Solar performance

[geem]

We have spent the last few years mainly in the Caribbean. Our solar used to keep our lead batteries topped up and all was fine. We swapped to lithium batteries that I built over a year ago in Antigua and we noticed a big increase in solar performance. The reason geing that the MPPTs rarely go off bulk charge so the solar works flat out.
In the Caribbean, our 920w of solar would generally produce 3 to 4kWh of power daily with the lithium batteries.
We are now in the Azores where we have long days. The Caribbean generally has circa 12 hours of sunshine summer and winter. Here we have a lot more summer sunshine hours.
The things that can influence this are solar panel temperatures. Cooler is better. Its a lot cooler here. We have 3 MPPTs and each one has hit a new peak daily output. Even though we haven't had any perfect cloud free days we have seen over 4kWh per day on several occasions.
The downside is the watermaker production has dropped from 240 litres/hr to 210litres /hr due to the cool seawater temperatures. The immersion heater needs to be on far longer as the water in the tank is cooler so needs more kw to heat it up.
The fridges are running less as the cabin temperature is far lower but they don't use much power anyway.
Overall, we have more solar power generation here than we made in the Caribbean.

 

[Stemar]

It isn't only changing the type of battery that can make an apparent improvement in solar performance. I recently tripled our domestic bank from 100AH to 300, and I've noticed the same thing. I've no figures, but our 200AH of solar struggled to keep up since we fitted a fridge before, but has no difficulty now.

 

[Neeves]

We have spent the last few years mainly in the Caribbean. Our solar used to keep our lead batteries topped up and all was fine. We swapped to lithium batteries that I built over a year ago in Antigua and we noticed a big increase in solar performance. The reason geing that the MPPTs rarely go off bulk charge so the solar works flat out.
In the Caribbean, our 920w of solar would generally produce 3 to 4kWh of power daily with the lithium batteries.
We are now in the Azores where we have long days. The Caribbean generally has circa 12 hours of sunshine summer and winter. Here we have a lot more summer sunshine hours.
The things that can influence this are solar panel temperatures. Cooler is better. Its a lot cooler here. We have 3 MPPTs and each one has hit a new peak daily output. Even though we haven't had any perfect cloud free days we have seen over 4kWh per day on several occasions.
The downside is the watermaker production has dropped from 240 litres/hr to 210litres /hr due to the cool seawater temperatures. The immersion heater needs to be on far longer as the water in the tank is cooler so needs more kw to heat it up.
The fridges are running less as the cabin temperature is far lower but they don't use much power anyway.
Overall, we have more solar power generation here than we made in the Caribbean.

Interesting - but so many variables. .

I don't often complain but - data overload

Another variable is the salinity of the seawater, maybe higher in the Caribbean, and also its solids content. Part of the Caribbean precipitates calcium. Have you noticed any change in the membrane and/or filter performance.

Glad to hear you are half way back

Take care, stay safe

Jonathan

 

[geem]

Interesting - but so many variables. .

I don't often complain but - data overload

Another variable is the salinity of the seawater, maybe higher in the Caribbean, and also its solids content. Part of the Caribbean precipitates calcium. Have you noticed any change in the membrane and/or filter performance.

Glad to hear you are half way back

Take care, stay safe

Jonathan

Watermaker output on positive displacement pumps is directly effected by temperature. Salinity only effects the TDS reading.

 

[noelex]

The advantage of the Caribbean is that the solar insolation is very high all year round. We have cruised areas with a higher output in the peak season, but then the production is much lower for parts of the year. For example, the Mediterranean has excellent solar insolation in summer, but is reasonably poor in winter. Northern latitudes such as Scotland and Norway are surprisingly good in summer due to the long days of daylight, but very poor in winter.

In the Caribbean we produce much more power than we can use. Without regulation we would average more than 5 Kw from our flat, but reasonably shade free (as much as possible on a yacht) 1005 W.

 

[Sea Change]

Charge acceptance is perhaps the single biggest reason to switch to lithium.
Although it's also quite nice to get ten times the cycle life compared to lead acid, with reduced size and weight, and these days comparable cost or lower (for the batteries themselves).

 

[geem]

The advantage of the Caribbean is that the solar insolation is very high all year round. We have cruised areas with a higher output in the peak season, but then the production is much lower for parts of the year. For example, the Mediterranean has excellent solar insolation in summer, but is reasonably poor in winter. Northern latitudes such as Scotland and Norway are surprisingly good in summer due to the long days of daylight, but very poor in winter.

In the Caribbean we produce much more power than we can use. Without regulation we would average more than 5 Kw from our flat, but reasonably shade free (as much as possible on a yacht) 1005 W.

720w (4x180w) of our solar are good, high output glass panels. They work really well. The 200w of felixible Renogy panels ( 4x50w) have appalling output. The best we have ever seen is 127w output from 200w installed. By comparison, the series wired 180w glass panels on port and starboard guarwires have peaked at 447w for 360w rated output. If I can find some high performance 50w flexible panels, I will swap out the Renogy panels this winter.

 

[noelex]

Charge acceptance is perhaps the single biggest reason to switch to lithium.

A high charge acceptance makes a significant difference if trying to squeeze energy into the battery in a short period of time. If you are using a generator or even a large output alternator, a battery chemistry such as lithium that can accept charge quickly is much better.

In contrast, solar charging is at a low C rate for a long period of time.

 

[Sea Change]

A high charge acceptance makes a significant difference if trying to squeeze energy into the battery in a short period of time. If you are using a generator or even a large output alternator, a battery chemistry such as lithium that can accept charge quickly is much better.

In contrast, solar charging is at a low C rate for a long period of time.

It never hurts to have high acceptance rate . But yes it's even more beneficial if you're generator or alternator charging.

As originally installed, we would peak at about 0.2C charge rate from solar. We've since doubled the battery capacity so now it's more like 0.1C.
What kind of current do lead acids accept once they come off bulk?

I forgot to mention one other benefit of lithium- they don't care a jot if they don't reach 100%. No sulphation to worry about

 

[noelex]

As originally installed, we would peak at about 0.2C charge rate from solar. We've since doubled the battery capacity so now it's more like 0.1C.

If our solar panels were producing their full output and we had no loads running, our peak charge rate would be 0.06 C. This is only a low charge rate for a lead acid battery, but in practice when solar production is high this is also when we run our high demand appliances such as the watermaker, electric cooking, electric heating for showers etc. I suspect you do the same. These loads significantly reduce the charge rate even further. In practice the low charge acceptance of lead acid batteries when compared to lithium is not an important factor when charging via solar. This applies to most boats.

If we are charging via our high output alternator (something we rarely do), the charge rate jumps to around 0.2 C and even with loads running, our lead acid batteries can create a bottle neck. Lithium would be better. Over 1 hr we can put around 0.15C into reasonably depleted batteries . However, we do have a much higher output alternator than most yachts. It will produce over 4 kW (although we have dialled this down to just over 3 kW in the interests of reliability).

What kind of current do lead acids accept once they come off bulk?

The amperage that our (or any other) lead acid bank is accepting when they transition from the bulk to absorption phase will depend significantly on the maximum current the charge source is capable of delivering. If charging via our alternator into depleted batteries it is around 3 kW (120 A @ 28 V). Charging by the lower capacity solar into almost full batteries the value is much lower. I will try and catch the point today to give you a figure for today’s conditions.

 

[Boater Sam]

720w (4x180w) of our solar are good, high output glass panels. They work really well. The 200w of felixible Renogy panels ( 4x50w) have appalling output. The best we have ever seen is 127w output from 200w installed. By comparison, the series wired 180w glass panels on port and starboard guarwires have peaked at 447w for 360w rated output. If I can find some high performance 50w flexible panels, I will swap out the Renogy panels this winter.

I to have found flexible panel failing to produce anything like the rated output -- ever.
A big part of the problem is panel temperature. With no air space underneath they overheat quickly and it shortens their life.
I went all rigid panels spaced off the roof, much better output and panel life.

 

[geem]

I to have found flexible panel failing to produce anything like the rated output -- ever.
A big part of the problem is panel temperature. With no air space underneath they overheat quickly and it shortens their life.
I went all rigid panels spaced off the roof, much better output and panel life.

unfortunately, I don't have much more space for fixed panels. Being a ketch, a solar arch is out of the question. I like the theory of the 4x50w flexible panels as I can leave then laid out on the foredeck, fit them to the sun cover or lash them to the upturned dinghy when on passage. It works but the Renogy panels we have are pathetic. How they have the nerve to call them 50W is beyond me

 

[noelex]

What kind of current do lead acids accept once they come off bulk?

For those interested in a snapshot, this is our battery monitor today just after our three Victron controllers transitioned from bulk to absorption at 11am local time.

This is for a 24v system so you have to double the currents if thinking in 12v.

The battery is shown at a slightly optimistic 99%. The solar controllers are regulating the solar panels to around 26A with a battery current of 22.8 A (equivalent to 45.6 A for a 12v system). The Victron app shows we have added a total of 2.1 KW at this time. From this point the current will drop very rapidly as the batteries aproach a true 100%.

The battery manufacturer suggests the batteries have reached 100% (and should be dropped to float) when the battery current drops to 12 A (2%). This was seen today with a true absorption time of around 20 mins. I prefer to charge the batteries more aggressively and typically continue the absorption phase until the battery current has dropped to 6 A (1%). This occurred today with a true absorption time of around 30 minutes (around 11:30 am).

Keep in mind solar production and power usage vary significantly from day to day. The timing of our electrical demand is heavily influenced by when we start high current devices such as electric cooking, electric hot water heating and watermaker use. So this just a snapshot of one day.

 

[noelex]

This is again today about an hour later while we doing some electric cooking. You can see we are drawing 75.3 A (the equivalent of 151 A for a 12v system) from the batteries.

Solar is now briefly unregulated and is contributing 913 W. After taking into account other house loads, the induction hotplate is drawing around 2400 W. However, the induction hotplate pulses so the average consumption is considerably less.

Just another (hopefully interesting) electrical snapshot of life aboard.

 

[geem]

This is again today about an hour later while we doing some electric cooking. You can see we are drawing 75.3 A (the equivalent of 151 A for a 12v system) from the batteries.

Solar is now briefly unregulated and is contributing 913 W. After taking into account other house loads, the induction hotplate is drawing around 2400 W. However, the induction hotplate pulses so the average consumption is considerably less.

Just another (hopefully interesting) electrical snapshot of life aboard.
View attachment 178655

When you have lithium batteries, you don't have to wait for the batteries get fully charged before you run large loads. If we are going out for the day, we will often make more water on the watermaker than normal and make a tank full of hot water just to use up some battery capacity to make room for the solar charge that we know will becoming during the day. I see little point in wasting good solar output by having the batteries switch to float.
If the batteries only reach say 90% full, its no problem. Lithium doesn't need an bulk/absorbtion/float regime, often. Once every 3 months would be fine for good quality cells and an active balance. We try to keep the batteries in bulk phase for as much as possible ad this maximizes our solar harvest.
We ran the generator today for 20 mins as its not been run for a month. We didn't need it but it needed some exercise

 

[noelex]

When you have lithium batteries, you don't have to wait for the batteries get fully charged before you run large loads.

Lithium is great, but this is also true with a good lead acid bank. Or highest continual load is boiling the kettle. We would not survive without several cups of coffee and tea, often before the sun even rises.

This still only represents a load of 0.15 C which is no problem at all for a healthy lead acid battery and a well designed electrical system.

 

[geem]

Lithium is great, but this is also true with a good lead acid bank. Or highest continual load is boiling the kettle. We would not survive without several cups of coffee and tea, often before the sun even rises.

This still only represents a load of 0.15 C which is no problem at all for a healthy lead acid battery and a well designed electrical system.

Boiling the kettle is a short duration load. OK for lead but if you were to run a watermaker pulling over 2kw for an hour, your lead may not be so happy.

 

[noelex]

Boiling the kettle is a short duration load. OK for lead but if you were to run a watermaker pulling over 2kw for an hour, your lead may not be so happy.

A 2 kW load is a discharge rate of 0.14C (less if there was solar input) for our sized battery bank. This is not an unreasonable load for a lead acid battery to sustain for an hour, but I agree that a lithium battery bank would be happier.

However, it is not relevant for our style of cruising. We could not produce enough energy to devote 2 kWh just to producing water when visiting areas of moderate or poor solar insolation. A generator (or frequent visits to a marina) would be needed when visiting some of the areas we love. We do not have a generator and last visited a marina several years ago.

 

[lustyd]

I to have found flexible panel failing to produce anything like the rated output -- ever.

Ours all manage 105% of rated output quite consistently. That's with Renogy ETFE panels, Victron controllers and lithium battery so you may get different results with pre-ETFE panels, poor controllers or bad batteries. It's not a flexi panel thing though, that's for certain. Rated output is rated output, end of story. Output per square metre might be worse than fixed panels but that's an entirely different conversation.

 

[geem]

A 2 kW load is a discharge rate of 0.14C (less if there was solar input) for our sized battery bank. This is not an unreasonable load for a lead acid battery to sustain for an hour, but I agree that a lithium battery bank would be happier.

However, it is not relevant for our style of cruising. We could not produce enough energy to devote 2 kWh just to producing water when visiting areas of moderate or poor solar insolation. A generator (or frequent visits to a marina) would be needed when visiting some of the areas we love. We do not have a generator and last visited a marina several years ago.

Yep. We last ran our generator a month ago, until yesterday. We only ran it to give it some exercise. I agree when solar output isn't there, you would need a generator or high output alternator. We have the generator. Our boat came with one and its useful, occasionally. We can charge at 110A @24v, make hot water or run the watermaker. It a 30 year old Perkins 5kVA unit thst is very simple with cheap parts.