Wouldn’t we all like to call the power company customer service line like so:
- “Power Company. May I help you?”
“Yes, I’d like to have my power disconnected, please.”
“That’s right. Disconnected!”
“May I ask, WHY???”
“I don’t need you any more. I generate my own electricity from the SUN!”
“Uh. OK, we just don’t get many disconnection requests.”
I would also like to do that with the phone company, the bank, the credit card company, and on and on, but that’s a different article.
Before you can make that magic phone call to the power company, you have some work to do. Solar power isn’t cheap, and it’s not easy, at least that needed to power your entire home. But there are many levels to solar power, depending on your needs and objectives.
Solar power capacity is measured in watts, the unit of electrical power. Here are the power requirements for common devices:
|Cell Phone Charger
| 7.5 watts
|CFL Light Bulb
| 23 watts (100W incandescent equivalent)
| 300 watts
|Computer Monitor, 21 inch
| 30 watts
| 200 watts
| 15 watts
| 512 watts
The solar power generating system must be sized to power the devices you wish to connect. Obviously, running your whole house takes more power than charging your cell phone. It takes more solar panels to collect more sunlight.
Let’s explore some solar power scenarios.
Very Small Scale Systems
To power some small products in your home, all you need is a tiny system. For example, to charge your cell phone, or charge rechargeable batteries for flashlight or radio use, a system of just ten to twenty watts would be adequate, and you don’t necessarily need a storage battery. The system would look like this:
The adapter converts the power from the solar panel to be compatible with your small device. These adapters are available where you buy solar panels. For example, there are many solar cell phone chargers on the market that you can just plug into your phone.
These tiny systems are available off the shelf at big box retailers and tool distributors. Be careful because these tiny systems are all made in Asia using the least expensive parts and assembly techniques. That is, they are not built to last! Use the maxim, two is one and one is none, when buying these small systems, and procure a spare.
Powering an Appliance
You may have need to power more than just your cell phone, but not your whole house. Powering just the fridge or freezer (to prevent food spoilage), or a circulating fan for your wood stove may be all that you need. These appliances draw more power, and you would want to have power at night or on a cloudy day. That requires a backup battery. The system looks like this:
The solar panel has to be sized to produce the average power needed to run your appliance. The charge controller ensures that the battery is charged properly, to give the battery long life. The battery stores energy from the sun for later use. The inverter converts the voltage from the battery to 120VAC typically.
This system is obviously more extensive and expensive than the small scale system, but it is more capable. From the appliance list, above, you see that you may need as much as 1500 watts to run your microwave oven to heat your dinner.
Sizing these components takes some know how. Here are some tips.
There are inefficiencies in each component, meaning that you need to oversize them. The inverter will have an efficiency of 80%-90% when running near full power. That means 10%-20% of the power going into it is wasted as heat.
The battery has a charging efficiency varying widely from perhaps 50% to 90%.
The charge controller has an efficiency of 70%-90%.
If you multiply out all these efficiencies, the overall efficiency is 28% on the low end to 73% on the high end. And the actual efficiency depends on how much power you are drawing from the system, because there are fixed losses in the charge controller and inverter.
Given these numbers, it’s good to oversize your solar panels by two times or more, to be sure you have enough power to keep the battery charged, and to ride out periods when the sun is not strong.
Add to that the difficulty that motorized appliances need a surge of power to start up. A microwave oven, or even window fan can take five or more times the normal running current to start up. Your inverter and battery must be able to handle that surge. Inverters typically have surge ratings and can deal with such loads.
Also consider whether the appliances you are running will be running continuously or intermittently. A fan on your wood stove would run all night, for example, to keep the house warm. The compressor on the refrigerator runs only 30% of the time (for example). In that case, compute the average power by multiplying the nameplate rated power by 30%.
Be careful when you have multiple intermittent appliances running at once. For example, a washer and a refrigerator both are intermittent loads, electrically. Your system may be rated to run both on average, but when they are both running at the same time, the inverter may be overloaded and click off.
The vendor of your equipment should be able to help you size them appropriately. You will need to compile a list of the devices you wish to run, and their power requirements (from the name plate on each device). Just add up the wattages. The solar panels should be rated at twice or more (even better, four times) of that power. The inverter should be rated at least twice that power.
This type of limited system is typically not wired into your electrical panel, but consists of a separate system of charge controller, battery, and inverter, all connected to the solar panels. Some have created rolling power carts that plug into special outlets in the home for charging from the solar panels. When the power goes out, the cart can be rolled where power is needed in the home, for temporary service. There are some carts like this for sale for two thousand dollars and up, but this type of system is not difficult to build if you have the tools and interest.
Powering Your Entire Home
This type of system is extensive and expensive. However, expense is a relative term. When the power company is up and running, you can be selling energy back to them, reducing your overall electric bill. The payback period can be lengthy. But when the main power is out, your whole house system will seem to be cheap, as you continue life as usual while your neighbors are heating bath water on the grill.
Whole house solar systems require professional design and installation, and can easily run into the hundreds of thousands of dollars. Solar power for a small cabin can run twenty thousand dollars, with all the work contracted out. There are many companies specializing in this work today, so look for a nearby contractor and check their references. Former customers may allow you to inspect their work.
The system setup for whole house systems is the same as for the appliance level system, above. But the complexity of each element increases. The solar panels are not the basic 12 volt variety, but are connected to output higher voltages, in order to reduce power loss in the wiring. The charge controller and inverter are typically one unit, capable of tens of thousands of watts. The battery is actually a bank of specially designed deep cycle batteries, created for long life in the solar application. These batteries must be maintained in a working temperature range, so auxiliary heating facilities just for the batteries may be required.
Security is a factor as well, because a whole house solar system is not inconspicuous. You may need several steel poles mounted in concrete to contain your solar panels. Inverters are mounted on the poles. All this equipment is susceptible to vandalism, rendering your multi-hundred thousand dollar investment useless in a few minutes. Consider this as you plan your system.
As with any preparedness item, it’s good to have redundancy. Having a simple solar phone charger (or two) is good and inexpensive. If you build a solar cart for powering appliances temporarily, build two while you are at it. And if you build out a whole house system, be sure you budget for spare batteries, inverters, charge controllers, and panels. In an emergency situation, the repair company will likely not be able to help, so learn as much as you can about your system so you can maintain it properly.
And understand that solar is still relatively new, at least to the consumer market. Shop around! Tiny systems will cost perhaps $4 per watt of power. Purchasing a couple commercial panels will cost you perhaps $3 per watt. A whole house system will cost $2 per watt (for the panels), or less.
Always check references for any contractors you use. Many of them are new to the market.
And be sure the whatever you install is secure from theft and vandalism.
We hope these tips help you in your solar power quest!