New Off Grid Storage Barn - PV System Design

SteveA · September 2013

First, thanks to everyone who has helped on my first thread: http://forum.solar-electric.com/showthread.php?5516-Off-Grid-Storage-Barn-in-Cold-Climate/ . i'm starting a new thread now as i have my loads and design figured out and need a sanity check on my plans.

I put together this spread sheet of my anticipated loads and sizing calculators. I used the January solar value from PVWatts2 becuase that is when we will be loading the barn's power the most with heating an that is the whole point of the system (and it's still pretty small).
https://docs.google.com/file/d/0ByOLtqSeyPktT1M3RWdhZl8xZG8
Attachment not found.

All loads that are anticipated for when there is work being done will be done on generator power including work lighting. I'm sure i've missed a load or two but they should be small.

I used the sizing calcualtions from another thread and came up with a system that is in the 400-600 watts range. I'm thinking of going with this http://www.solar-electric.com/solar-rv-kit-430-watts-mppt.html but getting a midnight 150 lite instead for the monitoring ability. since we won't be adding heat this winter I plan to get another of the Kyo 215 panels next year since they are pretty cheap. Alternatively i could for for the Trina 240's that cost less.

Should / can i run 2 or three of these panels in series with the classic or should i run them parallel into my 12V bank? Three panels is 75V and about 26A mp. Can i daisy chain the MC4 connectors to parallel three panels?

Thoughts? Gaps?

NorthGuy · September 2013

Re: New Off Grid Storage Barn - PV System Design

If you're going to add heating in the future, the system will have to be expanded substantially. Have you tried to do the math with heating is included, just to see how well the system will take the expansion?

SteveA · September 2013

Re: New Off Grid Storage Barn - PV System Design

I had assumed low/not power requirements for the boiler assuming standing pilot and the circulation pump would do all the work (which i accounted for). I'm now rethinking that.

Does anyone have experience to give me the power consumption of a Takaki (or such) on demand water heater or another low power consumption option? We are only going to heat to 50 degrees so i'm sure we can get away with a low BTU option. There are non-power vented options available correct? Should i go mod/con boiler instead (i assume they use more power???)? are there standing pilot on demand units still available?

Beside the potential need to add in some Wh for a boiler are my calculations correct on sizing? I erred towards our January sun hours seeing how our primary usage is in winter and it's a small system.

NorthGuy · September 2013

Re: New Off Grid Storage Barn - PV System Design

SteveA wrote: »

Does anyone have experience to give me the power consumption of a Takaki (or such) on demand water heater or another low power consumption option? We are only going to heat to 50 degrees so i'm sure we can get away with a low BTU option. There are non-power vented options available correct? Should i go mod/con boiler instead (i assume they use more power???)? are there standing pilot on demand units still available?

Sorry, I misunderstood you. I thought that you're doing electric heating. Gas-powered tankless water heater is totally different. I have Rheem and it consumes very little energy.

inetdog · September 2013

Re: New Off Grid Storage Barn - PV System Design

NorthGuy wrote: »

Sorry, I misunderstood you. I thought that you're doing electric heating. Gas-powered tankless water heater is totally different. I have Rheem and it consumes very little energy.

Standing pilot gas appliances in general are not available for new construction in the US because of energy codes, so the market is limited. There may still be some out there. You are trying to keep the inverter in standby mode and the igniter alone is not enough load to trip to full power? Some forced convection units draw enough power for the combustion air fan that it can turn on the inverter before the gas valve and igniter are energized. If you are just worried about energy efficiency, don't rule out fan-forced since it allows more efficient transfer of combustion heat to the water. Without the fan you need higher stack temperatures to keep the draft up.

One advantage of going with higher power is that it will allow you to draw hot water from more than one outlet at time without triggering flow reduction at the heater. If that is not a concern to you, go ahead with a low power unit.

I have my propane tankless set to 120F (49C) and it is quite satisfactory except for the dishwasher and kitchen sink. By the time it travels the 80 feet to the shower it produces a fine hot shower with little or no cold water added. Our dishwasher offers electric supplemental heat if the water is below 140F, but I can also use the remote control pad for the tankless to temporarily raise the setpoint as high as 180F if I want to. Try doing that with a storage type heater!

Only downside is that it would not play well with a solar preheat tank since there is a limit on how far down the on-demand unit can throttle its heat output. Since propane is pretty expensive here (comparable per BTU to electric) I would have liked to use some solar heating.
A heat pump type unit would actually be more economical for be since I am on-grid.

zoneblue · September 2013

Re: New Off Grid Storage Barn - PV System Design

The Bosch 'hydro' line dont require power, it works on water pressure peizo device. Then theres always the D cell powered peizo models generally in the cheaper units.

inetdog · September 2013

Re: New Off Grid Storage Barn - PV System Design

zoneblue wrote: »

The Bosch 'hydro' line dont require power, it works on water pressure peizo device. Then theres always the D cell powered peizo models generally in the cheaper units.

The ones that I have seen have been low capacity units intended for camp or vacation cabin installation. And some of them will not restart if wind blows the flame out while the unit is on. (Manual reset switch required.)

mike95490 · September 2013

Re: New Off Grid Storage Barn - PV System Design

I've got an "eternal" which is a SS 2 gallon tank, with a variable burner. The onboard thermal control won't let you get below 100F on the water heat, but is great with feeding it preheated water, so that it is able to throttle itself back. It fires up the blower and low flame, as needed, to keep it's tank at the set temp.
Many tankless units use a electric element to prevent freezing. It's rated 45w, but I would not use an inverter's SEARCH mode, bite the bullet and add enough battery capacity to run the inverter 24/7

solar_dave · September 2013

Re: New Off Grid Storage Barn - PV System Design

zoneblue wrote: »

The Bosch 'hydro' line dont require power, it works on water pressure peizo device. Then theres always the D cell powered peizo models generally in the cheaper units.

I wondered how they did that! Learn something new here everyday. My Sears gas water heater has an led that blips a few times a minute. No visible batteries and no electrical connection. It gets fed with 140-150F preheat from the solar thermal system so it seldom fires up for 10 months out of the year. I have it set to 110F and there is a cold water mixing valve down stream to get reasonable inside temps. Usually when the late fall temps keep it from heating adequately I will then turn up the gas unit.

SteveA · September 2013

Re: New Off Grid Storage Barn - PV System Design

Thanks all,
I'm planning on using a suresine300 as we really don't have any heavy loads since we'll be using generator power on the few occasions that we are working in the barn. It's primarily a storage unit that we just want to get at 50 degrees or so. The power usage of a suresine is only 6w when running so even if it's one all day that's only 150wh.

So if i got a high efficiancy modulating water heater what is the power draw of those units while running. Say a bosch micro turbine model. It is only the exhaust fan while on and the microcontroller right? What does that add up to? I'm calculating about 5 - 8 hours per day worst case for run time in the dead of winter.

inetdog · September 2013

Re: New Off Grid Storage Barn - PV System Design

solar_dave wrote: »

I wondered how they did that! Learn something new here everyday. My Sears gas water heater has an led that blips a few times a minute. No visible batteries and no electrical connection.

It may be leveraging heat differences to create a low power supply. (Does it have a standing pilot that could provide steady power?) Or there may be a button cell or primary lithium battery inside the control unit somewhere that will eventually need to be replaced.
They make smoke detectors with lithium batteries that are supposed to be able to blip their lights for 10 years without battery replacement.

zoneblue · September 2013

Re: New Off Grid Storage Barn - PV System Design

This is a kind of in between system size. If you decide to go with a full size mppt controller, bear in mind that the FM80 and CL150 draw about 4watts idle. Thats another 90Wh/d. On the flip side have you measured your loads accurately? Only reason i ask is that 5W for a rPi sounds high. Unless you have acessorys attached, itll be closer to 2W. See http://zoneblue.org/cms/page.php?view=cubieboard-and-debian

Now, given the price shift betw battery and pv, the thinking is becoming: use more pv to make up for battery lack.
On the same logic, you might say that a pwm controller, might produce less, but also draw less at idle.

Add some load managment, conservation, time of day shifting, and you might be able to reduce the projected and actual loads some more.

SteveA · October 2013

Re: New Off Grid Storage Barn - PV System Design

to get this thread back on topic (away from heat source) I pose this question.

Am i ok to run three trina 240 panels in series to a 150 classic lite on a 12v system? Right now it seems that is the most cost effective way for me to get the right amount of paneling for my requirements. Sure i could go with 4 smaller panels but that will cost more. I need the classic to run this panel setup right? I don't think any of the lower power CC's can do what i need right? Does the MS60 have a lower draw?

Other responses to questions above, the power draw of the rPi was a guesstimate but at this time i think i've got it so I don't even need it for logging if i go with the pentametric ethernet interface and the midnight controller. The DVR for the security has it's own webserver as does the webcam and weatherstation.

On the heat, The circulator pump has to kick on first and the draw on that is plenty to wake up the SS300.

thanks

Cariboocoot · October 2013

Re: New Off Grid Storage Barn - PV System Design

Specs on the Trina 240 say the Voc is 37.2 multiply by 3 in series you get 111.6. If it gets cold (and it will) that can go up to 146 - pretty close to the Classic 150's operating limit, but owing to the HyperVoc function in the controller it should be well.

I'd be more concerned about the conversion efficiency in down-converting a 90 Vmp array to a 12 Volt system. Could you put the panels all in parallel instead? You'd need a fuse each, but it should be more efficient.

I'm not sure the MS 60 would use less for itself than a Classic Lite. Neither has a display except as an option, and the power draw is usually only 3-4 Watts anyway.

SteveA · October 2013

Re: New Off Grid Storage Barn - PV System Design

I certainly could put them in parallel (but series wiring is easier LOL). Can i combine those without a combiner using the MC4 splitters as shown here http://lib.store.yahoo.net/lib/wind-sun/RVkit-315-2.pdf using two of them daisy chained or would it be best to use a combiner? I'll post up a schematic of all my components on my shopping list in a bit to make sure i'm thinking right.

Cariboocoot · October 2013

Re: New Off Grid Storage Barn - PV System Design

SteveA wrote: »

I certainly could put them in parallel (but series wiring is easier LOL). Can i combine those without a combiner using the MC4 splitters as shown here http://lib.store.yahoo.net/lib/wind-sun/RVkit-315-2.pdf using two of them daisy chained or would it be best to use a combiner? I'll post up a schematic of all my components on my shopping list in a bit to make sure i'm thinking right.

Technically three in parallel should have a fuse on each one, and that means some kind of combiner that incorporates over-current protection rather than just the MC4 'Y' adapters. Not that it won't work that way, just that it is safer with the fuses or breakers.

zoneblue · October 2013

Re: New Off Grid Storage Barn - PV System Design

As far as idle losses, the flexmax manual reports idle draw at below 2W. Thats becasue theres no arc fault, and no ethernet and asociated circuitry that are already inbuilt int he classic. Add a hub, flexnet, and mate3 and youll soon be at or above the 4-6 watts of the classic. Ditto the pentametric. Personally id avoid that route, as the classic will soon have its own battery monitor, and using one of several great monitoring functions/options, midnite is definately ahead on that field.

SteveA · October 2013

Re: New Off Grid Storage Barn - PV System Design

so the classic (lite) will have a built in battery monitor with the whiz bang jr that will monitor (and log) amps in and out? Do we know when that will hit the market? I don't need the display because i need to do all my monitoring off site. If i can do it all with mymidnite i'd be super happy. If i'm on site and need to see what's going on i can just use my phone or LAN? I'll still need a stand alond AGS but the magnum AGS looks perfect for that.

zoneblue · October 2013

Re: New Off Grid Storage Barn - PV System Design

Yes, amps to battery, amps to load. They started shipping to some markets already.

New Off Grid Storage Barn - PV System Design

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