Cost Effectiveness of Solar Water Heaters

My friend, a very smart geologist was showing me his Active Solar Water Heater system. He’d run calculations figuring how much money he was saving with it. (We’re in New England if it matters)

I then asked if he had accounted for the cost of electricity to run the circulator pump. After an embarrassed reaction it was back to the calculator and he realized he was actually losing money.

With just a little googling I found most analyses focus on the cost of equipment and factor in the use of a ‘backup’ system for cold seasons or when no sunlight is available. But I don’t easily find any accounting for the accompanying electrical energy usage.

So, what’s the scoop? Are they worth it in ‘Northern’ areas?

I did find this source

that says recent improvements in Photovoltaics make liquid collectors obsolete; just use PV panels to heat the water directly, without an intermediate exchanger.

In my experience no. With the initial cost and expected lifetime they can’t save enough energy in that time frame to exceed the price difference vs a standard electric tank.

Same goes for the heat pump water heaters that are being forced in.

As the equipment becomes more prevalent the initial cost will come down and it will be worth it imo. So far they’ve only been in the realm of wealthy do-gooders. As government mandates come into play the technology expands.

Just because there is a cheaper option doesn’t mean that the option you chose is “losing money”.

If house #1 chooses to heat their water with electricity and it costs 35 cents per day, and house #2 chooses propane which costs 32 cents per day, and house #3 chooses a combination of solar and electric which costs 38 cents per day… then I say big deal. so what? Why do you feel the need to shame the person who’s spending 38 cents and say they are “losing money”? Do you make similar judgmental observations about the person who’s spending 35 cents when they could be spending 32 cents?

When you try to choose which option you want, surely the cost is one of the factors in your decision. But you only know what the cost is NOW and you have to guess as to what the cost will be over the next several decades. And then there are lots of other factors, like safety, ease of maintenance, reliability, matters of conscience (would you use a water heater than runs on the blood of kittens, if it were the cheapest option available?), possible effect on the resale value of your home, aesthetics, and much more. For example, if you have a fireplace, that may seem like an inexpensive option until you consider that your homeowner’s insurance is more expensive, you have a higher risk of burning the house down, and when you sell the house it might be harder for the buyer to obtain a mortgage.

To answer the OP, running a solar system in New England might cost about the same as a conventional system (with current energy prices). If you live in a sunnier climate, or if the price of electricity goes higher, then solar might cost you less money. FWIW, solar is a very popular option in Germany, and there are only two states in the USA which get less sunlight than Germany does: Washington state and Alaska.

Sbunny8: the solar thermal system is going to take more maintenance, so if there is no money savings why do it at all?

I believe I already answered that question when I said there are lots of other factors, like safety, ease of maintenance, reliability, matters of conscience (would you use a water heater than runs on the blood of kittens, if it were the cheapest option available?), possible effect on the resale value of your home, aesthetics, and much more. Here’s another one to add to my list I already gave. If you live in an area where power outages are common (perhaps because of power lines being knocked down by storms) then it sure would be nice to have a solar water heater which can run off-the-grid (maybe with a battery backup for the recirculating pump?). Then you could still wash dishes and take showers even when the electricity is out. That’s just one example of a possible reason that someone might like.

Besides, just because there is no money savings NOW, doesn’t mean there won’t be any money savings in the years to come. It’s rather easy to imagine that electricity prices might go up in the future. But, aside from bad science fiction, we can be rather confident that the sun will keep on shining just like it always does.

How many BTU’s can I get out of a gallon of kitten blood? I’ll need to do the math.

I had a solar assist water heater. It had an electric element at the top and closed loop circulation coil at the bottom. A solar collector on the roof and a photovoltaic panel ran the circulation pump. Worked well for about three years.

Crud in the system requires cleaning and flushing. Then refill with antifreeze.

Circulation pump shot. $200

Circulation pump shot again. $200

Crud in system again.

Remove all solar equipment and replace with good electric water heater.

As always your milage may vary.

Assuming blood is fairly close to water, and assuming that kitten body temperature is close to humans, and you’ll be cooling the blood down to about room temperature (roughly 20 degrees), that works out to about 160 BTUs of thermal energy per gallon (8 BTUs per gallon per degree F).

Have fun with the math.

I have a baseboard hot water heating system for my house. The boiler also provides my domestic hot water. When the old boiler died a few years ago, I replaced it with exactly the same thing, which was hard to find since most folks wanted to sell me some high efficiency thing or some combination thing that would have required a separate water heater.

My boiler is definitely not the most cost efficient way to heat your domestic hot water. However, the heating system in general provides much more comfortable heat for the entire house than forced air, and by having it provide the domestic hot water as well, I never have to worry about running out of hot water. My kids can take their ridiculously long showers, and it doesn’t matter Since the boiler heats the water on-demand, I could literally run the shower 24 hours a day, 365 days a year, and never run out of hot water (until I couldn’t afford to pay the bill for it any more and they shut it off).

I like the comfortable heat, and I like never running out of hot water, and I like that I actually have hot water and not warm water.

For some people, money isn’t the only factor.

PV panels used to be ungodly expensive, which made the choice between a system that uses PV panels to provide resistance heat and direct water heaters with a circ pump a fairly obvious choice. The PV panels just couldn’t compete. But PV panels have gotten much, much cheaper in the past couple of decades. It wouldn’t surprise me if PV panels are the better solution now.

I haven’t done the math or the research though, so I don’t know which system is currently the better choice.

RE: “Why do you feel the need to shame the person who’s spending 38 cents and say they are “losing money”? Do you make similar judgmental observations about the person who’s spending 35 cents when they could be spending 32 cents?”

I don’t believe I or anyone else said anything about shaming him for his choice of a heating system. I did point out he was a little embarrassed to have forgotten to include the cost of the electricity for the circulator pump. That’s not ‘shaming.’ And I brought it up in the context of making me wonder about the ‘total cost of ownership.’

Yes, you need to factor in EVERYTHING when you want to do a cost of X vs Y sorta thing.

However, my impression is that even if it cost you a bit more for solar water heating rather than regular water heating, it is still MORE environmentally friendly.

Now, obviously, if solar water heating took a butt load of copper and man hours and electricity and other stuff at SOME point it would actually be LESS earth friendly than just doing it the old fashion way (ethanol I’m looking at you).

I’ve had a domestic solar water (DWS) system since 1986. First down in the Los Angeles area and now (the same one relocated) to FAR northern California. In 1986 I figured a 15-year payback only if I could turn off my natural gas fired tank, which I could and did. In 1992 the holding tank failed and moved my payback period an additional 8 years into the future. No other replacement parts have been needed since then. The system does require the replacement of a freeze control sensor every three years or so for $20.

The price of natural gas and then propane rose more or less as I expected and by 2010 I decided the system had actually paid for itself. In 2012 the cost of propane around here started to decline (competition with natural gas) and nowadays (2016) I figure my system is a wash, cost-wise. If something breaks I have spare parts but the reality is that my 30 year old system never saved anything close to what I expected.

I’m still glad I did it, but the next major component failure probably means the system gets scrapped.

Depends greatly if you’re cycling it through a live cat or a dead one. If it’s a live cat then you have to factor in food, water and kitty litter. It all sounds good on paper until you think of the smell generated from just taking one shower.

Who’d buy that type ? That type shouldn’t exist, the better type is the one that does not use circulating glycol. . btw its there to be anti-boil and raise the boiling temperature.

The glycol is a poor solution to a problem…

People noted that the units dripped hot water all summer long…
The cause was that when the storage tank was hot enough, the water in the solar panel would boil , and that would pressurise the system and cause the pressure relief valve to open… That was considered dangerous and wasteful. With the glycol in there, the water can get to a higher temperature before boiling, and it might not boil because the solar collector its now losing heat faster (to the air and as infra-red… ) … But you found out, its still boiling and that creates deposits of solid glycol. Glycol is a bad solution.
The proper solution is to only circulate water up to the collectors, and when the storage tank is full of hot water ( all up to temperature) , let the collectors go dry. Just make them Tonka tough.

As it happens, I am right now in Barbados. Certainly, the supply of sun is greater and more regular. Everybody has a solar water heater on their roof and they have to be saving money on it. Most places have a backup electric heater but the place I am staying at requests we use it only if we have to.

Electricity rate is also higher there. This page says $0.65/kWh, which is about 5 times higher than the US average.