Coal in a hard place.. expecte to produce < 30% of electricity by end of decade

I think I need to start ignoring your comments.

DOE says solar, heat pump, and tankless gas water heaters are more efficient than conventional water heaters. I agree, its fairly obvious.

What I was saying is

1) payback is better for grid tied solar PV than solar water heaters, and the solar PV adds power at peak demand often to the grid making that power more valuable.
2) solar PV is scalable, which means you can build a bigger system.
3) Solar PV is replacing grid electricity normally, while solar water heaters often replace abundant natural gas with electricity. This is often not worth the extra money from a ghg or pollution point of view.
4) If you want to heat water from PV you can, and you can heat all of it, not just a portion. IF you use a heat pump water heater, this often uses less roof space.

See DOE and I don't disagree at all.
When you look at today's prices and tomorrows energy needs, solar hot water heaters do not make sense in the United states for just about every household, solar PV is a better use of roof top. The two main cases for solar water heaters are swimming pools and those off the grid. A very high percentage of existing solar hot water heaters are for those with swimming pools, and my friends with pools and no solar hw, just don't heat them in the winter - big energy savings right there. If you don't need hot water all the time and live where it doesn't freeze, some of the cheap solar water heaters might make sense especially when self installed, but this is a very small portion of the population.

Run the numbers yourself. Post them here so we can all look at them. The prices of solar PV have dropped and water heaters have become more efficient. And simply because this thread is about coal, solar hot water heaters replacing gas water heaters do not reduce coal use at all, but solar PV has the potential to do that.

 

Well here's what DOE said on solar hot water heaters. They are least expensive, most efficient way to use solar energy to cut every home's utility usage.

 

AG is still unsure if earth climate is trending warmer let alone anthropogenic, so do not expect him to see too far beyond the tip of his ideological nose.

A home on crappy old tank electric for hot water would likely choose to switch to NG if they can, but as second alternatives can consider a new electric with a heat exchanger or solar heating. Which is better depends a lot on the local situation.

In my home, the extra money not spent on solar DHW instead of NG was spent on windows instead. Since NG use for air heating is 10x what I consume in hot water the opportunity cost was way in favor of windows. YMMV. By next year I'll know how effective my changes are. I am estimating my new annual household energy averages as:
150 - 200 kwh/month electric (from coal) down from 400 currently
23 therms/month NG down from 80 currently

Cost for windows, NG hot water about $5500. $200 window tax credit not included. Ignoring the subsidy, if my estimates are correct I will pay off the improvements in 6.5 years. The heater will last perhaps 10-15 years, while the windows barring damage are good for longer than I plan to live. No humans were injured or roofs punctured for this project. And of course the windows add to the beauty and enjoyment of the house, which few say about solar panels of any type.


Can we talk about something else now ?

 

Hey....did you hear that coal use declined by 15% in the US last year?

 

Again, they did not compare them to solar pv + efficient electric water heater. They also did not say what you are saying, but if they did I would say they are wrong. DOE has been wrong before.

TO get there you need to put numbers there, and not simply repeat you wrong headed prejudice. You are quite emotionally wrong. Let us go to energy star and compare a solar water heater to a heat pump water heater.

http://www.drintl.com/HtmlEmail/Water_Heater_Market_Profile_Sept2009.pdf

Solar Water Heaters : ENERGY STAR
Heat Pump Water Heaters Benefits and Savings : ENERGY STAR
and amazingly, that less expensive heat pump water heater uses less energy than the solar with electric back up. Your done, you have dropped energy bellow that of solar, without ever putting a panel on your roof. Solar with gas backup is slightly more efficient, but will never pay back within its useful life. Want to reduce the energy of that heat pump? Add solar PV. Now these systems must be priced locally and tax credits considered and the appropriateness of the system, but solar thermal, higher cost, less efficient, higher maintenance than heat pump water heaters that are new.

Why not just do them everywhere, natural gas water heaters are so cheap and efficient they don't do a great amount to reduce costs or CO2. On the other hand solar PV can help reduce dangerous pollutants from coal power plants as well as more ghg per dollar or roof than solar hot water heaters. Greece did a study and for anti-freeze type systems, accounting for maintenance and disposal of the antifreeze and production costs solar hot water heaters often had higher ghg than using gas hot water heaters.

 

...it is interesting to contrast and compare the CFC/ozone destruction issue with the Global Warming issue.
In the ozone case, after the obligatory initial condemnation of the theory and scientists who brought it forward, there developed a global consensus that the ozone problem needed to be addressed relatively promptly by elimination of the problematic chemicals. Global warming we do not seem to have a global consensus that immediate action is required (IMHO there is general global agreement it is man-made CO2 and it is happening).

 

That lower HPWH price is why I abandoned the search for solar DHW, and am now looking only at HPWH. But I hadn't yet noticed that HPWH actually used less electric energy than solar.

 

Nor will you, if the solar DHW installation is done right. Continuous water flow requires about 20 watts during the day's heating period.

I think there are two potential gothchas when it comes to HPWHs:
1) is reliability. New tech, so some manufacturers will be better than others, and quality standards will evolve. The GE HPWH I looked at from Lowe's has a 6 year warranty. Feel free to join the bleeding edge, just know what you are buying.
2) is local variation in a heat pump's COP. I assume the EPA average annual COP of 2.6 is correct, but I wonder what the variation across the US is. I have a very good idea how much sunlight I can collect at my home; I have no idea what the COP of a heat pump in my garage will be.

 

The HPWHs listed at Lowes now have a ten year warranty, and, as with other tank heaters, likely has more the do with the sacrificial anodes. They are more complex than a resistive type water heater. So there are more parts for potential problems, but heat pumps themselves aren't new tech. HPWHs themselves are only new here. The EPA site had an article on them long before they were available in a big box store. Only a couple of add on units for electric heaters were available stateside back then.

There were more models overseas. One brand, in Australia IIRC, had a remote condenser to collect solar heat as opposed to the ambient heat of the water heater's location. Many also had duct hook ups to direct the cold air byproduct into the central AC system.

So I wouldn't worry too much over reliability. Most likely it will need replacing for the same reasons as other tank heaters, a leaky tank. Regular flushing and anode replacement would keep that off.

We recently switched for an aging oil boiler to a gas condensing one and water heater this winter. A rough calculation has our costs cut to a third or quarter.

 

No need for DOE to compare, DOE simply notes that solar hot water heater is most efficient use of solar power and will save significant amount of energy and is cheapest to install as standalone. You keep trying to create a false either or decision.

More a case of much more powerful corporate interests (oil, coal, transport, automobile) who will lose money of world takes action on greenhouse gases. Ozone had a small constituency of a couple chemical companies, oil, coal etc. represents the biggest, most powerful corporate lobbying.

 

If you note, that link I gave you comparing the two was from energy star which is part of the DOE. The DOE when it compares says solar is less efficient and has a longer payback. That is right, the DOE comparing the two, says solar thermal is more expensive and less efficient than heat pump hot water. You have proven you are a troll by continuing this. What do you get kick backs from some solar hot water heater installers. You clearly are oblivious to the facts.

 

I'm seeing 10 year warranties on the HPWHs under consideration.

Year-round COPs in my climate seem to be testing out as about 1.8-1.9 on the better ones, and about unity on one particular model. Solar DHW here is severely hampered not only by short winter days, but also by cloudcover. Providing a decent energy fraction during our PNW fall / winter / spring requires a system seriously overbuilt for summer, or for your NM climate.

From one of AG's DOE links:

PS. From the same link, cost estimates for 2008:

The installation quotes I'm getting are double to triple these old estimates.

 

Remember its energy star only on average, your situation may vary. One thing is for sure, if you have an appropriate garage, basement, or other room HPWH will have a quicker payback, and is quite likely to produce lower lifecycle ghg.

What is new is the hybrid heat pumps now can be produced affordably It is newly commercialized tech, which means prices should drop as volume and r&d goes up. Solar PV also has prices going down with volume and r&d. Solar hot water is mature technology, and costs are increasing with raw materials.

YMMV, a warm garage in the south is going to add to efficiency, and you can feed it with passive solar heat. The most efficient systems here are geothermal HVAC heat pumps. When it's hot out they help aircondion, by making hot water

+1

For most of us a gas condensing unit is efficient enough, it is much more efficent than the average water heater. For those going to zero, I'm sure one of these HPWH powered by solar PV is the way to go.

 

Yep, local conditions are the deciding factor which tech to use. My high desert home has a lot of sun e.g., but it is a northern climate overall. We have 5500-6000 heating degree days, and less than 1000 cooling degree days.

​

 

Very important for solar, what fraction of potential December insolation do you actually get, after accounting for clouds and other weather? Up here, I think we get only about 25%. Your area likely gets triple that.

 

PVwatts estimates daily insolation at 5.25 kwh/m^2 average dec-january. Max in May at 7.3 kwh/m^2, and annual average is 6.5 kwh/m^2. My home would do even better for PV, since it is about 1000 ft above Albuquerque. I suspect my home is an example of possible very good matching of solar thermal to hot water consumption.

One additional advantage of thermal solar over PV is its relative insensitivity to clouds.

 

Nope, conventional electric is more efficient, approaching 100%.

Just like an EV car

​

 

Thanks. Saw it already.

 

I confess I didn't read the thread from start to finish, but the solr hot water caught my eye.

First, heating water with resistance electric heat is terribly inefficient. Unless you have a virtual unlimited supply of green hydro, you are way better off using a diffent method. Second, solar hot water from PV is insane! solar hot water is waaaaay cheap per BTU and way more effincint. A typical PV will convert less than 20% of solr to power, while a good designed hot water system can harvest well more than 50%.

Next, DYI solar hot water is pretty easy,a ns pretty cheap to do. Even if y of only serve to preheat the water, every BTU from solar is one btu you don't have to heat with conventional energy.

I built a simple flat plate collector, consisting of two used patios door tempered glass panels (free or nearly free) 150' of copper pipe, a piece of scrap 3/16 plate steel, a differential controller and a small circ. pump. The circ pump turns on when the delta is great enough, brining water into a preheat tank (once again, free) and on a reasonable day will heat 60 gallons from 60 f to ~150f. I then run that preheat into a demand propane (modern electronic control, so that it only fires as needed, or not at all if it is not needed.)

In the grey PAC NW we get about 50% of our hot water on an annual basis, 200% in the summer, 30% in the winter.
All for a cost under $500 including the pump. The controller also has an antifreeze mode that circs water when the temp is below freezing, perfect for the NW, not a great system where prolonged temps below ~15f. Evacuated tube systems with heat exchanger loops are freeze proof, come at a higher cost, but higher efficiency during grey days.

Finally, if you've in country whereA\C is a regular event,, a hot water recovery heat pump is the best solution, from an energ efficiency point of view, even better than solar hot water, due in large part from the fact that your A/Cworks way more

Bottom line, even though PV costs continue to go down, using PV to heat water is still not he way to go IMHO.

Icarus

PS to be clear, resistance electric water heat is 100% efficient in that it takes all the BTUs available in the kwh and converts it to heat. That said, it can take as many as 10 BTUs in generating and transmission loses to produce 1 at the heater. Granted there is a loses in getting gas to a burner from the well head, but it isn't ~90%.

 

know you did not. Pertinant figures
http://www.drintl.com/HtmlEmail/Water_Heater_Market_Profile_Sept2009.pdf
Heat pump hot water 2,195
Solar how water 2,429 kwh
Solar costs more and uses more energy to do the same work.

Here is the problem, you read none of the discussion, so you are making mistakes that were cleared up earlier. I fear I have wasted my breath.

First, if solar panel 1 is 10% efficient and costs $1000 and solar panel 2 is 90% efficient and costs $1,000,000 which would you use to build a system? That makes efficiency figures highly problematic. Efficiency at the panel level is a worthless factor. It is cost per work done that is important along with maintenance, and roof space and ascetics.

Now metrics should be hot water per $, and here you must actually do the work and calculate. I hope you agree. You can't just say A is stupid it must be worse, when many smart people find it to be better. If you have not done a calculation how can I honor your opinion? Read the link above and ask whether heat pump water heater + solar pv is better or worse than putting in a new solar hot water heater. IMHO many with condensing gas or heat pump hot water can stop, and not even consider solar to heat their water, but if they want to use solar, PV is the way to go.

I certainly will not discourage diy projects. I think they are great. You can definitely improve your system, but its not for everyone. I assume from this though you have electricity and not natural gas. Would replacing the propane system with a heat pump hot water heater, not have reduced more pollution if doing it today? That would have been my first step. As a second step your DIY project would make that more efficient, but a DIY grid tied solar PV system would also have made it more efficient allowing you to use no grid electricity or propane. It all depends on your goals.

Solar hot water is for a few people, probably less than 2% of households in the US that are grid tied and don't have pools. I do not think most could do the DIY, some would include their own labor costs in the calculations. I always love people that talk about things like 200%, no you made extra hot water that you did not use. We normally in engineering call that waste. If you used no propane in the summer its 100% solar, if you used any propane you threw away more than half. Net metered PV removes this waste, and at least here, provides electricity during peak demand. The project sounds like it was good for you, but would not scale to many. Certainly your system does nothing to make the argument that solar is appropriate for even a low percentage of households.

Solar PV is appropriate for a much much higher percentage of households. How many years would payback be if you DIY and installed solar PV? Do you have net metering? If so you can choose how much or how little of your electricity you want to produce, you are not limited by the hot water. If you are useing hydro or wind already no need to even put up the PV, you aren't using polluting power.