diy solar

diy solar

Selecting a new battery bank for holiday cottage

Indeed. I might have to do the audit now.


All of them facing directly at south at an angle of about 45-60 degrees.

Re-run the solar hours and click optimal year round:

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EDIT: While I'm doing the audit, what do you think about the Multiplus II 24V/3000VA/70A for the supposedly accurate new setup?

I have all Victron hardware. Never a bad choice provided it can meet your power needs. The MP II has low idle power consumption, which is an improvement over their prior model.
 
Re-run the solar hours and click optimal year round:

View attachment 43915


I have all Victron hardware. Never a bad choice provided it can meet your power needs. The MP II has low idle power consumption, which is an improvement over their prior model.

Damn, I'm going blind. Here it is for year round. I think the southern roof is quite close to 45 degrees.
 

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30° (from vertical/60° from horizonal) is optimal year round. If you have more at 45°, then that's an option you can select as well.

Since it's unused for 3 months, I'm going to shoot for the Feb/Oct hours as they're likely worst case around 2 hours/day. I assume this is primarily due to poor weather. 45° may yield worse results.

1000W of solar for 2 hours = 2kWh of solar/day. That's pretty anemic. That means if you use more than that, you're depleting your batteries. My guess it the dishwasher may have worked fine the first day if the batteries were fully charged in your absence, but it didn't on subsequent days.

For comparison purposes, 2kWh/day is about what a typical residential fridge uses.

On that basis alone, more solar is warranted.

Your battery has 630Ah * 12V = 7.56kWh of total energy storage, 50% of which is usable, 3.78kWh. In those months it takes you almost two full days to recharge your batteries with NO power used, and that's only charging from 50%.

I suspect the system is just under-designed for the usage. The audit and a refinement of the available solar should get you where you need to be.
 
I suspect the system is just under-designed for the usage.
Exactly his. There has been a large feature creep during these last few years.
Here is our current usage for a summer day without vacuum or dishwasher. I'm having difficulty believing this would require a 9-10 kW inverter, if I'm reading this right.

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Number 2 is with dishwasher.
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Exactly his. There has been a large feature creep during these last few years.
Here is our current usage for a summer day without vacuum or dishwasher. I'm having difficulty believing this would require a 9-10 kW inverter, if I'm reading this right.

Apparently it will if you simultaneously make coffee, make tea, heat dinner, chill beer, watch television, do the dishes, and vacuum the floor. With the lights on, because it's night.

One clue is that the total wattage is more than the watt-hours, > 1C discharge rate (if your battery is sized for 24 hours consumption.)

And you need even more watts from the inverter for the surge to start any motor (5x nameplate wattage).

You should be fine with a 4kW or 5kW inverter than can surge to 2x its rating for a few seconds.

1kW of solar panels might peak around 850W in the summer, produce about 5kWh. Lead-acid batteries may range from 65% to 90% efficient (I'm not sure of the exact figure), but if 80% you only get 4kWh to run loads (from the battery). That's short of your 6kWh anticipated consumption, even on the best sunny days.

Put in a lot more PV panels. Newer panels may be 50% more efficient that what you've got, in the same area will produce 50% more power, so consider removing the old ones. If you can put in 2500W of PV, that could run your loads and keep the batteries full.

My PV is about 70% of my battery capacity (but charge rate is regulated to 0.2C), so what's available to operate loads during the day is about 4x the kWh I store for use at night. PV is cheaper than batteries (except for DIY LiFePO4 which comes close), which is one of the reasons I proportioned it this way.

As for that dishwasher - mine has as setting for heating water, and one for no-heat dry. So heating element power consumption is an option for the user.
 
Apparently it will if you simultaneously make coffee, make tea, heat dinner, chill beer, watch television, do the dishes, and vacuum the floor. With the lights on, because it's night.

One clue is that the total wattage is more than the watt-hours, > 1C discharge rate (if your battery is sized for 24 hours consumption.)

And you need even more watts from the inverter for the surge to start any motor (5x nameplate wattage).

You should be fine with a 4kW or 5kW inverter than can surge to 2x its rating for a few seconds.

1kW of solar panels might peak around 850W in the summer, produce about 5kWh. Lead-acid batteries may range from 65% to 90% efficient (I'm not sure of the exact figure), but if 80% you only get 4kWh to run loads (from the battery). That's short of your 6kWh anticipated consumption, even on the best sunny days.

Put in a lot more PV panels. Newer panels may be 50% more efficient that what you've got, in the same area will produce 50% more power, so consider removing the old ones. If you can put in 2500W of PV, that could run your loads and keep the batteries full.

My PV is about 70% of my battery capacity (but charge rate is regulated to 0.2C), so what's available to operate loads during the day is about 4x the kWh I store for use at night. PV is cheaper than batteries (except for DIY LiFePO4 which comes close), which is one of the reasons I proportioned it this way.

As for that dishwasher - mine has as setting for heating water, and one for no-heat dry. So heating element power consumption is an option for the user.
Thanks for your input!
That described use case of 10kW is actually a perfect storm that never happens. As I said before, the only thing that is the issue at the moment is capacity and solar production, as the currently deployed 12V 2,6kW Outback itself can handle the dishwasher if batteries are full or fed from lawn generator. However, the enlargening of our current PV capability from 1kW to 1,5-2-2,5 kW is a good idea and not even that expensive. :) What I'm thinking about is scalability of the inverter-chargers:
How much efficiency loss (if at all) would we get from running a single Multiplus 24V 5000VA vs. running two Multiplus II 24V 3000VA? Because we could purchase a single Multiplus II now and second one later, but the Multiplus 5000 is quite an expensive upfront cost, older tech, greater idle power usage and currently even more expensive than 2 units of Multiplus IIs!
 
Can't tell you about that brand.

Some brands support a team of sleeping inverters, which are awakened only when their power is needed. My Sunny Island, for instance, consume 25W at idle and 6W when sleeping. You could have 4x 5750W inverters consuming 25 + 3 x 6W most of the time, increasing in steps to 4 x 25W when you need 23,000W. And they'll peak at 44,000W for 3 seconds to start motors. Sorry I can't help you with a suggestion 1/4 that size or smaller.

Inverters differ in idle consumption. Some have a sleep mode where they turn off and only make brief pulses of AC to check for loads turned on. You may find and efficient solution. Or a low-cost one. Maybe both in one unit?

Watts for idle consumption are cheap enough to cover with PV, but the batteries required tends to be a bigger deal. Mine for instance consume 5% of battery bank at night (I haven't tried the team configuration yet, which might cut consumption 40% not 60% because two need to remain operating for our 120/240V split-phase.)

Could be a 48V inverter would be more efficient, less boost of voltage required.
 
Thanks for your input again. The cottage is on island by the baltic coast and is completely inaccessible for at least 3 months during winter. During this time it can go as low as -20C, but -35C can happen for a day or two every year. Summer is a different story however. I'm still hoping that a flooded lead acid could survive the winter plugged in with solar and wind with a few PoE security cameras with 4G LTE antenna running. Or maybe not.
Growing up we had an outside dug well and the pump was in the well, to solve freezing issues, as the well had a lid, we used two old style 60w light bulbs, this was enough heat to keep the pump above freezing, one bulb worked but we used the second for added safey if a bulb burnt out. Its a draw but if the batteries were in an enclosure, might be an old school solution to a modern problem if you feel your system was large enough to handle the constant load, i am in a similar situation,i have an off grid cottage in Northern Ontario, i can only access for about 7 months a year.i am in the learning and enlarging system stage, but newer battery tech seems to a great benifit, if it can be made to work for ya.
 

Alea iacta est

I'm back again after having made some purchases. Thank you everyone for contributing so far!

A delivery was made for 12 units of 2V 620Ah forklift batteries. It was a nightmare to transport approx. 450kg of flooded lead acid across the sea in a small boat. ? They had 2,11-2,12 Volts of delivery charge. Unfortunately 1 unit capsized at the pier and about a teaspoon of acid spilled out. I suppose forklift batteries can handle a bump or two, but at least only little acid was lost and plates weren't uncovered.

The following setup is to be connected in the next few weeks:

Cerbo GX<-->Ethernet
24V battery pack+++Victron Power Switch 275A+++Victron<-->Multiplus II 24/3000-->230V fusebox
of24V DC-->Non-isolated 24V -> 12V-->12V fusebox
12 units 2V 620Ah---Victron SmartShunt 500A---Fused Busbar<--(Old) Outback Flexmax 60<--1kW PV
"Lynx Distributor"<--Chinese 24V MPPT charger<--Chinese 800W windmill (30W?)
Cerbo GX


Next question:

The flooded lead acid system is going to require balancing actively and equalization perhaps monthly. On this forum there have been several posts advertising 12V/24V/48V system balancers with 2V-12V battery units. However, googling only brings up chinese units on aliexpress and nothing else. Victron has a balancer for 12V batteries and found nothing from other reputable manufacturers. Do you have any recommendations on balancers for my system?
 
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