Solar Panels for heating off grid

[ontfarmer]

 Need help from you guys for using solar panels to power electric heater.

Are some panels better for this and will a charge controller be needed?

The wind turbine is used for this now.  Would like to try the solar also.

Ontfarmer

[DamonHD]

Depending on what you want heat for, eg space heating, there's less likely to be good sun around when you need the heat.

Rgds

Damon

[OperaHouse]

I do this to heat water and have written a few posts on it.  The same process would work for electric heat.   Panels have to operate at their power point voltage to be efficient.  There is one commercial product I know that does this, I don't recommend it.  It is fairly simple to build.  It would be extremely difficult to combine  wind and solar to use the same heater.  They would have to be kept separate.

[ontfarmer]

Thank you for getting back.  The heaters would be separate.

I will check back on your postings.

[sash]

heating by PV or wind  is not the way to go evacuated solar tubes would be a much cheaper and better option

I live in a zone 2 climate zone  -17c average winter temps... with weather that will sit at -40c  for a few week..   the best way to heat with solar are  evacuated solar tubes. matched to the output of  heat pump or what ever you other heat source is .. my house requires  7kw heat pump ( requires about 1.8kw to operate). the house is heated hydronically so I have 7 kw of evacuated  solar panels ., I have 2 large solar buffer tanks  about 100 gallons ,  which   I derive my domestic water and  heat for the house, the  heat heating system draws from the  secondary that the 7 kw of solar tubes  heat both tanks .. in the summer excess heat  is diverted into the  ground loop of the heat pump once both tanks reach ~70c ( if you were doing this as an off grid structure  divert it in the ground loop under the building or very large reservoir under the house . as me heating the ground loop only makes the heat pump work all that much more efficiently in the winter for me )..  this system has worked well for me. on a standard  construction house for the last 7 years .   basically  the heat pump only operates during dec, jan and feb  but even then it can be minimal.. for the entire year of heating  my electrical consumption is minimal at about <$150 per year.( considering normally it would be about 1500).  this year was quite warm due to el nino .. from the looks i doubt  it will be  50 $ for the entire year. and this winter  was pretty close to an average zone 5 -7c average..  but generally  if you only want to do solar.  this would be the approximate output i would expect..  from March - November you should be able to do pretty close to 100% of all your heating from solar on a standard R-2000insulated building .  Dec - Feb  you can do realistically about 30%-50%. but that all depends on the how sunny your location is and how cold your climate. for example if  I lived in a zone 7 climate zone  my system would nearly  heated completely by the sun in an sunny location . or  if I had a super insulated house ie SIP at 50R well zone 5 would probably be pretty close to nearly 100% solar heated too.. but the sun if finicky and tend not to be there everyday

[clockmanFRA]

Eco Warrior here, putting my head above the parapet.......!

If you have space for PV panels then shove them up as many as possible.

My whole complex of buildings is direct energy to Electric wire matt underfloor heating. Our buildings are to passive House standard.

With the price of PV down at sensible prices, if you do the comparison calculations on wet systems, Ground source heat pumps and the like, the initial cost of the installation, and the embedded energy, and the running energy used, sorry PV wins hand down. Especially if you add on the maintenance costs and the complexity factors.

With most modern PV panels I get a good 10% to 20% of rated output on those murky gloomy days.

I need about 3kW of electricity on those dim cold winter days, so 30kw of PV is ideal for us ......  

[DamonHD]

The view over at ebuild.co.uk seems to be to use PV rather than solar thermal, since it will work however cold it is outside and the cost per usable kWh is probably lower and it is MUCH easier to install and manage a few cables as opposed to pipework and so on.

Rgds

Damon

[ontfarmer]

   Hi Clockman
 Can you give more details?  panel volts, what is between panels and wire mat ( controller )

   Thanks Ontfarmer
 

[clockmanFRA]

I will try to expand and stay on subject…….. DamonHD may need to translate a bit as I do wonder around a bit, sorry.

I do have wind turbines on my system that DC charge the batteries, but dump to 8kW of independent air heaters 100 meters away in the main house.
 
However, some reasons why I have gone down particular concepts may need further explanation.

The readily well priced heating matts need a constant voltage, the element wire does not want to burn out, or your digging up the tiles. So dump loading is a NO NO, and direct feeding from the PV is inefficient.

The PV panels I use are the industry standard. Each is 250w with a VOC of 37.8 volts, (its max the panel puts out when in a working system). About 1.6 meters by 1 meter.

The manufacturers I use are good quality but not the Rolls Royce like LG, Panasonic etc, and what's at a good price when I want them, including taxes no more than £150 GBP each.

 I have Sharpe, PV, Yingli, Eurosolar, Renosolar, Rensu, Knive etc. All at that 37.8v VOC.

Now to get that 10% in murky gloomy days, I use Controllers that are MPPT, that takes a high DC voltage and converts it down to  a 48v DC battery voltage, 180vdc max with the Midnite Classic controller or 120vdc max with my Tristar MPPT controllers. However these controllers are expensive, rarely come up second hand, but they are good and their battery charging regimes excellent.

Or,........... and what I am now using is Solar Inverters that are GTI's Grid Tied Inverters that take a higher DC voltage about 550vdc and MPPT, get it down to match the Normal Grid. But I fool these GTI machines by running them from my OzInverter, 48vdc to 230vac, created Mini Grid to function.

 The power can be directly used at my buildings without having to go through the batteries or the Inverter.
Which means for my large system, I No longer need to increase my 1300ah battery bank in size.

These GTI's are now cheap as chips here in Europe, as Houses with PV installed for receiving the Government FIT grants etc, want the Max 4kW install, so under 3kW they are sometimes as little as £160 GBP, for brand New solar GTI SMA 2.5kW. Or even cheaper if a Used replaced from a enlarging installation.

I did purchase, very expensive, what I thought was one of the best manufactured battery Inverters, 48vdc to 230AC, a SMA Sunny Island 6kw, but sadly the manufacturer has done some odd things with the control software so it does not DC couple and AC couple, (what I am doing), without you spending vast amounts of money on just there manufactured interface equipment. What they have done is to allow the machines Frequency to climb so high that normal household equipment/appliances fail.
 I kicked the machine out and its on it way back, and I made my Own OzInverter from Oztules remarkable endeavours.
 
That's basically it.

Depends on how big you are going, how cost effective you want, and your sustainable philosophy.

[ontfarmer]

Clockman   Thanks for the details of your setup. That will be very help full

for what I am going to build. The solar should help when there is not enough

wind for the 20' turbine.

  Ontfarmer 

[ontfarmer]

Hi  Clockman  have you been using the solar converters for a while?

I don't under stand the ozinverter maybe you help me there?

You have a very impressive set up.

Ontfarmer

[clockmanFRA]

All our PV panels are Mono type, I did test with Poly but 15 years ago they were poor output in ambient light, I do not know of the latest modern Poly panels.

The DC battery charging controllers, MPPT high voltage, Tristar & Midnite 200, have need running about 5 years now. And they do what they say on the tin.
The AC coupling side has been working for over year.

I am putting together a A4  booklet, 70 odd pages, with drawings, loads of photos etc., on 'How I Made a OzInverter'.
Give me a few months.

Yes the set up works, but like most things its never big enough, especially as we look to the future. 

[OperaHouse]

Excellent expla nations, clockman. You are the poster child for what can be accomplished if an effort is taken to just read a little and investigate alternatives.

Another option is powering heaters off the raw DC buss. This is how I heat water with
excess PV.  Maintaining the panels at the power point is essential.  A micro to monitor
panel voltage, generate a PWM signal and drive a FET is simple, more efficient and cheap.  A capacitor bank is used to store the energy for the power pulse. 

While cheap and simple, the practical limit to this is about 1KW and water heating.
"Under 48V" is a magical number for many building codes and mechanical type switches.
Most switches, relays and over temp protection devices are not rated over 30VDC. Contacts made of silver have difficulty extinguishing an arc once started. With AC, the arc is naturally suppressed when the voltage goes to zero each cycle. This presents a problem with power distribution using commercial heaters with thermostatic controls and over temp switches not rated for DC.  Heating water is far simpler, with everything in one place it canbe treated as one big  black box.  I built a power shed separate from the house just so I cansay my homebrew stuff is not part of the house. 

I have been pressing for PV water heating in areas that use tanks for storage.  If one wants a cost effective solar project, water heating can't be beat. When an array is sized under 1KW,It can be guaranteed that 100% of the potential solar harvestable energy will be used to do actual heating. Grid power is used primarily for backup.  Enabling grid heating at 5-7am to get the system up to temperature will allow successful solar only the rest of the day. Controlling a couple KW of power can easily be done with a very simple home made MPPT controller costing less than $20 to build.  That savings will buy a half dozen panels vs a GTI inverter system.  As a dump load this is almost a must for PV.  Even an older PWM controller can be enhanced to harvest energy during the PWM off portion of the cycle. 

The DC problem with switch contacts by operating at higher PV voltages and insuring that the PWM duty cycle never reaches a DC condition and the off time is sufficient to extinguisha potential arc.  If a heater is operated at half voltage, the power is reduced to one quarter of that at the rted voltage.  With PV that acts as a safety feature.  Design a system to operate at around 50% PWM.  Should a FET short out, the excessive load drops the power to a level that may be inherently safe.

The big downside of direct DC space heating is what do you do in the summer.  At least
heating water is all year long.  That forces you into grid tie when space heating.

[ontfarmer]

Another option is powering heaters off the raw DC buss. This is how I heat water with
excess PV.  Maintaining the panels at the power point is essential.  A micro to monitor
panel voltage, generate a PWM signal and drive a FET is simple, more efficient and cheap.  A capacitor bank is used to store the energy for the power pulse. 

OperaHouse  maybe you can help, the micro will read the voltage which will trigger the

FET  ( switch ) to carry the load and the capacitor bank is like a condenser ?

Electronics where not around when I came through.

  Ontfarmer

t

[OperaHouse]

I'll address technical build issues in another post. While it seems I've posted a million
times on this, the information not all in one place.

Clockman, I would like to know how you control all these heaters. How they are brought
online and shed as sun conditions change. Are the GTI on independent sets of panels and
the OZ just syncs them?

In my system the power point voltage is calculated and normalized for typical operating
condition.  Multiple devices operate off the raw solar buss.  By setting the power point
voltage of each device slightly different the priority of each load is determined. Charging
the battery/fridge is the highest priority and the power point voltage is set 0.1V lower
than everything else. As charging demand reduces, heating seamlessly increases and the panels
remain fully loaded.  Heaters are also prioritized to operate the first, second, or both.

[clockmanFRA]

Clockman, I would like to know how you control all these heaters. How they are brought
online and shed as sun conditions change. Are the GTI on independent sets of panels and
the OZ just syncs them?

OH,....... its crude at present, the GTI's bang off when the Ozinverter ac voltage rises to about 250vac. I have access and can reset the SMA GTI's parameters. Each installation has its own sets of panels, but only 2 up at present out of the possible 6.

As regards the heaters, underfloor heating matts, they run from the Inverter ac, but I have an Arduino that switches them off if the battery falls below float level, yes a bit of hysterias is built in to it. But its code is set for DC battery first, but with the AC backfeeding through the inverter to the batteries, this Arduino is going extinct. 

My mate, (sadly no longer here), did the Arduino, but personally speaking, 'I just ride them, I haven't a clue what makes them work'.

I have to keep an eye on the DC 48vdc wind turbines dump controllers, 4off Tristars, set for diversion load. These can be problematic when the battery is at float and these diversion load start/allow dumping the 5kW trackers of DC charging solar. But as I said I have 8kW of Air Dump heaters, and it doesn't happen much.

   However, the project here has more constraints, like distances between installations and buildings, no more cables, aesthetics, etc, so I was going to start a new system with a new arduino set up down at my 'Power Station Building'.
 This would control each GTI installation with sequential shut off depending on the low dc battery voltage and shut off the GTI's at high voltage ac. This would be done by a multi channel Radio transmission/receiver units in a fail safe mode.

I was going to post on this during the spring. After I have done the DGD Arduino display with the OzInverter.

[Johann]

 
 Controlling a couple KW of power can easily be done with a very simple home made MPPT controller costing less than $20 to build.   

Would you have a link to build such a circuit?