diy solar

diy solar

Newbie exploring a PV array in my field about 50m from the house UK based

skostar

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Sep 14, 2021
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I have so many questions but at the moment I’m about to have a GSHP installation in the field adjacent to my home.
I am considering laying a cable into the trench for the GSHP flow and return pipes to leave an option for later PV array.
so yes an answer might be to put a conduit in place - probably cheapest and easiest. What size Conduit?
if I laid cable in do, what size cable for the loads?
AC or DC? AC = less losses, DC means an expensive inverter is not left ready to steal in the field! And the DC could feed a battery store at the property. But what are the losses over such a stretch? Negligible or worth worrying About? I also want to integrate with electric car charging too - as yet not installed. The run could be nearer 75 or 100m by the time it’s reached the best place for a battery store!

I’m sorry for so many questions to start with but the answers will help direct better questions!

thanks for your understanding and help in advance.
 
Some inverters allow higher DC (solar PV) input voltages. You can connect several panels in series and have 100v or even a lot more on your PV feed to your inverter. For a given power (in watts) the higher the voltage the lower the amps. The lower the amps, the lower the losses will be over a given distance.

Conduit size 1.5" or 50mm would be large enough to handle a lot of wire. Maybe overkill. If you know what you plan to do for an inverter and how many watts, a better guess would be possible.
 
That’s a useful response and already helped answer some questions. Space isn’t an issue, I planned to use some ex solar farm cells. I haven’t a clue how much power I’d like from the array.
Where do you start with this question?
 
If you want enough power or maybe someday enough power to replace what you use off the power grid, look at your electric bill. I was using about 1100Kwh per month the two years prior to starting with solar. I wanted to produce a little more than I use, so sized up from there. There are calculators that help you know what you can produce (per square meter of solar panel) based on where you live.
 
In my own system I have arrays with four grid-tie panels wired in series to get 120VDC. I'm running that ~135 feet (about 41 meters) through 10 gauge wire, and I'm not seeing any significant voltage drop. I ran my wiring through 1 inch PVC irrigation pipe. For longer distances, you can plug your values into a voltage drop calculator like this one to determine losses.
Keep in mind though that different manufacturers of different components have greatly different maximum specs for their equipment. And, a single manufacturer might have different models of the same components that differ only in the maximal voltage and amperage they can tolerate. So, you have to pick and chose your equipment to match your design parameters.

One very important thing to remember when designing a high-voltage solar system is that the voltage of your panels goes up as the temperature goes down. At freezing, your voltage will be ~12% higher than at room temp. You need to use a string calculator like this one when you plan on operating your system in cold, winter conditions.
 
AC or DC? AC = less losses, DC means an expensive inverter is not left ready to steal in the field! And the DC could feed a battery store at the property.
Use grid tied inverter(s) with high voltage MPPT inputs. Major brands all do this. Fronius, SMA, etc.

You can go up to 600V DC in most places, and in some cases up to 1000V DC. The high voltage will help a lot with the voltage drop and keep cable spec down. Check you local regulations on solar PV installations.

Then the inverter and batteries (if you have them) can be secured inside whatever structure you plan to house them in.

If however you plan to put an inverter at the location of PV array, then you'll probably also want to have a well shielded data cable in your trenching plans for the inverter to connect to your LAN. You'll have to consult local regs but normally such things are not to be run in the same conduit.
 
I was in the cable tv industry for quite a few years. When we went from Cable on poles to underground everyone went with the smallest conduit for the underground (because of price). As we found out later we needed more room for additional cables or replacement cables. Pulling more cables into small conduit is not easy. Use the largest conduit you can afford. Instead of 1 1/2" go to 2 1/2" or 3".Or run a second conduit for later use. Always use PVC for underground not steel. And if you need to turn corners use a "sweep" instead of a 90 degree corner (two 45 degree sweeps are also better than one 90 degree sweep when pulling multiple wires).
Planning ahead is always better than digging another trench to run another conduit at a later date. Adding wires/cables because you need to expand or replace bad or mis-sized wires is expensive and time consuming. Also run a number of extra pulling strings thru your conduit (makes it easier to run another cable together with with the existing wires later on. Harbor freight sells different colored twine for this. I have used red, green, and white in the same conduit run). Make sure to leave long tails well secured at each end of your conduit.
Just speaking from experience.
 
Thanks for the advice everyone, very well received and no smart answers either!
I did some calculations and my annual electricity consumption might be as much as 25000 KWH Per year
A big GSHP and aspirations for 2 electric cars! Plus normal household usage. So realistically without an enormous array I probably won’t make much of a dent on that number.
I’ll be researching different sized conduits, I like the advice of a few extra pull through too.
BUT if the run is getting any longer maybe as much as 100m to put the PV panels at the top of the field then should I break the run of conduit with some drain covers (I’m not sure of the correct phrase but effectively junction boxes) or would you just make long unbroken runs of conduit instead?
 
no smart answers either!
No smart or smart arse answers? ?

Can't answer your conduit questions. I know some use a special conduit grease on cables to reduce the pull friction. Inspection/connection pits might be helpful but also represent an extra point of failure/ingress. I can only imagine there are codes for this sort of stuff.
 
25000 KWH Per year / 365 days/year/5 hours sun per day = 13 kW PV array
Oh, sorry. Double that for the UK, always overcast. (Smart *ss enough for you?)

13 kW requires about 15 to 16 kW (STC) of panels, which can cost as little as $2000 if used panels are available. Up to maybe $8000 for new panels.
PV panels themselves are almost the least of your expenses.
This is not an unreasonable system (about what put in years ago, but wasn't so cost-effective then.)

What will be not nearly so attractive is batteries to store power when the sun shines, for charging electric cars at another time.
Batteries are the most expensive part of a system.

If you can use CHAdeMO to regulate DC charging so as to consume 100% of PV production, that would be ideal. A PV MPPT to DC charger, if those exist.


You can't actually pull as many wires in a conduit as code allows. Extra cross-section is useful.
However long the spools of wire could determine where you should put junction boxes for pulling.
I typically buy 500' spools, so 100m wouldn't necessarily need any. Maybe a 1000' spool would make 3 runs, better use of the wire length.
 
25000 KWH Per year / 365 days/year/5 hours sun per day = 13 kW PV array
Down under we consume 14MWh/year.

Our array is 11kW. Annual production is ~13.2MWh. I'd like to have a larger array but connection approval limits. At most I could add perhaps another 2kW of grid-tied PV but the approvals would be a PITA.

Anything else has to be off-grid. I have a 2.2kWh off grid array now looking after pool pump and my backup battery. I have enough roof space for another 120 panels if I ever wanted to go totally solar berko.
 
Down under we consume 14MWh/year.

Our array is 11kW. Annual production is ~13.2MWh. I'd like to have a larger array but connection approval limits. At most I could add perhaps another 2kW of grid-tied PV but the approvals would be a PITA.

Anything else has to be off-grid. I have a 2.2kWh off grid array now looking after pool pump and my backup battery. I have enough roof space for another 120 panels if I ever wanted to go totally solar berko.
I still envy you, your property, and your solar.

Properly inspiring individual you are.
 
How about adding more PV panels, oriented differently, paralleled with your existing panels into existing inverter?
No higher wattage exported, but more hours. I figure you can deliver up to 1.4x the kWh this way.
 
How about adding more PV panels, oriented differently, paralleled with your existing panels into existing inverter?
Approval limits are based on system PV array size. Plus orientation options are set by the roof you have, not the roof you want.
 
Can't answer your conduit questions. I know some use a special conduit grease on cables to reduce the pull friction.

It's called Cable Lube or Wire Pulling Lube and it's worth EVERY PENNY!! You can get a bottle of it at pretty much anywhere you can buy bulk networking or phone cable, including the big box stores. A 1l bottle is about $10usd at the hardware store down the street and will be more than enough to do all your runs.

Also, gotta second the call on larger conduit. Going for 100mm over 50mm will make the pulling much easier, especially if there are corners, and gives you plenty of room to add in later or oversize now. Dig once, not every time.

The higher the voltage you can get your arrays without frying anything on the other end (remember VoC +20%) will save you a fortune on wire costs and line loss.
 
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