diversion loads, air heater?

[Ralph Day]

On days like today with lots of wind and sun, i have a problem utilizing the excess energy without feeling guilty. Just letting the controllers either a) not harvest (MX60 solar) or b) dump to heat (H80 wind controller).

Right now i have the MX aux function driving a relay putting 120 house power to an outlet, the outlet now has a quartz heater running and in the summer, a de-humidifier. it works ok but i'm just wondering about peoples experiences with air-heater diversion units. Heating water is not an option at present.

This arrangement requires some personal attendence (1 or 2 elements on the heater) and timing when the diversion load comes on as each is relatively power intensive.

Any idears? THanks.

rd

[Paul Bailey]

Hi Ralph : As you probably are aware that I am somewhat biased towards water heating as the storage median for many applications. I am probably not the best to comment here plus I am not off grid with much differant home dynamics. Nothing wrong with what your doing... at least your using the power instead of just clipping it off when your battery is full. As you are aware and Im sure your digging deep on this to optimize household loads during days of good wind and sun which is a blessing where we live. . I can relate on those long sunny summer days and I have to dump hot water...Oh the Joys of energy. I'm sure this is your back yard today ..I know mine was. Paul:)

[Mark Parsons]

Greetings Ralph,

Sounds like you've got the best solution. Offset some of your space heating / cooling costs with power harvested from the abundance of energy in your back yard.

Maybe your lifestyle will lead you to use the power for other things. Charge your electric vehicle batteries. Electrolyze water and store the Hydrogen for future energy use on not so windy or sunny days. There are many other noble uses of the excess power. Use it to sequester carbon out of the atmosphere. :rolleyes:

If it was my problem, of having surplus power on a regular basis, I would buy another appliance or another power tool that would consume the excess. Hey that's just me. ;)

Regards,
Mark

[Les MacDonald]

Hi Ralph,

I was about to start a new string about this problem but figured someone on GPT has already been there. Sounds like you have been working on a problem similar to mine.

You know our system but for other members, it is well described in Rob Beckers' report of the GPT of Prince Edward County homes Aug 14 in Living the Green Life forum (3rd home). Essentially, it's a 24v PV solar-wind hybrid system with an MX-60 controller and separate Lakota Commander controller with it's own internal heating element for diversion, set to 30 v. The auxillary output on the MX-60 is set to be ON during float but is not currently wired to any output. On the thermal side, we have 4 Schott evacuated hot water panels which feed propylene glycol through a transfer coil in the hot water tank. In addition to domestic HW, the tank also feeds water to a pump and radiant heating coils in the concrete floors, controlled by thermostats in each room.

The main source of space heating is passive thermal, supplemented by burning wood in a masonry heater. We have discovered that we can greatly reduce the need for buring wood by taking better advantage of both the PV solar and solar thermal systems. When in float mode (and even during absorption stage on a promising day) we turn on a 500/1,000 watt space heater and, if the HWT temperature is above 60 deg C or so, turn up the termostats to run excess hot water through the floors. Combined, these two additional sources increase the house temparture by several degrees.

Trouble is, these operations are done manually. When we are away, the only source of heat is passive thermal. (Being sticklers on green energy, we are reluctant to turn on the propane boiler.) What we are looking for is a way to link the PV and termal systems via the auxillary output switch on the MX-60.
Fortunately, the 120 C AC panel is immediately below the renewables closet where the MX-60 is placed (See Rob's photo in his Aug. 14 post). I am planning to run a wire from the auxillary output of the MX-60 down through the floor to the AC panel and link it to a relay switch to control the two 120v circuits that supply the floor circulation pump and the outlet that will be dedicated to the electric space heater. Ideally, a single relay controlling the two circuits would be better than two separate relays. The max. output current from the MX-60 is given as 200 ma at 12v. On the 120 AC side, I guess the capacity should be 15 amp. (same as the breakers) or better. Is that right?

As I will want to use both circuits on occasion when not on float, I figure that I will also need a 15 amp manual switch on each circuit bypassing the relay.

Any advice and comments are most welcome, esp. on where I might get the relay and switches. Ottawa and Belleville locations would be most convenient but mail order would do if I knew the precise specs.

Thanks for your previous adivce on battery matters, Ralph! All is currently well on that front.

Les

[Ralph Day]

Hello Les

Relays: the relay i ended up with is really heavy duty. It takes 170ma to actuate, which is well within the MX's 200ma limit. Osso Electric on College street in Belleville is where i bought the unit...it had to be ordered and arrived the next day. I think this was because of the 12vdc component.

Is your house panel in a utility room/closet? The relay is noticable when operating...quite a clack sound...not something we run at night. If there's wind and the batteries are full, we just drop the turbine settings and let it divert itself.

When setting up the MX i use the diversion mode so absorb and float actuate the relay. When you start to absorb there's really not enough "extra" power to run much (maybe your pump would be ok), so i've put a plug in timer on the relay-ed outlet. That delays the heater coming on until there's enough power to run it. In your case, i wouldn't worry about it as the circulation pump is probably not a big draw (any ideas about what it's load is?).

As far as bypasing your relay, i think a dpdt (double pole double throw) switch would suffice. Probably available at Osso or even Home Hardware. Not my forte though, maybe someone else here could advise (Paul?).

Hope this helps somewhat...call for anything further.

Rlaph

[Paul Bailey]

Hi Les : Your diversion load should be handled with a silent SSR (solid state relay) as switched by the AUX out / from the MX-60. . Probably not a good idea to Dump the Thermal load( start a circ. pump) from the Evacs via control from the Mx just because there is excess battery power there may or may not be excess Thermal ready to dump.. I may have to see your set up ,but how is the floor water temps being controlled presently..with A TMV(thermostatic mixing valve)??? I'll get you a relay .Paul :) ( I'll send a private message shortly)

[Ralph Day]

Paul,
Where, what, how much for silent relay? How much current can they carry and such like? Mine clacks and clatters but is robust and cheap. I think it was about $30 or so.

The MX 12vdc drive limit is 200ma, and my load on the circuit can approach 1500 watts (11amps or so), where can i look into this?

Thanks Paul

Ralph

[Stewart Corman]

Ralph,

SS relays have been around for ever it seems.
I am planning on using them for a load switch on my bird.
They function by having a trip input anywhere from 3v->30v DC.
They switch an AC load depending upon max rating ..I have some here that run 30amps up to 230v.... 460v/50amps is not uncommon...they draw 10ma

Crydom is one of the leading suppliers:
http://www.crydom.com/products/productFamilyList.aspx?idProductLine=3

Let me know if you or Les can't get them from Paul , or inexpensively up there, or I can ship you a package if you simply cover the shipping expense.

Stew

[Paul Bailey]

Ralph I'll get you a couple to be delivered Via the Yellow streamliner. Be aware the input is Polarity consieous., and If running more than 6 amp load output on these models they should be Heat sunk to a small metal or alluminum plate so will last. Paul:) (check your e-mail)

[Les MacDonald]

Thanks Ralph, Paul and Stew for responding so quickly!

Responding first to Ralph's query about the location of the 120v house panel, it is at the main entrance to the house behind a light bi-fold door. Noise of the relay clacking might indeed be a problem. I guess it would clack whenever the system enters float, regardless of whether or not the bypass switch is thrown. So, the SSR that Paul (and now Stew) suggests seems a better bet. Questions of reliability would be important since it would be operating when the house is vacant and would be controlling a 10 amp current in the case of the circuit feeding the space heater. If the SSR draws less than 100 ma then I could use two separate SSRs to control the two circuits.

Ralph, you ask about the circulation pump load - the Xantrex meter shows an increase of about 1 amp at 120v when it operates. There is nothing else on that circuit aside from the transformer that feeds the pump. The space heater is normally plugged into a 1st floor bathroom outlet for this setup. It would draw about 10 amps but I figure that the relays should be able to handle as much current as the breakers for safe operation without intervention. Your idea of a timer to delay the heater during the early part of the absorption phase seems a neat way to harvest some of the energy otherwise discarded. We do that manually now but have to keep a close eye on the battery voltage.

Paul, you raise the problem that there might not be enough hot water to divert into the floors as the float stage begins. That's been our experience, and the HWT temp drops about 20 deg C or so in less than an hour. When you are at home you need to keep an eye on the HWT temp in order to be sure to have any for domestic uses. (I always check with Gwen before doing this!) However, the relays are intended for automatic operation when the house is vacant so we are content to allow all the hot water to be circulated into the floors - it increases the efficiency of the solar thermal panels. We have done this before simply by turning up the thermostats and leaving the breaker for the circulation pump on when we leave the house. Problem with that arrangement is the additional load on the batteries as the pump runs 24/7. I raised the low-voltage cutoff on the Xantrex to compensate but was a little nervous about that arrangement. The relay solution seems more reliable with few potential adverse consequences.

While writing this, I saw your note, Stew. The SSRs seem to be just what I need.

Thanks to everyone.
Les

[Stewart Corman]

Les,
A few quick points:

Questions of reliability would be important since it would be operating when the house is vacant and would be controlling a 10 amp current in the case of the circuit feeding the space heater. double redundancy ..these are a simple SPDT switch ..use two in parallel on each circuit to make it failsafe

BTW, they fail in the open position, so the only concern would be it not turning on, rather than being on constantly

If the SSR draws less than 100 ma then I could use two separate SSRs to control the two circuits.They are only 10ma ...use up to 10 of them

Your idea of a timer to delay the heater during the early part of the absorption phase seems a neat way to harvest some of the energy otherwise discarded.We do that manually now but have to keep a close eye on the battery voltagemanual schmanual ...Unless I reads you wrongly, you don't want the circ pump to click on while the vaccum tubes are absorbing?? a SSR connected thru a resistor bridge right off the battery bank could allow you to set a minimum battery voltage above that minimum for the tripping of any upstream SSR for heating. This primary one directly off the batteries could then drive the ones you have off the controller output. This simple circuit could be used for any other circuit you might want to delay?

Hope this helps and either Mark or I can draw you a diagram if you need one.

Stew

BTW, your circulator pump seems to be drawing a lot of watts ...my TACO is rated at 0.53 amps at 115v

[Ralph Day]

Stew
The absorption phase is on the pv charge cycle, not the sdhw. MX-60 is the solar charge controller (Outback).
Ralph

[Stewart Corman]

Ralph,
Thx for the correction, which is good , because after I posted it occurred to me that there is no voltage associated with passive SDHW ...PV charge cycle it will work on
Stew

[Paul Bailey]

Les, Stew, Ralph, . Les, your dump loads should have separated controls for the excess thermal and the electrical . ,although the Excess energy at any given time would and /or could be coming in at parity (possibly) on good solar days or low load days.. A larger Solar storage tank or a small bypass coil ( bus heater or Hot water Baseboard in the return off the Evac collector loop)to dump the thermal within the building envelope would suffice ( if your away) and would use no hydro and no controls!!! And as stated the excess electrical can be dumped with the Mx as control.:)

[Les MacDonald]

I see I have some catching up to do here.

Stew, your suggestion of using two SSRs per circuit sounds attractive. It should also reduce the amount of heating per SSR, right? I guess a heat sink would still be necessary, esp in the event that one fails. Could all 4 SSRs be mounted on the same heat sink plate?

Paul, I think a radiator of some kind in the glycol line from the solar HW panels would work, but that is probably a bigger job than using a relay to control the circulation pump circuit. And I know the latter works reliably as I am doing that now, manually. Installing a radiator in the glycol line would also be well beyond my very rudimentary technical capabilities. I must admit, Paul, that your point about the need for separate controls for the electrical and thermal was also beyond my high school physics. I don't see why both would not be effectively controlled by the event of the MX-60 going onto float. In the case of the PV, if it happens to be cloudy when the system goes on float, the extra load from the electric space heater will immediately send it back to MPPT, then, after a few seconds, the voltage will recover and resume float mode, thereby switching the heater on again. I imagine the cycle will take a few seconds but that should do no harm, should it? On a sunny day, there will be sufficient capacity to run the heater until clouds cover the sun or until late afternoon. As far as the hot water tank is concerned, by time the PV system reaches float there is always some warm water in the tank that could be usefully circulated through the floors. True, the water temp will drop sharply within an hour and will continue to circulate room-temp water through the floors while the system remains on float, but in the latter case, the system could only remain on float, with the 1,000W electrical heater diversion load operating, if the sun were shining. So (if my tortuous path is logical) the same control circuit from the MX-60 should be fine, in fact, better, controlling both diversion loads simultaneously. Please let me know if you think I have missed something here.

By the way, I should confirm that Ralph is right, Stew, with his correction regarding (items 11-13). On reflection, I am not too concerned about being able to automatically harvest excess PV power on the absorb cycle as I can simply reduce the length of the absorb cycle when I will be absent for a few days, setting the MX-60 auxillary to come on during float. I've found that reduces electrolyte evaporation, which is important when the house is vacant.

Thanks to all for the thought-provoking comments.
Les

[Les MacDonald]

Thanks again for bringing me three SSRs during yesterday's Green Tour, Paul! They should have more than sufficient capacity for the prospective loads. I am thinking of using two of them (one rated at 40 amp @ 240 v, and the other at 25 amp) in parallel to control the 1,000 watt space heater circuit between the two relays. That would be intended to provide the redundancy that Stew mentioned earlier. And use the third relay (rated at 10 amps @ 24 to 330 v) for the circuit running the circulation pump for the in-floor hot water heating. As I recall, the Crydom web site recommends mounting them on a metal heat sink. Is there any reason why I couldn't mount all three relays on a single sheet of aluminum? I presume the aluminum should be large enough to dissipate enough heat so that, in case of an overload, the 15 amp breakers on the panel would be the first to pop out?
Les

[Mark Parsons]

Greetings Les, Stew and Paul,

I know you can parallel for heavy loads using MOSFET type SSR's - i.e. Crydom Series 1 - DCL for DC loads. I'm not sure that SCR type SSR's will share the load properly. A quick look at Crydom's spec sheets don't lead me to believe any different on the paralleling capability - http://www.crydom.com/products/productFamilyList.aspx?idProductLine=3

A 1kW heater will draw far less than 40 amps anyway. On a 120VAC circuit it will draw 8.3A, on a 240VAC circuit it will only draw 4.2A. Redundancy and functionality will be lost if the SSR's fight each other to death. A back up circuit could be wired and switched into play if the primary circuit fails to address redundancy concerns.

My $0.02 worth - :)

Regards,
Mark

[Paul Bailey]

Ditto what Mark Has said on the relays> Haven't replied as its getting busy But was going to send Les a private message,since the Tour We just simply did not have time to talk but I'll get in touch later. In the heating application most of the relays I've changed ...maybe 150 total out of the thousands in use over the past 30 years ( 80% were shorted due to excessive fault current, from a rotating slip ring failure and 20% were open) . Others have and continue to cycle to several hundred millions of cycles with no issue. In other words ,One relay sized properly for the application should be fine. If you need a backup ,that can also be worked . I'll reply more later. Paul:)