Claims to be Net-Zero

[gar]

110606-1220 EDT

This post is not an ad and I do not suggest that you go on the tour.

The ad for the tour is at:
www.missionzerohouse.com.

This house was essentially gutted and heavily insulated, etc. It has a 10 KW rated array with microinverters. It has a ground referenced heat pump. The field is I believe several 80 ft deep vertical holes.

My judgement is the costs were high to achieve this. The owner is or was a lawyer and probably has a high enough income level to take quick advantage of the federal tax credit. So far he has not been assessed property tax on the solar system. He took advantage of the DTE Solar Currents Program, now fully subscribed and no longer available. His presentation at our recent Spark Energy Forum was inadequate in details. In this forum we are required to provide written questions, not a good method for a real discussion. I provided a number of specific technical questions and none were asked.

My comments should not mean I don't believe he has approximately achieved Net Zero. But at what real cost?

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[sgunsel]

A 10 kw array would essentially be net-zero for my house (gas heat and hot water) in NE Ohio. But I don't have enough roof area for a 10kw system. A 10 kw system would produce a little over 10,000 kwh annually at my location. I sure don't know how much he paid, prices are all over the map. It usually depends mostly on how much someone else (the rest of us) are willing to subsidize the owner. Some locations have generous subsidies. For me, 10,000 kwh costs about $1,300/year. If his system cost $40k, and he actually produces 10 kwh per year, and he received 50% subsidies, that would be a 6.5% return, much better than I can get at the bank.

Heat pumps with in-ground heat exchangers are fairly common, both with wells (two per system) and with buried tubing, even with no solar, since air/air heat pumps aren't very efficient when most heat is needed in these parts. I think the buried tubing type is more popular because it's not buried very deep and cheaper to install, but I don't have any figures. Are you sure he didn't mean a series of 80' trenches?

Solar panels are now available for $2/w and under, so it may not be all that bad. A few years ago I looked into generating solar power and it looked like a 50 year payback for a system with a 20 year life expectancy, not very economical. But solar component costs have plummeted since then and the utilities now provide net-metering so you can use the grid for storage (no batteries!). Still not very cost-effective here without a nice subsidy.

 

[sgunsel]

I watched the video and see that they installed 3 wells, 150 feet deep. The lot is small so they probably had no other choice. I also noticed that the roof is partially shaded by trees, which does not show up on any of the solar energy prediction programs that I have seen but will definitely have an adverse affect on solar power generation. It looked like only 36 panels, so the system may not even be capable of 10kw without the trees. Many of the projections that I have seen are hopelessly optimistic, almost the equivalent of increasing the mileage of your car by taping magnets to the fuel line. I'd like to see the results one year's (honest) monitoring.

 

[gar]

110606-1340 EDT

sgunsel:

Yes his lot is very small and thus requires vertical fields. My comment of 80 ft was wrong and probably relates to another installation in town. I believe he has cut the tree limbs that partially shaded the array. His array is south facing at nearly an optimum fixed angle. If he used a horizontal field it would probably require a 2 acre lot.

At our recent Spark meeting a comment was made that the vertical wells may cost $40,000 .

His yield per year may not be too incorrect and he may actually have data for a full year now. However, anything any of these people claim is suspect. Most are not engineers and do not fully understand what they are talking about.

From a couple actual installations that I have ask about it appears that yield my be at least 1.1 KWH/year per 1 W of panel rating. At the most recent discussion the presenter claimed his highest efficiency, mean greatest yield in a day occurred in February, and was attributed to the lower temperature of the panel. This person lives on a few acres, by education is a mechanical engineer and MBA, but most of his life was a manager, and I ask him why he did not use ground temperature water to cool his array. He did not have an answer, probably he did not think of this. His yield was about 1.14 KWH/1 W rating for last year. His inverter technology is older and not microinverters.

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[sgunsel]

The wells are for his geothermal heating/cooling system, not for the solar generation system, so they should be considered separately, just like using CFLs. Fixed angle panels can be selected to favor summer or winter, ideally you would select the angle that maximizes annual production at your location, but the reality of what space is available and reasonable (my wife would never accept panels on the front of the house) will dictate how many panels as well as the direction and angle.

I have often wondered if water cooling solar panels in the summer would help, but it may cause other problems, especially if more than a little water is required. I know my dark roof gets VERY hot as soon as the sun rises during the summer and I'm sure the solar panels do too. I'm also sure the long-term plumbing reliability would be far less than the electrical, whatever that really is.

I understand that http://mapserve3.nrel.gov/PVWatts_Viewer is reasonably accurate. It is interesting to see how much, and sometimes how little, different directions and angles affect potential generation at any given location. At the right price, even a small system that only replaces a small portion of your electric demand will be economically viable. Again, subsidies can make a big difference, but we don't have many available here.

 

[sgunsel]

The wells are for his geothermal heating/cooling system, not for the solar generation system, so they should be considered separately, just like using CFLs. Fixed angle panels can be selected to favor summer or winter, ideally you would select the angle that maximizes annual production at your location, but the reality of what space is available and reasonable (my wife would never accept panels on the front of the house) will dictate how many panels as well as the direction and angle.

I have often wondered if water cooling solar panels in the summer would help, but it may cause other problems, especially if more than a little water is required. I know my dark roof gets VERY hot as soon as the sun rises during the summer and I'm sure the solar panels do too. I'm also sure the long-term plumbing reliability would be far less than the electrical, whatever that really is.

I understand that http://mapserve3.nrel.gov/PVWatts_Viewer is reasonably accurate. It is interesting to see how much, and sometimes how little, different directions and angles affect potential generation at any given location. At the right price, even a small system that only replaces a small portion of your electric demand will be economically viable. Again, subsidies can make a big difference, but we don't have many available here.

 

[gar]

110606-1645 EDT

sgunsel:

When your goal is a Net Zero house, then the vertical fields become a part of the equation as well as any other components that relate to the goal.

Matt Grocoff's house is where it is and thus he is stuck with orientation and roof angle, but these are near optimum for him. Grocoff's Net Zero modifications to his house amount to probably more than half the value of the house when you exclude government handouts.

We have a very liberal town with a number of people that want to be Green for Green's sake, and somewhat to justify what they do I think they make some unrealistic assumptions as to their return on investment at the current time. But in terms of total population there are really very few installations. Certainly nothing that is of any consequence to the power company.

On plumbing life time. I believe copper systems are assumed to have a 70 ro 80 year life. In 45 years I have had no problem with my copper plumbing, tin-lead soldered, other than deposits within the hot water lines from hard water. If silver solder was used I would expect greater than 80 year life, and I do not know why tin lead solder would have an adverse effect on system life in this time frame.

If one used a closed loop in the earth it should be possible to achieve substantial cooling of an array. No problem with wasting water.

At present day costs there is no way I would consider a PV system on my home. I have a lot of roof space, possibly over 4000 sq-ft, but this is east west facing and and during the day there is considerable shading, in part from two 50 ft white pine trees that affect the east side.

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[gadfly56]

110606-1220 EDT

snip...10 KW rated array with microinverters...

sgunsel
...I have often wondered if water cooling solar panels in the summer would help...

Gar;

Maybe I don't understand the way PV systems are rated. If it's rated at 10KW and runs, say, 5 hours a day thats 5KW-hr or 150 KW-hr per month. I use about 110 KW-hr/mo, day and night combined. His roof area with 36 panels is about 16x72. Okay, that's a pretty big roof, but I'm amazed he can get that much power out of this array.

sgunsel;

I recall someone at one point actually marketed this concept; in fact the panels were matte black with the water running on the underside. I imagine it would get mighty toasty in the panel if the water shut off. In fact, now that I think of it, you couldn't shut the water off without risking damage to the panels. LOTS of hot water, whether you want it or not!

 

[gar]

110606-1945 EDT

gadfly56:

PV panels are rated in watts output under some standard conditions.

Suppose you had full power output for 6 hours of the day. That would be 6 watt-hr per day per rated watt under those standard conditions. Assume 365 days in a year, the the result is 2.19 KWH per year. In a particular location operation is unlikely to be at standard conditions. Also the profile of the intensity vs time of day has to be considered. Every day is not full sunshine, etc. So in a given area one determines what is a typical ratio from watt rating to KWH yield per year.

If a panel works without water cooling and you add water cooling, but the water ceases to flow, then how is that any different than if there was no water cooling attached to the panel?

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[sgunsel]

First, I haven't installed a solar array yet. But I am looking into it. Second, the solar array and associated equipment is expected to operate for at least 30 years with minimal intervention.

PVWatts is an online program that predicts solar panel output based on average weather conditions at your location. I undertand that it is reasonably accurate. The sun angle changes constantly during the day and every day during the year. There will be overcast and cloudy days as well. And temperature variations. It is a simple matter to go to the site and input your array size, direction, angle, and overall efficiency - and PVwatts will calculate the average expected output by month for the year. You can also get hourly output. You end up with a pretty good idea of what to expect.

Regarding water cooling, indoor piping is pretty easy. Outdoors, we have that nasty situation called freezing. Any piping above the frost line has to be protected against freezing. You can drain the pipes, heat, or come up with another scheme. We have at least 6 months a year with freezing weather. You also have to pump the water, which also consumes energy. Most of all, you only want to cool when it provides an advantage, so there must be a system to monitor temperatures and radiance(?) that can predict when cooling is optimum. I suspect the potential gains will be totally consumed and then some by these necessities. And I don't think it is reasonable to assume that pumps, automated valves, sensors, and controllers will be trouble free for 20 - 30 years. At least none that would be economicalliy viable, if any are. Even worse, if you have less than pure water and much evaporation, you would soon cover the arrays with mineral deposits that would be a real problem, if applying water to the top surface of the array. A permanant heat exchanger type mounted to the rear of the array would be prohibitively expensive up front and make freezing even more of an issue to deal with. Plus you probably need to deal with the roof temperature under the array, which will also get hot.

I see now why water cooling is seldom considered - many issues, more cost, and likely to be counter productive. Conservation is probably much more cost effective and works year round.

 

[gadfly56]

110606-1945 EDT

snip...

If a panel works without water cooling and you add water cooling, but the water ceases to flow, then how is that any different than if there was no water cooling attached to the panel?

The panels I recall were basically little greenhouses so you wouldn't lose water heating efficiency on a windy day. The PV panel was inside the greenhouse. What's the temperature performance coefficient for PV panels? Effect on life?

 

[gadfly56]

snip...
Regarding water cooling, indoor piping is pretty easy. Outdoors, we have that nasty situation called freezing. Any piping above the frost line has to be protected against freezing. You can drain the pipes, heat, or come up with another scheme. We have at least 6 months a year with freezing weather. You also have to pump the water, which also consumes energy. Most of all, you only want to cool when it provides an advantage, so there must be a system to monitor temperatures and radiance(?) that can predict when cooling is optimum. I suspect the potential gains will be totally consumed and then some by these necessities. And I don't think it is reasonable to assume that pumps, automated valves, sensors, and controllers will be trouble free for 20 - 30 years. At least none that would be economicalliy viable, if any are. Even worse, if you have less than pure water and much evaporation, you would soon cover the arrays with mineral deposits that would be a real problem, if applying water to the top surface of the array. A permanant heat exchanger type mounted to the rear of the array would be prohibitively expensive up front and make freezing even more of an issue to deal with. Plus you probably need to deal with the roof temperature under the array, which will also get hot.

I see now why water cooling is seldom considered - many issues, more cost, and likely to be counter productive. Conservation is probably much more cost effective and works year round.

I didn't explain the concept very well. What I recall wasn't a "swamp cooler" to keep the panels from overheating, it was a preheating system for domestic hot water. Water/glycol (or probably glycerin) stays inside the copper, and there is a heat exchanger loop running to the hot water storage tank. The panels were inside the "boxes" that the loop ran through.

Make a metal plate with a matte black front surface. On the back side of the plate mount/fasten/solder a 1/2" copper line that zig-zags back and forth, spaced about 3" on center. On the front surface mount the PV panel. Put the whole thing in a fairly tight box. There's enough black surface exposed (I think the cell substrate was semi-transparent) to get the box plenty hot and the water came out on the high side of 135F or so when you put a few in series, depending on flow rate. Obviously it didn't catch on.