I am dabbling with building solar systems. Currently I have a single panel single battery rig in my shop. I want to build up knowledge and experience and electrify the shop, the barn and a couple of other sites in the coming years.
This document tracks the progress of my solar education as well as the status of all of the solar systems I have in mind or am already building.
- But a Victron battery monitor: https://www.victronenergy.com/battery-monitors/bmv-712-smart https://www.naradihned.cz/monitorovaci-zarizeni/sledovac-stavu-bmv-712-smart
- Consider a Victron battery balancer: https://www.victronenergy.com/battery-monitors/battery-balancer
There is a bunch of solid solar resources online and I've already absorbed a few basic lessons, but I still have a lot to learn. The resource I find the most promising at the moment is the collective work of Will Prowse distributed across his:
I might come up with a study plan and I will definitely intertwine projects of increasing scale into the learing process, all of which will be covered in this repository.
I also bought Will's book.
- Calculate the theoretical panel/array performance
- Note that the panel voltage should be around 5 V above battery voltage
- Multiply amperage by voltage for wattage, e.g.: 10 A at 40 V (2s1p) = 400 W
- Multiply the power by the peak sun cover hours, e.g.: 400 W * 2.5 h = 1 kWh
- Multiply by the factor of 70 % to approximate real life performance = 700 Wh
- Calculate the battery capacity
- Multiply the amperage per hour by the voltage, e.g.: 200 Ah * 12 V = 2400 Wh
- Calculate the peak sun cover hours required to fully charge the battery
- Divide battery capacity by solar capacity, e.g.: 2400 Wh / 700 Wh = 3.5 h
- Calculate the desired load to see how long the battery can power it for
- Ensure you are using compatible load, 12 V load for a 12 V battery
- Divide the battery capacity by the power draw, e.g.: 2400 Wh / (15 W * 24 h) = 6.666 h
Since my current test setup only uses a single panel mounted at the exterior wall of my shop, I have decided to upgrade and buy a couple of solar panels to form an array. I will mount the array on a construction I will design and manufacture which will live on land so I don't have to mount it on the building.
I bought 5 of these Victron BlueSolar solar panels:
https://www.solar-eshop.cz/p/fv-panel-victron-energy-175wp
- Design and build a mount for the panels
- Mount the panels onto the construction
The panels are 175 W, ~10 A at ~18 V (under load). There are a few configurations these could be wired in:
- 5 in parallel: sum of amperages, same voltage, so 50 A, 20 V
- 5 in series: sum of voltages, same amperage, so 100 V, 10 A
- A series-parallel configuration - there are multiple options
Connecting them in parallel is not a great idea, because I would have to get some dummy thick wires and controller to be able to move 50 A of current. As I understand it, a 100 % parallel setup is mainly used with small systems which use PWM controllers, not really as much with MPPT controllers.
Connecting them in series could work, but only with a solar charge controller capable of handling 100 V at 10 A.
https://www.alza.cz/victron-mppt-regulator-smartsolar-100-15-d5855306.htm
This one matches exactly! But almost too exactly. It is my understanding that it is best to leave some headroom so that the solar charge controller can handle temperature change etc. Running it this close to the max spec could ruin it and they aren't cheap.
Let's run through the options for a series-parallel connection. I am going to consider only the options with equal array lengths. Here is an article which goes over mixing different solar panels (or strings) and it almost always results in lower efficiency:
https://www.explorist.life/using-mismatched-solar-panel-sizes
- 2 panels (400 W):
- 1s2p = 1 * (20 A, 20 V) = 20 A, 20 V
- 2s1p = 2 * (10 A, 20 V) = 10 A, 40 V
- 4 panels (800 W):
- 1s4p = 40 A, 20 V
- 2s2p = 2 * (20 A, 20 V) = 20 A, 40 V
- 4s1p = 4 * (10 A, 20 V) = 10 A, 80 V
- 6 panels (1200 W):
- 1s6p = 1 * (60 A, 20 V) = 60 A, 20 V
- 2s3p = 2 * (30 A, 20 V) = 30 A, 40 V
- 3s2p = 3 * (20 A, 20 V) = 20 A, 60 V
- 8 panels (1600 W):
- 1s8p = 1 * (80 A, 20 V) = 80 A, 20 V
- 2s4p = 2 * (40 A, 20 V) = 40 A, 40 V
- 4s2p = 4 * (20 A, 20 V) = 20 A, 80 V
- 8s1p = 8 * (10 A, 20 V) = 10 A, 160 V
Looking at Alza, my local electronics retailer who carry some Victron solar charge controllers, these are my options as I see them with the current stock:
https://www.alza.cz/victron-mppt-regulator-smartsolar-100-15-d5855306.htm
100 V / 15 A could support 1s4p and I would leave one of the panels out.
https://www.alza.cz/victron-mppt-regulator-smartsolar-100-30-d5855308.htm
100 V / 30 A could support 4s2p if I got three extra panels on top.
Everything else falls short.
Namely, the 75 V ones are all unusable because every configuration above that is
below 75 V is either or over 10 A.
At best I could use one with 2s1p but that's only two panels and even then I
would be pushing its amperage spec.
I am only looking at the Bluetooth models as I want to use the Victron app for monitoring.
I looked around to see if I can find a better deal and I found this store:
https://www.naradihned.cz/solarni-regulatory-victron-energy
100 V / 30 A is available for less than Alza!
However, I also learnt that the higher level solar charge controllers don't have a DC output that I could hook up a 12 V DC to 230 V AC invertor.
It seems one is supposed to get something called a battery protect, e.g.:
https://www.naradihned.cz/ochrana-baterii/ochrana-baterii-bp-100-12-24v
This will prevent the battery from draining. I am not sure how it would be wired exactly, I guess share ground and connect the load positive and the battery positive, but it seems suspicious that the ground connector is so small, I would expect a higher AWG connector.
I might try and push my luck with sizing my constant load (e.g.: lights) such that it never drains the battery before it has had a chance to replenish the next day.
But I am also thinking I just might push my luck with a 100 V / 10 A solar charge controller from this new vendor because it has load terminals:
If the solar panels get cold and produce too many volts or the sun is beating down on them perfectly and they are angled just right and exceed the 100 V spec of this solar charge controller, it will most likely get ruined.
But my math is it is better to potentially ruin a 3.5k CZK solar charge controller than to get a 5.7k one and either risk ruining a much more expensive battery than these controller are or buying an extra 1.5k battery protect to go along with it just so that I can connect a load to it.
I am going to get the 100 V / 15 A Bluetooth one from NaradiHned as it costs 3.5k CZK there as opposed to 5.3k on Alza. It will take longer to arrive, but I can wait.
- Get the 100 V / 15 A controller from NaradiHned delivered to the box
Once I get more panels, I will get the 100 V / 30 A one and sell this one.
I should have a 300 W 12 V DC and 230 V AC invertor somewhere, it should be this one:
https://www.alza.cz/auto/compass-menic-napeti-12-230v-300w-d4946056.htm
If I don't find it, I will get another off Alza as this store doesn't have any in stock, but if by then it does, I will use it, because Alza is overpriced for these like the solar charge controllers.
- Find or order a 12 V DC to 230 V AC invertor