Can over rated MPPT controlers be used in smaller system?

[Medic1507]

I am currently contemplating an off grid solar system for home. I have found several sites (including this one) that offer calculating assistance and, from those, have a pretty good idea of what the final system should be. However, due to the high wattage draw (I have electric baseboard heat) I will not be able to afford the full system all at once. My question: If I purchase enough components to power some of the house (using components that are rated for what the final system should be), and add additional panels and batteries to it later (adding in circuits as the system increases) Can I purchase the controller that would be appropriate for the final system and have it fuction correctly with less panels and batteries (lower input/output values) until upgraded? In other words, buy an MPPT controller that is significantly over rated for the initial system in anticipation of adding more batteries and panels. My goal is to avoid having to replace the controller (or an other part of the system for that matter) each tme I upgrade. I think I am wording all of this correctly.

[SunEagle]

I am currently contemplating an off grid solar system for home. I have found several sites (including this one) that offer calculating assistance and, from those, have a pretty good idea of what the final system should be. However, due to the high wattage draw (I have electric baseboard heat) I will not be able to afford the full system all at once. My question: If I purchase enough components to power some of the house (using components that are rated for what the final system should be), and add additional panels and batteries to it later (adding in circuits as the system increases) Can I purchase the controller that would be appropriate for the final system and have it fuction correctly with less panels and batteries (lower input/output values) until upgraded? In other words, buy an MPPT controller that is significantly over rated for the initial system in anticipation of adding more batteries and panels. My goal is to avoid having to replace the controller (or an other part of the system for that matter) each tme I upgrade. I think I am wording all of this correctly.

Hello Medic1507 and welcome to Solar Panel Talk

Your idea of getting a quality high amp MPPT CC has some merit. It is better to over size it then undersize or purchase a cheap MPPT knockoff.

Although based on the size and type of MPPT, they usually require a minimum amount of DC voltage to get it the system to run. You need to make sure you have enough panels to meet that minimum start up requirement.

That being said the bad part about starting small and then enlarging is that your battery system can't grow like the panel wattage. You should never mix old and new batteries together. The old ones will shorten the life of the new ones. So if your power needs goes up you will have to start over with a completely different battery system.

And any battery system should be designed to keep your daily discharge at or less than 25%. The battery system should also be designed out of a series wired system of low voltage (2, 4, 6,) high Ah batteries then wiring high voltage in parallel.

[solar pete]

I am currently contemplating an off grid solar system for home. I have found several sites (including this one) that offer calculating assistance and, from those, have a pretty good idea of what the final system should be. However, due to the high wattage draw (I have electric baseboard heat) I will not be able to afford the full system all at once. My question: If I purchase enough components to power some of the house (using components that are rated for what the final system should be), and add additional panels and batteries to it later (adding in circuits as the system increases) Can I purchase the controller that would be appropriate for the final system and have it fuction correctly with less panels and batteries (lower input/output values) until upgraded? In other words, buy an MPPT controller that is significantly over rated for the initial system in anticipation of adding more batteries and panels. My goal is to avoid having to replace the controller (or an other part of the system for that matter) each tme I upgrade. I think I am wording all of this correctly.

Hello Medic1507 and welcome to Solar Panel Talk.

Short answer is most probably. I am assuming that from your post the house is currently connected to the grid, if so you will be better off financially from a grid tied system especially if you have net metering where you are. You might want to look at a hybrid system that will allow you to use battery power at night and give you power if the grid goes out, this option is very expensive.

Adding to a system as you go can be very problematic, as you will generally need to re submit paperwork and get installers out to do bits and pieces of work, gets very expensive. Its a bad idea to add batteries to an existing bank, as the old batteries will kill the new ones prematurely, read up in the hybrid and grid tied and off-grid sub forums, it will help you a lot.

[paulcheung]

I am currently contemplating an off grid solar system for home. I have found several sites (including this one) that offer calculating assistance and, from those, have a pretty good idea of what the final system should be. However, due to the high wattage draw (I have electric baseboard heat) I will not be able to afford the full system all at once. My question: If I purchase enough components to power some of the house (using components that are rated for what the final system should be), and add additional panels and batteries to it later (adding in circuits as the system increases) Can I purchase the controller that would be appropriate for the final system and have it fuction correctly with less panels and batteries (lower input/output values) until upgraded? In other words, buy an MPPT controller that is significantly over rated for the initial system in anticipation of adding more batteries and panels. My goal is to avoid having to replace the controller (or an other part of the system for that matter) each tme I upgrade. I think I am wording all of this correctly.

Yes your oversized charge controller like the Midnite Classic 150 is the easiest piece equipment that will work from 200 watts to 4800+ watts panels depend on your battery bank voltage.

[bcroe]

I am currently contemplating an off grid solar system for home. I have found several sites (including this one) that offer calculating assistance and, from those, have a pretty good idea of what the final system should be. However, due to the high wattage draw (I have electric baseboard heat) I will not be able to afford the full system all at once.

Medic1507,

I don't know where you are or what the size of your heat load is. I can tell you
that I have been heating my house from solar using a grid tie PV system with net
metering, and a late model heat pump. I am about breaking even; using an off
grid battery system will be astronomically expensive and very high maintenance.

Generally the sun doesn't shine much in winter, just when you need heat. A
battery can't carry energy over from season to season, but a grid tie can.

Batteries are extremely expensive on this scale; grid tie here is free.

Batteries require a huge amount of maintenance; grid tie needs none.

Batterie systems lose a lot of the energy; grid tie doesn't.

So a grid tie is like a 100% efficient, infinite capacity, zero cost, zero
maintenance battery. That, and a heat pump greatly reduces the amount
of KWH required. Bruce Roe