Off grid solar with plan to power an electric car

[Proud Poppa]

Hi, I just got back from staying with my daughter and son-in-law in northern Europe (latitude about 57 degrees). They live on 3 acres surrounded by forest, and currently have a 1 panel, 1 battery temporary system. Connecting to the grid might cost about $15,000. Given the latitude, the low sun in the winter, and the trees blocking the low sun, they will probably need a 1-2 kw solar system (placed at the north end of the property facing south) in order to generate enough for lights, cell phone charging, and maybe some water pumping when the sun is lowest. That brings up the question what to do with the extra electricity during the rest of the year. I have seen some tables suggesting that the ratio of sun max (longest day)/min (shortest day) at their latitude is about 30, without accounting for the trees blocking the low sun. Their ratio might be 40-50. I suggested getting (maybe in a few years) an electric car. In the winter, the car can be charged somewhere else on grid, and the rest of the year, some or all of the car's charging can come from solar.

I haven't seen much of anything about how to design a solar system with that in mind. Other than for the car, probably they need only a few kwh battery capacity. Ideally, you could plug in the car and charge from both the panels and batteries, but not discharge the batteries below a certain point to reserve enough battery power for the critical uses. Also, as the car battery is so much bigger, it can be charged much faster than the solar battery pack can be discharged without reducing the lifespan of the solar batteries, as I understand it. Is this kind of application supported by existing equipment, or would they have to manually (with a switch) disconnect the solar panels from the battery/house system and connect them to the car when the car was charging? Any other ideas about 100% off grid systems in such northern conditions with the low sun being blocked? The forest also blocks the wind, and there are no streams through their property.

Thanks.

[NEOH]

57 Degrees North Latitude is like the northern part of the United Kingdom or Denmark?
The ratio between summer & winter is closer to infinity.
Because in Dec & Jan Solar production will be near 0 KWHr for many days in a row.
Do they currently use a generator for the two months of winter?

You need to compute the Loads and then estimate the monthly production.
The difference will be available for charging the Electric Car.

Many systems generate excess energy, and it can be "sold" back into the Grid Grid.
Your scenario of "generating excess energy" is not unique.

. Also, as the car battery is so much bigger, it can be charged much faster than the solar battery pack can be discharged without reducing the lifespan of the solar batteries, as I understand it.
Thanks.

Now that is a very interesting statement.

[Proud Poppa]

Grid tie to sell excess power is not an option unless they come up with about $15,000 to connect. They are literally in the woods, with a 200 year old gravel/dirt road to the town maintained dirt road. Since the normal thing to do with excess power is not available, I'm trying to figure out if they can use it to power a car without a major DIY effort in control electronics and without risking degradation of their battery pack. In an ideal world, they could charge a battery pack from solar when the car is disconnected, and then hook it up when they get home to charge from both solar and the battery pack. But I understand it is not an ideal world.

At a daily use of maybe 0.25 kwh with a 2 kw solar array, that means they need to get average effective solar power of about 8 minutes a day. With a 2 kwh battery pack, that means at 70% discharge they have more than 5 days power with no sun. Yes they have a generator. So it is not vital that they "never" run out of solar power. They have not wintered here yet - they are installing insulation and building rocket stove mass heater this month. The trees are on neighbor's property maybe 120 yards from the planned location of the solar panels, so there will hopefully some sun coming in even in the winter. The idea is that solar panels are cheap enough that they should try to cover their needs from solar as much as possible during the year. Whether that is 10 months, 11 months, or 12 months is not critical (but nice to minimize the number of times necessary to connect and run the generator). But there will be a lot of extra power for 6-9 months of the year under any reasonable sizing of the solar panels..

[kb58]

I think at the end of the research, PV will end up costing more than just connecting to the grid. Given the huge swings in exposure summer to winter, connecting to the grid makes the most sense.

[NEOH]

I haven't seen much of anything about how to design a solar system with that in mind.

You stated that, You haven't seen much of anything about how to design a solar system with that in mind.
I replied that, in fact, there are many threads on this website that discuss generating Excess Energy.
Most send their excess energy back into the Grid.
Many have batteries.
Some have electric vehicles.

Yes, I know that Grid-Tie is not an option for you, and that is why I wrote ...
You need to compute the Loads and then estimate the monthly production.
The difference will be available for charging the Electric Car.

The Electric Car is a load, a big load, bigger than the house per your numbers.
You have not yet specified what their biggest load will be.

Can you answers these questions:
Q1) Does the Electric Vehicle need a 240 Volt AC outlet for the Charger?
Q2) How many Amps does the Car Charger require?
Q3) How many hours to recharge the battery pack in the Electric Vehicle?

Also, when will the Electric Car be recharged ...
a) During the daylight hours from the PV Panels ?
b) Recharged after sunset from the Battery Bank ?

Answers to these questions would help you decide how you can inter-connect the Electric Car Charger to the PV system.

[SunEagle]

Question. How do you plan on charging that EV if you get multiple sunless days in a row?

Being off grid has a number of difficulties and requires a new way of living just to run your household appliances and lights let alone trying to keep an EV charged.

I believe to build an off grid system big enough to do what you expect will end up costing much more than that $15,000.

[NEOH]

Solar Edge EV Charger

https://www.solaredge.com/us/products/ev-charger

[SunEagle]

Solar Edge EV Charger
https://www.solaredge.com/us/products/ev-charger

Great. I am impressed. Looks like new technology is being introduced.

Question would be how much for that charger and how big a solar array wattage do you need to charge an EV?

[max2k]

Grid tie to sell excess power is not an option unless they come up with about $15,000 to connect. They are literally in the woods, with a 200 year old gravel/dirt road to the town maintained dirt road. Since the normal thing to do with excess power is not available, I'm trying to figure out if they can use it to power a car without a major DIY effort in control electronics and without risking degradation of their battery pack. In an ideal world, they could charge a battery pack from solar when the car is disconnected, and then hook it up when they get home to charge from both solar and the battery pack. But I understand it is not an ideal world.

At a daily use of maybe 0.25 kwh with a 2 kw solar array, that means they need to get average effective solar power of about 8 minutes a day. With a 2 kwh battery pack, that means at 70% discharge they have more than 5 days power with no sun. Yes they have a generator. So it is not vital that they "never" run out of solar power. They have not wintered here yet - they are installing insulation and building rocket stove mass heater this month. The trees are on neighbor's property maybe 120 yards from the planned location of the solar panels, so there will hopefully some sun coming in even in the winter. The idea is that solar panels are cheap enough that they should try to cover their needs from solar as much as possible during the year. Whether that is 10 months, 11 months, or 12 months is not critical (but nice to minimize the number of times necessary to connect and run the generator). But there will be a lot of extra power for 6-9 months of the year under any reasonable sizing of the solar panels..

you'll spend way more than $15,000 on this and end up in the dark at the end. Grid tie has another advantage- low maintenance costs. The batteries have limited lifespan, 5- 10 years tops depending on type and if you know what you're doing. Then you'll be back for fresh ones. Apparently they have money for EV, off grid solar system but not grid tie? This will end up badly.

The numbers are not realistic and this is plain dangerous if that place gets cold in winter. 0.25kW / day is about 10W load for 24 hrs, this is about how much 1 LED bulb consumes. Forget about any heating / pumping with electricity or EV charging as you have huge mismatch between what even energy efficient home requires and your proposed solution. That energy would only be enough to transmit SOS for 1 hr only and in complete dark. You need about x20 times system for extremely frugal lifestyle- simple fridge requires 0.5-0.8 kWh / day. On top of that it sounds the place doesn't see much sun during winter months. Have you seen many solar installs in the area? If none then locals might know something.

[J.P.M.]

OP: Do you understand the load an EV will require ? 1st guess might be miles driven/yr. /3.5. So, 10,000 miles/yr. /3.5 = ~ 2,800 kWh/yr. Forget winter additions from an array. Use off site charging or stay with an ICE powered vehicle. Or, use the petrol to power an on site generator to generate electricity to charge an EV battery. My guess is that if cost effectiveness is a consideration, let alone practicality, a high mileage ICE vehicle will be less costly and a lot more practical for this application.

Most folks jump to solar without understanding it's potential, and more importantly, its limits, after drinking the koolaid peddled by con men peddlers and a lot of what's false advertising that's masquerading as news to separate the solar ignorant from their assets.

I'd respectfully suggest reading up on the realities and look at everything with a cynical eye. Follow the money.

[Proud Poppa]

Currently they are driving about 125 miles/week in a small, gas powered car. That means about 40kwh hours a week if it were electric. In the summer, a 2kw panel array should generate about 70kwh or so a week. If the car is parked 4 days a week, and driven to part time work 3 days a week, that means it could charge 40kwh a week if done from the solar panels. The rest of the year, or if they drive more in a particular week, they would need to supplement with public charging or making arrangements with a friendly, on grid neighbor. They are planning to live with very modest electrical needs. Right now they have no electrical use except charging their cell phones and rechargeable flashlights. In the summer, but not the winter, they will want a small refrigerator. In the winter, they plan to use a root cellar. Heat from wood stoves, ditto hot water or from solar heaters. Right now they hand pump the water from the well. Of course, their thinking may change if they have young children. I agree that a full solar array makes no sense to purely power an electric car 52 weeks of the year. If they wanted "pure" off grid they could go to wood gasifier/generator, but that seems like too much work. A car is portable and easy to drive to where charging from the grid is available if necessary.

The real question I am asking is "are there decisions which should be made one way or the other NOW when they expand their solar array from the temporary 1 panel/1 battery near the house, to multiple panels and batteries at the north (sunniest) corner of the property, in order to preserve the option of solar charging LATER?" without having to replace electronics with a 10 year life span. Later might mean 5 years when the car needs to be replaced, or sooner if my daughter has a baby and my wife, who is retired, goes to live with them for months at a time and wants a second car to make runs to the store or for cabin fever escape. My wife will probably not be staying there in the winter (but with a grandchild, who knows). This would be our first grandchild.

[max2k]

...

too many mistakes in estimates to plow through, sorry. It all sounds like viking style of living - those didn't have electricity either and somehow made it. Although their life expectancy wasn't that high I recall.

[J.P.M.]

Currently they are driving about 125 miles/week in a small, gas powered car. That means about 40kwh hours a week if it were electric. In the summer, a 2kw panel array should generate about 70kwh or so a week. If the car is parked 4 days a week, and driven to part time work 3 days a week, that means it could charge 40kwh a week if done from the solar panels. The rest of the year, or if they drive more in a particular week, they would need to supplement with public charging or making arrangements with a friendly, on grid neighbor. They are planning to live with very modest electrical needs. Right now they have no electrical use except charging their cell phones and rechargeable flashlights. In the summer, but not the winter, they will want a small refrigerator. In the winter, they plan to use a root cellar. Heat from wood stoves, ditto hot water or from solar heaters. Right now they hand pump the water from the well. Of course, their thinking may change if they have young children. I agree that a full solar array makes no sense to purely power an electric car 52 weeks of the year. If they wanted "pure" off grid they could go to wood gasifier/generator, but that seems like too much work. A car is portable and easy to drive to where charging from the grid is available if necessary.

The real question I am asking is "are there decisions which should be made one way or the other NOW when they expand their solar array from the temporary 1 panel/1 battery near the house, to multiple panels and batteries at the north (sunniest) corner of the property, in order to preserve the option of solar charging LATER?" without having to replace electronics with a 10 year life span. Later might mean 5 years when the car needs to be replaced, or sooner if my daughter has a baby and my wife, who is retired, goes to live with them for months at a time and wants a second car to make runs to the store or for cabin fever escape. My wife will probably not be staying there in the winter (but with a grandchild, who knows). This would be our first grandchild.

To your question, I'd say yes, some decisions need to be made. But, making equipment choices would come after setting lifestyle goals and desires and then learning, really learning in a technical sense, about what's available in terms of equipment, both in terms of strengths that peddlers will overstate and weaknesses/limitations that peddlers often and conveniently forget.

In terms of economics - if that's important - an example of one consideration might be: What is the net present value (NPV) of the cost of petrol it takes to drive 125 *- 52 = 6,500 miles/yr. Then compare that to the combined initial cost of an array to meet that load 6 (sunnier) months, plus more generator capacity for the other 6 months, plus the NPV of the fuel/operating costs of the generator for., say, your 10 year time frame. I bet an high mileage ICE comes out ahead in $ terms, but there are other considerations besides $$.

Bottom line:Pay your money, take your choice. Just have as much real knowledge and realistic information. Knowledge is power. More real knowledge, not just advert. fluff and U-Tube idiot's bible B.S., can be a valuable tool.

[AzRoute66]

The real question I am asking is "are there decisions which should be made one way or the other NOW when they expand their solar array from the temporary 1 panel/1 battery near the house, to multiple panels and batteries at the north (sunniest) corner of the property, in order to preserve the option of solar charging LATER?"

I would say that the biggest thing for future expansion is to try to get equipment that will work at 48 volts. You may start at 24V, or god forbid 12 V, but to support any system over 3500W or so you will be wanting to go to 48V. I'm told that is hard to do with inverters, but charge controllers can be had which auto-sense the battery bank and work with more than one value. Another thing might be the ability to set a maximum bulk charging current with a setpoint rather than just the max output. Also, it kind of goes without saying that for flexibility and growth a MPPT charge controller is preferred. The throwaway is the batteries, they just don't like to be added to in increments. In other words, go cheap as possible with batteries if you know that a major expansion is going to occur in a couple/few years as you will be installing a whole new battery bank to support it. Finally, if the array is going to be moved out a considerable distance, keep in mind that the higher the voltage the lower the power loss in transmission, so try to get a charge controller with a 600V input, or plan to invert it to AC at the array.

[Mike90250]

Hi, I just got back from staying with my daughter and son-in-law in northern Europe (latitude about 57 degrees). They live on 3 acres surrounded by forest, and currently have a 1 panel, 1 battery temporary system. Connecting to the grid might cost about $15,000........

$15K will not get you very far with a solar PV system. Panels are cheap, but controllers, inverters and the batteries that go bad after 3-8 years, the $15K to run grid power is a bargain.
Going off-grid never saves money because of the reoccurring battery costs.