#148166  by myles
 Tue Jan 15, 2019 1:06 pm
You've asked the right question, but perhaps haven't yet got the right answer.

The answer to your question 'How Much', is, 'the amount you need'.

Any professional that kits out a Motorhome actually works out what is needed, they don't install the maximum amount of solar panels that can fit and some generically size battery. They sit down and work out the requirements of the equipment installed and the use case of the Motorhome owner.

It only costs you some time to sit down and go through the items that you'll have drawing power and how long they draw power, for your use case, and then work out the amount of generator/alternator, solar and battery capacity/combination you need.

You will end up with a much better system that works and doesn't need continuous adjustments/additions/deletions. If you do it right from the start, it will cost you less upfront and over time and there will be little/no need to continuously monitor your system.

If you take the time to do the following, you'll have the answer to your question:
  1. Create a list of all the items that will draw power, what they draw, and how long they will likely run for. Be generous and add in a 'future proof' value for those unknown extras that will be added later. From this you can calculate 'how much need'. [You may already have much of this detail from your current system and how you use it - turning on devices whilst watching an ammeter provides this detail.]
  2. Consider where you will travel, when you will travel and how long you will stay in one place. Some points to consider:
    • If you don't stay in one place very long, you can rely more on power generation from your alternator.
    • If you want to stay in one place for extended periods, or only travel very short distances, you will want to consider more solar panels.
    • If you travel in winter or expect extended stays in overcast conditions, battery capacity will need to be increased to allow you to stay longer before moving on to charge from the alternator.
  3. Consider the full cost of your decision.
    • Simply putting more panels up, does not just cost you the price of the panels. There is additional wiring, and additional or larger solar controllers that add considerably to the cost.
    • Batteries are a mind field of difficult decisions. Wet lead acid batteries are cheap, take a lot of punishment but require some maintenance and are heavy. AGM's are less tolerant, more expensive and typically have a shorter life expectancy but are maintenance free. LiFePO4 batteries are expensive, but light and compact. If installed with the correct (somewhat expensive) management system, offer significant benefits. New batteries based on Graphene are now just ramping up into production, manufacturers are hoping they will outperform LiFePO4's - it's a huge industry with the era of the electric car driving it. A cheaper battery system selected now, may see benefits when this new technology becomes main stream.
  4. Think outside the box. Many comments on this forum are very generalised on the personal systems/use cases/biases that the commenter has.
For example, I have 160W of solar permanently mounted on the roof, and live in the lower South Island - this is enough solar input for my use case in summer, as we have extended daylight hours - why would I want to add excess solar in this case (14+ hours of solar input). However, in winter, when days are very short and we have our fair share of cloud, I use an additional 300W of portable solar panels that I can tilt to get maximum solar input (with tilting this equates to an ~800W system on a flat roof). However, even with this amount of solar there are times when solar simply is not the answer. For these times I draw on a largish battery storage of over 400Ah along with charging capabilities from the alternator. [My use case covers many different aspects since we have such variation throughout the year and we travel extensively.]

If you are only going to travel in summer, there is little need for excess solar. If you travel almost every day, consider what the Rental companies use (their systems get considerable abuse, but mostly work). If you want the most flexibility - as others suggest get the most of everything you can afford. But start with a spreadsheet of your usage and build on it - that will give you the answer of 'how much'.
 #148242  by Kumarakid
 Wed Jan 16, 2019 7:48 pm
Neddy wrote:
Tue Jan 15, 2019 9:37 am
Paul and Rog, more than anything else, you both need to fit a Battery Monitor. Without one, you can only guess as to your solar and battery needs. For what it's worth, my take is that you are both focussing too much on battery capacity and need to place greater emphasis on power production.

Yes Neddy you are quite right, unfortunately with my limited knowledge now that the bus has two systems running and I dont know how the first system was wired I dont now know how or where to wire a battery monitor to. Is it a straight forward process? I do note there are 3 direct connections to the batteres now with one being quite heave to the inverter.
 #148244  by Neddy
 Wed Jan 16, 2019 9:26 pm
Fitting a battery monitor shunt is quite easy, Rog. The shunt connects directly to the 12v Negative battery terminal, and all cables that were connected to the 12v Negative terminal are then connected to the other end of the shunt.
The battery end of the shunt must be the ONLY thing connected to the 12v battery Negative terminal. That way, ALL charge and discharge currents must go through the Shunt and can therefore be measured.
 #148246  by Kumarakid
 Wed Jan 16, 2019 10:57 pm
Thank you for that Neddy sound very easy :oops: so the battery monitor then connects to the shunt also and any power lead is that right?
 #148248  by Neddy
 Thu Jan 17, 2019 9:26 am
Connection details vary, depending on the brand/model of the Monitor you select. Commonly, all that's required is the use of a light plug-in cable connection between the shunt and the monitor read-out. Often this is supplied with the monitor.
Some models feature a wireless link between the Shunt and the Meter.

 #148250  by Kumarakid
 Thu Jan 17, 2019 10:48 am
Thank you so much Neddy, I shall grab one.
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