With solar collector efficiencies going up and prices coming down perKw Hr, and with subsidies in place, it seems to me that most other modes of heating/cooling are more expensive and short sighted if we are truly "goin green". Am I missing something? Domestic hot water needs utilizes standing hot water, but in INDIA back in 1996 I saw my first on demand electric hot water heater. I have one today. Today even my clothes washer makes its own hot water. There has been a lot of ink about Geo Thermal heating/cooling, but I cannot see the cost effectiveness ROI of this form of heating. With liberal use of passive solar design and techniques coupled with tight, well insulated homes, is there a better (read less expensive)way to heat/cool/ our homes and run our appliances than using photovoltaic systems? If so what is/are they?

No disagreement here. A little common sense and ROI analysis goes a long way to making a good decision. Once you have electrons in your building, the conversion to heat is green, simple, and 100% efficient. Of course you should also try to obtain those electrons at the lowest cost possible using a green approach. That’s why we are big fans of hydroelectric if it is available at the site and PV too.

What about a micro wind turbine? Are they worth the money and time/maintenance to install and run. I don't know much about them other than what I've gleaned from the web, but wind is free when it blows. Seems like you could tap that energy source and keep a battery charged to use with 12v lighting if nothing else. Again the ROI may be relatively small, but everything helps. There are lots of turbines on the market, but I'm not educated in their uses and capacities to make a sensible decision. Any discussion on wind would be very helpful to me. But you engineers and physicists need to "dumb it down" a bit for me.

Sorry for the double post, I don't know how I did it.

Micro-wind is rarely more than just a roof-ornament, and higher maintenance than PV (whether grid-tied or off-grid).


At Q4 2013 US pricing small scale rooftop grid tied PV had an un-subsidised lifecycle per-kwh cost of about 8 cents, which is well below the residential retail rate in most of the US (the US average is on the order of 12-13 cents.)

Rather for setting for 100% efficiency out of the power once it's inside the house, leveraged against heat pump technologies, in most of the US you can get 300% or better. A better class geothermal unit will get you maybe 400% if you have a meticulous system designer, but for many/most the money is better spent on best-in-class air source heat pumps, improved buliding envelopes, and PV. The most-common and most cost-effective path to Net Zero Energy houses in my neighborhood (central MA, US climate zone 5) is an ~R40 whole-wall house with U0.20 windows (sized and oriented for optimal passive gain) and a gable roof with an east-west orientation with 5-7kw of grid tied PV. There is at least one Net Zero House in my area that is off-grid, using hydronic solar thermal for at least some of the heating, not mini-splits: http://www.telegram.com/article/20140112/NEWS/301129990/0

Only if you lived on a high coastal bluff would the economics of micro-wind begin to approach that of grid tied PV at $4/watt all-in cost. Currently in Germany grid tied PV is hitting the $2 range- most of the up-charge for the US market is in the marketing, multi-layered inspection & permitting, and somewhat higher cost/lower efficiency labor (which is improving as the installers get more experience.) In some hot markets in TX they are expecting to break the $2/watt barrier in 2014, using innovative racking designs from India that take a huge chunk of the labor out of it. We'll see...

At $2/watt the lifecycle cost of the PV output is under a nickel a kwh, making it ever harder to make the case for geo over air-source heat pumps in places that actually work with air source heat pumps. (A 99% design temp of +5F or higher is the current limit for ducted air source, but even -15F is fine for some ductless mini-splits.)

I agree with Dana, you really need a lot of wind to extract significant electrons...air being much less dense than water...

Thanks, I think I already knew micro-wind was a toy, but it helps to have my ideas debunked by others. I have seen PV systems that are mounted on a pole and track the sun up/down as well as east west to follow the suns path throughout the day and year for maximum solar exposure. I have not explored the prices, but the theory seems valid. What are your thoughts on this type of system? I have the unobstructed area for such a system. I don't want to put panels on my roof because the roof will be a metal SIP, and I don't want to punch holes in the metal. I don't mind a longer payoff timeframe. And I am of the opinion that money spent today is cheaper than money spent tomorrow, all things being equal.

Tracking PV system do significantly increase output, but tracking mounts are expensive and have to be maintained. If you have the real-estate, it's usually cheaper/better to just add more area to your PV array.

There are racking systems that don't require punching holes in our roof, and fixed non-tracking ground-mounted array are usually cheaper than a roof-top installation. Again- if you have the real estate, simpler racking and more PV area is usually the better bet.

Thanks Dana, so do I understand correctly that a ground mounted fixed array will equal or surpass a moving array WRT cost, and maintenance, and money saved by using the fixed array on the ground and adding more panels will trump the solar gains from a tracking array?
I think the answer is YES, but always better to run it by someone with experience.

That has been the experience of people in my area- at current PV panel costs you're far better off spending the money on more panel than spending it on tracking mounts.

This guy in a town next to me did it all with ground-mounted fixed-orientation racking. He didn't want to mess up his pretty standing seam roof, and with ground mounting it was cheaper to install, easier to maintain.

Posted By DAND on 14 Jan 2014 03:08 PM
With solar collector efficiencies going up and prices coming down perKw Hr, and with subsidies in place, it seems to me that most other modes of heating/cooling are more expensive and short sighted if we are truly "goin green". Am I missing something? Domestic hot water needs utilizes standing hot water, but in INDIA back in 1996 I saw my first on demand electric hot water heater. I have one today. Today even my clothes washer makes its own hot water. There has been a lot of ink about Geo Thermal heating/cooling, but I cannot see the cost effectiveness ROI of this form of heating. With liberal use of passive solar design and techniques coupled with tight, well insulated homes, is there a better (read less expensive)way to heat/cool/ our homes and run our appliances than using photovoltaic systems? If so what is/are they?

The cost for natural gas fueled heating in this area with a 97.5% efficient furnace is about $0.025 per kWh of heat delivered (including all natural gas subsidies). The cost of my solar PV energy is about $0.064 per kWh electric (including all subsidies at 2010 prices http://www.residentialenergylaboratory.com/comparison_of_pv_systems.html). If I converted the solar PV into heat using a heat pump with a COP = 2.0, the cost would be about $0.032 per kWh of heat.

Thus, there is a cost for the "greener" solution of using solar PV. Since 2010, the cost of panels has decreased, but the subsidies have also decreased.

The cost for running appliances, lighting, etc. at $0.064 per kWh electric from the solar PV is significantly lower than paying the utility at $0.108 per kWh.