Solar Electric

How much energy will a Solar Electric system generate?

Learn about different types of Solar Electric/PV

Are Solar Panels becoming more efficient?

How can we be sure a module will perform well?

How much energy will a Solar Electric system generate?

According to government supplied modeling software for photovoltaic output, systems in southern Michigan will get, on average, a little more than 100 kilowatt hours of electricity per month for every kilowatt (1000 watts) of solar you install. To learn how much space 1000 watts of solar takes up, read about efficiency below.

The average household uses around 850 kilowatt-hours of electricity per month. Actual usage varies greatly, and is not exactly dependent on the size of the house. We recommend conservation before investing in solar electricity. Most people could reduce their use of electricity with very minor changes to habits and lifestyle. To generate 850 kilowatt-hours per month from solar would require installing more than 8000 watts. Most residential systems are much smaller than that and just supplement the electrical needs of the household. Budget tends to be the driving factor in determining system size.

Learn About Different Types of Solar Electric/PV

SUR carries many types of solar electric modules from many different manufacturers. The most commonly used modules are of two basic varieties, thin film and crystalline. Crystalline are the traditional solar panels that have had many incremental changes over their history. The modules are made up of cells that are wired together and protected by a layer of high strength glass within an aluminum frame. While there have been no paradigm shifts in the technology it has improved much, and the associated cost has fallen at a rate similar to that of computer memory over the past 30 or so years.

Thin film modules tend not to be made of wafers but rather by depositing chemicals in layers on some sort of substrate, often glass, or in the case of Unisolar, a successful Michigan based PV manufacturer, stainless steel. Most people feel that thin film PV holds more promise for lowering the cost of energy, but that may or may not be the case today. Their efficiency tends to be lower so the area required to get the same amount of electricity tends to be larger. For the overall cost, and resulting cost of energy to be lower, the cost of racking and/or installing the additional area of thin film has to be lower than the savings realized when purchasing the lower cost materials. To make the decision more complicated yet, thin film often outperforms crystalline in a watt per watt race. Thin film products have the distinction of resulting in both the lowest and highest cost of energy we have worked with. Results vary greatly according to the application.

SUR has many options at their disposal and we are happy to walk you through the cost/benefit analysis required to make the choices you will be comfortable with.

How much does Solar Electric/PV cost?

We have recently seen a lengthy report on the installed cost of PV done by Lawrence Berkeley Labs for the federal government. The title of the report is, Tracking the Sun - The Installed Cost of Photovoltaics in the U.S. from 1998-2007. The report divided installed solar electric systems up by size. The statistics come from states that have excellent state based incentives for installing solar, such as California, New Jersey, New York, etc.. How does this compare to Michigan? At the time of this writing (early 2009) Michigan has almost no market for solar electric compared to these states. The result is that there is little opportunity to optimize processes, crews, and material flow. The report pointed out that most of the cost reductions in the time period came from non-module costs (the solar modules alone represent approximately half the installed cost of the system).

Highlights from the report are that the average cost of systems under five kilowatts (5000 watts) was $8.30 per watt in 2007. Systems under 2kW averaged $9/watt, while systems over 750kW were installed for an average of $6.80 per watt. They called this good economies of scale. These economies of scale are currently limited by the cost of the PV modules themselves. Also, other technologies like wind power have some advantages in the area of economies of scale. Read more about wind power.

Installed costs varied by state. Some of the average costs for systems under 10kW by state were $7.60/W, $8.10/W, $8.40/W, to a high of $10.6/W in one state.

Are solar panels becoming more efficient?

Efficiency is the most misunderstood concept for most renewable energy shoppers. The term is often confused with the value or payback of a system. Efficiency is a comparison of energy in to energy out. We typically measure the sun's energy in watts per square meter. To make things more simple this energy is averaged to 1000 watts of energy per square meter, also known as a peak sun hour. The watts mentioned here are not watts of electricity, but watts of sunshine. If the sun has 1000 watts per square meter you will be able to see as well and feel as warm as you do around a typical clear summer day at solar noon. If you stood in those conditions for an hour you would have experience close to a peak sun hour for yourself.

The most widely used type of photovoltaics is crystalline. Typical efficiencies are around 11-14 percent. That means for 1000 watts of sunshine on a square meter of solar PV modules (about 39 by 39) the solar would generate about 120 watts of electricity. We mentioned earlier that thin film tends to be less efficient. Some are around half to three fourths as efficient as crystalline. Is this a problem? It may or may not add to the ultimate cost of energy. Rather than concerning ourselves with area, the best way to compare apples to apples is to look at the per watt cost of the solar panels. The watt per watt comparison of cost of the material itself is in fact very close. As long as you have the real-estate without shading lower cost of energy is likely to rely on factors other than efficiency.

Modules in fact are becoming more efficient, but, as experts in the industry this doesnt excite us all that much. Once you explain what efficiency is most people no longer care about it. What they were looking for was a lower cost of energy. Read more about cost of energy.

How can we be sure a module will perform well?

If you listen to a particular manufacturer or their sales reps, of course their product is the best. We like to use objective third party testing on behalf of our customers. PVAmerica tests modules under conditions that are more like the real world conditions than the Standard Test Conditions (STC) used by all PV manufacturers.

It is helpful to know much performance falls off as the modules get hot, which is true of all PV. If you compare the CEC rated wattage to the wattage designated in the module name you will see the difference in performance. Honorable mention goes to our own Unisolar, which has one of the lowest differences in CEC rating (hot) and STC rating (room temp). This is another way of saying they will produce more electricity per rated watt when it is hot outside. Remember that in Michigan we have more sunshine in summer months, so they have a distinct advantage in that regard. Also note that sitting in the sunshine even in fall and spring, the modules can be too hot to touch comfortable.

PV System Components

The PV modules are just a portion of what is needed to get useful power into the home. Visit our Electric Systems Options Page to learn more about how the direct current electricity coming out of a solar module becomes useful alternating current running some or all of the loads in the home.