I have huge experience with energy storage as this is my hobby for the past 6 to 7 years and I currently live in an offgrid net zero energy house powered 100% by solar that means electricity and heating and it is the most cost effective solution possible.
My small house energy requirements are as follows peak month January requires 1000kWh for heating and 120kWh as electricity for appliances most of that electric cooking the 120kWh is included in the 1000kWh heating as any energy you use inside the house ends up as heat.
Heating season here in Saskatchewan Canada is about 7 months per year so total energy needed for heating is around 5000kWh to 6000kWh (depends on how cold it is in a particular year) and average of 120kWh/month as electricity that is about 1400kWh/year thus total energy requirement 5000kWh + 1400kWh = 6400kWh
My system is made out of a 10kWp PV array (can produce in a year about 14000kWh) so less than half of available energy is used but this makes sense as it is designed to use almost all available energy in winter and there is up to 90% unused energy in summer that makes perfect economic sense and will explain later.
There is a large thermal storage 158kWh capacity made of 97kWh 14m^3 concrete floor and a water storage tank 1500liter 61kWh capacity then for electricty I use a 5kWh LiFePO4 battery just enough for 24h autonomy as the huge PV array can produce worst case the minimum energy required about 4kWh in worst overcast day.
Total cost of the system $15K and expected life of the system at least 30 year thus $15000/30years/12month = $42/month total energy bill for heating and electricity.
Put this in another way $500/year / 6400kWh = 7.8cent/kWh but is not quite a fair representation as the energy used for heating is at around 5cent/kWh while the one used for appliances is around 18 cent/kWh
Thus heating with PV solar is the most effective heating option even cheaper than the next option natural gas.
Now with this out of the way I want to give you some numbers for perspective very relevant to this tread
Cost amortization for different elements sort of best case
PV panels cost amortization 2 cent/kWh
Thermal storage as low as 1 cent/kWh
LiFePO4 around 15 to 20 cent/kWh (best option but still not a good solution for grid energy storage so do not add a battery to your grid connected house just have a grid connected PV array if you care about costs and is valid anywhere in the world).
Tesla PowerWall or similar storage devices at least 40 cent/kWh very bad investment if you care about savings and not just want an UPS and do not care about costs.
Lead Acid 60 cent/kWh up to over $1/kWh depending on battery used and in what conditions still very bad for energy storage applications.
Car alternator or small gasoline or diesel generator at least $1/kWh so extremely bad idea in most cases.
This is a bit of advertising but for details about my open source devices making my house solution possible see the documentation in my
Kickstarter campaign description.