switching from gas to electric hot water heater after solar?

[dannieboiz]

we should have our solar system up in a few months. As I'm doing my homework and thinking about how to eliminate my utility bills, the only thing left is the hot water heater. Is it worth it to up the size of my system and swap out my hot water heater?

This would mean I should have 0 gas bill during the warmer months when we're not using the furnace

[Mike90250]

Keep the gas water heater, but install a solar thermal water heater, and feed your gas heater preheated water.

I do, and it works great. I installed a thermostat mixing valve to mix the 160F rooftop heater with cold water going to the inlet of the gas heater 120F water.

[max2k]

we should have our solar system up in a few months. As I'm doing my homework and thinking about how to eliminate my utility bills, the only thing left is the hot water heater. Is it worth it to up the size of my system and swap out my hot water heater?

This would mean I should have 0 gas bill during the warmer months when we're not using the furnace

Natural gas has density approx 0.05 lb/ft^3 and combustion energy 23000 BTU/lb. 1BTU = 0.00029 kWh. So, 1 cubic feet produces 0.005 x 23,000 x .00029 = 3.34 kWh of energy at a price of 1.5c/kWh (at most expensive rate of $50.00 for 1,000 ft^3)

6kW Solar system produces approx 10,000 kWh a year at the initial cost of $15,000 (after rebates) This gives 200,000 kWh over its lifetime of 20 years at the cost of 7.5 c/kWh.

You're better off to keep your gas bill - this rough estimate shows solar is still at least order of magnitude more expensive than natural gas when it comes to heating.

BTW, 'efficiency' of heat extraction can be greatly 'improved' by heating some heat transfer media (water) directly, without trying to convert it to electricity first. Such system will be at least 10x times cheaper and 4x times more efficient in extracting heat energy from sun. Pool owners use such systems to heat up water in the pool instead of burning gas.

[dannieboiz]

Based on my current use, it was already determined that I'll need at least a 5.5 kw system and you hit the price almost spot on.

My 17 yrs old gas water heater has been screaming "replace me" since we moved in 6 months ago.

So swapping to electric isn't the most efficient way? Figured they''ll be running wires on both sides of my garage for EV charger, might as well run a 220 as well.

we have a pool but opted for a gas heater in conjuction to a solar blanket. Works great!

All these other options you guys just gave me was like spoken in another language, I gotta do some googling on it

[max2k]

Based on my current use, it was already determined that I'll need at least a 5.5 kw system and you hit the price almost spot on.

My 17 yrs old gas water heater has been screaming "replace me" since we moved in 6 months ago.

So swapping to electric isn't the most efficient way? Figured they''ll be running wires on both sides of my garage for EV charger, might as well run a 220 as well.

we have a pool but opted for a gas heater in conjuction to a solar blanket. Works great!

All these other options you guys just gave me was like spoken in another language, I gotta do some googling on it

Those just numbers, the basic idea is the same- heat the water from the sun directly and then use it to feed your gas powered heater. I was not aware such setups exist but it would be the most efficient in utilizing sun heat energy. It can also ensure the output water has preset constant temperature, even at night- it would just burn more gas without sun 'help'.

[Mb190e]

I am also thinking about doing this we have a propane hot water heater. I was originally going to go solar thermal to preheat the propane hot water heater, but after some research and talking to people in the business. I'm thinking of going with the geothermal hot water heater. One thing that really got me thinking is somebody who has so solar thermal hot water. The water is up to temperature by 10 or 11 AM so the rest of the day the solar is basically wasted. If you throw an extra 1 kW on the roof of PV even after you heated your hot water you're still making some extra electricity the rest of the day. This hot water heater http://www.geappliances.com/heat-pump-hot-water-heater/ is estimated at 1514 kWh's a year.

[bridaus]

The numbers change completely when you say "17 year old heater screaming to replace me". In our area the state essentially paid for the cost of a new heat pump based electric water heater (not for installation though). Uses much less electricity, but also forces the teens to take normal length showers... due to it's slow recovery (there are settings that can make it recover faster if you so choose)

I always go with the assumption that energy costs are always going to rise fairly dramatically over the lifetime of these systems. I've converted my house to 100% electric because I feel it's the energy source I have the most ability to create on my own in reaction to volatile markets. Between reducing consumption, solar, generators, and the grid, I've got options. I can't drill for oil or gas, but I can make electricity.

[Sunking]

I always go with the assumption that energy costs are always going to rise fairly dramatically over the lifetime of these systems.

That would be the wrong assumption as there is not one bit of historical evidence of ever doing so going back 60 years. In those 60 years electric cost about 5-cents 60 years ago, today 11 cents. If you look back just 10 years electricity prices have dropped 13% nationwide average, and natural gas has plummeted by some 60%.

[bridaus]

Maybe it's just New England then? My electricity prices have gone up over 100% in the past 20 years (Currently about 23 cents per kwh), oil over 200%, (likely more, I can't remember exactly what it was 20 years ago, but it was much cheaper)...

Sure, I could pick a five or ten year period where it might go down, but I believe the trend is obvious. There are very few technologies that could change this trend, and I'm the kind of person who would choose those technologies anyways, and since it requires someone like me (us) to do that in enough volume to make it happen... chicken... meet egg.

Even if the POCO's suddenly lowered their pricing to 60 year ago rates (let's say for fun), it simply changes the break even time, NOT the fact that I will break even and not the fact that electricity is the most easily acquired form of energy.

[Samsolar]

That would be the wrong assumption as there is not one bit of historical evidence of ever doing so going back 60 years. In those 60 years electric cost about 5-cents 60 years ago, today 11 cents. If you look back just 10 years electricity prices have dropped 13% nationwide average, and natural gas has plummeted by some 60%.

Averages are just that -averages- I doubt you'll find many people relieved that someone else is paying less when their own bill goes up by 40 or 50%. In my neck of the woods, we just went from $0.084/kWh to $0.1544/kWh (energy only) last December. While I expect prices to come back down this summer, the volatility is something that no one likes and not all have budgets to cover.

Since you bring up natural gas, you can't look at just market prices of natural gas itself, you have to look at the price delivered to the power plants. In New England, pipeline capacity gets really tight in the winter and prices spike which directly translates into higher electricity costs.

[bridaus]

Got me interested, this link tells me electricity is 3x the cost it was in 1990 in my state. Even inflation adjusted numbers can't explain that away.

http://www.eia.gov/electricity/data/eia826/xls/sales_revenue.xls

[lagator]

Good thread. Have to agree that Natural Gas is so affordable heat energy per unit that it's going to be hard to justify getting rid of your gas hot water heater. Solar pre-heat sounds pretty good depending on the cost of such a system, since the break even point could be pretty long.

Honestly, I'm much more worried about the rising costs of the water rather than the cost to heat it. Out here water bills could double or more as soon the politicians get around to writing the new rates and taxes based on years of drought, and historical laws that pretty much give away the majority of the water through water rights to agribusiness.

[bridaus]

One more thing: I would certainly keep that Natural Gas appliance running as long as you can, it owes you nothing and NG is currently inexpensive and relatively clean in the grand scheme of things. When you are forced to replace it, if $$$ is your only parameter, the numbers in most places say that today another NG HW heater would make the most economic sense, followed by an electric HP HWH. If you like to overthink things like I do, break out a spreadsheet and do some math with actual numbers. It's educational. (However, I'm a big fan of renewable/solar, and would not myself choose NG for any reason as mentioned before, $$$ is not my only parameter)

[J.P.M.]

Good thread. Have to agree that Natural Gas is so affordable heat energy per unit that it's going to be hard to justify getting rid of your gas hot water heater. Solar pre-heat sounds pretty good depending on the cost of such a system, since the break even point could be pretty long.

Honestly, I'm much more worried about the rising costs of the water rather than the cost to heat it. Out here water bills could double or more as soon the politicians get around to writing the new rates and taxes based on years of drought, and historical laws that pretty much give away the majority of the water through water rights to agribusiness.

Solar H2O heaters are great. I own one and I'm keeping it. It works great. However, if I had a gas H2O heater, no solar, and it crapped the bed, AND I was considering Solar PV, AND I lived in a semi moderate climate, I'd consider replacing the dead heater with a heat pump water heater, and bump the array size by an appropriate amount. The life cycle cost of a solar flat plate water heater may be competitive to the heat pump + extra PV required. However, and even as a solar thermal fan, I've got to give the nod to the heat pump + PV by a nose based on likely lower maint. and some operational hassles, especially if the solar thermal was a closed glycol system w/ a heat exchanger.

On water bills: Everyone around here is talking about the drought. However, I see just as much watering going on as ever. Seems like another example of disconnect with reality. Folks still watering rose bushes and green lawns with H2O runoff filling the gutters.

I also hear people expressing fear that their "water bills" will skyrocket if the powers that be have their way. My last "water bill" was about $100. Of that, slightly over $10 of that $100 was for the commodity. The remaining $90 was fixed charges associated with delivery and sewer.

If the water charge doubled, my bill would go from $100 to about $110/month. Before I got the solar array my annual water bill was more than my electric bill, but the cost of the water I use had and still at this time has little to do with it.

As it is available in most developed countries, water is about the least expensive necessity of life.

[lagator]

Solar H2O heaters are great. I own one and I'm keeping it. It works great. However, if I had a gas H2O heater, no solar, and it crapped the bed, AND I was considering Solar PV, AND I lived in a semi moderate climate, I'd consider replacing the dead heater with a heat pump water heater, and bump the array size by an appropriate amount. The life cycle cost of a solar flat plate water heater may be competitive to the heat pump + extra PV required. However, and even as a solar thermal fan, I've got to give the nod to the heat pump + PV by a nose based on likely lower maint. and some operational hassles, especially if the solar thermal was a closed glycol system w/ a heat exchanger.

On water bills: Everyone around here is talking about the drought. However, I see just as much watering going on as ever. Seems like another example of disconnect with reality. Folks still watering rose bushes and green lawns with H2O runoff filling the gutters.

I also hear people expressing fear that their "water bills" will skyrocket if the powers that be have their way. My last "water bill" was about $100. Of that, slightly over $10 of that $100 was for the commodity. The remaining $90 was fixed charges associated with delivery and sewer.

If the water charge doubled, my bill would go from $100 to about $110/month. Before I got the solar array my annual water bill was more than my electric bill, but the cost of the water I use had and still at this time has little to do with it.

As it is available in most developed countries, water is about the least expensive necessity of life.

I wouldn't bet on that. There's nothing stopping them from raising all the associated charges by similar percentages and zero incentive not to. In SoCal there's no question rates are going to rise and a lot more than 10% total. The amount they can raise total charges will be capped on a yearly basis but I expect close to 10% increase per year for at least the next 5 years or so.