Off Grid Solar Systems

This thread is a result of discussions here:

http://www.diyaudio.com/forums/chip-amps/283845-pc-speaker-electronics-amplifier-conversion-3.html

The current sweltering heat and sunshine in this part of the world has made motivated me to look to solar powered systems for part time and blackout time power. We have power cuts every so many years when the hydro power systems reservoirs run low.

Given the fact that the most essential electrical equipment, sound and video equipment that is, does not consume a lot of power these days, it seems feasible.

Suppose we have a system that uses solar panels and batteries to run during the day only, to save costs, with the battery simply being there to compensate for cloudy days or clouds, how would one set about that?

Do we need to rewire the house or use DC power and DC fans and appliances or what?
 

Fenalaar

Member
2011-04-25 10:49 pm
No need for limiting yourself to DC. You can use an inverter to generate normal AC.

Inverters to deliver a healthy amount of power is expensive, if you want one that delivers pure sine waves, and needs a solid battery bank.

Victron has a product that delivers 1600W, has integrated MPTT solar charger for up to 3 panels and AC charger. You need to add a battery bank and solar panels. Whenever the panels doesn't charge enough, you can run a generator to both charge the battery and provide current.

https://www.victronenergy.com/inverter-charger-mppt/easysolar
This one retails around €1350 or so. You can get it in both 12V and 24V versions. The 12V version will charge batteries at up to 70A.
You'll need a pretty big battery bank. For a 1600VA inverter like the one shown, a 500Ah bank at 12V is the reccomended minimum. To preserve battery life, you don't want to discharge it too much, so go a bit bigger. If you use a 24V system, the battery capacity can be halved.

At the cabin, we have an old 60W solar panel, a 245Ah battery bank and a 600W sine wave inverter. We run lights, radio (a car head unit), 4G broadband and charge phones and iPads on 12V DC. For heavier stuff (Vacuum, waffle iron :rolleyes: and tools), we run a gasoline generator. We're planning on getting an extra panel and eventually a bigger battery. Heating is done with a wood stove, cooking and the fridge is handled with propane.

Johan-Kr
 
Last edited:
It's hard to beat the costs of currently being connected to the grid verses converting to a whole house alternative power system. The initial costs of installing such a system will take many years to recover. Also consider the cost of the need to replace batteries every 6-10 years..

However, designing a single area or a room for a back up is very feasible for most light load items. A place to hang out when everything else is dead.. *No toasters, coffee pots, or air conditioners.. ;)
 

Fenalaar

Member
2011-04-25 10:49 pm
Solar and wind installations need to come down a lot in initial cost, or be heavily subidized for it to be competitive with grid power.

However, when you are a long way from the grid, or you have an unstable power situation, it can make sense.

The trouble is when you either have a very high, but short term load (cooking) or a medium, but constant load (fridge or freezer). This will need considerations. The OP live in Colombo, so I think the sun densitty is high enough that fridge, freezer and lighting is easily covered with a few solar panels.

Cooking will either need a very powerful installation (i.e. expensive) or an alternative power or heat source - generator or propane.

Air conditioning is pretty much out, unless you cover the roof with panels.

What is your budget, by the way?

Johan-Kr
 
That was my situation. Too far from the grid to connect easily. They gave me a price to run their lines here but I pondered. I decided to invest in solar. The best decision I could have made, IMO..

Right now is a good time to invest. I paid $5/watt back 20+ years ago but now, PV can be found around a $1/watt if purchased by the pallet..

Wholesale Solar Panels - Bulk Solar Panels by the Pallet
 
Last edited:
Given the fact that the most essential electrical equipment, sound and video equipment that is, does not consume a lot of power these days, it seems feasible.

Suppose we have a system that uses solar panels and batteries to run during the day only, to save costs, with the battery simply being there to compensate for cloudy days or clouds, how would one set about that?

Do we need to rewire the house or use DC power and DC fans and appliances or what?

A small system can provide plenty of power for basic needs provided you don't expect it to be, or attempt to do as, a replacement for cheaper grid power. Outline your needs before planning and be willing to do without large AC powered devices and you'll be very happy with solar power.

I have a small 580 watts system that produces up to 40 amps max (measured) at 13.8 volts during bright, clear days and have never had the opportunity to use all that amperage. My battery bank is 1200 amp hours which is larger than necessary, but helps to lengthen the battery life since they rarely are discharged below 10% capacity during any given week.

I used to have a wind turbine as well, but quickly realized those are overhyped scams unless you happen to live in a wind tunnel between mountain passes somewhere. I lowered my tower and sold it all when I realized that kilowatts per month production was terribly lower than expected, and could not even produce 10% of what I get from 580 watts of solar per month. That wind turbine was no slouch either, I custom built it myself and in 10 mph wind it made 8 amps of power at 13.8 volts. With a 20+ mph wind it made between 24-32 amps, sometimes all night long! But at the end of each month my solar had produced over 10 times the Kw hours. So to the gutter it was kicked.

Solar does many times the work of wind turbines at a fraction of the cost of a wind powered system, provided the sun shines a few (or a couple) days each week. Full sunlight is not required for it to make some usable power each day either. My 580 watts system powers my entire house except for the larger appliances. Solar is great if you plan and design for it first, then implement sensibly.

Forget about running large inverters, its a DC power supply, so you must be prepared to use it that way. Conversion losses are very high with inverters (10% plus in real terms) and combined with the current multiplier (10 times amperage for 120 volts from 12v) required for boost conversion to AC power, its impractical and overly expensive to use solar for AC power. You are better off using a gas or diesel generator for all your AC devices requiring more than an amp or so current draw. I use a small inverter only when I need to use my soldering stations, as they don't require pure sine wave conversion to perform as they are capable of. Most everything else I own is either too large to convert to DC, or has been converted by me for DC. All high current AC devices, (vacuum cleaner, washer and dryer etc.) get generator power from my portable welder when needed.

Refrigeration is done using an overly insulated refrigerator that I converted myself using a small Dometic 12 volt DC compressor system commonly marketed for marine use. By adding thick styrofoam insulation over all outside surfaces of the fridge, then building a nice wooden cabinet around that thicker fridge, it keeps everything stuffed inside plenty cold (38 degrees) 24/7.

Audio and computer equipment and other small devices are DC powered through cheap DC-DC boost/buck converters. Cooking is done on a propane range along with a restored antique wood cooking range (with oven and water heater built in) for backup. Heating is done using a wood stove (which also provides all hot water needs) during winter. During summers hot water is produced by solar, stored overnight in a large overly insulated water tank. The well water comes into the house from an Artesian well and a small 12 volt pump (taken from a camper trailer) pressurizes the plumbing. Lighting throughout the house is by LED lights. Common wall switches turn things on or off and wall outlets are all 12 volts DC. Most of my small power tools are 12 volt DC as well. The table saw, radial arm saw etc. are powered from the portable (on wheels for mobility) welder.

Throw out all unreasonable expectations... DC from solar panels or wind turbine cannot replace cheap grid AC power. Plan for it, execute your plan precisely. Live well off-grid.

Edit: Yes, all wiring to/from solar panels, battery bank, charge controller and house wiring must be considerably larger than AC wiring due to increased voltage drop in cable runs from much lower voltage source. Get a wire size current chart off the Internet and print it out. Use larger cabling than required if you can afford to, so you'll have that extra capacity in place when you add devices to your system in the future. I use copper welding cable for all wiring needs because of the very high wire strand count, high current carrying capacity and flexibility found in that type of cable. Don't forget to install a high current DC breaker box for all connections to/from each component in the system and your end devices. You can buy the DC breakers and build the box yourself, just don't scrimp on this step else you'll burn yourself down first time something goes wrong!
 
Last edited:
Rolls are one of the best batteries money can buy for solar. Taken care of, the high end Rolls will last 15-20 years in normal service! Its money well spent for sure.

The C-40 and C-60 controllers are perfect for small DC systems too. The design hasn't changed since 1998! They are very reliable and not very expensive. Adjustability is superb as well, with auto/manual equalization as a very useful feature also built in.

My panels cost me $1.15 per watt shipped to my house a few years ago. Today you can get more wattage for less money. A 600 watt system can be installed yourself today for less than $950 including controller, cabling, volts/amps meter and DC breakers. Excluding batteries and homebuilt framing for the panels mounting of course.

If you just want to get your feet wet and try it out for 6-7 years or so before spending more, Walmart has 115 amp hour Deep Cycle batteries for about $100 each. Get 6 of them at least and keep them full of distilled water and equalized monthly. You'll be a happy camper for 7 years while you save up for Rolls batteries and more 19 volt panels.

Speaking of camping... My system also powers my brother's camper when he comes to visit to hunt, fish, snowmobile or just hang out. A 6 gauge welding cable run from my breaker box to his camper provides him free hookup throughout his visit. His furnace fan, lighting, TV, stereo, DC controlled fridge etc. are 100% free for him. He starts his generator only when he needs the air conditioner running on hot days.

If you think you will use it, build it. Have fun...
 
Thanks - many useful replies and it seems there are a lot of people running soalr power.

It will start with planning, and I think of using the 'Use case' method used in the software industry to outline all the different scenarios:

1. Daytime power use - to cut costs - 3 Fans, LCD TV, no lights virtually

Solar panels + battery bank to be used as a buffer when clouds pass by - is this feasible?

2. Three hour backup system for 3 fans (100Wx3) , LCD TV (60 W), CRT TV (80W) and blender 200W? The blender won't be on the full 3 hours

No plans to have backup for more than 3 hours, maybe 5 hours if needed but this will be rare.

3. This is the difficult one: Automated switching between grid and battery backup when needed, but only for the fans and equipment required during the outtage.

I think an inverter and some sort of intelligent load balancer is required here.

Need to think a little more about this. Do I need more scenarios?
 
Compressed air storage is an alternative to batteries and I believe a very good one.

Nope, not even close! There are no better alternatives for storing DC energy from sunlight than a battery bank at this time. Else all solar installations would include them!

Converting sunlight to compressed air requires massive expenditures of energy due to extensive losses in the conversion process/machinery from DC to stored air. Add the cost of those mechanical devices, the storage tank(s), plumbing, maintenance/repair needs, PLUS the necessary conversion from compressed air BACK to DC power on demand.... well, its too many lossy conversion steps to perform when the solution is already proven and simple. DC power should be stored in a device that IS DC compliant already.

Anything requiring a conversion to another form of stored energy is a waste of an already scarce resource. Those ideas are peddled to get you to waste your time and money on impossible dreams until you give up and pay the man the long dollar for grid power. They are out there on the 'net to destroy your independent thinking by insuring certain failure should you choose to try any of that silly nonsense.

Test it if you don't believe me.

None of this stuff relating to independent personal/home energy systems is complex or requires unobtainium technology to implement. There are no magic pills to swallow first. If you have occasional sunlight at your location (I am at 48 degrees North latitude and I'm doing fine!) you can have most of your electrical energy needs met with solar. If your location is down inside a mountain pass with 30-50 mph winds common, you can have a wind turbine or two providing your power.

Ready?
 
1. Daytime power use - to cut costs - 3 Fans, LCD TV, no lights virtually

Solar panels + battery bank to be used as a buffer when clouds pass by - is this feasible?

2. Three hour backup system for 3 fans (100Wx3) , LCD TV (60 W), CRT TV (80W) and blender 200W? The blender won't be on the full 3 hours

No plans to have backup for more than 3 hours, maybe 5 hours if needed but this will be rare.

3. This is the difficult one: Automated switching between grid and battery backup when needed, but only for the fans and equipment required during the outtage.

I think an inverter and some sort of intelligent load balancer is required here.

Need to think a little more about this. Do I need more scenarios?

1) Yes and yes to both questions. You can buy 12 (or 24 volt sometimes) volt DC appliances such as LCD TV, fans, etc. from any RV camper supply. Virtually everything you use daily can be sourced from marine or camping supply companies.

2) Buy all those appliances from a marine or camping supply and use them at will. A 600 amp hour battery bank will power those devices for many, many more hours than 5.... provided the blender is used sparingly to mix up a cold one every half hour or so. :D

3) This question is not difficult at all. You don't need a grid tie inverter to automatically switch over to grid power when it comes back on. A small mains transformer, bridge rectifier, capacitor and a relay will switch you over from DC to mains (and back to DC if the power fails again) automatically and you can build it yourself.

Keep thinking about how it should serve you and solve each question one at a time. Its simple stuff.

EDIT: A battery bank stores energy indefinitely. A small battery bank of 600 amp hours or so will power your house for days during successive dark, cloudy days, provided you aren't wasting your power on inverters and AC devices. During winter here it happens to me often. I never go without but sometimes after sevral days I do stay off the Internet until the sun shines again.
 
Last edited:
The suggestion for compressed air storage was motivated by the cost of batteries, however it seems that batteries last longer than the 3-4 years that I am quoted, as well as the fact that compressed air tanks seem to last a long time.

Other news on Tesla battery:

Tesla's New Battery Doesn't Work That Well With Solar - Bloomberg

This project will be driven mainly by the investment we are prepared to make in this year - which will be less than $1000, so it looks like it we will be going offline in stages.

Of course there is this option : Net Metering:

Sky rocketing electricity bills: Net metering or not metering? | The Sundaytimes Sri Lanka
 
The Tesla battery is a scam. Buy lead-acid deep cycle batteries only. NO gel cell batteries, NO AGM batteries... Lead-acid deep cycle batteries only. Do not buy dual-purpose marine starting/deep cycle batteries either, as those have thinned plates for high surge amps cranking power to start motors.

The single purpose, true deep cycle batteries last longer than GEL and AGM type and can be properly equalized monthly if you buy a good controller. Screw this part up and you'll be buying them all again soon.

No, you do not need any type of special enclosure for your batteries. A closet can work fine for batteries as long as the door is taken off, so the batteries can vent hydrogen to the air and escape. Do NOT confine the batteries inside a sealed area or container of any kind. You may put them inside a Marine battery box if you wish, as those are nicely vented all around the lids. Put them on the floor or just above the floor of an open storage area such as a closet, away from any sources of flame such as a furnace and you'll be fine. Its common sense, nothing more is required.

How much are you budgeting for batteries? Spend accordingly... the Johnson Controls batteries sold at Walmarts work great for 7 years and are cheap. rolls are the best... decide what you can afford and buy as many as you can afford.
 
Of course there is this option : Net Metering:

Another scam, another waste of your investment dollars, another waste of your scarce energy resource, another waste of your time, another waste of your independence. 'Nuff said.

Reread my posts... you'll find no such silliness going on in any successful installations. Stay away from that stuff its there to derail you and destroy you.
 
I'll add this: Those links you found are great if you intend to spend your money and property to power your nations' energy needs. I am thinking your intention is to help yourself though, not your nation.

You see, your nation already has the ability to tax you more to build more power plants if electrical power generation capability is low. They can tax you to pay for new power plants, then charge you more for power when they sell that newly generated power you already paid for through taxes, back to you. If you intend to help them using your money and property go ahead, its your decision.

If you want to have your own source of power to help offset your power bills and to fill in while the grid is down, then don't waste your time looking for ways to help your nation further enslave you.

In event you intend to help yourself, I'm willing to help you however I can to achieve your goal through my knowledge and experience. In event you intend to power your nation, I'm not available for any sort of help, whatsoever.