Most Texas homeowners considering a solar energy system or residential wind turbine system will quickly face sticker shock. Wind turbine systems can run as high as $65,000 installed. The average cost nationally for a professionally installed solar panel system is about $8 to $9 per watt. A 2 kilowatt (kw) grid-tied system (no battery back up) can run to $16,000. A similar 5 kw system can cost upwards of $40,000. Deep cycle back-up batteries for both wind and solar can add on 20 to 30 percent more. You might be able to save around $2 per watt by doing the work yourself, however, energy efficiency programs may have certification requirements.
But don’t give up!
Because both residential and commercial demand for wind and solar energy is increasing, the technology is improving, there are more manufacturers, and the price is dropping. In the case of solar energy, the cost of an average solar panel in 1980 was $21 per watt (eg: a 15 watt panel would cost $315.00). Today, the average cost is about $2.50 per watt (low =$1.42/watt, high=$3.75). In 25 years, that’s a cost reduction of 90%. Power output capacities have also improved. In 1980, a typical solar panel might put out 22 watts. Now, 100 watt panels are common, if not plentiful. That’s a 450% increase in output. Add to this new enhancements through tracking (a motorized mount tracks the sun through the day to improve efficiency) and concentrating sunlight to extract up to 75% of the sun’s rays that increases efficiency by 1000 times over regular flat panels. Even if incentives aren’t available in your area, any solar or wind energy system installed by December 31, 2010 the Federal Energy Efficiency Tax credit lowers the cost by 30%.
The reason residential renewables are expensive is simple: you are investing in a home-sized power plant. Like any large scale power plant, that’s a long term investment made over the course of 15 to 25 years. And, like any long term investment, you should first take a few minutes to consider your needs and goals:
- How much electricity do you use each day?
- In a rural setting, will it cost more to bring more to bring poles and wires to your home?
- Is your goal to have self-sufficiency while retaining a grid-tie?
- Is your goal a zero-energy home?
In considering these questions, remember home size is irrelevant. The issue is purely how much energy you use because you are going to want a system that can meet your usage needs. A 1,500 square foot home doesn’t use any energy; it’s the people living inside that do.
Figuring your usage
Figuring your usage can be tricky. There is a big difference in watts and watt-hours. The power (watts) required to run things in your house is not measured the same way as your utility bills show (watt-hours). A 50 watt light bulb burns 50 watts of power each time it’s turned on. So the electricity supply has to be able to provide that 50 watts of power when the light is turned on. If you have a 30 watt battery, the 50 watt bulb won’t light all the way and quickly run down the battery. Watt-hours, meanwhile are the units of measurement of energy used over time. So, a 50 watt light bulb will consume 50 watts per hour (or even 50 watts per second if you are measuring in seconds). To use an analogy, let’s say we are using a waterwheel that only turns when the water pressure is 50 pounds per square inch (psi). However, the amount of water we use is measured in gallons per hour.
The important thing to remember is that watts and watt-hours are NOT interchangeable in making your calculations.
That being said, the way to determine your usage is to review your utility bills. For example, let’s say you use an average of 1000 kWh per month. That divides out to 33.33 kWh per day. The next step is to find out what electrical appliances and devices you are using, how many watts they consume, and how long do you use them. To compute kWh of a device or appliance, multiply the watts times the hours it runs during the day. A 500 watt chest freezer running for ten hours will use 2kWh of energy. If you only know the voltage and amps an appliance is using, there are lots of web sites that calculate wattage.
Now that you’ve got an idea about your usage, let’s first look at the costs of off-grid solar energy.
The next thing to look up is the amount of direct sunshine your location receives. Otherwise known as “insolation”, it is controlled by the angle of the sun, the weather, atmosphere, elevation, and location on the globe. The further north or south from the equator you go, the fewer hours of insolation. In Texas, insolation amounts vary from 4.5 to 5 hours.
Now we can see how many panels you may need. A very handy tool is the Solar Panel Estimator. Assume your insolation hours equal 4.5. The system efficiency is a product of the efficiency ratings of the current handling hardware: inverter (to convert 12 volts DC to 120 volts AC and smooth it into a nice, clean 60 hertz cycle), a battery charge controller, and the deep cycle batteries. Inverters typically run about 95%, charge controllers at 98%, and batteries at 80%. So, if we multiply.95 ×.98 x.80, we get a system efficiency of.74 or 74%. That means our 100 watt solar panels actually produce 74 watts. If we compare the output from the Solar Panel Estimator, if our system was 99% efficient, we would only need 74 panels. Since our system is only 74%, we need 99 panels to make 33 kWh/day.
Either way, that’s a very large number of panels, and a lot of money, also.