diy solar

diy solar

Designer says my system size is limited by my mains disconnect?

Anyway, back to @hhtat's topic. Didn't mean to hijack it.
I've eight 272Ah LiFePO4 cells on order through Michael B Caro's group by so battery talk is not completely tangential. That said, I still wouldn't DIY a power bank for cost savings - just for fun + emergency power :)

Yes, 5KW is low. The power company said 10KW maximum export, but when I went to do the final export application, the fine print stated 5KW per phase.
I wonder if the future is neighborhood power banks. In central Texas, we're starting to see certain neighborhoods being build with a shared geothermal grid. A lot of these homes end up installing solar as well.
 
Your rates are quite low compared to mine. Highest peak is 1/2 of my off-peak.

PV panels + inverters, amortized over 10 years, costs about $0.025/kWh ($0.50/W). With mounting hardware and electrical stuff but not including labor, about $0.05/kWh ($1.00/W). Over 20 years, if you replace inverter once (which may not even be necessary), amortized cost $0.03/kWh.

With 3:1 peak to off-peak rates, better to just deliver extra PV watts, not use batteries. You can get 40% more kWh/day from an inverter if it has multiple PV array orientations.

HVAC is of course least efficient dumping heat to hot afternoon air. If a ground water heat pump & A/C, the hot side could dump to 50 degree F instead of 100 degree F.
A system can build ice during times of low rates, chill house during peak times with cold water. May or may not be so cost effective.
Got a pool? Should make a good place to dump heat.
Maybe with good insulation, awnings to keep sun out of windows, etc. the house can be kept cool with less power. Thermal mass could help too. I have a vaulted ceiling which gets hot. When I re-roof I plan to add a layer of insulation, maybe a gap for convection of air.

My baseline rate is $12/month. For now, utility would like to charge an extra $10 per kW of PV capacity.
If your AC draws 4kW and demand charge is $5/kW, that's $20 extra. Not too terrible when compared to batteries.

If you have East or South East facing panels you may be able to limit net consumption in late afternoon. Maybe A/C won't have to run as much early evening, but if it does that'll push up the demand charge.
 
Be sure to get PV panels that are "PID free", really reduced but not zero Potential Induced Degradation.

Any modern transformerless GT PV inverter like the current model Sunny Boy use an isolated PV string. The positive end of the string will be up to about +200V, and the negative end about -200V.
Solar cells made with P-type silicon are subject to PID if held at a negative voltage. N-type if held at a positive voltage. Half of your panels will see between zero and 200V of bias in the wrong direction.
Some PV panels degrade rapidly under these conditions, some much slower. So you want panels shown in stress tests to degrade slowly.
There have also been some gizmos designed to bias the string in the non-harmful direction during night time when disconnected from grid.

I've had P-type and N-type strings connected in parallel on a transformerless inverter for a year. I need to see if there is a way I can measure whether any damage was done. Voc and Isc aren't affected much, but power output at Vmp would be reduced. I'm rewiring the panels to transformer type inverters, with positive or negative grounding as appropriate for each model.
 
In the peak times, the big draw is the HVAC and unfortunately there's not much more we can are willing to do usage wise.
This is when you are typically generating peak solar, so this helps. As @Hedges mentioned, the only problem is that the air is warmer so an air-to-air heat pump (or air conditioner) will be less efficient. Water-source heat pumps (geo-sourced used to be called geothermal) will definitely be more efficient, but they are often much more expensive and slight behind the times in technology, so a high-efficiency air-to-air will close some of the gap and is a lot cheaper to install.

Deye has an AC/DC chiller (air-to-water) that can run off of dedicated solar panels directly: https://www.deyeinverter.com/product/solar-air-conditioner/hybrid-acdc-solar-air-water-cooler.html I don't have any experience with it, but saw it when I was first looking at their inverters.

I use an air-to-water heatpump with a hydronic air handler. Once I get the solar system installed, I'll add some insulated tanks to store hot water generated when the sun is shining which also reduces my nighttime HVAC load to just running a fan and circulation pump. That reduces my battery sizing dramatically compared to running the heat pump at night.

All that said, if you have an HVAC system already that is operating well, just add the PV system and in a few years, come back to revamp the HVAC.
 
I wonder if the future is neighborhood power banks. In central Texas, we're starting to see certain neighborhoods being build with a shared geothermal grid. A lot of these homes end up installing solar as well.
Interesting. Is that true geothermal (hot springs from the ground) or just geosource (water-to-water heat pump with coils in the ground). If there isn't a huge cost or efficiency gain, having your own system and no group politics is sometimes easier.
 
Be sure to get PV panels that are "PID free", really reduced but not zero Potential Induced Degradation.
Thanks, first time I'm hearing about this. I'm looking at LG NeON 2 360W panels - found some brochures saying they've "anti-PID." Still trying to figure out how big of a worry this is though. Check out https://www.photovoltaik4all.de/media/pdf/28/75/4c/LGE-PID-White-Paper-v1-1.pdf for example.

There have also been some gizmos designed to bias the string in the non-harmful direction during night time when disconnected from grid.
Looks like SMA makes a "PV Offset Box" - it's installed ground level so I can add it later if this becomes a worry.
 
Interesting. Is that true geothermal (hot springs from the ground) or just geosource (water-to-water heat pump with coils in the ground). If there isn't a huge cost or efficiency gain, having your own system and no group politics is sometimes easier.
I think they're just buried coils but not completely sure. Funny: a community started freaking out when their system started heating up over time - I think it plateaued in the end thou.
 
Thanks, first time I'm hearing about this. I'm looking at LG NeON 2 360W panels - found some brochures saying they've "anti-PID." Still trying to figure out how big of a worry this is though. Check out https://www.photovoltaik4all.de/media/pdf/28/75/4c/LGE-PID-White-Paper-v1-1.pdf for example.


Looks like SMA makes a "PV Offset Box" - it's installed ground level so I can add it later if this becomes a worry.

And this paper from SMA says, using PV Offset Box helped the PV panels but increased chance of damage to inverter.
Dated 2016, it recommends use only with newer (as of then) SMA inverters, not older models like I have. Don't know the situation regarding current models, I looked but no mention in the manuals or literature on the product page. Ideally it would be a built-in feature that could be enabled.



"Modules touted as being PID-free are anything but PID-free, as shown by this comparison test on modules from four different manufacturers for test periods of 168 (procedure 1) and 336 hours. The manufacturers are grouped by identical colors: manufacturer 1 and manufacturer 2 have claimed to be “PID-free.” It is interesting to note that for manufacturer 1, from which two batches were tested, there is a significant difference between modules. The modules with the worse results had degraded by more than 50% after the first test step. There is also a significant difference between modules from manufacturer 2, but this was not visible until the second week of testing. The dotted line indicates the 5% pass/fail criterion typically used in photovoltaics."


Also says, "Without moisture and dirt, there is little chance of PID occurring." I think that is because dirt and moisture on panel serve as an electrode, applying ground potential over face of panel.

"Due to moisture and impurities, a conductive layer is produced on the front of the glass. Through this, potential builds up between the glass and the solar cell, generating a small current as sodium (Na+ ) ions move from the glass toward the cell. On the front of the solar cell, these sodium ions create an accumulation of positive charges, which then cause short-circuiting (shunting) in the solar cell."

"PID can be reversed in certain cases by applying an opposing potential to counter the damage-inducing potential. For this reason, it would be a reasonable strategy to move the modules around in the string at regular intervals, such that the degraded modules can be regenerated. This is extremely time-consuming."

With a transformerless inverter, half the panels are above ground potential, and half below. If assigned to three or four groups, using extension cables they could be rotated through different orders of connection so they spend some time biased above ground, some time below. So much bother, though. And it only addresses the reversible portion of degradation.
 
Bugger. I'm going to have a hard time keeping my panels inclined greater than 15C.

1622608401483.png

This is my mental image of reclining at greater than 15C:
1622608547766.png
 
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