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Reducing power used for cooling

According to the EIA, US households use 183 billion kWh for A/C, and 156 billion kWh for refrigerators per year (Source: http://www.eia.doe.gov/emeu/reps/enduse/er01_us_figs.html#2) in 2001. In the same base year, the US produced 3736 billion kWh of electricity (Source: http://www.eia.doe.gov/cneaf/electricity/epa/epat1p1.html). This suggests that cooling applications in US homes used roughly 9% of total US power in 2001. More importantly, these two applications alone account for 30% of the power used in US households and constitute a significant portion of consumers non-discretionary spending. The EIA points out that this figure will rise as the proportion of homes having central A/C is increasing and as more people populate southern states. An additional problem with A/C loads is that they tend to require expensive peak power and therefore dicate the dimensioning of our power system.

The Pickens Plan calls for spending $1.2 trillion to generate 20% of US electricity with wind. For the record, I view this plan to be sound, as the Danish grid example already shows that even higher wind loads can be managed with existing technologies. However, the challenge of managing intermittent wind supply and matching this with peaky demand for cooling applications would have to be addressed by building additional gas or coal-fired power plants, pumped hydro or other investments. While it would more desirable to dramatically improve building insulation towards zero energy levels, this might not be feasible for many existing buildings.

This challenge could be addressed by switching to solar sorption-powered A/C systems (Not to be confused with PV powered conventional A/C systems or swamp coolers). These systems convert thermal heat into thermal cooling through a contained chemical sorption process using lithium bromide. Solar sorption-powered A/C systems are currently still more expensive but require very little electrical power. In addition, their cooling capacity closely matches solar radiation, thus reducing the need for expensive peak power and smoothing out the demand curve. For 24 hour cooling applications, cold storage BTUs generated during the day can be used at night.

Currently, solar sorption-powered A/C systems are already economically viable for large applications such as malls, offices and factories. The Festo Group cools its entire HQ campus with a solar sorption-powered A/C system. Other firms are working on reducing the size of these units so that they will be viable for single family home use. Other usage models could also be introduced: Solar sorption-powered ‘District Cooling Systems’ could provide refrigeration services as a utility service, much as existing ‘District Heating Systems’ do today. This would take advantage of scale economies present in sorption-based systems. With further innovation, refrigerators in homes could also be linked to solar sorption-powered cooling systems.

While not providing a 20% wedge as detailed in the Pickens Plan, solar sorption-powered A/C can play an important part in reducing expensive peak power consumption and 'freeing up' more natural gas. It can also play an important role in easing the burden of high electricity bills on consumers and businesses.

Editorial Notes: Also by EB contributor Thomas Christiansen: Mini case study: peak demand in Germany.

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