Solar batteries can be expensive and will be one of the biggest costs to a solar system.
Here are RenewSolar we have done all we can to keep hardware prices low and on average you can save around 50%, so your off to a good start!
Grid tied is a “cost saving” venture for most, but is it a false economy; Does adding a battery make it worth the additional costs?
lets start by looking at grid tied.
“you only save what you can use.”
Grid tied solar has no storage and relies on the live power from the solar array, its ups and downs means that you can fall short and over shoot you ability to meet your loads.
Here is this mornings power – 23.04.24.
looking at the chart, we see the morning sun and a few dips and then its all over the place, these are clouds. The production here in percentages will stand out more as we were making between 17% and 62% from the array.
What are we saving and giving away with grid tied solar?
To give you an example.
We will say we have a load at 400W, everything above 400W give away, everything below 400W we pay for.
So between 9 and 9:10 we can see we met our load and gave away some power. but after 9:10 we have some spikes over and a few drops under. Lets take a closer look:
Here we can see that above 400W would fit into the below 400W , and if you like Tetris you will see this working but we will have a little gap after 9:15 But we can see its a nice flat line to meet our load.
Lets Look at the battery solar installation and see how this compares.
The battery system is no different in terms of solar production but the difference is the buffer.
The solar battery can take the spikes over the load and store them, so that every time we fall short it can fill in the gap left by the sun.
If you are looing for a device to measure live data from your solar, we make systems to do so, this is are Growatt shineX replacement which plugs into the usb and makes it easy to see live data and harvest it locally at home, no subscriptions and no down time, its also private click to find out more
shineX replacement in the shop
The Battery Buffer
I often refer to solar with a battery as a “battery Buffer” this is where the battery is sized to be a buffer rather than a power source, You have probably seen the sales adverts that want to sell you a solar installation with a battery that you use its power at night. Well that usually not the case at all.
Small solar batteries are no more than a buffer and in some cases the “kit” can produce limited power, but the size in kWh is around 4.6Kwh capacity (advertised as 5kWh) , which is around 2.7kWh of usable power. This “deal” will see that the power is gone from the battery by dinner time for most of the year. it certainly would NOT provide overnight power.
They often only make around 2.1Kw output power. regardless the output power of the inverter ( which ever the lesser).
A battery Buffer is small and fills in the gaps where solar cannot provide power, they do not need to be big or special and the costs for these is around £700. ( solar battery link here.)
The Math on “worth it” for a buffer
If we look at our battery from the link above, it has a 8 year life (its longer, but we just use lower numbers)
That works out at £87.50 per year. Or that’s about 310kWh a calendar year.
As we have off grid, and grid attached as well as Grid tied we know in the real world what this is like. We have a lot of data and can see how these all perform for us and our clients. we are able to “do the math” and we have no upsell and candy coatings. so we can offer “plain English”.
Typically in solar calculations, it’s estimated that there are 275 sunny days and 90 less favorable days annually. Therefore, our yearly projections are based on 275 days. On average, we export about 65% of our production from the grid-tied system. On days when sunlight is present but not strong, we generate approximately 50% of our base load.
While it should be clear that our production is more than our loads, we could have this stored in a solar buffer battery. in the less favorable days, if we charged our battery at cheap rate, then we would need to provide 50% of our daily (day) power requirements. In the example above that’s around 200W short fall on the base load. but as the days are shorter the power demand grows and it could be that you would fall into the area where you would be best off to just turn off the battery and run as a grid tied, or BESS.
Off Topic a bit:
If you have a higher load, and a 3.6Kw inverter, you may want to match the inverter, but match your load more over.
Lets say 2000W load matching from the buffer battery.
if you bought our battery that we linked to above, that’s £700 and could load up to 5.1kW.
If you bought Pylontech at £1,350 you could load to 2.8kW
just saying…
There is a point where a buffer and a battery storage cross a point where there the function changes. The change to Battery storage (BESS) is a calculation of the day and night which would be a much larger system and investment. The solution here is the buffer plus night time power being provided by the battery, and that’s another post.
The Right inverter
Picking the right inverter requires calculations, this is to size the inverter to make the best savings, but for many the G98 limitation would put most peoples view of solar around 3.6kW inverters.
For the purpose of this post I will not address off grid, or grid attached. but we will look at Hybrid inverters and grid tied inverters.
its safe to say that hybrids are twice the price. Our 3.6kW Sunsynk Hybrid inverter is available for £750 which is a very good deal. A grid tied inverter with the same power is around £400-£520
If you look at a hybrid inverter and a battery then the cost difference is only around £1,100 and there are other costs involved, such as the protection and distribution as well as having to re think the power calculations. but if your on the fence to pull the trigger, the cost difference could be returned in just 2 years of savings. Ill let you do the math, you will save 50% of the power by storing it in the battery and it will act as a buffer. what is 50% of your monthly bill? that’s that over the year (12 times)?? make it worth it?
If you were to look at the batteries, either our 15kWh battery which is grounded on wheels, will be ideal or the wall mounted batteries. They are more expensive that the ABS batteries. but the wall mounted battery has a lot more hardware installed and safety features, and have a design life of 15 years.
BESS – Battery energy storage system.
With or without solar, charge cheap rate from the grid and use the power anytime.
Grid Attached
Grid attached is a non feed in (export) inverter type, it is connected to the grid to pass though or charge only. the pass though is when you need power but cannot provide it from the battery or solar.
Value:
Terms of returns and practicality; costs and savings as well as life time and ability to support the use case.
A balance of the pros and cons.
NOTES:
This post provides a summary of grid-tied solar installations without storage, which are typically designed to produce excess power, leading to potential power export. Conversely, insufficient solar capacity results in the need to purchase power from the grid. We examine whether battery storage can mitigate the variability of solar power input and assess its practicality and value.
Adding a battery system (hybrid) may offset the shortcomings of solar production and store excess energy, thus avoiding the exchange of power. We have analyzed the buffer battery, value thresholds, costs, and returns of both systems in summary only.
Many hybrid solar purchasers report significant savings compared to their previous grid-tied systems.
This article is a summary and omits detailed analysis and additional costs associated with hardware purchases. It also does not elaborate on the savings or other benefits of the systems, as that is beyond this post’s scope. For detailed information and to explore options, please review other posts or book a consultation through our website.
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