house eventually.

I like the fact that my electrical and heating systems help to reduce carbon emissions, a leading cause of global warming. Someday, everyone will have to do their part in this effort. If voluntary efforts fail to produce the desired results, conservation will become mandatory, or perhaps electricity will become so expensive that grid-connected consumers are forced to cut back. Either way, I’m glad I have a head-start.



Anonymous said...

Hi John,
Just stumbled accross your blog. Congrats on your efforts.

Forget the Sunfrost and upgrade to a current Amana or Kenmore and put the savings into more pv. The new Energy Star rated refers will pay for themselves in short order.

Also, make sure that you upgrade to a sine wave inverter. The modified sine wave units inefficiently run refrigeration compressors and cause very short lives.

Anthony said...

I saw you used the Kill-a-watt to measure the usage of your freezer. Does that tell you the energy costs or just the amount of kilowatts?