Can solar be a backup?

I get lot of enquiries about “solar inverters” and solar as a “backup” for power outages.

Solar, wind, tidel, hydro – all these kinds of renewable energy sources are what people call as “infirm power”. Why is it called “infirm power”? Because, we cannot control how much is produced at any point in time. It is for nature to decide. Take solar – it is confirmed to be zero every night. But, will it be 199% during the day? No. Depends on the day – intensity, timing, angle of sunlight on the module collector, temperature – everything varies every minute. So, it is not firm – hence the term – infirm.

Compare it against conventional generators – say a coal power plant. As long as coal is available, the plant can be run at full capacity any time.

Usually, all of these have a high initial investment, and near zero ongoing costs. And, once we make investments, we cannot control how much it produces.

Thus, solar cannot be a backup – but, it can be a “complementary” source of power.

I am often asked – even after investing on solar power or solar heating plant, I cannot replace or remove the conventional source – be it a diesel genset, or a boiler or a hot-water generator. Then what is the use.

Let’s understand this: Conventional energy sources have usually very low upfront capital costs, but have a very high running cost. Many coal based power plants running today have all depreciated fully with hardly any capital value left.  But, the cost of running it by consuming coal is what makes it expensive.

Boilers or hot water generators are relatively very low cost upfront. But, running costs are very high.

Against this, solar has high upfront costs, but is very low – almost nil – costs of running it. Maintenance is the only cost, and fuel is free.

This is a fundamental design principle of solar.