Solar panels

[bobgarrett]

A friend setting off for the Med dramatically reduced his fridge power consumption by replacing the insulation with vacuum insulation blocks. I'd never come across them before.

 

[noelex]

For those who want to check:
Ideally, at start up of the solar controller the delivered current should be very low but it should be positive. You need to be watching the battery monitor, but this only needs doing a couple of times. If the controller is waking up correctly it will tend to continue to perform in the same way. If the start up is reasonably correct there is no need to consider wiring the panels in series, which suffers from more shading problems.

If the start up is late, then the current delivered to the batteries will be more significant. If the start up is too early, the delivered current will be negative ie the controller will be drawing from the batteries.

The solar controller has some self consumption once all the circuitry to track the MPPT is fired up. So the controller goes to “sleep” to minimise this consumption. It monitors solar panel voltage to determine the correct point to wake up.

You may think that once the solar panel voltage is over the battery voltage the controller should wake up, but typically at this stage the solar panel is not capable of delivering more current than the self consumption of the controller. So a voltage delay is built in. On the better solar controllers this voltage delay is adjustable, but on the Victron controllers it is set at +5v for initial start up. This is a little higher than most, hence the concern that the controller could start late with “12v” panels in parallel, but as the solar panel voltage climbs so rapidly at dawn the difference is small. In practical terms the start up seems reasonable at least in the reported cases. It would be great if others could check.

 

[geem]

NASA BM1

Well i suspect its calibrated wrongly

 

[GHA]

NASA BM1

Could be right, if the sun rises early and it's not hot so the fridge rarely cycles. I've a BME monitor which sort of works OK but the default 'reset to 100%' was way out. In the hot Algarve on the hook with 300W I'd only just get back to 100% daily determined by closely watching current going in and voltage, that was with float set to same as absorption @ 14.9V. Takes a looong time to really get back 100%, especially with other loads going on during the day and some shading of even sometimes a cloud

This is accurate batt voltage from a typical day on the hook >>

 

[roaringgirl]

I can put an alternator in a circuit with a completely goosed battery and the battery will show a healthy 14.1V, but it still has no charge in it when I disconnect the alternator. That graph only tells you the voltage of the circuit, not the resting voltage of the battery - therefore the voltage you're seeing tells you diddly squat about the charge-state of the battery.

You need to use a shunt to measure the state of the battery.

 

[GHA]

I can put an alternator in a circuit with a completely goosed battery and the battery will show a healthy 14.1V, but it still has no charge in it when I disconnect the alternator. That graph only tells you the voltage of the circuit, not the resting voltage of the battery - therefore the voltage you're seeing tells you diddly squat about the charge-state of the battery.

You need to use a shunt to measure the state of the battery.

This I know, at that time there was no current logging which was just watched manually. Resting voltage is useless living aboard anyway, no one can really turn everything off for 24h to get a true reading and it's very much temperature dependant as well. SG similar. needs resting. ISTM the only practical way to double check for 100% when charging is watch the tail current at absorption voltage, various % comes up online, most seem too high. My T105's seem to be about 0.5% @ 14.9v absorbtion.

Below a test on the mains with current, charger turned off for 10 minutes at 08.43 >>

 

[noelex]

Well i suspect its calibrated wrongly

100% by 9am from solar alone is possible although this takes good conditions to achieve this. The case below recorded a month or so ago illustrates one example:

This morning I photographed the battery monitor app (a Pico). The solar regulators actually dropped back to float before I could take the photo. So I started another absorption cycle to show that the end amps had been reached.

So here the battery monitor is showing 100%. The solar controllers are regulating. The battery voltage is at the absorption voltage for these gel batteries. The end amps are at 4.36 amps, which is 0.7% of the nominal 600AHr battery capacity.

There are many definitions of 100% full lead acid batteries. The reality is actually that the battery SOC approaches the 100% in such a gradual way that a realistic definition is hard to standardise. The most common definition is when the battery charging drops to float, providing this is done at the correct point.

Most battery manufacturers suggest when the end amps reach 2-3% is the correct point. Many people suggest charging more aggressively holding the absorption phase for longer until the end amps reach 1 or even 0.5%. For gel batteries 1% is a good number so the 0.7% suggests the absorption phase has been held a little too long for this battery chemistry, but in practice the difference is only slight. At this SOC the end amps drop very rapidly so the difference in the time when these various definitions are reached is only small.

Note the time is 8:17.

 

[roaringgirl]

Seeing 0 current doesn't mean you can use the voltage to give you state of charge - the solar input might be balancing the output. The only way to establish state of charge by voltage is to disconnect everything and leave the battery to rest for an hour or more, then read voltage and adjust for temperature. Even then, you can be lied to by surface voltage, which drops quickly to 10.5 under load (in my dead batteries).

You need a shunt to know how much charge goes in and out of the batteries.

 

[GHA]

Seeing 0 current doesn't mean you can use the voltage to give you state of charge - the solar input might be balancing the output. The only way to establish state of charge by voltage is to disconnect everything and leave the battery to rest for an hour or more, then read voltage and adjust for temperature. Even then, you can be lied to by surface voltage, which drops quickly to 10.5 under load (in my dead batteries).

You need a shunt to know how much charge goes in and out of the batteries.

That last graph is current going in/out of the batteries logged from the shunt & battery voltage from the terminals.

" The only way to establish state of charge by voltage is to disconnect everything and leave the battery to rest for an hour or more, then read voltage and adjust for temperature.", sorry, forget that - from measuring it's more like 12h or 24h before the voltage finally stabilises (maybe more if it's cold) , 1h standing it will still have a long way to go.... no use really for us liveaboards.
https://www.pbase.com/mainecruising/battery_state_of_charge
SG apparently similar, needs a resting period to stabilise.

 

[geem]

100% by 9am from solar alone is possible although this takes good conditions to achieve this. The case below recorded a month or so ago illustrates one example:

This morning I photographed the battery monitor app (a Pico). The solar regulators actually dropped back to float before I could take the photo. So I started another absorption cycle to show that the end amps had been reached.

So here the battery monitor is showing 100%. The solar controllers are regulating. The battery voltage is at the absorption voltage for these gel batteries. The end amps are at 4.36 amps, which is 0.7% of the nominal 600AHr battery capacity.

There are many definitions of 100% full lead acid batteries. The reality is actually that the battery SOC approaches the 100% in such a gradual way that a realistic definition is hard to standardise. The most common definition is when the battery charging drops to float, providing this is done at the correct point.

Most battery manufacturers suggest when the end amps reach 2-3% is the correct point. Many people suggest charging more aggressively holding the absorption phase for longer until the end amps reach 1 or even 0.5%. For gel batteries 1% is a good number so the 0.7% suggests the absorption phase has been held a little too long for this battery chemistry, but in practice the difference is only slight. At this SOC the end amps drop very rapidly so the difference in the time when these various definitions are reached is only small.

Note the time is 8:17.

You dont say how much solar capacity you have. From my experience with an energy efficient fridge, led lights everywhere and on my previous boat in the Uk 220w of solar, i could never manage full charge by 0900. I would need very good conditions to be charged by 1030am. The fridge was keel cooled and quite small. Since my comments refer to an installation with only 100w I find it hard to believe full charge can be achieved by 0900 with 100w of solar

 

[noelex]

If solar was the only means of charging the batteries I agree that 100w of solar is going to make it tough to reach 100% charge by 9am in the UK if running a typical fridge.

Hitting 100% by 10:30 in the UK with 220w of solar running a fridge is doing very well.

Our first yacht we only had 75w of solar and we could occasionally hit 100% by 9am in very good solar conditions, but this yacht had minimal electrical demand (although there were no LED lights in those days) and no fridge. Our current yacht has just over 1000w, but has much greater electrical demand.

The overall SOC of the batteries time taken to reach 100% was similar for both yachts, as the balance between consumption and production was similar.

One important factor is that we cruise in both summer and winter. Hence the solar array is sized to be adequate for winter conditions leaving an excess of power in summer. This excess power, when available, can be utilised with electric cooking etc, so the power is not wasted, but the net result is a high battery SOC early in the day when solar conditions are very good.

 

[geem]

If solar was the only means of charging the batteries I agree that 100w of solar is going to make it tough to reach 100% charge by 9am in the UK if running a typical fridge.

Hitting 100% by 10:30 in the UK with 220w of solar running a fridge is doing very well.

Our first yacht we only had 75w of solar and we could occasionally hit 100% by 9am in very good solar conditions, but this yacht had minimal electrical demand (although there were no LED lights in those days) and no fridge. Our current yacht has just over 1000w, but has much greater electrical demand.

The overall SOC of the batteries time taken to reach 100% was similar for both yachts, as the balance between consumption and production was similar.

One important factor is that we cruise in both summer and winter. Hence the solar array is sized to be adequate for winter conditions leaving an excess of power in summer. This excess power, when available, can be utilised with electric cooking etc, so the power is not wasted, but the net result is a high battery SOC early in the day when solar conditions are very good.

Fully agree.
Apologies for thread drift in advance but rather than using our spare solar capacity for cooking I am currently rigging up a solution to heat hot water from solar and our 1200w immersion heater. Most afternoons our 760w of solar is redundant apart from dealing with the base demand. The batteries sit in float so lots of watts are simply wasted. I don't have sufficient solar capacity to run the 1200w immersion heater without pulling the batteries off float so I am using a 110v inverter to feed the 220v immersion heater. This will only pull 300w from the batteries so should keep the batteries on float on a sunny day whilst heating water. An hour or two heating water like this should be sufficient to give us enough water for a couple of showers and washing up without cycling the batteries.

 

[noelex]

In summer we also heat all our shower water via electricity which comes from solar.

Our shower water is pumped out of an aluminium tub so hot shower water can be produced in several equally effective ways. In summer it is all via an electric kettle (powered from the solar panels), in winter this switches to our Reflex diesel heater which has a hot plate on top. As an alternative or back up we have the propane stove. If we are running the engine the alternator will power the electric kettle without any solar input.

If cruising warm climates the water can be heated on deck but this is then transferred to the tub so the hot water can be utilised as pressure fed indoor shower with a normal shower rose etc

This versatility suits us as we are only very rarely plugged into to shore power and are often at an anchorage long enough that all engine heated hot water is depleted.

This type of system could easily be retrofitted to most yachts. It allows for a normal household shower in all situations.