A simple, inexpensive, yet powerful solar storage system

[ls99]

I think this is the concept you're describing.
He provides parts lists, wiring diagrams, etc.

I started futzing by buying his inverter, but the 1st two bought off Amazon had screws rattling around inside the cover (an antique test method for catastrophic short circuits) so I returned them. Haven't looked around for a replacement inverter yet.

Looks like a nice setup. However the cables from battery to inverter look pretty thin. In my setup the inverter is fed with 2/0 cable. Under full load thin cables limit the current available to the inverter.

 

[NW-Bound]

I think this is the concept you're describing.
He provides parts lists, wiring diagrams, etc.

I started futzing by buying his inverter, but the 1st two bought off Amazon had screws rattling around inside the cover (an antique test method for catastrophic short circuits) so I returned them. Haven't looked around for a replacement inverter yet.

I just glanced through his video, and took a quick look at his very complete part list. Yes, conceptually they are all the same, and what differs is just the selection of components.

He shows a very compact and portable design, and this may be something Sunset is interested in. However, the use of just 2 batteries will limit the storage capacity in order to run through the night, even with the AGM batteries that are the very best in the lead-acid category (and their price reflects that).

He shows a complete part list for $2K, while on post #1 I show $2K just for the major components. You would need to add wires, fuses, mounts for the solar panels, etc... I am not going to make a complete list like his.

What I describe is something a lot larger for home installation for not too much more money. By shopping carefully, you get 3.2kWh storage instead of 2.1kWh (computed using a better 80% depth of discharge for AGM and 50% for marine batteries). You also get 2kW of solar power instead of 400W, and the electronics to accept that 2kW power.

But then, I have not described the electronics, which will come up next.

 

[rodi]

Hmmm. After reading this thread 100% of the ads on the right side (both of them) are for solar panels. LOL

 

[NW-Bound]

It's a bit more expensive, but also take a look at Powerwall. The units are about the size of a thick card table, cost approximately $6K-$7K and can provide several days of power.

-Wino

Tesla's Powerwalls are very slick and well designed. An example of good engineering, from what I have read about.

However, the total bill will be more than the listed price for just the unit. You can search the Web to learn about the additional hardware cost for a gateway, the labor for installation, and the permit application.

Each unit can store 13.5kWh, which is quite decent. Still, when they say "several days of use", it of course depends on how much you use. My regular usage here in the hottest day of summer is 100kWh in a 24-hour period. In the shoulder season with no heating/cooling, I use around 20 kWh/day. Lest you think I use too much energy (I do ), my utility company says that I use about 75% of the average home of the same size.

And finally, you need to add the cost of solar panels to the Powerwalls.

In all, I am making a wild guess here that a package of $30-50K will get you a very nice system. But that's not the clean-looking solar tiles that they claim to just have perfected. Some early homeowners said it was $100K, if my memory serves.

PS. The PowerWalls look thin, but they are packed full of batteries and weigh 250lbs each. Two of them weigh about the same as my DIY 22kWh lithium battery and have the same volume, but mine does not look as pretty. I hide them and electronics in a garden shed in the backyard.

 

[NW-Bound]

Costco Interstate-branded 6V GC2 batteries get pretty poor reviews.

OTOH, Sam's Club has Duracell-branded 6V GC2 batteries for $90 at my local club & those get good reviews.

For those not space-limited a battery bank using 6V golf cart batteries would usually result in higher capacity than paralleling 12V "marine" batteries (which aren't really designed for deep cycling)

After the dismal experience with the 2 Costco GC2 6V batteries, I have not tried again. And so those 2 batteries are the first and last golf-cart batteries that I have personal experience with. On the other hand, the two 12V marine batteries also bought from Costco worked a lot better to run my 2kW inverter.

Now that I have replaced them with lithium batteries of a similar form factor, these marine batteries have been sitting in my garage, hooked up to a battery maintainer.

It may very well be true that golf-cart batteries last through many more cycles than marine batteries. However, you must have enough of them in parallel, so that the current drawn through them is sufficient low. The difference is the same as that between a marathoner and a sprinter. Both will perform poorly when put in the wrong race for them.

By the way, my experience with the golf-cart batteries bothered me greatly, and I spent quite a bit of time researching this issue. A fellow on some forum reported that when he replaced the batteries in his golf-cart with marine batteries, the acceleration was great, till he broke his transaxle. His theory was that the golf-cart batteries have higher internal resistance, and that limits the current to the motor, hence the torque to the drive line.

And here's another thing I just found. Trojan T105 batteries are the gold standard in golf-cart batteries. Yet, I just looked up their Peukert factor, and they are terrible compared to AGM, and even marine batteries. That's not too surprising. But when you use them right, I am sure they are great.

 

[CaptTom]

As an RV'er myself, I was disappointed with the use of golf-cart batteries with my 2kW inverter. They lasted one RV trip of 6 weeks, and their performance was lousy when they worked. The 12V marine batteries work MUCH better.

I think it's those Costco batteries.

My little house bank, 4 6V golf cart batteries, has lasted 7 years now, and thousands of miles of cruising. Much of that time at anchor or on moorings overnight, sometimes for days on end.

They're charged by a 100A charger with a 2,000W inverter. From the inverter we regularly run the microwave, the InstantPot, a bread maker, a vacuum cleaner, and a few lights. I'll usually fire up the generator for an hour or so when the house bank gets down to around 60%. That's usually twice a day.

Of course you need to size the battery bank right for your application. I'm pretty frugal with power, so even that relatively small house bank of just four, six-volt batteries is plenty. And given the kind of use it gets, I'm pretty happy to have them last this long.

If I was installing solar, or needed more power, I'd just add more 6V flooded batteries. Sure, you can go with newer technologies if you want to spend more. But simple, cheap and reliable isn't all that bad.

 

[NW-Bound]

I think it's those Costco batteries.

My little house bank, 4 6V golf cart batteries, has lasted 7 years now, and thousands of miles of cruising. Much of that time at anchor or on moorings overnight, sometimes for days on end.

They're charged by a 100A charger with a 2,000W inverter. From the inverter we regularly run the microwave, the InstantPot, a bread maker, a vacuum cleaner, and a few lights. I'll usually fire up the generator for an hour or so when the house bank gets down to around 60%. That's usually twice a day.

Of course you need to size the battery bank right for your application. I'm pretty frugal with power, so even that relatively small house bank of just four, six-volt batteries is plenty. And given the kind of use it gets, I'm pretty happy to have them last this long.

If I was installing solar, or needed more power, I'd just add more 6V flooded batteries. Sure, you can go with newer technologies if you want to spend more. But simple, cheap and reliable isn't all that bad.

OK. That sounds reasonable. The GC batteries I got had to be pure garbage. Could it be I had two of a bad batch? Here's more I can tell.

The batteries were lousy, but still working towards the end of the trip. After the trip, I parked the motorhome for a long time.

The batteries were maintained by a 220W solar panel mounted on the motorhome roof, hooked up through a Morningstar charge controller. This controller is among the best in the market, and commands a fairly high price for its 15A output.

When I next looked at the batteries a few months later, they were bone dry! What the heck! The Morningstar controller never failed me before, and not since. So, I had to say the batteries were bad, but thought that I stressed and ruined them earlier.

And here's another story, but about the Costco marine battery. The pair I had before the golf-cart ones had one failed, and I forgot how it did. So, I replaced them with the golf-cart pair, and kept the good one, which I later used as the starting battery for the motorhome.

When I parked the motorhome, I forgot to short across the battery isolator, in order for the solar charger to maintain the starting battery in conjunction with the golf-cart batteries. Worse, I forgot to disconnect the added-on backup camera display, which drained the starting battery. Dead as a door stop when I discovered my mistake, in addition to the dried out golf-cart batteries.

I tried to revive all 3 by adding water to the dried-out ones, and to connect up the marine battery to the charge controller.

After a week, I checked. The house batteries were still dead, but the marine battery got revived, and started up the engine. Son of a gun!

That dead-and-revived battery is still mounted in the motorhome, and still worked after 3 years and 3 long cross-country trips. Son of a gun! I have never had a battery like that. It's a mystery!

 

[NW-Bound]

Here's the last piece of the system, the combo solar charger/AC charger/inverter. It's the MPP Solar PIP-2424LV-MSD. It uses the battery voltage of 24V, has an inverter output of 110V/120V, accepts up to 2kW of solar power to charge the battery at 80A, and can use the line voltage from the grid or a generator to charge the battery at 60A.

I spent a lot of time looking at inverters and chargers, and found that MPP Solar, a Taiwanese company, has a line of very attractive combo inverters/chargers. I searched the Web for info on this company, and found a forum of Australian DIY'ers who had good experience with this brand. Their favorite model is the PIP-4048MS and PIP-5048MS, which run with a 48V battery and output 230VAC.

The forum is called forums.aeva.asn.au, and has a couple of members with technical expertise to hack into the above models' firmware to change some parameters. They know a lot about the internals of the inverters. Their consensus is that the machines are a good buy for the money, and that convinced me to get one myself to use. I ended up buying 2 more, and now have 3.

I really wanted to get a 48V model, as the higher voltage reduced the amperage, and would allow smaller gauge wires for interconnects. However, MPP Solar for some reason does not make 48V models that output 110/120. So, I had to use the 24V inverters.

I do not have the exact above model, but its close relatives. One of the 110/120 inverters has been running for almost a year. It powers my fridge and some of the kitchen outlets. The 230V, also of 2.4kW output, runs a 1.5-ton minisplit AC/heatpump since spring. I am waiting to tear down the system mounted in a garden shed to rewire everything neater and to mount another 110/120 inverter. This one will power additional AC circuits for the home.

This brand of inverters and its various clones are in use worldwide. Some say the other brands are copycats, and some say they are under license. I don't know what the truth is.

You can search the Web, and find many people using this brand. Look on Youtube too.

 

[NW-Bound]

I also have multiple solar charger controllers that you would not need for a smaller system. One is a Midnite Solar charge controller, and the other an Outback charge controller.

Both the above are American brands, and very popular with solar DIY'ers. They have good reputation. The only downside is cost. Each costs around $500, and they only do solar charging. For $618, MPP Solar gives you 3 functions in one.

 

[daylatedollarshort]

My system has been providing about 20kWh each day, and that's enough to run a 1.5-ton minisplit AC 24 hours. It helps offset my power bill. In the hottest day of the year when it hit 120F, my home uses 100kWh each day. Sounds like a lot, but that's only 4 kW x 24 hours, and that's what it takes to run a 5-ton central AC.

We only use 10kWhs when we aren't using central AC or heat, so that is really intriguing. Dinner tonight was a fruit salad, green salad, and a stew made in a thermal cooker so it only required 10 minutes on the stove in the morning.

 

[NW-Bound]

Our lowest usage happened in early winter (Nov, Dec), and early spring (Apr), when we used about 900kWh/month or 30kWh/day.

We have a swimming pool, and that takes a few kWh each day for the pump. Our two fridges burn 6 kWh/day combined. I cannot account for the rest. We do not take long hot showers, or use the main oven daily, although we cook quite a bit. We do just one load of laundry each week, and do not leave the lights on throughout the house. I've got a leakage somewhere.

Last month, we used 15kWh/day vs. 35kWh/day in the same period in previous years. The difference is due to the solar system.

 

[daylatedollarshort]

Our lowest usage happened in early winter (Nov, Dec), and early spring (Apr), when we used about 900kWh/month or 30kWh/day.

We have a swimming pool, and that takes a few kWh each day for the pump. Our two fridges burn 6 kWh/day combined. I cannot account for the rest. We do not take long hot showers, or use the main oven daily, although we cook quite a bit. We do just one load of laundry each week, and do not leave the lights on throughout the house. I've got a leakage somewhere.

Last month, we used 15kWh/day vs. 35kWh/day in the same period in previous years. The difference is due to the solar system.

At one time I went through the house with a Kill a Watt, and estimated the hard wired appliances, to try to break down where all our electricity usage came from and match it to the total used for each day. We also got reports by the hours on energy usage from PG&E. I never got to 100% reconciliation, but I could account for most of the usage. I haven't done that lately but at the time it helped to cut our kWhs quite a bit.

We still have quite few more energy saving projects we could tackle. Combined with a solar system like yours we could really get those energy bills down to the nubbins.

 

[NW-Bound]

I can log into my account at SRP (Salt River Project) to see the kWh used in each hour period. The early morning hours when we are asleep is when the energy usage is the lowest at 300 W. I guess the lights in front of the house, and the parasitic drains of all the electronics such as TV, HiFi, DVD players, desktop PCs and laptops, Internet modem and WiFi router, microwave, etc... can easily add up to 300 W. But that's 7.2 kWh/day!

What can one do? You cannot go around unplugging them all, and only plug them back in when you use them. We want everything at the ready to serve us when we push the On button on the remote control, and that's the price to pay. The "on/off" button on appliances and devices now is just a "on/standby" switch. A few watts here and there, and we talk 300 watts for the whole house.

If in the course of 24 hours, a family takes enough showers and uses enough hot water to empty a 50-gal water heater, it takes another 7 kWh to reheat that water from 60F to 120F.

It's amazing how you become more conscious of your usage when you have to worry about how to generate, obtain, or conserve a resource yourself. When we travel in the motorhome, it's amazing how little water we use for dish washing and shower.

 

[CaptTom]

... the parasitic drains of all the electronics such as TV, HiFi, DVD players, desktop PCs and laptops, Internet modem and WiFi router, microwave, etc... can easily add up to 300 W. But that's 7.2 kWh/day!

What can one do? You cannot go around unplugging them all, and only plug them back in when you use them.

I wonder if my parasitic loads are that high. I would have guessed less, but I'm afraid I'm probably not far behind you.

As to what to do, one option would be some sort of timer, or possibly a "smart" switch. Which, of course would add its own parasitic load...

Getting back to golf cart batteries (sorry), I forgot to mention that I generally start one of my engines (200HP, 6-cylinder diesel) off the wimpy little bank of 4 golf cart batteries, in addition to all the other stuff. Even when they're down to 60% discharged. So they are most certainly capable of a high current draw!

Your point about "marine" batteries is well taken. They're built to take a bit more punishment, in addition to being more tolerant of a deep discharge than straight starting batteries. They're probably a good choice for something like an RV starting battery.

 

[daylatedollarshort]

I can log into my account at SRP (Salt River Project) to see the kWh used in each hour period. The early morning hours when we are asleep is when the energy usage is the lowest at 300 W. I guess the lights in front of the house, and the parasitic drains of all the electronics such as TV, HiFi, DVD players, desktop PCs and laptops, Internet modem and WiFi router, microwave, etc... can easily add up to 300 W. But that's 7.2 kWh/day!

What can one do? You cannot go around unplugging them all, and only plug them back in when you use them. We want everything at the ready to serve us when we push the On button on the remote control, and that's the price to pay. The "on/off" button on appliances and devices now is just a "on/standby" switch. A few watts here and there, and we talk 300 watts for the whole house.

If in the course of 24 hours, a family takes enough showers and uses enough hot water to empty a 50-gal water heater, it takes another 7 kWh to reheat that water from 60F to 120F.

It's amazing how you become more conscious of your usage when you have to worry about how to generate, obtain, or conserve a resource yourself. When we travel in the motorhome, it's amazing how little water we use for dish washing and shower.

That is where the Kill a Watt can come in handy. We had some stand alone Bose speakers connected to a TV that were real energy hogs even on standby, so we unplugged them except to use for movies or games. Come to think of it, I don't know if anyone ever plugged them back in, so those could go to Goodwill. A DVD player was also high usage on standby, and we only watch DVDs once a month or so so that got unplugged, too.

 

[Jerry1]

That is where the Kill a Watt can come in handy. We had some stand alone Bose speakers connected to a TV that were real energy hogs even on standby, so we unplugged them except to use for movies or games. Come to think of it, I don't know if anyone ever plugged them back in, so those could go to Goodwill. A DVD player was also high usage on standby, and we only watch DVDs once a month or so so that got unplugged, too.

I’d put those types of things on a power strip and then you could just switch on the power when you needed it. Especially good for what you described because they are likely in the same area and used together when used.

 

[NW-Bound]

I used my Kill-A-Watt and was surprised to learn that my big 30 cu.ft. fridge draws 4.8 kWh/day, while the auxiliary 25 cu.ft. fridge draws only 1.6 kWh/day. I let the Kill-A-Watt record for 1 week to be sure that the numbers represent the true long-term average.

Both are of the early 2000's vintage. The difference is that the big fridge is opened multiple times a day. Its ice maker is also hooked up, and I use ice each day for drinking.

About the phantom 300W draw by electronics that I seem to have, that works out to an annual consumption of 0.3 kW x 24 hr/day x 365 days/year = 2628 kWh/year.

In California where the lowest you pay at Tier 1 rate is $0.18/kWh, that's $473/year. My average rate is $0.12/kWh, and that's $315/year.

 

[Sunset]

I’d put those types of things on a power strip and then you could just switch on the power when you needed it. Especially good for what you described because they are likely in the same area and used together when used.

Exactly, I know a guy that does this.

I bought 2 smart powerstrips, each has a master socket, when you turn on/off the master socket device, all 4 slave devices do the same.

So I plugged out tv in as the master, and when it goes off, the dvd, speaker bar, and Xbox all turn off. Makes it natural and easy.

Of course I didn't use killawatt to see what the smart power bar uses itself

 

[NW-Bound]

Now, if a reader is interested in this, how does she start?

The first thing to get is the inverter/solar charger/AC charger 3-in-1 unit. I already mentioned the MPP Solar PIP-2424LV-MSD model, which you can get for around $600 on eBay.

There's also a smaller PIP-812LV-MS, which runs on 12V, puts out 800W, and can take 600W of solar panel output. The approximate cost is $350. It will let you start out with a single 12V lead-acid battery for a very minimal cost. However, the 800W power is marginal to handle the surge demand of a refrigerator. I would rather spend a bit more to get the bigger 2400W device than be sorry.

Then, look on Craigslist or eBay to see if you can find used solar panels on sale locally that you can pick up without paying an arm and a leg for shipping. Instead of small panels meant for RVs, I prefer the larger residential panels, such as the SunPower 327W panel that I can get myself for $108. Its size of 61" x 41" is mid-size for residential use. There are smaller panels of 61" x 30" as well as larger ones up to 82" x 40". I found the 61" x 41" size quite easy to handle, and the output large enough to bother.

If you cannot get the preferred SunPower panels, you can use whatever generic panels available. In the next post, I will tell you what to look for.

 

[street]

Interesting NW-Bound. You have a great understanding of the generation and the electrical system. I'm impressed with your knowledge.

Do you install a transfer switch from PUD supply to your generation system? If so where do you install that switch on the electric system you have?

 

[NW-Bound]

People will be glad to know that the MPP Solar inverter has its own built-in transfer switch. More on this later.

However, I am trying to build a programmable system in order to take maximum benefit of my system. Hence, each of the 3 inverters I have will power more than one house circuit each, and each circuit is transferred to/from the grid individually. I am working on my own multi-circuit transfer switch in order to adapt to the amount of solar power available and the state-of-charge of the battery. This is continuing developmental work, and there is still a lot of head scratching.

While the solar/battery system is in a garden shed, the auto-transfer switches (the one built so far) are in a box mounted by the side of the utility entrance panel/meter.

 

[NW-Bound]

A solar panel is made of multiple cells wired in series. Each cell puts out about 1/2 V. This voltage stays constant with the amount of light shone on the cell. More light means more current, not a higher voltage. The voltage however drops with increasing temperature. This means that in the winter the voltage from the panels will be significantly higher than in the summer.

In order for the solar panel to charge the battery, the voltage of the panel output must be higher than that of the battery. There are boost charge controllers that will allow a low-voltage panel to charge a battery of a higher voltage, but these are not common and the ones I have seen are for low-wattage.

When we talk about kilowatt power level, the MPPT charge controllers are all of the step-down type, and they generally have the best efficiency when the panel voltage is about 2x the voltage of the battery. For this 24V system, this means panel voltages of 50V and above.

 

[NW-Bound]

A 12V lead-acid battery is only 12V when it is near exhaustion. When at rest, a battery should be kept at 13.8V, and battery maintainers that you plug in an AC outlet do this. For charging, a 12V lead-acid should be brought to 14.4V, but with the current properly limited according to the size of the battery. The MPP Solar does this for you.

There are small portable solar panels meant for charging 12V lead-acid batteries. They are made with either 32 or 36 cells, for a voltage of 16 or 18V in order to charge the battery. There's no electronics, and the panels are simply connected to the battery. Their output is puny, and cannot hurt a car battery. The only thing they may do is to cause a slow loss of electrolyte over time. Big solar panels like we talk about here will boil out your battery in no time without a charge controller.

With lithium batteries, even a trickle charge will eventually cause them to burst in flames. An LFP battery will vent and be ruined. Never charge a lithium battery without the proper electronics and the knowledge of its type.

 

[NW-Bound]

Residential solar panels come in 60, 72, or 96-cell types. The 60-cell type will not have an output voltage high enough to charge a 24V system in the middle of summer, when it is hot and their voltage drops. A single 72-cell or 96-cell panel will work.

You can wire two 60-cell panels in series. Or two of the 72-cell or 96-cell types. You can even go up to 3 of the 60-cell panels, but not 3 of the 96-cell panels. The MPP Solar unit has a limit of 145V max, which cannot be exceeded. What is OK in the summer heat may not be in the middle of winter.

You can start out with just one panel (or two of the 60-cell type) for fun. Then, add more in series and parallel when you see it works and start having fun.

You can just lay down the panels on the ground, with them tilted up to the sun with blocks. I did a lot of testing this way, while pondering how I would mount them permanently.

 

[NW-Bound]

When adding panels, you cannot mismatch them. Severe power loss will result. The panels in series/parallel have to match. If they are not of matching type, then different strings will have to be wired to different charge controllers.

It's the same with batteries. You can start out with just 2 of the 12V batteries, or 4 of the 6V batteries. Mismatching different strings will not cause them to blow up, but different internal resistances of the batteries will cause some to work harder than others. This imbalance may cause one string to wear out faster than others. More on this later.