Over the past few weeks, we have been examining micro solar systems, also known as balcony solar or plug-in solar. We have established that it is not truly plug-in solar and have explored the reasons why.
Our focus has been on assessing the cost-effectiveness and the offset benefits of micro solar.
Micro solar offers excellent scalability. You can install panels in the optimal locations for your needs without the requirement for a large solar array. This flexibility allows you to distribute the solar yield throughout the day or incrementally add and upgrade the system as desired. However, if you are limited to a single installation location, the costs may be higher.
Micro solar systems are available in several configurations, such as single-panel, two-panel, and four-panel setups, with capacities of 400W, 800W, and 2000W for simplicity.
A notable aspect of micro solar is that it is grid-tied, which has its drawbacks since savings are only realized on the power you consume directly.
A large array does not necessarily equate to significant savings; instead, it may simply feed excess power back into the grid without compensation, benefiting the power companies financially.
To counteract this, one could consider an AC-coupled inverter, which would store the surplus power in a battery for later use. However, this introduces the consideration of staying below the 3.6kW threshold of a G98 certification to avoid the additional expenses and requirements associated with a G99 certification.
Determining the ideal setup for micro solar power is not a universal solution; you need to calculate what suits your situation. Typically, it’s advised that your solar power matches your base load—the consistent power consumption of your home during the day, which could be around 400W or less. The challenge arises from the variability of solar energy between summer and winter, and the increased energy consumption in the winter months. Should you scale your system for winter, summer, or just use it to offset costs?
Offsetting means generating solar power during the day to meet your needs, which may cover summer usage, providing a significant amount of energy that doesn’t come from the grid. However, you will still pay for grid power, so the solar energy serves to offset your annual energy costs.
There is a balance to be found between the cost of installing solar power and the cost of grid electricity, considering what you can generate with solar and what you will need. It’s wise to view solar not as a complete solution but as a component of your energy strategy. Now, let’s look at some numbers.
We will convert this to kWh as it highlights the value more effectively for our purposes. The current unit price is £0.29, which equates to 1,379.31 kWh. That’s 1,723 hours of peak power from the 800W, amounting to 4.72 kWh of solar energy per day over a year. However, this is not feasible in reality; our “test rig” is suboptimal and experiences evening shade from 15:00. It’s April, and we’re generating around 3.7 kWh per day, but better conditions could yield the expected results.
For accurate calculations, we consider the 8 solar hours of summer, 4 hours of spring and autumn, and 2 hours of winter. Using an average of 4 hours for 275 days a year, the calculation is 0.800 x 4 x 275, resulting in an annual production of 880 kWh. This would balance out to zero in 1.567 years, but only if we utilize this power, equating to a saving of £255.20 per annum.
Looking at the long term, solar panels last about 25 years and inverters about 10 years. Over ten years, you could save £2,552 based on the current power price. This could be viewed as an investment yielding a return of 6.3 times the initial outlay.
Let’s consider doubling our solar capacity and examine the same figures. A 1.6Kw system is quite powerful, but it doesn’t cover high-energy appliances like kettles and cookers; for those, you’d need over 2.5Kw. Therefore, we’ll bypass this option and opt for a more robust solution.
Looking at our 1600W Hoymiles kit, now doubled, priced at £1,430, you’d need space for 8 solar panels. This could mean 4 on the garage and 4 on the shed, which is the equivalent of a full roof on an average home. Ideally, splitting the array would extend the duration of peak solar power. The total peak would be 3.44Kw, with the inverter outputting 3.2kw.
At £1,430, the system’s annual yield would be approximately 3,784kWh, or £1,097.36 per year, amounting to £10,973.6 over its lifetime, which is a return of 7.674 times the initial investment. The return is clearly better, and there are additional benefits: higher power generation means less reliance on the grid, as a 2kw device won’t need to draw power from it, unlike with an 800W inverter.
To explain how solar power inverters works for those unfamiliar: solar panels generate power when sunlight hits them, and the inverter boosts the voltage slightly. When power is consumed, it’s drawn from the power lines into the device using it. If we’re using 2.4kw of power with a solar contribution of 1.4kw, then the calculation is 2.4kw – 1.4kw, which equals 1kw drawn from the grid.
In monetary terms, that’s 0.696 pence worth of power being used, with 0.406 pence saved thanks to solar, and 0.29 pence paid for grid power.
When your solar power matches your household consumption, you draw nothing from the grid. If your solar system generates more power than you use, you feed the excess back to the grid.
Now to cause more confusion…
3,784kWh of solar per year is very similar to the average homes annual power use, you will not see this as the power yield will be in the day time and none of your night time power will be covered by the solar. For this you need a hybrid. With a cost of around £2,468.8 the hybrid will power your home and store solar for use later meaning that you would save rather than export for free. This is 8,513.10kWh with a Zero return time of 2.2497 years. In this scenario the panels are the same, the inverter is a hybrid string inverter and you have a 5.2kWh Battery. Adding the battery would add annual savings of about £529.
over ten years the total of around £16,265.60, which is 6.588 times the investment over ten years.
As you can see the initial 800W solution was around the same multiple at 6.3 times, however the value is different as your hybrid stores power within a battery, its also bigger to cover the loads reducing what you are drawing from the grid. The difference here is not what power you could make and the value of solar, but the value of not taking from the grid making a saving.
We can look at it like this: if we have a constant load of 1kwh.
24 x 365 =8,760kWh.
6 hours of which we make solar power.
12 hours we draw from the battery.
To charge the battery we need to know what the draw from the battery is, in this example this would be 12kWh
We then have 12kWh /6hrs, which means that the solar production would need to be 2 kWh over the 6 hours to charge the battery. We then have the load for the same 6 hours (1kwh) which now amounts the charging power would need to be 3Kwh. You will also note we are also missing 6 hours
If we look at the solar power curve in the image below, you will see this small array make power between 10 and 16:00, however around these sloaps there is also power being generated. The key here is that the power must exceed the required power over the day, here we see the production of this 775w array makes 4.5Kwh in the day. This would give only 4.5 hours of “load” supply. We would need to make the battery recharge requirements also.
The issue now is size and practicality to be able to make the most from solar, you need to have enough solar power generated to cover the loads as well as the recharge requirements. however this example would meet the needs of a off grid system. You are now at the point of compromise.
Solar is a compromise
We have looked at total solar and off set solar, as you can see there is no one size fits all and it is a requirement that you see what compromise you wish to make.
England in winter has so little sun hours that solar is pretty much pointless, in summer there is a good amount of power. for example a 2.5kw solar array will make around 16Kwh in early summer but only make around 2.5kwh in winter.
if we have a battery, we can charge this at cheap rates, but you can do this without any solar at all.
You can simply trade energy buying cheap and using it when you like. If you think in reverse, then the solar is a token. therefore this tops up and provides for the load when the sun is available.
Solar is unlikely to meet all your needs year round, to get the best solution you can chase a dream or work with reality. you could spend time and money making an array for winter in the sun famine, and make far too much power in the summer that you will have to shut part of the system down. do you waste money here or just use low rate power from the grid to charge a battery? this then means that your decision has to be made with space for the solar, as solar panels are very low cost.
Anything grid tied is a day load solution only. so no need for a big system unless your at home or a business owner. do you try for the off grid and grid attached? a lower cost system that’s off grid and a back up power solution?
The bottom line
Horses for courses is perhaps the right way to address solar installations and how they can or cant meet the needs of the user. There is the low cost off set of grid tied, this is a day system only, which is not as great as a battery system. if we look at solar totally differently and rather backwards, we would buy the battery that meets our needs, start with grid charging at low costs and add solar panels to take away some of the load and the charge power required.
This may seem a little battery upsell, but until you see the systems in action and understand how it all works, it can seem that way, but then we sell the one of the lowest cost battery systems in the UK.
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