Hot Water by Solar Electric direct via MPPT ?

[reptiles]

Greetings,

I've been reading these informative messages for a while and I have a question that I didn't come across here.

Is it feasible to place ~600-750W of panels feeding that power to a MPPT to the lower element on a well insulated residential hot water tank? Say 50 -80 gals. I'm in Philadelphia PA.

I saw a MPPT offered at http://techluck.com/index.php#buy but I'm not sure if this can really be so easy. Could I be looking at a scam?

Appreciate any advice. Regards, Mark

[DanKegel]

What's your goal?

Have you considered a heat pump water heater?

[Logan005]

that would be some expensive hot water. maybe you are thinking a diversion load when you have too much power. there are a lot more cost efficient ways to heat water with solar.

[Sunking]

Extremely horrible idea. If you want to heat water with solar, use Solar Thermal panels. Heck of a lot cheaper, more efficient, and actually works. You could not use a MPPT controller, nor would you want to if possible.

[DanKegel]

FWIW, solar PV driving heat pump water heaters seems to be cheaper than using solar thermal panels these days, going by

http://www.greenbuildingadvisor.com/blogs/dept/musings/solar-thermal-really-really-dead

[J.P.M.]

FWIW, solar PV driving heat pump water heaters seems to be cheaper than using solar thermal panels these days, going by
http://www.greenbuildingadvisor.com/...ly-really-dead

Generally agreed, except in moderate or non freezing climates where direct circulation of potable H2O is possible w/occasional nite recirc. to avoid freezing. Or, thermosiphon batch heaters.

However, on the referenced article, I'd question the $9K price for a solar thermal collector. I installed 2 high end 4 X 8 Sunearth selective surface units w/ new piping for $3,200, materials/labor before ITC Granted it was 2007, and the tank was already in place, but $3,200 vs. 9K is a stretch in my book. BTW, my solar fraction is >> .90 on the DHW load. Every situation is different.

[inetdog]

Greetings,

I've been reading these informative messages for a while and I have a question that I didn't come across here.

Is it feasible to place ~600-750W of panels feeding that power to a MPPT to the lower element on a well insulated residential hot water tank? Say 50 -80 gals. I'm in Philadelphia PA.

I saw a MPPT offered at http://techluck.com/index.php#buy but I'm not sure if this can really be so easy. Could I be looking at a scam?

Appreciate any advice. Regards, Mark

There is a serious lack of understanding of the terminology and technology going on here.

The MPPT circuitry found in PV Charge Controllers (CC) and Grid Tie Inverters (GTI) is designed to extract the maximum possible power from a panel array and deliver that power at a selected voltage and whatever current is then available.
But a water heater element is a fixed resistance. The only way to change the amount of power it is drawing is to change the applied voltage.

What you need instead is a circuit closer to the design of the Linear Current Booster (LCB). That type of unit delivers the maximum power panel to the load (usually a pump motor) at whatever voltage causes the load to draw the available amount of power. It operates an MPPT algorithm on the input side to change its effective input resistance to match the available current from the panels. But it also includes the complimentary output circuit to deliver the exact amount of power available to the actual load by adjusting the output voltage. Sort of the inverse of MPPT.

[reptiles]

What's your goal?

Have you considered a heat pump water heater?

My goal is to get into solar as an experiment. I can easily put up two or three panels for about $2/Watt.

Run just two conductors into the basement through one small hole. I already have grounding array on roof from several ham radio antennas.

Since domestic hot water is one of the greatest energy hogs in my small household, I think that any increase in my ground water temperature would be worthwhile. I can leave the top element on the grid, or feed into a tankless to top off the temp when required.

I did look into heatpump water heaters, but I'd have to replace the heat they suck out of the basement and since I run humidifiers for 3 months of the year, I'd have to replace the humidity as well. Not sure how that would play out.

I keep some expensive reptiles in the basement so I don't want to needlessly chill them with a heat pump.

Also a pv system is simple for me. Thermal with the pumps, leaks, stainless lines, fragile tubes, etc. is a maintaince problem.

Also, if this introduction doesn't work, I can reuse or expand the pv panels for other use.

Thanks to all for your advice.

Regards, Mark

[reptiles]

FWIW, solar PV driving heat pump water heaters seems to be cheaper than using solar thermal panels these days, going by

http://www.greenbuildingadvisor.com/blogs/dept/musings/solar-thermal-really-really-dead

Wow, that article sure was interesting. I read through it, and all associated links, and might revisit the heat pump electric with or without ductwork.

Thanks, Mark

[reptiles]

There is a serious lack of understanding of the terminology and technology going on here.

The MPPT circuitry found in PV Charge Controllers (CC) and Grid Tie Inverters (GTI) is designed to extract the maximum possible power from a panel array and deliver that power at a selected voltage and whatever current is then available.
But a water heater element is a fixed resistance. The only way to change the amount of power it is drawing is to change the applied voltage.

What you need instead is a circuit closer to the design of the Linear Current Booster (LCB). That type of unit delivers the maximum power panel to the load (usually a pump motor) at whatever voltage causes the load to draw the available amount of power. It operates an MPPT algorithm on the input side to change its effective input resistance to match the available current from the panels. But it also includes the complimentary output circuit to deliver the exact amount of power available to the actual load by adjusting the output voltage. Sort of the inverse of MPPT.

Actually the $249 gadget I was looking at, does change the voltage going into the hot water tank bottom element, perhaps up to 90 - 100volts but I'm not sure exactly what it does to maximize the power to a pure resistive load in the mornings or evenings. I tried to find a patent for it, but so far it's elusive. They are calling it a mppt but it seems to atypical.

Regards, Mark

[LucMan]

You would need approximately 8KWH input to heat the the water in a 50 gallon tank 60 Degrees F. You can do the math from there to figure out how many panels are required to do what you are attempting to do.
The site is misleading because they assume that the panels produce max power for 9 hrs per day all year long.
In the real world that doesn't happen, the average is about 4 hrs per day for the whole year. Go to PV watts and calculate the output of the panels for your location.

[DanKegel]

Wow, that article sure was interesting. I read through it, and all associated links, and might revisit the heat pump electric with or without ductwork.

Thanks, Mark

Here's a blog with a different viewpoint: http://www.halslater.com/Solar-Hot-Water.htm
And then there's this: http://waterheatertimer.org/Convert-...er-heater.html
Maybe you can find an old water heater, convert it to dc as described above, and use it as a preheater for
your existing water heater? Could be cheap, but you'd have to do it all yourself. Good luck.
- Dan

[Logan005]

depending on your latitude, I have found 500' of black PEC 1/2" tubing in the attic a great source of warm water and a great way to preheat water for an instant on water heater. Cheap and easy to install.

[Sunking]

Mark you really do not understand power, If you did, then you would know ground has no function with respect to power. Secondly to generate 8 Kwh per day is going to require a 2000 to 4000 watt panel system depending on your location. Anything you take off grid is going to cost you many times more than the power company will charge you for it for the rest of your life. You cannot do what you want th eway you think you can. You just do not understand the technology and how to apply it.

73's to ya

KF5LJW out.

[J.P.M.]

depending on your latitude, I have found 500' of black PEC 1/2" tubing in the attic a great source of warm water and a great way to preheat water for an instant on water heater. Cheap and easy to install.

You must have a warm attic.