Hi all - newbie residential DIY solar

hammertoe1

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Apr 6, 2022
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Hi All! I'm about to (hopefully) embark on my first residential solar project. I've got an engineering background, and previous converted a deliver van into a fulltime camper and installed solar in two campervans. So I've got some experience in solar, but on a much smaller scale. I'm also into home automation, and previously setup a home security setup with Home Assistant on a Raspberry Pi and a string of Zigbee door contacts/ PIRs.

Last year we moved from the UK to Barbados and this year we are hoping to purchase the house we are currently renting from our landlord. One of the first projects on my list will be to replace the old slightly leaky roof, and install a solar power system in the house. The house is a 3-bedroom, single level villa-style house with a swimming pool. Based on the readings from our electrical meter, we used about 250 kWh ofelectricity in a week, so approx 35 kWH a day. Our current electricity bill is around US $500 a month, and only going to be increasing. I think our largest power draws are: 2 x split wall-mounted a/c units in two of the bedrooms, the pool filter motor, and the dishwasher and washing machine (cold feeds only, heats the water).

My plan is to go for an off-grid system, but retain the grid supply on the odd occasion we need it (maintenance of solar, or prolonged overcast days). There are frequent power cuts here, and so I'd like a battery-based system, rather than grid-tie. Also for grid-tie I'd need to get it installed by a certified installer. With off-grid, that shouldn't be necessary.

My proposed setup:
- 48v system
- 10kW panels mounted on the roof
- LiFePO4 batteries, either rack-mount, or buying raw cells from China and a suitable BMS
- 2 x Victron solar chargers, one each for half the panels
- 2 x Victron Quattro charger/inverters to supply 2 x 120v legs, with 240v across both (split-phase)

My back-of-the-envelope estimations on sizing is that we want to go for (and can fit) approx 10kW of panels on the roof. The roof is slightly sloping south facing. Barbados has sun all year round, and I don't think much variance. We have a dry season and a wet season, but still seems to be a lot of sunshine regardless.

I've used Victron kit before and quite liked it. The Quattros seem pretty good from what I can see, and can be run in parallel in split phase and can have grid feed for backup. My thinking of the setup above is that I'd have some redundancy should something fail, I can at least limp by on one charger, or one inverter. The 240v is just a nice-to-have really. As far as I know, none of the appliances here in the house use it, but the house is completely wired for 240v European sockets throughout. And certain appliances like my espresso machine from the UK are 240v. If we installed a hot tub in the future I guess that might be 240v.

As for battery sizing, as I said, we seem to use approx 35kWH a day. I'm hoping this may come down a bit, as when we buy the place we'll be installing ceiling fans which will reduce the A/C usage. But then I'd also like to build a home office, so there may be a bit more draw there, and possibly install a hot tub at some future point. So I'm thinking we'd go for a max 35kWH battery. Maybe even smaller. I've learned from my campervan days, that you a best to err on the side of oversizing the solar rather than the batteries -- no point having batteries you can't charge properly. I'm hoping the solar panels will be enough to run some of the daytime load whilst charging the batteries, so we may even be able to get away with less than 35kWH battery if I'm happy to use grid power now and then, or to run the a/c less if needed.

We currently have solar hot water heating, and my thinking is I might be able to save some power if I can get the dishwasher and/or washing machine to take a hot water feed in, rather than just taking cold water and heating it. Also things like the pool filter pump can be timed/automated to run when power is spare as necessary.

The roof of the house is clay tiles, and it does leak a little bit in heavy rain. We had an inspection and it seems the waterproof membrane needs replacing throughout as now 30 years old and starting to degrade. Most of the other houses around us have tin roofs, and so we'd probably replace the clay tiles with a tin roof for easier maintenance, and I presume would be then easier to mount the solar panels on the roof. My plan is to do most of the installation myself, but if I'm getting the roof replaced, then I'd likely get the roofers to install some unistrut or whatever for mounting the solar panels on whilst they are up there.

Anyways... that is the plan! I welcome any feedback :)
 

hammertoe1

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Apr 6, 2022
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OK... having just written all that, I may have already changed my mind Having just seen iSwannie's posts: https://diysolarforum.com/threads/r...8v-growatt-solar-hybrid-30-day-overview.37391

Just seen the Growatt system and BigBattery products.


Certainly looks like it would a lot simpler install and would provide a more integrated package. I guess I'd just need to balance the convenience of that, versus the flexibility and redundancy of a more component-based system.
 

hammertoe1

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Apr 6, 2022
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Or a pair of LV6548's... decisions decisions. If I went for 24 x 400w panels, then I'd be able to run 4 strings of 6 panels, each string at 250v to each of the four solar inputs across the two units.
 

hammertoe1

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Apr 6, 2022
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Yes, you are right it might be a bit over. Temperature here is a pretty stable 24-30 degrees C.

When looking at the total voltage, is it the Voc you need to look at, or the voltage under load?
 

EntropicPoke

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Mar 29, 2022
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Just a couple of thoughts to consider....

1. I typically estimate average daily solar production at about 4.5 x the size of the array which you specified at 10kw, which mean about 45kwh per day of solar production. Well above you current estimated average daily consumption of 35kwh. That's a little bit more than necessary but not a bad thing as long as your charge controller can handle it without a divert load.

2. Your 10kwh array and 2 inverters makes me believe you plan to arrange them in about 2.5kw strings, with 2 strings in parallel per inverter/charge controller. You will just need to make sure your inverter charge controller can handle 5000w of solar. If I looked at the correct Victron charger it can handle up to 7,200w of solar so that would be fine. That Victron solar charge controller limits Voc at 450 and Isc at 20amps. So your panels need to have an Isc rating in the high 9amps range at max if you parallel 2 strings. The Voc will be determined by multiplying the # of panels by the Voc rating of the panels and the resulting figure cannot go over 450Voc. (10 panels at 42Voc = Array Voc of 420volts.)
- 40 x 250w panels (4 strings of 10 panels) = 10Kw total installation
- 10 x 250w panels per string (using LG 250w panels as example) 37.6Voc and 9.0 Isc gives you 376Voc and 18Isc per charge controller.

3. For battery sizing, I suggest a minimum of 2 days worth of consumption. In your case thats about 70kWh of battery storage. Even with LiFePo batteries Depth of Discharge (DoD) capabilities, I still dont recommend going below 50% DoD just to extend the life of the bank. Most rack mounted 48V LiFePo batteries (actually 51.2v) come in a 100ah per battery configuration. This gives you about 5.12kwh per battery. Most racks come in either 6 or 10 battery configurations. Assuming you will put one rack of batteries on each charge controller, you can go with 12 batteries and get 62kwh of storage in 2 x 6 battery rack configuration, or 20 batteries and get 102kwh of storage in 2 x 10 battery rack configuration. (or anything in between)

...hopefully your roof can handle 40 panels.

Just some thoughts from another DIY'er
 

Hedges

I See Electromagnetic Fields!
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Mar 28, 2020
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11,052
Yes, you are right it might be a bit over. Temperature here is a pretty stable 24-30 degrees C.

When looking at the total voltage, is it the Voc you need to look at, or the voltage under load?

Take Voc from the data sheet, also temperature coefficient of Voc. Look up the record coldest temperature for anywhere you might go. With that adjustment you get the highest open circuit voltage ever expected. It must be under the limit SCC allows. Otherwise, you let the magic smoke out.

Adjust Vmp for temperature coefficient and hot operation (panel heated by sun above typical hot weather.) Array Vmp as adjusted should remain above minimum MPPT voltage of SCC. Otherwise, you get a bit less power on hot days.
 

hammertoe1

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Apr 6, 2022
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Just a couple of thoughts to consider....

1. I typically estimate average daily solar production at about 4.5 x the size of the array which you specified at 10kw, which mean about 45kwh per day of solar production. Well above you current estimated average daily consumption of 35kwh. That's a little bit more than necessary but not a bad thing as long as your charge controller can handle it without a divert load.

Thanks for that, a helpful rule of thumb.

2. Your 10kwh array and 2 inverters makes me believe you plan to arrange them in about 2.5kw strings, with 2 strings in parallel per inverter/charge controller. You will just need to make sure your inverter charge controller can handle 5000w of solar. If I looked at the correct Victron charger it can handle up to 7,200w of solar so that would be fine. That Victron solar charge controller limits Voc at 450 and Isc at 20amps. So your panels need to have an Isc rating in the high 9amps range at max if you parallel 2 strings. The Voc will be determined by multiplying the # of panels by the Voc rating of the panels and the resulting figure cannot go over 450Voc. (10 panels at 42Voc = Array Voc of 420volts.)
- 40 x 250w panels (4 strings of 10 panels) = 10Kw total installation
- 10 x 250w panels per string (using LG 250w panels as example) 37.6Voc and 9.0 Isc gives you 376Voc and 18Isc per charge controller.

Yes, it would depend on the panels. I've seen some 370W panels with a VOC of 40v, which would work well in a string of 6 and be under the 250V input of many of the combined units (e.g Growatt or a MPP LV6548 if I went for them).

3. For battery sizing, I suggest a minimum of 2 days worth of consumption. In your case thats about 70kWh of battery storage. Even with LiFePo batteries Depth of Discharge (DoD) capabilities, I still dont recommend going below 50% DoD just to extend the life of the bank. Most rack mounted 48V LiFePo batteries (actually 51.2v) come in a 100ah per battery configuration. This gives you about 5.12kwh per battery. Most racks come in either 6 or 10 battery configurations. Assuming you will put one rack of batteries on each charge controller, you can go with 12 batteries and get 62kwh of storage in 2 x 6 battery rack configuration, or 20 batteries and get 102kwh of storage in 2 x 10 battery rack configuration. (or anything in between)

...hopefully your roof can handle 40 panels.

Just some thoughts from another DIY'er

OK, that is a larger bank than I was hoping to go for. I'm still taking some measurements of our current usage patterns to try and work out how much of the usage falls in daylight hours, versus at night. One thing I've noticed is it seems the swimming pool filter pump uses quite a lot of power. I've seen DC swimming pool pumps that are designed to run from solar and come with their own MPPT pump controller. That might be something I look at, and dedicate a few panels just to running the pump directly and separate it from the main battery system as it doesn't need a battery.
 

EntropicPoke

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I had the same issue with the needing more batteries than I wanted to purchase. I ended up splitting out my breaker panel into a grid panel and a critical load panel. I left the HVAC, electric stove, washer and dryer. And the hot water heater on the grid panel and it cut my battery need in half.

I can control the usage of those pretty easy by just using them or not. Also they tend to have the larger surge requirements so I didn’t have to scale up to their momentary needs.
 

hammertoe1

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Apr 6, 2022
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I had the same issue with the needing more batteries than I wanted to purchase. I ended up splitting out my breaker panel into a grid panel and a critical load panel. I left the HVAC, electric stove, washer and dryer. And the hot water heater on the grid panel and it cut my battery need in half.

I can control the usage of those pretty easy by just using them or not. Also they tend to have the larger surge requirements so I didn’t have to scale up to their momentary needs.
That makes a lot of sense. Similarly most of my 230v loads are non-essential like the pool pump and the washing machine.

The electricity cost here in Barbados is about USD $0.33 per kWh, so anything I can save is certainly welcome! We have plenty of sunshine, so solar is kind of a no-brainer. It looks like most setups here are grid-tie, which obviously has lower cost, but needs to be installed by a licensed company which adds to the cost. Also the feed-in tariff is lower than then cost per kWh, so you'd have to feed in a more than you consume just to break even. I'm happy to size my system to deal with 95% of my power requirements from solar/battery and use the grid on the 5% of the time it is needed.

Right now, by most prudent approach would probably to get some better stats of the current usage so I can understand it better. We have a smart meter (it has a zigbee sticker on it at least), but I'm not sure how to get any data from it.
 

EntropicPoke

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Have you looked into the Emporia Energy device from Amazon? I installed a couple of them to cover all my circuits and can get real time (second, minute, hour, day, etc) measurements of actual usage by each wire coming out of the breakers. The only down side was having to wait until the wife was out shopping for a couple of hours so I could cut the power to the house and install them.
 

hammertoe1

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Apr 6, 2022
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Have you looked into the Emporia Energy device from Amazon? I installed a couple of them to cover all my circuits and can get real time (second, minute, hour, day, etc) measurements of actual usage by each wire coming out of the breakers. The only down side was having to wait until the wife was out shopping for a couple of hours so I could cut the power to the house and install them.
Yes, I just saw them on another thread yesterday. I'm thinking about ordering one. I'm hoping that I could install them around the main 120v cables on the front of the house.
 

Hedges

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"Monitor with 16, 50A sensors" $150.
Only about $10 per CT, with WiFi controller thrown in for free!

I haven't found a link for the 200A main sensors yet.
 

Hedges

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Looks like all three selections include Emporia electronics unit and a pair of higher amperage CT, to clamp around a cable.
.pdf data sheet says those are 200A.
Good, that's included

Further down, "Do You have Metal Bus Bar Mains in Your Panel?" shows a flexible sensor for busbars, if meter configuration doesn't use a cable. Can't find that one.
 
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