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Solar hot water heater
Old 08-08-2009, 10:44 AM   #1
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Solar hot water heater

Ive been looking into getting a solar hot water system for my home. It looks like the cost would be around $6,500. With the 30% government give away I guess my cost would drop down to around $4,600.

This is a 80 gallon drain back system with two 4x8 collectors. The seller claims that it should generate 64,000 to 65,000 btu/day, and save me around $35-$40 per month on my electric bill. I am all electric and electric cost here are around .08. But the electric company is asking for an increase.

So does this sound about right? Is it worth spending $4,600 to save $35 per month? That is about an 11 year payback, will the system last that long?

Anyone here with a system?
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Old 08-08-2009, 01:10 PM   #2
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I always have a water solar heater. Up until 2 years ago that is. Here in AZ, one would feel foolish to pay for electricity to heat your water while the outside temperature is 110 degF and your AC is running non-stop. A no-brainer? Not so fast.

Though it rarely freezes in Phoenix, it does occasionally. My system is 20 yr old, and back then they all used the simple anti freezing method of circulating hot water back to the panels when needed. It is obvious that one loses heat, hence this method is only useful in places with few cold nights.

In walking around the neighborhood, I have seen so many similar systems in non-functional states, meaning disconnected from the plumbing but left on the roof. Simple as it is, these systems often failed due to corrosion in the electrical connections. Due to loss of sensor connections, the pump may fail to run to produce hot water, or runs all the time so that you lose all the hot water during the night, or fail to run during a cold night. The latter failure would cause catastrophic loss of the panels due to freezing.

Earlier, I said I had mine until 2 years ago. Being a handyman and an electrical engineer, I was able to maintain mine by verifying the proper operation, and even replace the circulator pump once. Then, one night I saw that the pump was leaking and decided to turn it off without draining the panels, and sadly without knowing that we had a freeze right that very night.

I have since taken apart one panel and reconstruct the internal copper grid, buying a welding torch and learning to braze copper in the process. It is a lot of work!

I have no experience with drain-back systems, but suspect that it would require periodic inspection and maintenance. In fact such systems are more complicated than mine.

I don't know about the payback in your case, but on the operating issues I would recommend that, if you install one, to pay attention to it and know how to fix or troubleshoot any failure before it becomes catastrophic like 99% of the systems I have seen, mine included.
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Old 08-08-2009, 01:32 PM   #3
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Originally Posted by dm View Post
Ive been looking into getting a solar hot water system for my home. It looks like the cost would be around $6,500. With the 30% government give away I guess my cost would drop down to around $4,600.
This is a 80 gallon drain back system with two 4x8 collectors. The seller claims that it should generate 64,000 to 65,000 btu/day, and save me around $35-$40 per month on my electric bill. I am all electric and electric cost here are around .08. But the electric company is asking for an increase.
So does this sound about right? Is it worth spending $4,600 to save $35 per month? That is about an 11 year payback, will the system last that long?
Anyone here with a system?
We've had one since early 2005, but they're a no-brainer in Hawaii. Something like 35% of residential homes use solar water and they have a 3-5-year payback.

I'd love to see your seller's unit-conversion factors from BTUs to $$s. It sounds so simple & straightforward from their sales perspective. And they know what the sun will deliver so precisely, too, within 1000 BTUs/day! Impressive!

The problem is that the payback depends on a number of factors outside the seller's consideration-- your family's hot-water use, your local temperatures & sunshine, whether your water heater has an insulating blanket, whether your house's hot water pipes are insulated and how far away from the water heater they run... you get the idea. Exterior piping insulation breaks down in sun/weather and has to be painted/replaced every 4-5 years. DC water pumps may die every 8-10 years. You may want extra temperature-limiting valves or isolation valves. Solar water tanks may only last 15-20 years. All of these issues can add several hundred dollars to the price and extend the payback. We did the math for our family and came up with $10-$15/month savings.

The best way to determine your savings would be to connect a 220V version of a Kill-A-Watt to your water heater's supply wiring and measure it directly. A second-best way would be if someone in your neighborhood has gone solar. Then you'd want to see their utility bills for the year before/after (12 months' average, especially if your winter is a lot colder than your summer). A very unpopular way to figure it out (unless you live alone) would be to shut off your water heater for a few days and see how your power use drops.

Is the system a drainback because of your area's weather? A better question might be whether it's as simple/low-cost as it can be. Ours was built with 30-year-old collectors and a used water heater so it's already paid for itself. But we don't have to worry about winter temperatures.

You may want to check your state's incentives:
DSIRE: DSIRE Home
If you get an additional state tax credit then that would factor into your payback. And it's even possible that your county/city govt might have some incentives, or that your local utility company would offer a rebate.

Finally, are you going to stay in the house for the entire payback? Only a buyer who's an engineering geek or a green zealot will give you extra money for your solar water system. Most buyers would be concerned that it'll "break" and so they'll be even more reluctant to offer full price.

Your payback spreadsheet might also want to factor in 3-5%/year utility-rate inflation. That actually tilts the calculation in the sales guy's favor but it's realistic.
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Old 08-08-2009, 02:04 PM   #4
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Your payback spreadsheet might also want to factor in 3-5%/year utility-rate inflation.
Yes, and also offset that by the investment opportunity loss of $4,600. Most salespeople ignore that.

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Old 08-08-2009, 04:28 PM   #5
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I'm outside of St. Louis so we definatly are in a freeze zone. There are also no state incentives.
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Old 08-08-2009, 11:31 PM   #6
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I'm building a summer only solar shower out by the pool. Not done yet, but it will consist of 200 feet of black garden hose, 20 feet or so of regular garden hose, a couple bucks worth of pvc pipe, a couple of inexpensive shut off valves, a couple connectors to attach the pvc to the garden hoses, and an inexpensive lo-flow shower head. All up, about $75. May add another 100ft to the black hose if the showers are too short.

Originally it was planned as a way to provide showers during a family reunion for those who decided to camp out at our place (expecting 25 people, and our septic tank is not likely to withstand the rigours of 25 people using the toilets and showers for a week), and to provide a shower for anyone wanting to shower off after pool parties in a saltwater pool. I'm thinking I will make use of itt in the summer though...save the propane.

I would love to put a solar water heater on the roof, but the type of on-demand water heaters I bought are not compatible as backup heaters. I may make the switch on one of them if it ever needs to be replaced. Otherwise the economics don't work for me.

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