Hot water options

[dodge man]

We just had geothermal installed last week. They also installed a hot water storage tank and a new electric water heater. Depending on how much the geothermal is running it will make most of the hot water or almost none. The electric for the hot water is about one third of the energy cost.

Our cost breaks down as follows for electric. Total cost is $994 per year. Air conditioning $78 per year, hot water 317 per year and heat $599 per year. In other words don't count on geothermal to be cheap for hot water. Overall though it will reduce our cost since we were using LP.

 

[tkappeler]

But, known that the hot water system is only drawing propane when there is actual a call for hot water I guess I am not sure why you would have to up grade the input line to 1? but what do I know??

I have to size for the maximum BTUs consumed by the appliances if they were all on at the same time. On demand unit would be 180K, furnace is another 120K, stove and gas dryer put it over the maximum carrying capacity of 3/4" with all units tee'd off that single line. There are standard charts for natural gas and propane.

 

[tkappeler]

I have the same size hot water heater. My average electrical bill for the last 13 months was 66kwh/day. This includes running a pellet stove all winter and an irrigation pump several hours daily all summer with intermittent A/C use. I have wondered how much the water heater actually uses versus my wife going crazy with the electric clothes dryer. She thinks nothing of running slightly damp or just clothes that dried but sat in there a while (supposedly now wrinkled?) through another 40-minute dry cycle!

As KTurner notes, without good information on actual electricity use per device it is hard to determine if something like solar hot water is really worth it. I know our hot water usage goes up in the winter because the kids tend to take hotter showers then. However that is also when a solar HW system is at its least productive (short days, snow cover on panels, clouds, fog, etc).

I am not sure if something like this: 5in1 AC264V30A LCD Digital Energy Power Meter Volt Amp kWh Watt Running Time | eBay and connecting it at the hot water heater elements would work to track KWH usage. Have to check it every so often to see how many kwh used and then do the math to see $$.

Maybe my 30Kw/day is not so far off. Thanks for the tip on the meter to check the usage on each line.

If you heat water with either electricity or propane, solar make tremendous sense. I have been doing so for the last 23 years, and I estimate it has saved at least $8,000 in propane. Having once been a salesman in the industry (early 80's when there were government incentives), I understood the economics and never understood why people hesitated or did not make the purchase decision. Later, I found a used system (owner's children had grown and moved out, time for a new roof and the panels had to come off) for $300. The best purchase I ever made! Installed it myself. Would do it again in a heartbeat.

Are you talking PV or solar hot water? I have thought about PV but for the 11K+ cost to put in a ground mount 20 panel, 5000W system, I would rather invest in the geothermal to cover heat and hot water.

 

[kenmac]

I use to have a 50 gallon electric wh that provided all the hot water I needed. Never ran out of hot water.. I converted to ng so. I would have hot water during power outages.. Do you really need to heat 80 gallons of water ? Yep , you have to size a gas line as if all gas appliances were on at the same time. With tankless, There will be some maintenance to keep them in top operating condition. Just my opinion,,, I would install a new 50 gal. elec. or a standard 40 gal. 40k BTU propane. Being a contractor, I can install any wh I want. I have a 40 gal. 40k BTU gas.. No tankless for me

 

[tkappeler]

I should add that the 8 gallon was not due to a need for that much hot water but a great deal. The 80 electric was less than 1/2 price of 50 gallon as the big box was freeing up space. Could have been penny wise and pound foolish.

 

[OldMcDonald]

Are you talking PV or solar hot water? I have thought about PV but for the 11K+ cost to put in a ground mount 20 panel, 5000W system, I would rather invest in the geothermal to cover heat and hot water.

I was wondering the same myself. Using PV to create electricity to then heat water is a very expensive and inefficient way of doing it. Direct solar is the norm. My wife and I use very little hot water. Our philosophy is that nobody ever needed a bath every day (before the invention of showers) so we do not need a shower every day. Washing machines and dishwashers here cannot be plumbed into HWS - I do not know why. Consequently we have never seen the need to change from the electrical heated HWS, but if I did it would be direct solar.

 

[dave1949]

I was wondering the same myself. Using PV to create electricity to then heat water is a very expensive and inefficient way of doing it. Direct solar is the norm. My wife and I use very little hot water. Our philosophy is that nobody ever needed a bath every day (before the invention of showers) so we do not need a shower every day. Washing machines and dishwashers here cannot be plumbed into HWS - I do not know why. Consequently we have never seen the need to change from the electrical heated HWS, but if I did it would be direct solar.

Solar hot water has many inefficiencies and potential maintenance headaches due to temperature sensors, pumps, valves, etc. In a climate which experiences overnight freezes and the occasional day so lacking in sun that the collector gains nothing, either a drain down system or a glycol-based collector fluid is needed. The plumbing on either of those types can fail with disastrous results. The glycol fluid requires a heat exchanger in or near the domestic hot water tank--more expense and efficiency loss. Water heated during the day and stored for later use has some heat loss even if minimal. The more hot water that is stored in good days (in expensive and space eating tanks), the longer the recovery takes following bad days.

For overall system efficiency with solar hot water there will inevitably be times when either too much or too little hot water is produced, that is an unavoidable inefficiency inherent to the system type. In northern climates for people on a fixed daily schedule (like most folks) it is common to need supplemental water heating via propane or electric.

All of that would be worth it in a totally off-grid situation. For grid-tied, given the falling cost of solar pv panels, in NJ, it is not. The cost of a good solar water heating system will buy a lot of solar pv panels. Regardless of solar panel efficiency the heating elements in an electric water heater are 100% efficient. In a grid-tied solar pv system every watt produced accomplishes something--heated water or a credit with the utility. There is no wasted production or additional plumbing and parts. More parts added to any sort of system increases the number of potential failure points.

I have lived in a technologically challenged desert environment (Iran) with a 100 gallon batch heater tank on the roof combined with a manually operated (light with a match and eyeball the drip rate from the tank to the burner pan) kerosene water heater for winter use. That worked. The solutions need to fit the available resources and conditions.

A home-built flat plate collector system combined with a propane on-demand flow through heater that modulates the flame btu's according to the incoming water temperature would be a starting point if a person wished to roll their own IMO.

 

[quicksandfarmer]

With advances in photovoltaic efficiency and the development of heat-pump water heaters, photovoltaic systems are now quite competitive for heating water.

Here is my effort to do an apples-to-apples comparison of the installed cost of a solar thermal water heater, versus the installed cost of a heat-exchanger electric water heater and a solar electric installation large enough to support it. A lot of the specifics of the comparison depends on your assumptions, so I’ll start out with the assumption that you need 40 gallons of hot water a day, and the water has to be raised 60F degrees. So that’s 19,920 BTU per day, or 5838 Watt-hours per day.

I’ll do the electric first. Over the course of the year, where I live averages 3980 Watt-hours of insolation energy per square meter. Commercially available panels (see Grid tie Solar Power Systems - Grid tie Solar Panel Systems) have an efficiency of 14.4%. Assuming a heat pump efficiency of 200%, to get 5838 Watt-hours of heating you need 2919 Watt-hours of electricity. At 14.4% efficiency, to get 2919 Wh of electricity you need 20,271 Wh of insolation. At 3980 Wh/sm you need just about exactly five square meters of panels. Those commercial panels are 1.6 square meters so you would need three of them. These panels are called 250 watt panels so this would be a 750 watt system. A complete 750 watt grid tied system kit costs about $1200 (See 1200W 900W 750W 600W 450W 300W Complete Kit Grid Tie 160W Solar Panel System | eBay, I'm not recommending it, it's just the first one I found on Ebay) . You’d also need a heat pump water heater, a GE Geospring 50 gallon is about $900. So $2100 for the pieces. I’m going to assume that the installation cost is going to be roughly the same for either system since the pieces are fundamentally similar. I’m also leaving out subsidies and credits because they seem to be similar as well.

Now for the thermal system. Interestingly, evacuated tube panels have almost completely replaced flat panels in the marketplace, I wasn’t even able to price a flat panel kit any more. Evacuated tubes have come way down in price and offer superior cold weather efficiency. A thermal system has to be sized to provide 100% of the energy needed on the lowest-output day of the year. Here, December is the lowest insolation month of the year, averaging 1810 watt-hours/square meter per day. The efficiency of thermal collectors depends on the temperature. The average daytime temperature in December here is 47F, a commercially available collector gives an efficiency of 27% at 47F (see Solar Water Heaters with Vacuum Tubes ) Efficency is lower in January when the temperature is lower, but January is sunnier, so December is the lowest producing month. To produce 5838 Watt-hours per day with 1810 watt-hours/square meter of insolation and 27% efficiency you need 11.9 square meters of panels. Those commercially available panels come in arrays of 18 tubes, each one is 2.35 square meters, so you’d need 90 tubes. They don’t come that big off the shelf, but you could get a 72 tube system for $4675 and an additional 18 tubes for $500. So $5175 for the pieces.

So $2100 for the PV and $5172 for the thermal, it’s not looking good for thermal. Now thermal systems are often sized to provide less than 100% of the hot water needs, the costs are much better that way. Often they are sized so that they provide 100% on the best day of the year instead of the worst day, that way 100% of the energy they provide is utilized. The best month for solar here is August, if you sized your system to provide 20,000 BTU on a typical August day it would only have to be 37% of the size. So instead of 90 tubes you could have 33 tubes. A 30-tube system is $2450, 36 tubes is about $125 more. Such a system would provide an average of 14,500 BTU per day year-round, or 72.5% of your annual heating need. It’s still not cost competitive, but it’s much closer, within a few hundred dollars. However, you would need a backup heating source to provide that other 27.5% of your hot water.

The advantages of PV swing even further if you look at two other factors. The first is economy of scale. The bigger your system, the less it costs per installed watt. That 750 watt system is $1.60 per installed watt. However, if you’re already installing a PV system the marginal cost of three additional panels is the cost of the panels. Those 250 watt panels cost $210 each at quantity 25, so that’s $0.84 per installed watt. The second factor is space on the rooftop. If there is limited space, PV makes even more sense. The 90-tube thermal system occupies 128 square feet. Even the modified 36-tube system occupies 47 square feet. The three-panel 750 PV system occupies 50 square feet. So if you only have limited space PV is a better use of that space.

It varies by state, but here the electric company allows reverse metering, so excess electricity produced by the PV panels is returned to the grid and I get a credit on my electric bill. Excess hot water produced by a hot water solar panel is just lost.

Where the jury is still out is on the efficiency claims of the heat pump. Interestingly, even without the efficiency of the heat pump PV is still more competitive than thermal. What’s telling is I’m starting to see gadgets that allow you to connect your PV panels directly to a resistance-heated water heater, bypassing the inverter and the grid-tie when the panels are producing and hot water is needed. See Solar Hybrid Hot Water Solution - No Plumbing Mods Required - At TechLuck

 

[buickanddeere]

I was wondering the same myself. Using PV to create electricity to then heat water is a very expensive and inefficient way of doing it. Direct solar is the norm. My wife and I use very little hot water. Our philosophy is that nobody ever needed a bath every day (before the invention of showers) so we do not need a shower every day. Washing machines and dishwashers here cannot be plumbed into HWS - I do not know why. Consequently we have never seen the need to change from the electrical heated HWS, but if I did it would be direct solar.

Around here using PV panels at 83 cents a watt into a 1000W, 48V electric heating element . Is cheaper, safer and more reliable than pumping water to outside outside thermal collectors.It's can be cold enough here to split pipework at night from October to May. Sunlight is a rare event from November to March. They don't call it the Grey-Bruce region for nothing.
I have grand plans for a 1500W PV array, a 2Kw 48V wind turbine, a 80 to 120 gallon electric heater with 240 element set to 140F in the top operated from an off peak timer. The water heater tank's lower element replaced with the PV powered 1000w 48V unit set to 180F. A 1500KVA grid tie inverter to supply 120V power if the tank ever reaches 180F .
It will never payback once the teenagers leave and quit showering here but it's a technical tinker project.

 

[tkappeler]

With advances in photovoltaic efficiency and the development of heat-pump water heaters, photovoltaic systems are now quite competitive for heating water.

Here is my effort to do an apples-to-apples comparison of the installed cost of a solar thermal water heater, versus the installed cost of a heat-exchanger electric water heater and a solar electric installation large enough to support it. A lot of the specifics of the comparison depends on your assumptions, so I’ll start out with the assumption that you need 40 gallons of hot water a day, and the water has to be raised 60F degrees. So that’s 19,920 BTU per day, or 5838 Watt-hours per day.

I’ll do the electric first. Over the course of the year, where I live averages 3980 Watt-hours of insolation energy per square meter. Commercially available panels (see Grid tie Solar Power Systems - Grid tie Solar Panel Systems) have an efficiency of 14.4%. Assuming a heat pump efficiency of 200%, to get 5838 Watt-hours of heating you need 2919 Watt-hours of electricity. At 14.4% efficiency, to get 2919 Wh of electricity you need 20,271 Wh of insolation. At 3980 Wh/sm you need just about exactly five square meters of panels. Those commercial panels are 1.6 square meters so you would need three of them. These panels are called 250 watt panels so this would be a 750 watt system. A complete 750 watt grid tied system kit costs about $1200 (See 1200W 900W 750W 600W 450W 300W Complete Kit Grid Tie 160W Solar Panel System | eBay, I'm not recommending it, it's just the first one I found on Ebay) . You’d also need a heat pump water heater, a GE Geospring 50 gallon is about $900. So $2100 for the pieces. I’m going to assume that the installation cost is going to be roughly the same for either system since the pieces are fundamentally similar. I’m also leaving out subsidies and credits because they seem to be similar as well.

Now for the thermal system. Interestingly, evacuated tube panels have almost completely replaced flat panels in the marketplace, I wasn’t even able to price a flat panel kit any more. Evacuated tubes have come way down in price and offer superior cold weather efficiency. A thermal system has to be sized to provide 100% of the energy needed on the lowest-output day of the year. Here, December is the lowest insolation month of the year, averaging 1810 watt-hours/square meter per day. The efficiency of thermal collectors depends on the temperature. The average daytime temperature in December here is 47F, a commercially available collector gives an efficiency of 27% at 47F (see Solar Water Heaters with Vacuum Tubes ) Efficency is lower in January when the temperature is lower, but January is sunnier, so December is the lowest producing month. To produce 5838 Watt-hours per day with 1810 watt-hours/square meter of insolation and 27% efficiency you need 11.9 square meters of panels. Those commercially available panels come in arrays of 18 tubes, each one is 2.35 square meters, so you’d need 90 tubes. They don’t come that big off the shelf, but you could get a 72 tube system for $4675 and an additional 18 tubes for $500. So $5175 for the pieces.

So $2100 for the PV and $5172 for the thermal, it’s not looking good for thermal. Now thermal systems are often sized to provide less than 100% of the hot water needs, the costs are much better that way. Often they are sized so that they provide 100% on the best day of the year instead of the worst day, that way 100% of the energy they provide is utilized. The best month for solar here is August, if you sized your system to provide 20,000 BTU on a typical August day it would only have to be 37% of the size. So instead of 90 tubes you could have 33 tubes. A 30-tube system is $2450, 36 tubes is about $125 more. Such a system would provide an average of 14,500 BTU per day year-round, or 72.5% of your annual heating need. It’s still not cost competitive, but it’s much closer, within a few hundred dollars. However, you would need a backup heating source to provide that other 27.5% of your hot water.

The advantages of PV swing even further if you look at two other factors. The first is economy of scale. The bigger your system, the less it costs per installed watt. That 750 watt system is $1.60 per installed watt. However, if you’re already installing a PV system the marginal cost of three additional panels is the cost of the panels. Those 250 watt panels cost $210 each at quantity 25, so that’s $0.84 per installed watt. The second factor is space on the rooftop. If there is limited space, PV makes even more sense. The 90-tube thermal system occupies 128 square feet. Even the modified 36-tube system occupies 47 square feet. The three-panel 750 PV system occupies 50 square feet. So if you only have limited space PV is a better use of that space.

It varies by state, but here the electric company allows reverse metering, so excess electricity produced by the PV panels is returned to the grid and I get a credit on my electric bill. Excess hot water produced by a hot water solar panel is just lost.

Where the jury is still out is on the efficiency claims of the heat pump. Interestingly, even without the efficiency of the heat pump PV is still more competitive than thermal. What’s telling is I’m starting to see gadgets that allow you to connect your PV panels directly to a resistance-heated water heater, bypassing the inverter and the grid-tie when the panels are producing and hot water is needed. See Solar Hybrid Hot Water Solution - No Plumbing Mods Required - At TechLuck

Wow. I was originally thinking of solar thermal but have been starting to look longer term and a ground mount pv may be a better choice. Certainly more aesthetically pleasing as it would be away from the house.

Thanks for the great information and comparison