Monday, March 06, 2017

The Road to Solar, Chapter 2

Good evening!  This blog post is going to be an attempt to detail the more technical information regarding our choices in attempting to set up a solar system.

So once we decided we were going to try to run some kind of solar system in Bison Hollow campground, we thought about what was out there for products.  We saw a 140-watt portable panel and a 1000-watt inverter in the Canadian Tire flyer.  Reading the reviews on their web site didn't really give me a lot of confidence in the products so I kept doing more research.  I'm sure glad I did!

The first web site I read, and maybe the most eye-opening, was HandyBob's Blog.  Bob, along with his wife and dog, live in their RV full-time and live almost completely without plugging in.  He installed his own solar system, and seems to do custom installs as a side business.  He's learned a lot a long the way, and developed some strong opinions about the industry.  But even if one doesn't necessarily agree with his commentary, it gave me a lot to think about and definitely helped me develop the system I'm working on putting together now.

What we did next was to find out how much energy we might use in a day.  What devices and appliances would be be running and for how long?  Most of them have labels with power consumption data, so we would check that and estimate time of usage.  A few items we looked online for information if we couldn't find it locally.  For example, while an RV refridgerator can run on propane, the front panel that controls it runs on 12V power.  Our fridge manual didn't have that sort of info in it.  By the way, it's still a bit of a power-hog even when running on propane!  The goal of all this is to come up with a total number of amp-hours consumed in a day.  This will determine the size of the battery bank and how many watts of solar panel we will need to recharge them.  Morning coffee, lighting, phone charging, we thought of it all.

So the number we came up with was just under 100 amp-hours, so we're using 100 as our base number.  Now that is just average daily use and doesn't take into account higher-power items we might have used occasionally, such as a slow-cooker or electric frying pan.  We knew from the start Carla's 1875-watt hair dryer would be out of the question.  Same with running air conditioning.  That would be a generator-only item.  But with some reading, I learned that we don't want to use our batteries any more than 50% discharge, as that's hard on them, and if we allow for some heavier usage now and then we decided to go for a 440 amp-hour battery bank.  It's a funny-looking number but it's because we're going to purchase four 6-volt golf-cart deep-cycle batteries and the most common type comes in 220ah size.  Two batteries will be wired in series to get 12-volts, and then those pairs will be wired in parallel to double the amp-hours.

The panel question took some thought as well.  12-volt panels (32 cell) or 24-volt panels (60-cell)?  Monocrystaline or polycrystaline?  This decision was connected directly to the choice of charge controller as well, so I'll talk about both items here.  There are two different technologies used in charge controllers.  Some use an older technology called Pulse-width modulation, or PWM.  The other kind is Maximum power point tracking, or MPPT.  PWM can only use the lower-voltage panels as they can't make use of the extra voltage or the 60-cell panels.  They would be fine in a small system, but for what we want to do, we figured the MPPT controller would be more effective as the 60-cell mono panels with an MPPT controller can supply more voltage earlier in the day and in low-light conditions enabling use to get charged up faster.  On the one hand, these panels are cheaper per watt than the smaller panels, but MPPT controllers are more expensive.    This is where more math came into the decision.  How long would it take to replace the 100 amps with a certain wattage of panel?  I'm looking at installing about 470-watts (2x235) so 470 watts divided about 12.2 volts in a discharged battery gives a amperage of 38.5.   That's what the charge controller would be putting out.  That means a less expensive 30-amp controller would not be optimum.   Something to consider.  Anyway, at that rate, we're charged up in three hours easily, keeping in mind that's a theoretical number as it will change with sun angle.  But I think it's safe to say this amount of panel would be adequate.  I'd expect to be charged by early afternoon and maintain full charge until evening.

So what have we actually chosen for equipment?  For panels and batteries we're waiting to attend a sale at SaskBattery later in March.  They have batteries for 99$ each and the panels for $250.  We'll probably purchase there as those two items would have killer shipping prices if we bought elsewhere online.  For a charge controller I chose a Morningstar Tristar 45-amp charge controller.  This will take the charge from the panels and then adjust it as needed to charge the batteries.   It's a very highly regarded controller.   For an inverter I've chosen Go Power 1500-watt Pure Sine Wave inverter to take the 12V power and convert it to house power.  I watched a YouTube video regarding this inverter and really liked how well it appeared to be built inside.  Big heat sink and heavy cabling.  Finally I also purchased Bogart Engineering Battery Monitor.  This is another highly rated product and an important part of the system as it's essential to know what's going into and out of the batteries.

Tomorrow I'll write a bit about the rest of the system.   The big parts of the system don't work to well without the little bits like switches, fuses and wires!  I got a shipment in the mail today with some of that so I'll show you some of it, too.

By the way, if anyone has any questions, don't hesitate to ask.  I haven't really provided all the sites and equipment I studied to get to this point.  I'd rather not overwhelm the reader right away!  But if anyone is interested I'll do what I can to help.

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