A Good Design Scheme: Whole System Thinking

Over the past year, in this column, I have emphasized the concept of whole system thinking when designing and installing a renewable energy system. I have talked about an energy system functioning as an integral part of the home rather than as an isolated piece of equipment.

Now it seems I have some pretty high powered support for that approach. The Rocky Mountain Institute’s (RMI) summer newsletter has an article which applies this principle to everything from manufacturing carpet to designing a home. They call it "Tunneling Through the Cost Barrier: Why Big Savings Often Cost Less than Small Ones". Here’s some of what they have to say:

"Big savings can be easier and cheaper to achieve than small ones if you combine the right ingredients in the right way.

The usual way to (design something) is to analyze its components or subsystems separately and optimize the cost-effectiveness of each in isolation. But components interact in ways that aren’t obvious when you’re looking at them separately, and optimizing one part may "pessimize" the whole. Often you can reduce the total cost of a technical system by spending extra on certain components."


That last sentence is critical to the approach I always recommend when analyzing or designing a renewable energy system. Let me give you an example.

I often get calls from people who have an existing home and want to install or upgrade a renewable energy system. Some have already gotten bids from a dealer/installer for a system and want to get my input, some want me to help them design a system. One of the things that all these homes have in common is the presence of a large, often 220v, AC powered well pump.

Invariably, whether the house has an existing renewable energy system or the homeowners have a bid from an installer, the energy system is sized large enough to run the pump. The problem with this approach is that these pumps in a standard rural water system are designed to operate on grid power, not on renewable energy. In most cases a water system like that will be by far the largest consumer of energy in the home.

This makes for a much larger and more expensive renewable energy system which often must be designed more to run the pump than to power the home itself. I always ask about the water system first (the depth of the well, the water level, etc.) to see if a low voltage DC system will work. In those cases where it can (the majority), the cost of swapping the well pumps and installing a cistern is more than made up by the reduction in cost of the renewable energy system.

Most people see an existing pump and take the position that it is silly to buy another water system when there is already one in place that works. This failure to recognize the overall savings that can be realized winds up costing homeowners more in the long run. RMI defines the problem this way, "…designers are now so specialized that they rarely understand all the working of an entire system, and tend to confine themselves to optimizing their particular component or subsystem."

RMI also points out that it is common practice to set budget priorities for individual components or systems without considering how those systems interact. We then optimize the costs for that particular component up to the budget limit. However by limiting the cost of one component we may actually increase the cost of other components.

I gave a prime example of this kind of thinking in my column on refrigeration. Homeowners often set a limit on how much they want to spend on their energy system. In trying to meet that limit a dealer/installer will often look at ways to reduce energy consumption and will invariably recommend a Sunfrost refrigerator to the homeowner because "it is the most efficient".

This will certainly result in a less expensive renewable energy system (the Sunfrost requires fewer expensive PV panels) but, as I illustrated in my column, the total cost to the homeowner is greater because of the high cost of the Sunfrost. It is actually cheaper overall to go over budget on the energy system and buy the cheaper Vestfrost.

The Rocky Mountain Institute is located in Snowmass, CO and is one of the leaders in finding new approaches to old (and new) problems. They call it whole-system engineering and apply it to problems of all kinds from economic systems, to automobiles, to energy, among others. Founded in 1982 by Hunter and Amory Lovins, the Institute gives tours of its unique facility and annually produces publications and articles on a variety of subjects.

They can be reached at Rocky Mountain Institute, 1739 Snowmass Creek Road, Snowmass, CO 81654-9199. Their phone number is 970-927-3851, email is and they can be found on the Internet.

All Contents © 1998
Wagonmaker Press
Thomas W. Elliot


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