Solar PV MPPT board for Hot Water heating

[Xringer]

Solar Hybrid Hot Water Solution - No Plumbing Mods Required - At TechLuck



Specs:
Abs Max Voltage: 250V DC
Abs Max Current: 20A (extra heat sink required)
Efficiency: 97%

There's a link on the http://techluck.com/ page to boards for sale on Ebay.


This looks like a board I could use on my brand new GE hotwater tank..
It should handle my 144Vdc 800W array just fine.. Maybe need a larger heat sink..?.
The guy that makes them said "The main mosfet is 40A at 1200V and the board traces can handle 20A"..

You would need a 5 KW PV array to fully test his spec!


If I was able to average just 400 watts for 4 or 5 hours a day, that would put 1,364 BTU into my tank each hour.
In the summer time, It would do a lot better.

Pretty sure that would keep the A7 from coming on as much..

I'm going to see if I can get the builder to register here, so he can
answer some questions about the product.

[Xringer]

Found this interesting site.
EDS USA - Energy Desing Solutions, Solar water heating systems, Green energy

And, an interesting study too.
http://www.usa-eds.com/userfiles/fil...ults_final.pdf

[Mikesolar]

I know you love your electronics BUT, it would be way more appropriate to get one SDHW panel to feed the tank and put all the PV power straight into the grid, assuming you are compensated in some way.

Probably a bit boring tho....

[Xringer]

It's not worth the investment to install a small grid-tie array.
If I did it, I would want the max kW my roof space could provide.


Years ago, I had three real nice Novan SDHW panels on my roof. The system worked great for a few years.
Then the leaks started. Followed closely by my wife wanting those 'things' off the roof. (Woburn water is hard on copper).
I'll never try another SDHW system. I doubt the city would even allow a DIY SDHW system, in these days of over-regulation.

I'm currently testing out the 800w array connected directly to the lower
heating element in my new GE water heater w/ A7 on top.
(No MPPT being used yet).

It seems like even the poor solar conditions we've had over the last 10 days
aren't stopping those 800w from doing some hot water heating.

I checked the log this morning, and the A7 has been using about 1 kWh per day, on average.
When the weather warms up and I'm in the shower all the time, that will change..
But, I'm collecting daily readings and making notes on solar conditions & HW use.
So it will be interesting to see how daily A7 power use impacted by the PV..

The load works well around noon time. If it's sunny, we get very good performance out of the array.
Sometimes in the 90% range.

My backyard panels are in a poor location.
However when the days get longer and, we see even better performance from the PV, I'll add MPPT to it.

[Mikesolar]

Originally Posted by Xringer

It's not worth the investment to install a small grid-tie array.
If I did it, I would want the max kW my roof space could provide.


Years ago, I had three real nice Novan SDHW panels on my roof. The system worked great for a few years.
Then the leaks started. Followed closely by my wife wanting those 'things' off the roof. (Woburn water is hard on copper).
I'll never try another SDHW system. I doubt the city would even allow a DIY SDHW system, in these days of over-regulation.

I'm currently testing out the 800w array connected directly to the lower
heating element in my new GE water heater w/ A7 on top.
(No MPPT being used yet).

It seems like even the poor solar conditions we've had over the last 10 days
aren't stopping those 800w from doing some hot water heating.

I checked the log this morning, and the A7 has been using about 1 kWh per day, on average.
When the weather warms up and I'm in the shower all the time, that will change..
But, I'm collecting daily readings and making notes on solar conditions & HW use.
So it will be interesting to see how daily A7 power use impacted by the PV..

The load works well around noon time. If it's sunny, we get very good performance out of the array.
Sometimes in the 90% range.

My backyard panels are in a poor location.
However when the days get longer and, we see even better performance from the PV, I'll add MPPT to it.

Don't be so hard on SDHW, you seem to have got a crappy system and the company seems to be gone anyway (which is a bit of a hint to its quality). It is not that hard to make a system that looks like skylights on the roof if that would appeal more to your wife and I am sure it could be done without hassle from either the city or the water supply.

One way or another you are using the grid as a battery whether officially or not, so it is grid tied

[Xringer]

It's hard enough to keep up with the regular plumbing leaks.. I hate plumbing anyways.
My hot water system was pretty good quality. We just have very corrosive water here in Woburn.
The panels were pristine.. The HX and the tank were the leaky parts.
The controls and the pumps were top notch hardware. I still have those parts.

"One way or another you are using the grid as a battery whether officially or not, so it is grid tied"

Not really. I have nothing going into the grid. My Nstar meter has backwards-flow detect.
It sets a flag that shows up in the data burst, when they come by to read the meter.


My 800w array is storing away hot water. Just like charging a battery..
http://i46.photobucket.com/albums/f1...ps42dbfce1.jpg
The 500w tracking array maintains my back-up system and can provide
re-charging, and day time power(if sunny), during an extended grid failure.

I say it's not worth the investment to put 800w on the grid,
because it would take decades to break even.
If I ever go grid-tie, it will be with at least 2 kW.
If they can't fit 2kW on my roof, I'll skip the roof and built a high fixed mount in the backyard.
Something up on a big 30 foot pole maybe..

[Xringer]

It's partly overcast today, and as usual, my back-up system is in float mode.

I'm thinking maybe I should use that 500w tracker PV to heat some water..
Since it's not being used, why not heat up some water?

The 800w fixed array is doing a pretty good job with helping keep the new GE DHW heater up to temp..


So, if the 500w Backup system PV float voltage is up around 85V (and it's cloudy right now),
that means the charge controller is ignoring the panels.
I could connect a water heater element to that 85V and the charge controller wouldn't even know it.
It would think some heavy clouds came over..

Just need a simple voltage level detector for the pack, (to see float level)
and a good DC switch to connect the 85V PV to a heating element (in parallel with the charge controller)..

An average of 300w off that tracker array would give me about 1,000 extra BTUh..

I'm wondering where that spare power should be connected.?.
To the old boiler, or to the upper element of the new GE (well insulated) tank?

I like the GE, it seems to have very low losses..
With both arrays connected, we could be getting around 1kW of power-to-the water,
during the sunny part of the day.. That's 3412 BTUh..

The technical term for this is, Dump Load..

[techluck]

Originally Posted by Xringer

It's hard enough to keep up with the regular plumbing leaks.. I hate plumbing anyways.
My hot water system was pretty good quality. We just have very corrosive water here in Woburn.
The panels were pristine.. The HX and the tank were the leaky parts.
The controls and the pumps were top notch hardware. I still have those parts.

The problems with a fluid based system were pointed out in that government study. They also concluded that when solar panel prices get below $1.50 a watt it will be worth going with PV panels instead of a fluid system.

"There are currently over 90 million water heaters in use within the United States (Zogg and Barbour 1996). The number of installed solar water heaters, by comparison, is less than 1 million due to durability and installation issues, as well as relatively high initial costs. Durability issues have included freeze and fluid leakage problems, failure of pumps and their associated controllers, the loss of heat transfer fluids under stagnation conditions, and heat exchanger fouling. The installation of solar water heating systems has often proved difficult, requiring roof penetrations for the piping that transports fluid to and from the solar collectors. The solar photovoltaic hot water system described in this paper avoids the durability and installation problems associated with current solar thermal water heating systems (Fanney and Dougherty 1997; Dougherty and Fanney 2001; Fanney et al. 1997)."

fire.nist.gov/bfrlpubs/build02/PDF/b02012.pdf

[Xringer]

Here's the clickable link to that PDF..

fire.nist.gov/bfrlpubs/build02/PDF/b02012.pdf



During the last 20 years, I've noticed a lot of non-functioning solar hot water panels in the local area.
Slowly over time, the collectors have been removed and re-shingling was done.
Some of the panels weren't very well made and were really dilapidated.

One problem with those older system was over-heating in the collectors,
whenever there was a pump failure etc.
The panels would really boil during a power loss. Any materials that couldn't hold up to the high temps got degraded.

I think they used to call it, 'solar collector stagnation'..

[Mikesolar]

Stagnation is a normal thing and any system needs to be designed for a reasonable amount of it. Go on vacation for a couple of weeks and it will stagnate.

But this is all normal. A properly designed system will last for 30 + years, with glycol changes every 6-8 years. It is the improperly designed/installed/maintained ones that fail.

The biggest problem now is oversizing the panel area vs the tank volume and not sizing it to the load. With glycol, you really should not size the system to do more than 60% of the annual load. This means 2 - 4x8 panels at most. Vacuum tubes are worse because they get hotter at the wrong times and they fail way faster than flat panels do.

Still, dollar for dollar, solar thermal supplies more energy than a PV system does (although the gap is closing). Different technologies for different jobs, I say. Still, it is fun to experiment.