Things to consider when you design your off grid setup.

[Mattb4]

Much of the advice of designing a Off grid PV system involves gathering up your loads (watt-hours per day) and insuring that your inverter can handle starting and running wattage.

With your daily watt-hours you can look at how much solar panel wattage (rated) that will be needed to cover it. You need to have an idea of the average sun hours a day during the various Seasons that you can expect. Example is 2 hours in Winter, 5h in Summer. So if you had an average days usage of 15kWh this would give you 15,000Wh/2h=7500W Winter amount of panels or 15,000Wh/5h=3000W Summer.

Storage (Batteries) come into play because the sun does not shine all the time so you need to bank power when it does, to draw later when the sun is not out. Many folks try for at least a days worth of storage and maybe a week if they live in an area of long term poor weather. From the example of 15kWh that would than be the minimum storage for a day.

All well and good but averages do not really cover things. Likely you will have days of higher loads than others. For instance if you need to run Aircon and you get several hot days. If you only size for the average daily watt-hour usage you will find yourself running up short. This might work out if your storage is enough to cover the uptick and you then have several days of lower than average demand. It however will not work if the periods of high demand and low demand are too far apart.

If you are Totally Off grid you must plan for Base loads (loads that will run every day) Seasonal loads (loads that run based on the Season) and Peak loads (loads that are used as needs dictate).

Inevitably you will find that you have to pick a median where at times you have more PV production than you can use, or store, and times that you have insufficient supply to keep up with the demand. During times of shortfall is where having a fossil fueled generator can cover. There is also conservation where you decrease the number of loads that you place on the system.

 

[MichaelK]

That's not the advice I've always given. I usually recommend identifying your single biggest load, and at least utilizing at least 2X that amount of solar. For example, I run my well-pump that draws about 2200W, so I started out with 4500W of solar.

I've never recommended planning for average days. I've always mentioned designing for the poorest day of the year, which might be Dec. 21st.

In terms of battery size, I've always recommended deciding how many how many days of autonomy do you need, and multiply that amount by 2X, assuming you have lead-acid.

In the real-world, I'm finding that my system only needs to make ~1/5th of what the system can make, and I've run my own system now for 7 years, without a single hiccup.

 

[Offgrid Jungle]

I’m amazed that a generator is rarely considered when sizing a system.

 

[Mattb4]

I’m amazed that a generator is rarely considered when sizing a system.

I think more often than not there is an assumption that you already have a generator. Maybe bought for RV'ing or after the last power outage when you were fortunate enough to snag one of the few available at Home Despot before the crowds of people had bought them all.

But it is a valid consideration to plan and source a generator adequate to the needs. Though with enough PV and battery I am finding my Honda inverter generator has sat unused. Course in my case I have grid as backup and true Off grid folks would not have that crutch to lean on.

 

[Chispas]

We are 100% off grid & having a generator for big, occasional loads meant a considerable saving in the past vs PV. When we were a young family, that meant running a washing machine maybe 4 hours a week & power tools for woodworking. Lately thats been a lot less, our water storage has improved, as has rainwater harvesting so we only run our water pump maybe 4 or 5 times a year, for about an hour each time. Sizing a system to run a 1200W 220 AC pump means big outlay.

There is also conservation where you decrease the number of loads that you place on the system.

Learning to live within our (energy production) means is a part of our life here. In the winter, we charge power tools & spend more time on the internet during the daytime, meaning that we ran our genny for about 4 or 5 hours in total last winter for battery charging.

 

[Crowz]

I’m amazed that a generator is rarely considered when sizing a system.

To me if a generator is needed while sizing the system its a failed system to start with.

Now purchasing the right generator to go with a system as a backup is something I put thought into.

 

[Quattrohead]

I have not planned on a generator for my off-grid system, I have an old Mitsubishi 4kw that I could use if I absolutely had too.

 

[Offgrid Jungle]

To me if a generator is needed while sizing the system its a failed system to start with.

Now purchasing the right generator to go with a system as a backup is something I put thought into.

Word salad - but you said the exact same thing I said. For example - why would you buy $30k worth of batteries to ride thru a grid outage/solar outage for more than 48 hours? I live in a place that has daily outages. Daily. None of them has ever lasted more than 8 hours. If you are totally off grid like my brother is, the same logic applies. If he has no means to generate solar power for more than a couple of days in a row, then a genset is the right move.

 

[Crowz]

Word salad - but you said the exact same thing I said. For example - why would you buy $30k worth of batteries to ride thru a grid outage/solar outage for more than 48 hours? I live in a place that has daily outages. Daily. None of them has ever lasted more than 8 hours. If you are totally off grid like my brother is, the same logic applies. If he has no means to generate solar power for more than a couple of days in a row, then a genset is the right move.

Actually I'd love to have $30k or more worth of batteries but the wife would kill me.

The reason for having enough to run for 48hours or more is rain. Ive had rain for the past week. Even with $30k worth of batteries I'd have a hard time working it right now. For people that really live completely off the grid you can NEVER have enough battery capacity.

As for long turn outages on the grid that's a loaded question. Normally our outages are 30 minutes to an hour. Alabama power is one of the best power grids in the country as far as preventive maintenance and crews available at all ours.

Now massive storms are a 1 day tops thing and that's once every two years kind of thing honestly.

So now were at 24hours worth of batteries.

Then there's those hail mary freak weather events. Usually snow or ice related (Alabama is allergic to ice and snow so it hits us hard) and those can be bad. The last snow and ice storm took out the power for 5 days. Now the batteries are not big enough even at $30k worth.

So I can't really fault someone for spending that kind of money on batteries. Wish I could without the wife killing me in my sleep over it

 

[OffGridInTheCity]

In my case, the goal has always been to be able to live in my home relatively comfortably 100% off-grid, all year long, even while being right in the middle of the city - e.g. 'OffGrid In The City'. Thus we've done solar and rain harvest and other stuff. Originally I wanted to be 100% Solar and converted everything in the house to electric (heat-pump) but after 6 years of operations, winter is the bugaboo - not even close to enough PV to run the heat-pumps.

While I agree a generator is a useful piece of an off-grid system, it depends on the scale/purpose of the system. In my case I need 50-70kwh/day to run my home. For 8 months of the year I have enough PV (15kw), battery (121kwh), inverters (24,000w) to manage but the 4 months of winter are not nearly enough (would need 150 more panels) and a generator isn't a viable way to make up the difference when heating is the primary issue. I have a Generator -> Chargeverter @ 100a capability setup as part of my off-grid system but I think of it more as an emergency option than a regular part of operations. It's just not efficient fuel wise to create heat by doing fuel -> generator -> heat-pump.

For a sustained apocalypse, heat in winter 4 months is my issue and in the Pacific Northwest we have abundant wood that I can harvest myself if gas/propane resupply are closed. So I'm trying to convince my wife to let me install a backup wood burning furnace w/forced air to supplement the heat-pump instead of going down the massive propane/generator route to run the heat-pump or even the hundreds of gallons of propane or kerosene needed to run heaters directly. This would fill out the missing piece (in my mind) to achieve 100% off-grid

 

[CVCPJared]

To me if a generator is needed while sizing the system its a failed system to start with.

We included a generator in ours to start with because we don't actually know our power needs. New house, sq footage is growing 50% from current home, but also going from gas heater/water heater to electric, going from hollow walls (1940s home) to heavy insulation. A generator helps smooth out the guesswork on production vs. demand. Hopefully won't need it too much, but the alternative is spending boatload of $ oversizing a system to meet the demand of a New Years Eve party with my 50 closest friends after 2 weeks of rain

 

[rhino]

I am off grid and have my largest array which is 14kW completely turned off during the summer. The other arrays which total about 9kW cover the summer loads. That larger array is solely needed for winter when not only is there less daylight hours but is considerably cloudier. I also only have wood heat for winter but do use electric water heater. My current battery bank is about 72kWh (all DIY) and am considering bringing that up to about 100kWh for extra buffer.

 

[Chispas]

What strikes me about this is the size of the systems and the loads ! Our current system 12V with 460 W & a Trojan T 1275 has been doing sterling service for almost 10 years. We have no mains services here , even the mobile coverage is sketchy but we have a comfortable life & want for nothing. Starting out with very little has shaped our lifestyle.
As for generators, over on Reddit ive been amazed at the size of "backup" generators that folks have, I mean 27 Kva for a house ? Doing a new factory project recently we had a 25Kva on site before the mains power was hooked up & that was for a crew of 12, running power tools & some 3 phase workshop machines. I guess that cheap fuel makes a difference.

 

[pollenface]

I've always believed that if you size everything for winter you can't go wrong.

It's ironic, the time of year when you need the most energy is when it's cold and/or wet and little to no sunshine.

 

[Quattrohead]

I've always believed that if you size everything for winter you can't go wrong.

It's ironic, the time of year when you need the most energy is when it's cold and/or wet and little to no sunshine.

Opposite here in the deep south. I was surprised to find out Florida is not as sunny as you might think in the summer.

 

[Mattb4]

I've always believed that if you size everything for winter you can't go wrong.

It's ironic, the time of year when you need the most energy is when it's cold and/or wet and little to no sunshine.

My size case is Summer. Summer is Aircon. Winter has better sun angle also until just about the Solstice when trees start to get in the way.

 

[Mattb4]

My local Elec Co-Op has announced an increase for the monthly base rate come October this year. It is going from ~$23 to $25 with a additional penny increase in kWh. It is causing me to consider how close my present PV setup is to not needing the grid at all. After my testing of keeping Aircon going this Summer, and the recent addition of 600W more of solar panels, it is looking like it may be justified to drop the grid.

I guess a big consideration I failed to mention in designing a Off Grid setup is the price. Not only in the components but also in building and operation/maintenance. You need to allow and plan for Sudden catastrophic failure moments. Spare parts are a must.

 

[Madcodger]

You need to allow and plan for Sudden catastrophic failure moments. Spare parts are a must.

Two is one. One is none. Words to live by.

There's a reason we always have two, separate forms of heat in our buildings in Maine (using two different fuels). The same logic made me install three separate (admittedly connected) 6000XP inverters, each connected to a Powerpro battery, instead of a single 18KPV. There's the big generator for cloudy stretches but also the little one that can recharge us over a full day if necessary (second chargeverter will be ordered this weekend). Spare fuses for the Lynx distributor and spare breakers, as well. Did I mention the extra Grundfos well pump we're ordering, just to have as a spare? I like your thinking.

 

[dfw_dude]

To me if a generator is needed while sizing the system its a failed system to start with.

Now purchasing the right generator to go with a system as a backup is something I put thought into.

same -- my solar/battery setup is used daily and works amazingly well, but I've thought of the "backup to the backup". Which would only be used in an exceedingly rare set of circumstances. I keep a 3kw gas/propane generator (with accompanying propane stock) stored nicely if some truly apocalyptic stuff happened. I just need to get a chargeverter for my EG4 system to properly integrate it.

It's a low priority honestly because even in cloudy/overcast conditions I can still generate a minimum useable amount of electricity needed. Only way I'd probably whip a generator out is if I wanted to fully charge my system and it was dark/cloudy for a week already or something.

 

[OM617YOTA]

To me if a generator is needed while sizing the system its a failed system to start with.

Not a practical view in a lot of places.

My 1.6kw array harvests ~5kwh/day during summer. There was a period last year where that same array took three weeks to harvest 4kwh.

A system that's built to handle the absolute doldrums of winter with solar alone would be 100x bigger, 100x more expensive, and take up 100x more space than the system that handles your needs for 90% of the year, and still might not be sufficient.

Or you can plan to run a generator for a bit. Either way, as long as the lights turn on when you flip the switch, you are successful.

 

[Madcodger]

To me if a generator is needed while sizing the system its a failed system to start with.

With respect, don't you have a grid-tied system? As such, many of us would say that anytime the grid is required (a label on your Home Assistant screen, as I recall), you have used the big generator called your local electric utility. For those of us without that big generator, we are sometimes forced to use our smaller, louder version to get us through those periods when Ol' Sol decides to take a vacation. As others note, that allows us to keep system sizing reasonable while still enjoy modern conveniences. Trying to size a system with no generator is, in my opinion, just not practical.

 

[Mike8061]

I have 3 years of grid. Winter sun angle is 14 degrees if I remember right for my location. Also November to January can be cloudy.

I have 7kw of panels but through a victron 450/100 charger so max is 5600 watts or so.

As long as I'm around to clean snow off panels ( I'm going to build an adjustable mount just because of snow and ice) I don't have to worry about power from March to October unless I want to run A/C all night. With larger batteries this probably wouldn't be a problem either.

For winter I can't see adding to the system what would be needed to garrenty making it through without the generator. I bought a used 20kw diesel generator so I could run bigger welders. So some fuel goes to welding but I don't think my fuel for a year would be over 300$ So with a 20 year life expectancy of equipment this would give me 6000$ to try to offset the generator.

Having already lost and inverter and charge controller to lighting. I would not use 20 years as a number for calculating pay back either. Maybe you can get lucky not a realistic I think.

I do all heat with wood or propane. I may add a small induction cook top for summer use when there is so much extra power. The A/C was added because there was so much extra power on sunny hot days.

I was lucky that only 1 of my 2 inverters blew from lighting. I reprogrammed the working one to stand alone and could run lights/fridge/freezer. If both had blown the generator would be the only means of power until new equipment arrived.

I think for any off grid system where reconnecting to grid is not possible a generator should be considered for both financial and backup reasons. Of course there are situations people can do without but I don't think it applies to a big percentage.

 

[Chispas]

Having already lost and inverter and charge controller to lighting.

I have an earth for the array. Someone local had a lightning strike on their array, the wires were running outside the roof & down the walls, SCC 7 inverter were blown & an arc went across the ground & blew out 2 tyres on a car. Our set up is quite sheltered & has some large pines along side, fortunately not causing shading.

 

[Crowz]

With respect, don't you have a grid-tied system? As such, many of us would say that anytime the grid is required (a label on your Home Assistant screen, as I recall), you have used the big generator called your local electric utility. For those of us without that big generator, we are sometimes forced to use our smaller, louder version to get us through those periods when Ol' Sol decides to take a vacation. As others note, that allows us to keep system sizing reasonable while still enjoy modern conveniences. Trying to size a system with no generator is, in my opinion, just not practical.

Not really. I don't call the power company and ask them what they have planned for the day and I don't stop the linemen to get their input on things either. To me the generator is the grid in this situation. When designing the system for offgrid its still panel/inverter/battery that concerns me on setting it up. I buy a generator in case a backup is needed thus the reason I said :

To me if a generator is needed while sizing the system its a failed system to start with.

Now purchasing the right generator to go with a system as a backup is something I put thought into.

 

[Wessss77]

For me...average of 350 days of sunshine per year means I don't have to plan too hard for a generator. But with most people in the area running gas heat, gas dryers, gas hot water and gas oven/stoves neighbors were no help in my planning. I just switched from evaporative cooler to central HVAC... Now changing from infra red heat panels last winter to the central HVAC. So this year I doubled my panels, changed inverters from dual 6500 to dual 10k. I built originally a 51kwh battery bank which did fine the first year so I planned to add the additional 15kwh storage.

If you have electric history to use, I generally recommend a person look for their highest usage day and at multiply by 2.5 to determine storage if going fully off-grid. Size the arrays to completely charge the pack on the shortest day of the year if full sun and that should be good. Always have a backup to the backup.