# Part 4—Consider Solar Energy Offsets

Note: This chapter was retired in July 2015 as the tools and data are no longer available. The pages are available here for reference.

## Step 1-Why Use Solar Power?

The reason that solar power is a good choice for some of our power needs is that you can offset harmful carbon dioxide emissions that are produced in many other power generating systems. With solar power, no carbon dioxide emissions are created. Here are the offset numbers that have been realized by the Abilene Texas and Harvard Forest solar panels to date.

At the Abilene installation:

At the Harvard Forest installation:

The Abilene installation is about 10 years old, so its 66,475 kWh of energy since its start will seem a larger number compared to Harvard Forest's 29,460 in two and a half years. However, going back to the maximum power production at each site (5 kW at Abilene and 12 kW at Harvard Forest) both sites are doing well. The savings of 92,565 lbs of CO2 emissions from Abilene plus 26,428 lbs from Harvard Forest could amount to a reduction in global CO2 emissions if they were never offset by vehicles driven or other fossil fuel (CO2 emitting) power plants. That is why we must try to look at other alternative energies, such as wind or hydro or develop technologies that have little emissions and little human hazards.

## Step 2-How Much Power do Solar Panels Generate?

In Part 3, we looked at some schools on Cape Cod, MA that are part of a group which have panels and have been monitored for about 3 years now. They have an installation that can produce 2.04 kW maximum power. Remember from the Case Study that the units of power are kilowatt-hours(kWh). So if we could have power at 2.04 kW for each hour of daylight in January, which is at best about 8 to 9 hours at this latitude, we would produce about 2 kW x 8.5hrs or about 17kWh. Here is the table comparison of the two schools for power for a week in January. The middle column is total energy (in kWh) for the day.

Notice that the numbers are never 17 here. They are higher in summer months. If you had this much energy (17kWh) for 31 days in January, you would have generated 527 kWh. If you look at your home electric bill, you can find how much electricity you might use just in your home, which is much smaller than a school. Can the school light all its classrooms with just solar power?

My electric bill usage for November 2009 was 421 kWh. This is my lights, stereo, TV, computers, and the little space heater in a den which we sometimes use to supplement our low thermostat settings. The power from the school's solar panels in winter seems to be about half of what the maximum potential is, and so if I had the same panels on my roof and no trees obscuring sunlight, I might be able to produce about 200-250 kWh in the winter. The school's panels do help, but the power needs are much greater than the school generates from solar power, so no, the school could not meet all its lighting needs from its solar panels.