Solar photovoltaic on the house as an investment

[alistair]

I definitely think people should not overlook energy efficiency before going the PV route. Lighting isn't your biggest electrical use, unless you're trying to have your house spotted from the space station at night. A/C, dryer, refrigerators, dishwasher and plasma TV individually use a lot more power than most of your lights together will (yes there are some people who this won't be true).
Consider wringing out max efficiencies out of appliances against the cost of PV. If you have ideal PV circumstances (e.g. big, open, unshaded south facing roof, tax credits, etc.) then PV may still make sense. For a lot of other people, extra attic insulation, caulk around leaky windows, etc. will make more dollars and sense than PV.

[target2019]

Quote:

Originally Posted by alistair I definitely think people should not overlook energy efficiency before going the PV route. Lighting isn't your biggest electrical use, unless you're trying to have your house spotted from the space station at night. A/C, dryer, refrigerators, dishwasher and plasma TV individually use a lot more power than most of your lights together will (yes there are some people who this won't be true). Consider wringing out max efficiencies out of appliances against the cost of PV. If you have ideal PV circumstances (e.g. big, open, unshaded south facing roof, tax credits, etc.) then PV may still make sense. For a lot of other people, extra attic insulation, caulk around leaky windows, etc. will make more dollars and sense than PV.

Very good point. When we moved in about 20 years ago, the dryer was an electric hookup. After a few years we redid the kitchen, and as part of that electrical upgrade we converted the 220 for the dryer to two circuits, and installed gas line for dryer.

[Mulligan]

Quote:

Originally Posted by alistair I definitely think people should not overlook energy efficiency before going the PV route. Lighting isn't your biggest electrical use, unless you're trying to have your house spotted from the space station at night. A/C, dryer, refrigerators, dishwasher and plasma TV individually use a lot more power than most of your lights together will (yes there are some people who this won't be true). Consider wringing out max efficiencies out of appliances against the cost of PV. If you have ideal PV circumstances (e.g. big, open, unshaded south facing roof, tax credits, etc.) then PV may still make sense. For a lot of other people, extra attic insulation, caulk around leaky windows, etc. will make more dollars and sense than PV.

My neighbor last year had more insulation blown into his attic (10 year old house) for $600 or so and has really crowed about his heating/cooling savings. Although he is 87 I believe, he crawled up there and marked the beams before they came so they wouldn't "rip him off".
I really need to add more to mine as it barely covers the cross beams. But since I had my metal roof installed it has cut my bill so much by that alone it has sapped the motivation to do it. Maybe next year...


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[NW-Bound]

Quote:

Originally Posted by meierlde ... But what I have not seen that would make sense for folks in the southern states would be a device that could take the heat thrown out by the AC and heat the pool with it. At least in the spring and fall it could extend the pool season...

+1

For years, it bothers me that there's nobody doing this, or that there's no mention of it. Except in the midst of the summer, my pool stays cool most of the time due to evaporation. And exchanging heat from the AC with that 80F water should allow much higher efficiency than with hot air of 120F up on the roof.

I often wonder if I could experiment myself by brazing together a heat exchanger between a freon line of a small AC and the pool water. But perhaps I will learn that the chlorine in the pool water will corrode that copper heat exchanger in no time.

Quote:

If you live by a lake you can use the lake as a heat dump in the summer and a source of heat in the winter. (Sort of geothermal heat without having to drill wells).

Only if you own the lake or pond. The warmer or colder water may disrupt aquatic life.

[meierlde]

Quote:

Originally Posted by NW-Bound +1 For years, it bothers me that there's nobody doing this, or that there's no mention of it. Except in the midst of the summer, my pool stays cool most of the time due to evaporation. And exchanging heat from the AC with that 80F water should allow much higher efficiency than with hot air of 120F up on the roof. I often wonder if I could experiment myself by brazing together a heat exchanger between a freon line of a small AC and the pool water. But perhaps I will learn that the chlorine in the pool water will corrode that copper heat exchanger in no time. Only if you own the lake or pond. The warmer or colder water may disrupt aquatic life.

There do exist water source heat pumps, typically used in geothermal hvac systems (the heat is extracted or rejected to the ground water). Also there are a number of small hvac to hot water systems. Ideally if money were no object, then one would build a double loop system with clean water flowing to one of 2 heat exchangers, 1 for the pool and the other for ground water. Essentially the system would set upper and lower pool temp limits and use the ground water loop outside the limits. (assuming one is in the right kind of soil area). At the pool filter you would have a water to water heat exchanger with pool water on one side and the fresh water on the other. This would minimize the length of refrigerant piping. I doubt the economics works today but then a while ago solar economics did not work either.
Note that water heating units can go to 55c or 80 c depending on requirements.

Lets assume a typical 20,000 gallon pool, which is 160,000 lbs of water. To raise it 1 degree F would take 160k btus, A 5 ton ac unit is 60k btus, so it would take about 3 hours of running flat out to raise the water 1 degree. In looking around the web I found the knock on the hvac based heating is that it is slow, although if one used a 100k btu furnace it woud just be twice as fast. Now you might want an other pipeing loop with a radiator to pump pool water thru if it gets to hot. (going from 70 to 90 would thus take 3,200,000 btus, or about 53 hours of continuous flat out running of the ac unit.

[skipro33]

Quote:

Originally Posted by alistair I definitely think people should not overlook energy efficiency before going the PV route.

This makes sense because of the expense of a solar installation is based on the generation capacity. In my design, I'll be paying $2.55 per watt for a solar installation that is turn-key. If there's cheaper way to pay for watts, such as higher energy efficiency appliances, lighting, insulation, etc. then that is the better solution. However, most of those don't have a 25+ year life expectancy. Even LED bulbs are not rated for 25 years. Half that at best. So consider the cost of two LED bulbs when comparing to buying a per-watt solar installation. Same with appliances and such.

If a 60 watt eq. LED bulb costs $9, and lasts 12 years, two bulbs would last 24 years, same as the solar warranty. The bulb uses 8.5 watts for 5 hours a day, every day, for 24 years is 372 watts @ 16 cents a kWh for a total electrical use of $60 in today's dollars, not counting for inflation. 8.5 watts of solar at $2.55 a watt is $21.67 and does count for inflation.

I pay $21.67 for 8.5 watts of solar panels installed today and can light that light for 24 years and would have paid $60 to the electric company, not adjusted for inflation.

That's about 1/3 the cost with solar.

You mentioned saving by replacing a 60watt regular bulb with a LED bulb. A regular incandescent bulb will use 60 watts in an hour, 300 watts for a 5 hour day, 109.5 kwh a year and 2,737 kwh over 25 years. That costs $438 to PG&E compared to $60 for the LED bulb and $21 for the solar powered LED bulb.

You will spend about $18 in LED bulbs over that time and about $6 in incandescent bulbs as well.

[NW-Bound]

Quote:

Originally Posted by meierlde ... Lets assume a typical 20,000 gallon pool, which is 160,000 lbs of water. To raise it 1 degree F would take 160k btus, A 5 ton ac unit is 60k btus, so it would take about 3 hours of running flat out to raise the water 1 degree. In looking around the web I found the knock on the hvac based heating is that it is slow, although if one used a 100k btu furnace it woud just be twice as fast. Now you might want an other pipeing loop with a radiator to pump pool water thru if it gets to hot. (going from 70 to 90 would thus take 3,200,000 btus, or about 53 hours of continuous flat out running of the ac unit.

If all pools are like mine, they have an aerator nozzle that sprays and cools the water by evaporation. As I rarely find my pool too warm for my taste, I do not use it.

So, I am all for using the pool as a heat sink for the AC, but there's nobody making such a system.

[skipro33]

Quote:

Originally Posted by NW-Bound So, I am all for using the pool as a heat sink for the AC, but there's nobody making such a system.

Take the condenser coils, add some longer lines and set them in the pool. If the AC is near the pool, that shouldn't cost too much in copper tubing plus some extra freon.

[NW-Bound]

In theory, that's all it's about. For aesthetic appeal, you need a heat exchanger to be built into the pool plumbing.

I do not believe nobody else has thought of this, so there must be a gotcha. I suggested copper corrosion by chlorine in the pool water as a serious detriment.

[samclem]

A nit -- I think the units could be confusing:

Quote:

Originally Posted by skipro33 . . . The bulb uses 8.5 watts for 5 hours a day, every day, for 24 years is 372 watts kWh @ 16 cents a kWh for a total electrical use of $60 in today's dollars, not counting for inflation. 8.5 watts of solar at $2.55 a watt is $21.67 and does count for inflation. [This reasoning works fine because we assume the panels also produce their 8.5 watts for 5 hours every day, just like the light bulb use. Otherwise, we'd need to convert to kWh]

Overall, an "illuminating" example . . .

PV beats LED in payback right now (with lots of probably reasonable assumptions). The bigger question: Does PV beat all other investment uses for that same dollar? At the present real rates of growth many are estimating for the big asset categories, (less than 2% real), maybe it has a shot. Much depends on future electric rates.

[folivier]

Another possible advantage to using the A/C waste heat to heat the pool since water is a much better thermal conductor the A/C might run more efficiently and save electricity and wear.

[meierlde]

Quote:

Originally Posted by folivier Another possible advantage to using the A/C waste heat to heat the pool since water is a much better thermal conductor the A/C might run more efficiently and save electricity and wear.

Since the efficiency of an HVAC system depends on the difference in temp between the heat source and the heat sink it will be more efficient, (i.e. move more heat per unit of electricity) using a pool as a heat sink as the pool water will likley not be above 90 degrees, where the air temp at times of max heat load would exceed 90.

[ERD50]

Quote:

Originally Posted by skipro33 Quote: Originally Posted by alistair I definitely think people should not overlook energy efficiency before going the PV route. .... This makes sense because of the expense of a solar installation is based on the generation capacity. In my design, I'll be paying $2.55 per watt for a solar installation that is turn-key. If there's cheaper way to pay for watts, such as higher energy efficiency appliances, lighting, insulation, etc. then that is the better solution. ...

skipro33 - I agree that conservation should be compared to generation, but I am completely lost on your figures. What are you comparing?

Quote:

Originally Posted by folivier Another possible advantage to using the A/C waste heat to heat the pool since water is a much better thermal conductor the A/C might run more efficiently and save electricity and wear.

True, I think the reason we don't see them is every installation would be custom, and only a small percentage of installs could utilize this. Chlorine is another issue I guess.

Same with refrigerators and freezers - a water tap feeding the water heater would improve things on both sides. The fridge would have a better heat sink, and the waste heat would lower water heating bills. But how to plumb that in every home? And the risk of a leak, etc.

I did experiment once with misting my condenser. Darn it - air temperature went up, not down! Well, the condenser fins are close together, and water surface tension made the water stick and 'clog' the air flow, reducing efficiency! So much for that experiment! But a properly designed unit should work well.

Homebrewers have been known to use their pools to chill their wort (beer before fermentation), from boiling down to closer to yeast-happy temperatures.

-ERD50

[Texas Proud]

I know people are talking about buying efficient appliances etc. instead of PV.... however, most people are not going to replace a working appliance with a new one that will not actually pay for itself...

My AC system is getting close to 15 years old... however, it would cost me close to $10K to put in a whole new system that would be energy efficient. (dual stage... have to replace whole system to do this)....

Since a system usually lasts less than 10 years... I will use that.... so, I would need to save $1,000 per year in electricity to pay for it... or $125 per month when I use electricity... (assume 8 months of AC use)...(not taking into account gas as my unit is pretty efficient now).... My total cost for AC is less than that for at least half of those 8 months and not a lot more on the others... so unless I do not have to pay for any electricity, a new HVAC system does not make sense...


Other appliances are probably worse in payback... so it only makes sense to replace when something dies... a PV system actually has a payback time frame... at least for some people....

[NW-Bound]

After the energy crisis of the late 70s, there was a rash of installations of precoolers for ACs. Does any of you remember this?

Basically a precooler is an add-on panel about 4" thick with a CELdek pad. It is mounted on the exterior of the AC, up against the condenser. Outside air drawn by the AC to cool its condenser goes through the precooler first. The CELdek pad is kept wet by a dribble of water, which is turned on by a solenoid wired into the AC so that the water runs only when the AC is running. The precooler cools the air down to at least 90F when the ambient air is as high as 120F. Thus, the AC consumes less power due to less head pressure of the freon which liquefies more readily. Its outlet air is also cooler.

The previous owner of the home had installed such a precooler when I bought the home. Simple as the precooler was, it took me a bit of work to maintain it, basically keep the water nozzles from clogging due to calcium deposit. This AC has been replaced, and nobody makes precoolers anymore.

[NW-Bound]

Quote:

Originally Posted by ERD50 I did experiment once with misting my condenser. Darn it - air temperature went up, not down! Well, the condenser fins are close together, and water surface tension made the water stick and 'clog' the air flow, reducing efficiency! So much for that experiment! But a properly designed unit should work well.

When I do this with my auto AC, this works very well. The spacing of the AC condenser fins is of course coarser.

[NW-Bound]

Precoolers are apparently still used on industrial installations, where there is maintenance personnel to take care of them.

Following is a link, which shows that a 10-ton AC has its EER improved from 9 to 12 with a precooler when the outside is 115F. That's a 33% electricity saving.

See: Evaporative Cooling Precoolers.

[ERD50]

Quote:

Originally Posted by NW-Bound Precoolers are apparently still used on industrial installations, where there is maintenance personnel to take care of them. Following is a link, which shows that a 10-ton AC has its EER improved from 9 to 12 with a precooler when the outside is 115F. That's a 33% electricity saving. See: Evaporative Cooling Precoolers.

Yes - just like a solar farm versus residential rooftop, a large scale install creates all sorts of possibilities for added efficiency, due to economy of scale.

I also thought about the 'swamp cooler' style pre-cooler around the outside condenser, but then I'd need to build something, drain the water away, our well water is very 'chunky with lots of iron, and I don't think I'd want to use up our softened water on this. And we don't use the A/C all that much, sometimes probably not more than 15 days a year, other years much more, but I'm just not doing anything like that for 10% (and I'd probably not get that either) delta.

But the ideas are interesting to contemplate.


-ERD50

[skipro33]

Quote:

Originally Posted by ERD50 skipro33 - I agree that conservation should be compared to generation, but I am completely lost on your figures. What are you comparing?

I am comparing the one time fixed cost of solar to the recurring charge for electricity from a utility. The figures I posted show that solar is very cost effective but that it's hidden in a longer timeline than most people view their energy use.
With a LED bulb, the cost of the bulb over the savings in electricity are examined. With both LED and conventional bulbs, the cost of the electricity from both solar and utility are examined.

My figures show conservation and cost savings can be realized with an LED bulb when tied to the utility company. With my own source of generation and zero costs to generate, conservation doesn't matter as much and cost savings not at all after realizing enough savings to pay for the project at 7 to 8 years.


BTW, my next project is to research to cost to put in a well before California regulates ground water. I pay more for a month of water than I do for a month of electricity. With this 'drought', I will soon be unable to buy the water I want to use at any price from the utility.

[daylatedollarshort]

LED prices continue to drop. Our local Lowe's ad has 60 watt bulbs on sale for $2.48. The local Costco also has them for a reasonable price, but I don't remember the exact dollar figure.