Newer tech? Lithium Iron Phosphate
Pros: can be used to 80% depth of discharge with no affect on life cycle count so you buy a 200AH LiFePO4 you get 160Ah usable, Fast absorption of power from solar panels, Long lived, will not catch fire like other lithium techs.
Cons: Cost, High initial cost (slightly higher than lead acid now days) , more temperature sensitive, must be kept above 5c. Must have a management system (commercially made ones come with it)
Actually, I think lots of models come with the BMS (Battery Management System) integrated, even the cheap Asian ones. Keep in mind that the cheap Asian ones have a tendency to be undocumented - ie. if you manage to wire a medium-sized battery bank without help from the vendor, you get a prize.
Deployment of photovoltaic power production deserves a thread of its own. When people asks me about advice, I always start with the basics:
Basic 1: How much power do you use daily?
This is surprisingly easy to estimate if you are currently connected to the grid. Just pick the power bills of the last two years. Find how many kilowatts.hour/joules/whatever you were billed each month and then divide it by the number of days that month had. That will give you your daily consumption.
Basic 2: How much power can you produce?
This is a bit too complex for the regular Joe to do without some education, but what I do is to pick a regular solar panel from the catalog and find out the average power it may generate per day, on average, for each given month in the location I want to install it (so you get the average power production in January, the average power production in February, and so on).
Many vendors can help you with this and some even have pre-calculated production charts.
Basic 3: How much power do you really need?
Things get tricky here. What percentage of the year do you want to be covered? 80%? 90%? Solar power is subject to the law of diminishing returns, so don't get greedy if you don't need to. 99% coverage (ie. ~80-90 blackout hours per year) is insanely expensive to achieve.
Getting Ready
Now you pick a number of solar panels you think you can pay as a base for your calculation, and check if an array that size would serve you well.
What you do is to compare the average power consumption you calculated in step one to the power production you calculated in step 2. For each month. An spreadsheet is nearly mandatory. Something like this:
| Month | Daily Consumption | Daily Production per Panel | Number of Panels | Daily Production | Balance |
| [...] | [...] | [...] | [...] | [...] | [...] |
| June | 20 | 2 | 6 | 12 | -8 |
| July | 19 | 2.3 | 6 | 13.8 | -5.2 |
| [...] | [...] | [...] | [...] | [...] | [...] |
The negative numbers in the "balance" row indicate months in which your solar would fall short on average.
You can (crudely) estimate your yearly power consumption by averaging all the values of the Daily Consumption row and multiplying them by 365. You can also (crudely) estimate your yearly deficit by adding all the negative values in the Balance row and multiplying them by 30 and then by the number of months in which Balance turned out negative.
Your coverage (as a percentage) will thus be:
100 * (Yearly Power Consumption - Yearly Deficit) / Yearly Power Consumption
If the coverage you get from the above calculation is smaller than your target, repeat the calculation with a bigger number of solar panels until you achieve your target coverage or you break your budget.
Battery sizing
I consider Lithium PO4FE batteries here since those are the ones I use for big banks.
My official recommendation is to get a battery bank capable of holding 133% of your average daily consumption, but I am also aware most people can't pay that. My rationale is that such a big battery bank will still provide you with a 100% power capacity once 30% of it has disappeared due to battery age (ie after 10 years) and because a slightly oversized battery tends to do better during streaks of cloudy days. It only makes sense to use big battery banks if your solar is actually capable of charging them (ie +85% solar coverage per year), otherwise you are just wasting money in batteries that will never be taken full advantage of.
What do I do when power runs out and my grandma is connected to a life support machine she needs to live?
Buy a fucking diesel powered generator.
There are some cool solar setups that can be configured to trigger the generator automatically if the day is dark and the batteries are running low. You can source some cheap Asian inverters (2k USD) with an integrated port for the generator. These are great because you can also charge the batteries from the generator in order to use the electricity later. A 3KW generator should more than suffice for a common family house in a pitch, but I have seen good deals in the 5-6KW range.
I installed an array that provides 90% of coverage. Now it is summer, batteries are already 100% charged by 11:00 am. The sun is shining but all my productivity is going to waste. You scammed me!
You will have too much electricity in the best months of the year. That is the price of having barely enough the worst months of the year.
Get domestic appliances to make the most of the extra electricity. Well pumps. Air conditioning. A 1KW server rack.
Or just hire a electrician next time instead of believing a random internet weirdo. Just keep in mind that most electricians doing solar will just install a commercial kit on your roof without bothering to ask how much power you do use and without bothering to estimate how much power your solar will produce, therefore leaving you with a generation system of unknown performance. It is not that electricians cannot calculate, it is that oftentimes they don't care.
EDIT:
If you have a standby emergency generator, it is a good idea to check its fuel and oil level every morning. You don't want it to be automatically started if its tank is empty or it has no oil. I also recommend running it half an hour each month just to check it is still in working condition. Nobody wants a generator to sit unused for years only to fail to start the day you really, really need it.
