GHX Cost per Watt - compared to solar PV cost per Watt

Proponents of solar PV systems often talk about the "cost / Watt" to install photo-voltaic cell systems. The cost has come down considerably in the last few years, and now averages in the range of $5.90 per Watt. It's come a long way...it was around $10.00 / Watt a number of years ago. How does that compare to a GCHP system?

Actually, PV does not compare well with a GCHP system at all. Let's compare the cost of a PV system at $5.90 / Watt to a comparable GHX. (*Based on installed cost of $5.90/watt from report “Tracking the Sun VI, An Historical Summary of Installed Price of Photovoltaics, July 2013 Lawrence Berkely National Laboratory”)

Why only compare to the GHX? Shouldn't it be compared it to a whole system? A PV system only supplies electricity...kWh... to a home or building. It doesn't include the toaster to toast the bread, or a light to brighten a room. It only supplies kWh. A GHX supplies Btu's or kWh to a heat pump. It supplies the energy the heat pump is connected to. And it doesn't matter what your energy source is, the energy is connected to some kind of appliance to convert the energy to heat your home. So, we're comparing the GHX to the solar panels. 

A GHX for a typical 4 ton (14 kW) GCHP system can be built for about $6,000 to $18,000 in North America. The cost depends on the land area available, the dirt or rock the GHX is being built in, the equipment used to install it, the temperature of the dirt or rock, the building loads, etc. But those are reasonable costs across the country. The heat pump connected to that GHX will produce about 35,000 Btu/hr, or about 10,250 Watts of heat. If the coefficient of performance of the heat pump is 4.0, about 7,700 Watts will be coming directly from the ground (the rest is from the electricity used to power the compressor, pumps and fan). That means the cost per Watt is about $6,000 / 7,700 Watts = $0.77 / Watt to $18,000 / 7,700 Watts = $2.33 / Watt. About 60% to 87% less than a solar PV array. 

But wait...let's compare the total energy supplied by a solar PV array versus a GHX over a year. A properly sized GCHP system will operate about 2,500 hours per year in heating in the northern half of the U.S. and Canada...drawing 2,500 hours x 10,250 Watts of energy from the GHX = about 19,250,000 Watts of energy from the ground. 

A 7.7 kW solar PV array will cost about 7,700 Watts x $5.90 = $45,430 to build. According to the National Renewable Energy Laboratory (NREL) website a 7,700 Watt system will produce about 9,000,000 to 12,500,000 Watt/hours of electricity annually, depending on the location. That's about 50% to 65% of the energy taken from a GHX that costs about 60% to 87% less than a solar PV array. That's because the sun only shines so many hours per day, and a GHX works all the time. 

Then consider how long a solar PV array will last. Typically they will only last about 20 to 25 years. A GHX will last for at least double that. The one I installed in 1992 is still running fine 21 years later and I don't expect I'll have to replace it in my lifetime. 

So what's the better investment? Solar PV or a GHX?