PV energy to power underfloor heating

[grassabrutta]

Hi guys. New to the forum.

I am looking to install (12 V) DC underfloor (aluminum tape) heating in the home.
We have installed it in one property already and it works great even at low temperatures, but the electrcity bills can get up there.

This heating system supports a 12V DC supply input, in addition to the more regular AC draw (with its own subsequent AC -> 12 V DC conversion).

I want to see, using solar panels, how much of the energy draw for this heating it would be practical to harness and push to the unit.

I will roof-mount 20 x 300 Watt solar panels, each with this spec:

Maximum Power (W) 300±3% W
Open Circuit Voltage Voc (V) 20.8±3% V
Max Power Voltage Vmp (V) 17.5±3% V
Max Power Current Imp (A) 17.14±3% A
Short Circuit Current Isc (A) 18.85±3% A
Solar Cells Efficiency 23%
Series Fuse Rating 20A

I am looking for the optimal solution WITH NO GRID TIE to basically power just the heating installation.

So, what is our heaing energy need ?

Power Consumption Reqirement in the coldest month: 30 W/m2 (maintains a 23C temperature, which is comfortable).
If we run it all day (which we likely will do during the cold months) : 24 x 30 WH/m2 = 720 WH/m2
And we have say 100 m2, leaving us a consumption of 72 kWH (per day).

Using https://re.jrc.ec.europa.eu/pvg_tools/en/#api_5.2
with the "PERFORMANCE OF GRID-CONNECTED PV" calulation profile
which takes into consideration location, altitude, horizons, solar mounting method, angle and azimuth,
we get a report that says a 6 kW solar array (assuming a 14% loss) will typically deliver 10630.67 kWH per DAY.
That's a whopping 10 megawatts hours. If it is correct, then we potentially have energy to burn.

So, all of that energy has to go somewhere, and without a grid tie, we will not have the sink to accept such loads.

So, now to my questions.

[1] If I consider the direct-DC-supply route to the heating system, is it possible to push that DC energy with some large capacity DC-to-DC converter and supply sufficient on-demand energy ?

[2] If I consider the inverter-to-AC route to the heating system, is it possible to push that AC energy DIRECTLY as it comes off the array though an inverter (without a battery in the middle, and no grid tie) and supply sufficient on-demand energy ?

In each case I would look to capture via MPPT excess to batteries for overnight use.

Advice greatly appreciated.

Thanks
Julian

 

[kommando]

I took a random spot in Slovenia, took the std slopes etc for 6kw array and got.

Slope angle [°]:	35
Azimuth angle [°]:	0
Yearly PV energy production [kWh]:	7088.45

Note the 7088kwh per year, worst month is 300kwh per month.

Back to drawing board as at 72kwh per day you are 62kwh short per day in the worst month.

 

[grassabrutta]

I took a random spot in Slovenia, took the std slopes etc for 6kw array and got.

Slope angle [°]:	35
Azimuth angle [°]:	0
Yearly PV energy production [kWh]:	7088.45

Note the 7088kwh per year, worst month is 300kwh per month.

Back to drawing board as at 72kwh per day you are 62kwh short per day in the worst month.

Random in Slovenia means really anything from a valley to a mountain peak.
Here is report from the "PERFORMANCE OF GRID-CONNECTED PV" report.
Should I still be pessimistic ?

 

[kommando]

You have entered a solar array of 6000kw not 6kw, you are out by a factor of 1000.

 

[grassabrutta]

Yep, we're hosed for energy then.
I any case, from the perspective of getting a physical set-up, are either of my 2 installation options feasible ?

 

[kommando]

I run an 8kw array with diversion of summer excess to a hot water heater, as a DIY install with 2nd hand panels and inverters with electricity price of 30p per kWh it will pay for itself in 4 years. Have it professionally installed with new kit and it becomes 10 to 15 years before you get a return.

Start small with say 4 panels and an inverter and teach yourself how it works, if you take to it then extend if not then 4 panels worth of electricity will be easy to consume.

 

[Madcodger]

So, it seems that's a resistive heating element. With solar? Oof! Can't even begin to imagine the number of panels needed for that, much less the batteries (well, we could take the time to calculate it, but there's really no point in doing so). May we suggest mini-splits instead? You're using electricity to concentrate and move heat rather than generate it. Trying to use resistive heat with solar (for anything other than a "dump load" of excess production) is just a non-starter for almost all situations.