Several people will tell you that solar panels, both photovoltaic and thermal, increase climate change, aka global warming due to the local “Heat Islanding” effect.
Others have said the cost (in CO2) of manufacturing and shipping solar panels is more than their subsequent use would eliminate.
Solar panel Heat Islanding
There is some validity to the first concern. If you take an area that was normally light reflective and put a solar panel in it, less light is being reflected and thus more heat is being generated. However, in the case of a solar thermal panel, most of that heat is then conducted away by Heat Transfer Fluid (HTF) for use or storage. A typical solar thermal panel is 65-70% efficient at converting and removing the energy striking it. The remaining 30-35% of the energy is either reflected off of the glazing or the absorber plate or it is lost due to heat transfer inefficiencies, insulation losses, etc. In short, a solar thermal panel is very efficient at collecting energy and removing it. Having a solar thermal panel on the roof of your house would reduce the solar gain because most of the heat energy is being removed to another location and the panel shades the roof it is attached to.
Photovoltaics however, are not as efficient as solar thermal. The average PV panel in use today is around 15% efficient. Some of the energy passes through the panel and some of it is reflected. Therefore, about 80% the energy striking the panel is converted to heat. The average insolation on earth at mean sea level is 1,000 watts per square meter per hour.
A 4.3 KW grid tied solar system has 24 Sanyo HIP190BA3 PV modules. Each Module is 1.16 M2. The total area is 26.78 M2. Therefore, the total energy striking this array is 26.78 KW/hr. The total heat being generated by this array on a sunny day is about 22 KW/hr or about 75,000 BTU/hr. In the meantime, it is producing 4.3 KW of electricity. The average peak sun hours in the Hudson Valley is 4.5 per day so this system can be expected to produce an average of 19.35 kWh per day or 7063 kWh per year. Electricity production in the United States is about 32% efficient. Therefore, that 19.35 kWh if purchased from the power company, would have produced 13.16 KW of waste heat and 32.9 pounds of CO2 vs 99 KW of waste heat and zero pounds of CO2. This system will save 12,000 pounds of CO2 per year or 150 tons of CO2 over a 25-year life.
This should trigger two questions; How much of the sun’s energy would have been absorbed by the surface of the earth and turned into heat regardless of the solar panel and what importance does CO2 have on climate change. To answer the first question is rather complicated. It depends on the color of the surface, the angle of the sun striking the surface and the atmospheric insulative effect. The second question is a little easier to answer
CO2 in the production of solar panels
It takes about 3.6 years (in average insolation) for a PV cell to make the energy used in its production. Therefore, over a PV cell’s 25-year life, it will produce electricity and contribute 86% less CO2 than electricity generated by fossil fuels. This reducing in CO2, a known Green House Gas (GHG) which is thought to be significantly contributing to the global rising in temperatures more than off sets the local heat island effect that PV panels have.
Solar thermal panels take much less time to payback because they are made mainly from copper (absorber plate and piping), aluminum (frame and mounting), insulation and glass. These materials are readily recyclable which greatly reduced the energy required for extraction and refining. Additionally, a solar thermal panel is much more efficient at collecting energy, so the energy payback comes in about 1.5 years. Most solar HW systems have some type of AC pump. Taking that into consideration, the Energy Returned on Energy Invested (EROEI) while the system is operational is about 15, or for every 1 watt of electricity used, 15 watts of energy are gained. In the Hudson Valley, a two panel SDHW system can expect to save about 3,350 kWh per year. That equals about 5,690 pounds of CO2 per year or 71 tons of CO2 over a 25-year life span.
How long do Solar Systems last?
That is a very common question. The answer is, it depends. Solar systems, like all other mechanical systems require some maintenance. Last week, I came across a solar hot water drain back system that was 28 years old. The great thing is, it was still working just like the day it was installed. The only problem the home owner had encountered was a bad circulator pump, which the plumber replaced.
Properly installed drain back solar hot water systems using distilled water could, in theory, last almost indefinitely. Solar Hot water systems that use antifreeze will likely last only 30 years or so. Still, that is a great payback. For either system, over the course of its operational life, it should easily pay for itself 4 to 5 times over.
Photovoltaics are said to last 25 years however, their output slowly declines over time. After 25 years, most current photovoltaic panels will be producing about 80% of their rated power. Still, that is not bad, and a well-designed photovoltaic system should pay for itself at least two to three times over its operational life (with current incentives).
The advantages of renewable energy systems, for those that are in it for the long haul, are:
- Stabilizes energy prices at or below their current levels, gives the property owner more control over expenses.
- Increases the property value of the residence or building they are installed on.
- Reduces emissions and environmental pollutants from nearby electrical plants.
- Reduces overall electrical load on grid, thus reducing the need for more power plants and high-tension distribution lines.
- Spreads out electrical generation capacity, thus making it more difficult for anyone catastrophic event to cause a regional blackout (distributed generation).
- Reduces the use of fossil fuels and thus dependence on other countries to provide energy for us.
As you can see, there are many advantages to a solar thermal, photovoltaic, wind, or microhydro system.