Solar PV versus GCHP systems - how does the design process differ?

We had an interesting discussion about how the design of a GCHP system compares to the design of a GCHP system in the Certified GeoExchange Designer (CGD) class in the IGSHPA classes in Stillwater this week. The question about why the design of a photo-voltaic cell system could be so easily standardized, while the design of a GCHP system is so site specific and is difficult to standardize. We came up with a few reasons that the design process is more onerous for a GCHP system. 

The majority of the solar PV systems being installed across North America are connected to the electric grid, and basically use the grid as the battery. This has a number of implications in the design of a PV system:

• First, it means that the size and capacity of a PV system is not critical. The number of panels installed can be simply based on the roof area available and the purchaser's budget. It simply doesn't matter if the power supplied by the PV is 5% or 75%. The system is still connected to the grid and it provides complete backup when needed. 
• A GCHP system, however, is designed to meet to meet the entire heating and cooling load for the home or building. In some cases, auxiliary heating or cooling may provide a small portion of the heating or cooling, but the designer is generally responsible to supply all space conditioning needs. 

To meet the total heating and cooling loads, a designer must first know what the loads are, and to design a cost-effective GCHP system it's critical that the loads are known accurately. And to really optimize the system the designer will work closely with the owner and architect to recommend changes to the building that can reduce and balance the energy to and from the GHX. 

It's comparable to designing a PV system designed to meet the total electricity needs of a home that's not connected to the grid and relies on stored electricity to meet the needs when the sun drops below the horizon. To do that, the electricity needs of the occupants must be carefully calculated, and the designer will have to spend some time working with the owners to select the most efficient lighting and appliances. If they don't, and simply install a larger PV system, there's a good chance it will be to expensive for the owner. 

Currently, Solar City installs PV panels on your roof and sells you all the electricity you can use and the remainder is pushed into the grid. If it provides 20% of your electricity, great. If it provides more or less, it doesn't matter. 

But, if Solar City starts selling systems to homes not connected to the grid, using batteries to store energy for night time use, everything changes. To make the systems cost-effective, someone will have to calculate with a high degree of accuracy how much electricity the homeowners will use during the longest period of time that the solar panels can't produce electricity. If the system is being installed in Rhode Island, what's the longest period that the clouds are blocking the sun? How about Arizona? or Alaska? 

Much greater emphasis will have to be placed on ensuring the owner and architect are considering designing homes to allow maximum penetration of day light into the home to reduce lighting requirements, selecting appliances to reduce phantom loads, etc. The design process becomes much more complex...much more similar to the design process that must be followed by a good GCHP system designer.  An article at New England Clean Energy describes the problems surrounding solar PV / battery storage design quite eloquently.